GENERATION OF HEAT-SHOCK PROTEIN-BASED VACCINES BY INTRACELLULAR LOADING OF GP96 WITH ANTIGENIC PEPTIDES

Several studies have shown that immunization with heal shock proteins (HSPs) purified from tumors of virus-infected cells induces specific c ytotoxic T-cell (CTL) activity. This immune response is directed again st peptides bound to the HSPs rather than against the HSPs themselves. The peptides are derived from tumor- or virus-specific proteins which are degraded in the course of normal protein turnover and processing for presentation by MHC class I molecules. The HSPs appear to function as carriers for the antigenic peptides. Upon immunization they ensure their uptake by specialized macrophages and their introduction into t he MHC class I presentation route which is otherwise accessible only f or intracellular proteins. Using influenza virus nucleoprotein (NP) as a model antigen, we have tested whether an HSP-based vaccine can be p roduced by overexpressing an antigen in cultured cells prior to purifi cation of the HSP's. The transfection system based on the Semliki Fore st virus (SFV) replicon was employed to achieve high expression of NP. Since SFV-mediated transfection of murine cells was inefficient we us ed the hamster-derived cell line BHK21, which can be transfected with 100% efficiency, as a source for NP peptide-loaded gp96. The protein w as purified from transfected cells and used for first vaccination stud ies. The hamster gp96 preparation was well tolerated in mice, an antib ody response against the foreign protein was not observed. Preliminary results suggest that a cellular immune response against NP was indeed induced. SFV transfection is applicable for any known antigen and is therefore considered to be an elegant means for the production of HSP- based vaccines capable of inducing a cellular immune response. (C) 199 7 Elsevier Science B.V.