Despite the success of immune checkpoint inhibitors (ICIs) in multiple malignant tumors, a significant proportion of patients remain unresponsive to treatment. Radiotherapy (RT) elicits immunogenic antitumor responses but concurrently activates several immune evasion mechanisms. Our earlier research demonstrated the efficacy of YM101, an anti-TGF-β/PD-L1 bispecific antibody, in stroma-rich tumors. Nevertheless, YM101 has demonstrated reduced effectiveness in non-inflamed tumors characterized by poor immune cell infiltration. This study investigated the potential synergy between RT and YM101 in overcoming immunotherapy resistance and mitigating RT-induced pulmonary fibrosis.

Our findings suggest that RT combined with YM101 enhances antitumor immunity and overcomes resistance in non-inflamed tumors in preclinical models, while simultaneously showing potential in mitigating RT-induced fibrosis. This combination therapy demonstrates promise in overcoming ICI resistance, while potentially sparing normal pulmonary tissue, thereby providing a strong rationale for further clinical investigations.

The antitumor activity and survival outcomes of RT plus YM101 treatment in vivo were explored in several non-inflamed murine tumor models. Furthermore, the inhibition of pulmonary metastases was assessed in a pulmonary metastasis model. The impact of RT on dendritic cell (DC) maturation was quantified by flow cytometry, whereas cytokine and chemokine secretions were measured by ELISA. To comprehensively characterize changes in the tumor microenvironment, we utilized a combination of methods, including flow cytometry, IHC staining, multiplex inmunofluorecence and RNA sequencing. Additionally, we evaluated the impact of YM101 on RT-induced pulmonary fibrosis.

RT plus YM101 significantly inhibited tumor growth, prolonged survival and inhibited pulmonary metastases compared with monotherapies in non-inflamed tumors with poor immune infiltration. RT promoted DC maturation in a dose-dependent manner and increased the secretions of multiple proinflammatory cytokines. Mechanistically, RT plus YM101 simultaneously increased the infiltration and activation of intratumoral DCs and tumor-infiltrating lymphocytes and reshaped the tumor microenvironment landscape. Notably, YM101 attenuated both RT-induced peritumoral fibrosis and pulmonary fibrosis. Conclusions: Our findings suggest that RT combined with YM101 enhances antitumor immunity and overcomes resistance in non-inflamed tumors in preclinical models, while simultaneously showing potential in mitigating RT-induced fibrosis. This combination therapy demonstrates promise in overcoming ICI resistance, while potentially sparing normal pulmonary tissue, thereby providing a strong rationale for further clinical investigations.