Mecanismos imunológicos envolvidos na imunoterapia com BCG em modelo singênico de melanoma murino

Abstract

Bacillus Calmette-Guérin (BCG) is an attenuated bacterium used as vaccine on newborns to prevent the most severe forms of tuberculosis and has been applied for more than 40 years in bladder cancer immunotherapy. Reference guidelines propose the use of BCG in other types of cancer and melanoma is also included. BCG can modulate the tumor microenvironment (TME), modifying the cellular infiltrate and inducing an antitumoral response in order to control tumor remission and metastasis. However, the mechanism of antitumoral immune response still poorly understood. In order to investigate how innate immunity is involved in the activation of B16-F10 murine melanoma cells, BCG and other agonists for different pathways were used, such as TLRs, inflammasome, cGAS/STING pathway and type I IFN. Furthermore, we established a subcutaneous B16-F10 melanoma model for intratumoral BCG treatment using different mice deficient (KO) for molecules related to innate immunity (TLR3-/-, TLR4-/-, TLR7-/-, TLR3/7/9-/-, Caspase 1-/-, Caspase 11-/-, IL-1R-/-, cGas-/-, STING-/-, IFNAR-/- e MyD88-/-) and adaptive immunity (Rag-/- and IFN-γ-/-). BCG was not able to stimulate B16-F10 to produce inflammatory cytokines related to the different mentioned pathways, and the opposite was observed in bone marrow-derived macrophages (BMDMs) from C57BL/6 (WT) animals. Despite this, BCG was able to infect B16-F10 cells, which in turn can activate BMDMs and splenocytes from WT animals in co-culture with these cancer cells. The effect of BCG stimulation was not observed in MyD88-/- cells. Taken together all KO animals evaluated, only MyD88-/-, Rag-/- and IFN-γ-/- mice did not show complete tumor control in response to BCG treatment compared to C7BL/6 WT. MyD88 signaling is also important for the recruitment of CD8+ T cells, NKT, NK cells, neutrophils and macrophages in the TME infiltrate, favoring tumor control in response to BCG. This work contributes to a better understanding of the immune pathways related to the immunotherapy with BCG in murine melanoma and may imply in future improvements for the treatment and its possible application in melanoma cases.