RelB/ILF2-GM-CSF loop drives prostate cancer immunosuppression; SN52 peptide sensitizes tumors to PD-1 blockade.

Advanced prostate cancer (PCa) remains a highly lethal malignancy with poor prognosis, often characterized by an immunologically "cold" tumor microenvironment (TME). This TME is significantly enriched with immunosuppressive myeloid-derived suppressor cells (MDSCs), which contribute to tumor progression and limit the efficacy of immune checkpoint blockade (ICB) therapies. Despite extensive research, the precise tumor-intrinsic signals that educate and sustain MDSC expansion and function have remained largely unelucidated, representing a critical gap in improving PCa immunotherapy outcomes.

Researchers investigated the molecular mechanisms driving myeloid-derived suppressor cell (MDSC) expansion and immunosuppression in prostate cancer (PCa). They employed cellular and molecular biology techniques to identify the RelB/ILF2 complex and its role in GM-CSF production. The study explored the effects of disrupting this complex and tested a RelB-targeting peptide, SN52, on PCa tumors. This included assessing its ability to sensitize tumors to PD-1 blockade therapy in preclinical models, with primary endpoints focusing on MDSC expansion, CD8+ T cell activity, and tumor growth inhibition.

The study identified a previously unrecognized RelB/ILF2-GM-CSF feed-forward loop as a central regulator of PCa immunosuppression. They found that nuclear interaction between RelB and ILF2 restricts ubiquitin-mediated degradation, thereby sustaining RelB nuclear stability. This enhanced RelB-mediated CSF2 transactivation, leading to increased GM-CSF (granulocyte-macrophage colony-stimulating factor) production and secretion. The secreted GM-CSF, in turn, promotes further RelB nuclear accumulation, perpetuating this feed-forward loop for sustained GM-CSF generation. In MDSCs, GM-CSF was shown to activate STAT3, driving MDSC expansion and their immunosuppressive functions. While specific numerical data (e.g., percent reduction, fold-change) were not provided in the abstract, the mechanistic findings were clear.

Disruption of the RelB/ILF2 complex significantly attenuated GM-CSF-driven MDSC expansion, restored CD8+ T cell-mediated antitumor activity, and inhibited tumor growth in preclinical models. Furthermore, the RelB-targeting peptide SN52 was demonstrated to sensitize PCa tumors to PD-1 blockade therapy, suggesting a potential synergistic therapeutic approach.