Immune consequences of tyrosine kinase inhibitors that synergize with cancer immunotherapy

Combination therapy for the treatment of cancer is becoming increasingly essential as we gain improved understanding of the complexity of cancer progression and the mechanisms by which cancer cells become resistant to single-agent therapy. Recent studies, both clinical and preclinical, have suggested that immunotherapy is a promising approach to the treatment of cancer; however, strategies to improve its clinical efficacy are still needed. A number of recent studies have indicated that antiangiogenic tyrosine kinase inhibitors (TKIs) target multiple components of the tumor microenvironment and are an ideal class of agents for synergizing with cancer immunotherapy. TKIs are well known to modulate tumor endothelial cells, leading to vascular normalization; however, these agents have also been recently shown to decrease tumor compactness and tight junctions, thereby reducing solid tumor pressure and allowing for improved perfusion of collapsed vessels and increased tumor oxygenation. In addition, some TKIs are capable of inducing immunogenic modulation, whereby tumor cells are sensitized to killing by T lymphocytes. Moreover, a number of TKIs have been shown to be involved in immune subset conditioning, increasing the frequency and function of effector immune elements, while decreasing the number and function of immune suppressor cells. The alteration of the immune landscape, direct modification of tumor cells, and improved vascular perfusion leads to improved antitumor efficacy when antiangiogenic TKIs are combined with immunotherapy. Collectively, the data presented in this review support the clinical combination of multi-targeted antiangiogenic TKIs, including but not limited to cabozantinib, sunitinib, and sorafenib, as well as to other antiangiogenic therapies, such as the anti-VEGF antibody bevacizumab, with cancer vaccines for improved treatment of solid tumors.