Gag-specific cytotoxic T lymphocytes from human immunodeficiency virus type 1-infected individuals: Gag epitopes are clustered in three regions of the p24gag protein.

Virus-specific cytotoxic T lymphocytes (CTL) may be an important host defense mechanism in the control of virus replication in persons infected with human immunodeficiency virus type 1 (HIV-1). Cytotoxic T-cell lines generated by nonspecific stimulation with anti-CD3 monoclonal antibodies and interleukin 2 were used to identify regions within the HIV-1 Gag protein that are the most frequently recognized. Using autologous Epstein-Barr virus-transformed target cells infected with recombinant vaccinia viruses encoding p18gag, p24gag, and p55gag proteins of HIV-1/Lai or selected truncations of p24gag, we show that within a group of 29 infected subjects, the p24gag protein is the target of Gag-specific CTL in most donors. Using autologous Epstein-Barr virus-transformed target cells coated with different synthetic peptides spanning the Gag amino acid sequence, we found clusters of partially overlapping peptides in three conserved regions of the p24 protein (amino acids [aa] 169 to 192, aa 219 to 304, and aa 335 to 372) that are frequently recognized by CTL and presented by a variety of human leukocyte antigen class I molecules. Since there are experiments both in vitro and in vivo showing the role of CTL in the control of virus replication in HIV and simian immunodeficiency virus infections, these results may be particularly important for vaccine development.