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Whole blood aggregometry is a functional assay for determination of platelet function. Until now, whole blood aggregometry has not been considered feasible at low platelet counts. Hence, the objectives of the present study were to explore platelet function in thrombocytopenia using a novel index of impedance aggregometry adjusted for platelet count and evaluate the association to platelet function assessed by flow cytometry. Hirudin anticoagulated blood was collected from 20 healthy volunteers, 20 patients with primary immune thrombocytopenia (ITP), and 17 hematological cancer patients. Platelet function was analyzed by impedance aggregometry and by flow cytometry. Collagen, adenosine diphosphate, thrombin receptor agonist peptide-6, and ristocetin were used as agonists for both analyses. Thrombocytopenia in healthy whole blood was induced in vitro employing a recently published method. Platelet aggregation of thrombocytopenic patients was evaluated relative to the aggregation of healthy volunteers at the same platelet count. In flow cytometry, platelet function was described as expression of the platelet surface glycoproteins: bound fibrinogen, CD63, and P-selectin. Similar platelet counts were obtained in the patient groups (p = 0.69) (range: 13-129 × 109/l). Aggregation adjusted for platelet count was significantly increased in ITP patients compared to healthy platelets across all agonists. The platelet aggregation was high in the 95% prediction interval, with 18 ITP patients above the prediction interval in at least two agonists. In contrast, the platelet aggregation was low in the prediction interval in cancer patients, and three cancer patients with platelet aggregation below the prediction interval in at least one agonist. ITP patients displayed increased expression of bound fibrinogen and CD63 following activation, compared with particularly cancer patients, but also compared with healthy platelets. This study demonstrated the feasibility of a novel approach to perform platelet function analyses in thrombocytopenia using impedance aggregometry adjusted for platelet count.

Background: Data from the phase 2, single-arm ENESTfreedom study (NCT01784068) have demonstrated the feasibility of treatment-free remission (TFR) following front-line nilotinib (NIL) treatment, with substantial TFR rates being sustained over time among patients (pts) with chronic myeloid leukemia in chronic phase (CML-CP). Results for long-term outcomes after a 5-year follow-up are presented here. The current subanalysis evaluated the efficacy and safety of TFR after upfront treatment with NIL in older (≥65 years [yrs] at study entry) vs younger ( Methods: Adult pts enrolled in ENESTfreedom had achieved MR4.5 after ≥2 years of front-line treatment with NIL. They then entered a 52-week consolidation (CONS) phase in which they continued treatment with NIL 300 mg twice-daily; pts still in MR4.5 at the end of CONS entered the TFR phase. NIL treatment was re-initiated upon loss of major molecular response (MMR). Rates of MMR and MR4.5, as well as safety, were evaluated according to age group ( Results: The total number of pts analyzed was 215, of which 171 were Disclosures García Gutiérrez: Novartis Pharma AG: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy, Honoraria, Research Funding; Incyte: Consultancy, Honoraria, Research Funding. Radich:Jazz: Consultancy; Amgen: Consultancy; Bristol-Myers Squibb: Consultancy; Novartis Pharmaceuticals Corporation: Consultancy, Research Funding. Hochhaus:MSD: Research Funding; Bristol-Myers Squibb: Honoraria, Research Funding; Incyte: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding; Takeda: Honoraria. Saglio:Roche: Research Funding; Ariad: Research Funding; Incyte: Research Funding; Novartis: Research Funding; Bristol-Myers Squibb: Research Funding; Pfizer: Research Funding. Conneally:Novartis: Consultancy, Research Funding; Bristol-Myers Squibb: Honoraria; Pfizer: Honoraria; Gilead: Honoraria. le Coutre:Incyte: Honoraria; Pfizer: Honoraria; Novartis: Honoraria. Gattermann:Novartis: Honoraria, Research Funding. Saussele:Pfizer: Honoraria; Incyte: Honoraria, Research Funding; Bristol-Myers Squibb: Honoraria, Research Funding; Novartis: Honoraria, Research Funding. Giles:Actuate Therapeutics Inc: Consultancy; Pfizer: Research Funding; Novartis: Consultancy, Research Funding. Aimone:Novartis: Current Employment. Li:Novartis: Current Employment. Titorenko:Novartis: Current Employment. Ross:Celgene: Research Funding; Bristol-Myers Squibb: Honoraria; Novartis: Honoraria, Other: Participated in advisory board meetings, Research Funding.

Changes in the immune system induced by tyrosine kinase inhibitors (TKI) have been shown to positively correlate with therapy responses in chronic myeloid leukemia (CML). However, only a few longitudinal studies exist and no randomized comparisons between two TKIs have been reported. Therefore, we prospectively analyzed the immune system of newly diagnosed CML patients treated with imatinib (n = 20) or bosutinib (n = 13), that participated in the randomized BFORE trial (NCT02130557). Comprehensive immunophenotyping, plasma protein profiling, and functional assays to determine activation levels of T and NK cells were performed at diagnosis, 3, and 12 months after therapy start. All results were correlated with clinical parameters such as Sokal risk and BCR-ABL load measured according to IS%. At diagnosis, low Sokal risk CML patients had a higher frequency of cytotoxic cells (CD8 + T and NK cells), increased cytotoxic potential of NK cells and lower frequency of naïve and central memory CD4 + T cells. Further, soluble plasma protein profile divided patients into two distinct clusters with different disease burden at diagnosis. During treatment, BCR-ABL IS% correlated with immunological parameters such as plasma proteins, together with different memory subsets of CD4+ and CD8 + T cells. Interestingly, the proportion and cytotoxic potential of NK cells together with several soluble proteins increased during imatinib treatment. In contrast, no major immunological changes were observed during bosutinib treatment. In conclusion, imatinib and bosutinib were shown to have differential effects on the immune system in this randomized clinical trial. Increased number and function of NK cells were especially observed during imatinib therapy. This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License (http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited, and is not altered, transformed, or built upon in any way.

Background Recombinant Interferon Alpha-2a (r-IFNα) is a potent immunomodulating agent, which has been used off-label for the treatment of polycythemia vera (PV) for more than three decades and has been demonstrated to induce high rates of clinical, hematological and molecular responses. Only few studies have compared efficacy and safety of r-IFNα vs. hydroxyurea (HU), which is considered first line therapy for PV patients > 60 years in most parts of the world. However, recent studies have provided encouraging results for the treatment of PV with r-IFNα compared to HU irrespective of age (R. Hoffmann 2016; H. Gisslinger 2018). Aims To examine the difference in efficacy and safety of low-dose r-IFNα in PV patients ≤ 60 or > 60 years of age compared to HU > 60 years of age. Methods Ninety newly diagnosed or previously phlebotomized PV patients only (WHO 2008) were enrolled in the DALIAH trial (NCT01387763). All patients provided written informed consent. Patients ≤ 60 years were randomized (I:I) to r-IFNα-2a (Pegasys®) or to r-IFNα-2b (PegIntron®) whereas patients > 60 years were randomized (I:I:I) to either r-IFNα-2a, r-IFNα-2b or to HU. The starting dose of r-IFNα-2a and r-IFNα-2b was 45 or 35 µg/week, respectively. The HU dose was 500 to 2000 mg/day. Patients randomized to r-IFNα who presented with major thrombosis or platelets > 1500 109/L received HU from inclusion and until normalization of the platelet count. Efficacy assessment consisted of the clinicohematological and the molecular response rates by intention to treat analysis (ITT) using the European Leukemia Net (ELN) 2009 criteria. JAK2V617F analysis was performed by qPCR. Groups were compared by Fisher's Exact Test. Results Three-year analysis was available in all but five patients (n=85) at time of abstract submission (Table 1). The analysis was performed after a median of 36 months (range: 33-39 months). The median treatment dose was 684 mg/day (IQR: 131 - 942) for HU, 51 μg/week (IQR: 30-90 μg/week) and 54 μg/week (IQR: 30-66 μg/week) for r-IFNα-2a age ≤ 60 and > 60, respectively, and 41 μg/week (IQR: 29-45 μg/week) and 36 μg/week (IQR: 31-37 μg/week) for r-IFNα-2b age ≤ 60 and > 60. The overall clinicohematological response rate (ORR) was 68% (13/19) for HU, 42% (14/33) for r-IFNα ≤ 60 years and 39% (13/33) for r-IFNα > 60 years. The partial clinicohematological response rate (PHR) and the complete clinicohematological response rate (CHR) was 53% (10/19) and 16% (3/19) for HU, 9% (3/33) and 33% (11/33) for r-IFNα ≤ 60 years and 9% (3/33) and 30% (10/33) for r-IFNα > 60 years. Neither the ORR, CHR nor the PHR was significantly different between the three groups. Maintenance of CHR from first occurrence to data analysis after 36 months was 11% (2/19) for HU, 21% (7/33) for r-IFNα ≤ 60 years and 18% (6/33) for r-IFNα > 60 years. Forty-seven JAK2V617F positive patients were available for molecular response analysis after 36 months of therapy. A partial molecular response (PMR) was detected in 21% (4/19) of HU treated patients and in 24% (7/29) of r-IFNα treated patients ≤ 60 years and 18% (6/33) of r-IFNα > 60 years. Notably, 7% (2/29) of the r-IFNα treated patients ≤ 60 years obtained a complete molecular response (CMR). The median JAK2V617F reduction from baseline was 38% (IQR: 31-63%) for HU, 79% (IQR: 59-92%) for r-IFNα ≤ 60 years and 73% (IQR: 49-97%) for r-IFNα > 60 years. There was no statistically significant difference in the PMR between groups. Discontinuation of treatment for any reason after 36 months of therapy was 21% (4/19) for HU, 52% (17/33) for r-IFNα ≤ 60 years and 45% (15/33) for r-IFNα > 60 years. Toxicity related discontinuation was 5% (1/19) for HU and 30% (10/33) for both r-IFNα ≤ 60 and > 60 years. Grade 3-4 AEs occurred in 32% (6/19) of HU treated patients, 27% (9/33) in r-IFNα treated patients ≤ 60 years and in 42% (14/33) r-IFNα treated patients > 60 years. SAEs were reported in 21% (4/19) for HU, 9% (3/33) for r-IFNα ≤ 60 years and 24% (8/33) for r-IFNα > 60 years. The numbers of grade 3-4 AEs as well as SAEs were comparable between groups. Conclusion After 36 months of therapy CHR was non-significantly higher in PV patients treated with r-IFNα compared to HU by ITT, irrespective of age. Also, maintenance of CHR was longer for r-IFNα. However, ORR was non-significantly higher for HU. PMR was almost similar between the three groups but the median JAK2V617F reduction was greater for r-IFNα. Toxicity related discontinuation from study therapy was higher for r-IFNα compared to HU. Disclosures Stentoft: Bristol-Myers Squibb: Research Funding; Merck Sharp&Dohme: Research Funding. Hasselbalch:Novartis: Research Funding.

Purpose Tyrosine kinase inhibitors (TKIs) have well-characterized immunomodulatory effects on T and NK cells, but the effects on the humoral immunity are less well known. In this project, we studied TKI-induced changes in B cell-mediated immunity.Methods We collected peripheral blood (PB) and bone marrow (BM) samples from chronic myeloid leukemia (CML) patients before and during first-line imatinib (n = 20), dasatinib (n = 16), nilotinib (n = 8), and bosutinib (n = 12) treatment. Plasma immunoglobulin levels were measured, and different B cell populations in PB and BM were analyzed with flow cytometry.Results Imatinib treatment decreased plasma IgA and IgG levels, while dasatinib reduced IgM levels. At diagnosis, the proportion of patients with IgA, IgG, and IgM levels below the lower limit of normal (LLN) was 0, 11, and 6% of all CML patients, respectively, whereas at 12 months timepoint the proportions were 6% (p = 0.13), 31% (p = 0.042) and 28% (p = 0.0078). Lower initial Ig levels predisposed to the development of hypogammaglobulinemia during TKI therapy. Decreased Ig levels in imatinibtreated patients were associated with higher percentages of immature BM B cells. The patients, who had low Ig levels during the TKI therapy, had significantly more frequent minor infections during the follow-up compared with the patients with normal Ig values (33% vs. 3%, p = 0.0016). No severe infections were reported, except recurrent upper respiratory tract infections in one imatinib-treated patient, who developed severe hypogammaglobulinemia.Conclusions TKI treatment decreases plasma Ig levels, which should be measured in patients with recurrent infections.

Background: To investigate the role of genomics in determining response and resistance to front line treatment in MPN, we performed somatic mutational profiling of the DALIAH trial, a randomized controlled phase III trial of interferon versus hydroxyurea in newly diagnosed MPN patients. Methods: We performed genomic analyses on 202 pre-treatment primary MPN samples obtained from patients enrolled on the DALIAH trial (NCT01387763) and 135 samples obtained after 24 months of treatment. Genomic profiling comprised targeted next generation sequencing (NGS) of 100 genes, selected on the basis of their known or suspected involvement in the pathogenesis of myeloid malignancies, and 1609 informative single nucleotide polymorphisms (SNPs) on chromosome 9p. Clinicohematological response was determined by central review using ELN 2009 (ET, PV and pre-MF) and EUMNET 2005 (PMF) criteria. We evaluated the association of somatic mutations with clinical parameters and with attainment of clinicohematological complete response (CR) at 24 months. Results: Prior to treatment, 191 of 202 (95%) patients had somatic mutations, including 93% with canonical MPN phenotypic drivers: JAK2 (74%), CALR (14%), and MPL (5%). Among those with JAK2 mutations 37% had JAK2 copy-neutral loss of heterozygosity (JAK2 CN-LOH). Patients with PV were more likely to have JAK2 CN-LOH (p = 0.0001) as compared with patients with other MPN subtypes. At baseline, patients with JAK2 CN-LOH had significantly higher hemoglobin (p = 0.0001), higher white blood cell count (WBC, p = 0.002) and lower platelet count (p=0.0001) than patients without JAK2 CN-LOH. Mutations in TET2 (24%), DNMT3A (16%), and ASXL1 (10%) were the most frequent co-occurring non-MPN phenotypic driver mutations and they occurred across all MPN subtypes. In addition, 5% of patients had spliceosome gene mutations, and 6% had mutations in genes involved in RAS/MAPK signaling. Patients with TET2, DNMT3A or ASXL1 mutations were significantly older than patients without these mutations (p= 0.0001) and there was a significant association between the presence of a TET2, DNMT3A or ASXL1 mutation and prior stroke (p = 0.004). There were no other significant associations between somatic mutation status and baseline clinical characteristics. The probability of attaining clinicohematological CR at 24 months was independent of baseline somatic mutations. Among patients with JAK2 mutations who remained on interferon treatment at 24 months, those with CR had a greater reduction in mean variant allele fraction (VAF) (28% to 8%, p Among patients who remained on treatment for 2 years, 44 mutations in 35 patients were newly detected or expanded on serial sampling. DNMT3A mutations were the most frequently acquired, accounting for 41% of new mutations. ASXL1, TET2, PPM1D, TP53, IDH2, and CBL mutations were also recurrently acquired. 97% of patients who acquired new mutations were JAK2-mutant. Among those with acquired DNMT3A mutations, 85% were treated with interferon, and 23% had CR at 24 months. Among those that acquired non-DNMT3A mutations, 38% were treated with interferon and 47% had CR at 24 months. The VAF of newly detected mutations was low (median 1.5%), and half of the patients with newly acquired mutations had at least 50% reduction in JAK2V617F VAF, suggesting that new mutations could either have arisen independently or be subclonal to the dominant JAK2-mutant clone. Conclusions: Using sequential genomic analyses of a phase III clinical trial of interferon versus hydroxyurea in MPN patients, we found mutation-specific and treatment-specific patterns of response. We uncovered distinct patterns of response to interferon in JAK2-mutant MPN as compared with CALR-mutant MPN. We found that DNMT3A mutations were the most frequent acquired mutations at 24 months and that these were enriched in patients treated with interferon. In aggregate, these results provide insights into molecular response and resistance to interferon and inform the clinical use of interferon in MPN patients. Disclosures Hansen: Alexion: Research Funding. Neuberg:Pharmacyclics: Research Funding; Madrigal Pharmaceuticals: Equity Ownership; Celgene: Research Funding. Hasselbalch:Novartis: Research Funding; AOP Orphan Pharmaceuticals: Other: Data monitoring board. Lindsley:Jazz Pharmaceuticals: Research Funding; Takeda Pharmaceuticals: Consultancy; Medlmmune: Research Funding. Mullally:Janssen: Research Funding.

Monitoring of single cell signal transduction in leukemic cellular subsets has been proposed to provide deeper understanding of disease biology and prognosis, but has so far not been tested in a clinical trial of targeted therapy. We developed a complete mass cytometry analysis pipeline for characterization of intracellular signal transduction patterns in the major leukocyte subsets of chronic phase chronic myeloid leukemia. Changes in phosphorylated Bcr-Abl1 and the signaling pathways involved were readily identifiable in peripheral blood single cells already within three hours of the patient receiving oral nilotinib. The signal transduction profiles of healthy donors were clearly distinct from those of the patients at diagnosis. Furthermore, using principal component analysis, we could show that phosphorylated transcription factors STAT3 (Y705) and CREB (S133) within seven days reflected BCR-ABL1IS at three and six months. Analyses of peripheral blood cells longitudinally collected from patients in the ENEST1st clinical trial showed that single cell mass cytometry appears to be highly suitable for future investigations addressing tyrosine kinase inhibitor dosing and effect. ©2017 Ferrata Storti Foundation Material published in Haematologica is covered by copyright. All rights are reserved to the Ferrata Storti Foundation. Use of published material is allowed under the following terms and conditions: https://creativecommons.org/licenses/by-nc/4.0/legalcode. Copies of published material are allowed for personal or internal use. Sharing published material for non-commercial purposes is subject to the following conditions: https://creativecommons.org/licenses/by-nc/4.0/legalcode, sect. 3. Reproducing and sharing published material for commercial purposes is not allowed without permission in writing from the publisher.

Understanding leukemia heterogeneity is critical for the development of curative treatments as the failure to eliminate therapy-persistent leukemic stem cells (LSCs) may result in disease relapse. Here we have combined high-throughput immunopheno-typic screens with large-scale single-cell gene expression analysis to define the heterogeneity within the LSC population in chronic phase chronic myeloid leukemia (CML) patients at diagnosis and following conventional tyrosine kinase inhibitor (TKI) treatment. Our results reveal substantial heterogeneity within the putative LSC population in CML at diagnosis and demonstrate differences in response to subsequent TKI treatment between distinct subpopulations. Importantly, LSC subpopulations with myeloid and proliferative molecular signatures are proportionally reduced at a higher extent in response to TKI therapy compared with subfractions displaying primitive and quiescent signatures. Additionally, cell surface expression of the CML stem cell markers CD25, CD26, and IL1RAP is high in all subpopulations at diagnosis but downregulated and unevenly distributed across subpopulations in response to TKI treatment. The most TKI-insensitive cells of the LSC compartment can be captured within the CD45RA(-) fraction and further defined as positive for CD26 in combination with an aberrant lack of cKIT expression. Together, our results expose a considerable heterogeneity of the CML stem cell population and propose a Lin(-) CD34(+) CD38(-/low) CD45RA(-) cKIT(-) CD26(+) population as a potential therapeutic target for improved therapy response.

Biologic and clinical observations suggest that combining imatinib with IFN-α may improve treatment outcome in chronic myeloid leukemia (CML). We randomized newly diagnosed chronic-phase CML patients with a low or intermediate Sokal risk score and in imatinib-induced complete hematologic remission either to receive a combination of pegylated IFN-α2b (Peg–IFN-α2b) 50 μg weekly and imatinib 400 mg daily (n = 56) or to receive imatinib 400 mg daily monotherapy (n = 56). The primary endpoint was the major molecular response (MMR) rate at 12 months after randomization. In both arms, 4 patients (7%) discontinued imatinib treatment (1 because of blastic transformation in imatinib arm). In addition, in the combination arm, 34 patients (61%) discontinued Peg–IFN-α2b, most because of toxicity. The MMR rate at 12 months was significantly higher in the imatinib plus Peg–IFN-α2b arm (82%) compared with the imatinib monotherapy arm (54%; intention-to-treat, P = .002). The MMR rate increased with the duration of Peg–IFN-α2b treatment (< 12-week MMR rate 67%, > 12-week MMR rate 91%). Thus, the addition of even relatively short periods of Peg–IFN-α2b to imatinib markedly increased the MMR rate at 12 months of therapy. Lower doses of Peg–IFN-α2b may enhance tolerability while retaining efficacy and could be considered in future protocols with curative intent.

Wilms' tumor 1 mutation accumulated during therapy in acute myeloid leukemia: biological and clinical implications

In the present study we combined interferon (IFN) and hydroxyurea (HU) treatment, intensive chemotherapy and autologous stem cell transplantation (SCT) in newly diagnosed chronic myelogenous leukemia patients aged below 56 years, not eligible for allogeneic SCT. Patients who had an HLA-identical sibling donor and no contraindication went for an allogeneic SCT (related donor, RD). After diagnosis, patients not allotransplanted received HU and IFN to keep WBC and platelet counts low. After 6 months patients with Ph-positive cells still present in the bone marrow received 1–3 courses of intensive chemotherapy. Those who became Ph-negative after IFN + HU or after 1–3 chemotherapy courses underwent autologous SCT. Some patients with poor cytogenetic response were allotransplanted with an unrelated donor (URD). IFN + HU reduced the percentage of Ph-positive metaphases in 56% of patients, and 1 patient became Ph-negative. After one or two intensive cytotherapies 86 and 88% had a Ph reduction, and 34 and 40% became Ph-negative, respectively. In patients receiving a third intensive chemotherapy 92% achieved a Ph reduction and 8% became Ph-negative. The median survival after auto-SCT (n = 46) was 7.5 years. The chance of remaining Ph-negative for up to 10 years after autologous SCT was around 20%. The overall survival for allo-SCT RD (n = 91) and URD (n = 28) was almost the same, i.e. ≈60% at 10 years. The median survival for all 251 patients registered was 8 years (historical controls 3.5 years). The role of the treatment schedule presented in the imatinib era is discussed.

Background Treatment of Philadelphia chromosome negative chronic myeloproliferative neoplasms (MPNs) with recombinant pegylated interferon alpha2a/b (rIFN-alpha) has proven effective. It is well known that prolonged therapy with recombinant type 1 interferons (IFN-alpha and IFN-beta) may induce neutralizing antibodies (nAbs) against the drug leading to treatment failure. Most data on type 1 IFN immunogenicity are available from studies of patients with multiple sclerosis treated with rIFN-beta, and patients with hepatitis C treated with rIFN-alpha. A few reports have demonstrated nAbs in MPN patients not responding adequately to rIFN-alpha treatment, but the phenomenon has not been thoroughly investigated in MPNs. Patients and Methods Newly diagnosed patients with MPNs enrolled in the Danish multicenter trial - DALIAH (Low-dose rIFN-alpha versus Hydroxyurea in The Treatment of Ph-Negative MPNs) were included. Patients were randomized to treatment with either rIFN-alpha 2a or 2b at a starting dose of 45 and 35 mikrograms once weekly, respectively. The occurrence of neutralizing Abs (nAbs) against rIFN-alpha was investigated at baseline, month 12 and month 24 by reporter gene assays (iLiteTM alphabeta and iLiteTM antialpha, Biomonitor A/S, Copenhagen, Denmark). JAK2 V617F quantitative mutation analyses were performed as previously described (Larsen TS, BJH 2007). Statistical analyses were performed using STATA version 9.0. Results Ninety-two patients on sustained treatment with rIFN-alpha2a (n=48) and rIFN-alpha2b (n=44) for 12 months were analyzed for this study. Forty-five patients had ET, 39 patients had PV and 8 patients had proliferative PMF. Thirty-six out of 39 (92%) PV patients, 22 out of 45 (49%) ET patients and 4 out of 8 (50%) PMF patients were JAK2V617F mutated. Hematological responses at 12 months: ET: 67% CR, 29 % PR; PV: 64% CR, 31% PR (ELN 2009 criteria); PMF: 50% had at least a minor response (EUMNET). The median serum concentration of bioactive IFN-alpha at 12 months was 12,4 (range Conclusions Development of nAbs in MPN patients completing treatment for 12 months with rIFN-alpha seems exceedingly rare as no patients, neither complete responders nor patients not meeting criteria for complete hematological remission developed nAbs after 12 (24) months of therapy. Its apparent rarity does not justify a routine investigation of nAbs in patients not responding to rIFN-alpha treatment. There was no significant correlation between serum concentration of rIFN-alpha 2a and -2b and clinical or molecular responses. The intriguing finding that one of 24 patients had pre-existing cross reacting nAbs against rIFN-alpha 2a and 2b before commencing rIFN-alpha treatment is interesting and was associated with an insufficient response. Disclosures Off Label Use: Recombinant interferon-alpha 2a and -2b in the treatment of chronic Philadelphia-negative myeloproliferative neoplasms.. El Fassi:Novartis Denmark: Honoraria, Other: Have conducted an educational session for Novartis Denmark, regarding MPNs and ruxolitinib, for this a honorarium was received.. Bjerrum:Bristoll Myers Squibb, Novartis and Pfizer: Other: educational activities. Hasselbalch:Novartis: Research Funding. Bendtzen:Pfizer: Honoraria; Eurodiagnostica AB: Equity Ownership; Novo-Nordisk: Equity Ownership.

The activated tyrosine kinase, which arises as a result of the balanced t(9,22) translocation in chronic myeloid leukemia (CML), is thought to be essential for the development of the leukemic phenotype. Recently, designer drugs have been introduced which specifically inhibit such specific kinases. Among these, STI571 (Glivec) has entered clinical trials and shown promising activities in chronic phase (CP), accelerated phase (AP) and blast crisis (BC) as evidenced by significant hematological and cytogenetic responses in CML patients. To evaluate the effect of STI571 at the molecular level we have employed quantitative real-time PCR (RQ-PCR) to measure the amount of BCR-ABL fusion transcript in a series of 19 patients treated with STI571, either in CP(11) or in (AP)(8) of the disease for 3--9 months (median 6 months). Employing this method, which is able to detect at least one BCR-ABL+ cell in 500,000, in serial blood and bone marrow specimens we found decreases in transcript levels in 10/11 CP patients, but only in 1/8 of the AP patients. When present such decreases were gradual and became evident only after 3 months of STI571 treatment, and their kinetics in blood closely mirrored those seen in parallel marrow samples. Moreover, decreases were between 10- and 100-fold in 11/13 patients, with only two patients reaching residual disease levels below 10(-2) (a 900-fold decrease). Thus, no patient reached PCR negativity. We conclude that the RQ-PCR method is a highly suitable tool for following the effect of STI571 in CML and that further validation of the method, performed in a prospective manner, will contribute significantly to the elucidation of the proper role of STI571 in CML.

As a group of more than 100 experts in chronic myeloid leukemia (CML), we draw attention to the high prices of cancer drugs, with the particular focus on the prices of approved tyrosine kinase inhibitors for the treatment of CML. This editorial addresses the multiple factors involved in cancer drug pricing and their impact on individual patients and health care policies, and argues for the need to (1) lower the prices of cancer drugs to allow more patients to afford them and (2) maintain sound long-term health care policies.

Although chronic myeloid leukemia (CML) originates from a primitive hematopoietic stem cell (HSC), it is the more differentiated progenitor cells that drive the expansion of the malignant clone. In addition, previous studies of chronic phase CML have shown that, despite the marked leukocytosis observed here, megakaryocyte-erythroid progenitors dominate the progenitor fraction. We sought to elucidate this by employing the new marker for leukemic stem cells, the human myeloid inhibitory C-type lectin-like receptor (hMICL), in the study of progenitor cell expansion in CML. Bone marrow or peripheral blood stem cells were acquired from 11 normal donors and 31 CML patients at diagnosis in chronic phase and/or after 3-119 months of tyrosine kinase inhibitor (TKI) treatment. Cells were stained with fluorescent monoclonal antibodies and FACS sorted into HSCs (CD34+CD38-), hMICL+ progenitors (MpP; CD34+CD38+hMICL+), and hMICL- progenitors (MnP; CD34+CD38+hMICL-). Sorted cell subsets were subjected to growth in a 14-day methylcellulose assay and analyzed quantitatively for expression of the BCR-ABL fusion transcript. In normal donors, hMICL expression reproducibly identified a well-defined subpopulation of the CD34+CD38+ cells (fig 1A). The MpPs were highly enriched for cells of granulocyte-macrophage progenitors (GMP) phenotype compared to the MnPs (p=0.012) (fig 1B). Sorted MpPs produced almost exclusively granulocyte and/or macrophage (CFU-GM) colonies (median: 92% of colonies), while colonies from MnPs were dominated by BFU-Es (91%) and, as opposed to the MpPs, also contained CFU-GEMM colonies (0.64%) (fig 1C). Thus, hMICL seems to be a useful marker for the GMP population.Figure 1Immunological and functional properties of MpPs in normal donors. (A) Identification of MpPs, MnPs, and HSCs within the CD34+ compartment. (B) Cells with GMP phenotype (CD34+CD38+CD123lowCD45RA+) in MpP and MnP subsets. (C) Colony growth of bone marrow mononuclear cells (MNC) and sorted MpPs and MnPs in a 14-day methylcellulose assay. Error bars denote SDs.Figure 1. Immunological and functional properties of MpPs in normal donors. (A) Identification of MpPs, MnPs, and HSCs within the CD34+ compartment. (B) Cells with GMP phenotype (CD34+CD38+CD123lowCD45RA+) in MpP and MnP subsets. (C) Colony growth of bone marrow mononuclear cells (MNC) and sorted MpPs and MnPs in a 14-day methylcellulose assay. Error bars denote SDs. In CML at diagnosis we found decreased numbers of MpPs (mean 23% of CD34+CD38+ cells (range: 6.3-48%)), compared to the normal donors (33% (18-48%), p=0.030) (fig 2A). Extraordinarily, the MpP fraction varied considerably in size among CML patients, and 12/23 patients had MpP fractions within the 90% reference range (RR) of normal donors (MpPHIGH patients) and thus distinctly higher than the remaining patients (MpPLOW patients) (fig 2B-C). High MpP fractions significantly correlated with high WBC (Spearman's r = 0.47, p=0.049) (fig 2D), high neutrophil counts (r = 0.55, p=0.043), large spleen size (r = 0.66, p=0.0069), and low hemoglobin at the time of diagnosis (r = -0.58, p=0.014). Within the progenitor compartment, high ratio of BCR-ABL in the MpP to BCR-ABL in the MnP significantly correlated with large MpP fractions (r = 0.54, p=0.021).Figure 2Human MICL expression in chronic phase CML patients. (A) Fraction of MpPs in normal donors and CML patients at diagnosis. (B) Typical immunological profiles of MpPLOW patients and (C) MpPHIGH patients. (D) Correlation between MpP fraction size and total white blood cell count at the time of diagnosis. (E) Development of MpP fraction size in individual patients after 3-6 months (solid lines) and after 12-119 months (dotted lines) of TKI treatment in MpPLOW patients and (F) MpPHIGH patients.Figure 2. Human MICL expression in chronic phase CML patients. (A) Fraction of MpPs in normal donors and CML patients at diagnosis. (B) Typical immunological profiles of MpPLOW patients and (C) MpPHIGH patients. (D) Correlation between MpP fraction size and total white blood cell count at the time of diagnosis. (E) Development of MpP fraction size in individual patients after 3-6 months (solid lines) and after 12-119 months (dotted lines) of TKI treatment in MpPLOW patients and (F) MpPHIGH patients. During the first 6 months of TKI treatment differing developments in MpP fraction size were observed for MpPLOW and MpPHIGH patients. While MpPLOW patients showed increasing MpP fractions during the first 6 months of treatment (fig 2E), 4/4 and 2/4 MpPHIGH patients displayed a decrease in MpPs at 3 and 6 months, respectively (fig 2F). Thus, in these patients, the majority of the Ph+ progenitor cells being cleared seemed to be GMPs. In conclusion, our data demonstrate that hMICL is an early marker of granulocyte-macrophage differentiation, and provides a readily accessible approach to assessing the GMP population during TKI therapy in CML. Using the present approach we have uncovered a higher degree of variability in the composition of the progenitor compartment at diagnosis than previously reported, and shown that a significant proportion of the patients have expanded GMP populations. Ongoing studies are aimed at determining whether these patients may represent patients with a more advanced form of disease at the time of diagnosis. Disclosures: Stentoft: Novartis: Consultancy, Financial support for relevant congress participation Other, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Bristol-Myers-Squibb: Membership on an entity’s Board of Directors or advisory committees, Research Funding; Danish Regions: Membership on an entity’s Board of Directors or advisory committees. Hokland:Novartis: Research Funding.

Background: Many patients (pts) with chronic myeloid leukemia in chronic phase (CML-CP) achieve a sustained deep molecular response (DMR) with frontline nilotinib (NIL) therapy. ENESTfreedom (NCT01784068) is an ongoing phase 2 study evaluating the potential for such pts to stop treatment and remain in treatment-free remission (TFR). Initial results from ENESTfreedom showed that 51.6% of pts who attempted TFR remained off treatment without loss of major molecular response (MMR [BCR-ABL1 ≤ 0.1% on the International Scale, BCR-ABL1IS]) at 48 weeks. Despite the enrollment of pts with established tolerance of NIL, the frequency of adverse events (AEs) decreased during the first 48 weeks of TFR compared with the year prior to stopping treatment (65.8% vs 83.2%, respectively), while AEs related to musculoskeletal pain were more common during TFR (24.7% vs 16.3%, respectively). The quality of life (QOL) of tyrosine kinase inhibitor-treated pts has gained increasing interest in recent years. To evaluate the impact of TFR on QOL, we analyzed patient-reported outcomes prior to and during TFR. Methods: Pts with CML-CP and ≥ 2 years of frontline NIL therapy (400 to 600 mg/day for the previous ≥ 1 year) who achieved MR4.5 (BCR-ABL1IS ≤ 0.0032%) on NIL were enrolled and entered a 1-year consolidation phase, during which they continued NIL with RQ-PCR assessments every 12 weeks. Pts with sustained DMR during the consolidation phase (no assessment worse than MR4 [BCR-ABL1IS ≤ 0.01%], ≤ 2 assessments between MR4 and MR4.5, and MR4.5 in the last assessment) entered the TFR phase and stopped treatment. Pts with loss of MMR during the TFR phase reinitiated NIL treatment (reinitiation phase). At specified time points, pts completed the MD Anderson Symptom Inventory for CML (MDASI-CML, in which pts rate the levels of severity and interference with daily life for a defined set of symptoms on a scale from 0 to 10, with 0 indicating the lowest severity/interference). At each time point, pts also completed the EQ-5D-5L questionnaire, in which they report the presence/absence and severity (slight, moderate, severe, or extreme) of problems related to mobility, self-care, usual activities, anxiety/depression, and pain/discomfort and rank their overall level of health from 0 to 100 using the EQ VAS scale, with 0 indicating the poorest level of health. Results: Among 215 pts enrolled, 190 remained in sustained DMR during the consolidation phase and entered the TFR phase. Mean MDASI-CML severity and interference scores and EQ VAS scores, respectively, among pts who completed each questionnaire were 1.4, 1.7, and 80.5 at week 48 of the consolidation phase; 1.1, 1.3, and 81.1 at week 12 of the TFR phase; and 1.2, 1.4, and 81.4 at week 48 of the TFR phase (Table). Among pts who sustained TFR and who had scores at both week 48 of the consolidation phase and week 12 or 48 of the TFR phase, no impact of stopping treatment on MDASI-CML or EQ VAS scores was detected. Among evaluable pts who lost MMR during the TFR phase and reinitiated NIL, mean scores at 24 weeks after treatment reinitiation were 1.3 (MDASI-CML severity), 1.5 (MDASI-CML interference), and 77.8 (EQ VAS). Among pts evaluable at both week 48 of the consolidation phase and week 24 of the reinitiation phase, mean scores were similar at both time points. Among pts who completed the EQ-5D-5L questionnaire, the proportions reporting problems (of any severity) at week 48 of the consolidation phase, weeks 12 and 48 of the TFR phase, and week 24 of the reinitiation phase tended to be similar. The proportion of pts reporting problems with anxiety/depression was lowest during the reinitiation phase (Table). Conclusion: Minimal changes in patient-reported outcomes were observed after stopping treatment. This may be related to pts having a relatively high QOL prior to stopping treatment, given that they had tolerated ≥ 2 years of NIL prior to enrollment. These data suggest that the higher frequency of musculoskeletal pain-related AEs in the TFR phase did not substantially impact pts' QOL; however, only a subset of pts were evaluable for changes in reported outcomes over time. Although many pts have fears about TFR, reported levels of anxiety/depression were similar before and after stopping treatment but decreased among pts who reinitiated treatment. Disclosures Hochhaus: BMS: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding; ARIAD: Honoraria, Research Funding. Casares:Novartis: Consultancy, Speakers Bureau; BMS: Consultancy, Speakers Bureau; Ariad: Consultancy, Speakers Bureau. Stentoft:Pfizer: Research Funding; Ariad: Research Funding; Bristol-Myers-Squibb: Research Funding; Novartis: Research Funding. Conneally:Novartis: 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; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees. García-Gutiérrez:Ariad: Consultancy, Research Funding; BMS: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding. Gattermann:Celgene: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Other: travel, accomodation expenses, Research Funding. Wiktor-Jedrzejczak:Sandoz: Consultancy; BMS: Research Funding; Novartis: Consultancy, Research Funding; Janssen-Cilag: Consultancy; Angelini: Consultancy; Novartis: Consultancy, Research Funding; Celgene: Consultancy; Amgen Inc.: Research Funding. Le Coutre:Ariad: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria; BMS: Consultancy, Honoraria, Other: travel, accomodations, expenses; Novartis: Consultancy, Honoraria, Other: travel, accomocations, expenses, Research Funding. Saussele:ARIAD: Honoraria; Novartis: Honoraria, Other: Travel grants, Research Funding; Pfizer: Honoraria, Other: Travel grants; BMS: Honoraria, Other: Travel grants, Research Funding. Giles:Novartis: Consultancy, Research Funding. Radich:Ariad: Consultancy; BMS: Consultancy; Novartis: Consultancy, Research Funding. Ross:BMS: Honoraria; Novartis Pharmaceuticals: Honoraria, Research Funding. Menssen:Novartis Pharma AG: Employment. Deng:Novartis Phamaceuticals Corp.: Employment. Brandt:Novartis: Employment. Gnanasakthy:Novartis: Consultancy, Equity Ownership, Research Funding. Bedoucha:Novartis: Employment. Saglio:Novartis: Consultancy, Honoraria; BMS: Consultancy, Honoraria; Ariad: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria; Roche: Consultancy, Honoraria.

Background: In chronic myeloid leukemia (CML) the combination treatment of tyrosine kinase inhibitors (TKIs) with interferon-α (IFN-α) has proved to be effective and well-tolerated. IFN-α has long-term immunomodulatory effects, and when combined to TKI therapy, it may increase the success rates for treatment free remission. In our recent clinical trial NordCML007, a low-dose pegylated IFN-α was combined with dasatinib therapy. As dasatinib is also known to have immunostimulatory effects (activation of T and NK cells and downregulation of regulatory T cells), we aimed to monitor the immune effects of dasatinib and IFN-α combination treatment. Methods: 40 newly diagnosed CML patients participated in the NordCML007 clinical trial (NCT01725204). Patients were treated with 100 mg dasatinib QD and after 3 months IFN-α treatment was added (first 3 months 15 μg/week, then 25 μg/week of pegylated IFN-α). After 12 months of combination treatment, patients resumed to dasatinib monotherapy. In this immunological substudy, peripheral blood samples were collected at the diagnosis, 3, 12, and 24 months after the start of therapy. T- and NK-cells were phenotyped with multicolor flow cytometry, and their function (degranulation and cytokine secretion) was studied. In addition, a multiplexed cytokine and growth factor panel was performed (Proseek Multiplex Inflammation I96×96, Olink). Results: Dasatinib monotherapy led to an increase of NK-cell frequencies when compared to pre-treatment values (median diagnosis 6.8% vs. 3 months 12.8%, p The more detailed immunophenotyping showed that at 3 months NK cells were more mature when compared to pre-treatment values. This could be observed as the increased proportion of CD16+ (86% vs. 77%, p=0.008) and CD57+ (79% vs. 67%, p=0.0001) NK cells. Correspondingly, the frequencies of CD56bright (median 3 months 3.9% vs. dg 6.1%, p Similar effects of dasatinib treatment were also observed within the T cell population, and at 3 months patients had more CD8+ terminally differentiated effector memory CD45RA+ (Temra) cells (22% vs. 32%, p=0.03). Correspondingly, both CD8+ and CD4+ effector memory (EM) populations decreased (CD8+ EM 34% vs. 24%, p=0.007; CD4+ EM 21 % vs. 14 %, p=0.0003). As observed with the NK cells, the degranulation and Th1 type cytokine secretion of T cells decreased during dasatinib treatment (CD107a/b+ 19.4% vs. 18.4% of CD8+ T cells, p=0.02; CD107a/b+ 12.7% vs. 8.8% of CD4+ T cells, p=0.005). Interestingly, 3 out of 4 patients who suffered from pleural effusion (PE) had exceptionally high CD57+CD8+ T cell frequencies (>70% of CD8+ T cells, median 38% in all patients) at diagnosis and during the treatment. The combination of IFN-α did not significantly affect the number of NK cells. Interestingly however, the addition of IFN-α treatment seemed to have an opposite effect on the NK cell phenotype than dasatinib treatment. The proportion of CD56bright NK cells increased (median 3 months 3.9% vs. 12 months 5.2%, p=0.03), and a decreasing trend was observed among CD16+ and CD57+ NK cells at 12 months. Similarly, the T cell surface markers shifted towards more immature phenotype (CD4+ EM 14% vs. 19%, p=0.002; CD4+ CM 36% vs. 28%, p=0.002; CD8+ Temra 32% vs. 17%, p=0.003) and the degranulation of CD4+ T cells and NK cells returned to the diagnosis level. The initiation of dasatinib treatment was associated with a decrease in several plasma protein concentrations (IL-18, IL-8, CXCL5, MCP-2, MCP-3, VEGF-A, CD244, LAP TGFβ1, TGFA, 4E-BP1, ADA, STAMPB, Casp8, OSM) and an increase in others (SCF, MCP-1). After IFN-α addition, the concentration of MCP-1 was further increased. Conclusions: These results show that dasatinib and IFN-α modulate both innate and adaptive immune systems. Interestingly, where dasatinib seems to induce a more mature immunophenotype, IFN-α counteracts this by driving a shift towards a more immature phenotype. Comparative analysis of the changes in the immunophenotype and function with the clinical outcome of the patients is ongoing. Disclosures Stentoft: Ariad: Research Funding; Pfizer: Research Funding; Novartis: Research Funding; Bristol-Myers-Squibb: Research Funding. Richter:Pfizer: Honoraria, Research Funding; BMS: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Ariad: Honoraria, Research Funding. Höglund:Akinion Pharmaceuticals: Consultancy; Janssen-Cilag: Honoraria. Mustjoki:Ariad: Research Funding; Bristol-Myers Squibb: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding; Novartis: Honoraria, Research Funding.

BACKGROUND:The monocyte/macrophage system plays important roles in host defense, regulation of immune responses, tissue repair, neovascularization, and inflammation. These diverse roles are performed by specific subpopulations of macrophages that are differently activated by surrounding stimuli, simplified by the M1-M2 dichotomy of classically activated (M1), pro-inflammatory cells and alternatively activated (M2), anti-inflammatory cells. Macrophages, however, display a large degree of flexibility and are able to switch between activation states (1).The hemoglobin scavenger receptor CD163 is expressed exclusively on monocytes and macrophages, and its expression is strongly induced by anti-inflammatory stimuli like IL10 and glucocorticoid, making CD163 an ideal M2 macrophage marker (2). Furthermore a soluble variant of CD163 (sCD163) is shed from the cell surface to plasma by protease mediated cleavage of the receptor. The shedding of sCD163 is dependent on a pro-inflammatory signal such as toll-like receptor (TLR) activation by LPS (3).These unique properties led us to investigate whether an index of combined soluble- and monocyte membrane CD163 could be used as a surrogate marker for macrophage activation. MATERIALS AND METHODS:Blood sample were obtained from 53 patients with malignant hematological disease and 74 healthy individuals. The cellular (mCD163) and soluble (sCD163) CD163 expression were measured by flow cytometry and ELISA respectively. In addition, blood mRNA expression of inflammatory markers (IL-1β, IL-6, IL-8, IL-10, and TNF-α) was determined by RT-qPCR. Normalized values of sCD163 and mCD163 were calculated by dividing each value by the median value of the healthy population. The MAcS-index was then calculated as the ratio between normalized sCD163 and normalized mCD163. A MAcS-index > 1 indicates relative increase in sCD163 as compared to mCD163, suggested to reflect a predominant M1 activation. RESULTS AND DISCUSSION: The MAcS-index of healthy individuals clustered around 1 (2.5-97.5 percentile: 0.28-3.11), whereas the MAcS-index of the patients varied from 0.06 to 5139, with 4% below the 2.5 % limit of healthy individuals, and 60% above the 97.5 upper limit of healthy individuals. The MAcS-index in infected patients (with assumed M1 activation) was clearly elevated. The index was significantly higher in patients with clinical signs of infection (median: 9.01; range: 1.41-3490) and patients in antibiotic therapy (median: 9.74; range: 0.91-5139) compared to non-infected patients (median: 2.53; range: 0.058-551.5, p treatment (median: 9.4; range: 0.57-3490), ppatients with MAcS-index within reference range. Patients with malignant myeloma (median: 0.89; range: 0.63-1.51) had significantly lower MAcS-index than patients with AML (median: 20.71; range: 0.57-2214) (pa differentiation towards an anti-inflammatory state. CONCLUSION:We present a CD163-derived macrophage activation switch (MAcS)-index, which seems able to differentiate between (predominantly) pro-inflammatory and anti-inflammatory macrophage activation. The index needs further validation, however, may be very useful for monitoring diseases with macrophage involvement and response to therapeutic interventions. REFERENCES:1. Porcheray F, Viaud S, Rimaniol AC, Léone C, Samah B, Dereuddre-Bosquet N, Dormont D, Gras G. Macrophage activation switching: an asset for the resolution of inflammation. Clin Exp Immunol. 2005 Dec;142(3):481-9.2. Mantovani A, Sica A, Sozzani S, Allavena P, Vecchi A, Locati M. The chemokine system in diverse forms of macrophage activation and polarization. Trends Immunol. 2004 Dec;25(12):677-86.3. Weaver LK, Hintz-Goldstein KA, Pioli PA, Wardwell K, Qureshi N, Vogel SN, Guyre PM. Pivotal advance: activation of cell surface Toll-like receptors causes shedding of the hemoglobin scavenger receptor CD163. J Leukoc Biol. 2006 Jul;80(1):26-35.

Rationale: Dasatinib (DAS) and interferon have different modes of action and may have synergistic activity in CML, due to both antineoplastic and immunostimulatory mechanisms. Addition of pegylated interferon (PegIFN) to imatinib therapy in CP-CML has in previous clinical trials (French SPIRIT and NordCML002) resulted in deeper molecular responses. Thus, an optimal combination of DAS and PegIFN may increase the proportion of patients who reach deep molecular response with potential for treatment-free remission (TFR). Design: Newly diagnosed CP-CML patients were treated with DAS (Sprycel, BMS) 100 mg OD as single drug for three months. Thereafter weekly subcutaneous injections of Peg-IFN α2b (PegIntron, MSD) were added to DAS; from end of month 3 (M3) to M6, 15µg/week, thereafter 25µg/week until M15. Primary end points were safety and the rate of MMR at M12. The doses of PegIFN were lower than in the SPIRIT and NordCML002 studies to increase adherence. Population: Forty patients were included at 14 university centers. One patient was lost to follow-up after M6. All patients were included in analysis up to M12. Mean and median age was 48 years (range 19-71). The proportions of high risk patients were 25% (Sokal), 15% (Hasford), and 15% (EUTOS). Safety and dosing: Treatment was well tolerated with expected DAS and PegIFN related side effects. Six patients had seven serious adverse events (AEs), all hospitalizations. 1 episode each of bradycardia/atrial fibrillation (possibly PegIFN-related), headache (DAS), fever (PegIFN), anaphylaxis-like reaction (PegIFN), fever/malaise/headache (PegIFN), pneumonia and a knee effusion (both unrelated). One pleural effusion occurred (grade 2, 3%). Grade 3-4 neutropenia and thrombocytopenia occurred in 6 and 9 patients respectively. Prolonged hematological toxicity (>2 months) occurred in 8 patients, causing dosing problems in 5. One patient suffered grade 3 depression. Grade 3 flu-like symptoms occurred in 2 patients. One patient had lipase elevation grade 3 and one patient developed hypothyroidism attributed to PegIFN. Grade 2 dermal AEs like rash and acne occurred in about 20%, attributable to both drugs. 94% (DAS) and 76% (PegIFN) of assigned dose was given. Dose reductions occurred in 19 patients for DAS and 20 patients for PegIFN. Two patients discontinued DAS and switched to nilotinib, 1 for headache at M3 and 1 at M12 for lack of efficacy/hematological toxicity. Two patients could not start PegIFN for hematological toxicity (one lost to follow-up after M6). PegIFN was discontinued because of bradycardia/atrial fibrillation (1 patient), anaphylaxis (1 patient), flu-like syndrome (2 patients) and long-term hematological toxicity (2 patients). At 12 months 31/38 pats (82%) were still on PegIFN, a higher proportion than in the French Spirit or NordCML002 studies. Efficacy: We have used the DAS arm of the Dasision study (Kantarjian NEJM 2010) as a historical control. Early response at M3 was very similar between studies. In the present and the Dasision cohorts respectively, 18% vs 16% missed the 10% BCR-ABLIS landmark, 66% vs 56% achieved a CCyR and 8% vs 8% achieved MMR. At M6, three months after introduction of PegIFN, a steep increase in MMR rate was observed compared with Dasision. This was also reflected in deep responses, MR4.0 (see tables) and MR4.5 at M12, 18% vs 5%. The primary efficacy endpoint was MMR at M12, 82% vs 46%. Table 1.MMRDAS+PegIFN (%)DAS (Dasision)(%)Difference (%)M3880M6532726M9663927M12824636Table 2.MR4.0DAS+PegIFN (%)DAS (Dasision) (%)Difference (%)M3303M620614M938830M12481236 Progressions and treatment failure defined by ELN 2013: Failures: No progression was noted. At M3, 2 patients still had >95% Ph+ metaphases (MF). At M6, four patients (11%) had > 35% Ph+MF or >10% BCR-ABL levels. At M12, one patient failed CCgR and two more patients failed Conclusion: The combination of DAS and low dose PegIFN could be safely administered in newly diagnosed CP CML. No unexpected autoimmune phenomena were observed, and pleural effusions were rare. Efficacy appears very promising with high early MMR rates and deep molecular responses. A randomized comparison DAS +/- PegIFN is warranted. Support: Study drug from BMS and MSD. Grant from BMS. Figure 1. Figure 1. Disclosures Hjorth-Hansen: Ariad: Honoraria; Novartis: Honoraria; Pfizer: Honoraria, Research Funding; Bristol-Myers Squibb: Research Funding. Off Label Use: Dasatinib and Pegylated IFN combination in CML. Richter:Ariad: Honoraria; Bristol-Myers Squibb: Honoraria; Novartis: Honoraria. Porkka:Bristol-Myers Squibb: Honoraria; Celgene: Honoraria; Novartis: Honoraria; Pfizer: Honoraria. Mustjoki:Bristol-Myers Squibb: Honoraria, Research Funding.

Earlier evaluation of therapy effect in patients with CML would assist in optimal use of available tyrosine kinase inhibitors (TKI). Single cell analysis by mass cytometry has enabled the quantification of up to 46 antibody epitopes, making it ideally suited for exhaustive immunophenotyping of the haematological hierarchy, and evaluation of associated dynamic signal transduction events, in a clinical setting. By integrating time resolved single cell signalling data with clinical parameters, we searched for prognostic and efficacy-response mass cytometry biomarkers within a month of TKI therapy. We report data from experiments used to validate the custom panels of antibodies, highlighting the power of mass cytometry in the analysis of primary patient material obtained on clinical studies. Peripheral Blood (PB) samples were collected before, 3 hours, 7 days and 28 days, after start of nilotinib (300 mg BID) treatment in a subset of patients (n=55) enrolled in the ENEST1st trial. PB cells were stained with two panels of antibodies, allowing a comprehensive immunophenotyping of numerous cellular subsets, and also the evaluation of intracellular phosphorylation status of several epitopes. Moreover, using a straightforward barcoding scheme, the time-resolved samples from each individual patient were pooled after barcoding and stained with the antibody panels to minimize sample variation. In a pilot study, 7 and 10 cell subsets were identified in PB samples from 4 untreated healthy donors and 2 complete sets of 4 patients enrolled in this sub study, respectively. Furthermore, a robust signal was measured for pCrkL, pStat5, pStat3, pCreb, pAbl Y412 and pAbl Y245. The two sets of samples from study patients showed substantial changes in activation status over the course of therapy. Some changes, such as pStat3 alterations are only detectable in neutrophils and monocytes, while the activity of others i.e. pCreb was found to be ubiquitous. CD34+ cells indicated decreased phosphorylation of CrkL, Stat5, and Abl Y412/245. To increase the immunophenotyping resolution of the myeloid lineage, 3 additional cell surface markers were incorporated into the cell surface panel. In 1 healthy donor, and in diagnostic samples from three patients enrolled in this sub study, this allowed the identification of 13 cell subsets: CD3+, CD4+, and CD8+ T cells, regulatory T cells (Tregs), monocytes, dendritic cells (DCs), plasmacytoid dendritic cells (pDC's), neutrophils, basophils, B cells, hematopoietic stem cells (Lin- CD34+ CD38-) and progenitor cells (Lin- CD34+ CD38-) (Figure 1 A,B). With respect to the relative number of cells identified for each cell type, the three diagnosis samples differed from the single healthy control. In the patients, we observed an expansion of the granulocytic compartment, as well as the emergence of CD34+ progenitor and stem cells in the peripheral blood. In conclusion, the here presented developed assay is able to resolve most of the cell subpopulations found in the hematopoietic tree, and also robustly measure the activity of central signalling substrates known to be involved in CML pathogenesis. With the addition of new phospho-specific antibodies, the methodology may facilitate the detailed characterization of CML in an immunological context, and may shed new light on both the disease and therapeutic mechanism. Analysis of variation in signal responses and immune profile are now in progress in the subset of patients (n=55) in the ENEST1st trial. Figure 1. Manually annotated SPADE tree from healthy donor and patient (3581_0002). With the incorporation of additional cell surface markers, the protocol was able to identify 13 cellular subsets in healthy donors (A) and a typical CML patient (B): CD3+, CD4+, and CD8+ T cells, regulatory T cells (Tregs), monocytes, dendritic cells (DCs), plasmacytoid dendritic cells (pDC's), neutrophils, basophils, B cells, hematopoietic stem cells (Lin- CD34+ CD38-) and progenitor cells (Lin- CD34+ CD38-). Figure 1. Manually annotated SPADE tree from healthy donor and patient (3581_0002). With the incorporation of additional cell surface markers, the protocol was able to identify 13 cellular subsets in healthy donors (A) and a typical CML patient (B): CD3+, CD4+, and CD8+ T cells, regulatory T cells (Tregs), monocytes, dendritic cells (DCs), plasmacytoid dendritic cells (pDC's), neutrophils, basophils, B cells, hematopoietic stem cells (Lin- CD34+ CD38-) and progenitor cells (Lin- CD34+ CD38-). Disclosures Thaler: AOP Orphan: Research Funding. Lang:Celgene: Consultancy. Hjorth-Hansen:Bristol-Myers Squibb: Research Funding; Ariad: Honoraria; Novartis: Honoraria; Pfizer: Honoraria, Research Funding. Hellmann:Novartis: Consultancy, Other: funding of travel, accomodations or expenses, Research Funding, Speakers Bureau; BMS: Consultancy, Other: funding of travel, accomodations or expenses, Speakers Bureau. Giles:Novartis: Consultancy, Honoraria, Research Funding. Hochhaus:Novartis: Honoraria, Research Funding; Bristol-Myers Squibb: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding; ARIAD: Honoraria, Research Funding. Janssen:ARIAD: Consultancy; Bristol Myers Squibb: Consultancy; Pfizer: Consultancy; Novartis: Research Funding. Porkka:Bristol-Myers Squibb: Honoraria; Celgene: Honoraria; Novartis: Honoraria; Pfizer: Honoraria. Ossenkoppele:Novartis: Honoraria, Research Funding; BMS: Honoraria, Research Funding; ARIAD: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding. Mustjoki:Signe and Ane Gyllenberg Foundation: Research Funding; Finnish Cancer Institute: Research Funding; Sigrid Juselius Foundation: Research Funding; Pfizer: Honoraria, Research Funding; the Finnish Cancer Societies: Research Funding; Academy of Finland: Research Funding; Bristol-Myers Squibb: Honoraria, Research Funding; Novartis: Honoraria, Research Funding. Gjertsen:Bergen University Hospital: Research Funding.

Background Nilotinib is a selective BCR-ABL tyrosine kinase inhibitor (TKI) that has been shown to be more active than imatinib at inducing earlier and deeper molecular responses in the frontline treatment of chronic myeloid leukemia (CML; Larson, et al. Leukemia. 2012). ENEST1st (Evaluating Nilotinib Efficacy and Safety in clinical Trials as First-Line Treatment, NCT01061177) is the largest study ever in TKI-treated patients (pts) with CML. Its primary endpoint was the rate of MR4 (defined as BCR-ABL ≤ 0.01% on the International Scale [BCR-ABLIS] or undetectable BCR-ABL in cDNA with ≥ 10,000 ABL transcripts) at 18 mo. Molecular response (MR) was assessed by standardized quantitative polymerase chain reaction (RQ-PCR) in the 14-laboratory network of the European Treatment and Outcomes Study (EUTOS). Methods ENEST1st is a phase 3b, open-label study of nilotinib 300 mg twice daily (BID) in adults with newly diagnosed BCR-ABL-positive CML in chronic phase. MR was assessed every 3 mo by peripheral blood RQ-PCR at 1 of 14 EUTOS laboratories. Following completion of the 18-mo primary efficacy time point, all pts continued to receive treatment and were followed for an additional 6 mo. Results 1160 pts were screened, with 1086 eligible pts treated in 26 European countries. Overall, median age was 53 y (range, 18-91 y); 59.2% of pts were male, 96.9% had typical b2a2 and/or b3a2 BCR-ABL transcripts (intent-to-treat population for MR analyses), and 90.3% were Philadelphia chromosome–positive by bone marrow metaphase cytogenetics. Per protocol, efficacy and safety analyses were conducted in the initial 819 pts (75.4% of enrolled pts) who were on study for 24 mo or discontinued early. In this group, median age was 53 y (range, 18-91 y), and 58.5% were male; Sokal risk scores were low, intermediate, and high in 33.7%, 39.5%, and 18.7% of pts, respectively (8.1% missing). EUTOS scores were low in 83.8% and high in 9.2% of pts (7.0% missing). A total of 658 pts (80.3%) completed 24 mo of treatment; 161 pts (19.7%) discontinued early. The most common reasons for discontinuation included adverse events (AEs; 10.5%), withdrawal of consent (2.7%), and disease progression (as indicated by the investigator; 1.7%). MR4 rate at 18 mo was 43.0% (95% CI, 39.3-46.8). Rates of major MR (MMR, BCR-ABLIS ≤ 0.1%), MR4, and MR4.5 (BCR-ABLIS ≤ 0.0032% or undetectable cDNA with ≥ 32,000 ABL transcripts) at 18 and 24 mo are shown in the Table. Cumulative incidence of MR4 by 18 mo was 50.1%. All pts were followed up for progression or death for 24 months after start of treatment: 7 pts (0.85%) experienced progression to accelerated phase/blast crisis (AP/BC) while on core treatment or after discontinuation. Overall, 12 pts (1.5%) died; 2 of them died following progression to AP/BC. The safety profile of nilotinib was similar to that observed in other frontline studies. The most common AEs of any relationship were rash (21.4%), pruritus (16.8%), and headache (15.0%); most AEs were grade 1-2. Rates of grade 3-4 hematological AEs were low, with thrombocytopenia and neutropenia reported in 8.2% and 2.9% of pts, respectively. Peripheral arterial occlusive disease (PAOD) occurred in 13 pts (1.6%), ischemic heart disease in 31 (3.8%), and ischemic cerebrovascular conditions in 4 (0.5%). Three cases of pain in extremities are under investigation for potential relationship to PAOD. Conclusions ENEST1st confirms that frontline nilotinib results in high rates of deeper and earlier MR and very low rates of progression to AP/BC. By 18 mo, half of pts achieved a response of MR4. This MR4 rate supports the use of frontline nilotinib as a treatment of choice on which to develop treatment-free remission studies. Finally, the molecular response rates measured in a standardized and validated network of 14 EUTOS laboratories in ENEST1st provide prospective confirmation of the centrally reviewed molecular response rates reported in the ENESTnd trial. Disclosures: Giles: Novartis: Consultancy, Research Funding. Baccarani:Novartis: Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees, Speakers Bureau; Bristol Myers Squibb: Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees, Speakers Bureau; Ariad: Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees, Speakers Bureau; Pfizer: Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees, Speakers Bureau. Brümmendorf:Novartis: Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees, Patents & Royalties, Research Funding; Bristol Myers Squibb: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria; Ariad: Consultancy. Mahon:Novartis: Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Brisol Myers Squibb: Consultancy, Honoraria; Ariad: Honoraria; Pfizer: Honoraria. Rosti:Novartis: Consultancy, Speakers Bureau; Bristol Myers Squibb: Consultancy, Speakers Bureau; Ariad: Consultancy, Speakers Bureau; Roche: Speakers Bureau; Pfizer: Speakers Bureau. Saglio:Novartis: Consultancy, Honoraria; Bristol Myers Squibb: Consultancy, Honoraria; Ariad: Consultancy, Honoraria; Celgene: Consultancy, Honoraria. Steegmann:Novartis: Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau; Bristol Myers Squibb: Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau; Pfizer: Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau. Ossenkoppele:Novartis: Consultancy, Research Funding, Speakers Bureau; Bristol Myers Squibb: Consultancy, Speakers Bureau. Echeveste:Celgene: Consultancy; Novartis: Consultancy. Gattermann:Novartis: Honoraria, Research Funding, Speakers Bureau. Griskevicius:Novartis: Consultancy, Research Funding. le Coutre:Novartis: Honoraria, Research Funding, Speakers Bureau; Bristol Myers Squibb: Honoraria; Pfizer: Honoraria. Masszi:Novartis: Honoraria, Membership on an entity’s Board of Directors or advisory committees. Rea:Novartis: Honoraria; Bristol Myers Squibb: Honoraria; Pfizer: Honoraria; Ariad: Honoraria. Richter:Novartis: Consultancy, Research Funding, Speakers Bureau; Bristol Myers Squibb: Consultancy, Speakers Bureau. Stentoft:Novartis: Consultancy, Financial support for relevant congress participation Other, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Bristol Myers Squibb: Membership on an entity’s Board of Directors or advisory committees, Research Funding; Danish Regions: Membership on an entity’s Board of Directors or advisory committees. Tulliez:Novartis: Honoraria, Membership on an entity’s Board of Directors or advisory committees. Schuld:Novartis: Employment, Equity Ownership. Pellegrino:Novartis: Employment. Walasek:Novartis: Employment. Cross:Novartis: Honoraria, Research Funding; Bristol Myers Squibb: Honoraria. Hochhaus:Novartis: Research Funding; Bristol Myers Squibb: Research Funding; Ariad: Research Funding; Pfizer: Research Funding.

Imatinib and dasatinib modulate immune responses in vitro and in vivo . Immunological surveillance in the MRD-situation might be of particular relevance for long-term control or even elimination of CML-repopulating stem cells. Little is known about potential immune-modulatory effects of nilotinib in vivo . The ENEST1st study ([NCT01061177][1]) is focused on examining the role of firstline nilotinib therapy in CML-CP - this ENEST1st substudy involves a comprehensive immunological monitoring program. To evaluate and characterize the immunomodulatory effects of nilotinib therapy in newly diagnosed CML-CP patients. Peripheral blood was taken prior to treatment initiation and after 6 and12 months (mo) from 50 patients treated on the ENEST1st study. Samples were analyzed by nine color flow cytometry employing six panels of antibodies to determine various leukocyte populations including lymphocyte subsets (e.g. T cell subpopulations including Treg and NKT cells, NK cells, B cells), myeloid populations (e.g. monocytes, MDSC) and dendritic cell subsets (e.g. mDC, pDC), respectively. Changes in immune cell parameters were correlated to clinical endpoints and PK data. 55% of the patients included into this substudy achieved MMR at 6mo, 75% at 12mo and 79% at 12mo of therapy. MR4 was achieved by 21%, 31%, 50% of patients at 6, 12 and 24 mo of therapy, respectively. A high proportion of CD14+ monocytes with aberrant expression of CD56, present at baseline, dropped to undetectable levels at 6 and 12 mo of treatment. The most prominent immunological change from baseline to 12 mo was a dramatic increase of CD19+ B cells. The abundance of CD19+ B cells at baseline was negatively correlated with SOKAL score. Among T-cell subpopulations, the proportion of CD56+ NKT-cells decreased. Similarly, the proportion of CD8+ T cells significantly decreased concomitant with increasing CD4+ T cells during therapy. In parallel to a decrease of CD45RA+ expressing T cells among both CD8+ and CD4+ T cell subsets, the proportion of CD45R0+ memory cells increased. This increase was mainly due to an increase of the CD95+CD28+ central memory population. In contrast to our expectation, CD25high FoxP3+ Treg cells were even increased transiently 6 months after treatment initiation but at 12 months dropped back to levels seen at diagnosis. None of the immunological changes were associated with plasma levels of nilotinib or response to therapy. Various immunological changes were detected during nilotinib therapy. However, most changes after therapy are most likely due to normalization of the peripheral blood compartment. Correlation of a specific immunological signature with response to nilotinib could not be identified. However the increased proportion of memory T cells during therapy suggests a potential contribution of the cellular immune response to the eradication of malignant cells. Molecular analyses of NKT-cells will show whether the increased proportion before therapy is due to aberrant expression of CD56 as in monocytes or a specific expansion of this subset. Mustjoki: Novartis: Consultancy, Speakers Bureau; BMS: Consultancy, Speakers Bureau. Greil: Roche: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding. Thaler: Roche: Honoraria, Research Funding. Richter: Novartis: Consultancy, Research Funding, Speakers Bureau; Bristol Myers Squibb: Consultancy, Speakers Bureau. Verhoef: MedImmune: Research Funding. Mark: Novartis: Employment. Haenig: Novarts: Employment. Jurjonas: Novartis: Employment. Gastl: Novartis: Honoraria, Research Funding. Giles: Novartis: Consultancy, Research Funding. Hochhaus: Novartis: Consultancy, Honoraria, Research Funding, Travel Other; BMS: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy, Honoraria; Ariad: Consultancy, Honoraria. Ossenkoppele: Novartis: Consultancy, Research Funding, Speakers Bureau; Bristol Myers Squibb: Consultancy, Speakers Bureau. Porkka: BMS: Consultancy, Research Funding, Speakers Bureau; Novartis: Consultancy, Research Funding, Speakers Bureau. Wolf: Novartis: Honoraria, Research Funding; Pfizer: Honoraria; Bristol-Meyers Squibb: Honoraria. [1]: /lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT01061177&atom=%2Fbloodjournal%2F122%2F21%2F2731.atom

Abstract 4667 Introduction: Primary immune thrombocytopenia (ITP) is an autoimmune disorder characterized by a low platelet count and an increased risk of bleeding. Hemostatic treatment modalities, bypassing the need for platelet transfusion, would be desirable for control of serious acute bleeds in patients with ITP. This study aimed at (i) performing a thorough characterization of the coagulopathy of ITP, (ii) investigate new ways to obtain acute correction of the coagulopathy performing in vitro experiments with recombinant factor VIIa (rFVIIa, NovoSeven®), fibrinogen (RiaSTAP®), and the combination of rFVIIa and fibrinogen, and finally (iii) investigate the correlation of the hemostatic response to the baseline platelet counts of the ITP patients. We challenged the hypothesis that rFVIIa combined with fibrinogen concentrate can correct whole blood (WB) clot formation in patients suffering from ITP even at very low platelet counts. Methods: Blood from 12 ITP patients and 15 healthy controls was drawn into 3.2% citrate containing corn trypsin inhibitor 18.3μg mL−1 to inhibit artificial contact activation. The WB (mean platelet count 22 × 109L−1 (range 0–42)) was spiked in vitro with buffer (control), fresh donor platelets (+40×109 L−1), rFVIIa (1 or 4μg mL−1), or fibrinogen (1 or 3mg mL−1) as well as the combination of rFVIIa and fibrinogen. Dynamic WB coagulation profiles were recorded by ROTEM® Thromboelastometry using activation with tissue factor (0.03pM) and re-calcification. Parameters of clot initiation (clotting time, CT), clot propagation (maximum velocity, MaxVel) as well as clot termination (maximum clot firmness, MCF) were evaluated. Thrombin generation in “platelet-rich” ITP plasma was evaluated using calibrated automated thrombography. Overall differences between groups were evaluated by paired and unpaired t-tests as appropriate. Simple linear regression analyses were performed using the differences observed after addition of the various interventions (intervention – baseline) as the dependent variable (y) and the platelet count as the independent variable (x). The slope was used to evaluate dependency of the hemostatic response on the platelet count, whereas the intercept was used to evaluate the hemostatic response at very low platelet counts. A p-value less than 0.05 was considered statistically significant. Results: Compared with healthy controls the WB coagulation profiles of the ITP patients were characterized by a prolonged CT (mean: 1490 vs. 941s, p 0.45) and the intercept showed a significant improvement at very low platelet counts (1μg mL−1: −643s, p Conclusions: Data suggest that rFVIIa combined with fibrinogen can correct the coagulopathy of ITP even at very low platelet counts, and may be an alternative to platelet transfusion. Clinical trials are needed to further investigate if this new treatment modality holds the potential to serve as an effective acute treatment option in ITP. Disclosures: Off Label Use: Recombinant activated factor VII (NovoSeven) and fibrinogen concentrate (RiaSTAP). In vitro data suggesting a haemostatic effect in primary immune thrombocytopenia will be presented. S∅rensen:Novo Nordisk: Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau; Baxter: Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau; CSL Behring: Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau; Bayer: Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau; SOBI: Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau; Pentapharm: Membership on an entity’s Board of Directors or advisory committees, Speakers Bureau; Grifols: Research Funding; LFB: Research Funding; Octapharma: Research Funding.

Abstract 2759 BACKGROUND Nilotinib, a highly potent, selective inhibitor of BCR-ABL, is now approved for frontline treatment of Philadelphia chromosome positive (Ph+) CP CML. ENEST1st (Evaluating Nilotinib Efficacy and Safety trial as first line treatment) is a phase IIIb, open-label study of nilotinib in adult patients with newly diagnosed CP CML (ClinicalTrials.gov NCT01061177). The primary study aim is to establish the rate of molecular remission with a sensitivity of 4 log (MR4) rate through EUTOS (European Treatment and Outcomes Study) laboratories to improve the sensitivity and standardisation of RT-PCR for low level BCR-ABL detection and further refine the working definition of deep molecular response. The attainment of sustained MR4 will identify a patient population potentially eligible to join studies of tyrosine kinase inhibitor discontinuation in CP CML. METHODS 806 patients (pts) with newly diagnosed BCR-ABL+ CML-CP, diagnosed within 6 months, were to be treated with nilotinib 300 mg BID for a study period of 24 months. The primary study endpoint is MR4 rate at 18 months, initially defined as undetectable BCR-ABL transcripts by quantitative RT- PCR in a peripheral blood sample of at least 10 ml with a minimum sensitivity of 1:10,000. Molecular monitoring was performed by 13 EUTOS laboratories with conversion factors to the International Scale to facilitate standardised measurement. Key secondary endpoints include: rate of progressions to accelerated phase (AP) or blast crisis (BC) in year 1 and 2; rate of events in patients achieving MR4 at 1 year; rate of MMR ( RESULTS The 1st IA results are as follows: Baseline demographics: 208 pts were recruited in 102 sites in 15 countries. Median age was 53 years, median time from diagnosis 1.1 months (range 0.07–5.39). 39.0% pts were female, 91.8% had typical b2a2 or b3a2 BCR-ABL transcripts, 71.2% had been previously treated. 37.6% with standard dose imatinib (maximum of 12 weeks) and 55.1% with hydroxyurea. 34.0%, 37.2% and 17.8% pts were classified as Sokal low, intermediate and high risk. 80.4% and 9.3% pts were classified as EUTOS score low and high risk. The median dose intensity was 600 mg/day. 29.8% pts experienced a dose interruption of a median cumulative duration of 14 days. Rate of MMR by 3 and 6 months was 22.5% and 50.3%. MMR by 3 and 6 months was 43.9% and 61.1% for EUTOS low risk and 17.6% and 41.2% for EUTOS high risk pts. Quality control of molecular responses beyond MMR is ongoing. Adverse events (AE) were mostly grade 1 and 2, mainly rash (22.4%), pruritus (17.1%), alopecia (11.7%), fatigue (11.7%), headache and nausea (10.2%) which were usually manageable with appropriate dose interruptions/reduction. Grade 3–4 hematological AE rates were low, with thrombocytopenia and neutropenia reported in 5.3 and 3.5% pts respectively. The incidence of treatment –related Grade 3–4 non-hematological AEs was low, with lipase increase and hyperbilirubinaemia reported in 2.4% and 1.5% pts respectively. 8.8% patients reported study drug related SAEs. 7.8% and 0.5% of pts showed a prolongation of QTcF above 450ms and 500ms respectively. At 6 months, 88.8% pts remain on study, 14 pts (6.8%) have discontinued due to AE (3 discontinued due to hyperbilirubinemia), 1 due to abnormal laboratory value, 5 withdrew consent, 1 died due to a metastatic neoplasm, and 2 discontinued due to protocol violations. No pt has progressed during the first 6 months of study. Methodological improvements in RT-PCR have allowed refinement of the working definition of MR4 as either (i) detectable disease ≤0.01% BCR-ABLIS or (ii) undetectable disease in cDNA with ≥10,000 ABL transcripts. CONCLUSIONS Results of the ENEST1st first IA with over 100 pt years of nilotinib treatment demonstrate nilotinib's efficacy and safety to be similar to that reported in other front line trials. Through methodological improvements of RT-PCR, a network of EUTOS laboratories are now able to define and measure MR4 in a standardised and validated manner. Disclosures: Giles: Novartis: Consultancy, Honoraria, Research Funding. Rosti:Novartis: Consultancy; Bristol Myers Squibb: Consultancy; Novartis: Research Funding; Novartis: Honoraria; Bristol Myers Squibb: Honoraria. Ossenkoppele:Novartis Pharmaceutical: Consultancy, Honoraria, Research Funding; Bristol Myers Squibb: Consultancy, Honoraria. Tulliez:Novartis: Investigator in Novartis Study. Stentoft:Novartis: Investigator in Novartis Study. Giagounidis:Novartis: Investigator in Novartis Study. Nobile:Novartis: Investigator in Novartis Study. le Coutre:Novartis: Honoraria, Research Funding, Speakers Bureau; BMS: Honoraria. Gattermann:Novartis: Honoraria, Research Funding. Griskevicius:Novartis: Investigator in Novartis Study. Cross:Novartis: Research Funding. Hill:Novartis: Employment. Schuld:Novartis: Employment. Pellegrino:Novartis: Employment. Magazzù:Novartis: Employment. Hochhaus:Novartis Pharmaceutical: Consultancy, Honoraria, Research Funding; Bristol Myers Squibb: Consultancy, Honoraria, Research Funding; Ariad: Consultancy, Honoraria, Research Funding; Merck: Consultancy, Honoraria, Research Funding.

Abstract 667 Background: Targeted tyrosine kinase inhibitor (TKI) therapy efficiently induces rapid hematologic and cytogenetic responses in most CML patients. In vitro studies have suggested that CML stem cells are resistant to TKIs and therefore the treatment may need to be life-long. However, the in vivo effects of TKIs on the leukemic stem cell pool in a patient population have not been prospectively assessed. In addition, the biological impact and prognostic value of leukemic stem cell burden at diagnosis is unknown. Aim: To analyze the proportions of Ph+ cells in the stem cell compartment in newly diagnosed CP CML patients at diagnosis, and correlate the initial leukemic stem cell burden to biological variables and hematological toxicity during first 3 months of TKI therapy. Patients and Methods: 42 newly diagnosed CP CML patients within the Nordic countries were randomized to receive either dasatinib 100 mg (n=21) or imatinib 400 mg (n=21) once daily. Stem cell assays were performed at diagnosis and at 1, 3, and 6 months from start of TKI therapy. After pre-selection of CD34+ cells from large volume bone marrow (BM) aspirates with paramagnetic beads, the CD34+ cells were fractionated into CD38 positive and negative pools using a sorting flow cytometer. The proportion of Ph+ cells in the stem cell fractions was assayed by counting 1000 cells with interphase FISH for BCR-ABL1. Results: Measurement of Ph+ stem cells was feasible in most patients at diagnosis and results from 36 evaluable patients will be presented. The median volume of BM aspirate was 28, 37, 40 and 36 ml at diagnosis, 1, 3, and 6 months after therapy start, respectively. The median yield of BM mononuclear cells was 1000, 110, 93 and 79 ×106, respectively. The median proportion of Ph+ cells was significantly lower in the more primitive CD34+CD38neg fraction when compared to the CD34+CD38+ fraction or to unfractionated BM (79%, range 0.6–100%; 96%, 50–100%; and 96%, 57–100%, respectively, p=0.0001). The proportion of Ph+ cells in the CD34+CD38neg fraction at diagnosis correlated with high leukocyte count (r=0.59, p Conclusions: The proportion of Ph+ stem cells at the time of diagnosis varied from 1 to 100% between individual CML patients. It was correlated with hemoglobin concentration, leukocyte count, blast percentage and spleen size at diagnosis and with hematological toxicity during early course of treatment, mirroring paucity of healthy hematopoietic stem cell reservoir. The size of the leukemic stem cell pool at diagnosis may be a powerful prognostic marker and a major biological determinant for the high Sokal risk group. The effect of TKI therapy on the malignant stem cell pool size and correlation to therapy responses will be evaluated when all patients have reached the primary study endpoint of 6 months. Disclosures: Mustjoki: BMS, Novartis: Honoraria. Richter:BMS, Novartis: Consultancy, Honoraria. Simonsson:BMS, Novartis: Consultancy, Honoraria, Research Funding. Porkka:BMS, Novartis: Consultancy, Honoraria, Research Funding. Hjorth-Hansen:BMS, Novartis: Consultancy, Honoraria, Research Funding.

Abstract 3280 Poster Board III-1 Background: Imatinib mesylate (IM) 400 mg once daily (OD) is the current standard first-line therapy for CML. Several biological and clinical observations suggest that combining IM with interferon alpha (IFNa) may improve the outcome of treatment. Aim: To compare the effects of standard-dose IM to combination of IM and IFNa in newly diagnosed chronic phase CML patients with an intermediate or low Sokal risk score. The primary end point was to compare the major molecular response (MMR) rate after 12 months between the treatment arms (intention-to-treat analysis). Patients and therapies: In a Nordic CML Study Group (NMCLSG: Denmark, Finland, Norway and Sweden) and Israel multicenter study we randomized 114 newly diagnosed CML patients in complete hematological remission following 3 months of IM 400 mg OD induction therapy. The study arms were IM (Glivec, Novartis) and the combination of IM and IFNa 2b (PegIntron, Schering-Plough). IM dose was fixed at 400 mg OD. IFNa was started at 30 μg/week but could be escalated to 50 μg/week or reduced down to 15 μg/week depending on tolerability. Molecular response was evaluated by blood RQ-PCR for BCR-ABL1 and was expressed on the international scale (IS). Results: As of August 17, 2009, 79 patients were evaluable for primary endpoint and 47 of these were in MMR (59%) The rate of complete cytogenetic response (CCgR) was 68/79 (86%). Nineteen patients (17%) were considered as treatment failures (grade 4 nonhematological adverse event, refusal, loss of CCgR, progression to advanced phase, protocol violation or other reason). Conclusions: A final analysis will be performed when we have complete data on all randomized patients. The comparison by treatment arm on molecular and cytogenetic responses as well as other relevant data (treatment failures, patients off-treatment for protocol violations, refusal or toxicity) will be presented on site. Supported by European LeukemiaNet, WP 4. Disclosures: Simonsson: Novartis: Consultancy, Honoraria, Research Funding; BMS: Consultancy, Honoraria, Research Funding. BjÖreman:BMS: Consultancy, Honoraria. Mustjoki:BMS: Honoraria. StrÖmberg:Novartis: Honoraria; BMS: Honoraria. Weiss Bjerrum:Novartis: Consultancy, Honoraria; BMS: Consultancy, Honoraria. Gruber:Novartis: Research Funding. Nagler:Novartis: Consultancy. Porkka:Novartis: Consultancy, Honoraria, Research Funding; BMS: Consultancy, Honoraria, Research Funding.

The purpose of the registry is to collect existing cases of pts who failed imatinib therapy. Since the drug has been registered most of information on safety and efficacy were collected through clinical trials. Thus the true rate of failure is currently unknown. Members of the European LeukemiaNet agreed to establish a subregistry with the aim of collecting these cases. Failure is defined as efficacy failure i.e. no hematological response (HR) or cytogenetic response (CyR), unsatisfactory response, loss of response, according to the European Guidelines criteria (Baccarani et al, Blood 2006) and documented toxicity leading to discontinuation of imatinib. Objectives are to describe the sub-categories of failure and main toxicities, demographic patterns, clinical and biological profiles of pts (at diagnosis, at the beginning of imatinib therapy, at time of failure), dose and duration of imatinib therapy until failure was recorded, therapeutic decision after failure, and survival status. Eligibility criteria: To be included in the Registry, pts who failed imatinib therapy must be 18 years old or more with Ph+ CML in chronic phase at the onset of imatinib therapy. Pts are eligible, being included in prospective studies or not. Data collection: based on notification, data is prospectively centralized and quality controlled. The planned period for registration is 2005–2007 and 1000 cases are expected. Final analyses will be conducted overall, by groups: imatinib first line/not first line and by categories of failures. Results: As of July, 2006, 378 pts,(M: 56%, F 44%), were recorded. Median age at diagnosis was 51 (range 12–80). Participating countries were: Austria (4 pts), Denmark (13), Finland (18), France (236), Germany (39), Israel (34), Italy (10), Netherlands (11), Spain (13). Thirty seven percent of pts were never included in prospective studies at the time of failure. Reason for registration was no or unsatisfactory response in 30% of the cases including no complete HR (2%), not any CyR (12%), no major CyR (16%). Loss of responses occurred in 41% of the cases including hematological relapse (6%) cytogenetic relapse or progression (12%), progression to accelerated phase or blast crisis (23%). Discontinuation because of toxicity was recorded in 13% of the cases. Sixteen percent of the pts presented toxicity combined with unsatisfactory response. Policy: The IFP sub-registry is supported by a grant from the 6th European framework program “LifeSciHealth”. This collaborative study is linked with the European CML Registry (Work Package 4). This study is conducted in accordance with principles and guidelines of the European Community and Helsinki protocol and was approved by French authorities. In conclusion, this registry has been successfully established and already provides important information on subcategories of imatinib failure pts.

5 heavily pretreated patients with chronic lymphocytic leukaemia or non-Hodgkin lymphoma resistant to alkylating agents were treated with low-dose cytosine arabinoside (ARA-C). 3 of the patients showed a clinical and laboratory improvement lasting from 8 to more than 20 months. Low dose ARA-C may be therapeutically effective in terminal stages of lymphoproliferative disorders.

Introduction Tyrosine kinase inhibitor (TKI) trough plasma level testing and pharmacodynamic evaluation (i.e. quantification of phosphorylated BCR-ABL downstream targets) may help to optimize patient-tailored dosing in CML-CP. For 2nd generation TKIs the clinical value of TKI plasma level and protein phosphorylation quantification remains unclear. The ENEST1st study (NCT01061177) is focused on examining the role of first-line nilotinib therapy in CML-CP. This ENEST1st substudy addresses the value of plasma-level testing and protein single cell phosphorylation pharmacodynamics as predictors of response and long-term outcomes. Methods Nilotinib levels were centrally quantified by means of mass spectrometry (HPLC-MS/MS) in 54 patients at 3 hours after first drug intake at day (d) 1 (Cmax) and at d7, d28 as well as at months (mo) 3, 6, 12 prior to morning drug intake (Cmin=trough level). Single cell quantification of intracellular protein phosphorylation was performed by flow cytometry (phosphoflow) in the myelocyte cell population after full blood fixation/cell permeabilization/erythrocyte lysis and analyzed 3 hours after first drug intake at d1 and on d7 and d28. Primary endpoint of the study was MR4 (BCR-ABL Results Our initial analysis focuses on correlation of drug levels with molecular response by correlating PK data to early molecular response, i.e. ≤10% BCR-ABL (IS) reduction at 3 mo as well as 0.1% IS (MMR), MR4 and MR5. At 3, 6, 12 and 18 mo, 24%, 56%, 74% and 77 % of the here investigated patients achieved MMR; 2%, 22%, 34% and 44% achieved MR4 and MR5 was detected in 0%, 5%, 15% and 14% of patients at the respective time points. Only 1 patient at 3mo had >IS 10% BCR-ABL. On d1 at 3 hours after intake of the first tablet the median peak plasma levels reached 408 ng/ml increasing to a median trough level of 834 ng/ml at d7, 888 ng/ml at d28, 919 ng/ml at 3mo, 1122 ng/ml at 6m and 1003 ng/ml at 12mo. Initial Cmax-levels at d1 significantly correlated with steady state levels thereafter (e.g. with trough levels at 12mo: r=0.56, p=0.004). Three mo drug levels were significantly negatively associated with lower BCR-ABL mRNA burden at 12m and 24m (r=-0.44, p=0.011 for m12 and r=-0.35, p=0.014 for m24). When median steady state drug levels were compared in different response categories (yes/no: MR4, MR5, MMR, >IS 10% at 3mo), significantly higher nilotinib trough levels at day 90 and mean trough level (day 28-180) were seen in patients achieving the primary endpoint of the study (MR4 at 18mo). Similarly, 3mo and mean through levels were also significantly higher in patients achieving MR5 at 12 or 18mo. As only one patient did not reach Conclusions Single cell myelocyte phosphoprotein detection allowed monitoring of the BCR-ABL signalling network. Inter-individual plasma levels show a relatively wide variability and Cmax levels upon first drug exposure correlate with later trough levels pointing out to a potential individual pharmacogenetic background regulating drug availability. PK-based optimizing of nilotinib-dosing may help to further improve response depth (i.e. reaching MR4 or MR5), which is assumed to be a prerequisite for treatment discontinuation. Disclosures: Wolf: Novartis: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding. Mustjoki:Novartis: Honoraria, Research Funding. Greil:Novartis: Honoraria, Research Funding. Hjorth-Hansen:Pfizer, BMS: Honoraria, Travel expenses Other. Verhoef:Novartis: Research Funding. Mark:Novartis: Employment. Haenig:Novartis: Employment. Jurjonas:Novartis: Employment. Giles:Novartis: Consultancy, Research Funding. Hochhaus:Novartis: Research Funding. Porkka:Novartis: Honoraria, Research Funding. Ossenkoppele:Novartis: Consultancy, Research Funding; BMS: Consultancy. Gjertsen:Novartis: Honoraria, Research Funding.

Abstract 784 Background: In vitro studies have suggested that CML stem cells are resistant to tyrosine kinase inhibitors (TKIs), but in vivo effects in patients have not been prospectively assessed. Furthermore, the inter-individual variation of the leukemic stem cell pool at diagnosis and its possible prognostic value is unknown. Patients: 46 newly diagnosed CML-CP patients were randomized 1:1 to receive either dasatinib 100 mg or imatinib 400 mg QD. The primary endpoint was a comparison of the proportion of Ph+ cells in CD34+CD38− and CD34+CD38+ compartment at 6 months between the study arms. Key secondary endpoints were the fraction of Ph+ cells in the stem cell compartments at 1 and 3 months, and molecular and cytogenetic responses at 3, 6, 12 and 18 months. Experimental endpoints included the percentage of Ph+ cells in the stem cell compartment at diagnosis and its correlation with therapeutic response. Results: One patient in the imatinib arm and none in the dasatinib arm progressed to blast crisis within first 12 months. 4/22 of dasatinib patients have discontinued the treatment due to side-effects (mainly pleural effusion) and 1 patient due to insufficient response. 3/24 imatinib patients have discontinued the therapy (1 blast crisis, 1 side-effects, 1 other malignancy). Early cytogenetic responses were superior in the dasatinib arm: the median percentage of Ph+ cells in the bone marrow was 81% (imatinib) vs. 70% (dasatinib) at 1 month (p=0.15) and 5% vs. 0% at 3 months (p=0.0085). At 12 months all dasatinib (n=20) and 19/20 imatinib patients were in CCyR (results based on patients on treatment at 12 months). MMR rate was significantly higher in the dasatinib arm already at 6 months (70% vs. 20%, p=0.002) and similarly at 9 (75 vs. 26%, p=0.004) and 12 months (88% vs. 40%, p=0.009). Undetectable BCR-ABL1 transcripts (at least CMR4) were observed in 20% of the dasatinib patients at 6 months compared to none in the imatinib arm (p=0.11) and 44% in the dasatinib arm at 12 months compared to 7% in the imatinib arm (p=0.037). The median percentage of Ph+ cells, as measured by FISH (1000 cells analyzed), in the CD34+CD38− fraction at diagnosis was 79% (range 1–100%) compared to 96% (range 50–100%) in CD34+CD38+ fraction. The proportion of Ph+ cells in CD34+CD38− fraction correlated with WBC count (r=0.50, p79% of Ph+ cells in CD34+CD38− fraction at diagnosis. During TKI therapy, the proportion of Ph+ cells decreased rapidly in the stem cell fractions. At 1 month, the median proportion of Ph+ cells was 14% and 56% in CD34+CD38− and CD34+CD38+ fractions compared to 69% in whole BM (p Dasatinib-treated patients had significantly lower proportion of Ph+ cells in CD34+CD38+ fraction at 3 months than imatinib patients (0.05% vs. 0.68%, p=0.0318). A similar trend was also observed at 1 month (24% vs. 69%, p=0.05), but no difference existed at 6 months. In CD34+CD38− fraction the proportions of Ph+ cells did not differ significantly at 1 (11 vs. 17%, p=0.91), 3 (0.2 vs. 0.3%, p=0.44) or 6 months (0 vs. 0%, p=0.75). Conclusions: In comparison to imatinib, dasatinib induced superior therapeutic responses with remarkably high MMR and CMR rates. This was associated with a faster reduction of Ph+ cells at the progenitor CD34+CD38+ cell level. Surprisingly, both drugs rapidly depleted Ph+ cells from the more primitive CD34+CD38− compartment. The proportion of Ph+ stem cells at diagnosis varied significantly among individual patients and bore prognostic value. Patients with a low proportion of Ph+ leukemic stem cells at diagnosis achieved faster and better cytogenetic and molecular responses. The leukemic stem cell burden at diagnosis may be a biomarker predicting treatment outcome and reflecting key biological factors in CML. Disclosures: Mustjoki: Novartis: Honoraria; Bristol-Myers Squibb: Honoraria. Richter:Novartis: Honoraria; Bristol-Myers Squibb: Honoraria. Dybedal:Novartis: Travel support. Fioretos:Cantargia AB: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Qlucore AB: Equity Ownership, Membership on an entity's Board of Directors or advisory committees. Weiss Bjerrum:Novartis: Consultancy; Bristol-Myers Squibb: Consultancy. Simonsson:Novartis, BMS, Merck, Pfizer: Consultancy, Honoraria. Porkka:Novartis: Honoraria, Research Funding; Bristol-Myers Squibb: Honoraria, Research Funding. Hjorth-Hansen:Novartis: Honoraria; Bristol-Myers Squibb: Honoraria.

Background: Tyrosine kinase inhibitors (TKIs) used in the treatment of chronic myeloid leukemia (CML) are not entirely selective for the BCR-ABL1 kinase but also inhibit a variety of other kinases, sometimes triggering unpredicted biological effects. As an example, the TKIs dasatinib and bosutinib both inhibit Src-kinases, which are important mediators of T-cell function. Earlier in vitro data has shown that dasatinib can suppress activation and proliferation of T and NK cells, but it can also elicit signs of immunostimulation in patients, including rapid mobilization of lymphocytes and LGL lymphocytosis. No extensive analyses of the immunological in vivoeffects of bosutinib have been performed thus far. Therefore, we aimed at characterizing T and NK cell phenotypes and functional features in CML patients in a clinical setting in the context of first-line bosutinib and imatinib treatment. Methods:Peripheral blood samples were obtained from newly diagnosed CML CP patients enrolled in the BFORE clinical trial (NCT02130557), receiving bosutinib (n=13) or imatinib (n=20) as frontline TKI treatment. Samples were drawn at diagnosis and following 3 and 12 months of therapy. Detailed immunophenotyping of NK and T cells was performed with multicolor flow cytometry. In addition, mononuclear cells were used to study the function of NK and T cells (CD107ab degranulation upon stimulation with K562 cells and detection of IFN-γ/TNF-α secretion after stimulation with anti-CD3/anti-CD28 antibodies, respectively). Moreover, blood differential counts were taken before and 2 hours after drug intake at 3 and 12 months to examine the direct effects on lymphocyte counts (mobilization). Results: No significant changes were observed in absolute white blood cell or lymphocyte counts directly (2 hours) after bosutinib or imatinib intake, in contrast to what has been observed in dasatinib treated patients. Analysis of T cell subsets during bosutinib treatment revealed that the proportion of CD4+ cells increased after the start of treatment (median dg. 60.0% vs. 3 months 62.0% p=0.06; vs. 12 months 72.8% p=0.03), but no significant changes were observed in the phenotype. Correspondingly, the proportion of CD8+ T-cells decreased moderately (dg. 31.6% vs. 3 months 25.5% p=0.01) after the therapy start. Interestingly, the proportion of PD1+ (dg. 19.6% vs. 3 months 11.9%, p=0.06; vs. 12 months 14.3%, p=0.11) and DNAM+ CD8+ T-cells decreased (dg. 73.1% vs. 3 months 66.2% p=0.004; vs. 12 months 64.6% p=0.02). No changes in the cytokine production of any of the studied subgroups of T-cells was observed. Moreover, the proportion, phenotype and function of NK-cells were not affected by bosutinib treatment. In contrast, during imatinib treatment the proportion of CD56+CD16+ NK-cells significantly increased (dg 4.3% vs. 3 months 9.9% p=0.0005; vs 12 months 14.4% p=0.002; 8.1% in bosutinib treated patients). Moreover, in imatinib patients NK-cells downregulated CD27 (dg 9.0% vs. 3 months 5.2% p=0.004; vs. 12 months 4.9%; p=0.002). Further, NK-cells from imatinib-treated patients expressed more CD107ab upon stimulation with K562 at 3 and 12 months, when compared to samples from diagnosis (dg 13.0% vs. 3 months 16.1%, p=0.01; vs. 12 months 23.2%, p=0.008). The proportion of CD4+ T-cells increased 3 months after the start of imatinib treatment (dg 60.1% vs. 3 months 63.5% p=0.01), whereas the percentage of CD8+ T-cells decreased (dg. 38.6% vs. 3 months 31.5% p=0.02). Decreased expression of DNAM (dg 73.5% vs. 3 months 67.9% p=0.0008; vs. 12 months 62.4% p=0.002) was observed in the CD4+ T-cells. Similarly as in bosutinib treated patients, the proportion of PD1+ CD8+ cells decreased during imatinib treatment (dg 18.2% vs. 3 months 14.7%, p=0.02; vs. 12 months 14.8%, p=0.03). Both CD4+ and CD8+ T-cell subsets from imatinib-treated patients secreted less cytokines after the start of treatment when compared to the pre-treatment samples. Conclusions: Despite of the Src-kinase inhibitory profile of bosutinib, no major changes were observed in T- or NK-cell phenotype or function during first-line bosutinib treatment. In contrast, in imatinib treated patients the proportion of NK-cells increased and their degranulation responses were significantly higher than in untreated CML patients. Comparison of these data with the clinical variables and treatment outcome is warranted. Disclosures Stentoft: Novartis: Research Funding; Bristol-Myers-Squibb: Research Funding; Pfizer: Research Funding; Ariad: Research Funding. Gjertsen:BerGenBio AS: Consultancy, Research Funding. Janssen:Pfizer: Honoraria; Novartis: Research Funding; Ariad: Honoraria; BMS: Honoraria. Brümmendorf:Pfizer: Research Funding; Novartis: Research Funding. Richter:BMS: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Ariad: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding. Mustjoki:Pfizer: Honoraria, Research Funding; Ariad: Research Funding; Bristol-Myers Squibb: Honoraria, Research Funding; Novartis: Honoraria, Research Funding.