Shigella IpaB and IpaD displayed on L. lactis bacterium‐like particles induce protective immunity in adult and infant mice

Abstract

Shigella spp. are among the enteric pathogens with the highest attributable incidence of moderate-to-severe diarrhea in children under 5 years of age living in endemic areas. There are no vaccines available to prevent this disease. In this work, we investigated a new Shigella vaccine concept consisting of non-living, self-adjuvanted, Lactococcus lactis bacterium-like particles (BLP) displaying Shigella invasion plasmid antigen (Ipa) B and IpaD and examined its immunogenicity and protective efficacy in adult and newborn/infant mice immunized via the nasal route. Unique advantages of this approach include the potential for broad protection due to the highly conserved structure of the Ipas and the safety and practicality of a probiotic-based mucosal/adjuvant delivery platform. Immunization of adult mice with BLP-IpaB and BLP-IpaD (BLP-IpaB/D) induced high levels of Ipa-specific serum IgG and stool IgA in a dose-dependent manner. Immune responses and protection were enhanced by BLP delivery. Vaccine-induced serum antibodies exhibited opsonophagocytic and cytotoxic neutralizing activity, and IpaB/D IgG titers correlated with increased survival post-challenge. Ipa-specific antibody secreting cells were detected in nasal tissue and lungs, as well as IgG in bronchoalveolar lavage. Bone marrow cells produced IpaB/D-specific antibodies and contributed to protection after adoptive transfer. The BLP-IpaB/D vaccine conferred 90% and 80% protection against S. flexneri and S. sonnei, respectively. Mice immunized with BLP-IpaB/D as newborns also developed IpaB and IpaD serum antibodies; 90% were protected against S. flexneri and 44% against S. sonnei. The BLP-IpaB/D vaccine is a promising candidate for safe, practical and potentially effective immunization of children against shigellosis.

Monophosphoryl Lipid A Enhances Efficacy of a Francisella tularensis LVS-Catanionic Nanoparticle Subunit Vaccine against F. tularensis Schu S4 Challenge by Augmenting both Humoral and Cellular Immunity

“…immunizations. F. tularensis-specific antibody titers were determined by ELISA on plates coated with whole F. tularensis LVS, using HRPconjugated secondary antibodies (goat anti-mouse IgA, goat anti-mouse IgM, or a pool of goat anti-mouse IgG1, IgG2b, IgG2c, and IgG3; all human adsorbed [Southern Biotech, Birmingham, AL]) and the 2,2=-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS; Sigma) reaction in 0.05 M phosphate-citrate buffer (Sigma) for detection as previously described (25,34,65). IFN-␥ ELISA on cell culture supernatants was carried out by the Cytokine Core Facility at UMB.…”

A novel protein‐based subunit Shigella vaccine candidate

“…Subsequent lethal pulmonary challenge with virulent S. flexneri 2a as well as S. sonnei demonstrated 80–90% protection against both serotypes. Protection correlated with high titers to IpaB and IpaD‐specific IgG and IgG2a response 1 . Besides the humoral responses, significant mucosal and systemic responses were also observed in the nasal‐associated lymphoid tissues, lungs, spleen and bone marrow as measured by the frequency of IpaB and IpaD‐specific IgG and IgA antibody secreting cells 1 .…”

“…A recent paper by Heine et al , 1 in Immunology and Cell Biology describes a novel approach to Shigella subunit vaccine development in which two of the major protein antigens, IpaB and IpaD, are displayed on the surface of a bacterium‐like particle (BLP) from Lactococcus lactis and evaluated in mice. The novelty of the method lies in the use of a safe Gram‐positive carrier strain with an extensive peptidoglycan (PGN) that is released after hot acid treatment to form a shell to which foreign proteins can be attached and displayed.…”

“…The BLPs target TLR‐2 on antigen‐presenting cells as well as on T and B cells activating both the innate as well as the adaptive arm of the immune response 2 . Thus, using BLPs that display conserved protein antigens, this approach has the potential to develop a safe and broadly cross‐protective subunit Shigella vaccine candidate 1 , 2 …”

“…In the Heine et al 1 paper purified IpaB and IpaD were separately fused to a peptidoglycan anchoring (PA) domain of a L. lactis cell‐wall hydrolase and the tagged Ipa proteins are mixed with BLPs obtained from hot acid‐treated L. lactis (Figure1). The BLPs exhibit the IpaB‐PA and IpaD‐PA fusion proteins on the surface of the peptidoglycan wall to which they are non‐covalently bound with high avidity 1 (Figure 1). Intranasal immunization of adult mice with the BLP‐IpaB/D demonstrated robust serum IgG responses to both Shigella antigens and sustained stool IgA responses to IpaB that increased in a dose dependent manner.…”