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A 17-gene stemness (LSC17) score determines risk in acute myeloid leukaemia patients treated with standard chemotherapy regimens. The present study further analysed the impact of the LSC17 score at diagnosis on outcomes following allogeneic haematopoietic cell transplantation (HCT). Out of 452 patients with available LSC17 score, 123 patients received allogeneic HCT. Transplant outcomes, including overall (OS), leukaemia-free survival (LFS), relapse incidence (RI) and non-relapse mortality (NRM), were compared according to the LSC17 scored group. The patients with a low LSC17 score had higher OS (56.2%) and LFS (54.4%) at 2 years compared to patients with high LSC17 score (47.2%

The HCT Frailty Scale is an easy prognostic tool composed of (a) Clinical Frailty Scale; (b) Instrumental Activities of Daily Living; (c) Timed-up-and-Go test; (d) Grip Strength; (e) Self-Health Rated Questionnaire; (f) Falls tests; (g) Albumin and C-reactive protein levels. This scale was designed to classify allogeneic hematopoietic cell transplant (alloHCT) candidates into fit, pre-frail and frail groups, irrespective of age. This study evaluates the ability of this frailty classification to predict overall survival (OS) and non-relapse mortality (NRM) in adult patients of all ages, in a prospective sample of 298 patients transplanted between 2018 and 2020. At first consultation, 103 (34.6%) patients were fit, 148 (49.7%) pre-frail, and 47 (15.8%) were frail. The 2-year OS and NRM of the three groups were 82.9%, 67.4%, and 48.3% (P

Donor clonal hematopoiesis may be transferred to the recipient through allogeneic hematopoietic stem cell transplantation (HCT), but the potential for adverse long-term impact on transplant outcomes remains unknown. A total of 744 samples from 372 recipients who received HCT and the corresponding donors were included. Bar-coded error-corrected sequencing using a modified molecular inversion probe capture protocol was performed, which targeted 34 genes covering mutations involved in clonal hematopoiesis with indeterminate potential (CHIP) and other AML-related mutations. A total of 30 mutations were detected from 25 donors (6.7%): the most frequently mutated gene was TET2 (n=7, 28%), followed by DNMT3A (n=4, 16%), SMC3 (n=3, 12%) and SF3B1 (n=3, 12%). With a median follow-up duration of 13 years among survivors, the presence of CHIP in the donor was not associated with recipient overall survival (p=0.969), relapse incidence (p=0.600) or non-relapse mortality (p=0.570). Donor CHIP did not impair neutrophil (p=0.460) or platelet (p=0.250) engraftment, the rates of acute (p=0.490), or chronic graft-vs-host disease (p=0.220). No significant difference was noted for secondary malignancy following HCT between the two groups. The present study suggests that the presence of CHIP in allogeneic stem donors does not adversely affect transplant outcomes after HCT. Accordingly, further study is warranted to reach a clearer conclusion on whether molecular profiling to determine the presence of CHIP mutations is necessary for the pre-transplant evaluation of donors prior to stem cell donation.

During 2020, the concurrent novel COVID-19 pandemic lead to widespread cryopreservation of allogeneic hematopoietic cell transplant grafts based on National Marrow Donor Program and European Society of Blood and Marrow Transplantation recommendations, in order to secure grafts before the start of conditioning chemotherapy. We sought to examine the impact of this change in practice on patient outcomes. We analyzed the outcomes of 483 patients who received hematopoietic stem cell transplantation (HSCT) between August 2017 and August 2020, at Princess Margaret Cancer Centre, Canada, in the retrospective study, comparing the outcomes between those who received cryopreserved or fresh peripheral blood stem cell grafts. Overall compared with those who received fresh grafts (n = 348), patients who received cryopreserved grafts (n = 135) had reduced survival and GRFS, reduced incidence of chronic graft-versus-host disease (GvHD), delay in neutrophil engraftment, and higher graft failure (GF), with no significant difference in relapse incidence or acute GvHD. However, recipients of cryopreserved matched-related donor HSCT showed significantly worse OS, NRM, GRFS compared with fresh grafts. Multivariable analysis of the entire cohort showed significant impact of cryopreservation on OS, relapse, cGvHD, GF, and GRFS. We conclude that cryopreservation was associated with inferior outcomes post-HSCT, possibly due to the combination of ATG and post-transplant cyclophosphamide impacting differential tolerance to cryopreservation on components of the stem cell graft; further studies are warranted to elucidate mechanisms for this observation.

Purpose: Allogeneic Stem Cell Transplant (allo-HSCT) patients are at risk of malnutrition and weight loss from impaired oral intake resulting from gastrointestinal toxicities, dysgeusia, and psychological effects. Methods: A retrospective review of 264 adult patients transplanted at Princess Margaret Cancer Centre who achieved relapse-free survival up to 3 months after allo-HSCT was performed. Results: Overall incidence of patients who experienced WL (WL) ≥10% from HSCT to 3 months post-transplant was 45.9% and from HSCT to 6 months was 56.6%. Patients with ≥10% WL from allo-HSCT at 3-months and 6 months had similar 2-year overall survival (OS) compared to those with Conclusion: Approaches to WL post allo-HSCT should be multifaceted and include members of the interdisciplinary team in order to decrease TRM.

INTRODUCTION Allogeneic hematopoietic cell transplantation (HCT) can be curative for acute myeloid leukemia (AML). Novel therapies may render patients' bone marrow hypocellularity and lead to prolonged post-therapy pancytopenia. Patients' bone marrow cellularity (BMC) at pretransplant assessment and post-treatment pancytopenia (classification CR-incomplete [CRi]) may manifest AML persistence. METHODOLOGY We retrospectively examined the impact of BMC and ELN response (ELNr) on a single-center cohort of 337 patients who underwent allogeneic HCT for AML in CR1. RESULTS Median follow-up was 33 months. Overall survival (OS) for the whole cohort was 55.8% at 2 years, while cumulative incidence of relapse (CIR) was 20.8%, and non-relapse mortality was 27.5%. OS and CIR were not significantly different between BMC groups; and neither was ELNr. ELNr CRi was associated with BMC aplastic and hypocellular marrow states (P

While ruxolitinib is emerging as the treatment of choice for steroid refractory/dependent chronic graft vs host disease (cGVHD) based on randomized control trial data, there is relatively little real world data published on ruxolitninb for this indication.to evaluate the real world efficacy and safety of ruxolitinib in cGVHD patients who have failed any previous systemic therapy for cGVHD STUDY DESIGN: We retrospectively evaluated the efficacy of ruxolitinib in 115 heavily pre-treated patients with steroid-refractory or dependent chronic GVHD across 5 transplant centres.The majority of the study population had severe chronic GVHD (60%) and received ruxolitinib at the 4Overall, this study demonstrates the therapeutic efficacy of ruxolitinib for cGVHD in a heavily pretreated real-world population.

This prospective study designs an HCT Frailty Scale to classify alloHCT candidates into groups of frail, pre-frail, and fit, and to be implemented in the first consultation at no additional cost. The present scale is composed of the following eight variables: Clinical Frailty Scale, Instrumental Activities of Daily Living, Timed Up and Go Test, Grip Strength, Self-Health Rated, Falls, Albumin, and C-Reactive Protein. The Frailty score of a patient is the weighted sum of scores for each item, with weights assigned according to the hazard ratios of a multivariable Cox proportional hazards model estimated and validated with data on OS as the dependent variable, and the scores of the eight variables as explanatory ones, from 298 adults split into training (n = 200) and validation (n = 98) sets. For clinical use, the scale scores were transformed into three categories: scale score ≤1: fit; 1scale score ≤5.5: pre-frail; scale score5.5 frail. The estimated probabilities of 1-year OS in each group of frailty, were, respectively: 83.7%, 48.5%, and 16.5% (p 0.001). In the validation cohort, the respective values were 90.3%, 69.5%, and 46.2% (p 0.001). Pending further external validations, the HCT Frailty Scale is a low cost-highly informative prognostic signal of outcomes at the pre-transplant stage.

Although total duration of tyrosine kinase inhibitor (TKI) therapy and of molecular response at 4 log reduction or deeper (MR4) correlates with treatment-free remission (TFR) success after TKI discontinuation, the optimal cut-off values of the duration remain unresolved. Thus, 131 patients were enrolled into the Canadian TKI discontinuation study. The molecular relapse-free survival (mRFS) was defined from imatinib discontinuation till molecular recurrence, that is, major molecular response (MMR) loss and/or MR4 loss. We evaluated mRFS at 12 months after imatinib discontinuation, analyzed it according to the imatinib treatment duration and MR4 duration, and calculated P value, positive (PPV) and negative predictive value (NPV) in the yearly cut-off period of time. The shortest cut-off was sought that met the joint criteria of a P value ≤ 0·05, PPV ≥ 60% and NPV ≥ 60%. We propose six years as the shortest imatinib duration cut-off with a P value 0·01, PPV 68% and NPV 62%: The patients treated with imatinib duration ≥ 6 years showed a superior mRFS rate (61·8%) compared to those with less treatment (36·0%). Also, 4·5 years MR4 duration as the shortest cut-off with a P value 0·003, PPV 63% and NPV 61%: those with MR4 duration ≥ 4·5 years showed a higher mRFS rate (64·2%) than those with a shorter MR4 duration (41·9%).

BCR-ABL1 plays a key role in the pathogenesis of chronic myeloid leukemia (CML), and it has been investigated as a druggable target of tyrosine kinase inhibitors (TKIs) over two decades. Since imatinib, the first TKI for anti-cancer therapy, was successfully applied in CML therapy, further generation TKIs and a novel allosteric inhibitor targeting the myristate binding site have been developed as alternative options for CML management. However, significant concerns regarding toxicity profiles, especially in long-term treatment, have emerged from TKI clinical data. Efforts to reduce adverse events and serious complications are warranted not only for survival, but also quality of life in CML patients. A better understanding of the mechanism of action will help to identify on- and off-target effects of TKIs, and guide personalized TKI drug selection in each individual CML patient. Herein, this review summarizes the biologic mechanism of BCR-ABL1 inhibition and differential target spectra, and related off-target effects of each TKI.

The impact of adverse risk genetic profiles on outcomes in acute myeloid leukemia (AML) patients following allogeneic hematopoietic stem cell transplantation (HCT) has not been fully elucidated. Accordingly, we have profiled somatic mutations at diagnosis using next-generation sequencing (NGS) in 178 AML patients who received allogeneic HCT. NGS revealed 598 somatic mutations in 165/178 patients (92.7%). Frequently mutated genes include DNMT3A, TET2, NPM1, RUNX1, IDH2, and FLT3. Commonly detected cytogenetic profiles include normal karyotype, trisomy 8, monosomal karyotype (MK), deletion 5, complex karyotype (CK), and monosomy 7. In univariate analyses, TP53 mutation, MK, CK, and monosomy 7 were associated with decreased overall survival (OS), relapse-free survival (RFS), and a higher relapse incidence (RI). We defined adverse molecular-genetic profile as harboring at least one of the molecular/genetic abnormalities of TP53 mutation, MK, CK, monosomy 7, and deletion 5. The patients harboring adverse molecular-genetic profile (n = 30) showed a lower 2-year OS (24.9% vs. 57.9%; p = 0.003), RFS (23.7% vs. 57.9%; p = 0.002), and higher RI (47.2% and 17.2%; p = 0.001) after HCT when compared to patients without those lesions. Multivariate analysis confirmed adverse molecular-genetic profile as an independent prognostic factor, associated with decreased OS (HR 2.19), RFS (HR 2.23), and higher RI (HR 2.94).

OBJECTIVES Hepatic grading systems for categorizing severity in chronic graft-versus-host disease (cGvHD) were determined arbitrarily, leading us to initiate the present study to provide objective evidence for the determination of optimal cutoff values and devise a hepatic grading system to predict prognosis. METHODS Of 842 patients who received allogeneic hematopoietic stem transplant (HCT), 336 patients diagnosed with cGvHD were evaluated for overall survival (OS) and non-relapse mortality (NRM) after cGVHD development. Multiple statistical parameters were evaluated to define optimal cutoff values of liver profile, including negative predictive value (NPV), positive predictive value (PPV), accuracy, and p-values as measures of risk stratification power. RESULTS We found that alkaline phosphatase (ALP) ≥ 146 IU/L (NPV: 83.4%; PPV: 32.8%; accuracy: 52.7%) and bilirubin ≥ 14 µmol/L (NPV: 81.8%; PPV: 39.4%; accuracy 68.1%) significantly correlated with OS. We developed a refined hepatic cGvHD grading score (RHS), stratifying patients into a low-RHS group with RHS score 0, OS at 3 years (n = 162) to 80.5%, compared to high-RHS group with score 1-2 (n = 172) 62.7%. Regarding NRM, score 0 segregated NRM at 3 years to 11.9%, compared with score 1-2 19.6%, P = .1. CONCLUSIONS Refined hepatic score is promising for stratifying patients with cGVHD and liver involvement according to long-term outcomes.

In patients with acute myeloid leukemia (AML) consolidation treatment options are between allogeneic hematopoietic stem cell transplantation (HCT) and chemotherapy, based on disease risk at the time of initial presentation and age. Measurable residual disease (MRD) following induction chemotherapy could be incorporated as a useful parameter for treatment decisions. The present study evaluated treatment outcomes according to the next-generation sequencing (NGS)-based MRD status and the type of consolidation therapy in patients with normal karyotype (NK)-AML. By sequencing 278 paired samples collected at diagnosis and first remission (CR1), we identified 361 mutations in 124 patients at diagnosis and tracked these at CR1. After excluding mutations associated with age-related clonal hematopoiesis, 82 mutations in 50 of the 124 patients (40.3%) were detected at CR1. Survival benefit was observed in favor of allogeneic HCT over chemotherapy consolidation in the MRDpos subgroup with respect to overall survival (HR 0.294, p = 0.003), relapse-free survival (HR 0.376, p = 0.015) and cumulative incidence of relapse (HR 0.279, p = 0.004) in multivariate analysis, but not in the MRDneg subgroup. In summary, these data support allogeneic HCT in NK-AML patients with detectable MRD by NGS in CR1. Randomized clinical trials will be required to confirm this observation.

BACKGROUND AND AIMS The overwhelming majority of individuals of West African ancestry carry an ‘erythroid silent’ FyB(ES) SNP in the promoter region of ACKR1 that causes a selective loss of ACKR1 in erythroid cells but does not affect its expression in endothelial cells. The FyB(ES) polymorphism is of a special interest for understanding human kidney disease as individuals of West African ancestry have higher incidence of chronic kidney disease. Moreover, multiple chemokine ligands of ACKR1 are known to contribute to the inflammatory pathology in experimental nephrotoxic serum nephritis (NTS), a murine model of immune complex glomerulonephritis. METHOD We developed two humanized transgenic mouse strains that are genetically deficient for mouse ACKR1 but instead carry either West African FyB(ES) or Caucasian FyB human polymorphic ACKR1 variants. These strains as well as ACKR1-deficient and WT mice were subjected to NTS. The parameters of immunopathogenesis and kidney disease were evaluated after 14 days after the induction of NTS. RESULTS Albuminuria, PAS and tubular injury scores were significantly increased in FyB(ES)tg and ACKR1-deficient mice as compared with their respective control strains. While monocytes were unchanged in peripheral blood, we found significantly increased numbers of macrophages and neutrophils infiltrating the kidneys of FyB(ES)tg and ACKR1-deficient mice. Interestingly, T cell numbers in the draining lymph nodes were comparable between FyB(ES)tg and ACKR1-deficient mice and their respective controls. CONCLUSION We found that NTS was more severe in ACKR1-deficient and FyB(ES) mice as compared with their respective controls. Our results show that ACKR1 expression in the erythroid compartment has a significant impact on the development of kidney disease. These findings have important implications for the pathomechanisms of glomerulonephritis in individuals of West African ancestry who lack ACKR1 selectively in the erythroid lineage.

In donor selection for allogeneic stem cell transplant, several factors are considered for potential impact on transplant outcome. Previous publications suggested single HLA-mismatched unrelated donors (MMUD) may be equivalent to 10/10 matched unrelated donors (MUDs). We retrospectively examined factors affecting outcome in a single-center study using ATG followed by post-transplant cyclophosphamide, termed ATG-PTCy, GvHD prophylaxis. Fifty-two patients who received grafts from MMUD and 188 patients transplanted from MUD between January 2015 and December 2019, at Princess Margaret Cancer Centre, Canada, were enrolled. All patients received reduced-intensity conditioning. Overall survival for 9/10 recipients at 2 years was significantly worse, 37.2% versus 68.5% for 10/10 MUDs, p .001, as were NRM at 1 year 39.5% versus 11.7%, p .001, and GRFS at 2 years 29.8% versus 58.8%, p .001, respectively, potentially due to higher incidence of infections including CMV. By multivariable analysis, factors correlating with survival negatively were DRI, and MMUD, whereas for NRM MMUD and increasing age were unfavorable. For GRFS significant unfavorable factors included donor age ≤32 years, female donor to male recipient, DRI high-very high and MMUD. These data suggest that MMUD, primarily HLA-A and HLA-B MMUD, confer significantly inferior outcome despite use of ATG-PTCy. Further development of novel conditioning regimens and GvHD prophylaxis is needed to mitigate these risks.

The implementation of dual T-cell depletion comprising 4.5 mg/kg of antithymocyte globulin (ATG), post-transplantation cyclophosphamide, and cyclosporine A for reduced-intensity allogeneic hematopoietic cell transplantation (HCT) independent of donor source in 2015 significantly improved graft-versus-host disease (GVHD) control at our Institution. Further advances were made between 2017 to 2020 in supportive care of allogeneic HCT recipients and were the subject of this study, with 651 adults included. Transplant outcomes were compared between patients who underwent transplantation during Period 1 (2017-2018) and Period 2 (2019-2020). Main changes implemented during the study period were reduction of ATG dose from 4.5 to 2 mg/kg in matched unrelated donor transplants, abandoning of dual T-cell depletion in matched related donor transplants, combining dual T-cell depletion with myeloablative conditioning for selected patients, and reduction of the target therapeutic cyclosporine level from 200 to 400 ng/L to 150 to 250 ng/L. Other improvements included addition of ursodiol until day 100, implementation of a double responsible physician model, and personalized patient supportive care plan focused on activity and calorie intake. The reduction in intensity of GVHD prophylaxis provided comparable acute GVHD and moderate-severe chronic GVHD between both time periods. Altogether the described improvements in transplant methodology and supportive care showed that compared to Period 1, patients transplanted in Period 2 had superior 1-year overall survival, relapse-free survival, and non-relapse mortality and showed a trend toward better GVHD- and relapse-free survival, without an increase in relapse risk. This study reports the results of outcomes-directed improvements in transplantation design, GVHD prophylaxis, and supportive care, highlighting how transplantation outcomes can be improved through careful modifications in response to meticulously monitored outcomes.

This study investigated the single-center incidence and risk factors for bloodstream infections (BSIs) in 651 adults who underwent allogeneic hematopoietic cell transplantation (alloHCT) between 2015 and 2019 and explored the impact of these BSIs on post-transplantation outcomes. Antibiotic prophylaxis with ciprofloxacin was given during the aplastic phase. Overall, the median patient age was 57 years, 79.7% of patients received an alternative donor graft, and 68.7% received post-transplantation cyclophosphamide (PTCy) as part of their graft-versus-host disease (GVHD) prophylaxis. Of the 651 patients, 358 (55.0%) had at least 1 episode of BSI, and the overall mortality rate secondary to this complication was 7.5% (12.6% among those diagnosed with at least 1 episode of BSI). BSI was more often diagnosed during the first 30 days (58.7%), and gram-positive bacteria were the most prevalent microorganisms isolated during the entire post-transplantation follow-up (62%). A high Disease Risk Index (hazard ratio [HR], 1.47; P < .029) and receipt of PTCy-based GVHD prophylaxis (HR, 3.33; P < .001) were identified as risk factors for BSI. Additionally, univariate analysis showed that patients diagnosed with a BSI during post-transplantation follow-up had worse overall survival (HR, 2.48; P < .001) and higher nonrelapse mortality (HR, 2.68; P < .001) than those without BSI. In conclusion, alloHCT recipients with a BSI had a higher risk of mortality compared with those who did not develop BSI. The inclusion of PTCy as part of GVHD prophylaxis was identified as an independent risk factor for BSI during early post-transplantation follow-up. Single-center analyses focused on reporting the incidence and risk factors for BSI highlight the need for active implementation of preemptive strategies to decrease BSI incidence in the alloHCT setting. © 2021 American Society for Transplantation and Cellular Therapy. Published by Elsevier Inc.

The doubling time (DT) of the BCR-ABL1 quantitative polymerase chain reaction (qPCR) transcript level reflects the re-growing fraction of leukaemic cells after discontinuation of tyrosine kinase inhibitor (TKI). The present study analyzed monthly DT within six months after imatinib discontinuation in 131 patients. Monthly DT was calculated as x = ln(2)/K, where x is the DT and K is the fold BCR-ABL1 change from the previous value divided by the number of days between each measurement. The optimal DT value was determined as 12·75 days at two months using a recursive partitioning method. The patients were stratified into three groups: the high-risk group (DT12·75 days but0, with rapidly proliferating chronic myeloid leukaemia (CML) cells; n = 26) showed the lowest molecular relapse-free survival (mRFS) of 7·7% at 12 months, compared to 53·6% in the intermediate-risk group (DT≥12·75 days, with slowly proliferating CML cells; n = 16) or 90·0% in the low-risk group (DT≤0, i.e., without proliferating CML cells; n = 71; P 0·001). Monthly assessment of DT helps identify high-risk patients for treatment-free remission failure with an imminent risk of molecular recurrence, and to define low-risk patients who can be spared the frequent monitoring of monthly molecular tests.

Background Several agents have been investigated for beyond second-line treatment of chronic graft-versus-host disease (GVHD). Ruxolitinib has been recently approved for steroid-refractory acute GVHD, while a prospective randomized study is ongoing to examine its efficacy in steroid-resistant chronic GVHD (cGVHD). The present study evaluated the efficacy of Ruxolitinib in terms of 1) overall response rate (ORR), 2) clinical benefit (CB), 3) dose reduction of corticosteroid exposure, 4) failure-free survival (FFS) and 5) overall survival (OS), in patients heavily pretreated for steroid-resistant cGVHD. Patients and methods A total of 47 patients who developed cGVHD after HCT and treated with Ruxolitinib for cGVHD from March 2016 to April 2020, at three different sites (Princess Margaret Cancer Center, Canada; Vancouver General Hospital, Canada and Saint Vincent Hospital, Australia), were evaluated in the retrospective study. Patients and disease characteristics are as follows: median age 52 years; classical 35 (71%), overlap syndrome 14 (29%). Of note, 27 patients (57.4%) had a previous history of acute GVHD. The ORR and CB were assessed at months 3, 6 and 12, retrospectively. Responses were evaluated according to NIH scoring/staging/response assessment as part of standard clinical practice. CB was assessed considering clinical response as well as steroid dose reduction. For systemic steroid dose reduction, prednisone dose per kg per day was captured prior to Ruxolitinib start, at months 3, 6 and 12. Treatment failure was defined as 1) resistance requiring treatment switch, 2) non-relapse mortality (NRM), 3) relapse, 4) intolerance to treatment. FFS and OS were calculated from the day of starting Ruxolitinib therapy for cGVHD treatment. Results A total of 47 patients had moderate (11/47, 24.4%) to severe (33/47, 73.3%) cGVHD except one who had mild grade cGVHD with a high-risk feature (thrombocytopenia at the time of Ruxolitinib start). The median number of organ involvement was 3 (range 1-7). Over half of patients (63.8%) received Ruxolitinib as 4th line or beyond for cGVHD treatment, while median number of previous lines of therapy was 3 (range 1-9). All 47 patients (100%) had been previously treated with systemic steroids; other previous treatments included ECP therapy (53.2%), Imatinib (29.8%), Ibrutinib (23.4%), Rituximab (21.3%). Ruxolitinib was started at 10-15 mg daily as initial dose, then maintained at 20mg daily in two divided doses on months 3, 6 and 12.With a median follow-up duration of 12 months, ORR was attained in 35.7%, 36.0% and 35.0% at 3, 6 and 12 months, respectively (Figure A). Of note, ORR in patients with sclerotic changes was 56%, and 61.5% in those with lung involvement. Patients resistant to TKI (i.e. Imatinib or Ibrutinib) for cGVHD treatment showed similar ORR compared to those naïve to TKI therapy.The CB was observed in 53.5%, 66.7% and 72.2% at months 3, 6 and 12, respectively (Figure B). Patients resistant to TKI for cGVHD treatment did not show any difference in CB compared to those naïve to TKI therapy.In terms of prednisone dose reduction, by 12 months , half of patients (50.0%) could taper prednisone doses below 0.1mg/kg/day, while the proportion of patients on prednisone dose below 0.1mg/kg/day was 9.3%, 20.0%, 17.4%, and 50.0% at month 0, 3, 6 and 12, respectively (Figure C). The group who achieved CB at 3 months showed a significantly lower dose of prednisone at 12 months (0.078mg/kg/day) compared to those without clinical benefit at 3 months (0.197mg/kg/day; p=0.033; Figure D).Out of 37 patients evaluated, 11 failures (29.7%) were noted, including resistance requiring a switch to other therapy (n=7), NRM (n=2) and intolerance (n=2). The FFS rate at 1 year in the overall population was 68.5% (Figure E). The FFS at 1 year in those having CB at 3 months vs not was 86.5% vs 51.4% (p=0.025).The OS at 1 year was 90.9% (Figure F). The OS at 1 year in those having a CB at 3 months vs not was 100% vs 78.8% (p=0.053). Conclusion: This multicenter retrospective study revealed that Ruxolitinib is an effective treatment option for patients with cGVHD, with good ORR and CB. The achievement of CB in the first 3 months correlated well with steroid dose reduction. It suggests that Ruxolitinib is a feasible GVHD treatment option, even for patients who were heavily pretreated for cGVHD or failed previous TKI drug. Figure 1 Disclosures Hamad: Abbvie: Honoraria; Novartis: Honoraria. OffLabel Disclosure: Ruxolitinib treatment for steroid resistant chronic GVHD

Leukemic transformation (LT) is the main cause of death for patients with myeloproliferative neoplasms (MPNs). To study genetic changes associated with the LT, we performed targeted sequencing in 26 MPN patients including 21 with paired samples. We observed that, besides three driver genes, IDH2 (19%) and ASXL1 (14%) were also frequently mutated at MPN diagnosis. Although variant allele frequencies (VAFs) of mutations in DNA methylation and spliceosome did not expand during LT, they were enriched in patients with LT (the LT group). At follow-up, we also observed acquisition of mutations, mostly in the LT group. When considering dynamics of VAF from diagnosis to follow-up, VAFs in the LT group expanded (median VAF, 36.7-43.7%, p = 0.045). In contrast, mutations in patients with no clinical progression was stable (median VAF, 36.3-35.7%, p = 0.739). Overall, the present study demonstrates genetic changes during LT and provides the potential for prognostic application.

The impact of adverse risk genetic profiles on outcomes in acute myeloid leukemia (AML) patients following allogeneic hematopoietic stem cell transplantation (HCT) has not been fully elucidated. Accordingly, we have profiled somatic mutations at diagnosis using next-generation sequencing (NGS) in 178 AML patients who received allogeneic HCT. NGS revealed 598 somatic mutations in 165/178 patients (92.7%). Frequently mutated genes include DNMT3A, TET2, NPM1, RUNX1, IDH2, and FLT3. Commonly detected cytogenetic profiles include normal karyotype, trisomy 8, monosomal karyotype (MK), deletion 5, complex karyotype (CK), and monosomy 7. In univariate analyses, TP53 mutation, MK, CK, and monosomy 7 were associated with decreased overall survival (OS), relapse-free survival (RFS), and a higher relapse incidence (RI). We defined adverse molecular-genetic profile as harboring at least one of the molecular/genetic abnormalities of TP53 mutation, MK, CK, monosomy 7, and deletion 5. The patients harboring adverse molecular-genetic profile (n = 30) showed a lower 2-year OS (24.9% vs. 57.9%; p = 0.003), RFS (23.7% vs. 57.9%; p = 0.002), and higher RI (47.2% and 17.2%; p = 0.001) after HCT when compared to patients without those lesions. Multivariate analysis confirmed adverse molecular-genetic profile as an independent prognostic factor, associated with decreased OS (HR 2.19), RFS (HR 2.23), and higher RI (HR 2.94).

In patients with acute myeloid leukemia (AML) consolidation treatment options are between allogeneic hematopoietic stem cell transplantation (HCT) and chemotherapy, based on disease risk at the time of initial presentation and age. Measurable residual disease (MRD) following induction chemotherapy could be incorporated as a useful parameter for treatment decisions. The present study evaluated treatment outcomes according to the next-generation sequencing (NGS)-based MRD status and the type of consolidation therapy in patients with normal karyotype (NK)-AML. By sequencing 278 paired samples collected at diagnosis and first remission (CR1), we identified 361 mutations in 124 patients at diagnosis and tracked these at CR1. After excluding mutations associated with age-related clonal hematopoiesis, 82 mutations in 50 of the 124 patients (40.3%) were detected at CR1. Survival benefit was observed in favor of allogeneic HCT over chemotherapy consolidation in the MRD

Relapse remains the most common cause of treatment failure for patients with acute myeloid leukemia (AML) who undergo allogeneic stem cell transplantation (alloSCT), and carries a grave prognosis. Multiple studies have identified the presence of measurable residual disease (MRD) assessed by flow cytometry before alloSCT as a strong predictor of relapse, but it is not clear how these findings apply to patients who test positive in molecular MRD assays, which have far greater sensitivity. We analyzed pretransplant blood and bone marrow samples by reverse-transcription polymerase chain reaction in 107 patients with NPM1-mutant AML enrolled in the UK National Cancer Research Institute AML17 study. After a median follow-up of 4.9 years, patients with negative, low (

Background The REACH3 study has reported greater overall response and failure-free survival (FFS) with Ruxolitinib (RUX) as 2 nd line therapy for steroid-refractory chronic graft versus host disease (cGVHD) in comparison to best available therapy (BAT; NEJM 2021). In addition, our Canadian retrospective study as a real-world experience has reported a promising activity of 64.6% FFS and 83.3% overall survival (OS) at 12 months in 115 patients (pts) treated with RUX from 2016 to 2021 for heavily pretreated cGVHD (ASH 2021). Also, 47.6% pts could reduce corticosteroid dose below 0.1mg/kg/day within 6 months. The present study compared treatment outcomes using a propensity-score matching (PSM) analysis between RUX pts ("RUX group", n=115) and a historical cohort of cGVHD pts treated with BAT as 2 nd line therapy or beyond from 2005 to 2013 ("BAT group", n=311). Statistical endpoints such as FFS, OS and steroid dose reduction were evaluated instead of overall response due to limited response assessment available from retrospective chart reviews. Patients and methods BAT included mycophenolate (43%), prednisone (29%), prednisone/cyclosporine (12%), extracorporeal photopheresis (6%), rituximab (3%), and others (7%). The pts and disease characteristics between the RUX vs BAT groups were not well balanced, as expected: RUX group showed a higher number of pts with severe grade GVHD (59.1% in RUX vs. 20.3% in BAT; p FFS and OS were calculated from the day of starting RUX or BAT therapy, while daily prednisone doses at months 0, 3 and 6 were calculated divided by body weight (kg). PSM analysis was applied to adjust risk factors that were unbalanced between the 2 groups, including GVHD severity at therapy start (mild/moderate vs severe grade), HCT-CI score (0-2 vs 3 or beyond), and treatment line (2nd vs 3rd vs 4th line or beyond). A total of 100 patients (i.e. 50 case-control pairs) were finally extracted through PSM process within 0.2 of calliper difference. PSM analysis balanced out the risk factors between the 2 groups: GVHD severity (p=1.0), HCT-CI score (p=1.0) and treatment line (p=1.0). The FFS and OS rate at 12 months were compared using Cox's proportional hazard model. Results In the overall population (n=426), with a median 19 months follow-up duration, 244 failures (57.3%) were noted. While both groups showed similar failure rates due to non-relapse mortality (NRM), the RUX group showed significantly lower failure rate from cGvHD resistance requiring therapy switch. Failure was noted in 40 pts (33.4%) in RUX due to resistance requiring a switch of therapy (n=23; 20.0%), NRM (n=14, 12.2%) and relapse (n=3; 2.6%), while failure occurred in 204 pts (65.6%) in BAT due to resistance requiring a switch of therapy (n=142; 45.7%), NRM (n=36; 11.6%) and relapse (n=26; 12.7%). The 12 months' FFS rate were 64.7% and 40.1% in RUX vs. BAT group (p Multivariate analysis in the PSM cohort confirmed that RUX is superior to BAT for FFS (p The prednisone dose was gradually reduced over time: the median doses of prednisone at months 0, 3, and 6 were 0.34, 0.16 and 0.02 mg/kg/day in the RUX group, and 0.95, 0.24 and 0.15 mg/kg/day at months 0, 3 and 6 in the BAT group. RUX facilitates the discontinuation of prednisone. The proportions of patients who discontinued prednisone at months 0, 3 and 6 were 8.7%, 15.9% and 24.1% in RUX, and 0.7%, 0% and 2.0% in BAT group. The differences in proportions of pts that discontinued prednisone between the RUX vs BAT groups at months 0, 3, and 6 were 8.0%, 15.9% and 22.1% (Fig 3). Conclusion: The current PSM analysis study suggests that RUX showed a superior FFS to BAT as 2nd line therapy or beyond in cGVHD patients after therapy failure. RUX showed better steroid tapering compared to BAT. Figure 1 Figure 1. Disclosures White: Novartis: Honoraria. Elemary: Pfizer, Janssen: Membership on an entity's Board of Directors or advisory committees; Jazz, BMS, Abbvie, Novartis, Pfiz: Membership on an entity's Board of Directors or advisory committees. Hamad: Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Law: Novartis: Consultancy; Actinium Pharmaceuticals: Research Funding. Kim: Bristol-Meier Squibb: Research Funding; Paladin: Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Honoraria, Research Funding.

Background During 2020, the novel COVID-19 pandemic lead to cryopreservation of allogeneic hematopoietic stem cell (HSCT) grafts based on NMDP and EBMT recommendations, to secure grafts before start of conditioning chemotherapy. We examined the impact of this change in practice on patient outcomes. Methods We retrospectively analyzed the outcomes of 483 patients who received HSCT between Aug 2017 and Aug 2020, at Princess Margaret Cancer Centre, Canada, comparing the outcomes between those who received cryopreserved (CRYO, n=135) or fresh peripheral blood stem cell grafts (FRESH, n=348). Median follow-up: 12.3 months. Probability of overall survival (OS) was calculated using the Kaplan-Meier product-limit method and heterogeneity of time-to-event distribution functions were compared by the log-rank test. Cumulative incidences of aGvHD and cGvHD, relapse, and non-relapse mortality (NRM) were estimated using the cumulative incidence method considering competing risk, and groups were compared using Gray's test. Death was considered as a competing event for relapse, aGvHD and cGvHD, and relapse was considered a competing event for NRM, aGvHD and cGvHD. Results Median age was 58y; 54.5% were males. Acute myeloid leukemia was commonest HSCT indication (n=248, 49.1%). Donors: MUD 10/10 n=233; MUD 9/10 (MMUD) n=48, matched related donor (MRD) n=112, Haploidentical n=88. Transplant conditioning: 79 (23%) and 23 (17%) patients received myeloablative conditioning (MAC) in the FRESH and the CRYO groups, respectively (p ns). In the FRESH group, 253 (73%) patients and 114 (84%) patients in the CRYO group received ATG followed by posttransplant cyclophosphamide (PTCy) and Cylosporine GvHD prophylaxis. OS at the 2y timepoint, FRESH group (n=348), was 67.0% (61.1-72.3%), compared to 48.7% (38.1-58.4%) for patients in the CRYO group (n=135), p=0.002, Figure 1a. This was mainly due to MRD cohort outcomes: 2y OS in MRD FRESH group (n=65), was 85.2% (73.3-92.0%), compared to 45.1% (29.9-59.1%) in MRD CRYO group (n=47), p NRM at 1y for FRESH (n=348) 17% (13.2-21.2) vs CRYO (n=135) 22.1 % (14.8-30.4), p ns . However, in the MRD cohort, NRM at 1y for FRESH group (n=65), was 1.5% (0.1-7.4%), compared to 15.4% (6.6-27.4%) for CRYO group (n=47), p=0.003, Figure 2b . On MVA, NRM adverse significant factors were patient age, DRI high/v.-high, Donors: Haplo and MMUD, Table 1. Cumulative incidence (CI) of relapse at 2y for FRESH 22.4% (17.5-27.7) vs CRYO 27.0 % (18.8-35.9) p=0.07 . The CI of moderate-severe cGvHD at 1y for FRESH group (n=315) was 21.5% and 10.8% in the CRYO group, p=0.027, Figure 1c . Patients with FRESH 10/10 MUDs (n=180), had CI of moderate-severe cGvHD at 1y of 20.6%, compared to CRYO 10/10 MUDs (n=35), 6.0% p ns for MUDs; FRESH MRD (n=64) CI was 30.1%; and CRYO MRD (n=43) 10.3%, p=0.008 for MRD, Figure 1d. On MVA, significant adverse factors for chronic GvHD were increasing donor age, male recipient/female donor, whilst graft CRYO was protective, Table 1. GvHD-and Relapse free Survival (GRFS) at 2y for FRESH 54.0% (47.9-59.6) vs CRYO 43.4% (33.4-53.0) p Compared to FRESH group, CRYO group experienced reduced cGvHD, delay in neutrophil engraftment, higher graft failure and increased CMV reactivation, with no difference in relapse incidence or acute GvHD. Conclusion Cryopreservation was associated with inferior outcomes post-HSCT particularly in the MRD cohort, possibly due to combination ATG and post-transplant cyclophosphamide impacting differential tolerance to cryopreservation on components of the stem cell graft; further studies are warranted to elucidate mechanisms for this observation. Figure 1 Figure 1. Disclosures Law: Novartis: Consultancy; Actinium Pharmaceuticals: Research Funding. Lipton: Bristol Myers Squibb, Ariad, Pfizer, Novartis: Consultancy, Research Funding. Kim: Bristol-Meier Squibb: Research Funding; Paladin: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Mattsson: MattssonAB medical: Current Employment, Current holder of individual stocks in a privately-held company.

*DB and DK contributed to the work equally. Background Extracorporeal photopheresis (ECP) is a recommended second or later line of therapy for chronic GVHD (cGVHD), and is beneficial not only because of increased response but also for its lack of adverse effects, specifically systemic immune suppression, mainly from steroids. In this single centre study, we attempted to evaluate not only therapeutic efficacy of ECP, but also its steroid-sparing effect by regularly analyzing steroid dose per body weight. We also attempted to identify any predictors of response or survival after ECP, which was not well defined before. Patients and methods A total of 75 cGVHD patients (pts) who received ECP for cGVHD from 2007 to 2021 at Princess Margaret Cancer Centre were included and evaluated retrospectively. Patients and disease characteristics are as follows: median age 48.5 years (range 17-70); male 42/75 (56%); organ involvement at the time of ECP: skin (93%), oral (53%), eye (51%), gastrointestinal (25%), liver (49%), lung (57%), and musculoskeletal (n=50, 67%). Sixty-eight (91%) and 7 pts (9%) had severe and moderate grade cGVHD, respectively. Sixty-eight pts (91%) received ECP as 4 th line or beyond. They were heavily pretreated with prednisone (98%), cyclosporine (57%), tacrolimus (24%), mycophenolate mofetil (64%), azathioprine (65%), rituximab (7%), imatinib (8%), ibrunitib (3%) and ruxolitinib (1%). ECP was started twice weekly for the first 12 weeks, then twice every 2 weeks in 2012-2021, while the schedule was twice every 2 weeks from 2007-2012. If there was no response or clinical benefit noted in first 24 treatments, then ECP was discontinued. In general, we attempted to provide up to around 60 sessions based on the clinicians' discretion. The overall response rate (ORR) and clinical benefit (CB) were assessed at months 3, 6 and 12 after staring ECP. As part of standard clinical practice, NIH consensus criteria were used for grading and response assessment. CB was assessed considering clinical response as well as steroid dose reduction. Treatment failure was defined as 1) resistance to ECP requiring treatment switch, 2) non-relapse mortality (NRM), 3) relapse, 4) intolerance to ECP. Failure free survival (FFS) and overall survival (OS)were calculated from the day of ECP initiation until the endpoints of failure or death, respectively. Results ECP was started a median of 28 months (range 1-125) after development of cGVHD. ECP was performed a median of 35 times (range 6-174) with a median duration of 11 months (range 1-53). Out of 75 pts, 48 completed planned ECP successfully and 27 stopped due to no response or benefit including, of whom 14 required additional therapy, 1 stopped due to line infection, and 1 stopped due to relapse of AML. With a median 72 months of follow-up, ORR was attained in 21% (16/75), 57% (36/63) and 70% (32/46) at month 3, 6 and 12, respectively. At 6 months, ORR was observed in 47-64% across all organs assessed. No difference in ORR was noted according to the cGVHD grade; at 6 months, severe cGVHD showed similar ORR (57%) to those with moderate cGVHD (60%) (p=0.893). CB was noted in 23% (17/75), 62% (39/63), and 76% (35/46) at month 3, 6 and 12, respectively. A total of 27/75 failures (36%) and 20/75 death (27%) occurred, due to the following: ECP resistance requiring switch to other therapy (n=14, 19%), NRM (n=11, 15%), relapse of primary disease (n=1, 1%) or ECP-related complication (n=1, 1%, line infection). In the overall cohort, FFS and OS at 12 months were 68.3% and 85.9%, respectively (Figure 1). More than a half of pts stopped steroids completely within 12 months after starting ECP. The proportion of pts off steroids was 16%, 17%, 32%, and 64% at month 0, 3, 6 and 12 after starting ECP, respectively (Figure 2). Risk factor analysis did not show any predictive markers for ORR at 6 months, while prognostic factor analysis suggested the development of musculoskeletal involvement as favorable prognostic factor for FFS (p=0.003, HR 0.315 [0.147, 0.673]) even with multivariate analysis. Conclusion Our study showed that: 1) ECP is a very effective treatment for heavily pre-treated cGVHD pts who have failed other therapies; 2) More than a half of pts can stop steroids completely within 12 months after starting ECP, thus avoiding long-term toxicity risk. Further study is warranted comparing ECP with other cGVHD treatment modalities. Figure 1 Figure 1. Disclosures Patriquin: BioCryst Pharmaceuticals: Honoraria; Alexion: Consultancy, Honoraria, Speakers Bureau; AstraZeneca: Consultancy, Honoraria, Speakers Bureau; Apellis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi: Honoraria. Law: Novartis: Consultancy; Actinium Pharmaceuticals: Research Funding. Lipton: Bristol Myers Squibb, Ariad, Pfizer, Novartis: Consultancy, Research Funding. Mattsson: MattssonAB medical: Current Employment, Current holder of individual stocks in a privately-held company. Kim: Paladin: Consultancy, Honoraria, Research Funding; Bristol-Meier Squibb: Research Funding; Pfizer: Honoraria; Novartis: Consultancy, Honoraria, Research Funding.

*DB and DK contributed to the work equally Background Prospective randomized controlled data comparing extracorporeal photopheresis (ECP) to other treatments for chronic graft vs host disease (cGvHD) as third-line or later therapy are limited, despite its clinical benefit observed in patients (pts) who failed ≥ 2 lines of previous therapy. Our single-center experience has reported promising results, including 68.3% failure-free survival (FFS) and 85.9% overall survival (OS) at 12 months in 75 heavily pre-treated cGvHD pts treated with ECP (ASH 2021 Abstract ID 152640). The present study compared outcomes, using propensity-score matching (PSM), between ECP ("ECP group", n=74) and a historical cohort treated with best available therapy (BAT) as third-line or later treatment from 2007 to 2021 ("BAT group", n=132). Statistical endpoints such as FFS and OS, as well as steroid dose reduction were evaluated instead of overall response due to limited response assessment data available from retrospective chart review. Patients and methods The BAT group received MMF (n=71, 53.8%), prednisone (n=37, 28.0%), prednisone/cyclosporine (n=7, 5.3%), rituximab (n=7, 5.3%), and others (n=10, 7.6%). There was an imbalance in characteristics between the two groups, as expected; the ECP group had more pts with severe cGVHD (91.1% vs 20.5%; p FFS and OS were calculated from the day of starting ECP or BAT, and were compared using Cox's hazard model. Daily prednisone dose at months 0, 3 and 6 were calculated divided by body weight (kg), and the proportions of pts on prednisone ≤ 0, 0.1, 0.2 and 0.5mg/kg/day were compared. Results In the overall cohort (n=206), with a median 29 months of follow-up, 114 treatment failures (55.3%) occurred. While the non-relapse mortality (NRM) was similar in both groups, the ECP group showed a lower rate of resistance requiring therapy switch. Failure was noted in 27 ECP pts (36.4%) due to causes including resistance/intolerance requiring a switch to other therapy (n=15; 20.3%), NRM (n=11, 14.8%), and relapse (n=1; 1.4%), while 87 failures (65.9%) were noted in BAT pts due to resistance requiring a switch to other therapy (n=63; 47.7%), NRM (n=7; 5.3%), and relapse (n=17; 12.9%). In the overall cohort, the 12-month FFS was 68.3% and 32.0% in ECP and BAT groups (p Multivariate analysis in the PSM cohort confirmed that ECP was superior to BAT for FFS (p=0.024, HR 0.317 [0.117-0.859]) when adjusted for other risk factors including cGVHD severity, aGvHD history, age, HCT-CI score and prednisone dose ≤0.5mg/kg/day. Prednisone doses were gradually reduced over time; the median doses of prednisone at months 0, 3, and 6 were 0.35, 0.22 and 0.11 mg/kg/day, respectively, in the ECP group vs. 0.96, 0.24 and 0.19mg/kg/day in the BAT group. ECP also showed better kinetics of steroid dose reduction over time; the proportions of pts who discontinued prednisone at months 0, 3 and 6 were 16.2, 17.6% and 32.4% in ECP group vs. 0.8%, 0% and 2.5% in BAT group (Fig 3). The differences in the proportion of pts (delta) who discontinued prednisone in the ECP vs. BAT groups were 15.4%, 17.6% and 29.9% at 0, 3, and 6 months, respectively. Conclusion In the current study using PSM analysis, use of ECP was associated with a superior FFS to BAT when used as third-line or later therapy in cGVHD patients who failed at least 2 lines of previous therapy. Use of ECP also allowed for better steroid tapering in comparison to BAT. Figure 1 Figure 1. Disclosures Patriquin: Alexion: Consultancy, Honoraria, Speakers Bureau; BioCryst Pharmaceuticals: Honoraria; AstraZeneca: Consultancy, Honoraria, Speakers Bureau; Apellis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi: Honoraria. Law: Novartis: Consultancy; Actinium Pharmaceuticals: Research Funding. Lipton: Bristol Myers Squibb, Ariad, Pfizer, Novartis: Consultancy, Research Funding. Mattsson: MattssonAB medical: Current Employment, Current holder of individual stocks in a privately-held company. Kim: Novartis: Consultancy, Honoraria, Research Funding; Paladin: Consultancy, Honoraria, Research Funding; Bristol-Meier Squibb: Research Funding; Pfizer: Honoraria.

Background The REACH3 trial evaluating Ruxolitinib (RUX) treatment for steroid-refractory chronic GVHD concluded that RUX leads to significantly greater overall response and failure-free survival (FFS) than best available therapies (NEJM 2021). We reported a real-world experience of RUX in 47 chronic GVHD (cGVHD) patients, with 36% overall response rate (ORR) at 6 months (ASH 2020). The present study expanded this to 115 pts, evaluating ORR, FFS and overall survival (OS), and explored prognostic factors associated with clinical outcomes. Patients and methods A total of 115 patients treated with RUX for cGVHD from 2016 to 2021 at 5 sites were evaluated retrospectively. Patients and disease characteristics are as follows: median age 57.5 years; males 67 (60%); organ involvement at the time of RUX: skin 75.7%, mouth 51.3%, eye 42.6%, gastrointestinal 19.1%, liver 39.1%, lung 31.3%, and musculoskeletal 38.3%. Out of 108 pts with available HCT-CI prior to HCT, 29 pts (26.9%) had HCT-CI score 3 or higher, while 79 (73.1%) had HCT-CI score 0-2. The ORR were assessed at months 3, 6 and 12, retrospectively. Treatment failure was defined as 1) resistance requiring treatment switch, 2) non-relapse mortality (NRM), 3) relapse, 4) intolerance to treatment. FFS and OS were calculated from the day of starting RUX therapy for cGVHD treatment. For risk factor analysis, logistic regression was adopted for ORR at 6 months, while Cox's proportional hazard model was implemented for FFS and OS at 12 months. The following variables were evaluated for risk factor analysis: GVHD-related factors (cGVHD severity, no. of organ involvement, prednisone dose or RUX dose at start, previous history of acute GVHD); host factors (age or performance status at RUX starts, sex, HCT-CI comorbidity score pre-HCT); transplant factors (conditioning intensity; donor type, HLA match, T-cell depletion). From those variables identified as significant in the multivariate analysis, a prognostic risk score was generated as the sum of adverse risk factor scores. Results A total of 115 pts had severe (n=69, 60%) or moderate grade (n=44, 38.3%) cGVHD except 2 (1.7%) who had mild grade cGVHD with high-risk features. The median number of organ involvement was 3 (range 1-7). 96 pts (84.2%) received RUX as 4 th line or beyond for cGVHD treatment. The previous treatments included mycophenolate mofetil (n=46, 40.0%), extracorporeal photopheres (n=45, 39.1%), Imatinib (n=13, 11.3%), and Ibrutinib (n=9, 7.8%). RUX was started at 10-20 mg daily as the initial dose, then maintained at 20mg daily in two divided doses on months 3, 6 and 12. With a median follow-up duration of 12 months, ORR was attained in 46.8%, 61.8% and 62.3% at 3, 6 and 12 months, similar to 49.7% ORR rate at 6 months in the REACH3 study. ORR in the range of 48.1-64.5% at 6 months was observed across all the organs involved. No difference in ORR was noted between steroid-resistant vs steroid-dependent cGVHD, or according to previous treatment with TKI drug for GVHD. For ORR, severe grade cGVHD showed a lower ORR rate at 46.8% at 6 months compared to those with moderate/mild grade cGVHD at 81.1% (p=0.001). In terms of prednisone dose reduction, by 12 months, more than half of pts (63.8%) could taper prednisone doses below 0.1mg/kg/day, while the proportion of pts on prednisone dose below 0.1mg/kg/day was 14.83%, 33.6%, 47.6%, and 63.8% at month 0, 3, 6 and 12, respectively. A total of 39 failures (33.4%) were noted, including resistance requiring switch to other therapy (n=17), NRM (n=14), relapse of primary disease (n=3) and intolerance (n=5). The FFS rate in the overall population was 64.6% (54.1-73.2), while the OS rate was 83.3% (74.4-89.4%) at 12 months. For FFS, two risk factors were identified for FFS (Figure): 1) Severe grade cGVHD at RUX start (p=0.008, HR 2.496 [1.229-5.072]); 2) HCT-CI comorbidity 3 or higher (p=0.001, HR 2.802 [1.493-5.259]). When a risk score model was generated, it stratified pts according to the FFS at 12 months (p=0.0001): 85.8% in score 0 (n=32); 58.7% in score 1 (n=57); and 36.8% in score 2 (n=19). Conclusion: Updated results confirm that RUX is an effective treatment option for cGVHD pts, even including heavily treated pts. Also, favorable response was observed across all organs involved with GVHD. Failure of RUX is associated with cGVHD severity and HCT-CI score. Figure 1 Figure 1. Disclosures White: Novartis: Honoraria. Elemary: Jazz, BMS, Abbvie, Novartis, Pfiz: Membership on an entity's Board of Directors or advisory committees; Pfizer, Janssen: Membership on an entity's Board of Directors or advisory committees. Hamad: Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Law: Novartis: Consultancy; Actinium Pharmaceuticals: Research Funding. Mattsson: MattssonAB medical: Current Employment, Current holder of individual stocks in a privately-held company. Kim: Novartis: Consultancy, Honoraria, Research Funding; Pfizer: Honoraria; Paladin: Consultancy, Honoraria, Research Funding; Bristol-Meier Squibb: Research Funding. OffLabel Disclosure: This presentation discusses the use of ruxolitinib for chronic GVHD. This indication is under FDA review.

Background: The Canadian tyrosine kinase inhibitor (TKI) discontinuation trial, named "Treatment Free Remission Accomplished By Dasatinib " (NCT#02268370), has reported 56.8% molecular relapse-free survival (mRFS) rate at 12 months after imatinib (IM) discontinuation. MMR loss occurred quickly after IM discontinuation, typically within 2-4 months, while those who lost MR4 on two consecutive measurements tended to lose their molecular response more gradually. BCR-ABL transcript doubling time (DT) after TKI discontinuation is a reciprocal concept to transcript halving time following TKI therapy. Due to inter-individual differences in DT after TKI discontinuation, DT can be used as a potential biomarker to identify those patients at high-risk for TFR failure when measured before they experience a clinically significant event of molecular relapse. The present study has not only evaluated the kinetics of BCR-ABL transcript rise after IM discontinuation, but also explored the predictive/prognostic role of DT of BCR-ABL transcript level as an early predictor of TFR failure. Patients and methods: Changes of BCR-ABL1 transcript level in each patient were assessed monthly by estimating the number of days required for BCR-ABL1 to double from the previous expression level/measurement, termed the DT. Based on the BCR-ABL1 qPCR value taken monthly in the first 6 months after IM discontinuation, DT was calculated monthly, as x = ln(2)/K, where x is the DT and K is the fold BCR-ABL1 change from the previous value divided by the number of days between each measurement. K was determined as follows: K = [ln(b) - ln(a)]/t, where a is the BCR-ABL1 value of the previous measurement, b is the BCR-ABL1 at the relevant time point, and t is the number of days between measurements. The baseline qPCR level from the prior month to TKI discontinuation was referenced. The distribution of DT was assessed at each time point of DT measurement within the first 6 months. In order to define cut-off levels for BCR-ABL1 qPCR and DT for the first 6 months, multiple statistical parameters were taken into account including positive (PPV) and negative predictive value (NPV), accuracy and F1 score of DT value, resulting in the DT value of 12.75 days at 2 months as the optimal cut-off value of DT value. Patients were stratified into the 3 groups based on the DT value of 12.75 days at 2 months after IM discontinuation. The high-risk group was defined as the patients showing DT < 12.75 days but above 0, i.e. rapidly proliferating CML cells, implying a high risk for TFR failure with a shorter DT. The intermediate-risk group was defined as those patients with DT ≥ 12.75 days, i.e. more slowly proliferating CML cells implying intermediate risk for TFR failure. The low-risk group was defined as patients showing DT of zero or below, i.e. no increase in the size of the pool of cells expressing BCR-ABL, implying a low risk for TFR failure. The mRFS was analyzed for each of these risk groups at 6 monthly intervals after TKI discontinuation. Results: We compared the DT values of the patients that failed TFR with those from the patients who maintained their molecular response at last follow-up. The DT values at 2 months were much shorter in patients who failed TFR after IM cessation (median 8.32 days) compared to those who maintained molecular response (median 20.7 days; p The DT value of 12.75 days was defined as the optimal value for DT at 2 months with the NPV, PPV, accuracy and F1 score of 80.90%, 96.43%, 84.62% and 0.75, respectively, as the -log10(p-value), accuracy and F1 score reached a plateau at a DT of 12.75 days as presented in the Figure A. At a DT value of 12.75 days at 2 months after IM discontinuation, patients were stratified into 3 groups: high- (n=26), intermediate- (n=16) and low-risk groups (n=71; Figure B). With respect to mRFS rate, the high-risk group showed 7.7% mRFS rate at 12 months compared to 53.6% in the intermediate-risk group or 90.0% in the low-risk group (p Conclusion: Monthly assessment of DT based on the monthly BCR-ABL qPCR is useful to identify the patients with an imminent risk of molecular recurrence after IM cessation for TFR. Figure Disclosures Bence-Bruckler: Merck: Membership on an entity's Board of Directors or advisory committees. Keating:Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Hoffman La Roche: Membership on an entity's Board of Directors or advisory committees; Sanofi: Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Consultancy; Merck: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Servier: Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Shire: Membership on an entity's Board of Directors or advisory committees; Taiho: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Busque:Novartis: Honoraria; BMS: Honoraria; Pfizer: Honoraria. Delage:Novartis: 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. Lipton:BMS: Consultancy, Research Funding; Takeda: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Honoraria; Ariad: Consultancy, Research Funding; Pfizer: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Research Funding. Leber:Pfizer: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Abbvie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; BMS/Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Treadwell: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda/Palladin: Honoraria, Membership on an entity's Board of Directors or advisory committees; Alexion: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Lundbeck: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Otsuka Pharmaceutical: Honoraria, Membership on an entity's Board of Directors or advisory committees.

BACKGROUND: Multiparameter flow cytometry (MFC) has increasingly been used for measurable residual disease (MRD) assessment in patients with acute myeloid leukemia (AML), while next-generation sequencing (NGS)-based MRD monitoring tool is in clinical development for its application. Clonal hematopoiesis (CH), in which leukemia-associated somatic mutations gene are present in individuals with no apparent hematologic disease, adds a challenge in the detection of MRD. In patients with AML, CH could be potentially pre-leukemic, while persistent mutations in DNMT3A, TET2 orASXL1 (DTA) in remission marrow are usually removed from the analysis of residual leukemic cells. However, reports suggest that persistent DTA mutations in remission may be correlated with an increased relapse risk. In the patients with DTA mutations, the use of NGS for MRD monitoring is limited or modified due to the presence of CH clone in the remission marrow. We evaluated whether MFC-MRD can be adjunctive to predict the risk of AML relapse in this population of 221 patients with DTA mutation (DNMT3A (n=123), ASXL1 (n=56) or TET2 (n=100). METHODS: The present study evaluated long-term outcomes in AML patients who achieved first complete remission (CR1) and compared outcomes according to MFC-based MRD status (was defined as negative if patients achieved 0.1 or less) assessed at the time of CR1. A total of 435 patients diagnosed with AML and treated with induction chemotherapy between 2015 and 2018 were included. MFC-MRD was assessed in 336 patients in CR1 (77%). NGS was performed using samples obtained at the time of initial diagnosis and used for mutational subgroup classification. Overall survival (OS) was calculated as the date of CR1 to the date of death and censored on the date of the last follow-up. Relapse-free survival (RFS) was defined as the time from the date of CR1 to the date of relapse or death from any cause. Cumulative incidence of relapse (CIR) and non-relapse mortality (NRM) were calculated considering competing risk. The Kaplan-Meier method using a log-rank test and a multivariate Cox proportional hazard model was used for analyses of time-to-event endpoints. For CIR and NRM, Gray test was performed for the risk factors and the Fine-Gray model was adopted for the multivariate model. RESULTS: According to the MFC-MRD status, i.e., the group with positive MRD (MRDpos; n=118, 35%) vs. those with negative MRD (MRDneg; n=218, 65%), we evaluated OS, RFS, and CIR. The MFC-MRDneg group showed better OS at 2 years 67.0% than the MFC-MRDpos group 40.7% (p We divided the groups according to the number of induction treatment courses, AML type, cytogenetics risk, and age ( Also, we evaluated MFC-MRD status at CR by mutational profile subgroup. Long-term outcomes such as OS, RFS, CIR or NRM were compared by the mutational subgroup. It consistently showed a trend of superior OS, RFS and lower risk of CIR in patients with MFC-MRDneg compared to MFC-MRDposTab1. Of interest, in the subgroup of patients carrying any DTA mutations (n=221), those with MFC-MRDneg (n=103) showed better OS (HR 1.61 [1.01-2.55%]; p=0.042), RFS (HR 1.66 [1.06-2.61%]; p=0.026) and CIR (HR 1.99[1.03-3.83%]; p=0.04) compared to those MFC-MRDpos (n=64; Fig 1). Multivariate analysis confirmed that the MFC-MRDneg is an independent prognostic factor in patients with DTAmutwith respect to OS: MFC-MRDpos (HR 1.63, p=0.04) and age (≥60; HR 2.04, p=0.008) for OS; for RFS, MFC-MRDpos (HR 1.71, p=0.02) and age (≥60; HR 2.32, p= 0.001); for CIR, MFC-MRDpos (HR 2.31, p=0.01) and HCT (HR 0.14, p= Conclusion: These findings suggest that in AML patients with DTAmut, MFC-MRD status at the time of remission assessment can be a tool for MRD assessment when NGS-based MRD assessment is limited. Further study is strongly warranted to reach a clearer conclusion with multiple cohorts. Disclosures Schimmer: Takeda: Honoraria, Research Funding; Novartis: Honoraria; Jazz: Honoraria; Otsuka: Honoraria; Medivir AB: Research Funding; AbbVie Pharmaceuticals: Other: owns stock . Tierens:Amgen: Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Astellas Pharma: Membership on an entity's Board of Directors or advisory committees. McNamara:Novartis: Honoraria. Maze:Pfizer: Consultancy; Novartis: Honoraria; Takeda: Research Funding. Gupta:Pfizer: Consultancy; Bristol MyersSquibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Sierra Oncology: Consultancy, Membership on an entity's Board of Directors or advisory committees; Incyte: Honoraria, Research Funding.

Background Secondary malignancies (SM) are a recognized complication following allogeneic hematopoietic stem cell transplant (HCT). It is unclear whether specific immunosuppressive therapies (IST) may contribute to this risk. We have reported that Azathioprine (AZP) is a relevant option as a steroid-sparing agent in chronic graft versus host disease (cGvHD) treatment (Uhm et al BMT 2018) by evaluating its failure-free survival and overall survival. AZP is known to increase the risk of SM in patients with inflammatory bowel disease or autoimmune disease. Also, cGvHD in of itself increases the risk of SM. However, SM risk was not extensively investigated in patients treated with AZP for cGvHD. Thus, we performed a retrospective chart review to evaluate IST and analyze for correlations with SM risk and whether treatment with distinct IST, including AZP, may be associated with added risk for SM development. Patients and methods A total of 502 patients who received HCT from Jan 2000 to Dec 2012 and had a diagnosis of cGvHD according to NIH criteria after HCT, treated from April 2000 to Mar 2013, at Princess Margaret Cancer Center, Canada, were enrolled in the retrospective study. Patients and disease characteristics are as follows: median age of 48 years; male 289 (57.6%), classical 217 (43.6%), overlap syndrome 281 (56.4%). Of note, 394 patients (78.6%) had a previous history of acute GvHD. Subtype, severity and organ involvement of cGvHD were assessed at initial presentation of cGvHD. The most common treatment used for cGvHD was systemic corticosteroid (82.7%) followed by AZP (40.8%), cyclosporine (CSA) (40.1%) and mycophenolate mofetil (MMF) (26.5%). The incidence of SM was calculated from HCT to the first day of confirmed diagnosis of SM using cumulative incidence method considering competing events such as relapse or death. Risk factors for SM development were compared using Gray model. Survival after diagnosis of SM was calculated using Kaplan-Meier estimates and compared using log-rank test. For multivariate analysis, Fine-Gray regression model and Cox proportional hazard model were used to analyze the effects of variables on SM risk and survival (OS), respectively. Results With a median follow-up duration of 12.3 years, 101 patients were diagnosed with SM with a median onset of 5.7 years (range 0.3-18.3 years). The most common types of SM were basal cell skin cancer (n=29), followed by squamous cell skin cancer (n=22) and head & neck cancer (n=17). The overall incidence of SM was 19.5% (95% CI, 15.9-23.4%) at 12 years. We evaluated multiple risk factors for the risk of SM, and the following variables were not statistically significant: the use of fludarabine, total body irradiation, stem cell source, donor type, previous acute GvHD, use of T-cell depletion, subtype and severity of cGvHD, organ involvement of mouth, eye, liver, gut, lung, musculoskeletal system at initial presentation. In addition, we evaluated the use of systemic IST including corticosteroid, CSA, tacrolimus, MMF and ECP but with no effect on SM risk. Of interest, the use of AZP was found to increase the risk of SM: The cumulative incidence of SM was 22.7% (16.9-29.1%) at 12 years in the AZP group, whereas it was 16.9% (12.5-21.9%) in those treated without AZP (p=0.023) (Fig A). Exposure duration of AZP showed good correlation with increased risk of SM: patients treated with AZP for 5.85 years or longer showed 46% higher risk of SM development than those not (HR 1.46 [1.11-1.91], p=0.007). Multivariate analysis confirmed the following factors as risk factor for SM: exposure to AZP (HR 1.65, p=0.012), age at transplant >60 years (HR 2.40, p=0.007), male sex (HR 1.56, p=0.039) and skin involvement at cGvHD presentation (HR 1.59, p=0.018) (Fig B). A refined SM risk score was developed, giving a point each for age over 60 years, male sex, skin involvement at cGvHD presentation, and exposure to AZP. The summed scores were grouped 0-1 (n=244), low risk of 13.3%; 2 (n=174), intermediate risk of 19.9% (HR 1.614); above 2 (n=80), high risk for SM, 38.1% at 12 years (HR 3.502; p Median survival duration was 3.9 years after SM diagnosis, while 5 year survival rate was 43.6% (33.8-52.9%) (Fig D). The use of AZP does not appear to affect survival after diagnosis of SM. Conclusions The present study suggests that the use of AZP correlates with the risk of SM after adjustment of other confounding covariates such as skin involvement of GVHD, patient age or sex. Figure 1 Disclosures Lipton: Takeda: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Research Funding; Pfizer: Consultancy, Honoraria, Research Funding; BMS: Consultancy, Research Funding; Ariad: Consultancy, Research Funding; Bristol-Myers Squibb: Honoraria. Mattsson:Jazz Pharmaceuticals: Honoraria; ITB: Honoraria; Gilead: Honoraria; Mallinkrodt: Honoraria; Takeda: Membership on an entity's Board of Directors or advisory committees. OffLabel Disclosure: Azathioprine is being used to treat chronic gvhd

Background Chronic graft-versus-host-disease (cGVHD) is one of the main causes of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (HCT). Tyrosine kinase inhibitor such as Ruxolitinib, Ibrutinib and Imatinib showed a promising efficacy in cGVHD treatment. Ruxolitinib is a JAK-STAT inhibitor, reducing inflammation and immune pathway. Ibrutinib is a BTK inhibitor, blocking B cell-activating factor (BAFF), while Imatinib inhibits the platelet-derived growth factor receptor pathway activated by cGvHD-induced antibodies. The present retrospective study evaluated the efficacy of 3 TKIs for cGVHD at a single-centre in terms of 1) overall response rate (ORR), 2) clinical benefit (CB), 3) dose reduction of steroid, 4) failure-free survival (FFS) and 5) overall survival (OS). Patients and Methods A total of 43 patients who developed cGVHD after HCT and treated with TKI therapy for cGVHD at Princess Margaret Cancer Centre, Canada from August 2014 to April 2020 were evaluated in this retrospective study. 16 patients were treated with more than one TKI drug. A total of 62 lines of TKI therapy was evaluated, including Ruxolinitib (n=18), Ibrutinib (n=13) and Imatinib (n=31). The ORRs and CBs were assessed at months 3, 6 and 12, retrospectively. Responses were evaluated according to NIH scoring/staging/response assessment as part of standard clinical practice. CB was assessed considering clinical response as well as steroid dose reduction. For systemic steroid dose reduction, prednisone dose per kg per day was captured prior to Ruxolitinib start, at months 3, 6 and 12. Treatment failure was defined as 1) resistance requiring treatment switch, 2) non-relapse mortality (NRM), 3) relapse, 4) intolerance requiring treatment discontinuation. FFS and OS were calculated from the day of starting TKI therapy for cGVHD treatment. Results The patients and disease characteristics are summarized as follow: median age was 54 years (range 16 -70); 33 patients (53%) presented with classical cGVHD, while 29 patients (47%) with overlap syndrome; 14 (23%) presented with moderate and 48 (77%) with severe grade cGVHD. There was no difference in cGVHD subtype among 3 TKI subgroups (p= 0.478). The median number of organ involvement was 3 (range 1-5), and number of previous lines of therapy was 5 (range 3-9), implying that most of the patients were heavily pretreated for cGVHD. The mean (±S.E.) dosage of TKI treatment was as follows: Ruxolitinib was started at 15±1.1mg as initial dose and 20±0.7, 19±1.5, 22±4.4 mg per day in two divided doses on months 3, 6 and 12, respectively. Ibrutinib dose was 226±37, 256±37, 308±40 and 370±33 mg per day, while Imatinib dose was 106±6, 189±18, 196±16 and 190±19 mg per day prior to TKI starts, at months 3, 6 and 12, respectively. With a median follow up duration of 12 months, 19 (31%), 20 (32%), and 17 patients (27%) responded to TKI therapy at 3, 6, and 12 months without any difference of ORR among the TKIs (p=0.126, 0.554, 0.721 at 3/6/12 months; Figure A). The CBs were achieved in 47 (76%), 34 (55%), and 23 patients (37%) at 3, 6 and 12 months without any difference of CBs among the TKIs (p=0.187, 0.499, 0.750 at 3/6/12 months; Figure B). Prednisone dose (mg/kg/day) was 0.238±0.03 prior to TKI initiation, 0.177±0.03, 0.173 ± 0.03 and 0.110 ± 0.02 at 3, 6, and 12 months, respectively. No difference was noted in steroid dose among the 3 TKIs at each time point. However, the Ibrutinib group tends to require higher prednisone dose over time than other 2 groups. The FFS at 12 months was higher in Imatinib (71%) or Ruxolitinib groups (67%) than Ibrutinib group (46%; Figure C). The OS rate at 12 months was similar: 100 % in Ruxolitinib and Ibrutinib, and 96% in Imatinib group (Figure D). With regard to those patients treated with TKI for sclerotic GVHD (n= 39), the ORR were 11 (28%), 15 (38%) and 13 (33%) for 3, 6 and 12 months, while CB was noted in 32 (82%), 25 (64%) and 16 patients (41%) at 3, 6 and 12 months respectively. Of interest, Ruxolitinib was as effective as Imatinib in improving PROM score of sclerotic GVHD, while no significant improvement of PROM score was observed in the patients treated with Ibrutinib. Conclusion This retrospective study evaluated the efficacy of TKI drugs for cGVHD treatment in heavily pretreated patients. Ruxolitinib seems as effective as Imatinib to treat sclerotic GVHD. No difference was observed in OS at 12 months; while FFS appears better with Ruxolitinib and Imatinib over Ibrutinib. Figure Disclosures Lipton: Ariad: Consultancy, Research Funding; Pfizer: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Honoraria; Novartis: Consultancy, Research Funding; BMS: Consultancy, Research Funding.

Background Donor selection for allogeneic stem cell transplant is a complex process, where several factors are considered for potential impact on transplant outcome. Several publications have suggested that 9/10 mismatched unrelated donors (MMUD) may be equivalent to 10/10 MUDs. However, there is debate as to whether all 9/10 mismatches (MM) are equivalent. We sought to examine this in a single centre retrospective study using ATG followed by post transplant cyclophosphamide (ATG PTCy) as standard GvHD prophylaxis and correlated outcomes in terms of donor MM, donor age and CMV serostatus. Patients and methods A total of 414 patients who received HCT from unrelated donors between Jan 2015 and Dec 2019, at Princess Margaret Cancer Centre, Canada, were enrolled in the retrospective study. Patients and disease characteristics, and outcomes are detailed in Tables 1-3. The probability of overall survival (OS) was calculated using the Kaplan Meier product limit method and heterogeneity of time to event distribution functions was compared by the log rank test. The cumulative incidences of chronic and acute GvHD, relapse, and transplant related mortality (TRM) were estimated using the cumulative incidence method considering competing risk, and groups were compared using Gray's test. Death was considered a competing event for relapse, acute and cGvHD, and relapse was considered a competing event for NRM, acute and cGvHD. GvHD outcomes shown in Table 4. Results Median OS at 5y for the whole cohort (n=414) was 45.8% (38.2-53.0), and relapse free survival was 40.2% (32.9-47.4), with TRM at 1y 23.7% (19.6-28.0), Table 5. Compared to the whole cohort (median OS 38.8mo [21.6-NA]), patients who received grafts from MMUD (n=86) had median OS 9.2mo (6.0-17.3), p GVHD-Free Relapse free Survival (GRFS) at 5y for the whole cohort was 36.8% (29.7-43.9). GRFS At 2y for 9/10 MMUD was 25.2% (16.1-35.4), HLA-A MM 21.6% (9.9-36.2) HLA-B MM 15.4% (2.5-38.8) vs MUD 51.4% (45.3-57.2), p Median OS for patients who received ATG PTCY (n=298) was 49.2mo (49.2-NA), for 9/10 (n=58) 10.2mo (6.1-19.6), with HLA-A MMUD (n=26) 9.6 mo (5.8-27.4), HLA-B MMUD (n=9) 4.6mo (1-11.8) (p A number of donor factors significant by univariate analysis (incl. donor age, recipient/donor CMV, CD34 dose, presence of HLA MM, type of MM, female donor to male recipient), were selected to determine correlates with all mortality by multivariable analysis (MVA). The only significant factor was 9/10 MMUD HR 2.27 (1.65-3.14), p The same donor factors significant by univariate analysis were examined for correlation with TRM and significance was found for HLA MM HR 2.36 (1.57-3.55) p=0.00004, specifically HLA-A MM HR 2.44 (1.42-4.17), p=0.0012, HLA-B MM HR 2.39 (1.03-5.57) p=0.0034. Graft failure (GF) occurred in 4.6% of patients. Significant donor factors for GF were CD34 dose Among AML patients, CMV negative patients in receipt of grafts from CMV negative donors (CMV-/-) (n=64) had worse survival (HR 2.05, 1.03-4.09, p=0.04) compared to recipient/donor pairs where any were CMV positive. There was a significantly higher relapse rate in the CMV-/- (15/64, 23.4%), compared to CMV positive (30/236, 12.2%, any combination), p=0.01 by Chi-squared test. Conclusions These data suggest that HLA-A and HLA-B mismatched donors confer a significantly inferior outcome despite the use of ATG PTCy. Cryopreserved stem cells from unrelated donors were associated with graft failure, and CMV-/- were associated with higher incidence of relapse. Further work is required to develop novel conditioning regimens and GvHD prophylaxis to mitigate these risks. Disclosures Lipton: BMS: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Ariad: Consultancy, Research Funding; Pfizer: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Honoraria; Takeda: Consultancy, Honoraria, Research Funding. Mattsson:Gilead: Honoraria; ITB: Honoraria; Takeda: Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Honoraria; Mallinkrodt: Honoraria.

(1) Background: Refractory acute graft-versus-host disease (R-aGvHD) remains a leading cause of death after allogeneic stem cell transplantation. Survival rates of 15% after four years are currently achieved, deaths are only in part due to aGvHD itself, but mostly due to adverse effects of R-aGvHD treatment with immunosuppressive agents as these predispose patients to opportunistic infections and loss of graft-versus-leukemia surveillance resulting in relapse. Mesenchymal stromal cells (MSC) from different tissues and those generated by various protocols have been proposed as a remedy for R-aGvHD but the enthusiasm raised by initial reports has not been ubiquitously reproduced. (2) Methods: We previously reported on a unique MSC product, which was generated from pooled bone marrow mononuclear cells of multiple third-party donors. The products showed dose-to-dose equipotency and greater immunosuppressive capacity than individually expanded MSCs from the same donors. This product, MSC-FFM, has entered clinical routine in Germany where it is licensed with a national hospital exemption authorization. We previously reported satisfying initial clinical outcomes, which we are now updating. The data were collected in our post-approval pharmacovigilance program, i.e., this is not a clinical study and the data is high-level and non-monitored. (3) Results: Follow-up for 92 recipients of MSC-FFM was reported, 88 with GvHD &ge, &deg, III, one-third only steroid-refractory and two-thirds therapy resistant (refractory to steroids plus &ge, 2 additional lines of treatment). A median of three doses of MSC-FFM was administered without apparent toxicity. Overall response rates were 82% and 81% at the first and last evaluation, respectively. At six months, the estimated overall survival was 64%, while the cumulative incidence of death from underlying disease was 3%. (4) Conclusions: MSC-FFM promises to be a safe and efficient treatment for severe R-aGvHD.