COMPARISON OF INNATE IMMUNITY CHANGES FOLLOWING IBRUTINIB AND VENETOCLAX TREATMENT OF RELAPSED CHRONIC LYMPHOCYTIC LEUKAEMIA

Introduction: Chronic Lymphocytic Leukaemia (CLL) is associated with profound immunodeficiency and immune dysregulation. Dysfunction of cells of the innate immune system including NK cells, monocytes, and DCs may play important roles in CLL progression, limiting anti-tumour immune response and contributing to the CLL supportive microenvironment. CLL has been shown to be sensitive to immunological control either via monoclonal antibody therapy, immunomodulatory drug therapy or allogeneic transplant. Targeted small molecule inhibitors, including the BTK inhibitor Ibrutinib and the Bcl-2 inhibitor Venetoclax have revolutionised CLL treatment, yet detailed understanding of their immunological impact is still unfolding. Methods: Peripheral blood mononuclear cells were isolated from patients enrolled on ethically approved biomarker studies appended to either approved clinical trials or standard of care. Patients were treated with either Ibrutinib (n = 12) or Venetoclax (n = 6) for CLL progressing after initial standard chemotherapy. Samples were obtained immediately prior to treatment initiation (baseline) and after 12 months of therapy and from healthy age-matched donor controls (n = 10). Analysis was performed by flow cytometry using a BD LSRFortessa™ to profile the immune cell subsets using standard antibody panels to identify CD4+ and CD8+ T cells, NK cells, monocytes, myeloid-derived suppressor cells (MDSC), dendritic cells (mDC) and γδ T cells. The relative frequencies and absolute count of immune subsets were calculated. Wilcoxon test or Kruskal–Wallis ANOVA using p < 0.05 determined statistical significance. Results: Compared to pre-treatment baseline samples, both Ibrutinib and Venetoclax treatment resulted in a significant increase in the frequency and absolute number of both MDSC (HLADR-CD11b+CD33+) and normal monocytes (HLADR+CD11b+CD33+) to the same level (Ibrutinib) or in excess (Venetoclax) to those seen in healthy controls (Fig. 1). The frequency of mDC (HLADR+CD11c+) was significantly increased following Ibrutinib (but not Venetoclax) treatment. Following both Ibrutinib and Venetoclax treatment, a significant increase in the frequency of NK cells (CD3-CD56+) was seen, although only Venetoclax treatment resulted in a normalisation of NK cells comparable to healthy controls. Both Ibrutinib and Venetoclax treatment resulted in a significant increase in the frequency of γδ T cells. Keywords: chronic lymphocytic leukemia (CLL); immune system.