Human immunodeficiency virus-1 Tat protein: immunological facets of a transcriptional activator.

Human immunodeficiency virus-1 (HIV-1) infection is characterized by chronic immune activation and progressive loss of CD4+ T cells, leading to a wide array of immune dysfunction, particularly involving immune response directed against viral antigens. HIV-1 encodes for fifteen proteins, which might serve as a target for immune recognition. Immune response to the envelope proteins have been studied more due to their presence on the surface of the virus. Recent studies on HIV vaccine development have focused on the Gag and Pol proteins. The transactivator Tat and Rev proteins have also been the focus of immunization studies due to their potent regulatory activity. The Tat (transactivator of transcription) protein although being nuclear in localization is also released from infected cells and acts on uninfected cells. Extracellular Tat seems to play an important role in AIDS pathogenesis. Furthermore, a correlation has been found between anti-Tat immune response and slow progression of the disease. Although several studies have shown Tat as a potential vaccine candidate with encouraging results, there are also reports raising doubt about its efficacy in multi-component HIV vaccine strategy. Here, we have addressed the issue of immune response to the most indispensable HIV-1 regulatory protein Tat.