Cytotoxic T lymphocytes play a central role in the control of persistent human CMV (HCMV)
infection and reactivation. In healthy virus carriers, the specific CD8(+) CTL response is almost entirely directed against the virion tegument
protein pp65 and/or the 72-kDa major immediate early
protein, IE1. Studies that included a large panel of HCMV(+) donors suggested that immunorelevance of pp65 and IE1 was directly related with individual HLA haplotype difference. Nevertheless, there are no data on the incidence of HCMV natural polymorphism on virus-specific CTL responses. To assess the impact of IE1 polymorphism on CTL response, we have sequenced in 103 clinical isolates the
DNA region corresponding to IE1(315-324), an
immunodominant epitope presented by
HLA-A*0201 molecules. Seven peptidic variants were found with extensive difference in their frequencies. The response of four
HLA-A*0201-restricted anti-IE1 T lymphocyte clones, which were previously generated from one donor against autologous B lymphoblastoid cells expressing a recombinant clinical variant of IE1, was then evaluated using target cells loaded with mutant synthetic
peptides or expressing rIE1 variants. One of four clones, which have been sorted 19 times among 22 clones targeted against IE1(315-324), recognized six of the seven tested variant
epitopes. All three other clones showed distinct reactivity patterns to target cells loaded with the different mutant
peptides or expressing IE1 variants. Therefore, in the
HLA-A2 context, clonal expansions of anti-IE1 memory CTLs may confer a protection against HCMV successive
infections and reactivations by killing cells presenting most of the naturally occurring IE1(315-324)
epitope variants.