Both humoral and cellular immune responses are important components of a protective immune response in human immunodeficiency virus-type I (HIV-1) infection. Neutralizing antibodies are believed to be responsible for preventing initial virus infection, and to reduce or clear viral load from the circulation while cytotoxic T cells (CTL) are presumed to control the initial viremia and limit the severity and duration of viral infection. Therefore, it would be ideal to generate a vaccine which can elicit both neutralizing antibody and antigen specific CTL; and most importantly, to generate a vaccine that elicits a protective immune response against viral infection. The applicants have recently demonstrated the capability to assemble SIV virus-like particles (VLPS) containing SIV envelope proteins using a baculovirus expression system. Some reports have suggested that the carbohydrate on gpl20 can shield potential antigenic determinants which can be unmasked by deglycosylation. The deglycosylated gpl20 showed increased ability to induce cellular immune responses and greater cross-reactivity with other strains of HIV. Therefore, the overall goal of the proposed study is to develop conditions to prepare deglycosylated envelope proteins in SIV-VLPS, and to determine the immunogenicity and the correlation of the immune response with protective immunity in a macaque monkey model. Specifically, the applicants propose to (i) produce deglycosylated non-infectious SIV-VLPs expressed by the baculovirus expression system; (ii) and to compare both humoral and cellular immune responses to deglycosylated and fully glycosylated SIV-VLPs in mice and macaque monkeys models. Furthermore, they plan to use different glycosidases for the treatment of the assembled SIV-VLPs to remove the carbohydrates from the glycoproteins. The deglycosylated SIV-VLPs are expected to retain the native conformation of the envelope protein with little or no glycosylated units present on the protein surface. As an alternative, these investigators will also pursue production of deglycosylated VLPs by using glycosylation inhibitors such as tunicamycin (TM) or the alpha-glucosidase inhibitor 1-deoxynojirimycin (DNM) in the culture medium. Alternative culture conditions will be employed to obtain particles which contain optimal amount of fully glycosylated or deglycosylated envelope proteins. Several reports have suggested the use of VLPs as particulate immunogens to generate not only humoral immune responses but also to induce a strong cellular immune response. It has also been suggested that oligosaccharides may camouflage potential epitopes which exist on the surface glycoprotein of primate lentiviruses. Based on these findings, the applicants will test primarily in the macaque monkey model the hypothesis that deglycosylated envelope proteins presented on the surface of baculovirus produced SIV-VLPs will enhance the env-specific immunogenicity of these particles, especially the induction of antigen specific CTL responses.
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