Exploring the immunology of small molecule inhibitors in chronic lymphocytic leukaemia

© 2019 Chia Elizabeth SharpeChronic lymphocytic leukaemia (CLL) is the most common adult leukaemia in the western world. CLL is associated with profound immunodeficiency which leaves patients with insufficient anti-tumour immunity and is often compounded by immunosuppressive treatments. Recent advances in the development of targeted small molecule inhibitors, including Bruton’s tyrosine kinase (BTK) and B-cell lymphoma 2 (Bcl-2) inhibitors, has provided new, highly effective and less immunosuppressive treatment options. However, targeted therapies have not yet provided a cure for CLL, and there is still a need to improve the depth and durability of patient responses. Immunotherapies harness the patient’s own immune system to target cancer cells and are an attractive modality for combination with targeted therapies. However, by both on- or off-target mechanisms targeted therapies also been shown to have the potential to disrupt normal immune populations. This study aimed to understand the effects of targeted therapies on the immune system, thereby providing insight into the potential opportunities and pitfalls for the combination of immunotherapy with targeted therapies in CLL. This thesis explored the immunological impacts of the first-generation BTK inhibitor ibrutinib, as well as two more selective second-generation inhibitors zanubrutinib and acalabrutinib. The Bcl-2 inhibitor venetoclax was also investigated both as monotherapy and in combination with BTK inhibition. In Chapter 3, gene expression analysis was used to faithfully replicate a comprehensive immune profile comparable to more time consuming and costly flow cytometry analysis. Chapter 4 demonstrated that BTK and Bcl2 inhibitors had distinct effects on the immune profile of patients after long-term treatment with targeted therapies. Chapter 5 utilised in vitro functional assays to demonstrate how effector functions of T cells and natural killer (NK) cells, including cytotoxicity, cytokine production, and proliferation, are impaired by BTK inhibitors whereas NK cells, but not T cells were sensitive to venetoclax treatment. Subsequently, Chapter 6 explored the effect of the immunomodulatory drugs lenalidomide and a PD-1 inhibitor BGB-A317 in combination with ibrutinib, showing that T cell activation is modulated by both ibrutinib and the immunotherapies. These finding presented in this thesis demonstrate that targeted therapies have clear and distinct immunological effects. Ibrutinib broadly impair the function of multiple immune populations and in particular cellular cytotoxicity, suggesting that more selective BTK inhibitors are better candidates for combination with immunotherapies. Venetoclax affected the survival of specific T cell and NK cell populations, suggesting that long-term venetoclax treatment may result in alterations in the immune profile that may be exploited by combination therapy. These findings highlight the importance of understanding the immunological impacts of targeted therapies when incorporating immunotherapies into treatment combinations