Rationalistic Modulation of Immune Mechanisms Synergizes the Anti-Tumor Effects of Targeted Radiation Therapy in Pre-clinical Models

In this study, we employed a diverse set of pre-clinical syngeneic murine tumor models with varying immune profiles to investigate the immunological impact of radiotherapy. We observed that immunologically 'hot' tumors demonstrated stronger tumor growth inhibition (TGI) following RT compared to 'cold' tumors. Additionally, RT induced both pro- and anti-inflammatory shifts within the tumor immune microenvironment, with significant changes noted in the spleen and tumor-draining lymph nodes. Importantly, radiotherapy led to an intratumoral increase in proliferating CD8 T cells, while the population of proliferating macrophages was notably reduced. Our findings also reveal that STING deficiency compromises TGI, particularly in tumors with a high baseline population of macrophages expressing an interferon response signature. Moreover, we identified a synergistic tumor growth control effect when combining HPK1 deficiency with RT. Collectively, these results provide insights into the complex interplay between RT and the immune response, offering potential avenues for novel therapeutic combination strategies. Overall design: Syngeneic cancer cell lines were implanted subcutaneously in the flanks of mice, and established tumors were treated with 12 Gy radiotherapy. Six days post-treatment, tumors were harvested, immune cells were isolated by magnetic-assisted cell sorting, and analyzed by single-cell RNA sequencing.