Shimon Sakaguchi shared the 2025 Nobel Prize in Physiology or Medicine for his identification of regulatory T cells that suppress autoimmune responses. His work laid the foundation for RegCell, a company he co-founded to develop cell therapies that provide targeted treatments for autoimmune disease without compromising healthy immune function. RegCell epigenetically reprograms patient T cells into regulatory T cells. We spoke to Michael McCullar, CEO of RegCell, about the role of dysfunctional Tregs in autoimmune diseases, the firm’s use of epigenetically modified regulatory T cells to treat these conditions, and how this approach can selectively suppress harmful immune responses without causing broad immunosuppression.