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Abstract 1201 Background. Before the era of tyrosine kinase inhibitors (TKIs), interferon alpha (IFN-α) was the treatment of choice in CML and prolonged survival of responding patients. Recent studies suggest that combination of IFN-α with TKI improves therapy outcome. Significantly, a proportion of IFN-α treated patients in prolonged complete cytogenetic remission (CCyR) have been able to discontinue treatment without disease relapse (Mahon et al. JCO 2002). The mechanism of action of IFN-α therapy is incompletely understood; the drug exerts both direct cytotoxic and immunomodulatory effects on leukemic cells. The aim of this project was to study the immunomodulatory effects of IFN-α in CML patients in prolonged remission and isolate biological markers predicting response. Patients and methods. The study population consisted of CML patients treated with IFN-α monotherapy (n = 10, median therapy time 146 months, range 63–231 months) and CML patients who had discontinued IFN-α therapy but remained in remission for >2 years (n = 9, median therapy time 120 months, range 80–184; median time without therapy 53 months, range 24–96). None of the patients were previously treated with TKI therapy. In addition, non-CML patients (3 patients with essential trombocythemia and one patient with polycythemia vera) treated with IFN-α and healthy volunteers (n = 43) were included as controls. Lymphocyte populations in all four groups were characterized with comprehensive immunophenotyping panels. The clonality of T-cells was analyzed by a TCR γ/δ rearrangement assay by PCR. Lymphocytes were further sorted into CD3+ TCR αβ+ and CD3+ TCR γδ+ populations (n = 8). Additionally, plasma levels of 25 cytokines were measured with a multiplex bead-based cytokine assay (Luminex®). Results. The proportion of NK-cells from lymphocytes was significantly increased in IFN-α discontinued patients (median 26%, range 18–51%) compared to healthy volunteers (11%, 5–21%) or patients on IFN-α therapy (12%, 6–31%)(P=0.0005). Similarly the proportion of CD8+ cells from T-cells was significantly increased in both CML IFN-α groups (55% in IFN-α discontinued patients, 44% in IFN-α treated patients vs. 31% in healthy volunteers; P Clonal TCR γ/δ rearrangements were observed in 18 of 19 (95%) IFN-treated CML patients as compared to 3 of 22 (14%) in healthy volunteers (P IFN-α treatment was associated with a distinct plasma cytokine profile in CML patients. IP-10, IL-6, IL-12, eotaxin, MCP-1, and IFN-γ levels were significantly increased in IFN-α treated CML patients. In particular, eotaxin and MCP-1 levels differed significantly between healthy controls and IFN-α patients who had successfully discontinued IFN-α therapy (428 vs. 1173 pg/ml, P Conclusions. Our results show that IFN-α treatment induces distinct changes in the immunoprofile of CML patients. Patients who had successfully discontinued IFN-α therapy differed markedly from healthy controls. IFN-α therapy was associated with increased numbers of NK-cells and clonal γδ+ T-cells. These cells possess potent anti-leukemic activity and may contribute to the prolonged therapy responses in this group of patients. Furthermore, plasma cytokine profile could be a helpful biomarker when considering which patients can discontinue the IFN-α treatment without imminent disease relapse. Disclosures: Faber: BMS, Novartis: Consultancy, Honoraria. Porkka:BMS, Novartis: Consultancy, Honoraria, Research Funding. Mustjoki:BMS, Novartis: Honoraria.

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.

Tyrosine kinase inhibitors (TKIs) targeting the BCR-ABL fusion protein are an effective therapy for Philadelphia chromosome positive (Ph+) leukemia. Dasatinib, a 2nd generation pan-TKI, also inhibits wild-type kinases, which may result in unexpected clinical responses. Recent data suggest that dasatinib has a potent immunosuppressive effect on T- and NK-cells in vitro. In contrast, we have noticed a marked expansion of lymphocytes in blood in a subset of dasatinib patients, but its clinical significance and molecular mechanisms are unclear. In this multicenter study, 19 Ph+ leukemia patients with marked lymphoproliferation in blood while on dasatinib (9 CML CP, 2 CML AP, 2 CML BC, 6 Ph+ALL) were identified. Clonality, immunophenotype, and intracellular signaling was analyzed and related clinical information was collected. In addition, prevalence and prognostic significance of the phenomenon was retrospectively assessed in a Phase II clinical study on 46 Ph+ ALL patients. An abrupt lymphocytosis (peak count range 4–20×109/L) with large granular lymphocyte (LGL) morphology was observed after a median of 3 months from the start of therapy (range 1–8 months). In most patients, LGL lymphocytosis was long-lasting and continued throughout dasatinib therapy, albeit with marked fluctuations in absolute lymphocyte count (Fig. 1a). In all evaluable patients (n=4), lymphocyte counts normalized after drug discontinuation. All patients were previously exposed to imatinib without similar changes in lymphocyte count or morphology. By immunophenotyping, 14 patients had a cytotoxic T-cell and 5 patients a NK-cell phenotype. After initiation of dasatinib therapy, the CD4/CD8 ratio shifted, expression of activation antigens HLA-DR and CD57 increased, expression of homing antigen CD62L decreased and relative numbers of regulatory T-cells were significantly decreased (p Figure Figure

In addition to therapeutic efficacy in imatinib-resistant BCR-ABL positive malignancies, dasatinib may have off-target immunomodulatory effects by inhibiting kinases (e.g. SRCs, c-KIT) in immune effector cells. In a proportion of patients, dasatinib treatment is associated with non-infectious pleural effusions and panniculitis, which may reflect aberrant immune reactivity. Here we describe a marked expansion of clonal LGL lymphocytes in blood among 11 BCR-ABL positive patients on dasatinib therapy (5 CML CP, 1 CML AP, 1 CML BC, 4 Ph+ALL). All patients were previously exposed to imatinib without similar changes in lymphocyte count or morphology. The median time to LGL lymphocytosis was 2 months from the start of dasatinib (range 1–8 months). It developed abruptly, with a peak lymphocyte count of 4–20 ×109/L, and was often preceded by low-grade fever. In all evaluable cases, lymphocyte counts normalized after drug discontinuation. By immunophenotyping, 6 patients had a CD3/CD8+ cytotoxic T-cell phenotype and 4 patients had a CD56+ NK-cell phenotype. The LGL lymphocytes were BCR-ABL negative. All CD3-positive cases had a clonal rearrangement of TCR gamma/delta genes by PCR; clonality was not detected in samples prior to dasatinib therapy (n=3). In TCR beta gene repertoire assay, oligoclonal patterns were seen in selected genes. All patients with HLA data had the A2 allele (n=8). Dasatinib-related complications were common: pleural effusions and/or pulmonary infiltrates (n=8), modest CMV reactivation (n=5), severe colitis (n=5), which developed after appearance of LGL lymphocytosis. Immunophenotyping was available from 2 patients with pleural effusions: in both cases the majority of cells were CD3+CD8+ T-cells and no leukemic cells were detected. TCR gamma assay was done from one patient sample and it showed similar clonal pattern as in peripheral blood. However, despite frequent side-effects, response to dasatinib treatment was very good in all cases, including complete molecular responses in 5 advanced phase patients. Transient clonal LGL lymphocytosis has been described in few patient cases with a primary herpesvirus infection. Our patients share striking pheno/genotypic similarities with LGL leukemia, in which an antigen driven expansion of LGLs precedes the occurrence of oncogenic events. However, in our patients LGL lymphocytosis appeared to be a benign phenomenon. We postulate that by virtue of inhibition of key non-BCR-ABL kinases, dasatinib induces a reversible state of autoimmune-like reactivity upon antigen challenge in a proportion of patients with a distinct genetic and/or environmental background. The aberrant immune response may also result in enhanced anti-leukemic control driven by the cytotoxic T/NK LGL cells. Dasatinib could be a valuable tool in uncovering the pathogenesis of LGL lymphoproliferation, putatively related to mutations in kinases targeted by the drug.