Regulatory T cells (Tregs) play a crucial role in mediating immunosuppression in the tumor microenvironment.1,2 They dampen anti-cancer immune responses through multiple mechanisms: limiting the availability of Interleukin (IL)-2 for effector cells, Cytotoxic-T-lymphocyte-associated protein 4 (CTLA-4)-mediated suppression of antigen-presenting cells, adenosine triphosphate degradation by CD39 and CD73, and secreting immunosuppressive cytokines including IL-10 and Transforming growth factor (TGF)-β.3,4 Thus, Tregs are considered a promising target in cancer immunotherapy. The gene discussed is CTLA4; the disease is cancer.