481 Single cell sequencing of human ICI-thyroiditis and ICI-colitis reveals a shared role for T follicular and T peripheral helper cells in the development of IRAEs across tissues

<h3>Background</h3> Targeting multiple checkpoints via immune checkpoint inhibitor (ICI) therapies has allowed for the enhancement of anti-tumor effects compared to single agents. In spite of these benefits, ICI therapies have also led to an increased incidence of immune related adverse event (irAEs) in various tissues, with colitis and thyroiditis being two of the most common. Given that T follicular helper (TFH) cells have been shown to contribute to both spontaneous and irAE autoimmunity, TFHs and their tissue localized T peripheral helper (TPH) cell counterparts may be a shared component in the pathogenesis of irAEs across different tissues. <h3>Methods</h3> To understand the role of CD4+ TFH and TPH cells in irAEs across different tissues, we analyzed single cell RNA sequencing (scRNA-Seq) data for immune infiltrates from ICI-thyroiditis and ICI-colitis. Data for ICI-thyroiditis were prospectively collected by thyroid fine needle aspirates from 9 individuals with ICI-thyroiditis, as well as healthy controls. Data for ICI-colitis were analyzed from a published dataset of immune infiltrates from 8 patients who had developed ICI-induced colitis and controls.¹ <h3>Results</h3> ScRNA-Seq analyses revealed a 4-fold expansion of TPH cells in ICI-thyroiditis and a 3-fold expansion in colitis compared to matched tissue from healthy controls. CD4T cell trajectory analysis revealed a dominant transition in both ICI-thyroiditis and colitis patients from a naïve SELL+ CCR7+ phenotype to the CXCR5+ TFH and later PRDM1+ TPH phenotypes (p&lt;0.0001). Differentiation correlated with upregulation of IL21, CD40LG, BCL6, and CXCR5 and later PRDM1, IFNG, and CXCR6 expression. Differential gene expression analysis showed enrichment of Tertiary Lymphoid Structure (TLS) gene sets in TFH and TPH cells. While CD8T cell analysis indicated a dominant expansion and differentiation towards a CXCL13+ IFNG+ phenotype in ICI-thyroiditis and colitis, there was only a slight differentiation towards a CD8T resident memory phenotype and upregulation of PRDM1+ (p&lt;0.0001). Cell interaction analysis showed upregulated TPH-mediated IL21 signaling in both ICI thyroiditis and colitis compared to tissue-matched healthy controls. Conclusions irAE-effected tissues during ICI therapy exhibited an upregulation activation markers and preferential differentiation of CD4T cells towards TFH, and subsequently TPH cells, accompanied by upregulation of TLS signaling pathways. These data provide further evidence for TFH and TPH cells not only in spontaneous autoimmunity but in cancer immunotherapy-associated autoimmune disease and suggest a common lineage from TFH to TPH cells in this context. <h3>Reference</h3> Luoma A, Suo S, Williams H. Molecular pathways of colon inflammation induced by cancer immunotherapy. <i>Cell</i> 2020;<b>182</b>:P655–671.E22. <h3>Ethics Approval</h3> Patients were prospectively enrolled from two academic medical centers [University of California, Los Angeles (UCLA) Health and University of Southern California Keck Medical Center] under Institutional Review Board–approved protocols (21-000633, 19-001708, and HS-19-00715).