Abstracts

Priming of HBV core antigen-specific CTL activity by immunization with a HBcAg-heat shock protein fusion protein

Abstract presented at Experimental Biology 2001 - Orlando, FL, USA - March 31-April 4, 2001 as printed in FASEB J 2001 Volume 15 Number 5: page A1006

Liu H.; Anthony L.S.D.; Rowse G.J.; Recktenwald A.; Siegel M.I. (1); Mizzen L.A.

Stressgen Biotechnologies Corporation, Victoria, BC, Canada
1) Stressgen Biotechnologies Inc., Collegeville, PA, USA

In humans, recovery from acute infection with hepatitis B virus (HBV) is associated with development of a strong, multi-specific T lymphocyte response directed against a variety of HBV antigens. In particular, CD8+ CTL activity is believed to be critical in the resolution of acute disease, possibly through non-cytopathic, cytokine-mediated mechanisms. In marked contrast, individuals suffering from chronic type B hepatitis exhibit a weak and narrowly focused T cell response. Successful therapy of chronic HBV infection may depend, at least in part, upon priming of an effective CTL response. We have engineered a chimeric plasmid encoding sequences from the core antigen of HBV (HBc) fused to the 5ê end of the 65 kDa heat shock protein (Hsp) gene from Mycobacterium bovis BCG. Recombinant Hsp65-HBc fusion protein was expressed in E. coli and purified to >90% homogeneity. Endotoxin analysis indicated the presence of <0.05 EU/microgram protein in the final product. Mice were immunized subcutaneously with fusion protein in the absence of additional adjuvant. Immune spleen cells were restimulated in vitro with known HBc-derived CTL epitope peptides. Effector cells were assayed against either peptide-pulsed target cells or HBc-transfected target cells in a standard 4 h 51Cr release assay. Lysis of target cells by effector CTL from mice given a single immunization with Hsp65-HBc was as high as 60-80%. Hsp65-HBc priming of CTL activity was effective in mice of both H-2b and H-2d haplotypes, and two different H-2d mouse strains responded similarly. In contrast, immunization with HBc alone was less effective thanHsp65-HBc in priming CTL activity. The results of these studies clearly demonstrate the potential efficacy of Hsp65-HBc in the immunotherapy of chronic HBV infection.