Tu193 - Decoding Regulatory T Cell Identity and Stability to Inform Better Regulatory T Cell Therapies

Maya Arce – UCSF, Gladstone Institutes; Patrick Ho; Cody Mowery – UCSF, Gladstone Institutes; Qizhi Tang; Alexander Marson – UCSF, Gladstone Institutes

Abstract Text: Regulatory T cells (Tregs) are a specialized subset of CD4+ T cells that maintain self-tolerance and immune homeostasis. Due to their natural capacity to suppress excessive inflammatory immune responses without causing global immune deficiency, Tregs are a promising candidate for cellular therapeutics to treat autoimmune disease, prevent transplant rejection, and perhaps more broadly, heal inflamed tissues. However, Tregs can destabilize when exposed to chronic inflammation, a phenomenon marked by loss of suppressive capacity and the lineage-defining transcription factor FOXP3. Understanding the genetic factors controlling FOXP3 expression may nominate regulators important for Treg stability and reveal manipulable targets to improve Treg cellular therapies. Advances in CRISPR technologies have enabled rapid and scalable identification of genetic elements controlling gene expression in primary human cell types. Using CRISPRi and CRISPRn-based genetic screens, we identified novel cis- and trans-regulators controlling FOXP3 maintenance and suppression in primary human Tregs. Notably, these regulators included nine FOXP3-suppressive trans-regulators and a suppressive cis-element associated with lncRNA expression. Ablation of these elements under destabilizing conditions revealed a subset that prevents destabilization and enhances FOXP3 expression. Overall, this work reveals a network of novel cis- and trans- regulators governing FOXP3 expression and Treg stability and informs the rational design of next-generation Treg cellular immunotherapies.