Inactivated Lactobacillus plantarum Carrying a Surface-Displayed Ag85B-ESAT-6 Fusion Antigen as a Booster Vaccine Against Mycobacterium tuberculosis Infection

Abstract

Vaccination is considered the most effective strategy for controlling tuberculosis (TB). The existing vaccine, the Bacille Calmette-Guérin (BCG), although partially protective, has a number of limitations. Therefore, there is a need for developing new TB vaccines and several strategies are currently exploited including the use of viral and bacterial delivery vectors. We have previously shown that Lactobacillus plantarum ( Lp ) producing Ag85B and ESAT-6 antigens fused to a dendritic cell-targeting peptide (referred to as Lp _DC) induced specific immune responses in mice. Here, we analyzed the ability of two Lp -based vaccines, Lp _DC and Lp _HBD (in which the DC-binding peptide was replaced by an HBD-domain directing the antigen to non-phagocytic cells) to activate antigen-presenting cells, induce specific immunity and protect mice from Mycobacterium tuberculosis infection. We tested two strategies: (i) Lp as BCG boosting vaccine (a heterologous regimen comprising parenteral BCG immunization followed by intranasal Lp boost), and (ii) Lp as primary vaccine (a homologous regimen including subcutaneous priming followed by intranasal boost). The results showed that both Lp constructs applied as a BCG boost induced specific cellular immunity, manifested in T cell proliferation, antigen-specific IFN-γ responses and multifunctional T cells phenotypes. More importantly, intranasal boost with Lp _DC or Lp _HBD enhanced protection offered by BCG, as shown by reduced M. tuberculosis counts in lungs. These findings suggest that Lp constructs could be developed as a potential mucosal vaccine platform against mycobacterial infections.

Anchoring of heterologous proteins in multiple Lactobacillus species using anchors derived from Lactobacillus plantarum

“…Because lactobacilli are safe and may have immune-stimulating adjuvant effects [3][4][5][6][7][8] , they are promising delivery vectors for antigens and other medical molecules. Studies with animal models have repeatedly demonstrated the potential of antigen producing lactobacilli to induce specific immune responses [9][10][11][12][13][14][15][16] and one such Lactobacillus has even reached clinical tests 17 . Ideally, the antigens should be sufficiently protected from proteolytic digestion and other damage in the harsh environment of the gastro-intestinal tract, while at the same time being sufficiently exposed to provoke favorable immune responses at mucosal surfaces.…”

Preclinical Progress of Subunit and Live Attenuated Mycobacterium tuberculosis Vaccines: A Review following the First in Human Efficacy Trial

“…Lactic acid bacteria, non-sporulating Gram-positive bacteria, have also been widely used as vaccine vectors due to their known safety and well-established genetic toolkit [106]. Specifically, inactivated Lactobacillus plantarum was recently investigated as a booster to BCG due to its immunomodulatory effects and adjuvant properties.…”

“…Specifically, inactivated Lactobacillus plantarum was recently investigated as a booster to BCG due to its immunomodulatory effects and adjuvant properties. L. plantarum expressing Ag85B-ESAT-6 fused to a DC targeting peptide on the bacterial surface was the first inactivated L. plantarum vectored vaccine to show increased protection in the lungs against M. tb H37Rv when used as an intranasal boost to BCG (p < 0.05) compared to BCG alone [106]. This observed protection may be due, in part, to high levels of IFNγ, high frequency of polyfunctional T cells, and production of lung IgA [106].…”

“…L. plantarum expressing Ag85B-ESAT-6 fused to a DC targeting peptide on the bacterial surface was the first inactivated L. plantarum vectored vaccine to show increased protection in the lungs against M. tb H37Rv when used as an intranasal boost to BCG (p < 0.05) compared to BCG alone [106]. This observed protection may be due, in part, to high levels of IFNγ, high frequency of polyfunctional T cells, and production of lung IgA [106]. However, further studies are required to determine the best immunogenic design for its use as a candidate TB vaccine [106].…”

“…This observed protection may be due, in part, to high levels of IFNγ, high frequency of polyfunctional T cells, and production of lung IgA [106]. However, further studies are required to determine the best immunogenic design for its use as a candidate TB vaccine [106].…”