It is now clear that the mucosa of the rectum, duodenum and vagina function as reservoirs for HIV infection, colorectal cell lines can be infected in vitro, suggesting that the sexual transmission of AIDS may not be dependent on the introduction of virus into the bloodstream. Particularly if infection through the mucosa is the primary route of HIV infection, it will be necessary to develop immunization strategies which induce immunity at mucosal sites. Parenteral immunization is rarely effective in this respect, and mucosal immunity is most often achieved through direct immunization of mucosal tissues, such as the gut-associated lymphoid tissues (GALT). We will exploit a novel vaccine delivery system which involves the microencapsulation of antigens in the biodegradable copolymers poly (DL-lactide-co-glycolide). Our studies have shown that the administration of antigens incorporated into appropriately sized microcapsules of this composition: 1) results in up to a 500-fold potentiation of the circulating antibody response, 2) enterally administered microcapsules protect the antigen from degradation in the GI tract and target the antigen to the GALT, and 3) following enteral vaccination a strong secretory IgA response is induced concurrent with a circulating antibody response. A variety of HIV (gp120, gp160t, subunit peptide-conjugates) and Simian immunodeficiency virus (whole SIV, core proteins, envelope proteins) vaccine antigens will be incorporated into this immunopotentiating vaccine delivery system and evaluated for their ability to induce immunity following both parenteral and enteral immunization. An additional approach to the induction of mucosal immunity which will be investigated in these studies involves the co-administration of these vaccine antigens with the oral adjuvant Cholera toxin and its purified subunits. Immune sera and mucosal secretions will be evaluated for their levels and isotype distribution of anti-vaccine, virus neutralizing and syncytia inhibiting antibodies. ELISPOT assays will be used to quantitate the number and isotype distribution of splenic and gut lamina propria lymphocyte (LPL) anti-vaccine antibody producing cells. In addition, the induction of cell-mediated immunity by each of these vaccine formulations will be evaluated through the assay of delayed-type hypersensitivity and the ability of splenic and LPL lymphocytes to kill syngeneic target cells expressing viral proteins. The specific objective of this subcomponents is to systematically evaluate each vaccine/adjuvant formulation in mice (antigens, Projects 1, 3 and 5), in order that the most promising may be advanced to nonhuman primates (Project 3) for further immunologic evaluation (Project 4).
