A canarypox vector-expressing cytomegalovirus (CMV) phosphoprotein 65 induces long-lasting cytotoxic T cell responses in human CMV-seronegative subjects

The major matrix phosphoprotein 65 (pp65) of cytomegalovirus (CMV) is an im portant target of HLA-restricted cytotoxic T cells (CTL) after natural infe ction. A canarypox-CMV pp65 recombinant was studied for its ability to indu ce CMV pp65-specific CTL, helper T lymphocytes, and antibodies in a phase I clinical trial. Twenty-one CMV-seronegative adult volunteers were randomiz ed to receive immunizations at months 0, 1, 3, and 6 with either canarypox- CMV pp65 or placebo. In canarypox-CMV pp65-immunized subjects, pp65-specifi c CTL were elicited after only 2 vaccinations and were present at months 12 and 26 in all subjects tested. Cell-depletion studies indicated that the C TL were phenotype CD8(+). Peripheral blood mononuclear cells proliferated i n response to stimulation with purified pp65, and antibodies specific for p p65 also were detected. Canarypox-CMV pp65 is the first recombinant vaccine to elicit CMV-specific CTL responses, which suggests the potential usefuln ess of this approach in preventing disease caused by CMV.