Avaliação da imunogenicidade de epítopos da proteína estrutural spike do SARS-CoV-2 racionalmente selecionados por vacinologia reversa e associados ao BCG vacinal como carreador e indutor da imunidade inata treinada

Abstract

COVID-19 is related to a severe acute respiratory syndrome in the lower respiratory tract caused by SARS-CoV-2. Observational analyzes have shown that people vaccinated with Bacillus Calmette-Guérin (BCG) are less likely to develop severe forms of COVID-19. Thus, it was hypothesized that the association of this bacillus with immunogenic epitopes selected by reverse vaccinology techniques of the structural proteins of SARS-CoV-2 may lead to the development of a trained innate immune response capable of increasing the protective immune response against this virus. Thus, this work aimed to identify immunostimulatory epitopes of the SARS-CoV-2 spike protein and associate them with vaccine BCG for the specific stimulation of a trained innate immune response. For this, 53.838 genomes deposited in SARS-CoV-2 databases were used and the putative predicted protein sequences of the virus spike were aligned to determine a worldwide consensus protein. The structure of this protein was predicted by molecular modeling and it was possible to identify two peptides with greater promiscuity to bind to BCR, MCH-I and MHC-II, as well as the characteristics regarding stability, immunogenicity, non-allergenicity, and physical-chemical properties compatible chemicals for the development of immunogenic peptides. By molecular anchoring it was possible to identify the points and the forces of interaction with the MHC molecules. Epitope 1 presents points of alterations already identified in the novel coronavirus variants, as well as an n-glycosylation point. On the other hand, epitope 2 is not found in positions of high variability in the variants currently in circulation, including the new variant omicron. Two formulations containing BCG and each peptide were used to stimulate macrophages derived from murine bone marrow, demonstrating a significant increase in the secretion of IL-6, IL-1 and TNF- upon previous contact with this formulation. In addition, the MAPK pathway was more activated in these cells, highlighting the greater activation of p38. In vivo analyzes using C57BL/6 mice vaccinated intramuscularly with the formulations showed a significant increase in the production of total IgG, IgG1 and IgG2c specific for the spike protein peptides in serum, as well as increased secretion of IFN-γ, IL- 6, TNF-α and IL-17. In summary, the rational approach of predicting immunogenic epitopes when associated with vaccine BCG was able to induce effective immunity both innate and adaptive in vitro and in vivo models.