In the past decade, effector T cells, engineered to express highly specific chimeric antigen receptors (CARs) or antigen-specific T cell receptors (TCRs) that recognize tumor antigens, have been shown to be highly effective adoptive cell therapies (ACTs) that have revolutionized certain cancer treatments. In 2017, the first two CAR–T cell therapies were approved by the U.S. Food and Drug Administration for the treatment of various CD19⁺ B cell lymphomas, and extensive clinical trials are now under way to expand the therapies to multiple solid tumor settings (1, 2). Here, we speculate on the next generation of immune cell therapies for non-cancer diseases. Specifically, we highlight the progress toward developing a new class of ACT using regulatory T cells (T_regs) to treat autoimmune diseases—including type 1 diabetes (T1D), rheumatoid arthritis, inflammatory bowel disease (IBD), graft-versus-host disease (GvHD) that can occur after bone marrow transplantation, and organ transplant rejection—and potentially to treat nonimmune diseases such as Alzheimer's disease, Parkinson's disease, heart disease, and type 2 diabetes (3).