Among all human T-cell leukemia virus type 1 proteins, tax, polymerase, and envelope proteins are predicted as preferential targets for the HLA-A2-restricted cytotoxic T-cell response.

The human T-cell leukemia virus type 1 (HTLV-1) is a human retrovirus associated with two diseases for which no successful treatment is yet available; the development of a vaccine is therefore an important issue. Since HTLV-1 is a persistent virus, an efficient vaccine will probably require a cytotoxic T-lymphocyte (CTL) response in addition to the production of antibodies. To identify potential CTL epitopes, we have selected, within all of the HTLV-1 proteins, nonapeptides containing anchor residues required for association with HLA-A2 molecules (residues at positions 2 and 9), which is the most frequently occurring A allele in all human populations. A set of 111 peptides was synthetized and tested in vitro in two assembly assays using processing-defective T2 cells. Anchor motifs selected were those containing two major anchor residues (L2/M2/12-V9/L9/I9) (one letter amino-acid code) and those including tolerated anchor residues (V2/A2/T2 and/or A9/M9/T9). The analysis of the binding capacity of the peptides confirms the high efficiency of the L2-V9 anchor motif and shows that a systematic research of potential binding peptides should exclude peptides containing known detrimental residues rather than select only peptides with known favored residues. We show that 39 peptides representative of all the HTLV-1 proteins are able to bind to HLA-A2 molecules. Strong binder peptides which are very likely good CTL epitopes were identified in three HTLV-1 proteins, Tax, envelope, and polymerase. Three of the strong binder peptides correspond to previously described HLA-A2-restricted CTL epitopes in the Tax protein, and two others are localized in a domain of the viral envelope recognized by natural neutralizing antibodies. This latter result has important implications for the development of an anti-HTLV-1 vaccine.