Stressgen granted new U.S. patent for treatment of Hepatitis B

Stressgen Biotechnologies announced today that the U.S. Patent and Trademark Office granted Patent Number 6,921,534 covering fusion protein compositions comprised of a hepatitis B virus (HBV) antigen fused to a heat shock protein (Hsp), as well as DNA encoding such fusion proteins, and methods of treating an HBV infection using these fusion proteins.

Preclinical data from the Company's therapeutic vaccine for hepatitis B, HspBcor, another CoVal(TM) fusion candidate, demonstrate that mice immunized with the HspBcor fusion protein activate cellular immunity by generating cytotoxic T lymphocytes (CTLs), peptide-specific white blood cells that can recognize and kill infected cells expressing the HBV core antigen. This CTL activity was triggered in normal mice that have been genetically modified to contain components of a human immune system, and also in HBV-transgenic mice that express the entire HBV genome.

"In individuals with chronic HBV infection, viral persistence may be related to an insufficient HBV-specific killer T cell (CTL) response," said Marvin I. Siegel, Ph.D., Stressgen's Executive Vice President of Research and Development. "A major hurdle for the development of an effective therapeutic vaccine for HBV is the presumptive existence in many clinical situations of immune tolerance for the HBV antigens. The immunity demonstrated in our animal model is significant because it demonstrates effective immunity in the face of preexisting tolerance."

HBV-transgenic mice are commonly employed as a model of chronic HBV infection. Transgenic mice that are immunologically tolerant to HBV normally do not rid themselves of cells expressing viral antigens. This tolerance is similar to what is observed in humans suffering from chronic HBV infection. Nevertheless, a single injection of HspBcor has been observed to break immune tolerance to the HBV core antigen in some of these transgenic mice by eliciting a specific CTL response, one of the hurdles to an effective therapeutic vaccine for HBV.