rBCG-LTAK63 Outperforms BCG in Bladder Cancer Immunotherapy: Dendritic and T Cell Coordination Drives Superior Tumor Control in a Mouse Model

Bacillus Calmette-Guérin (BCG) remains the standard treatment for non-muscle invasive bladder cancer (NMIBC), yet approximately 30% of patients fail to respond. To enhance therapeutic efficacy, we developed rBCG-LTAK63, a recombinant BCG strain, as a novel immunotherapeutic candidate. <i>In vitro</i>, rBCG outperformed BCG in MB49 cell/splenocyte co-cultures by enhancing T cell activation and improving spheroid growth control. <i>In vivo</i>, rBCG demonstrated superior antitumor efficacy, significantly reducing the growth of subcutaneously implanted MB49 tumor cells. Immune profiling revealed that rBCG uniquely promoted systemic activation of both CD4⁺ and CD8⁺ T cells, alongside stronger activation of NK and dendritic cells in the spleen. Within the tumor microenvironment, rBCG increased immune cell infiltration, enhanced activation of CD8⁺ T cells and dendritic cells, and decreased the frequency of regulatory T cells, fostering a less immunosuppressive environment. Unlike parental BCG, rBCG-LTAK63 sustained a potent immunostimulatory profile, marked by robust activation of dendritic cells and effector T cells. Similar results were also observed in the orthotopic model, suggesting a translational potential of rBCG-LTAK63. Collectively, our findings demonstrate that rBCG outperforms conventional BCG and represents a promising strategy for improving NMIBC treatment.