A recombinant adeno-associated virus (rAAV)-based HIV vaccine has shown sustained and vigorous antibody and T-cell immune responses in nonhuman primates, U.S. researchers reported at the annual Pediatric Academic Societies meeting in Seattle (May 3-6). These findings support data from earlier studies in which the rAAV vaccine elicited sustained immune responses like those observed in macaques with pathogenic simian immunodeficiency virus (SIV).

"This vaccine is distinct from other approaches in clinical and preclinical development. With a single dose we get measurable and distinct immune responses, and no other vaccine approach has shown this with one dose," said lead researcher Philip Johnson of Columbus Children's Hospital in Ohio.

During the six-month study period, 24 macaques received a single intramuscular injection of the vaccine at varying doses. Dose-dependent antibodies to the transgene product (HIV-1 Gag) increased slowly and were sustained throughout the study. Titer differences between the highest dose groups were insignificant after two weeks, and at six months, more than 70 percent of the macaques had persistent ELISPOT (enzyme-linked immunospot) responses to Gag peptides.

Johnson considers the study results promising. "The International AIDS Vaccine Initiative has done a review and picked our approach as one of several that they are pushing into human clinical trials this year," said Johnson. In October, Phase I trials are due to begin.

Karen Slobod, of St. Jude Children's Research Hospital in Memphis, said this report of the development of another vector to deliver HIV is interesting, but she points out that it may not be the solution to the challenge facing HIV vaccine design. "The solution may lie instead in addressing the diversity of HIV," suggested Slobod. The persistence of the delivery vector, which was identified at 20 weeks postinjection, is another concern for Slobod. "It does raise questions regarding potential long-term use and the possible induction of immune tolerance over time."

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