Recombinant BCG overexpressing a STING agonist elicits trained immunity and improved antitumor efficacy in non-muscle invasive bladder

BCG remains first-line therapy for non-muscle invasive bladder cancer (NIMBC) but its mechanism of action is not fully understood. We developed a recombinant BCG (rBCG) that releases the STING agonist, c-di-AMP. Compared with BCG, rBCG demonstrated superior antitumor efficacy in models of NMIBC, more potent pro-inflammatory cytokine responses, greater myeloid cell reprogramming (M1 shift) and enhanced epigenetic and metabolomic changes favoring antitumor immunity. These findings are signatures of trained immunity and reveal that STING pathway activation is a proximal trigger in trained immunity remodeling. Trained immunity may be a central mechanism for both BCG and rBCG antitumor activity in NMIBC.