Tat protein alone does not protect animals.(Brief Article)

2002 APR 10 - (NewsRx.com & NewsRx.net) -- by Michael Greer, senior medical writer - Vaccines based solely on the HIV Tat protein may not provide sufficient protection from the virus, researchers report.

"The regulatory proteins Nef, Rev, and Tat of human immunodeficiency virus type 1 (HIV-1) are attractive targets for vaccine development, since induction of effective immune responses targeting these early proteins may best control virus replication," explained Dr. Peter Silvera and colleagues at the Southern Research Institute in Frederick, Maryland, Temple University in Philadelphia, and Pierre and Marie Curie University in France.

Although vaccines that make exclusive use of Tat could be highly immunogenic, they failed to protect animals from a highly virulent hybrid of simian and human immunodeficiency viruses (SHIV), Silvera and coauthors said.

The researchers evaluated the efficacy of several Tat-based vaccines in a group of rhesus macaques. One of the treatments tested used a biologically active form of the protein, while the other two vaccines were based on inactive Tat derivatives from the SHIV[subscript]89.6p or HIV-1[subscript]IIIB strains, according to the report.

By the time the immunized macaques were challenged with SHIV[subscript]89.6p, most of the animals had demonstrated strong Tat-specific cell- and antibody-mediated immune activity. However, this activity failed to prevent infection, reduce viral load, or help maintain CD4 cell counts, study data showed.

The primates studied were given 30 times the SHIV[subscript]89.6p 50% minimal infective dose ...