Chronic Lymphocytic Leukemia (CLL): effect of the Syk kinase-inhibitors, Fostamatinib (R406) and Entospletinib (GS-9973), on T cell function and rituximab activity

COLADO ANA; ALMEJÚN MARÍA BELÉN; PODAZA ENRIQUE; RISNIK DENISE; FERNÁNDEZ GRECCO HORACIO; CABREJO MARÍA; CRANCO SANTIAGO; BURGOS RUBEN; SÁNCHEZ-ÁVALOS JULIO CÉSAR; BEZARES RAIMUNDO F; GIORDANO MIRTA; GAMBERALE ROMINA; BORGE MERCEDES

Mar del Plata

Congreso; XXII Congreso Argentino de Hematología; 2015

Leukemic cells from chronic lymphocytic leukemia (CLL) patients proliferate within lymphoid tissues in particular areas called proliferation centers, where they are in close contact with non-leukemic cells including activated CD4+ T cells, stroma and myeloid cells(1, 2). There, CLL cell proliferation, survival and resistance to cytotoxic agents is driven by molecules such as CD40L, expressed by activated T cells(3), the chemokines CCL19, CCL21 and CXCL12 secreted by stromal and myeloid cells(4,5), and stimulation throw the B-cell antigenic receptor (BCR)(6) favoring disease progression. At the present CLL is an incurable disease. Current therapies are effective in inducing initial remission in most patients but they are not curative and relapse is inevitable(7). In the past few years several inhibitors targeting kinases involved in the BCR-signaling have been developed, such as the Syk inhibitors R406 and GS-9973, the Btk inhibitor ibrutinib and the PI3Kδ inhibitor idelalisib. Results obtained in clinical trials with these agents have generated great excitement because of their clinical efficacy and excellent tolerability(7). We(8) and others(9-11) have recently reported that BCR-associated kinases inhibitors have immunomodulatory effects on the tumor microenvironment from CLL patients. Thus, we found that ibrutinib impaired the phagocytosis of rituximab-coated leukemic cells from CLL patients by human macrophages(8) and others found that ibrutinib inhibits the activation of Th2 cells after TCR stimulation(12), reducing the signals that drive leukemic cell expansion. Here, we aimed to evaluate the effect of R406 and GS-9973 on: 1) the physiology of CD4+ T from CLL patients and 2) macrophage mediated phagocytosis of rituximabcoated CLL cells. We first asked whether R406 and GS-9973 were able to inhibit T cell activation and proliferation. We used clinically relevant doses of the drugs and confirmed that these doses (between 0.1 and 5 μM) did not induce T cell apoptosis (not shown). In order to induce T cell activation, peripheral blood mononuclear cells from CLL patients were cultured in the presence of anti-CD3 antibodies with R406, GS-9973 or the vehicle of the drugs as a control (DMSO). We found that both inhibitors impaired the expression of the activation markers CD25, CD69 and CD40L on CD4+ T cells, evaluated by flow cytometry at 24 hs (p˂0.05) and the T-cell proliferation evaluated by the CFSE dilution assay at 5 days (p˂0.05). We also observed, by using the Transwell system assay, that both drugs inhibited T cell migration towards CCL19 and CCL21 (p˂0.05), key molecules involved in T cell homing to lymph nodes. Finally, we found that R406 and GS-9973 inhibited macrophagemediated phagocytosis of CLL cells coated with the anti-CD20 antibody rituximab as evaluated by flow cytometry (p˂0.05). Our results suggest that R406 and GS-9973 affect the tumor microenvironment, by inhibiting CD4+ T cell activation and thus reducing the supportive signals given to the malignant clone. Nevertheless, these results also suggest that in patients treated for long periods with these agents, the T cell-mediated immune response might be affected. We also found that both R406 or GS-9973 interfere with the macrophage-mediated anti-tumor activity of rituximab suggesting that the sequential and not the concurrent administration might enhance their antitumor activity in vivo and improve CLL therapy.