ABSTRACT Cancer immunotherapies represent a powerful and newly emergent therapeutic paradigm, both because of their durable clinical responses and applicability to a wide variety of tumors. Immune checkpoint therapies block inhibitory receptors on T cells in order to augment anti-tumor immune responses. Programmed cell death protein 1 (PD-1) is a critical inhibitory checkpoint for T cells. The identification and clearance of malignant cells can be brought about by antibodies which block PD-1. Despite the success of these antibodies, most patients do not respond to PD-1 blockade, and many experience immune-related adverse events. New studies indicate that some 5-10% of patients demonstrate accelerated cancer progression after anti-PD-1 treatment, in contrast to predicted responses based on current mechanistic models. With both the potential successes and failures of PD-1 being so significant, the need to understand PD-1 signaling is evidently very urgent, both for explaining the mechanism of clinical responses and for developing therapeutics that go beyond simply interfering with ligand binding. We have developed a new method to analyze mass spectrometry data and discovered novel effectors of PD-1 signaling. Most excitingly, we have identified multiple candidates, including the kinase VRK2 which we intend to investigate further. The overarching goal of this proposal is to study PD-1-associated kinases in order to better define novel signaling pathways and to uncover T cell-intrinsic mechanisms which contribute to resistance to PD-1 blockade. In the first aim, we will discover the molecular mechanism by which VRK2 controls PD-1 signaling in T cells. We will perform structure-function analyses to test the hypothesis that VRK2’s enzymatic domain is required for mediating specific PD-1 functions and utilize biochemical and imaging approaches to uncover the contribution made by VRK2 interactions with MAPK8IP1 and MAP3K7 towards PD-1 signaling. In the second aim we will test the hypothesis that VRK2 is required for PD-1 inhibition of cellular functions in vivo. We will utilize VRK2 KO mice to uncover the mechanism by which VRK2 supports tumor growth in vivo in the context of PD-1 blockade and resistance. Given the large impact of PD- 1 on public health, the proposed work is incredibly significant.

NARRATIVE Cancer immunotherapies represent a powerful therapeutic paradigm because they are applicable to a wide variety of tumors and can produce durable clinical responses; however, only a fraction of patients experience clinical benefit from current immunotherapies, and as such there is an urgent need to develop new therapies. Our studies will focus on the immune cells underlying the resistance to current immunotherapies. Uncovering novel aspects of the immune system is crucial not just for better understanding the biology of the immune response to tumor, but also for designing the next generation therapeutics.