Combined mucosal and systemic immunity following pulmonary delivery of ISCOMATRIX™ adjuvanted recombinant antigens

Abstract

Deep pulmonary delivery of an influenza ISCOMATRIX™ vaccine has previously been shown to induce a combined mucosal and systemic antibody response. To explore whether this combined response is influenced by intrinsic properties of the component antigen, we examined the efficacy of deep pulmonary delivery of ISCOMATRIX™ vaccines containing different recombinant antigens, specifically gB glycoprotein from cytomegalovirus and a fragment of catalase from Helicobacter pylori. Both these vaccines induced antigen-specific mucosal and systemic immunity, as well as antigen-specific proliferative cellular responses. Pulmonary immunisation with ISCOMATRIX™ vaccines may therefore be a generic way of inducing combined systemic and mucosal immunity.

Introduction

While pathogens infect hosts through mucosal surfaces, the vast majority of current vaccines are administered subcutaneously, where they typically stimulate a potent systemic immune response but relatively poor mucosal immunity [1]. A combined systemic and mucosal immune response could be highly beneficial for protective immunity against some pathogens. For example, some pathogens such as Salmonella bacteria and the Human Immunodeficiency Virus commonly infect initially at a mucosal surface and then proceed from there to invade the host systemically. Effective mucosal immunity may protect the host against initial colonisation by such pathogens, while systemic immunity may be valuable if the mucosal barrier is penetrated. In the case of mucosal pathogens which do not invade the host, a systemic immune response may still potentially contribute to mucosal protection, as an inflammatory response to a mucosal pathogen opens up epithelial tight junctions, potentially exposing the pathogen to leaking serum-derived antibodies.

One of the largest mucosal surfaces is that found in the lungs, where the pulmonary mucosa is constantly exposed through inhalation, to a variety of antigens most of which are harmless. While the immune responses within the lungs are tightly regulated to prevent inappropriate inflammation which could have dire consequences for the host, the capacity remains for a potent immune response following either exposure to a pathogen or, as in the case of this study, vaccination. A small number of human studies have explored the potential of pulmonary delivery of vaccines. For example, lung delivery of human papillomavirus type 16 virus-like particle vaccine induced a serum IgG antibody response equivalent to that of injected vaccine [2], while inhalation of a pneumococcal polysaccharide vaccine was found in one study to induce a serum IgG response in a proportion of recipients [3], although this was not reproduced in a subsequent similar study [4]. More importantly an examination of aerosol vaccination during the influenza pandemic of the late 1960s demonstrated considerably improved protection from illness, compared with parenteral delivery of the same vaccine [5]. In all of these studies, vaccines were given without an adjuvant.

Injection of ISCOMATRIX™ adjuvant, comprising typically 40 nm cage-like structures made up of a purified fraction of Quillaia saponin, cholesterol and phospholipid, induces strong cellular and humoral immunity against co-delivered antigen [6]. Recently, we demonstrated the potential superiority of pulmonary delivered vaccines containing ISCOMATRIX™ adjuvant over subcutaneously administered vaccines [7]. Using influenza vaccine we showed not only an antigen dose-sparing effect following pulmonary vaccinations, when compared to a parenterally administered conventional unadjuvanted vaccine, but also the induction of both mucosal and systemic immune responses. The potent immune response induced by pulmonary delivery in this study required the addition of ISCOMATRIX™ adjuvant, shown by this study to be a powerful mucosal adjuvant, as well as delivery to the deep regions of the lung [7]. This finding was supported by our demonstration that deep lung delivery of an influenza ISCOMATRIX™ vaccine was required to induce protective immunity in mice [8].

While the requirement for adjuvant for effective lung vaccination is clear, any possible effect of the component antigen on the mucosal and systemic immune response induced following pulmonary delivery has not been examined. Given the influenza antigen used in the initial study contained haemagglutinin which has cell-adhesive potential and demonstrated immunogenicity in the absence of exogenous adjuvant, it was possible that at least part of the observed effect following lung vaccination was related to properties of the influenza antigen. Therefore, in the current study, we explored whether similar combined mucosal and systemic immune responses could also be induced by pulmonary delivery of ISCOMATRIX™ vaccines containing two quite different purified recombinant antigens.