2022 - Prolonged treatment with ibrutinib modulates phenotypic and functional features of immune cell compartments in chronic lymphocytic leukemia

Introduction
CLL is characterized by a wide range of immune alterations, responsible for the increased susceptibility to infections, the occurrence of autoimmunity and the failure to control disease progression. Besides its direct anti-tumor activity, ibrutinib has shown to exert immunomodulatory effects. The aim of this study was to analyze immune changes occurring in CLL patients treated with ibrutinib.
Materials and Methods
Thirty-one patients with progressive CLL and the indication to start ibrutinib therapy were included. Peripheral blood samples were collected before and after 1, 6, 12 and 24 months of ibrutinib treatment. Fifteen additional patients with early-phase disease (ES-CLL) and 10 healthy donors (HD) were analyzed. Immune cell counts, the expression of surface markers and functional assays were performed by flow cytometry. Clinical response was assessed according to the IWCLL guidelines.
Results and discussion
At the 6-month timepoint, we observed a significantly lower value in the number of CLL cells, which persisted after 12 and 24 months of ibrutinib treatment. We detected a significant reduction of CD3+ and CD4+ T-cell counts at month 12, and a decrease of CD8+ T-cell number already at month 6 of therapy. Regarding γδ T-cell compartment, the count of Vδ1 T cells – but not Vγ9Vδ2 T cells – significantly decreased by 12 months of treatment. A prolonged (i.e. 24-month) therapy with ibrutinib also favored the normalization of Tregs, NK and NKT-cell counts. Before treatment, we found a higher expression of the activation marker CD69 on T cells from pre-treatment compared to ES-CLL and HD, which normalized after 6 months of therapy. Phenotypic analysis revealed that PD-1 expression on CD8+ T cells was significantly lowered by 6 and 12 months of ibrutinib treatment. Ibrutinib also induced a significant downmodulation of other inhibitory checkpoints expressed on T cells: CTLA-4, CD96, Tim-3 and TIGIT. Of note, TIGIT expression was reduced on Tregs at 12 months of therapy. Similar to T cells, CD69, CD96, TIGIT and Tim-3 were significantly decreased overtime by ibrutinib therapy on NK and NKT cells. Functional data showed that, besides a positive phenotypic modulation, 12 months of ibrutinib treatment enhanced Vγ9Vδ2 T-cell cytotoxicity and NK-cell-mediated ADCC of obinutuzumab towards MEC-1 cell line. An improvement in the proliferation of both CD4+ and CD8+ T cells was also detected at month 24. The correlation of phenotypic changes with clinical response at 12 months demonstrated that the positive immunomodulatory effects of ibrutinib were mainly observed in patients achieving a partial (n=21) or complete (n=2) response and not in patients with a stable disease (n=8).
Conclusions
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.