Cellular immunity and memory is required for clearance of viruses and for protection from viral infection. Cellular immunity by CD8 CTL and NK cells is initiated through activation of the innate immune response, maturation of dendritic cells (DC) and antigen cross presentation to CD8 T cells. Anti viral vaccines stimulating cellular immunity have to imitate this process. Adjuvants for the stimulation of antibody responses are used effectively however our knowledge about adjuvants for the stimulation of CTL immunity is limited. We have demonstrated that the endoplasmic reticulum resident heat shock protein gp96, a chaperone for peptides transported to be presented by MHC-I, is a natural adjuvant for the activation of DC, NK and cognate CD8 T cells. DC and macrophages have receptors for gp96-peptide complexes and become activated upon gp96-binding. Gp96 together with its associated peptides is taken up the APC, the peptide moiety is transported to the ER and used to charge MHC-I molecules. Concomitant activation of DC results in more than million fold enhanced cross priming of cognate CD8 T cells when compared to cross priming by intact protein taken up by DC. To take advantage of this unique adjuvant effect and the ability to transport relevant peptides, we have made a secretable form of gp96, gp96-lg, by replacing the KDEL ER-retention signal with the Fc portion of lgG1. We hypothesize that cell-based gp96-lg vaccines, by prolonged in vivo secretion of gp96-lg-peptide, imitate viral replication and provide immune stimuli comparable to attenuated viruses. In model systems in mice we have shown that gp96-lg transfected, antigen expressing tumor cells secrete gp96-lg in vivo and stimulate the innate DC and NK as well as adaptive, cognate cellular CD8 CTL immune response and generate specific CD8 memory independent of CD4 help and in the absence of lymph nodes. Both systemic and strong mucosal immunity in intraepithelial, lamina propria and Peyer's patch CD8 CTL is generated by gp96-lg vaccines. Because of their unique properties we now plan to evaluate the gp96- vaccines in non-human primate models for SIV for their immunogenicity for mucosal and systemic cellular immunity (R21). In addition we will examine the protective power of SIV-gp96-vaccines against subsequent viral challenge (R33). To maximize the chances of success, the team in Miami (Podack/Pahwa) has entered into a collaboration with experts (Franchini lab) at the NIH bringing together basic immunologists with experts in human and non human primate HIV/SIV pathogenesis.
