Immune-stimulating complexes as adjuvants for inducing local and systemic immunity after oral immunization with protein antigens.

Orally active synthetic vaccines containing purified antigens would have many benefits for immunizing against systemic and mucosal diseases. However, several factors have limited the development of such vaccines, including the poor immunogenicity of purified proteins and their usual ability to induce tolerance when given orally. Here, we show that incorporation of ovalbumin (OVA) into immune-stimulating complexes (ISCOMS) containing saponin prevents the induction of oral tolerance in mice. In parallel, the spleen and mesenteric lymph node of mice fed OVA ISCOMS are primed for class I major histocompatibility complex (MHC)-restricted cytotoxic T-cell activity which recognizes physiologically processed epitopes on OVA. Oral immunization with OVA ISCOMS also stimulates high secretory IgA antibody responses in the intestine itself, as well as serum IgG antibodies. None of these active immune responses are detectable in mice fed OVA alone. Despite the potent priming of mucosal priming by OVA ISCOMS, re-exposure to antigen does not induce the intestinal immunopathology found in other systems after the breakdown of oral tolerance. Thus, ISCOMS have several unique properties as vectors for oral immunization and could provide a basis for future mucosal vaccines.