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The native HIV-1 Tat protein was chosen as a vaccine candidate based on its key role in the virus life cycle and on the correlation of Tat-specific immune responses with the asymptomatic stage and lower disease progression rates, but also due to its sequence conservation amongst the various HIV clades as well as the adjuvant effects on dendritic cells. Safety, immunogenicity and efficacy data in monkeys support the development of this vaccine concept.

It has been reported that the period of latency between HIV-1 infection and the production of antibodies against the virus is sometimes prolonged for greater than 6 months. However, the data supporting this are still controversial and it is not known whether these individuals are actually infectious, especially through body fluids. We have performed a prospective study of 65 high-risk HIV-1-antibody-negative individuals who were followed-up for a period of at least 1 year. Twelve of these individuals were shown by polymerase chain reaction (PCR) to be carriers of HIV-1 proviral sequences. The virus was isolated from lymphocytes in five out of 10 PCR-positive subjects and from cell-free plasma in two. Our data indicate that in some cases delayed seroconversions may be associated with productive infection, suggesting that mechanism(s) other than viral latency may be responsible for the absence of antibody responses to HIV-1 proteins.