Comparative Analysis of Bacillus subtilis Spores and Monophosphoryl Lipid A as Adjuvants of Protein-Based Mycobacterium tuberculosis-Based Vaccines: Partial Requirement for Interleukin-17A for Induction of Protective Immunity

Abstract

The development of adjuvants for vaccines has become an important area of research as the number of protein-based vaccines against infectious pathogens increases. Currently, there are a number of adjuvant-based Mycobacterium tuberculosis vaccines in clinical trials that have shown efficacy in animal models. Despite these novel adjuvants, there is still a need to design new and more versatile adjuvants that have minimal adverse side effects but produce robust long-lasting adaptive immune responses. To this end, we hypothesized that Bacillus subtilis spores may provide the appropriate innate signals that are required to generate such vaccine-mediated responses, which would be sufficient to reduce the mycobacterial burden after infection with M. tuberculosis. In addition, we compared the response generated by B. subtilis spores to that generated by monophosphoryl lipid A (MPL), which has been used extensively to test tuberculosis vaccines. The well-characterized, 6-kDa early secretory antigenic target of M. tuberculosis (ESAT-6; Rv3875) was used as a test antigen to determine the T cell activation potential of each adjuvant. Inoculated into mice, B. subtilis spores induced a strong proinflammatory response and Th1 immunity, similar to MPL; however, unlike MPL formulated with dimethyldioctadecylammonium (DDA) bromide, it failed to induce significant levels of interleukin-17A (IL-17A) and was unable to significantly reduce the mycobacterial burden after pulmonary infection with M. tuberculosis. Further analysis of the activity of MPL-DDA suggested that IL-17A was required for protective immunity. Taken together, the data emphasize the requirement for a network of cytokines that are essential for protective immunity.

Evaluation of the effect of MPL and delivery route on immunogenicity and protectivity of different formulations of FimH and MrpH from uropathogenic Escherichia coli and Proteus mirabilis in a UTI mouse model

“…Similar to other studies our findings showed that MPL enhanced titers of both serum IgG1 and IgG2a antibody when administered subcutaneously or mucosally, indicative of a mixed type 1 (Th1) and type 2 (Th2) immune responses [17,[24][25][26][27]. It has been suggested that MPL enhanced antigen-specific humoral responses by recruiting antigenpresenting cells (APCs) and inducing increased surface expression of MHC and the costimulatory molecules [28].…”

“…Immunization with MPL and vaccine antigens has been shown to result in a mixed Th1 and Th2 or a shift toward either Th1 or Th2 response and it has been suggested that in addition to the route of administration, variables such as strains of the mice used, type of antigens as well as the concentration of antigen and MPL may affect the Th1/Th2 phenotype [25,26,39,42,43]. Baldridge et al [13] showed that hepatitis B and influenza antigens formulated with MPL and administered IN produced significantly higher IgG2a than IgG1, whereas tetanus toxoid mixed with MPL induced a lower IgG2a than IgG1.…”

Mycobacterium tuberculosis sigE mutant ST28 used as a vaccine induces protective immunity in the guinea pig model

“…There is no doubt that IL-17 expression is up-regulated during M. tuberculosis infection, but the question remains as to the importance of this cytokine in vaccine mediated immunity. The importance of IL-17 may also depend on the type of vaccine used and, as we demonstrated, the requirement for IL-17 in an MPL based vaccine for induction of protective immunity was not absolute [23]. IL-10 mRNA expression was significantly up regulated in the spleens of ST28 inoculated animals and may reflect the ability of the mutant to prevent pathology in extra-pulmonary sites.…”

Tuberculosis vaccines — perspectives from the NIH/NIAID Mycobacteria vaccine testing program

“…However, if produced prior to infection, antibodies may become significant in prevention of infection. Vaccines studied in mice have reported induction of post-vaccination antibodies, but could not demonstrate contribution to protective immunity [33, 71] since no effect on the mycobacterial burden was seen despite antibody production to vaccine antigens [72]. This is also highlighted by the fact that maternal antibodies do not seem to play a role in protecting new born against infection, although maternal antibodies were shown to inhibit PPD-specific T cell responses in BCG vaccinated infants [73].…”