Diphtheria in the 1990s: Return of an old adversary

Significant systemic and mucosal immune response induced on oral delivery of diphtheria toxoid using nano-bilosomes

BACKGROUND AND PURPOSE

Over the last decade apprehension has been growing over the effectiveness of existing parenteral vaccines for diphtheria and has created an interest in the development of a mucosally active vaccine. Oral immunization appears to be an effective alternative, but is not without the inherent disadvantages of antigen destruction and tolerance. Therefore, our objective was to investigate the incorporation of diphtheria toxoid (DTx) into bilosomes, which could provide protection as well as aid transmucosal uptake and subsequent immunization. Another objective was to determine the oral dose that will produce serum antibody titres comparable with those produced by i.m. doses of DTx.

EXPERIMENTAL APPROACH

Bilosomes containing DTx were prepared by thin film hydration and characterized in vitro for their shape, size, percent antigen entrapment and stability. In the in vivo study the anti-DTx IgG and anti-DTx sIgA response was estimated using elisa, in serum and in various body secretions, respectively, following oral immunization with different doses of DTx entrapped in nano-bilosomes.

KEY RESULTS

High dose loaded nano-bilosomes (DTxNB3, 2Lf) produced comparable anti-DTx IgG levels in serum to those induced by i.m. alum-adsorbed DTx (0.5Lf). In addition, all the nano-bilosomal preparations elicited a measurable anti-DTx sIgA response in mucosal secretion, whereas i.m. alum-adsorbed DTx (0.5Lf) was unable to elicit this response.

CONCLUSIONS AND IMPLICATIONS

The orally administered nano-bilosomal DTx formulation produced comparable serum antibody titres to i.m.alum-adsorbed DTx, at a fourfold higher dose and without the induction of tolerance. This approach will provide an effective and comprehensive immune protection against diphtheria with better patient compliance.

Induction of protective and mucosal immunity against diphtheria by a immune stimulating complex (ISCOMS) based vaccine

There is increasing concern over the efficacy of existing vaccines for diphtheria and there is interest in the development of a mucosally active formulation which might improve local protection. Lipophilic immune stimulating complexes (ISCOMS) containing Quil A are active by both parenteral and mucosal routes and here we have established methods for incorporating palmitified diphtheria toxoid (DT) into ISCOMS. The resulting formulation was immunogenic by the subcutaneous, oral and intranasal routes, with very low doses of DT inducing systemic humoral immune responses, as well as cell mediated immunity including both gammaIFN and IL5 production. Intranasal immunisation with DT in ISCOMS also stimulated significant local antibody production in tracheal washes, as well as cellular immunity in draining lymphoid tissues and serum neutralising antibodies. Finally, subcutaneous immunisation of guinea pigs with DT in ISCOMS primed protective immunity against challenge with diphtheria holotoxin more efficiently than the equivalent doses of DT in the conventional alum vaccine. ISCOMS based vaccines may provide a novel strategy for mucosal and systemic immunisation against diphtheria.