An immunostimulant nanomedicine enhances radioimmunotherapy by remodeling the tumor immunosuppressive landscape after radiotherapy

Studies have shown that radiotherapy (RT) has powerful immune-stimulating effects. However, RT-mediated distal tumor regression is rare in clinical practice. Here, with an animal experimental model, we found that RT shaped an immunosuppressive landscape characterized by a high-influx of myeloid-derived suppressor cells (MDSCs), and the induction of immunologically silent tumor apoptosis, hindering the efficacy of radioimmunotherapy. To address this issue, we developed a spatiotemporally controlled nanomedicine for remodeling the immunosuppressive tumor microenvironment (TME) post-RT. Decitabine (DAC)-loaded ferritin (Ft) were crosslinked <i>via</i> an azobenzene linker, and meanwhile encapsulated with all-trans retinoic acid (ATRA) to construct a Ft@DAC@ATRA nanoassembly (denoted as FD@ATRA), which dissociated into monodispersive Ft@DAC units in hypoxia TME. The released ATRA could eliminate immunosuppressive MDSCs, and meanwhile Ft@DAC selectively induced immunogenic pyroptosis of the tumor by targeting the transferrin receptor 1 overexpressed on the tumor to effectively activate CD8⁺ T cells. FD@ATRA treatment reshaped the tumor immune landscape post-RT with an increase of 16.8% in tumor-infiltrating IFN-<i>γ</i> ⁺CD8⁺ T cells. Moreover, FD@ATRA-enhanced RT remained effective in large, treatment-resistant tumors, and the inhibition rate of FD@ATRA-enhanced RT on distant tumors improved by 47% compared to the RT group alone, providing an effective therapeutic approach to improve the clinical outcomes of radioimmunotherapy.