Imunoterapia baseada em Bacillus Calmette-Guérin (BCG) recombinante para o tratamento de câncer de bexiga em modelo murino

Abstract

Bladder cancer is the 10th most common and 13th most deadly cancer in the world. Approximately 75% of diagnosed bladder tumors are non-muscle invasive, and transurethral resection followed by instillation of Bacillus Calmette-Guerin (BCG) is recommended as treatment. To increase the adjuvant potential of BCG, our research group developed a recombinant BCG strain (rBCG) expressing detoxified pertussis toxin S1 (rBCG-S1PT). Previous results from the group showed that mice with bladder tumors treated with rBCG-S1PT had longer survival than mice treated with native BCG. However, little is known about the immune response associated with this anti-tumor protection. In this project, we set out to characterize the anti-tumor effect promoted by rBCG-S1PT in a murine model of heterotopic bladder tumors. To this end, murine urothelial carcinoma cells (MB49) were implanted subcutaneously into the direct flank of female C57BL-6 mice (day "zero" - D0), which were then treated with three cycles of immunotherapy (BCG or rBCG-S1PT) via the peritumoral/intratumoral route on day 1 (D1), D8 and D15. Tumor volume was measured throughout the experiment to assess tumor progression. Seven days after the last treatment (D22), mice were euthanized to collect tumors and spleens to assess the immune response of these anatomical sites. As previously observed, the rBCG-S1PT strain showed greater tumor control potential compared to the parental BCG. Using flow cytometry, we analyzed the immune populations in the spleen and tumors and observed a better inflammatory response induced by rBCG-S1PT compared to the BCG group and the untreated group, with emphasis on 1) a lower frequency of regulatory T cells in the spleen and tumor; 2) a greater activation of CD4 and CD8 T lymphocytes in the spleen and tumor. 3) higher frequency of mature and activated NK cells in the spleen. Our results suggest that immunotherapy with rBCG-S1PT positively modulates the response of T lymphocytes and NK cells while controlling the immunosuppression mediated by regulatory T cells, resulting in the potentiation of the immunotherapeutic effect of rBCG-S1PT in tumor control.