Type III interferon inhibits bladder cancer progression by reprogramming macrophage-mediated phagocytosis and orchestrating effective immune responses

Background: Interferons (IFNs) are essential for activating an effective immune response and play a central role in immunotherapy-mediated immune cell reactivation for tumor regression. Type III IFN (λ), related to type I IFN (α), plays a crucial role in infections, autoimmunity, and cancer. However, the direct effects of IFN-λ on the tumor immune microenvironment have not been thoroughly investigated. Methods We used mouse MB49 bladder tumor models, constructed a retroviral vector expressing mouse IFN-λ3, and transduced tumor cells to evaluate the antitumor action of IFN-λ3 in immune-proficient tumors and T cell-deficient tumors. Furthermore, human bladder cancer samples (Cohort 1, n = 15) were used for IHC and mIF analysis to assess the expression pattern of IFN-λ3 in human bladder cancer and correlate it with immune cells’ infiltration. IHC analysis was performed in neoadjuvant immunotherapy cohort (Cohort 2, n = 20) to assess the correlation between IFN-λ3 expression and the pathologic complete response rate. Results In immune-proficient tumors, ectopic Ifnl3 expression in tumor cells significantly increased the infiltration of cytotoxic CD8 + T cells, Th1 cells, natural killer cells, M1-like macrophages, and dendritic cells. Transcriptomic analyses revealed significant upregulation of many genes associated with effective immune response, including lymphocyte recruitment, activation, and phagocytosis, consistent with increased antitumor immune infiltrates and tumor inhibition. Furthermore, IFN-λ3 activity sensitized immune-proficient tumors to anti-PD-1/PD-L1 blockade. In T cell-deficient tumors, increased Ly6G – Ly6C + I-A/I-E + phagocytic macrophages still enhanced tumor cell phagocytosis in Ifnl3 over-expressing tumors. IFN-λ3 is expressed by tumor and stromal cells in human bladder cancer, and high IFN-λ3 expression was positively associated with effector immune infiltrates and the efficacy of immune checkpoint blockade therapy. Conclusions Our study indicated that IFN-λ3 enables macrophage-mediated phagocytosis and antitumor immune responses and suggests a rationale for using Type III IFN as a predictive biomarker and potential immunotherapeutic candidate for bladder cancer.