RESUMO
Natural killer (NK) cells are cytotoxic lymphocytes that substantially contribute to the therapeutic benefit of antitumor antibodies like Rituximab, a crucial component in the treatment of B-cell malignancies. In chronic lymphocytic leukemia (CLL), the ability of NK cells to lyse the malignant cells and to mediate antibody-dependent cellular cytotoxicity upon Fc receptor stimulation is compromised, but the underlying mechanisms are largely unclear. We report here that NK-cells activation-dependently produce the tumor necrosis factor family member 'B-cell activating factor' (BAFF) in soluble form with no detectable surface expression, also in response to Fc receptor triggering by therapeutic CD20-antibodies. BAFF in turn enhanced the metabolic activity of primary CLL cells and impaired direct and Rituximab-induced lysis of CLL cells without affecting NK reactivity per se. The neutralizing BAFF antibody Belimumab, which is approved for treatment of systemic lupus erythematosus, prevented the effects of BAFF on the metabolism of CLL cells and restored their susceptibility to direct and Rituximab-induced NK-cell killing in allogeneic and autologous experimental systems. Our findings unravel the involvement of BAFF in the resistance of CLL cells to NK-cell antitumor immunity and Rituximab treatment and point to a benefit of combinatory approaches employing BAFF-neutralizing drugs in B-cell malignancies.
Assuntos
Anticorpos Monoclonais Humanizados/farmacologia , Anticorpos Monoclonais Murinos/farmacologia , Citotoxicidade Celular Dependente de Anticorpos/efeitos dos fármacos , Fator Ativador de Células B/imunologia , Células Matadoras Naturais/imunologia , Leucemia Linfocítica Crônica de Células B/tratamento farmacológico , Leucemia Linfocítica Crônica de Células B/imunologia , Antineoplásicos/farmacologia , Apoptose , Fator Ativador de Células B/antagonistas & inibidores , Fator Ativador de Células B/genética , Linfócitos B/efeitos dos fármacos , Linfócitos B/imunologia , Western Blotting , Proliferação de Células , Ensaio de Imunoadsorção Enzimática , Citometria de Fluxo , Humanos , Técnicas Imunoenzimáticas , Imunossupressores/farmacologia , Células Matadoras Naturais/efeitos dos fármacos , Fragmentos de Peptídeos/análise , RNA Mensageiro/genética , Reação em Cadeia da Polimerase em Tempo Real , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Rituximab , Espectrometria de Massas por Ionização e Dessorção a Laser Assistida por Matriz , Células Tumorais CultivadasRESUMO
Natural killer (NK) cells play an important role in the immunosurveillance of hematopoietic malignancies. Their reactivity is influenced by activating and inhibitory signals mediated by tumor-expressed ligands for NK receptors. Many members of the tumor necrosis factor (TNF) family modulate differentiation, proliferation, activation and death of both tumor and immune effector cells. The TNF receptor family member glucocorticoid-induced TNFR-related protein (GITR) stimulates anti-tumor immunity in mice, but available data indicate that GITR may mediate different effects in mice and men and impairs the reactivity of human NK cells. Here, we comprehensively studied the expression and function of GITR ligand (GITRL) in leukemia. Among the different leukemia entities, pronounced expression of GITRL on leukemic cells was observed in chronic lymphocytic leukemia (CLL), and the GITR receptor was expressed at significantly higher levels on NK cells of CLL patients compared with healthy controls. Upon GITR-GITRL interaction, signaling via GITRL into the leukemia cells induced the release of interleukin (IL)-6, IL-8 and TNF, which act as growth and survival factors for CLL cells. In addition, GITRL impaired both direct and Rituximab-induced degranulation, cytotoxicity and interferon-γ production of NK cells, which could be restored by GITR blocking antibodies. Thus, GITRL may contribute to disease pathophysiology and resistance to direct and Rituximab-induced NK reactivity in CLL.