The present invention provides compositions, including immunogenic compositions, comprising acetylated Tat protein of an immunodeficiency virus. The present invention further provides antibodies that specifically bind an acetylated Tat polypeptide. The present invention further provides methods of inducing an immune response to an immunodeficiency virus Tat protein in an individual. The present invention further provides methods of inhibiting transcriptional activation of an immunodeficiency virus in a cell of an individual.