Abstract 2268: Single cell RNA sequencing defines dynamic immune cell subsets in serial colon and peripheral blood samples in a patient with checkpoint inhibitor-induced colitis

Background: Immune checkpoint inhibition is an increasingly popular strategy for the management of numerous malignancies. Unfortunately, severe inflammatory toxicities affect up to 60% of patients, often leading to treatment discontinuation in settings where few alternative therapies are available to control disease. Checkpoint inhibitor induced colitis is a common toxicity for which the underlying mechanisms are poorly defined. Methods: To better understand the changing colon-specific and peripheral immune environments over the course of disease progression and treatment, we collected blood and colon tissue from a Merkel Cell carcinoma patient who developed colitis after treatment with pembrolizumab. We performed 10X Genomics single cell RNA sequencing on samples collected before, during and after checkpoint inhibition and various interventions to mitigate toxicity. Results: We identified both shared and colon-exclusive clonal expansion of T cells defined by distinct transcriptional programs, including cytotoxicity, memory, and proliferation markers, at various stages of the disease process. These clones decreased dramatically in the colon after infliximab and vedolizumab therapies. Conclusions: We identified several distinct T cell subsets as potential drivers of colitis in the colon. T cell clones that potentially recognize colonic tissue with a high degree of specificity can be harnessed for therapeutic intervention. Our findings emphasize the need for a more detailed understanding of the immune environment in the colon and suggest the potential for peripheral blood as a readout for immune activity during CPI treatment. Citation Format: Jacqueline E. Mann, Liliana Lucca, Matthew Austin, Ross D. Merkin, Lilach Aizenbud, Kevan Herold, Marie Robert, Harriet M. Kluger. Single cell RNA sequencing defines dynamic immune cell subsets in serial colon and peripheral blood samples in a patient with checkpoint inhibitor-induced colitis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2268.