A live attenuated BCG vaccine overexpressing multistage antigens Ag85B and HspX provides superior protection against Mycobacterium tuberculosis infection

Abstract

Tuberculosis (TB) remains one of the most menacing infectious diseases, although attenuated Mycobacterium bovis Bacillus Calmette-Guerin (BCG) vaccine has been widely used to protect children against primary TB. There are increasing evidences that rapid growing and dormant Mycobacterium tuberculosis (M. tuberculosis) coexist in vivo after infection. However, BCG vaccine only elicits cell-mediated immune responses to secretory antigens expressed by rapid growing pathogen. BCG vaccine is thus unable to thwart the reactivation of latent tuberculosis infection (LTBI), and its protection wanes over age after neonatal immunization. In order to extend its ability for a durable protection, a novel recombinant BCG (rBCG) strain, named rBCG::XB, was constructed by overexpressing immunodominant multistage antigens of Ag85B and HspX, which are expressed by both rapid replicating and dormant M. tuberculosis. Long-term protective effect and immunogenicity of rBCG::XB were compared with the parental BCG in vaccinated C57BL/6 mice. Our results demonstrated that rBCG::XB provided the stronger and long-lasting protection against M. tuberculosis H37Rv intranasal infection than BCG. The rBCG::XB not only elicited the more durable multistage antigen-specific CD4(+)Th1-biased immune responses and specific polyfunctional CD4(+)T cells but also augmented the CD8(+) CTL effects against Ag85B in vivo. In particular, higher levels of CD4(+) TEM and CD8(+) TCM cells, dominated by IL2(+) CD4(+) and CD8(+) TCM cells, were obtained in the spleen of rBCG::XB vaccinated mice. Therefore, our findings indicate that rBCG::XB is a promising candidate to improve the efficacy of BCG.

Polyfunctional CD4+ T Cells As Targets for Tuberculosis Vaccination

“…Several studies have shown that BCG induces polyfunctional mycobacteria-specific CD4 + T cells detected among lung (9, 38) and splenic (9, 39–44) lymphocyte populations (Table 1). Darrah et al found that polyfunctional mycobacterial CD4 + T cells produced more cytokine on a per cell basis than do those producing two or one cytokines, similar to Leishmania -specific polyfunctional CD4 + T cells (9).…”

“…Darrah et al found that polyfunctional mycobacterial CD4 + T cells produced more cytokine on a per cell basis than do those producing two or one cytokines, similar to Leishmania -specific polyfunctional CD4 + T cells (9). In the murine TB model, these T cell responses constitute minor (38, 39, 42, 44), predominant (43), or major (9) subsets within the first 2–4 months after immunization. In addition, polyfunctional CD4 + T cells have been detected among CD44 + memory T cell populations as early as 3 weeks after vaccination (40) and persist as a major subset more than 40 weeks after vaccination (38).…”

“…Similarly, recombinant BCG constructs (42, 44) induce polyfunctional CD4 + T cell responses in mice (Table 2). Yuan et al compared BCG overexpressing Ag85B and HspX (rBCG:XB) to non-recombinant BCG and demonstrated that rBCG:XB elicited comparable PPD- and Ag85B-specific and stronger HspX-specific polyfunctional T cell responses 12 and 32 weeks after vaccination (44).…”

“…Yuan et al compared BCG overexpressing Ag85B and HspX (rBCG:XB) to non-recombinant BCG and demonstrated that rBCG:XB elicited comparable PPD- and Ag85B-specific and stronger HspX-specific polyfunctional T cell responses 12 and 32 weeks after vaccination (44). Comparing a recombinant BCG expressing membrane-perforating listerolysin (with the rationale of promoting CD8 + T cell responses from cytosolic antigens) and deficient in urease C (ΔureC hly + , VPM1002), Tchilian et al demonstrated low-frequency splenic PPD- and Ag85A-specific polyfunctional CD4 + T cells, comparable to those induced by BCG, 13 and 22 weeks after immunization (42).…”

“…Somewhat better correlative evidence comes from studies comparing two or more vaccine candidates to one another. Comparing rBCG:XB to BCG, Yuan et al showed that rBCG:XB elicited stronger HspX-specific polyfunctional T cell responses than BCG, which was associated with greater protection than was observed in BCG-vaccinated mice (44). Ballester et al showed that recombinant Ag85B delivered in CpG (Ag85B:CpG) with polypropylene sulfide nanoparticles (NP) delivered i.n.…”