Recent advances in mucosal vaccine development

Comparison of the immune responses induced by local immunizations with recombinant Lactobacillus plantarum producing tetanus toxin fragment C in different cellular locations

Lactobacillus plantarum NCIMB8826 was selected as a bacterial carrier for the development of live mucosal vaccines. This strain was reported to display interesting pharmaco-kinetic properties when fed to human volunteers and is also able to persist in the mouse intestine. The non-toxic C fragment of tetanus toxin (TTFC) was used as a model antigen. Recombinant strains producing TTFC in three cellular locations, intracellular, secreted or cell-surface exposed were compared to each other by immunizing mice through the subcutaneous, intranasal and intragastric routes. The three types of constructs were able to induce strong specific immune responses against TTFC by all routes tested. While cell-surface presentation required lower antigen doses to be immunogenic, the highest IgG serum antibody titers were obtained with the strain producing large amounts of TTFC in the cytoplasm.

Pharmacotherapy by intracellular delivery of drugs using fusogenic liposomes: application to vaccine development

We prepared fusogenic liposomes by fusing conventional liposomes with an ultra-violet inactivated Sendai virus. Fusogenic liposomes can deliver encapsulated contents into the cytoplasm directly in a Sendai virus fusion-dependent manner. Based on the high delivery rates into the cytoplasm, we originally planned to apply the fusogenic liposomes to cancer chemotherapy and gene therapy. We have recently also examined the use of fusogenic liposomes as an antigen delivery vehicle. In terms of vaccine development, cytoplasmic delivery is crucial for the induction of the cytotoxic T lymphocyte (CTL) responses that play a pivotal role against infectious diseases and cancer. In this context, our recent studies suggested that fusogenic liposomes could deliver encapsulated antigens into the cytoplasm and induce MHC class I-restricted, antigen-specific CTL responses. In addition, fusogenic liposomes are also effective as a mucosal vaccine carrier. In this review, we present the feasibility of fusogenic liposomes as a versatile and effective antigen delivery system.

Murine female reproductive tract intraepithelial lymphocytes display selection characteristics distinct from both peripheral and other mucosal T cells

Despite immense effort, the development of vaccines effective at mucosal sites has proceeded at a faltering pace. Efforts concentrating on humoral immunity but neglecting cellular immunity may be misdirected by ignoring many viral mucosal pathogens. Improved understanding of the development and maintenance of lymphocytes populating the reproductive tract (rtIELs) may inform advances in vaccination strategies for sexually transmitted diseases. Recent studies highlight tissue-specific differences in the development of mucosal immunity and suggest that the local milieu may play a role in selection, maintenance and function of resident lymphocytes. Here, we describe MHC class I and thymus dependence of subpopulations of rtIELs. TCRalphabeta+ CD8alphabeta+ T cells in the periphery, intestine, and female reproductive tract are all developmentally dependent on classical class I MHC and the thymus. TCRalphabeta+ CD8alphaalpha+ are absent from the periphery and the rtIELs, but are present and classical MHC class I-independent, in the intestine. In contrast to intestinal TCRgammadelta+ cells, TCRgammadelta+ rtIELs are CD8 negative and thymus dependent. In contrast to peripheral TCRgammadelta+ cells, murine TCRgammadelta+ rtIELs express not a diverse array of Vdelta genes, but rather, a canonical Vdelta1. In summary, lymphocytes isolated from the murine female reproductive tract have characteristics distinct from both peripheral T cells and those found at other mucosal sites. Therefore, for the purpose of vaccination strategies, the female reproductive tract should be regarded neither as peripheral nor mucosal, but rather as a tissue with distinctive immunological characteristics.

Polymeric lamellar substrate particles for intranasal vaccination

In recent years, several strategies have been under investigation to achieve safe and effective immunisation, in terms of new antigens, adjuvants and routes of vaccination. The latter include mucosal sites such as oral, rectal, vaginal and nasal. Biodegradable microparticles produced from polymers such as poly(D,L-lactide) (PLA) and poly(D,L-lactide-co-glycolide) (PLGA) containing encapsulated vaccine antigens have been extensively studied for immunisation. These microparticles allow controlled release of vaccines with the aim to develop as single dose vaccines. However there are concerns regarding the integrity and immunogenicity of the antigen during the encapsulation process when the antigen is exposed to organic solvents, high shear stresses and the exposure of antigen to low pH which is caused by polymer degradation. Polymeric lamellar substrate particles (PLSP) produced by simple precipitation of PLA, form a novel polymeric system for the adsorption of antigens. This procedure avoids pH changes, exposure to organic solvents and hence allows the integrity of the antigen to be retained. The aim of this article is to discuss the factors affecting the characteristics of PLSP and adsorption of antigens onto PLSP and consider their potential as adjuvants for the nasal delivery of protein, peptide or viral vaccines.