A recombinant multi-epitope protein MEP1 elicits efficient long-term immune responses against HIV-1 infection

The effective protective HIV vaccine should elicit either protective antibodies or effective T cell response, or both. To improve the efficacy of HIV-1 vaccines, HLA polymorphism and HIV-1 diversity are 2 key factors to be considered for vaccine development. In this study, we expressed a recombinant multi-epitope protein MEP1 which has the same amino acid sequence as a DNA vaccine for Chinese population in our previous report. We found that MEP1 alone could elicit moderate levels of humoral and cellular immune responses, but these responses could not provide protection from challenge with a recombinant virus rTTV-lucgag, which expresses Gag of HIV-1 CRF_07BC. Nevertheless, when MEP1 was immunized with aluminum adjuvant, both humoral and cellular immune responses were significantly increased, and they were protective against virus infection; meanwhile, MEP1 with aluminum not only elicited early (10 d post immunization) but also a long-term (at least 44 weeks post immunization) immune responses in BALB/c mice. These results suggested that MEP1 has the potential to be developed as an effective vaccine candidate, and that suitable adjuvant is necessary for this protein to generate protective immune responses.

Recombinant Bivalent Fusion Protein rVE Induces CD4+ and CD8+ T-Cell Mediated Memory Immune Response for Protection Against Yersinia enterocolitica Infection

Studies investigating the correlates of immune protection against Yersinia infection have established that both humoral and cell mediated immune responses are required for the comprehensive protection. In our previous study, we established that the bivalent fusion protein (rVE) comprising immunologically active regions of Y. pestis LcrV (100–270 aa) and YopE (50–213 aa) proteins conferred complete passive and active protection against lethal Y. enterocolitica 8081 challenge. In the present study, cohort of BALB/c mice immunized with rVE or its component proteins rV, rE were assessed for cell mediated immune responses and memory immune protection against Y. enterocolitica 8081. rVE immunization resulted in extensive proliferation of both CD4 and CD8 T cell subsets; significantly high antibody titer with balanced IgG1: IgG2a/IgG2b isotypes (1:1 ratio) and up-regulation of both Th1 (TNF-α, IFN-γ, IL-2, and IL-12) and Th2 (IL-4) cytokines. On the other hand, rV immunization resulted in Th2 biased IgG response (11:1 ratio) and proliferation of CD4+ T-cell; rE group of mice exhibited considerably lower serum antibody titer with predominant Th1 response (1:3 ratio) and CD8+ T-cell proliferation. Comprehensive protection with superior survival (100%) was observed among rVE immunized mice when compared to the significantly lower survival rates among rE (37.5%) and rV (25%) groups when IP challenged with Y. enterocolitica 8081 after 120 days of immunization. Findings in this and our earlier studies define the bivalent fusion protein rVE as a potent candidate vaccine molecule with the capability to concurrently stimulate humoral and cell mediated immune responses and a proof of concept for developing efficient subunit vaccines against Gram negative facultative intracellular bacterial pathogens.