Th200 - Tissue Spatial Analysis by Imaging Mass Cytometry and Longitudinal Peripheral Blood Flow Cytometry in Checkpoint Inhibitor Toxicity

José ter Linde – Center for Translational Immunology, Department of gastroenterology – University Medical Center Utrecht; Rik Verheijden – Department of medical oncology – University Medical Center Utrecht; Matthijs Baars – Center for Molecular Medicine – University Medical Center Utrecht; Mojtaba Amini – Center for Molecular Medicine – University Medical Center Utrecht; Miangela Laclé – Department of pathology – University Medical Center Utrecht; Eelco Brand – Center for Translational Immunology, Department of gastroenterology – University Medical Center Utrecht; Bas Oldenburg – Department of gastroenterology – University Medical Center Utrecht; Yvonne Vercoulen – Center for Molecular Medicine – University Medical Center Utrecht; Karijn Suijkerbuijk – Department of medical oncology – University Medical Center Utrecht; Femke van Wijk – Center for Translational Immunology – University Medical Center Utrecht

Abstract Text: Immune checkpoint inhibitor (ICI) colitis is among the most prevalent immune-related adverse events (irAEs). Deeper pathophysiological understanding of irAEs can contribute to evidence-based irAE management. We used imaging mass cytometry (IMC) along with in-house developed cell-segmentation, data-normalization and lineage-annotation pipelines to study ICI colitis (N=18) spatially in high immunological detail. Tissue analyses were complemented with longitudinal immunophenotyping and serum proteomics in ICI-treated patients that developed irAEs or remained irAE-free (N=44).

CD8+ T cells (CD8s) dominated the infiltrate of both αPD-1 and combined ICI (CICI) colitis. CICI-colitis showed highest CD8 granzyme B (GzmB) production across groups and serum GzmB was also higher in CICI than αPD-1-colitis. Activated CD8s with CD69hiCD103hi tissue resident (TRM)-like phenotype, more abundant in epithelium than lamina propria, mainly explained high GzmB in CICI-colitis. We found elevated Th1/Th17 balance in CICI vs αCTLA-4-colitis and, accordingly, in peripheral blood CICI irAEs (not limited to colitis) were mainly characterized by significantly enhanced proliferation of CD4+ Th1-associated effector memory T (TEM) cells. IrAEs following αPD-1 were associated with modestly enhanced Th1 response reflected by increasing CXCL9/CXCL10, but without Th1/Tc1 subset changes.

Our data demonstrate that epithelial cytotoxic CD8+ TRM cells and local Th1 skewing are associated with the highest cytotoxicity in CICI-colitis. In peripheral blood, we demonstrate marked increases in proliferation of CD4EM T cells and mainly Th1-associated cytokines. These findings indicate that tissue TRM cells play an important role in colitis development. They may be directly activated by ICI, or dependent on CD4EM T cells, which drive especially CICI irAEs.