Abstract: Despite idelalisib approval in relapsed follicular lymphoma (FL), a complete characterization of the immunomodulatory consequences of phosphatidylinositol 3-kinase δ (PI3Kδ) inhibition, biomarkers of response, and potential combinatorial therapies in FL remain to be established. Using ex vivo cocultures of FL patient biopsies and follicular dendritic cells (FDCs) to mimic the germinal center (n = 42), we uncovered that PI3Kδ inhibition interferes with FDC-induced genes related to angiogenesis, extracellular matrix formation, and transendothelial migration in a subset of FL samples, defining an 18-gene signature fingerprint of idelalisib sensitivity. A common hallmark of idelalisib found in all FL cases was its interference with the CD40/CD40L pathway and induced proliferation, together with the downregulation of proteins crucial for B–T-cell synapses, leading to an inefficient cross talk between FL cells and the supportive T-follicular helper cells (TFH). Moreover, idelalisib downmodulates the chemokine CCL22, hampering the recruitment of TFH and immunosupressive T-regulatory cells to the FL niche, leading to a less supportive and tolerogenic immune microenvironment. Finally, using BH3 profiling, we uncovered that FL–FDC and FL–macrophage cocultures augment tumor addiction to BCL-XL and MCL-1 or BFL-1, respectively, limiting the cytotoxic activity of the BCL-2 inhibitor venetoclax. Idelalisib restored FL dependence on BCL-2 and venetoclax activity. In summary, idelalisib exhibits a patient-dependent activity toward angiogenesis and lymphoma dissemination. In all FL cases, idelalisib exerts a general reshaping of the FL immune microenvironment and restores dependence on BCL-2, predisposing FL to cell death, providing a mechanistic rationale for investigating the combination of PI3Kδ inhibitors and venetoclax in clinical trials.

Abstract: BACKGROUND: An important progress has been made in understanding the pathophysiology of lower risk MDS in recent years. This progress has been more relevant in some specific subtypes such as del(5q) MDS or MDS with RS ( & gt;15% RS in BM or & gt;5% RS + SF3B1 mut). In fact, for the latter subtype, in-depth knowledge of its pathophysiology has led to the recent development of new therapeutic strategies (luspatercept). In this regard, new WHO 2017 classification identify in the lower risk MDS setting 2 categories of patients with different clinical and biological features: those without RS ( & lt;5%) and those with RS, involving 2 subgroup of patients (those with & gt;15% of RS and those with & lt;15% and & gt;5% of RS and the presence of SF3B1 mutations. Unfortunately, no clear data regarding disease characteristics and outcome have been analyzed to identify these 3 new subgroups of patients, are those with 5-15RS really like those with & gt;15RS? Therefore, improving knowledge in real life setting of these subgroups of patients will lead to optimize the therapeutic management and the potential development of new therapeutic strategies. AIMS: Our aim was to describe baseline clinical characteristics and their implication in overall survival (OS), progression free survival (PFS) and transfusion free survival (TfFS) among LR-MDS according to the presence of RS. We compare 3 sub-categories within the current WHO classification. METHODS: A retrospective study from the Spanish MDS registry was performed in which patients diagnosed with low-risk MDS (Very low to int risk IPSS-R) were selected. MDS with excess of blasts, del(5q) and/or MDS/MPS were excluded. Finally, 2250 patients were selected which were classified according to the percentage of RS into three groups: 1) patients without RS (defined as less than 5% RS, & lt;5RS) (n=1256), 2) patients with ≥5% and & lt; 15% RS (5-15RS) (n=196) and 3) patients with ≥ 15% RS( & gt;15RS) (n=1098). Descriptive analysis and survival estimation was done according to classical definitions (OS, PFS). Transfusion free survival (TfS) was defined from diagnosis to the development of transfusion dependency. RESULTS: In & lt;5RS group, median age at diagnosis was 75.0 years [p25-p75 68.0;81.0] and 61% patients were male. Main clinical characteristics are summarized in table 1. Patients with & lt;5RS had higher hemoglobin level than the others with also a smaller MCV. However, neutrophils and platelets counts were lower in & lt;5RS subgroup compared to 5-15RS and & gt;15RS patients. Ferritin level at diagnosis was also lower for & lt;5RS. Less than 50% of & lt;5RS patients had an hypercellular BM as opposed to almost 70% in & gt;15RS group and as expected, erythroid cellularity was lower in & lt;5RS as compared to & gt;15RS. Regarding single or multiline dysplasia, patients with & lt;5RS and 5-15RS generally developed multiline dysplasia (74% and 77%, respectively) as compared to those with & gt;15RS (47%). Median blast% was higher in patients with & lt;5RS compared to the other groups. Moreover, the percentage of micromegakaryocytes (adverse prognosis) observed was higher in the group with & lt;5RS and 5-15RS. No clear differences were observed according to cytogenetic abnormalities. Median follow-up was 4.1 years. Interestingly, median OS and range (p25-p75) for & lt;5RS pts was 5.67 yr (2.4-10.2), close similar to 5-15RS pts (4.93 yr 2.4-10.6) and inferior to & gt;15RS pts (7.66 yr 3.7-12.3) p & lt;0.0001 (Figure1). Progression to RAEB/AML was observed in 11.3%, 9.69% and 7.01% of patients in & lt;5RS, 5-15RS and & gt;15RS groups respectively (p=0.002). In this sense, PFS for LR-MDS with & lt;5RS was 5.1 yr (2.1-9.8), close similar to the 5-15RS group (4.77 yr (1.9-10.7)) and inferior to & gt;15RS pts (7.01 yr (3.5-12.3) (p & lt;0.0001). Contrary to OS/PFS, TfFS was favorable to the & lt;5RS group (median 3.2 yr 0.1-10.4) as compared to 5-15RS (2.13 yr 0.1-6.6) and & gt;15RS (2.4 yr 0.1-7.6) patients (Figure2, p=0.02). SUMMARY: Clinical and biological characteristics of LR-MDS patients according to RS are different and impact on survival, disease evolution and need of treatment. Patients with 5-15RS are in an intermediate situation from & lt;5RS and & gt;15RS regarding clinical and biological variables and with poorer outcome than & gt;15RS patients. A better understanding of these subgroups could help us to personalize therapeutic options in this heterogeneous subset of patients. Figure 1 Figure 1. Disclosures Sanz: Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Roche: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Travel, accommodations, and expenses; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Boehringer Ingelheim: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Travel, accommodations, and expenses, Speakers Bureau; Gilead Sciences: Other: Travel, accommodations, and expenses; Helsinn Healthcare: Consultancy, Membership on an entity's Board of Directors or advisory committees; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, accommodations, and expenses, Research Funding. Tormo: Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Jazz Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Valcárcel: Sanofi: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizzer: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; MSD: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Jazz: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Jansen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene/BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Astellas: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Sobi: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Diez-Campelo: BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Takeda Oncology: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau.

Abstract: INTRODUCTION: Recently, new understanding of monoclonal gammopathy pathogenesis highlighted possible disease initiation by viral infection in subsets of patients, notably by hepatitis C virus (HCV). If the infectious pathogen targeted by the monoclonal Ig could be eliminated at the monoclonal gammopathy of undetermined significance (MGUS) stage, chronic antigen-stimulation could disappear, leading in turn to the disappearance of the monoclonal Ig. Here we report a series of patients with monoclonal gammopathy and HCV infection, whose disease prognosis clearly improved, even reached complete remission, after antiviral treatment. METHODS: Nine patients diagnosed with MGUS (n=6) or multiple myeloma (MM) (n=3) after HCV infection were included in the study and classified into two groups: patients who received antiviral treatment, and patients who did not receive anti-viral treatment. Disease status was monitored by the quantification of the monoclonal immunoglobulin (mc Ig) level. The HCV burden was determined by RT-qPCR. Each patient's mc Ig was isolated from polyclonal immunoglobulins by agarose gel electrophoresis and mc Ig purity was evaluated by isoelectric focusing. The multiplex infectious antigen microarray (MIAA) was used to analyze the reactivity of serum immunoglobulins and of monoclonal Ig against commercially available antigens and/or lysates from different microorganisms. The INNO-LIA™ HCV Score assay (Fujirebio) was used to analyze the reactivity of monoclonal Ig to HCV proteins. RESULTS: Regarding patients treated with antiviral drugs (4 MGUS, 2 MM), mc Ig levels in serum decreased after antiviral treatment. MGUS patients remained in a stable status without disease progression. After antiviral treatment, one MM patient who was in third relapse achieved complete remission with minimal residual disease negativity. As expected, the HCV load decreased after antiviral therapy to undetectable levels. Serum samples from patients were reactive against antigens of various viruses and other microorganisms, but analysis of the specificity of recognition of the purified mc Ig of each patient revealed that it targeted HCV, either the core protein (C1, C2), NS3, or NS4. In contrast, for patients who did not receive antiviral treatment (2 MGUS, 1 MM), MGUS and MM disease progressed and the mc Ig level remained stable or increased. Serum samples from these patients were reactive against various viruses and other microorganisms, but their mc Ig did not recognize HCV proteins. CONCLUSION: In this study of monoclonal gammopathies where the mc Ig targeted HCV, successful HCV eradication with antivirals resulted in improvement of MGUS and MM disease as well as of hepatitis C. Our findings suggest that for HCV-positive individuals who were infected before being diagnosed with MGUS or MM, a causal relationship exists between HCV infection and the development of MGUS and MM, and both MGUS and MM patients infected with HCV may benefit from early anti-HCV therapy. Disclosures No relevant conflicts of interest to declare.

Abstract: Daratumumab (DARA) is a human CD38 antibody with broad-spectrum killing activity. DARA induces killing of tumor cells, mainly via complement-dependent cytotoxicity (CDC) and antibody-dependent cell-mediated cytotoxicity (ADCC) (de Weers M, J Immunol 2011). DARA is currently being evaluated in phase I/II clinical trials in patients with multiple myeloma. In these clinical studies the adverse events have been manageable and marked reductions in paraprotein and bone marrow plasma cells have been observed. We have previously reported (Blood (ASH annual meeting abstracts). Nov 2012, 120 (21): 3935) that DARA induces cytotoxic activity in vitro via ADCC in primary cells and cell lines from Mantle Cell Lymphoma (MCL), Follicular Lymphoma (FL) and Chronic Lymphoctic Leukemia (CLL). CDC induction was low, which is associated to high expression of the complement inhibitors and reduced number of CD38 molecules per cell in these indications. This suggests a threshold for CD38-targeted CDC lysis. In addition, based on known interactions between CD38-CXCR4, we also demonstrated that in the CLL subtype, with high CD38 and more migratory capacity, DARA (10-30 µg/mL) inhibited in vitro CXCL12/SDF1α-mediated migration up to 70%. Here, we present the first preclinical in vivo results of DARA in mouse models of MCL, transformed FL(tFL) and CLL. We generated heterotopic and systemic mouse models of these entities by subcutaneous or intravenous inoculation of tumor cell lines in SCID mice, that retain both NK cells and macrophages as potential effector cells. In MCL (REC cell line) and tFL (RL cell line) subcutaneous mouse models, we tested DARA activity in both prophylactic (treatment initiation simultaneous to lymphoma cell inoculation) and therapeutic settings(treatment initiation one week after lymphoma cell inoculation, when tumors were about 100 mm3 in size). In the prophylactic setting, mice received 3 doses of DARA or control IgG bi-weekly (20/10/10 mg/kg). In the therapeutic setting, treatment was intensified to 4 doses of DARA or control IgG weekly (20/10/10/10 mg/kg). In both schedules, mice were sacrificed one week after the last dose. DARA completely abrogated tumor growth of REC or RL cells in the prophylactic setting. Moreover, in the therapeutic setting, DARA induced total tumor regression of REC tumors in 4 out of 6 mice, and prevented the splenomegaly observed in control IgG treated mice. In the case of tFL and therapeutic setting, DARA reduced 60% of tumor growth compared to control IgG treated mice at day 32, when experiment was finished. In CLL, we analyzed the effect of DARA on cell homing to lymphoid organs together with its therapeutic properties in a systemic CLL mouse model. Using NOD/SCID/gamma null mice (lacking NK cells and effective macrophages), we analyzed the effect of DARA on primary CLL cell migration from Peripheral Blood (PB) to bone marrow (BM) and Spleen. In this system, NSG mice were pretreated (day 0) with DARA, control IgG or anti-CXCR4 as positive control for inhibition of cell homing, followed by fresh CLL cell inoculation (50×106 cells/per mice) on day 1. PB, BM and spleen cells were isolated on day 2 and CLL cells were identified by staining for CD45/CD19/CD5 and counted using a flow cytometer. Cell counting showed that CLL cells mainly migrate to the spleen, and that DARA significantly reduced this migration (55% inhibition on average, p 〈 0.05). Migration of CLL cells to BM was limited and was not affected by pretreatment of mice with DARA. Finally, we tested DARA therapeutic activity in a systemic CLL mouse model (MEC2 cell line), following the schedule described before (4 doses of control IgG/ DARA weekly (20/10/10/10 mg/kg)), and assessed efficacy on mice overall survival. Mice treated with control IgG started to lose weight and showed signs of disease between days 30-40 and were sacrificed for ethical reasons. In the DARA treated group, in 7 out of 8 mice survival was extended up to day 90, when the experiment was stopped. In conclusion, DARA demonstrated strong in vivo activity in immunocompromised mouse models of MCL, tFL and CLL cell lines and interfered with homing of primary CLL cells to the spleen. These results warrant further investigation of DARA in clinical trials for these indications. Disclosures: Lopez-Guillermo: Roche: Membership on an entity’s Board of Directors or advisory committees. Lammerts van Bueren:Genmab: Employment, Stocks Other. Bakker:Genmab: Employment, Stocks Other. Parren:Genmab: Employment, Stocks Other. Perez-Galan:Genmab: Research Funding.

Abstract: Abstract 3935 Daratumumab (DARA) is a human CD38 antibody with broad-spectrum killing activity. DARA induces killing of tumor cells, mainly via complement-dependent cytotoxicity (CDC) and antibody-dependent cell-mediated cytotoxicity (ADCC) (de Weers M, J Immunol 2011). DARA is currently being evaluated in phase I/II clinical trials in patients with multiple myeloma. In these clinical studies the adverse events have been manageable and marked reductions in paraprotein and bone marrow plasma cells have been observed. In the present study, we have analyzed the potential of targeting CD38 using DARA in two types of B-cell non-Hodgkin lymphoma (B-NHL) (follicular lymphoma (FL) and mantle cell lymphoma (MCL)), and in chronic lymphocytic leukemia (CLL). Flow cytometry analysis demonstrated that MCL and CLL tumor cells show heterogeneous expression of CD38, while FL cells showed invariable high CD38 levels. CD38 has attracted special attention in CLL where high CD38 expression is a marker of bad prognosis (Hamblin et al, Blood 1999 and 2002) and is expressed preferentially in the proliferating fraction of the tumor (Damle RN, Blood 2007). In addition, we have recently shown that high CD38 expression in MCL was associated with resistance to the proteasome inhibitor bortezomib (Pérez-Galán P, Blood 2011). Here, we tested the cytotoxic activity of DARA in tumor cell lines and in fresh tumor cells obtained from patients. DARA did not induce CDC in MCL cell lines (MINO, REC, HBL2, JEKO), irrespective of CD38 expression levels. Also, FL cell lines (WSU-FSCCL, RL) expressing relatively high CD38 levels were insensitive to DARA-induced CDC. This low CDC was associated with high expression of the complement inhibitors CD55 and CD59. In addition, the number of CD38 molecules per cell in these MCL and FL cell lines was lower than that found on the CDC-sensitive Daudi Burkitt lymphoma cell line, suggesting a threshold for CD38-targeted CDC lysis. In the presence of PBMC effector cells obtained from healthy donors, DARA showed significant levels of ADCC in cells from MCL, FL and CLL. In CLL primary cases (n=8) tested, DARA (14–43% lysis) was generally superior or at least equally effective (mean+/−SD=28,78 +/− 9,78) in inducing ADCC as compared to the anti-CD20 antibodies ofatumumab (mean+/−SD=21,35 +/− 15,71) and rituximab (mean+/−SD=29,30 +/− 15,90). The immunomodulatory agent lenalidomide shows considerable single agent activity in MCL, FL and CLL. Interestingly, it has been shown that lenalidomide may be able to increase ADCC, probably via activation of NK cells. We therefore tested whether the combination of lenalidomide and DARA could enhance ADCC. Noteworthy, DARA-induced ADCC in MCL, FL cell lines and primary CLL cells was significantly (p 〈 0,05) enhanced when effector cells were pretreated with the immunomodulatory agent lenalidomide (3 μM, 72 h) with DARA doses ranging from 0,01–1 μg/ml. Finally, CD38 is important for cell migration and adhesion, especially for CXCR4-CXCL12-induced migration of tumor cells (Vaisitti et al, Leukemia 2010). Our preliminary results suggest that in the CLL subtype with high CD38 and more migratory capacity DARA (10–30 μg/ml) inhibits CXCL12/SDF1α mediated migration up to 70%. These results are of high importance because inhibition of tumor cell trafficking to tissue sites as bone marrow and lymph nodes, may be clinically relevant, as increasing evidence indicates that tumor–microenvironment interactions may play an important role in drug resistance and contribute to clinical failures. We are currently validating this in vitro results in a CLL mouse model. Taken together, these results suggest that DARA may be a promising therapeutic agent both for MCL, FL and CLL, in which DARA exerts its effects mainly via ADCC and for CLL also via inhibition of migration of tumor cells. Interestingly, the cytotoxic activity of DARA by ADCC could be further augmented by addition of lenalidomide in these three models. Disclosures: Lammerts van Bueren: Genmab: Employment. Bakker:genmab: Employment. Parren:genmab: Employment. Perez-Galan:Genmab: Research Funding.

Abstract: Positron emission tomography (PET) with 18fluorine-fluoro-deoxyglucose (FDG) integrated with computed tomography (PET/CT) is a functional imaging technique helping us to assess bone marrow infiltration as well as unsuspected disease sites involving the bones and/or extramedullary sites. PET/TC has proved to be an independent prognostic factor for overall survival (OS) in symptomatic multiple myeloma (MM)(Zamagni,2011). However, its role in other monoclonal gammopathies (MG) is still a matter of debate. We have prospectively analyzed the contribution of baseline PET/TC in a unselected consecutive series of 158 patients with MG, including 88 MM, 7 MM smoldering (MMS), 11 Waldenstrm's macroglobulinemia (WM), 3 WM smoldering (WMS), 3 solitary bone plasmacytoma (SBP) and 46 monoclonal gammopathy of uncertain significance (MGUS). Patients with only palliative care were excluded. The pattern of bone marrow uptake on PET/TC was described as negative (NEG), diffuse involvement (DI) or focal lesions (FLs). Patients with more than 3 FLs as well as the presence of extramedullary disease (EMD) were analyzed separately. Overall survival (OS) was estimated by the Kaplan-Meier method. The main characteristics of PET/TC findings according to the type of MG are shown in Table 1. PET/TC was positive in 70 (79,5 %) of MM and 8 (72,7%) of WM. PET/TC was NEG in 100 % of MMS, WMS and SBP (except for the primary lesion). In MGUS, the findings reflect the clinical heterogeneity of this group: 19,6 % had bone disease (all but one case of probable inflammatory etiology), 17,4 % positive lymphadenopathy, 15,2 % lung disease (infection, fibrosis, pulmonary nodules), 6,5 % splenomegaly, 6,5 % liver disease, 6,5 % positive uptake in adrenal gland and other organs such as thyroid, stomach, colon or skin were affected less frequently. Median age of MM patients was 62 years (12-91), 51 men and 37 women (42%), the distribution according ISS was I (36,5 %), II (28,2 %) and III (35,3%). Among PET-positive MM, 39 (55,7 %) had 〉 3 FLs, 17 (24,3 %) 3 or less FLs and 14 (24,3 %) DI. Median OS was 40 months, not reached (NR) and 85,7 months, respectively (p=ns). Mean bone marrow plasma cells in the 〉 3 FLs group vs 3 or less FLs was 25 vs 12 (p=0,028). EMD was present in 13 (18,6 %) of PET-positive MM. Response with PET/CT was available in 32 patients: 18 achieved CR, 8 PR and 8 progressed. OS was NR for CR and PR vs 40 months (p 〈 0,0001). In WM, patients with NEG or FL had NR OS vs 26 months in those with DI (p=0,16). PET/CT is positive in the majority of MM and WM patients, helping to separate patients with true indolent disease. At baseline, PET/TC is a useful tool to improve prognostic assessment in patients with MG. MM with 〉 3 FLs or EMD at baseline had a trend towards lower OS. Negative serial PET/CT in MM is associated with favorable prognosis. Table SEQ Tabla \* ARABIC 1. Characteristics of main PET/TC findings according to the type of MG Type MM MMS WM WMS SBP MGUS n 88 7 11 3 3 46 Positive n /% 70/79,5 0 8/72,7 0 0 9/19,6 - 〉 3 FLs 39/55,7 0 0 0 0 0 -3 or 〈 FLs 17/24,3 0 1/12,5 0 0 1/2,2 -DI 14/20 0 5/62,5 0 0 1/2,2 -EMD 13/18,6 0 0 0 0 0 -Adenopathy 2/2,9 2/28,6 2/25 0 0 8/17,4 -Spleen 3/4,3 0 1/12,5 0 0 3/6,5 MG: Monoclonal gammopathy; MM: Multiple myeloma symptomatic; MMS: Smoldering myeloma; WM: Waldenstrm's macroglobulinemia; WMS: Smoldering Waldenstrm's macroglobulinemia; SBP: Solitary bone plasmocytoma; MGUS: Monoclonal gammopathy of uncertain significance; FL: Focal lesion; DI: Diffuse involvement; EMD: Extramedullary disease. Disclosures No relevant conflicts of interest to declare.

Abstract: Abstract 1815 AICAR (5-aminoimidazole-4-carboxamide riboside or acadesine) induces apoptosis in chronic lymphocytic leukemia (CLL) cells, without affecting primary T lymphocytes (Campàs et al, Bood 2003). Available treatments for this disease generally induce remission, although nearly all patients relapse and CLL remains incurable. Thus, AICAR is a promising drug for the treatment of this B-cell neoplasm. It has been recently published that AICAR induces apoptosis by a p53- and AMPK-independent mechanism through upregulation of BIM and NOXA in CLL cells (Santidrián & González-Gironès et al, Blood in press). A clinical phase I/II study of AICAR is currently being conducted in CLL patients (http://clinicaltrials.gov/ct2/NCT00559624 ). This clinical study has shown that AICAR plasmatic levels in the micro molar range are achievable and safe when CLL patients are treated with the drug. In vivo assays were performed in mice to analyze the effects of AICAR on the peripheral lymphocyte population. Thus, 0.5 mg/g AICAR was administered intraperitoneally to Balb/c mice every 12 hours and every day blood was collected from the tail of treated (n = 3) and untreated (n = 3) mice. Significant differences (p 〈 .05) were observed between control and treated groups in the number of lymphocytes from day 3 to 6 while the number of total leucocytes did not change. From day 4 the peripheral lymphocyte population started to recover and mice were sacrificed at day 8. In addition, AICAR induced a significant reduction (p 〈 .05) on the percentage of B cells from day 3 to 5. Therefore, AICAR is effective in vivo decreasing the number of peripheral B lymphocytes. From the therapeutic point of view, it is interesting to analyze whether AICAR could synergize with the cytotoxic activity of the current chemotherapy used in CLL patients. Thus, cells from CLL patients (n = 4) were treated with AICAR (0.125, 0.25, 0.5 and 1 mM) and/or dexamethasone (1, 2.5, 5 and 10 μM), fludarabine (0.3, 0.6, 1.5 and 3 μM), chlorambucil (1.25, 2.5, 5 and 10 μM), mafosfamide (the active metabolite of cyclophosphamide) (0.25, 0.5, 1 and 2 μg/mL), rituximab (10, 25, 50 and 100 μg/mL) or alemtuzumab (1.25, 2.5, 5 and 10 μg/mL). The cytotoxic effect of the alkylating agents chlorambucil and mafosfamide was synergic or additive with the effect of AICAR in CLL cells depending on the concentration used of both drugs. The glucocorticoid dexamethasone synergized with AICAR in half of the samples analyzed. As for the nucleoside analogue fludarabine and the monoclonal antibodies rituximab and alemtuzumab, their apoptotic effect was additive with AICAR at some concentrations. Together, AICAR induces apoptosis in B lymphocytes from Balb/c mice when administered intraperitoneally and its cytotoxic effect in CLL cells is synergic or additive with the most common chemotherapy used in CLL treatment. Disclosures: de Frias: Advancell: Employment. Campàs:Advancell: Employment.