O uso de terapias adjuvantes e seus efeitos antitumorais no melanoma experimental em camundongos C57BL/6

Abstract

Imiquimod (IMIQ) is a TLR7 agonist that potentiates the antitumor response quickly and persistently, and BCG is an attenuated vaccine (strain) of Mycobacterium bovis, which induces a increase in the activation of the immune system, which can be an essential aid in the antitumor response. This research aimed to test the effects of IMIQ on experimental melanoma to determine if it is essential to restrict tumor growth and to prolong animal survival after treatment in C57Bl/6 wild-type (WT) and C57Bl/6 CD1-knockout mice (CD1-/-). This study also aimed to test the BCG vaccine as an adjuvant anti- melanoma therapy in wild C57Bl/6 animals. Mice were treated with IMIQ or BCG after injection of tumor cells subcutaneously (s.c) into the pinna of the ear. Parameters for both treatments were evaluated, such as tumor size, survival, and splenic cell phenotypes were analyzed. Furthermore, intracellular cytokines were evaluated after stimulation with anti-CD3. Treatment with IMIQ effectively restricted initial tumor growth and increased survival only in WT animals. Antigen-presenting cell (APC) frequencies were higher in WT animals than in CD1-/- animals, regardless of IMIQ treatment. There was an increase in the number of splenic perforin+ NK+ cells in WT mice and an increase in splenic IFN-γ-producing CD4+ T cells stimulated with anti-CD3 when compared to WT mice with CD1-/- treated with IMIQ. In addition, there was also an increase in splenic CD8+ T cells producing TNF+ in unstimulated splenic cells from WT animals compared to CD1-/- animals. In animals treated with BCG injection in situ, there was reduced tumor growth and increased survival compared to animals that only received tumor cells. There was an increase in dendritic cells and a decrease in splenic Treg cells at the splenic level. Cytokine production revealed a decrease in IL-10, an increase in INF-γ by splenic CD4+ and CD8+ T cells, an increase in INF-γ and perforin and granzyme B factors by NK cells, and an increase in INF-γ by NKT cells. Also, at the tumor level, the histopathological analysis indicated that the animals treated with BCG had a greater cellular infiltrate and a lower percentage of necrosis and muscle tumor invasion. In conclusion, animals treated with IMIQ: WT mice were protected by IMIQ from early mortality, with a decrease in melanoma development. Besides, BCG treatment limited tumor development and significantly increased survival in C57Bl/6 mice, which parallels with strong activation of the immune system, characterized by innate and adaptative responses, and had a more significant infiltration of inflammatory cells and less necrosis, and muscular tumor infiltration.