Summary/Abstract This is a request for an Administrative Supplement for the INCLUDE Project for R01 CA231226 “Defining the features of T cell response to tumor and self-antigens as predictors of response to checkpoint therapy”. The proposed studies for the Administrative Supplement are within the scope of the active parent grant, focused on Down syndrome (DS) and address two of the three components prioritized by the INCLUDE Project (Component 1: Targeted high risk – high reward basic science studies highly relevant to DS and Component 2 Assembly of a large cohort of individuals with DS across the lifespan to perform deep phenotyping and study co-existing conditions. Our objectives are: 1) To define an optimal anti-tumor signature by characterizing the immune landscape in individuals with DS with co-occurring autoimmune disease and then comparing to the immune landscape in patients with solid tumors who develop irAE after immune checkpoint inhibitor (ICI) therapy in order to identify an optimal anti-tumor signature (Component 1); and 2) Expand our existing DS biorepository to include more adults and more individuals with co-occurring autoimmune disease (Component 2). The central hypothesis for the proposed studies is that the immune features in DS that promote autoimmunity are the same immune features that protect from solid tumors and promote therapeutic response to ICI therapy. It is based on 1) observations that people with DS are protected from developing solid tumors and also predisposed to autoimmunity; and 2) Growing evidence of an association between therapeutic response to ICI therapy and development of autoimmune irAEs. The goal of Aim 1 is to increase both the number of adults and the number of individuals with co-occurring autoimmune disease in our existing biorepository. The goal of Aim 2 is to define an optimal anti-tumor signature by identifying shared characteristics of the immune architecture between people with DS and those treated with ICI who develop an irAE. These studies will determine the global immune landscape and antigen-specific T cell responses in individuals with DS and co-occurring autoimmune thyroid disease and then compare to cancer patients who develop ICI induced-autoimmune thyroiditis. The global immune landscape will be characterized using mass cytometry and RNA-sequencing. Antigen-specific T cell frequency and phenotype will be determined using activation-induced assays and single cell Cellular Indexing of Transcriptomes and Epitopes by Sequencing (scCITE-seq). The proposed work will extend understanding of anti-tumor mechanisms and thus improve ICI outcomes and elucidate potential ways to mitigate autoimmunity in people with DS without diminishing anti- tumor effect. Importantly, it is within the scope of the parent award as it focuses on understanding T cell responses in individuals that develop irAEs after ICI therapy. It also leverages the expertise and resources already in place in the parent grant and utilizes the same approach and experimental design as the parent grant to assess the global immune landscape and antigen-specific T cells.

Narrative The proposed research is relevant to public health because it investigates why individuals with Down syndrome are at increased risk for autoimmune disease yet are protected from development of solid tumors. It will advance our understanding of anti-tumor mechanisms and thus provide insight into how to improve cancer immunotherapy. This knowledge will also be important for developing therapeutic approaches to treat autoimmune disease in Down syndrome.