Tat is a regulatory protein of HIV-1 virus, well conserved among different isolates. Tat is produced early after infection and it's essential for virus replication and infectivity. Tat protein is also immunogenic and antibodies (Ab) against tat have been found to correlate with delayed disease progression and may exert protective effects by inhibiting both HIV-1 replication and the effects of extracellular tat. Moreover, tat is efficiently taken up by monocyte-derived dendritic cells, promotes their maturation and antigen presenting since it enters the major histocompatibility complex class I pathway. Finally, murine vaccination with a biologically active tat protein has been shown to be safe, immunogenic and elicits anti-tat neutralizing Ab and CTL.