Host and microbe-dependent mechanisms of enhanced autoimmune susceptibility driven by checkpoint inhibitors

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Project Summary Immune checkpoint inhibitor therapy has drastically improved the prognosis of patients with several advanced- stage cancers that were initially considered terminal. However, the increased use of checkpoint inhibitors has resulted in the common emergence of immune-related adverse events (irAEs). Even though they are typically excluded from clinical trials, in clinical practice, patients with autoimmune predisposition are offered checkpoint inhibitors and have the greatest risk for developing irAEs. The mechanism driving this immune toxicity is poorly understood, and even less is known about how checkpoint inhibitors interact with immune systems prone to autoimmunity. Since malignancies are life-threatening diseases, there is an unmet medical need to decouple autoimmune toxicities from checkpoint inhibitor antitumor response. I hypothesize that individuals can be predisposed to irAEs based on a combination of their genetics and specific gut microbes. In this proposal, I established a mouse model that reflects the emerging paradigm of autoimmune predisposition and the role of the microbiome in the development of irAEs. I will use the Act1-/- mice, which develop spontaneous systemic lupus erythematous and Sjogren-like autoimmune diseases in specific pathogen free conditions with elevated baseline Th17 and B cell activity after aging. Combined treatment with anti-PD-1 and anti-CTLA-4 antibodies significantly expedited and exacerbated the onset and severity of autoimmune attack. In Aim 1, I will test the hypothesis that B cells drive irAEs in Act1-/- mice while still maintaining checkpoint inhibitor efficacy. I also determined that GF Act1-/- mice are not susceptible to irAE development, which aligns with the growing evidence of the microbiome’s critical role in defining responsiveness to checkpoint inhibitors as well as the mitigation of irAEs. In Aim 2, I will test the hypothesis that while ICI efficacy has been linked to certain members of the intestinal microbiota community, a distinct subset of microbes can allow for the induction of irAEs in a genetically susceptible host. The mechanisms studied in this proposal may prove useful for the foundation of a clinical genetic screening approach for the patient population prior to ICI delivery.