Steroid receptor coactivator 3-deficient regulatory T cells eradicate multiple solid tumors in syngeneic mouse models.

Steroid receptor coactivator 3 (SRC-3) is highly expressed in regulatory T cells (Tregs) and is important for their immunosuppressive activity. Recently, we demonstrated that disrupting SRC-3 expression in Tregs eliminates triple-negative breast cancer (TNBC) and prostate cancer in syngeneic animal models by generating an anti-tumor immune microenvironment without inducing immune-related adverse events (irAEs). Further analysis of these mice revealed that SRC-3 knockout (KO) Tregs infiltrated breast tumors and facilitated the infiltration of CD8+, CD4+, and natural killer (NK) immune cells into the tumor microenvironment (TME). Given the anti-tumor effects of SRC-3KO Tregs in two different solid cancers, we sought to extend our studies to additional cancer types. Here, we showed that SRC-3KO Tregs exerted a potent antitumor immunity-like effect, capable of eradicating glioblastoma, melanoma, and lung cancer in their respective syngeneic mouse models by generating an anti-tumor immune environment. These results support the translational development of SRC-3-targeted Treg modulation as a safe and effective immunotherapy platform for treatment-refractory cancers.