AMINO-TERMINAL ALTERATION OF THE HLA-A-ASTERISK-0201-RESTRICTED HUMAN-IMMUNODEFICIENCY-VIRUS POL PEPTIDE INCREASES COMPLEX STABILITY AND IN-VITRO IMMUNOGENICITY

Initial studies suggested that major histocompatibility complex class I-restricted viral epitopes could be predicted by the presence of particular residues termed anchors, However, recent studies showed that nonanchor positions of the epitopes are also significant for class I binding and recognition by cytotoxic T lymphocytes (CTLs). We investigated if changing nonanchor amino acids could increase class I affinity, complex stability, and T-cell recognition of a natural viral epitope, This concept was tested by using the HLA-A*0201-restricted human immunodeficiency virus type 1 epitope from reverse transcriptase (pol). Position 1 (P1) amino acid substitutions were emphasized because P1 alterations may not alter the T-cell receptor interaction. The peptide with the P1 substitution of tyrosine for isoleucine (I1Y) showed a binding affinity for HLA-A*0201 similar to that of the wild-type pol peptide in a cell lysate assembly assay, Surprisingly, I1Y significantly increased the HLA-A*0201-peptide complex stability at the cell surface, I1Y sensitized HLA-A*0201-expressing target cells for wild-type pol-specific CTL lysis as well as wild-type pol. Peripheral blood lymphocytes from three HLA-A2 HIV-seropositive individuals were stimulated in vitro with I1Y and wild-type pol. I1Y stimulated a higher wild-type pol-specific CTL response than wild-type pol in all three donors. Thus, I1Y may be an ''improved'' epitope for use as a CTL-based human immunodeficiency virus vaccine component, The design of improved epitopes has important ramifications for prophylaxis and therapeutic vaccine development.