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Introduction While exposure to sulfur mustard (SM) is commonly associated with the production of vesicating dermal, ocular, and respiratory injuries, systemic damage to bone marrow and lymphatic tissue can decrease critical immune cell populations leading to higher susceptibility to life-threatening infection and septicemia. There are currently no approved medical countermeasures for SM-induced myelosuppression. An intravenous SM challenge model was developed in adult rats as a preliminary proof-of-principle platform to evaluate the efficacy of candidate immunostimulants. Materials and Methods Adult male and female Sprague Dawley rats were exposed to SM through tail vein injection. Toxicity progression was monitored through clinical observations, body weights, body temperatures, hematology, serum clinical chemistry, and flow cytometry of blood and bone marrow samples. Results Following SM exposure, overt toxicity progression was characterized by weight loss, changes in body temperature, and manifestation of toxic clinical signs (diarrhea, lethargy, hunched posture, rough hair coat, respiratory distress, and death). Drastic alterations in complete blood cell profiles included an early-onset lymphopenia followed by a delayed-onset neutropenia and thrombocytopenia. Only transient changes in serum clinical chemistry parameters were observed. Flow cytometry analysis of circulating blood revealed that B-cells were more predominantly affected by SM exposure than T-cells. Challenge with SM resulted in loss of hematopoietic and mesenchymal stem cell populations in the bone marrow. Conclusions The small animal model developed in this study replicates many key aspects of human SM exposures and should serve as a relevant, rapid, and cost-effective platform to screen candidate medical countermeasures for SM-induced hematologic toxicity.

Myositis is a known complication of chronic graft-vs-host disease (cGVHD) following allogeneic haematopoietic stem cell transplantation, but can be difficult to diagnose and manage. We present the case of a 57 year old man with cGVHD in whom the full manifestations of myositis were suppressed for some time, likely due to partial treatment of his condition with immunosuppression including ibrutinib. Though initial muscle biopsy showed necrotising myopathy without significant inflammation, on cessation of ibrutinib he developed increasing weakness and creatine kinase levels, with repeat muscle biopsy showing histological changes more in keeping with dermatomyositis. The close temporal correlation of his clinical course with commencement and cessation of ibrutinib suggests a potential role for ibrutinib in treating inflammatory myopathy in cGVHD.

Ganciclovir (GCV) and valganciclovir (VGCV) are the first-line agents used to prevent and treat cytomegalovirus (CMV) infection in allogeneic haematopoietic stem cell transplant (alloHCT) patients. The aim of this work was to describe available data for the clinical pharmacokinetics, pharmacodynamics and toxicodynamics of GCV and VGCV and the potential of a therapeutic drug monitoring strategy to improve outcomes in the alloHCT population. We systematically reviewed the pharmacokinetics (dose-exposure), pharmacodynamics (exposure-efficacy) and toxicodynamics (exposure-toxicity) of GCV and VGCV in alloHCT patients with CMV infection. Studies including alloHCT patients treated for CMV infection reporting the pharmacokinetics, pharmacodynamics and toxicodynamics of GCV or VGCV were searched for using the PUBMED and EMBASE databases from 1946 to 2019. Only studies involving participants > 12 years of age and available in the English language were included. A total of 179 patients were included in the 14 studies that met the inclusion criteria, of which 6 examined GCV pharmacokinetics only, while 8 also examined GCV pharmacodynamics and toxicodynamics. Reported pharmacokinetic parameters showed considerable interpatient variability and were different from other populations, such as solid organ transplant and human immunodeficiency virus-infected patients. Only one study found a correlation between neutropenia and elevated peak and trough GCV concentrations, with no other significant pharmacodynamic and toxicodynamic relationships identified. While therapeutic drug monitoring of GCV is performed in some institutions, no association between GCV therapeutic drug monitoring and clinical outcomes was identified. Further studies of the pharmacokinetics, pharmacodynamics and toxicodynamics of GCV/VGCV in alloHCT patients are required to identify a more robust therapeutic range and to subsequently quantify the potential value of therapeutic drug monitoring of GCV/VGCV in the alloHCT population.

The therapeutic potential of donor-derived mesenchymal stromal cells (MSCs) has been investigated in diverse diseases1, including steroid-resistant acute graft versus host disease (SR-aGvHD)2. However, conventional manufacturing approaches are hampered by challenges with scalability and interdonor variability, and clinical trials have shown inconsistent outcomes3,4. Induced pluripotent stem cells (iPSCs) have the potential to overcome these challenges, due to their capacity for multilineage differentiation and indefinite proliferation5,6. Nonetheless, human clinical trials of iPSC-derived cells have not previously been completed. CYP-001 (iPSC-derived MSCs) is produced using an optimized, good manufacturing practice (GMP)-compliant manufacturing process. We conducted a phase 1, open-label clinical trial (no. NCT02923375) in subjects with SR-aGvHD. Sixteen subjects were screened and sequentially assigned to cohort A or cohort B (n = 8 per group). One subject in cohort B withdrew before receiving CYP-001 and was excluded from analysis. All other subjects received intravenous infusions of CYP-001 on days 0 and 7, at a dose level of either 1 × 106 cells per kg body weight, to a maximum of 1 × 108 cells per infusion (cohort A), or 2 × 106 cells per kg body weight, to a maximum dose of 2 × 108 cells per infusion (cohort B). The primary objective was to assess the safety and tolerability of CYP-001, while the secondary objectives were to evaluate efficacy based on the proportion of participants who showed a complete response (CR), overall response (OR) and overall survival (OS) by days 28/100. CYP-001 was safe and well tolerated. No serious adverse events were assessed as related to CYP-001. OR, CR and OS rates by day 100 were 86.7, 53.3 and 86.7%, respectively. The therapeutic application of iPSC-derived MSCs may now be explored in diverse inflammatory and immune-mediated diseases. A GMP-compliant process for generating human iPSC-derived mesenchymal stromal cells tested in a phase 1 trial is safe and well tolerated in subjects with acute steroid-resistant graft versus host disease.

Barbara J. McClure, Susan L. Heatley, Jacqueline Rehn, James Breen, Rosemary Sutton, Timothy P. Hughes, Ram Suppiah, Tamas Revesz, Michael Osborn, Daniel White, David T. Yeung, Deborah L. White

Hematopoietic stem cell transplantation (HSCT) recipients are vulnerable to invasive pneumococcal disease (IPD), with reported IPD rates ranging from 3.81 to 22.5/1000 HSCT. This IPD risk could relate to immunodeficiency, low vaccination uptake, and poor immunogenicity of pneumococcal polysaccharide vaccine (PPV). Literature comparing the clinical effectiveness of pneumococcal conjugate vaccination (PCV) and PPV after HSCT is limited. In this retrospective analysis of HSCT recipients at our center from 2004 to 2015, we evaluated vaccination uptake and compared IPD rates in patients receiving PPV (pre-2010 group) and PCV (post-2010 group). IPD was determined from microbiological results for all HSCT recipients from January 2004 to June 30, 2019. Eight hundred patients had a total of 842 HSCT events, including autologous HSCT (auto-HSCT; n = 562) and allogeneic HSCT (allo-HSCT; n = 280). More than 90% of the HSCT recipients were enrolled, and93% of surviving HSCT recipients completed the vaccination protocol. Fifteen IPD episodes occurred in 13 patients between 2004 and June 30, 2019. Thirteen episodes occurred in the pre-2010 group, even though 9 of 13 (69%) serotyped isolates were covered by PPV. Two episodes occurred in the post-2010 group; neither serotype was covered by PCV. Thus, with PCV introduction, IPD rate was significantly reduced from 38.5/1000 unique HSCTs pre-2010 to 4.0/1000 unique HSCTs post-2010 (P.001). A significant reduction was seen in both auto-HSCTs (from 29.4 to 3.1 /1000 unique auto-HSCTs; P = .011) and allo-HSCTs (from 58.3 to 5.6/1000 unique allo-HSCTs; P = .011). PCV demonstrated superior clinical effectiveness over PPV, highlighting its importance in preventing infectious complications after HSCT. Robust vaccination programs at transplantation centers are needed to optimize vaccination uptake and completion.

OBJECTIVE: To develop a novel inhalation exposure system capable of delivering a controlled inhaled HD dose through an endotracheal tube to anesthetized rats to investigate the lung pathophysiology and evaluate potential medical countermeasures. MATERIALS AND METHODS: Target HD vapor exposures were generated by a temperature-controlled vapor generator, while concentration was monitored near real-time by gas chromatography. Animal breathing parameters were monitored real-time by in-line EMKA/SciReq pulmonary analysis system. Individual exposures were halted when the target inhaled doses were achieved. Animals were observed daily for clinical observations and lethality with scheduled termination at 28 days post-exposure. Upon scheduled or unscheduled death, animals underwent a gross necropsy and lung and trachea were collected for histopathology. RESULTS: Controlled HD concentrations ranged from 60 to 320 mg/m(3). Delivered inhaled doses range from 0.3 to 3.20 mg/kg with administered doses within 3% of the target. The 28-day inhaled LD(50) is 0.80 mg/kg (95% CI = 0.42–1.18 mg/kg). Post exposure respiratory abnormalities were observed across all dose levels though the higher dose levels had earlier onset and higher frequency of occurrence. Histopathologic alterations were not qualitatively altered in accordance with dose but instead showed a relationship to an animals’ time of death, with early deaths demonstrating acute damage and later deaths displaying signs of repair. DISCUSSION/CONCLUSION: This novel exposure system administers targeted HD inhaled doses to generate a small animal model that can be used to evaluate physiological toxicities of inhaled HD on the lungs and for evaluation of potential medical countermeasure treatments.

Key Points Pediatric ALL therapy is equally as deliverable in AYA patients as in children.MRD assessment and body mass index predict survival in AYA ALL., Visual Abstract, Pediatric regimens have improved outcomes in adolescent and young adult (AYA) acute lymphoblastic leukemia (ALL). However, results remain inferior to children with ALL. The Australasian Leukaemia and Lymphoma Group (ALLG) ALL06 study (anzctr.org.au/ACTRN12611000814976) was designed to assess whether a pediatric ALL regimen (Australian and New Zealand Children’s Haematology and Oncology Group [ANZCHOG] Study 8) could be administered to patients aged 15 to 39 years in a comparable time frame to children as assessed by the proportion of patients completing induction/consolidation and commencing the next phase of therapy (protocol M or high-risk [HR] treatment) by day 94. Minimal residual disease (MRD) response stratified patients to HR treatment and transplantation. From 2012 to 2018, a total of 86 patients were enrolled; 82 were eligible. Median age was 22 years (range, 16-38 years). Induction/consolidation was equally deliverable in ALL06 as in Study 8. In ALL06, 41.5% (95% confidence interval [CI], 30.7-52.9) commenced protocol M or HR therapy by day 94 vs 39.3% in Study 8 (P = .77). Median time to protocol M/HR treatment was 96 days (interquartile range, 87.5-103 days) in ALL06 vs 98 days in Study 8 (P = .80). Induction mortality was 3.6%. With a median follow-up of 44 months (1-96 months), estimated 3-year disease-free survival was 72.8% (95% CI, 62.8-82.7), and estimated 3-year overall survival was 74.9% (95% CI, 65.3-84.5). End induction/consolidation MRD negativity rate was 58.6%. Body mass index ≥30 kg/m2 and day 79 MRD positivity were associated with poorer disease-free survival and overall survival. Pediatric therapy was safe and as deliverable in AYA patients as in children with ALL. Intolerance of pediatric ALL induction/consolidation is not a major contributor to inferior outcomes in AYA ALL.

The Chemical Countermeasures Research Program (CCRP) was established in 2006 by the National Institute of Allergy and Infectious Diseases (NIAID/NIH) on behalf of the National Institutes of Health Office of the Director (NIH OD). It is a trans-NIH initiative to expedite the discovery and early development of medical countermeasures (MCMs) that can reduce mortality and serious morbidity during and after large consequence public health emergency involving the deliberate or accidental large-scale release of highly toxic chemicals (HTCs).

In chronic-phase chronic myeloid leukemia (CP-CML) patients treated with frontline imatinib, failure to achieve early molecular response (EMR; EMR failure: BCR-ABL1 >10% on the international scale at 3 months) is predictive of inferior outcomes. Identifying patients at high-risk of EMR failure at diagnosis provides an opportunity to intensify frontline therapy and potentially avoid EMR failure. We studied blood samples from 96 CP-CML patients at diagnosis and identified 365 genes that were aberrantly expressed in 13 patients who subsequently failed to achieve EMR, with a gene signature significantly enriched for stem cell phenotype (eg, Myc, β-catenin, Hoxa9/Meis1), cell cycle, and reduced immune response pathways. We selected a 17-gene panel to predict EMR failure and validated this signature on an independent patient cohort. Patients classified as high risk with our gene expression signature (HR-GES) exhibited significantly higher rates of EMR failure compared with low-risk (LR-GES) patients (78% vs 5%; P < .0001), with an overall accuracy of 93%. Furthermore, HR-GES patients who received frontline nilotinib had a relatively low rate of EMR failure (10%). However, HR-GES patients still had inferior deep molecular response achievement rate by 24 months compared with LR-GES patients. This novel multigene signature may be useful for selecting patients at high risk of EMR failure on standard therapy who may benefit from trials of more potent kinase inhibitors or other experimental approaches.

Although second-generation tyrosine kinase inhibitors (TKIs) show superiority in achieving deep molecular responses in chronic myeloid leukemia in chronic phase (CML-CP) compared with imatinib, the differing adverse effect (AE) profiles need consideration when deciding the best drug for individual patients. Long-term data from randomized trials of nilotinib demonstrate an increased risk of vascular AEs (VAEs) compared with other TKIs, although the natural history of these events in response to dose modifications or cessation has not been fully characterized. We retrospectively reviewed the incidence of nilotinib-associated AEs in 220 patients with CML-CP at 17 Australian institutions. Overall, AEs of any grade were reported in 95 patients (43%) and prompted nilotinib cessation in 46 (21%). VAEs occurred in 26 patients (12%), with an incidence of 4.1 events per 100 patient-years. Multivariate analysis identified age (P = .022) and dyslipidemia (P = .007) as independent variables for their development. There was 1 fatal first VAE, whereas the remaining patients either continued nilotinib (14 patients) or stopped it immediately (11 patients). Recurrent VAEs were associated with ongoing therapy in 7 of 14 who continued (with 2 fatal VAEs) vs 1 of 11 who discontinued (P = .04). Nineteen of the 23 evaluable patients surviving a VAE ultimately stopped nilotinib, of whom 14 received an alternative TKI. Dose reduction or cessation because of VAEs did not adversely affect maintenance of major molecular response. These findings demonstrate that in contrast to other AEs, VAEs are ideally managed with nilotinib cessation because of the increased risk of additional events with its ongoing use.

With treatment-free remission (TFR) rapidly becoming the ultimate goal of therapy in chronic myeloid leukemia (CML), there is a need to develop strategies to maximize sustained TFR by improving our understanding of its key determinants. Chronic-phase CML patients attempting TFR were evaluated to identify the impact of multiple variables on the probability of sustained TFR. Early molecular response dynamics were included as a predictive variable, assessed by calculating the patient-specific halving time of BCR-ABL1 after commencing tyrosine kinase inhibitor (TKI) therapy. Overall, 115 patients attempted TFR and had ≥12 months of follow-up. The probability of sustained TFR, defined as remaining in major molecular response off TKI therapy for 12 months, was 55%. The time taken for the BCR-ABL1 value to halve was the strongest independent predictor of sustained TFR: 80% in patients with a halving time of 21.85 days (last quartile) (P < .001). The e14a2 BCR-ABL1 transcript type and duration of TKI exposure before attempting TFR were also independent predictors of sustained TFR. However, the BCR-ABL1 value measured at 3 months of TKI was not an independent predictor of sustained TFR. A more rapid initial BCR-ABL1 decline after commencing TKI also correlated with an increased likelihood of achieving TFR eligibility. The association between sustained TFR and the time taken for BCR-ABL1 to halve after commencing TKI was validated using an independent dataset. These data support the critical importance of the initial kinetics of BCR-ABL1 decline for long-term outcomes.

SUMMARY Patients with chronic myeloid leukaemia and chronic lymphocytic leukaemia are now predominantly managed in an outpatient setting, with infrequent need for hospital-based therapy. New targeted oral treatments have transformed survival outcomes. An increasing number of patients now have a life expectancy approaching that of the general population. Suboptimal drug adherence is common and a key reason for therapy failure and poor clinical outcomes. The pharmacokinetics of new oral targeted drugs are significantly impacted by drug–drug interactions and an altered gastric pH. Long-term use of some of the new oral drugs is associated with complications, including cardiovascular events and infections, which can be fatal if not recognised.

DUX4-rearrangement (DUX4r) is a recently discovered recurrent genomic lesion reported in 4–7% of childhood B cell acute lymphoblastic leukaemia (B-ALL) cases. This subtype has favourable outcomes, especially in children and adolescents treated with intensive chemotherapy. The fusion most commonly links the hypervariable IGH gene to DUX4 a gene located within the D4Z4 macrosatellite repeat on chromosome 4, with a homologous polymorphic repeat on chromosome 10. DUX4r is cryptic to most standard diagnostic techniques, and difficult to identify even with next generation sequencing assays. This review summarises the clinical features and molecular genetics of DUX4r B-ALL and proposes prospective new diagnostic methods.

The United States Department of Health and Human Services (HHS) leads the nation in preventing, preparing for, and responding to the adverse health effects of public health emergencies and disasters. In addition to biological, radiological and nuclear agents, the risk of a high consequence public health emergency due to the intentional and/or accidental release of chemical agents is a major growing concern of the US government. As such, the federal government is fully committed to address public health security threats posed by chemicals. To enhance chemical emergency preparedness and response, HHS oversees the interdepartmental research, advanced development, regulatory review and approval, procurement, and stockpiling of medical countermeasures (MCMs). Within the National Institute of Health (NIH/HHS), the National Institute of Allergy and Infectious Diseases (NIAID) is responsible for the fundamental research and early development of MCMs to prevent deaths and/or treat injuries during and after emergencies due to large scale chemical exposure. This commentary provides an overview of the NIAID/NIH Chemical Countermeasures Research Program (CCRP) and resources to facilitate the research, discovery, and early development of chemical MCMs. Available product development resources include research funding opportunities, expert advice from the NIH, and preclinical and efficacy service support cores to reduce opportunity costs and entry barriers for prospective developers interested in entering or accelerating the development of chemical MCMs.

High consequence chemical emergency is a major public health concern. In the United States, the National Institute of Allergy and Infectious Diseases within the National Institutes of Health (NIAID/NIH) pioneers discovery and early development of critical medical countermeasures against chemical threats.

On August 6th, 2019, a two-day trans-agency scientific meeting was convened by the United States (U.S.) National Institute of Allergy and Infectious Diseases (NIAID/NIH) on the research and development of medical countermeasures (MCMs) and treatment strategies to mitigate synthetic opioid-induced toxicities. This trans-agency meeting was an initiative of the Chemical Countermeasures Research Program (CCRP) and organized by the NIAID in collaboration with the National Institute of Drug Abuse (NIDA), the Biomedical Advanced Research and Development Authority (BARDA), the Food and Drug Administration (FDA), and the Defense Threat Reduction Agency (DTRA). The CCRP is part of the larger NIH biodefense research program coordinated by NIAID, which also includes MCM research and development programs against biological, radiological, and nuclear threats. Its overarching goal is to integrate cutting-edge research and technological advances in science and medicine to enhance the nation’s medical response capabilities during and after a public health emergency involving the deliberate or accidental release of toxic chemicals. The potential of a mass casualty public health event involving synthetic opioids is a rapidly growing concern. As such, the overall goals of this trans-agency meeting are to better understand opioid-induced toxicities and advance the development of MCMs to mitigate and reverse opioid-induced respiratory depression (OIRD) to prevent consequential mortality. The primary objectives of the meeting were (1) highlight the latest research on mechanisms of OIRD and related toxicities, animal models, diagnostics, delivery technologies, and emerging new treatment options to prevent lethality; (2) identify current knowledge gaps to advance medical countermeasure development; (3) hear from the U.S. FDA on regulatory considerations to support new technology and treatment approaches; and (4) provide a forum for networking and collaborative partnerships. To accomplish this, a diverse group of almost 200 US domestic and international subject matter experts spanning fundamental and translational research from academia, industry, and government came together in-person to share their collective expertise and experience in this important field. This report briefly summarizes the information presented throughout the meeting, which was also webcast live in its entirety to registered remote attendees. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s13181-019-00750-x) contains supplementary material, which is available to authorized users.

usc Background: Some patients receiving a tyrosine kinase inhibitor (TKI) for the first-line treatment of chronic phase chronic myeloid leukemia (CML-CP) experience intolerable adverse events. Management strategies in-clude dose adjustments, interrupting or discontinuing therapy, or switching to an alternative TKI. Methods: This multicenter, single-arm, Phase IIIb study included CML-CP patients intolerant of, but responsive to, first-line treatment with imatinib or dasatinib. All patients were switched to nilotinib 300 mg bid for up to 24 months. The primary endpoint was achievement of MR4.5 (BCR-ABL transcript level of ≤ 0.0032% on the International Scale) by 24 months. Results: Twenty patients were enrolled in the study (16 imatinib-intolerant, 4 dasatinib-intolerant); which was halted early because of low recruitment. After the switch to nilotinib 300 mg bid, MR4.5 at any time point up to month 24 was achieved in 10 of 20 patients (50%) in the full analysis set. Of the non-hematological adverse events associated with intolerance to prior imatinib or dasatinib, 74% resolved within 12 weeks of switching tonilotinib 300 mg bid. Conclusion: Nilotinib 300 mg bid shows minimal cross intolerance in patients with CML-CP who have prior toxicities to other TKIs and can lead to deep molecular responses. Refereed/Peer-reviewed

Neurofibromatosis type 1 (NF-1) is an autosomal dominant disorder affecting approximately 1:3000 individuals globally. While approximately 50% are familial, with over 3000 causative germline variants in the neurofibromatosis (NF1) gene identified, the remainder occur sporadically. These mutations lead to haploinsufficiency of NF1 and neurofibromin, a tumor suppressor and important negative regulator of RAS signaling. Children with NF-1 have a higher risk of developing juvenile myelomonocytic leukemia and acute myeloid leukemia, but rarely develop acute lymphoblastic leukemia (ALL). A 9-year-old male presented in 2015 with persistent migratory subcutaneous swellings and multiple bony aches with lytic lesions on bone imaging. He had a high white cell count with eosinophilia (WCC 43.4 x 10 9/L, eosinophils 23.87 x 10 9/L) with no circulating blasts, 10% marrow blasts (CD10+/CD19+/CD34+) and was CNS negative. Although previously undiagnosed, NF-1 was clinically suspected due to typical skin changes. He was diagnosed with iAMP21 ALL and NF-1 was confirmed with the identification of a germline NF1 donor splice site mutation (c.1845G>A:p.L615=). Bone marrow cells were sorted by flow cytometry on CD19 positivity and underwent transcriptomic sequencing. This revealed a P2RY8-CRLF2 gene fusion, with no other clinically relevant variants, while a custom Taqman low density array indicated high-risk B-ALL subtype Ph-like ALL. Multiplex ligation-dependent probe amplification (MLPA) confirmed iAMP21 and also identified IKZF1 exon 2-3 and BTG1 deletions. Treatment followed the high-risk B-ALL arm of the AEIOP-BFM ALL2009 protocol due to persistent end-consolidation MRD in addition to iAMP21 and the Ph-like phenotype. He relapsed three years later off treatment and was refractory to both salvage chemotherapy and blinatumomab. The iAMP21, P2RY8-CRLF2 gene fusion, IKZF1 exon 2-3 and BTG1 deletions remained detectable. Whole exome sequencing of CD19 positive samples from diagnosis, relapse and mesenchymal stem cells (germline control) was performed, identifying a NF1 c.7400dupT:p.L2467 frameshift (fs) mutation only at relapse. To understand the implications of NF1 p.L2467fs, the P2RY8-CRLF2 gene fusion was first transduced into the interleukin 3 (IL3) dependent murine pro-B cell line Ba/F3. P2RY8-CRLF2 alone is not transforming and is thought to be a secondary event in iAMP21 ALL, providing an ideal model to study the cumulative effect of the NF1fs. The NF1fs was then introduced to the P2RY8-CRLF2 cells by CRISPR/Cas9. A proliferation assay was performed without IL3 and demonstrated the P2RY8-CRLF2+NF1fs cell line was IL3 independent, indicative of leukemic transformation, whereas all other lines were not (vs Ba/F3, p = 0.001). Neurofibromin can be constitutively phosphorylated at the c-terminus, negatively regulating NF1-GAP activity, suppressing RAS signaling and inducing cell cycle arrest. Therefore, to demonstrate loss of function due to the c-terminus NF1 p.L2467fs and increased RAS signaling, western blotting for pERK was performed. Significant upregulation of pERK was confirmed in P2RY8-CRLF2+NF1fs in comparison to Ba/F3 control cells (p=0.007) (Figure 1). The MEK inhibitors trametinib and mirdametinib are in clinical trials for NF-1 patients and have shown efficacy in ALL models with RAS mutations. In a 3-day cell death assay, only P2RY8-CRLF2+NF1fs demonstrated sensitivity to trametinib (LD 50 P2RY8-CRLF2 = >6.4 µM, NF1fs = >6.4 µM, P2RY8-CRLF2+NF1fs =1.7µM; p < 0.001) and mirdametinib (LD 50 P2RY8-CRLF2 = >16 µM, NF1fs = >16 µM, P2RY8-CRLF2+NF1fs = 8.3 µM; p < 0.0001) (Figure 2). Here, we have demonstrated a LOF NF1fs mutation using an in-vitro model of ALL. Germline NF1 haploinsufficiency and a second hit NF1 mutation in ALL is limited to one report of monozygotic twins with neurofibromatosis. We propose that NF1 p.L2467fs caused bi-allelic LOF and therefore contributed to relapse in this patient. An understanding of the genomic complexities that lead to relapse may also inform personalized treatment strategies. While this patient subsequently achieved remission with inotuzomab and underwent successful stem cell transplantation, the sensitivity to MEK inhibitors is an exciting development for neurofibromatosis patients with ALL. Figure 1 Figure 1. Disclosures Yeung: Amgen: Honoraria; BMS: Honoraria, Research Funding; Pfizer: Honoraria; Novartis: Honoraria, Research Funding. White: BMS: Honoraria, Research Funding; Novartis: Research Funding.

Dasatinib has shown superiority over imatinib in achieving molecular responses (MRs) in chronic phase chronic myeloid leukemia but with a different toxicity profile, which may impact its overall benefit. Reported toxicities include pleural effusions and pulmonary hypertension, and although the incidence of these events is well described, response to therapy and impact of dose modifications on toxicity has not been comprehensively characterized in a real-world setting. We retrospectively reviewed the incidence of dasatinib adverse events in 212 chronic phase chronic myeloid leukemia patients at 17 Australian institutions. Adverse events were reported in 116 patients (55%), most commonly pleural effusions (53 patients, 25%), which was the predominant cause of permanent drug cessation. Age and dose were risk factors for pleural effusion (P < .01 and .047, respectively). Recurrence rates were higher in those who remained on 100 mg compared with those who dose reduced (P = .041); however, recurrence still occurred at 50 mg. Patients who developed pleural effusions were more likely to have achieved MR4.5 after 6 months of dasatinib than those without effusions (P = .008). Pulmonary hypertension occurred in 5% of patients, frequently in association with pleural effusion, and was reversible upon dasatinib cessation in 6 of 7 patients. Dose reductions and temporary cessations had minimal impact on MR rates. Our observations suggest that by using the lowest effective dose in older patients to minimize the effusion risk, dose modification for cytopenias, and care with concomitant antiplatelet therapy, the necessity for permanent dasatinib cessation due to toxicity is likely to be minimal in immunologically competent patients.

Background HLA-matched sibling and unrelated donors are not always available for patients that are in need of an allogeneic haematopoietic stem cell transplant. Partially HLA-mismatched related (haploidentical) donors can be identified for the vast majority of patients but these transplants were historically complicated by excessive graft versus host disease (GVHD), nonrelapse mortality (NRM), and poor overall survival (OS). Haploidentical haematopoietic stem cell transplantation (Haplo HSCT) has become increasingly common over the last ten years, predominately due to the successful use of post-transplant cyclophosphamide (PTCy) in mitigating graft versus host disease (GVHD). Most studies using PTCy have been retrospective with various conditioning regimens and stem cell sources making interpretation of results difficult. ANZHIT-1 is a prospective Australian multi-centre phase II study of Haplo HSCT with defined conditioning and GVHD prophylaxis regimens. Methods: This is an ethics approved Phase II study (ACTRN: 12617000151336) conducted between 2015-2020 at six Australian allogeneic HSCT centres. All patients received peripheral blood Haplo HSCT from haploidentical family members. The reduced intensity regimen (RIC) was fludarabine, cyclophosphamide and 200cGy TBI and the myeloablative regimen (MAC) was fludarabine with IV busulfan 3.2mg/kg x 4. PTCy 50mg/kg D+3, D+4 was used with MMF (to D35) and a calcineurin inhibitor (CNI) as GVHD prophylaxis. CNIs were weaned and ceased by D+120 in patients who did not have evidence of GVHD. Choice of conditioning regimen was based on age and hematopoietic cell transplantation comorbidity index (HCT-CI) scores. Patients who had an HCTCI >3 or age >50yrs received RIC. Data collection was through the Australian Bone Marrow Transplant Recipient Registry. Survival was analysed using the Kaplan-Meier method. Results: Seventy eight patients were included in the study with a median follow up of 402.5 days (28-1259). There was a male predominance (66%). The median age was 53 years (range 18-69) and the median HCT-CI score was 1 (range 0-5). Thirty nine patients had acute myeloid leukaemia, 12 acute lymphoblastic Leukaemia, 14 Non Hodgkin lymphoma or Hodgkin lymphoma, 4 myelodysplastic syndrome and 9 other diagnoses. The majority received RIC (59%). Median neutrophil and platelet engraftment times were 18 days (range: 12-92) and 28 days (range: 13-262) respectively. Acute GVHD grade III-IV occurred in 14.1% of patients whilst chronic GVHD occurred in 20.5%. Moderate to severe cGVHD according to NIH consensus criteria occurred in 10.3% of patients. Overall survival probability at one year was 74.1% (95% CI: 52.9-86.8) for MAC recipients and 77.8% (95% CI: 61.6-87.8) for RIC recipients (Figure 1). Non relapse mortality (NRM) at D100 and 1 year were 2.2% and 8.7% respectively in the RIC group compared to 6.3% and 18.8% respectively in the MAC group. Causes of NRM included infection (n=5), GVHD (n=3) and VOD, respiratory failure and multi-organ failure in one patient each. Haemorrhagic cystitis and poor graft function were relatively common post-transplant morbidities but rarely contributed to NRM. Despite the use of peripheral blood stem cells and early weaning of CNIs, only 3/11 NRM deaths were due to GVHD. Relapse was the most common cause of death in the RIC group with 17.4% of patients relapsing at a median of 114 days (range 36-564) compared to only 6.3% at a median of 90.5 days (range 64-154) in the MAC group. Conclusion: This prospective Haplo HSCT trial utilising PTCY demonstrates encouraging overall survival rates. The RIC regimen had a promising toxicity profile but early relapse remains a concern despite early weaning of CNIs. In contrast, the MAC regimen is associated with a low relapse rate but NRM at one year remains significant. Further refinement of the conditioning and GVHD prophylaxis regimens will be incorporated in the follow-on study, ANZHIT-2, which will begin accrual in late 2020. Disclosures Bajel: Pfizer: Honoraria; Amgen: Honoraria, Speakers Bureau; Novartis: Honoraria; Astellas: Honoraria; Abbvie: Honoraria. Greenwood:Servier: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; MSD: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Hamad:Novartis: Honoraria; Abbvie: Honoraria.

Introduction Mantle cell lymphoma (MCL) is a mature B lymphoproliferative disorder with a frequently aggressive clinical course. Although the response rates in patients eligible for conventional chemoimmunotherapy are high, relapses are virtually inevitable, with a median overall survival (OS) of three to five years. For some patients allogeneic stem haematopoietic cell transplantation (alloHCT) is a potential therapeutic option. AlloHCT for MCL has been associated with long term overall survival (OS) of around 40%, with high rates of non-relapse mortality (NRM) of 20-40% and relapse rates of 20-30% (Urbano-Ispizua et al., Biol Blood Marrow Transplant 2015;21:1746, Robinson et al., Leukemia 2015;29:464). Whilst there is evidence of a graft-versus-lymphoma effect in MCL, it has not been shown to translate into improved OS. We performed a retrospective national registry study to examine alloHCT practice and outcomes for MCL in Australia and New Zealand in the modern era. Methods Data was collected through the Australasian Bone Marrow Transplant Recipient Registry (ABMTRR) for patients receiving an alloHCT for MCL between January 2009 and December 2019. This time range was chosen to capture the era of widespread rituximab use. Survival, relapse and toxicities of alloHCT were investigated, as well as transplant trends over time. Survival was analysed using the Kaplan-Meier method, with comparisons between the transplant periods 2009-2014 and 2015-2019 performed using the log-rank test. Cox proportional hazards regression was performed to determine significant risk factors for transplant outcome. The following risk factors were analysed for impact on outcomes: age, transplant before 2015, previous autologous HCT (autoHCT), remission status at transplant, use of myeloablative conditioning (MAC), haploidentical donor and use of T cell depletion (TCD). Results A total of 86 patients were included in the analysis. The median age was 56 (range 39-71). There was a male predominance with only 12% female patients. At the time of transplant, 51% were in complete remission, 26% had a partial response and 20% had stable or progressive disease (data missing in 3%). Sixty-seven percent had undergone previous autoHCT. The majority of donors were HLA-matched siblings (51%), followed by HLA-matched-unrelated (42%) and haploidentical (7%). Myeloablative conditioning was utilised in 14%, and T-cell depletion (TCD) in 24%. The median times to neutrophil engraftment (>0.5x109/L) and platelet engraftment (>20x109/L) were 16 and 20 days respectively. NRM at 1 and 5 years was 23% (95% confidence interval [95%CI] 10-39%) and 30% (95%CI 15-48%) respectively. The 100-day cumulative incidence of grade II to IV acute GVHD was 29%. The 3-year cumulative incidence of chronic GVHD was 27%. The median duration of follow up was 4.17 years (range 0-9.6 years). Median OS was 4.2 years, with an estimated 5-year OS of 47% (95%CI 35-58%) and 10-year OS of 23% (95%CI 8-43%) (figure 1). Five-year relapse free survival (RFS) was 38% (95%CI 26-50%) (figure 2). The cumulative incidence of relapse (CIR) was 20% at 1 year and 33% at 4 years, with a flattening of the curve after this point (figure 3). On multivariate analysis (MVA), the use of myeloablative conditioning (MAC) was associated with inferior RFS (hazard ratio 2.33; 95%CI 1.05-5.17; p=0.038) and OS (hazard ratio 3.11; 95%CI 1.39-7.00; p=0.006) (figure 4). No risk factors on MVA impacted NRM or CIR. Chronic GVHD was not associated with RFS or CIR. An average of nine alloHCTs were performed each year. There was an increase in the proportion of haploidentical transplants between 2009-2014 and 2015-2019 (4% to 10%). There was no significant change over time in OS, RFS or NRM, or in the use of MAC or TCD. Conclusion There has been no significant change in the rates of alloHCT for MCL in Australia and New Zealand over the past decade. Trends show an increasing utilisation of haploidentical donors. Overall outcomes were comparable to those previously published with favourable OS and durable remissions seen in a subset of patients. MAC was associated with inferior OS and RFS, however the cause for this is unclear given the lack of association with NRM or CIR. Ongoing reporting of alloHCT outcomes in MCL is important given the emerging role of novel therapies, such as Bruton tyrosine kinase inhibitors, bispecific T cells and CAR-T cell therapy. Figure 1 Disclosures Di Ciaccio: Jansen: Honoraria, Other: travel and accomodation grant. Greenwood:MSD: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Servier: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Hamad:Novartis: Honoraria; Abbvie: Honoraria.

Background We previously reported a high incidence of mutated cancer-related genes at CML diagnosis in selected chronic phase patients with a poor outcome compared to those with a good outcome. We also found a novel class of variant associated with the formation of the Ph chromosome comprising fusions and/or rearrangement of genes on the translocated chromosomes, with evidence of fragmentation, inversion, and imperfect sequence reassembly. These were termed 'Ph-associated events' and were more frequent in patients with poor outcome. However, the risk attributable to these mutational events at diagnosis has not been defined in unselected cohorts. Aim To assess the impact of genomic events in a cohort of consecutively treated patients at diagnosis of chronic phase CML. Methods A hybridization capture sequencing method targeting genes implicated in myeloid and lymphoid malignancies was applied to diagnostic RNA of patients enrolled in the TIDEL II trial. Patients were treated with upfront imatinib with active intervention, dose escalation or nilotinib switch, primarily for lack of time-dependent molecular milestones. Single base variants, small insertions/deletions, splice variants, gene fusions, and focal gene deletions were assessed with pre-defined criteria for pathogenicity. These were further classified as pathogenic mutations in cancer-related genes or Ph-associated events. Univariate and multivariate analyses were performed to evaluate the influence of mutational events and other key clinical and demographic variables on outcome at 4 years. Failure events were as defined by the ELN 2020 recommendations. Results 160/210 TIDEL II patients have so far been sequenced. 33 relevant mutations with variant allele frequencies ≥5% were identified in 9 genes in 25 patients (16%). ASXL1 was most frequently mutated (10% of all patients) and other recurrently mutated genes at diagnosis were RUNX1, BCORL1, IKZF1 and DNMT3A. Ph-associated events occurred in 25 patients (16%). Most of these (14/25 patients) involved fusions between genes on chromosomes 9 and 22 consistent with deletions adjacent to BCR and ABL1, or fusions between BCR or ABL1 and genes/regions on chromosomes other than 9 or 22. These were consistent with variant translocation and some were cytogenetically cryptic. Among these and other Ph-associated events were complex rearrangements involving inversions and large duplications. These were detected in 14/25 patients. Five patients had both cancer-related gene mutations and Ph-associated events, totalling 45 patients (28%) with at least 1 genomic event. Cancer-related mutations at diagnosis were associated with inferior progression-free survival (PFS) 82% vs 91% P=.03, and failure-free survival (FFS) 55% vs 83% P Independent predictors of all survival and molecular outcomes were assessed with univariate and multivariate modelling (Table). Candidate prognostic variables were age at diagnosis, sex, transcript, Sokal and ELTS scores and the genomic variables. The only independent predictor of PFS was mutations in cancer-related genes. Cancer-related gene mutations, Ph-associated events and the ELTS score were independent predictors of FFS, MMR and MR4. We evaluated whether genomic data could be additive to the ELTS risk score. Low risk ELTS patients with any mutational event had inferior outcomes: FFS 76% vs 86%, P=.07; MMR 75% vs 92%, P=.02; MR4 41% vs 75%, P=0.006. Similar findings were observed in Intermediate risk ELTS patients: FFS 22% vs 91%, P Conclusion Despite a proactive strategy for TKI switch and a higher imatinib starting dose, the presence of cancer-related gene mutations or Ph-associated events conferred inferior outcomes. Combining the ELTS score with any mutational event further differentiated patient outcomes, demonstrating the power of integrating genomic data with current risk stratification. Disclosures Shanmuganathan: Janssen: Other: travel expenses; Novartis: Honoraria, Other: Travel expenses; Gilead: Other: Travel expenses; Amgen: Other: travel expenses. Hughes:BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Branford:Bristol Myers Squibb: Honoraria; Cepheid: Honoraria, Membership on an entity's Board of Directors or advisory committees; Qiagen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding.

With the increasing adoption of treatment-free remission (TFR) as a goal for patients with chronic myeloid leukemia (CML), rigorous molecular monitoring has been recommended to ensure timely tyrosine kinase inhibitor (TKI) recommencement in the event of molecular relapse. The National Comprehensive Cancer Network (NCCN) has now incorporated TFR into its most recent guidelines, recommending monthly quantitative polymerase chain reaction monitoring of BCR-ABL1 for the first 12 months following TKI discontinuation.1 Molecular relapse, the trigger to restarting TKI, is currently defined as loss of major molecular response 2 (MMR; BCR-ABL1 ≤ 0.1% International Scale), and predominantly occurs in the first 6 months following TKI cessation.3,4 Delay in detection of molecular relapse may place patients at unnecessary risk of adverse outcomes, such as loss of complete hematological response. At a minimum, it delays the reachievement of MMR and deep molecular response (MR4; BCR-ABL1 ≤ 0.01% or MR4.5; BCR-ABL1 ≤ 0.0032%). Conversely, an overly rigorous monitoring schedule imposes unnecessary costs associated with a TFR attempt, adding to logistical difficulties experienced by some patients in accessing highly sensitive, standardized BCR-ABL1 testing,5 and may prevent some patients from stopping therapy. This is especially important in countries where funding of molecular testing is limited, and patients may be required to pay for additional tests. Refereed/Peer-reviewed

Introduction A majority of patients with diffuse large B cell lymphoma (DLBCL) will be cured with frontline chemoimmunotherapy, however a significant number of patients will relapse. Although autologous haematopoietic stem cell transplantation (autoHCT) may lead to sustained survival in some relapsing patients, long term survival with relapsed DLBCL is approximately 25% (Larouche et al., J Clin Oncol 2010;28(12):2094). Allogeneic HCT (alloHCT) is a potential treatment strategy in some DLBCL patients with relapsed disease. We performed a retrospective national registry study to examine alloHCT practice and outcomes for DLBCL in Australia and New Zealand in the modern era. Methods Data was collected through the Australasian Bone Marrow Transplant Recipient Registry (ABMTRR) for patients receiving an alloHCT for DLBCL between January 2009 and December 2019. Survival was analysed using the Kaplan-Meier method, with comparisons between the transplant periods 2009-2014 and 2015-2019 performed using the log-rank test. Both univariate and Cox proportional hazards regression were performed to determine significant risk factors for transplant outcome. The following risk factors were analysed for impact on outcomes: age, transplant before 2015, previous autoHCT, remission status at transplant, use of myeloablative conditioning (MAC), haploidentical donor (HD) and use of T cell depletion (TCD). Results A total of 154 patients were included in the analysis. The median age was 52 years (range 19-71) and 68% were male. Disease status at transplant was complete remission (CR) in 49%, partial response in 31% and stable or progressive disease in 17% (missing data in 3%). Fifty-five per cent had undergone a previous autoHCT. Approximately equal proportions of donors were HLA-matched siblings or matched unrelated (45% and 46% respectively) and 9% were HDs. MAC was utilised in 26%, and TCD in 24% (alemtuzumab in 3%, anti-thymocyte globulin in 21%) (data missing in 12%). The median times to neutrophil engraftment and platelet engraftment were 16 and 18 days respectively. Non-relapse mortality (NRM) at 1-year and 5-years was 20% (95%CI 7-30%) and 26% (95%CI: 13-38%). The 100-day cumulative incidence of grade II to IV acute graft versus host disease was 15% (95%CI 5-31%). The 3-year cumulative incidence of chronic graft versus host disease (cGVHD) was 56% (95%CI 46-65%) (figure 1). The median duration of follow up for the cohort was 3.98 years (range 0-9.64 years). Median overall survival (OS) post-transplant was 4.01 years, with 5-year OS of 47% (95%CI 38-56%) and 10-year OS of 40% (95%CI 26-54%) (figure 2). The 5-year relapse free survival (RFS) was 45% (95%CI 26-50%) (figure 3). The cumulative incidence of relapse (CIR) was 21% at 1 year and 32% at four years, however relapses were not seen after this point, suggesting a subpopulation with durable remissions (figure 4). On univariate analysis, TCD was associated with both reduced incidence of cGVHD (HR 0.35 95%CI 0.19-0.66, p=0.012) and increased NRM (HR 2.10 95%CI 0.88-4.99 p=0.043). These associations were maintained on multivariate analysis (MVA) (HR 0.29 95%CI 0.16-0.76, p=0.011; HR 2.19 95%CI 1.02-4.70, p=0.045) (figures 5, 6). TCD did not impact on RFS. The vast majority of TCD was given in unrelated donor alloHCTs. CR at time of transplant was associated with improved RFS on univariate analysis (HR 1.65 95%CI 1.04-2.64, p=0.034), however this association was not seen on MVA. No other analysed risk factors impacted OS, RFS, NRM, CIR or GVHD rates on either univariate or MVA. An average of 14 alloHCTs were performed each year, with a trend towards increasing annual numbers over time. There was a significant increase in the proportion of haploidentical transplants between 2009 and 2019 (p=0.003), though total numbers were low (n=14). There was no significant change over time for the use of MAC, TCD, nor in OS, RFS or NRM. Conclusion There has been an increase in the rates of alloHCT with HDs for DLBCL in Australia and New Zealand over the past decade. Survival and relapse rates are relatively favourable compared to the published literature, with sustained remissions observed (5 and 10-year OS of 47% and 40% respectively). TCD is associated with reduced cGVHD rates, as well as increased NRM. Ongoing reporting of alloHCT outcomes in DLBCL is important given the emerging role of novel therapies such as bispecific monoclonal antibodies and chimeric antigen receptor T cell therapy. Figure 1 Disclosures Di Ciaccio: Jansen: Honoraria, Other: travel and accomodation grant. Greenwood:Servier: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; MSD: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Spencer:Celgene, Janssen and Takeda: Speakers Bureau; AbbVie, Amgen, Celgene, Haemalogix, Janssen, Sanofi, SecuraBio, Specialised Therapeutics Australia, Servier and Takeda: Honoraria; Amgen, Celgene, Haemalogix, Janssen, Servier and Takeda: Research Funding; AbbVie, Celgene, Haemalogix, Janssen, Sanofi, SecuraBio, Specialised Therapeutics Australia, Servier and Takeda: Consultancy. Arthur:Royal North Shore Hospital: Current Employment. Hamad:Novartis: Honoraria; Abbvie: Honoraria.

The clinical significance of ABCB1 overexpression in predicting outcome of CML patients undergoing first-line imatinib treatment

The third-generation tyrosine kinase inhibitor (TKI) ponatinib shows activity against all common BCR-ABL1 single mutants, including the highly resistant BCR-ABL1-T315I mutant, improving outcome for patients with refractory chronic myeloid leukemia (CML). However, responses are variable, and causal baseline factors have not been well-studied. The type and number of low-level BCR-ABL1 mutations present after imatinib resistance has prognostic significance for subsequent treatment with nilotinib or dasatinib as second-line therapy. We therefore investigated the impact of low-level mutations detected by sensitive mass-spectrometry before ponatinib initiation (baseline) on treatment response in 363 TKI-resistant patients enrolled in the PONATINIB for Chronic Myeloid Leukemia Evaluation and Ph+ Acute Lymphoblastic Leukemia trial, including 231 patients in chronic phase (CP-CML). Low-level mutations were detected in 53 patients (15%, including low-level T315I in 14 patients); most, however, did not undergo clonal expansion during ponatinib treatment and, moreover, no specific individual mutations were associated with inferior outcome. We demonstrate however, that the number of mutations detectable by mass spectrometry after TKI resistance is associated with response to ponatinib treatment and could be used to refine the therapeutic approach. Although CP-CML patients with T315I (63/231, 27%) had superior responses overall, those with multiple mutations detectable by mass spectrometry (20, 32%) had substantially inferior responses compared with those with T315I as the sole mutation detected (43, 68%). In contrast, for CP-CML patients without T315I, the inferior responses previously observed with nilotinib/dasatinib therapy for imatinib-resistant patients with multiple mutations were not seen with ponatinib treatment, suggesting that ponatinib may prove to be particularly advantageous for patients with multiple mutations detectable by mass spectrometry after TKI resistance. Refereed/Peer-reviewed

Genomic events associated with poor outcome in chronic myeloid leukemia (CML) are poorly understood. We performed whole-exome sequencing, copy-number variation, and/or RNA sequencing for 65 patients to discover mutations at diagnosis and blast crisis (BC). Forty-six patients with chronic-phase disease with the extremes of outcome were studied at diagnosis. Cancer gene variants were detected in 15 (56%) of 27 patients with subsequent BC or poor outcome and in 3 (16%) of 19 optimal responders (P 5 .007). Frequently mutated genes at diagnosis were ASXL1, IKZF1, and RUNX1. The methyltransferase SETD1B was a novel recurrently mutated gene. A novel class of variant associated with the Philadelphia (Ph) translocation was detected at diagnosis in 11 (24%) of 46 patients comprising fusions and/or rearrangement of genes on the translocated chromosomes, with evidence of fragmentation, inversion, and imperfect sequence reassembly. These were more frequent at diagnosis in patients with poor outcome: 9 (33%) of 27 vs 2 (11%) of 19 optimal responders (P 5 .07). Thirty-nine patients were tested at BC, and all had cancer gene variants, including ABL1 kinase domain mutations in 58%. However, ABL1 mutations cooccurred with other mutated cancer genes in 89% of cases, and these predated ABL1 mutations in 62% of evaluable patients. Gene fusions not associated with the Ph translocation occurred in 42% of patients at BC and commonly involved fusion partners that were known cancer genes (78%). Genomic analysis revealed numerous relevant variants at diagnosis in patients with poor outcome and all patients at BC. Future refined biomarker testing of specific variants will likely provide prognostic information to facilitate a risk-adapted therapeutic approach. Refereed/Peer-reviewed

Following the achievement of deep molecular response on tyrosine kinase inhibitors (TKIs), approximately half of patients with chronic myeloid leukemia (CML) can discontinue TKI and remain in treatment-free remission (TFR). The ALLGCML8 study enrolled 40 imatinib-treated patients with undetectable BCR-ABL1 mRNA (approximately MR4.5). Molecular relapse was defined as detectable BCR-ABL1 on two consecutive tests or any single value >0.1%. With a median follow-up of 8.6 years (range 5.7–11.2 years), 18 patients remain in continuous TFR (45.0%; 95% confidence interval 31.9−63.4%).The latest relapse detected was 27 months after stopping imatinib. No patient progressed to advanced phase. Twenty-two patients met criteria for imatinib re-treatment and all regained undetectable molecular response. Nine patients in long-term TFR were monitored by highly sensitive individualized BCR-ABL1 DNA PCR in a sufficient number of samples to enablemore precise quantification of residual leukemia. BCR-ABL1 DNA decreased from a median of MR5.0 in the first year of TFR to MR6.1 in the sixth year of TFR. Our results support the long-term safety and remarkable stability of response after imatinib discontinuation in appropriately selected CML patients. Serial high sensitivity testing provides a new and unexpected findingof gradually reducing CML cells in patients in long-term TFR. Refereed/Peer-reviewed

Mesenchymal stem cells (MSCs) have been widely investigated as a treatment for graft versus host disease (GvHD), but with mixed results. Factors such as MSC donor variability and the effects of prolonged culture expansion may have contributed to disappointing outcomes. The novel Cymerus™ manufacturing process facilitates virtually limitless production of well-defined and consistent MSCs from a single iPSC bank, using proprietary clonogenic progenitor-based technology. This avoids both inter-donor variability and the need for excessive culture expansion once MSCs are formed. This is a multi-center, open label study of Cymerus MSCs (CYP-001) in adults with steroid-resistant acute GvHD, following allogeneic hematopoietic stem cell transplantation (NCT02923375). Prior to enrolment, all subjects had failed to respond to at least three days of steroid treatment (≥1 mg/kg/day), administered in accordance with standard management at each center. Subjects received two intravenous infusions of CYP-001 one week apart, at a dose of 1 × 106 cells/kg (Cohort A) or 2 × 106 cells/kg (Cohort B), in addition to standard of care medications. The study involves follow-up over two years, with primary evaluation at 100 days. GvHD was staged and graded according to the 1994 Consensus Conference on Acute GvHD Grading. An Overall Response (OR) was defined as at least a one-grade improvement in GvHD severity, while a Complete Response (CR) was defined as the absence of any GvHD signs or symptoms. The primary objective was assessment of safety and tolerability, while the secondary objective was efficacy, based on overall survival (OS) and best responses by Day 28/Day 100. Eight subjects were enrolled per cohort, but one subject in Cohort B withdrew prior to the initiation of CYP-001 treatment. All subjects had Grade II or III GvHD at baseline. The treatment was well tolerated in all cases, and there were no treatment-related Serious Adverse Events (SAEs) reported. One patient in Cohort A died after developing pneumonia, which was not considered to be CYP-001 treatment-related. One patient in Cohort B did not show a response to CYP-001 treatment, and withdrew from the trial on Day 22 to commence palliative care. All other patients showed an OR and remained alive at Day 100. Overall, outcomes by Day 100 were similar in both cohorts, but Day 28 data suggest a faster response to the higher dose level used in Cohort B (see Table 1 and Figure 1). In conclusion, CYP-001 infusions were found to be safe and well tolerated in this study, and we believe the encouraging treatment response and overall survival rates support progression to a Phase II trial.

A 55-year-old man presented with splenomegaly (10 cm below left costal margin) and leucocytosis (145 × 109/L). Differential showed neutrophilia with increased basophils (2%), eosinophils (1.5%), and left shift including myeloblasts (3%). A diagnosis of chronic myeloid leukemia in chronic phase was established after marrow cytogenetics demonstrated the Philadelphia chromosome. Molecular studies showed a BCR-ABL1 qPCR result of 65% on the International Scale. Imatinib therapy at 400 mg daily was initiated due to patient preference, with achievement of complete hematological response after 4 weeks of therapy. BCR-ABL1 at 1 and 3 months after starting therapy was 37% and 13%, respectively (all reported on International Scale). Is this considered an adequate molecular response?

The oral toxicity of phorate oxon (PHO), with emphasis on gender- and age-related effects, was characterized in the Sprague-Dawley rat. The oral LD50 (95% fiducial limits) for PHO in corn oil was 0.88 (0.79, 1.04) mg/kg in males and 0.55 (0.46, 0.63) mg/kg in females with a probit slope of 15. Females had higher baseline blood cholinesterase titers, but males were significantly more tolerant. Younger rats generally had lower absolute cholinesterase blood titers. However as PHO challenges increased, baseline-normalized cholinesterase inhibition was independent of age and gender. Butyrylcholinesterase (BChE) and especially acetylcholinesterase (AChE) in brains of younger females were affected more than that in either males or older females. In summary, while female rats, especially older females, had higher titers relative to males, female rats were more susceptible in terms of absolute cholinesterase inhibition and 24-hr lethality data, but the differences were not observed when titers were normalized to baseline levels.

Scoring systems used at diagnosis of chronic myeloid leukemia (CML), such as Sokal risk, provide important response prediction for patients treated with imatinib. However, the sensitivity and specificity of scoring systems could be enhanced for improved identification of patients with the highest risk. We aimed to identify genomic predictive biomarkers of imatinib response at diagnosis to aid selection of first-line therapy. Targeted amplicon sequencing was performed to determine the germ line variant profile in 517 and 79 patients treated with first-line imatinib and nilotinib, respectively. The Sokal score and ASXL1 rs4911231 and BIM rs686952 variants were independent predictors of early molecular response (MR), major MR, deep MRs (MR4 and MR4.5), and failure-free survival (FFS) with imatinib treatment. In contrast, the ASXL1 and BIM variants did not consistently predict MR or FFS with nilotinib treatment. In the imatinib-treated cohort, neither Sokal or the ASXL1 and BIM variants predicted overall survival (OS) or progression to accelerated phase or blast crisis (AP/BC). The Sokal risk score was combined with the ASXL1 and BIM variants in a classification tree model to predict imatinib response. The model distinguished an ultra-high-risk group, representing 10% of patients, that predicted inferior OS (88% vs 97%; P =.041), progression to AP/BC (12% vs 1%; P =.034), FFS (P

We present three cases of the rare hepatosplenic T-cell lymphoma (HSTCL); two patients suffering from Crohn disease who developed HSTCL on azathioprine without exposure to biologicals, and a third patient who had psoriasis treated using etanercept, cyclosporine and methotrexate. The evidence for an association between HSTCL and immunosuppressive drugs and biologicals is reviewed. We argue for improved pharmacovigilance processes to help determine the benefit to risk ratios for the use of these and other new agents.

The aims of this study were to determine the effects of the CYP2C8*3 and *4 polymorphisms on imatinib metabolism and plasma imatinib concentrations in chronic myeloid leukaemia (CML) patients.We genotyped 210 CML patients from the TIDELII trial receiving imatinib 400-800 mg/day for CYP2C8*3 (rs11572080, rs10509681) and *4 (rs1058930). Steady-state trough total plasma N-desmethyl imatinib (major metabolite):imatinib concentration ratios (metabolic ratios) and trough total plasma imatinib concentrations were compared between genotypes (one-way ANOVA with Tukey post hoc).CYP2C8*3 (n = 34) and *4 (n = 15) carriers had significantly higher (P 0.01) and lower (P 0.01) metabolic ratios, respectively, than CYP2C8*1/*1 (n = 147) patients (median ± standard deviation: 0.28 ± 0.08, 0.18 ± 0.06 and 0.22 ± 0.08, respectively). Plasma imatinib concentrations were consequently 50% higher for CYP2C8*1/*4 than for CYP2C8*1/*1 and CYP2C8*3 carriers (2.18 ± 0.66 vs. 1.45 ± 0.74 [P 0.05] and 1.36 ± 0.98 μg/mL [P 0.05], respectively).CYP2C8 genotype significantly alters imatinib metabolism in patients through gain- and loss-of-function mechanisms.

Background - Conventional chemotherapy for adults with Acute Lymphoblastic Leukaemia (ALL) is associated with considerable treatment-related toxicity. Blinatumomab is a CD19/CD3 targeting bi-specific T-cell engager that has demonstrated promising efficacy in relapsed/refractory ALL, and in combination with chemotherapy in newly diagnosed patients. Preliminary studies also suggest less toxicity and good efficacy (CR/CRh 66%) when delivered as induction to older adults (median age 75) with newly diagnosed B-ALL (Advani, ASH 2018). Of responders, Minimal Residual Disease (MRD) negativity in this trial was achieved in 92%. Given this, the Australasian Leukaemia & Lymphoma Group (ALLG) has explored the potential for upfront Blinatumomab as induction for younger adults with Ph- B-lineage Acute Lymphoblastic Leukaemia, alternating with CNS-directed chemotherapy cycles. Aim - To assess response to therapy of the first 10 patients enrolled on this study by molecular MRD analysis as a surrogate measure of short-term efficacy of this combination. Method - The ALLG ALL8 study (ACTRN12617000084381) is a phase II proof-of-concept front-line study for patients fit for treatment with a Hyper-CVAD-like regimen (between 40-65 years) with newly diagnosed Ph- B-lineage ALL. Those with CNS positive disease are excluded. Patients receive a steroid pre-phase (Prednisolone 100mg daily for 7 days) followed by a disease debulking phase of cyclophosphamide 150mg/m2 BD day 1-3, vincristine 2mg day 1 & 11 and dexamethasone 10mg/m2 day 1-4 and 11-14. Patients then receive alternating cycles of Blinatumomab (at 9mcg/d for the first 7 days of cycle 1 followed by 28mcg/d until day 28) with B-cycles of Hyper-CVAD (Methotrexate 1g/m2 day 1, Cytarabine 3g/m2 BD day 2,3, Methylprednisolone 50mg BD day 1-3) (figure 1). All patients receive intrathecal prophylaxis with methotrexate, cytarabine and hydrocortisone prior to blinatumomab treatment blocks and day 1 and 8 of each B-cycle until a total of 8 doses were administered. At the completion of therapy, high-risk patients (MLL translocations, hypodiploid, complex karyotype or MRD positive at TP3) are recommend to proceed to allogeneic stem cell transplant while others receive 24 months of POMP maintenance. Minimal residual disease analysis was performed at a centralised EuroMRD accredited laboratory utilising Taqman probes and patient specific PCR primers targeted at immunoglobulin heavy chain or T-cell receptor (Ig/TCR) gene rearrangements. MRD positivity was defined as a detectable level of ≥ 1 x 10-4. Results - The following results are based upon the first 10 patients enrolled on ALL8. Median age of 54.7 years (range 43 to 66 years) and 70% were male. Median ECOG PS was 0 (range 0 - 2). 6 patients had an abnormal karyotype, 2 high-risk (one with hypodiploid karyotype, one with t(1;19). Median white cell count at diagnosis was 3.36 x 109/L (range 1.95 - 12.05 x 109/L). All patients (10/10) attained CR/CRi following induction therapy with no treatment related deaths. At the end of the induction phase (MRD TP1) 4 out of 10 had attained MRD negativity, 2 had detectable unquantifiable MRD and 4 were MRD positive. By the end of the 1st consolidation cycle (MRD TP2) 1 additional patient had become MRD negative and 1 MRD positive patient had become MRD unquantifiable. 1 patient was not evaluable at TP2 being withdrawn prior to this, 2 do not have TP2 available at this time (1 being MRD negative at TP1, 1 with unquantifiable low-level MRD). One patient had MRD increase between TP1 and TP2, this subject had a hypodiploid karyotype. Thus, by completion of 1st consolidation an aggregate of 7 out of 10 patients were MRD negative or had unquantifiable low-level MRD, 3 remaining MRD positive (with 1 MRD progression). Updated results will be presented at the meeting. Conclusion - Front-line therapy with Blinatumomab in combination with chemotherapy is feasible in adults and results in high levels of MRD response by the end of the first consolidation block with the majority of MRD negative responses attained after the first treatment block. Despite early incorporation of Blinatumomab into this treatment protocol, MRD progression was seen in one patient with high-risk cytogenetic abnormalities. Disclosures Fleming: Astellas: Membership on an entity's Board of Directors or advisory committees; Ariad: Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria. Reynolds:Novartis Australia: Honoraria; Novartis AG: Equity Ownership; AUSTRALASIAN LEUKAEMIA & LYMPHOMA GROUP (ALLG): Consultancy; Alfred Health: Employment, Other: Biostatistician for trials funded by the Australian government and Abbvie, Amgen, Celgene, GSK, Janssen-Cilag, Merck, Novartis, Takeda, but sponsored by Alfred Health.. Nguyen:Australasian Leukaemia & Lymphoma Group: Employment. Yeung:Novartis: Honoraria, Research Funding; BMS: Honoraria, Research Funding; Pfizer: Honoraria; Amgen: Honoraria. Greenwood:Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Verner:Janssen-Cilag Pty Ltd: Research Funding. Bajel:AbbVie: Membership on an entity's Board of Directors or advisory committees, Other: travel funding. Wei:AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties: AHW is a former employee of the Walter and Eliza Hall Institute and receives a fraction of its royalty stream related to venetoclax, Research Funding, Speakers Bureau; Astellas: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Macrogenics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Genentech: Honoraria, Membership on an entity's Board of Directors or advisory committees; Servier: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Astra Zeneca: Honoraria, Research Funding; Janssen: Honoraria. OffLabel Disclosure: Blinatumomab is not currently approved for the front-line treatment of adults with Ph- B-ALL

Dasatinib treatment leads to excellent molecular responses in chronic phase chronic myeloid leukemia (CP-CML). Pleural effusions, an adverse event related dasatinib treatment, may lead to intolerance and drug discontinuations. Strategies aimed at minimising this may improve outcomes. In the Phase III Dasision study, pleural effusion affected ~22% of patients after 4 years of dasatinib treatment at 100mg/d (Cortes et al, 2016 JCO 34(20) 2333-40). The elderly are at particular risk (Latagliata et al 2013 Hem Onc 31(2) 103-9), and there is suggestion that higher dasatinib trough (Cmin) levels may increase the risk of pleural effusions. The randomised OPTIM study (EHA 2014 abstract 5678) has previously reported that patients with Cmin >3nM benefited from dose reductions with preservation of molecular responses. The CML12 (DIRECT) study, run by the Australasian Leukaemia & Lymphoma Group (ALLG) with financial support from BMS, is a single arm phase II study with the aim of minimizing dasatinib related toxicity whilst preserving efficacy using a similar treatment schema to the OPTIM study. Here, we report results of a per-protocol interim analysis based on early molecular response (EMR; BCR-ABL1 ≤10% at 3 months) and MMR (BCR-ABL1 ≤0.1%) at 12 months, both key secondary endpoints of the study. The primary endpoint of the study- the cumulative incidence of pleural effusion at 24 months - is not yet evaluable. DIRECT initially only enrolled patients >60 years old, predicted to derive the greatest potential benefit from a reduction in toxicity. The protocol was amended after 34 pts were accrued to include patients >18 years old at the recommendation of the trial management committee. All patients started treatment with dasatinib 100mg/day. Dasatinib Cmin was taken at 7, 28 and 56 days after treatment commencement. All Cmin directed dose adjustments were made prior to assessment of BCR-ABL1 at 3 months. Patients sequentially dose reduced to 70mg/day, then to 50mg/day, for Cmin results >3nM. Doses As of June 2019, 71 patients (of 80 planned) from 14 centres have been enrolled, with a median follow up of 7 months (range 0-31). Median age was 64 years (range 21-86) and 48% were female. Sokal risk was low in 40% and high in 9.2%. The median dasatinib Cmin at days 7, 28, 56 and 90 were 4.9, 3.5, 3.5 and 2.7nM respectively (Table). At these time points, 83%, 59%, 73% and 44% of patients had Cmin ≥3nM. There was a trend to lower Cmin after protocol directed dose reduction. The number of patients remaining on 100mg/day after 1, 2 and 3 months of therapy were 11/69 (16%), 5/63 (8%) & 5/55 (9%) respectively. Molecular response data were available for 48 patients at 3 months and 22 patients at 12 months. At 3 months, BCR-ABL1 ≤ 10% was achieved by 46 of 48 patients (96%), of whom 13 (27%) had achieved MMR (27%). At 12 months, MMR was achieved by 20/22 patients (91%), of whom 7 have achieved MR4.5 (BCR-ABL1 Adverse events occurred in 91.5% of patients at all grades - the majority of which were mild. Grade III/IV events occurred in 36.6% and 1.4% of patients respectively. Six of the 71 patients have discontinued dasatinib treatment early, all due to adverse events / dasatinib intolerance. Detailed adverse event data is embargoed until primary endpoint analysis. No patient has progressed to accelerated or blast phase CML. The DIRECT study demonstrated the feasibility of using dasatinib Cmin levels to optimise dosing. Early molecular response rates are encouraging and predict for excellent achievement of long-term molecular response. Long term efficacy and safety data are awaited. Table Disclosures Yeung: Novartis: Honoraria, Research Funding; BMS: Honoraria, Research Funding; Pfizer: Honoraria; Amgen: Honoraria. Grigg:Abbvie: Membership on an entity's Board of Directors or advisory committees; MSD: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Roche: Other: Travel. Shanmuganathan:Novartis: Honoraria, Other: Travel Support; Bristol-Myers Squibb: Honoraria, Other: Travel Support; Amgen: Other: Travel Support; Janssen: Other: Travel Support; Gilead: Other: Travel Support. White:BMS: Honoraria, Research Funding; AMGEN: Honoraria, Speakers Bureau. Branford:Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau; Bristol-Myers Squibb: Honoraria, Speakers Bureau; Qiagen: Consultancy, Honoraria; Cepheid: Consultancy, Honoraria. Mills:Abbvie: Membership on an entity's Board of Directors or advisory committees; Novartis: Other: Speaker Fees; Amgen: Other: Conference Sponsorship; Specialised Therapeutics: Honoraria; MSD: Membership on an entity's Board of Directors or advisory committees. Shortt:Celgene: Consultancy, Speakers Bureau; BMS: Consultancy, Speakers Bureau; Novartis: Consultancy, Speakers Bureau; Astex: Research Funding; Amgen: Research Funding; Gilead: Speakers Bureau; Takeda: Speakers Bureau. Ross:Celgene: Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees. Harrup:Cancer Council of Tasmania: Membership on an entity's Board of Directors or advisory committees; Cooperative Trial Group for NeuroOncolog: Other: Collaborative Clinical Trials Group. Hughes:Novartis, Bristol-Myers Squibb, Celgene: Research Funding; Novartis, Bristol-Myers Squibb: Consultancy, Other: Travel.

Introduction and Aim. Achievement of deep molecular response (DMR) is the prerequisite for treatment-free remission in chronic phase CML (CP-CML) patients (pts). Pts who fail to achieve early molecular response (BCR-ABL1 > 10% IS) at 3-months (mths), or have high ELTS score at diagnosis have inferior achievement of DMR. We and others have shown that the levels of NK-cell, T-cell, myeloid-derived suppressor cell, and neutrophils in the blood at diagnosis have an impact on DMR achievement. We hypothesized that Cluster of Differentiation (CD) (cell surface marker) gene expression might provide a surrogate marker to characterize immune cell composition. We aimed to identify pts who had a low probability of achieving DMR by 5 years (yrs) by combining 3-mths BCR-ABL1% and CD gene expression. This may enable clinicians to determine whether an individual patient is on a pathway towards DMR and potentially TFR or should be considered for a different therapeutic approach if TFR is the eventual goal. Methods. 119 blood samples from the imatinib-based TIDEL-II trial were subjected to transcriptomic microarray profiling. A total of 357 CD genes classified by the HUGO Gene Nomenclature Committee CD molecular gene group were assessed. We defined DMR as achieving MR4.5 (BCR-ABL1 < 0.0032%) at two consecutive time points. To construct a predictive model, the samples were randomly assigned to discovery and validation cohorts. Recursive partitioning and construction of a regression tree with tenfold cross-validation based on expression of 357 CD genes and 3-mths BCR-ABL1% were used as inputs in the discovery cohort. The performance was assessed based on accuracy of prediction of DMR by 5 yrs. The final model was validated using the independent validation cohort. All the analysis was performed using R statistical software. Results. Clinical variables (age, gender, ELTS, 3-mths BCR-ABL1%, MMR, and MR4.5) were well matched in the discovery (n=60) and independent validation cohort (n=59). The predictive model was constructed using the discovery cohort to reveal two risk groups: poor-risk (PR, 15% achieving MR4.5 at 5 yrs, n=19), and good-risk (GR, 88% achieving MR4.5 at 5 yrs, n=41) groups (Figure 1A-B). This model classified PR group by BCR-ABL1 ≥ 7.5% at 3 mths OR BCR-ABL1 < 7.5% at 3 months with high CD302 gene expression (≥7.9 log2 gene expression; top 15%) at diagnosis. GR group was defined as having both BCR-ABL1 < 7.5% and low CD302 gene expression ( We asked whether using the more conventional BCR-ABL1 10% cutoff instead of 7.5% in our model would give similar results, but the performance in predicting long-term DMR achievement was inferior: Pts predicted as PR with this criteria had ~2x higher achievement of DMR (e.g. 26% vs 14% using 3-mths BCR-ABL1 10% vs 7.5% cutoff respectively). ELTS score have been associated with the probability of DMR achievement. We compared the performance of ELTS in combination with 3-mths BCR-ABL1% by replacing CD302 gene expression with ELTS. The predictive accuracy was inferior. Pts with 3-mths BCR-ABL1 ≥7.5% OR BCR-ABL1 Conclusion. We have constructed a predictive model for DMR achievement for pts who receive optimised frontline imatinib therapy. This model performs better than combining ELTS and 3-mths BCR-ABL1%. We postulate that this predictive model could enable identification of poor risk pts at 3 mths who would benefit from intensified therapeutic approaches to obtain eligibility for TFR and potentially optimal clinical outcome. Disclosures Yeung: Novartis: Honoraria, Research Funding; BMS: Honoraria, Research Funding; Pfizer: Honoraria; Amgen: Honoraria. Hughes:Novartis: Other: Advisory Board and Symposia, Research Funding; BMS: Research Funding.

Eighty-six newly diagnosed Philadelphia-negative ALL pts were enrolled from 2012 to 2018, from 14 Australian centres; 82 pts were evaluable. Pts were stratified and treated as per the pediatric ANZCHOG Study 8 protocol based on BFM 2000. Response was assessed on day 33 and 79 by morphology, flow cytometry and RQ-PCR measurable residual disease (MRD) at a central lab according to EuroMRD criteria. Allogenic stem cell transplantation was permitted for high and very high-risk disease groups. Detailed genomic analysis was performed in 47 pts (to date), using whole transcriptome sequencing (mRNA Seq) and multiplex ligation-dependent probe amplification (MLPA) for recurrent ALL related gene deletions. Median age of the study was 24 (16 - 38) years; 28% were female; 59/82 (72%) had B-ALL. Median follow up was 36 (range 3-73) months. Induction mortality was 3.6%. CR rate at day 33 was 90.4% and day 79 (time point 2, TP2) 97.6%. Relapse free survival (RFS) at 2 years was 75.6% (95%CI 65.6 - 85.5%). CR rates at day 33 and day 79 were 90.4% and 97.6% respectively. The 2-year overall survival (OS) was 79.3% (18/82 events). In concordance with other studies, TP2 MRD predicted outcome in ALL06. MRD positive (pos) pts had a 2yr RFS of 68%, vs 98% in MRD negative (neg) pts (p=0.003). To date, 47 pts had mRNA Seq & MLPA; 11/47 pts had T cell ALL; 1/47 died during induction (2.1%). The median age of this subset was 21 (15-37) years, 23% were female and the RFS at 2 years was 73.97% (95%CI 65.6 - 91.44%). TP2 MRD remained predictive of outcome in this group with 2-year RFS in MRD pos pts 54% vs 95% in MRD neg pts (p=0.013, n=44). 13/47 pts have died with a 2-year OS of 73% (95%CI 62.7 - 90%). MPLA and mRNA Seq analysed independently of outcome data revealed 28/47 pts had genomic lesions categorise as High Risk (HR). These included fusions and structural genomic abnormalities involving KMT2A, IKZF1, IGH, ABL1, JAK, CRLF2, CDKN2A/B, PAX5, RAS and ZNF384. The remaining cases were classified as Standard Risk (SR) and included mainly hyperdiploid, T cell and ETV6-RUNX1 cases. Eleven of 13 pts who relapsed were genomic HR with poorer 2-RFS vs SR (59% vs 78.8%, p=0.023 respectively) (Fig 1.). We examined the relationship between genomics risk group and TP2 MRD, a known prognostic marker. Of the 22 pts who were MRD pos, 19 (86%) pts were in the HR genomics group. In contrast, for MRD neg pts, 13/22 were in the SR group (59%) (p=0.004 Fishers exact, Table 1). This demonstrates that the TP2 MRD positive group is strongly enriched for pts with HR genomics. Pts with HR genomics who were TP2 MRD pos had a 2 year RFS of 27% vs HR MRD neg or SR pts with a 2 yr RFS of 78% (p=0.001)(Fig. 2). Further, of the 13 deaths that were observed in this subset 9/13 (69%) fell within the group of pts with HR genomics/TP2 MRD+. The single induction mortality, for whom TP2 data was not available was also genomic HR. This is one of the first genomic surveys in a cohort of AYA pts, a group known for their inferior outcomes compared to children, treated on a pediatric inspired ALL protocol. Our overall outcomes compare favourably to other cohorts (EHA 2019 abstract 2416). In ALL06, genomic risk stratification based on previous published HR lesions, identified a HR cohort with significantly lower RFS and trend for inferior OS, vs a SR cohort. HR genomics was also associated with significantly higher rates of TP2 MRD positivity. Elucidation of targetable genomic lesions at the time of diagnosis may allow interventions to minimise MRD positivity and relapse in HR pts. Genomic information also improves understanding of underlying disease biology, providing targets for novel treatment discovery. Disclosures Yeung: Pfizer: Honoraria; Amgen: Honoraria; Novartis: Honoraria, Research Funding; BMS: Honoraria, Research Funding. Greenwood:Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Wei:AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties: AHW is a former employee of the Walter and Eliza Hall Institute and receives a fraction of its royalty stream related to venetoclax, Research Funding, Speakers Bureau; Astellas: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Macrogenics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Genentech: Honoraria, Membership on an entity's Board of Directors or advisory committees; Servier: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Astra Zeneca: Honoraria, Research Funding; Janssen: Honoraria. White:AMGEN: Honoraria, Speakers Bureau; BMS: Honoraria, Research Funding.

Pegylated interferon (Peg-IFN) increases molecular response rates when used in combination with imatinib (IM) and dasatinib compared with tyrosine kinase inhibitor (TKI) monotherapy in de novo chronic phase chronic myeloid leukemia (CP-CML). (Preudhomme NEJM 2010, Hjorth-Hansen Leukemia 2016). The phase II Pinnacle (ALLG CML 11) study evaluated the tolerability and molecular response rate of nilotinib (NIL) with Peg-IFN alfa-2B (PegIntron, MSD) in CP-CML patients. Co-primary end points were MMR (BCR-ABL1 ≤ 0.1%) at 12 mths and MR4.5 (BCR-ABL1 ≤ 0.0032%) at 24 mths. Key secondary end points were survival and overall molecular response. Patients were screened for cardiac / vascular disease and associated risk factors at baseline (EKG, left ventricular ejection fraction, arterial duplex of carotids and lower limbs, blood HbA1c and lipid profiles). Those with uncontrolled vascular risk factors (diabetes, hypertension, dyslipidemia) or a history of vascular events were excluded. Eligible pts received NIL 300mg BID alone for the first 3 months (mths). PegIntron was then added at 30mcg/week in pts without persistent hematological toxicities, increasing to 50mcg/week as tolerated over the following mth. Combination therapy continued until 24 mths, when pts reverted to TKI monotherapy. Switching to IM 400-600mg QD was allowed for pts with persistent grade II or any grade III/IV toxicity from NIL. Sixty pts were enrolled from 12 Australian centres. Median age was 48.5 years (range 19-72); 45% were female. Sokal risk was low in 43% and high in 18%. Median follow up (FU) was 34 mths (24-60). Data is presented on an intention to treat basis. Eight pts (13%) did not commence Pegintron (2 due to persistent haem toxicities, 4 from GI disturbance, liver/pancreatic enzyme derangements, and 2 from pt preference). Considering Pegintron as a product of protocol assigned dose and duration, adjusted for time from study entry, 21 pts (35%) received >85% of their assigned dose, 13 (22%) received between 50-84% and 18 pts (30%) received 85% of their assigned dose versus those wwho took Adverse events (AE) are reported at a similar frequency compared to the interim analysis. Grade III/IV AEs attributed to NIL were increased lipase and neutropenia (each 12%), pancreatitis (6%), thrombocytopenia and rash (each 5%). Grade III/IV AEs attributed to Pegintron were neutropenia (10%), atrial fibrillation (6%), and myalgia, depression and rash (4% each). Three vascular revents occurred: one case each of ischaemic colitis, femoral artery occlusion, coronary artery disease. The former occurred on imaitnib and the latter 2 occurred after 2.5 and 4 years of niloitnib respectively; both patient have since switched to imatinib. Eighteen pts (30%) have withdrawn from study: 2 withdrew consent, 6 due to intolerance (diarrhoea, pancreatitis, GI upset, rash, high amylase and LFT derangements), 4 for failing to consistently achieve BCR-ABL MMR, 2 for loss of response; 4 pts withdrew for other reasons. Fig 1B shows BCR-ABL1 transcript levels over time. At 3 mths, 22 (37%) have achieved MMR, 23 (38%) had BCR-ABL between 0.1-1%, and 6 (10%) had BCR-ABL between 1-10%; 3 have already withdrawn. Six pts (10%) had BCR-ABL1 ≥10%; 3 subsequently achieved and maintained MMR, 1 has BCR-ABL Combination therapy with NIL and Peg-IFN leads to favourable rates of molecular responses that may be superior to NIL monotherapy (Table). While the majority of patients did not durably tolerate full dose Pegintron, there was minimal interference with TKI dose intensity. Such strategies may maximise achievement of deep molecular response, allowing a trial of TKI cessation and the benefit of treatment free remission to an increased number of patients. Disclosures Yeung: BMS: Honoraria, Research Funding; Pfizer: Honoraria; Amgen: Honoraria; Novartis: Honoraria, Research Funding. Shanmuganathan:Gilead: Other: Travel Support; Janssen: Other: Travel Support; Amgen: Other: Travel Support; Bristol-Myers Squibb: Honoraria, Other: Travel Support; Novartis: Honoraria, Other: Travel Support. Grigg:Abbvie: Membership on an entity's Board of Directors or advisory committees; Roche: Other: Travel; Janssen: Membership on an entity's Board of Directors or advisory committees; MSD: Membership on an entity's Board of Directors or advisory committees. Reynolds:AUSTRALASIAN LEUKAEMIA & LYMPHOMA GROUP (ALLG): Consultancy; Novartis AG: Equity Ownership; Novartis Australia: Honoraria; Alfred Health: Employment, Other: Biostatistician for trials funded by the Australian government and Abbvie, Amgen, Celgene, GSK, Janssen-Cilag, Merck, Novartis, Takeda, but sponsored by Alfred Health.. Harrup:Cooperative Trial Group for NeuroOncolog: Other: Collaborative Clinical Trials Group; Cancer Council of Tasmania: Membership on an entity's Board of Directors or advisory committees. Ross:BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding. Mills:Novartis: Other: Speaker Fees; Specialised Therapeutics: Honoraria; Abbvie: Membership on an entity's Board of Directors or advisory committees; Amgen: Other: Conference Sponsorship; MSD: Membership on an entity's Board of Directors or advisory committees. Yong:BMS: Honoraria, Research Funding; Celgene: Research Funding; Novartis: Honoraria, Research Funding. White:BMS: Honoraria, Research Funding; AMGEN: Honoraria, Speakers Bureau. Branford:Qiagen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Cepheid: Honoraria; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Hughes:Novartis, Bristol-Myers Squibb, Celgene: Research Funding; Novartis, Bristol-Myers Squibb: Consultancy, Other: Travel. OffLabel Disclosure: Pegylated interferon is not registered for use in chronic phase CML

Rising BCR-ABL1 transcripts indicate potential loss of imatinib response in CML. We determined whether the BCR-ABL1 doubling time could distinguish nonadherence from resistance as the cause of lost response. Distinct groups were examined: (1) acquired clinical resistance because of blast crisis and/or BCR-ABL1 mutations; and (2) documented imatinib discontinuation/interruption. Short doubling times occurred with blast crisis (median, 9.0 days; range, 6.1-17.6 days; n = 12 patients), relapse after imatinib discontinuation in complete molecular response (median, 9.0 days; range, 6.9-26.5 days; n = 17), and imatinib interruption during an entire measurement interval (median, 9.4 days; range, 4.2-17.6 days; n = 12; P = .72). Whereas these doubling times were consistently short and indicated rapid leukemic expansion, fold rises were highly variable: 71-, 9.5-, and 10.5-fold, respectively. The fold rise depended on the measurement interval, whereas the doubling time was independent of the interval. Longer doubling times occurred for patients with mutations who maintained chronic phase (CP: median, 48 days; range, 17.3-143 days; n = 29; P < .0001). Predicted short and long doubling times were validated on an independent cohort monitored elsewhere. The doubling time revealed major differences in kinetics according to clinical context. Long doubling times observed with mutations in CP allow time for intervention. A short doubling time for a patient in CP should raise the suspicion of nonadherence.

The use of the polymerase chain reaction (PCR) was a revolutionary step in molecular biology, allowing for small amounts of genetic material to be amplified and studied. The advent of real-time PCR was a further refinement that led to reliable quantification of RNA and DNA. This allowed response monitoring and the detection of minimal residual disease, which proved to have important correlations with outcome in certain malignancies. The technology is indispensable for physicians and pathologists caring for oncology patients. In this article we will review the applications of molecular technology in the diagnosis and management of malignancies. Using chronic myeloid leukaemia (CML) as an example, technical aspects and clinical correlations will be discussed, with emphasis on the importance of quality assurance and standardisation to allow for comparability of results across laboratories. We will also examine emerging technologies that allow for high throughput and rapid turnaround of specimens and speculate how these would affect outcomes in future health care. The established and emerging molecular technologies have applications in many fields of oncology.

Long-term follow-up of clinical studies has demonstrated the efficacy of imatinib therapy in newly diagnosed chronic phase-chronic myeloid leukemia patients (CML). However, recent updates of two separate randomized Phase III studies demonstrated higher complete cytogenetic and major molecular response rates with dasatinib and nilotinib compared with imatinib 400 mg/day. Hence, for newly diagnosed chronic phase-CML patients there are multiple treatment options, including standard-dose imatinib, high-dose imatinib, and combination therapy of imatinib and interferon, dasatinib and nilotinib. This article critically analyzes the current literature and provides guidelines for the management of newly diagnosed CML. Disease and therapy-related prognostic factors, which may aid in the selection of therapeutic strategies to enable optimal treatment outcomes, are discussed. In addition, we provide commentary on the therapeutic options for patients who fail imatinib therapy.

Alfa Interferon, commonly used in chronic phase chronic myeloid leukemia (CML-CP) in the pre-imatinib era, was able to induce a cytogenetic response in a minority of patients (pts). Pegylated interferon (Peg-IFN) is better tolerated than IFN, and increases molecular response rates when used in combination with imatinib (IM) compared with IM monotherapy (Preudhomme NEJM 2010). The phase II Pinnacle (ALLG CML 11) study evaluated the tolerability and molecular response rate of nilotinib (NIL) with Peg-IFN alfa-2B (PegIntron, MSD) in de novo CML-CP. Pts were screened for cardiac / vascular disease and associated risk factors at baseline (EKG, left ventricular ejection fraction, arterial duplex of carotids and lower limbs, blood HbA1c and lipid profiles). Those with uncontrolled vascular risk factors (diabetes, hypertension, dyslipidemia) or a history of vascular events were excluded. Eligible pts received NIL 300mg BID alone for the first 3 months (mths). PegIntron was then added at 30mcg/week in pts without persistent hematological toxicities, increasing to 50mcg/week as tolerated over the following mth. Combination therapy continued until 24 mths, when pts reverted to TKI monotherapy. Switching to IM 400-600mg QD was allowed for pts with persistent grade II or any grade III/IV toxicity from NIL.. Sixty pts were enrolled from 12 Australian centres. Median age was 48.5 years (range 19-72); 45% were female. Sokal risk was low in 43% and high in 18%. Median follow up (FU) was 28 mths (16-51). Data is presented on an intention to treat basis. Figure 1a shows BCR-ABL1 transcript levels over time. The co-primary end points are MMR (BCR-ABL1 ≤0.1% IS) AT 12 mths and MR4.5 (BCR-ABL1 ≤0.0032% IS) at 24 mths. At 12 mths, MMR and MR4.5 rates were 76.7% (95% CI 63.4-87%). and 43.4% (95% CI 30.1-57.3%), respectively. In 40 evaluable pts at 24 mths, MR4.5 was 50% (95% CI 29.9-70.1%). The median time to MMR and MR4.5 was 5.8 mths and 18 mths respectively for pts achieving these responses (Figs 1B & C). Six pts (10%) had BCR-ABL1 ≥10% at 3 mths - 2 of whom had multiple dose interruptions due to toxicity; 3/6 have since achieved MMR, 1 has BCR-ABL Dose intensities of NIL were assessed in 3 mth blocks. Median and lower quartile NIL dose intensity was 600mg/d for all 3 mth blocks up to mth 24, except for the lower quartile NIL dose of 567mg for the first 3 mths. Eight pts (13%) did not commence Pegintron (2 due to persistent haem toxicities, 4 from GI disturbance, liver/pancreatic enzyme derangements, and 2 from pt preference). Considering Pegintron as a product of protocol assigned dose and duration, adjusted for time from study entry, 22 pts (37%) received >90% of their assigned dose, 13 (22%) received between 50-90% and 25 pts (41%) received Grade III/IV adverse events (AE) attributed to NIL were increased lipase and neutropenia (each 12%), pancreatitis (6%), thrombocytopenia and rash (each 5%). Three thrombotic events occurred: ischemic colitis in a patient on IM monotherapy, femoral artery thrombosis in a 56yo man after 2.5 yrs of NIL, and coronary disease in a 51yo man after 4 yrs of NIL. Grade III/IV AEs attributed to Pegintron were neutropenia (10%), and myalgia, depression and rash (4% each); other common AEs included fatigue (35%), myalgia (23%), flu-like symptoms (21%) and depression (17%). Ten pts (13%) have withdrawn from study: 2 withdrew consent, 5 due to toxicity (pancreatitis, GI upset, rash, high amylase and fatigue), and 3 for failing to consistently achieve BCR-ABL 90% of assigned NIL/IM and Pegintron doses. This interim analysis suggests that combination therapy with NIL and Peg-IFN leads to favourable rates of molecular responses when compared with with NIL monotherapy (Table 1). While the majority of patients did not durably tolerate full dose Pegintron, there was minimal interference with TKI dose intensity. Longer term results, and impact upon treatment free remission outcome of this combination is awaited. Disclosures Yeung: Pfizer: Honoraria; BMS: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Specialised Therapeutics Australia: Honoraria; Amgen: Honoraria. Grigg:Takeda: Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees. Shanmuganathan:Janssen: Honoraria; Royal Adelaide Hospital Research Fund: Other: Scholarship; Novartis: Honoraria, Other: Travel sponsorship; Bristol-Myers Squibb: Honoraria, Other: Travel sponsorship. Reynolds:Novartis: Equity Ownership, Other: former employee of Novartis AG and holds stock in the company. . Ross:BMS: Honoraria; Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau; Celgene: Research Funding. Yong:Celgene: Research Funding; Novartis: Honoraria, Research Funding; BMS: Honoraria, Research Funding. White:Novartis: Honoraria, Research Funding; BMS: Research Funding. Branford:Qiagen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Cepheid: Honoraria; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Hughes:BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees; Incyte: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Introduction. Imatinib has revolutionised the treatment of chronic phase-chronic myeloid leukemia (CP-CML), with up to 70% of patients (pts) achieving major molecular response (MMR, BCR-ABL1 < 0.1% IS). Achievement of MMR by 2 years (yrs) is associated with an excellent prospect of long term survival. Currently, three baseline prognostic scoring systems - the Sokal, Hasford (Euro) and EUTOS risk scores - have all been used to identify pts with a poor response and/or an adverse prognosis in CP-CML. Recently, the EUTOS long-term survival (ELTS) score is shown to have strong predictive power for overall survival in CML pts. We have previously reported bioassays that have significant value for predicting MMR. Combinations of these biomarkers, together with clinical risk score, may provide a better indicator of high risk pts at the time of diagnosis. Aim. To identify high-risk pts by combining selected predictive bioassay, determine whether the ELTS score is more discriminating, and determine whether it provides additional predictive value when combined with the biomarker score. Methods. Bioassays including CRKL IC50 imatinib (White, Blood, 2005), OCT-1 Activity (OA)(White, JCO, 2010), leves of 39 plasma cytokines (Nievergall, Leukemia, 2016), expression of 20 most prognostic gene by qPCR TLDA (Kok, ASH abstract, 2015), ABCB1 gene expression (Eadie, Leukemia, 2016), KIR2DL5B genotype (Yeung, Blood, 2015), BIM and ASXL1 polymorphisms (Marum, Blood advances, 2017) were used in this study. High-risk by biomarker score (HR) was defined as pts who did not achieve MMR by 2 yrs. 210 TIDEL-II pts (frontline imatinib with early switch to nilotinib for failure to meet optimal time-dependent molecular targets) were used in this study (Yeung, Blood, 2015). Only 201 pts had ELTS scores. The Recursive Partitioning and Regression Trees (rpart) algorithm was used to identify important bioassays in predicting high-risk pts. Fisher's-exact test was used for statistical analysis. Results. In the TIDEL-II cohort, there were 21 high ELTS and 180 low/intermediate ELTS pts. Pts with high ELTS had significantly lower rates of MMR by 2 yrs compared to those pts with low/intermediate ELTS (57% vs 81%, p=0.02). We constructed a predictive model using multiple different bioassays as variables to predict high-risk pts. The rpart based model used in this analysis yielded four variables (IGFBP2 gene expression, KIR2DL5B genotype, OA, and MCP-1 cytokine plasma level) as most important for predicting high-risk pts. The accuracy of the model was 84%. Pts predicted as high-risk (HR, n=27) had significantly lower MMR achievement rate compared to those predicted as low-risk (LR), (26% vs 86%, n=183, p Conclusion. We developed a combined bioassays model that is predictive of MMR failure and adverse clinical outcomes for pts who receive optimised frontline imatinib therapy. This model performs well even without adding clinical parameters. Our model has additional predictive value when used together with the ELTS score, and can distinuguish HR pts within the low/intermediate ELTS group, as well as LR patients within the high ELTS category. Further confirmation of the predictive performance of this model, using a large independent patient cohort is now indicated. We postulate that this bioassay-based model could be used, in combination with ELTS, for identifying HR pts who would benefit from intensified therapeutic approaches to obtain optimal clinical outcome. Disclosures Yeung: Amgen: Honoraria; Pfizer: Honoraria; BMS: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Specialised Therapeutics Australia: Honoraria. Yong:Celgene: Research Funding; Novartis: Honoraria, Research Funding; BMS: Honoraria, Research Funding. White:BMS: Research Funding; Novartis: Honoraria, Research Funding. Hughes:Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Incyte: Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Background: For patients with chronic-phase chronic myeloid leukemia (CML), treatment-free remission (TFR) is increasingly becoming a goal of therapy. While the safety of TFR has been established [Mahon, Lancet Oncol 2010; Ross, Blood 2013], the ability to predict success following attempted TFR remains limited. Recent publication of Euro-Ski [Saussele, Lancet Oncol 2018], the largest tyrosine kinase inhibitor (TKI) cessation study to date, demonstrated that duration of MR4 (BCR-ABL1 Aim: To identify the predictors of TFR in a single academic centre. Methods: We performed a retrospective analysis of adult CML patients receiving their primary CML management at the Royal Adelaide Hospital between January 2008 and March 2018, reviewing both clinical and molecular data. Criteria for qualifying for a TFR attempt included a minimum of 3 years (yrs) of TKI therapy and 2 yrs of deep molecular response (DMR: BCR-ABL1 Results: A total of 298 patients were treated at our institution within the defined time frame and 280 patients qualified for inclusion into our retrospective analysis. TFR eligibility was attained in 114 patients and 96 (84%) attempted TFR. Table 1 details patient characteristics of patients attempting TFR. Of the 82 patients with >12 months of follow-up, 52% (n=43) remain off TKI at 12 months in MMR. Variables were assessed by univariate Cox proportional hazards regresssion analysis for their association with TFR. The most significant finding was that patients attempting TFR with e14a2 BCR-ABL1 transcripts were more likely to remain in TFR at 12 months (65%; n=24/37) in comparison to the e13a2 transcript (34%; n=10/29), p = 0.008. This advantage also translated to patients with both e14a2 and e13a2 transcripts when grouped with the e14a2 cohort and compared with e13a2 alone, p = 0.006. The negative effect of the e13a2 transcript was further confirmed on multivariate analysis (Figure 1a) as patients with either e14a2 or both transcript types were 2.24 times more likely to remain in TFR at 12 months compared with the e13a2 transcript, p=0.032. Patients with sustained MR4.5 >3.4 yrs prior to cessation were more likely to remain in TFR at 12 months (42 vs. 64%, p = 0.014). We postulated that the higher rate of TFR in patients with e14a2 might be due in part to the longer time in MR4.5 prior to cessation. The median duration of MR4.5 prior to stopping in the e14a2 cohort was 4.1 yrs (2.05 - 10.76) compared to 3.01 yrs (2 - 10.41) in the e13a2 group (Table 2). Cumulative incidence curves of all 280 patients in our analysis demonstrated that by 6 yrs of TKI therapy, 70% of patients with e14a2 transcripts achieved MR4.5 whereas only 52% of patients with e13a2 transcripts attained MR4.5; confirming that patients with e14a2 transcripts are more likely to achieve DMR earlier (Figure 1b). Furthermore by 8 yrs, 48% of patients with e14a2 transcripts became eligible for a TFR attempt compared with only 32% of e13a2 transcripts (Figure 1c). While patients with e13a2 transcripts eventually achieve the same frequency of MR4.5 as the e14a2 group, the earlier achievement of MR4.5 in e14a2 patients may have contributed to the difference in TFR success. Conclusion: The factors that we identified as most predictive for TFR success were duration of MR4.5 and the presence of the e14a2 transcript, which has not been described previously. We also observed earlier achievement of MR4.5 in the e14a2 cohort, consistent with other studies [Jain, Blood 2016]. These observations, taken together, raise important questions about the impact of transcript type on disease biology, drug sensitivity, and immunological response which warrant further investigation. Disclosures Shanmuganathan: Novartis: Honoraria, Other: Travel sponsorship; Janssen: Honoraria; Royal Adelaide Hospital Research Fund: Other: Scholarship; Bristol-Myers Squibb: Honoraria, Other: Travel sponsorship. Branford:Qiagen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Cepheid: Honoraria; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Yong:BMS: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Celgene: Research Funding. Hiwase:Celgene: Research Funding; Novartis: Research Funding. Yeung:Novartis: Honoraria, Research Funding; BMS: Honoraria, Research Funding; Pfizer: Honoraria; Amgen: Honoraria; Specialised Therapeutics Australia: Honoraria. Ross:BMS: Honoraria; Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau; Celgene: Research Funding. Hughes:BMS: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Takeda: Honoraria.

Introduction Mesenchymal stem cells (MSCs) isolated from donated tissue have been widely investigated as a treatment for acute graft versus host disease (GvHD), but with mixed results. Factors including MSC donor variability and the effects of prolonged MSC culture expansion may have contributed to inadequate outcomes. Induced pluripotent stem cells (iPSCs) can proliferate indefinitely without loss of pluripotency. The novel Cymerus™ manufacturing process facilitates a virtually limitless supply of well-defined and consistent MSCs from a single donation. Production is achieved by differentiating iPSCs into MSCs using proprietary clonogenic progenitor-based technology. This avoids both donor to donor variability and the need for excessive culture expansion once MSCs are formed. We are undertaking a Phase I clinical trial of Cymerus iPSC-derived MSCs (CYP-001) in steroid-resistant acute GvHD (NCT02923375). We believe this will be the first completed clinical trial involving iPSC-derived cells. Methods This is a multi-center, open label, dose escalation study to assess the safety, tolerability and efficacy of CYP-001 in adults with grade II-IV steroid-resistant acute GvHD, following allogeneic hematopoietic stem cell transplantation. All subjects had failed to respond to at least three days of steroid treatment (≥1 mg/kg/day), administered in accordance with standard management at each center. The first eight subjects enrolled in Cohort A received two intravenous (IV) infusions of CYP-001 one week apart, at a dose of 1 x 106 cells/kg, in addition to standard of care medications. After an independent data and safety monitoring board review, the next eight subjects entered Cohort B, in which the MSC cell dose was doubled. Primary evaluation was performed over eight study visits to day 100. Subjects then entered a follow-up phase of up to two years. Data for subjects in Cohort A with a minimum of six months follow-up are presented here. GvHD was staged and graded according to the 1994 Consensus Conference on Acute GvHD Grading. A Partial Response (PR) was defined as improvement in the severity of GvHD by at least one grade compared to baseline, while a Complete Response (CR) was defined as the absence of any GvHD signs or symptoms. The Overall Response (OR) rate was defined as the proportion of subjects showing either a PR or CR. The primary objective was assessment of the safety and tolerability of two infusions of CYP-001. The secondary objective was efficacy, assessed by best response to treatment, by Day 28 and Day 100 and overall survival at Day 28 and Day 100. Results Four males and four females, with an average age of 57 years (range: 45-66) were enrolled in Cohort A during 2017. At baseline, subjects had Grade II (n=3) or Grade III (n=5) steroid-resistant acute GvHD. One subject had skin, gastrointestinal (GI) and liver involvement; four subjects had skin and GI involvement; two subjects had GI involvement only; and one subject had skin involvement only. The treatment was well tolerated in all cases, and there were no treatment-related Serious Adverse Events (SAEs) reported. Three subjects experienced SAEs that were not considered to be study drug related: (i) febrile neutropenia, hypokalemia and parainfluenza, each of which resolved; (ii) a lower respiratory tract infection, which resolved; (iii) pneumonia, which was fatal. All eight subjects showed at least a PR. Four subjects achieved a CR by Day 100. In all four cases where a CR was achieved, it was then sustained until Day 100. The median GvHD grade at Day 100 was 0 (range: 0-II), compared to a median grade of III (range: II-III) at baseline. Disease progression (an increase in the severity of GvHD by at least one grade compared to baseline) was not observed in any subject at any study visit. Overall survival was 7/8 (87.5%) six months after the first infusion of CYP-001. The best response rates by Day 28 and Day 100 are summarized in Table 1, while the maximal response by individual subject is illustrated in Figure 1. Conclusion Infusion of CYP-001 at 1 x 106 iPSC-derived MSCs/kg was safe and well tolerated in this patient cohort. Treatment response and overall survival rates are encouraging compared to previously published outcomes. The Cohort B primary evaluation period is expected to be completed by September 2018, and progression to a Phase II trial in this clinically challenging disease will then be considered. Disclosures Bloor: AbbVie: Research Funding; Janssen: Research Funding. Radia:Mallinckrodt: Research Funding. Yeung:Novartis: Honoraria, Research Funding; BMS: Honoraria, Research Funding; Pfizer: Honoraria; Amgen: Honoraria; Specialised Therapeutics Australia: Honoraria. Slukvin:Cynata Therapeutics Limited: Consultancy, Equity Ownership. Kelly:Cynata Therapeutics Limited: Employment, Equity Ownership. Rasko:Gilead: Honoraria; Abbvie: Speakers Bureau; Takeda: Speakers Bureau; International Society for Cellular Therapy: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Speakers Bureau; Cynata: Consultancy, Honoraria; bluebird bio: Honoraria, Other: Clinical trials ; Spark: Consultancy; FSHD Global Research Foundation: Membership on an entity's Board of Directors or advisory committees; Current Cure The Future Foundation: Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria; Pfizer: Honoraria; GSK: Honoraria; Genea: Equity Ownership; IMAGO Biosciences: Consultancy; Rarecyte: Consultancy, Equity Ownership; Gene Technology Technical Advisory, OGTR, Australian Government: Other: Chair; Advisory Committee on Biologics, Therapeutics Goods Administration, Australian Government: Other: Past Chair.