Neoadjuvant BO-112 and Hypofractionated Radiation Therapy with or without Nivolumab in Soft-Tissue Sarcoma: Preclinical and Phase I Results.

Neoadjuvant immune checkpoint blockade (ICB) and radiotherapy (RT) improve disease-free survival in select patients with soft-tissue sarcoma (STS). However, most STS are myeloid-rich and lack preexisting T cells associated with ICB response. In preclinical models, we observed that intratumoral BO-112 [nanoplexed polyinosinic: polycytidylic acid (poly I:C)] engages myeloid cells that persist after RT, ultimately enhancing T cell-dependent tumor control. We evaluated BO-112 and hypofractionated RT, with or without nivolumab, in 14 patients with high-risk STS in a phase I neoadjuvant trial. Consistent with its immunologic potency, the triple combination induced rare immune-related adverse events (myositis-myocarditis-myasthenia gravis spectrum), mitigated by BO-112 and nivolumab dose adjustment. BO-112 and RT reprogrammed tumor-associated myeloid cells toward antigen-presenting states, promoted clonal replacement by less exhausted T cells, and enhanced malignant cell depletion compared with standard RT. These immunologic changes coincided with encouraging disease control in a small, high-risk cohort, supporting further clinical development. SIGNIFICANCE: Intratumoral BO-112 and hypofractionated RT activate systemic T-cell immunity in mouse models and in a phase I neoadjuvant study of high-risk, resectable sarcoma. Engaging myeloid cells with BO-112 represents a potent strategy with RT to replete T cell-deficient tumors and expand the benefits of neoadjuvant ICB.