Virion-Based Vaccine Protects Animals Against Disease

A DNA vaccine containing viral particles prevents many symptoms of infection in primates exposed to SIV, the simian version of HIV, Maryland researchers reported. To be effective, an HIV vaccine will "very likely have to elicit both cellular and humoral responses to control HIV-1 strains of diverse geographic and genetic origins," according to Ronald L. Willey and colleagues of the National Institutes of Health in Bethesda, the National Cancer Institute in Frederick, and Rockville-based Bioqual Inc.

The virion-based vaccine induced both cell- and antibody-mediated responses to SIV, and protected animals from disease despite imperfect virologic control, the report said. The researchers evaluated the efficacy of a vaccine containing inactivated but intact HIV and SIV virions, in addition to vaccinia virus engineered to express key viral proteins. Inoculated rhesus macaques demonstrated virus-specific cytotoxic T-cell activity and neutralizing antibody responses after exposure to simian-human immunodeficiency virus, a highly virulent viral chimera that contains genes from both HIV and SIV, according to the report.

Data showed that vaccinated animals stayed healthy for at least 15 months after SHIV exposure, and maintained nearly normal CD4 cell counts. However, immunization did not protect the macaques against SHIV infection, although it reduced viral load compared to control animals. Infectious SHIV was "readily" recovered from all the immunized macaques more than five months after exposure, the authors reported in "Control of Viremia and Prevention of Simian-Human Immunodeficiency Virus-Induced Disease in Rhesus Macaques Immunized with Recombinant Immunodeficiency Virus Type 1 Particle," Journal of Virology (2003;77(2):1163-1174).

"These results indicate that despite the protection from SHIV-induced disease, the vaccinated animals still harbored replication-competent and pathogenic virus," Willey and colleagues concluded.

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