Analysis of the intraclonal diversity of HLA-A0201-restricted T lymphocyte epitopes in follicular lymphoma idiotype

Lymphoma-derived immunoglobulin idiotype (Id) is a tumour-specific antigen used for antitumour vaccination in follicular lymphoma (FL). However, FL Ids are subject to hypermutation and subclones may escape antitumour cytotoxic T-cell response. To investigate the intraclonal epitope diversity, we sequenced the FL heavy chain gene (consensus Id gene) and subclones of 24 patients. The derived polypeptide sequences were analysed by bioinformatics for human leucocyte antigen (HLA)-A0201-restricted epitope prediction. Epitopes were classified according to BIMAS and SYFPEITHI scores. Surprisingly in these highly mutated polypeptides, the epitopes concentrated in short hotspots in the conserved framework regions (FRs), both in HLA-A0201(+) and HLA-A0201(-) patients. Similar hotspots have been observed by others in chronic lymphocytic leukaemia Ids which in contrast to FL have low mutation frequency. FR3 amino acids 78-88 displayed the best-score epitopes in Ids containing a VH3-family segment, the most represented in FL Ids. Such VH3-FR3(78-88) epitopes were previously demonstrated as immunogenic. Modifications of the epitope pattern in subclones of HLA-A0201(+) patients were generally absent from high-score peptides, including VH3-FR3(78-88) epitopes (83% unmodified). Therefore, no tendency for loss of HLA-A0201-restricted epitopes was evidenced and, given their limited intraclonal diversity, VH3-FR3(78-88) epitopes may provide a useful target for the induction of cytotoxic response in Id-vaccinated FL patients.