Chimeric peptide vaccine composed of B- and T-cell epitopes of human T-cell leukemia virus type 1 induces humoral and cellular immune responses and reduces the proviral load in immunized squirrel monkeys (Saimiri sciureus)

A squirrel monkey model of human T-cell leukemia virus type 1 (HTLV-1) infection was used to evaluate the immunogenicity and protective efficacy of a chimeric peptide vaccine composed of a B-cell epitope from the envelope region (aa 175-218) and three HLA-A*0201-restricted cytotoxic T-lymphocyte epitopes derived from Tax protein (Tri-Tax). These selected Tax peptides induced secretion of gamma interferon (IFN-gamma) in peripheral blood mononuclear cells obtained from monkeys chronically infected with HTLV-1. After immunization, a high titre of antibodies and a high frequency of IFN-gamma-producing cells were detected against the Env and the Tri-Tax immunogens, but not against the individual Tax peptides. This might indicate that epitope(s) distinct from those recognized by humans are recognized by responder monkeys. After challenge, it was shown by competitive PCR that partial protection against HTLV-1 infection could be raised in immunized animals. Further studies should be developed to determine the duration of this protection.