Engineered BCG selectively triggers trained immunity in tumor-associated macrophages and sensitizes glioblastoma to radiotherapy in mice

Radiotherapy plays a crucial role in antitumor immunity in glioblastoma, yet its efficacy is often limited, resulting in tumor recurrence. Here, we engineer a macrophage membrane-camouflaged Bacillus Calmette-Guérin (BCG) via bioorthogonal chemistry to enhance radiotherapy against glioblastoma. This engineered BCG penetrates the blood-brain barrier, targets tumors, and alleviates hypoxia through intrinsic catalase activity, exerting antitumor effects in both murine orthotopic glioblastoma and humanized mouse models. Notably, it also initiates trained immunity in tumor-associated macrophages. Depletion and adoptive transfer of tumor-associated macrophages demonstrate that trained immunity promotes inflammatory cytokine production, reactive oxygen species release, phagocytosis and the recruitment of CD8+ T cells, ultimately amplifying immune responses to radiotherapy. Moreover, immune checkpoint blockade further augments the antitumor efficacy of engineered BCG combined with radiotherapy. Here, we show that trained immunity in tumor-associated macrophages is a promising strategy to sensitize glioblastoma to radiotherapy and improve treatment outcomes. Radiotherapy (RT) is standard-of-care in cancer management; however, RT efficacy remains limited. Here, the authors test whether membrane camouflaged BCG bacteria (MBCG) enhance response to RT in preclinical models of glioblastoma. MBCG efficiently targets tumor tissues, induces trained immunity in tumor-associated macrophages, and enhances the RT-induced anti-tumor responses.