Deletion of a Distal IRF4 Element Prevents Inflammation-induced Reprogramming of Human Regulatory T-cell Fate

Adoptive regulatory T cell (Treg) therapy is an emergent treatment paradigm in which ex vivo-expanded Tregs are administered to promote immune tolerance in transplant and autoimmune disease patients. While preclinical models have demonstrated remarkable efficacy, lineage-tracing studies have also revealed that chronic inflammatory exposures can cause a subset of murine Tregs to undergo Foxp3 downregulation and epigenetic reprogramming toward a dysfunctional, proinflammatory state. Despite the potential ramifications for clinical translation, whether human Tregs exhibit a similar susceptibility to inflammatory cytokine-mediated lineage decommitment remains inconclusive. Here, we present an in vitro model of human Treg destabilization characterized by FOXP3 downregulation, Treg-specific demethylated region (TSDR) re-methylation, loss of suppressive activity, and gain of proinflammatory functions. Analysis of single-cell ATAC and transcriptomic profiles from destabilized Tregs revealed a switch in chromatin accessibility between two elements at the IRF4 locus. Excision of the distal IRF4 element enabled Tregs to resist inflammatory cytokine-induced reprogramming, presenting a potential strategy to design more effective Treg therapies.