VICAL (VICL) AND DNA VACCINE
Antigen-specific memory T-cell responses to cytomegalovirus (CMV), which may be important in protecting against CMV disease, were detected six months after DNA vaccination in a majority of CMV-seronegative subjects in a previously completed Phase 1 study. Memory T-cells are known to respond quickly upon subsequent infection with virus, transforming into active, effector T-cells that can control disease.
The recent results were obtained with a highly sensitive assay, a cultured ELISPOT assay, which detects memory T-cells.
When the firm was using the ex vivo ELISPOT assay, it was able to detect transient only the vaccine-induced effector T-cells in a minority of subjects in the same Phase 1 study, hence may have underestimated the extent of T-cell priming by DNA vaccination.
Larry Smith, Ph.D., Vical’s Vice President of Vaccine Research stated that an assay that measures pathogen-specific immune memory may provide a more meaningful metric for DNA vaccines. We view the cultured ELISPOT assay results as an important step toward understanding responses to DNA vaccination in humans and in advancing DNA vaccines toward approval.
The highly sensitive cultured interferon-gamma ELISPOT assay detected the following:
Memory T-cell immune responses in 15 of 22 CMV-seronegative subjects (68%) using archived samples from the company’s completed Phase 1 trial of its bivalent DNA vaccine encoding CMV phosphoprotein 65 (pp65) and glycoprotein B (gB).
Memory T-cell responses against these antigens 10 to 12 weeks after the first vaccine dose and persisted for at least 24 weeks after the last vaccine dose (the last point in time for which specimens were available).
Antigen-specific memory responses in some subjects who failed to show effector T-cell responses at any point in time by an ex vivo ELISPOT assay.
Mary K. Wloch, Ph.D., the company’s Associate Director of Vaccinology, presented the data at the 11th International Cytomegalovirus/Betaherpes Virus Workshop (Toulouse, France, May 13 - 17).
Vical conducted these studies in part under a grant from the National Institutes of Health.
Comments: The news is a big step forward in understanding the value of Vical’s DNA vaccine technology and towards the approval of these vaccines. It makles Vical more visible to interested pharmaceutical firms.