IDENTIFICATION OF AMINO-ACIDS INVOLVED IN RECOGNITION BY DENGUE VIRUSNS3-SPECIFIC, HLA-DR15-RESTRICTED CYTOTOXIC CD4(-CELL CLONES() T)

The majority of T-cell clones derived from a donor who experienced den gue illness following receipt of a live experimental dengue virus type 3 (DENS) vaccine cross-reacted with all four serotypes of dengue viru s, but some were serotype specific or only partially cross-reactive. T he nonstructural protein, NS3, was immunodominant in the CD4(+) T-cell response of this donor. The epitopes of four NS3-specific T-cell clon es were analyzed. JK15 and JK13 recognized only DENS NS3, while JK44 r ecognized DEN1, DEN2, and DENS NS3 and JK5 recognized DEN1, DENS, and West Nile virus NS3. The epitopes recognized by these clones on the DE NS NS3 protein were localized with recombinant vaccinia viruses expres sing truncated regions of the NS3 gene, and then the minimal recogniti on sequence was mapped with synthetic peptides. Amino acids critical f or T-cell recognition were assessed by using peptides with amino acid substitutions. One of the serotype-specific clones (JK13) and the subc omplex- and flavivirus-cross-reactive clone (JK5) recognized the same core epitope, WITDFVGKTVW. The amino acid at the sixth position of thi s epitope is critical for recognition by both clones. Sequence analysi s of the T-cell receptors of these two clones showed that they utilize different VP chains. The core epitopes for the four HLA-DR15-restrict ed CD4(+) CTL clones studied do not contain motifs similar to those pr oposed by previous studies on endogenous peptides eluted from HLA-DR15 molecules. However, the majority of these dengue virus NS3 core epito pes have a positive amino acid (K or R) at position 8 or 9. Our result s indicate that a single epitope can induce T cells with different vir us specificities despite the restriction of these T cells by the same HLA-DP15 allele. This finding suggests a previously unappreciated leve l of complexity for interactions between human T-cell receptors and vi ral epitopes with very similar sequences on infected cells.