Protective antibody response following oral vaccination with microencapsulated Bacillus Anthracis Sterne strain 34F2 spores

Abstract

An oral vaccine against anthrax ( Bacillus anthracis ) is urgently needed to prevent annual anthrax outbreaks that are causing catastrophic losses in free-ranging livestock and wildlife worldwide. The Sterne vaccine, the current injectable livestock vaccine, is a suspension of live attenuated B. anthracis Sterne strain 34F2 spores (Sterne spores) in saponin. It is not effective when administered orally and individual subcutaneous injections are not a practical method of vaccination for wildlife. In this study, we report the development of a microencapsulated oral vaccine against anthrax. Evaluating Sterne spore stability at varying pH’s in vitro revealed that spore exposure to pH 2 results in spore death, confirming that protection from the gastric environment is of main concern when producing an oral vaccine. Therefore, Sterne spores were encapsulated in alginate and coated with a protein shell containing poly-L-lysine (PLL) and vitelline protein B (VpB), a non-immunogenic, proteolysis resistant protein isolated from Fasciola hepatica . Capsule exposure to pH 2 demonstrated enhanced acid gel character suggesting that alginate microcapsules provided the necessary protection for spores to survive the gastric environment. Post vaccination IgG levels in BALBc/J mouse serum samples indicated that encapsulated spores induced anti-anthrax specific responses in both the subcutaneous and the oral vaccination groups. Furthermore, the antibody responses from both vaccination routes were protective against anthrax lethal toxin in vitro, suggesting that further optimization of this vaccine formulation may result in a reliable oral vaccine that will conveniently and effectively prevent anthrax in wildlife populations.

In Vitro Protection and Titer Duration of Anthrax-Specific Antibodies Following Subcutaneous Vaccination of White-Tailed Deer (Odocoileus virginianus) with Bacillus anthracis Sterne 34F2 Strain Spores

“…This demonstration of vaccine-induced antibody neutralization of anthrax lethal toxin suggests, in the absence of a full challenge study, that positive detection of anti-PA titers by ELISA in WTD serum correlates with, although it does not confirm, in vitro protection (Reuveny et al 2001). Our data also demonstrate the utility of the adapted ELISA and TNA protocols from mice to WTD (Benn et al 2020). Consistent and reliable detection of anthrax-specific serum antibodies in WTD with two different diagnostic assays may be valuable for future serosurveillance of WTD as potential sentinels (Peterson et al 1993).…”

“…In vitro protection was determined by a toxin neutralization assay (TNA) protocol previously reported for mice and adapted to WTD (Benn et al 2020). The TNA protocol was standardized with mouse serum and murine macrophages to evaluate the in vitro protective potential of serum-derived anti-PA antibodies (Benn et al 2020).…”

“…In vitro protection was determined by a toxin neutralization assay (TNA) protocol previously reported for mice and adapted to WTD (Benn et al 2020). The TNA protocol was standardized with mouse serum and murine macrophages to evaluate the in vitro protective potential of serum-derived anti-PA antibodies (Benn et al 2020). Because the availability of WTD macrophages for laboratory use is extremely limited, the protocol was adapted to WTD serum while still using murine macrophages, so it was unknown how the macrophages would respond.…”

“…Furthermore, standardizing these and other diagnostic assays will be essential for improving vaccines and enabling quantitative comparisons between vaccine formulations, dosing schedules, routes of administration, species-specific responses, and so on. Continued application of these assays will be pivotal for the development of an oral vaccine against anthrax because of the challenges associated with maintaining viable vaccine through the harsh gastric environments before entering the small intestine for absorption (Cross et al 2007; Benn et al 2020).…”

СИБИРСКАЯ ЯЗВА: ЖИЗНЕННЫЙ ЦИКЛ, МЕХАНИЗМЫ ПАТОГЕНЕЗА И НОВЫЕ КОНЦЕПЦИИ В РАЗВИТИИ ВЕТЕРИНАРНЫХ ВАКЦИН (Обзор)

“…В 2020 году поступило сообщение о разработке вакцины на основе спор микрокапсулированного атеннуированного штамма B. anthracis Sterne 34F2 для перорального введения. Эксперименты на мышах продемонстрировали иммуногенность и нейтрализующую активность против летальной дозы LT in vitro после одной иммунизации с помощью желудочного зонда (70). Это направление может оказаться перспективным.…”