Dysregulation of CD4⁺and CD8⁺resident memory T, myeloid, and stromal cells in steroid-experienced, checkpoint inhibitor colitis

Background Colitis caused by checkpoint inhibitors (CPI) is frequent and is treated with empiric steroids, but CPI colitis mechanisms in steroid-experienced or refractory disease are unclear. Methods Using colon biopsies and blood from predominantly steroid-experienced CPI colitis patients, we performed multiplexed single-cell transcriptomics and proteomics to nominate contributing populations. Results CPI colitis biopsies showed enrichment of CD4 + resident memory (RM) T cells in addition to CD8 + RM and cytotoxic CD8 + T cells. Matching T cell receptor (TCR) clonotypes suggested that both RMs are progenitors that yield cytotoxic effectors. Activated, CD38 + HLA-DR + CD4 + RM and cytotoxic CD8 + T cells were enriched in steroid-experienced and a validation data set of steroid-naïve CPI colitis, underscoring their pathogenic potential across steroid exposure. Distinct from ulcerative colitis, CPI colitis exhibited perturbed stromal metabolism (NAD + , tryptophan) impacting epithelial survival and inflammation. Endothelial cells in CPI colitis after anti-TNF and anti-cytotoxic T-lymphocyte-associated antigen 4 (anti-CTLA-4) upregulated the integrin α4β7 ligand molecular vascular addressin cell adhesion molecule 1 (MAdCAM-1), which may preferentially respond to vedolizumab (anti-α4β7). Conclusions These findings nominate CD4 + RM and MAdCAM-1 + endothelial cells for targeting in specific subsets of CPI colitis patients.