Studio degli effetti immunomodulanti del trattamento con ibrutinib nei pazienti affetti da leucemia linfatica cronica

Chronic lymphocytic leukemia (CLL) is a very common type of leukemia, characterized by clonal expansion and accumulation of mature CD5+ B lymphocytes in the peripheral blood and in secondary lymphoid organs. CLL is characterized by a wide range of immune alterations, which often associates to increased susceptibility to infections, occurrence of autoimmune phenomena and failure to control disease progression. From the clinical standpoint, CLL is a very heterogeneous disease. Some patients present an indolent course and do not require any therapy for years, whereas in others, the disease is rapidly progressive and specific treatment is needed. Ibrutinib, a Bruton’s tyrosine kinase (BTK) inhibitor, has become the standard of care for the majority of patients with CLL. Besides its direct anti-tumor activity, ibrutinib has shown to exert immunomodulatory effects. The aim of this study was to analyse phenotypic and functional immune changes occurring in multiple cell populations in CLL patients treated with ibrutinib. Forty patients with progressive CLL and the indication to start ibrutinib therapy were included in the study. Peripheral blood mononuclear cells (PBMC) were collected before treatment and after 1, 6, 12 and 24 months of ibrutinib therapy. A group of 15 CLL patients with early-stage disease, who were not fulfilling criteria for treatment start, and 15 healthy donors were analysed as comparison. PBMC were analysed by flow cytometry in order to assess: i) the percentage and the absolute number of lymphoid cell populations; ii) the expression of activation markers (i.e CD69) and inhibitory immune checkpoints (i.e PD-1, CTLA-4, TIM-3, TIGIT and CD96) on different cell populations. The proliferation ability of T cells in response to polyclonal stimuli, the cytotoxic activity of Vγ9Vδ2 T cells stimulated with zoledronic acid and IL-2, and the antibody dependent cellular cytotoxicity (ADCC) were evaluated by cell culture, immune assays, and flow cytometry. Results from our study show that ibrutinib treatments determined a progressive and significant reduction of the number of circulating leukemic CLL cells, which was paralleled by a normalization in the count of different immune cell populations. The phenotypic characterization of different immune compartments revealed that the expression of the CD69 activation marker and of the inhibitory immune checkpoint molecules were significantly downmodulated on T cells and NK cells after prolonged ibrutinib treatment (i.e 12 and 24 months). From the functional standpoint, we observed that the positive modulation of phenotypic markers was associated to an improvement in T-cell proliferative ability, Vγ9Vδ2 T-cell cytotoxicity and NK-cell-mediated ADCC of anti-CD20 antibody. Interestingly, the positive modulation of immune parameters occurring during ibrutinib treatment was mainly observed in patients achieving complete or partial clinical response. In conclusion, our results show that ibrutinib exerts a wide range of immune-modulating effects, which are mainly associated with the achievement of a clinical response to therapy.