Pharmacological induction of MHC-I expression in tumor cells revitalizes T cell anti-tumor immunity

Antigen presentation by Major Histocompatibility Complex Class I (MHC-I) is crucial for T-cell-mediated killing, and aberrant surface MHC-I expression is tightly associated with immune evasion. To address MHC-I downregulation, we conducted a high-throughput flow cytometry screen, identifying bleomycin (BLM) as a potent inducer of cell surface MHC-I expression. BLM-induced MHC-I augmentation renders tumor cells more susceptible to T cells in co-culture assays and enhances anti-tumor responses in an adoptive cellular transfer mouse model. Mechanistically, BLM remodels the tumor immune microenvironment, inducing MHC-I expression in an ATM/ATR-NF-κB-dependent manner. Furthermore, BLM improves T-cell-dependent immunotherapeutic approaches, including bispecific antibodies therapy, immune checkpoint therapy (ICT), and autologous tumor-infiltrating lymphocytes (TILs) therapy. Importantly, low-dose BLM treatment in mouse models amplified the anti-tumor effect of immunotherapy without detectable pulmonary toxicity. In summary, our findings repurpose BLM as a potential inducer of MHC-I, enhancing its expression to improve the efficacy of T-cell-based immunotherapy.