PilVax: A novel peptide carrier for the development of vaccines against tuberculosis

Abstract

PilVax is a peptide delivery strategy for the generation of highly specific mucosal immune responses. The food-grade bacterium Lactococcus lactis (L. lactis) is used to express selected peptides engineered within the Streptococcus pyogenes (S. pyogenes) pilus, allowing for peptide amplification, stabilization, and enhanced immunogenicity. The present study aimed to demonstrate the suitability of PilVax for the generation of novel peptide vaccines against tuberculosis. Selected peptides (B cell and T cell epitopes), derived from tuberculosis vaccine targets ESAT- 6 and Ag85B, were genetically engineered into loop regions of the pilus backbone subunit and expressed in L. lactis. Western blots and flow cytometry confirmed pilus formation on L. lactis. Mice were vaccinated the PilVax constructs and the B cell response analysed by ELISA while T cell responses were analysed by flow cytometry. Moderate serum and titers of anti-peptide IgG and IgA were detected confirming the ability to produce antibodies against the cognate peptide. Peptide specific IgA was also detected across a number of mucosal sites sampled. However it remains to be seen whether these antibodies are protective. In PilVax-Ag85B vaccinated mice, peptide specific CD4+ T cells were detected at levels similar to when mice were immunised with BCG. This has been repeated and the same trend has been seen with similar levels of Ag85B peptide specific CD4+ T cells detected. However no ESAT-6 peptide specific CD4+ T cells were detected. Vaccination with PilVax resulted in the large scale proliferation of CD3+CD4-CD8- T cells. Analysis of cytokine production following stimulation with the cognate peptide showed the major cytokine producing cells to be CD4+ T cells (INF-γ) and CD3+CD4-CD8- T cells (IL- 17) in PilVax-Ag85B and BCG vaccinated mice. This study provides insight into the humoral and cellular immune responses generated by PilVax vaccination and has identified at least one construct that will be used in future protection studies.