Legumain-activated radio-immunological synergist potentiates the abscopal effect via dual CD47/PD-L1 blockade and macrophage repolarization.

Despite its critical role in treating localized breast cancer, radiotherapy (RT) rarely provokes systemic immune responses or abscopal effects. In this work, immunological profiling reveals that RT upregulates CD47 and PD-L1 expressions in tumor cells and promotes the accumulation of M2-type tumor-associated macrophages (TAMs), suggesting a potential immunosuppressive mechanism that restricts abscopal responses. To overcome this limitation, a legumain-activated radio-immunological synergist (LARIS) is rationally designed to amplify RT-induced abscopal effects through dual CD47/PD-L1 blockade and TAM repolarization. LARIS is constructed from a bispecific immune checkpoint blockade chimeric peptide (BiCCP) linking CD47-and PD-L1-blocking peptides via a legumain-cleavable linker, and co-formulated with the Toll-like receptor 7/8 agonist R848. Within the tumor microenvironment, abundant legumain can cleave LARIS to release R848 together with the checkpoint blockade peptides, thereby reprogramming TAMs toward an M1 phenotype and mitigating CD47/PD-L1-mediated immune evasion. Both in vitro and in vivo studies demonstrated that LARIS significantly enhances systemic antitumor immunity and effectively induces abscopal responses of RT, thus suppressing the growth of distant and rechallenged tumors. Overall, this work offers a promising strategy to counteract RT-induced immunosuppression and potentiate abscopal effects for improved breast cancer therapy.