Cross-reactive Crf1/p41-specific T cells show a diverse TCR Vβ repertoire, multiple MHC class II restriction, and high proliferative capacity. (A) The TCR Vβ repertoire of p41-specific CD4⁺T-cell clones is diverse in different donors. TCR Vβ chains were determined by flow cytometry, PCR, nucleotide sequence analysis, or a combination of these techniques. *TCRs differ on the level of nucleotide sequence. Nomenclature is according to Wei et al.⁵⁰  (B) The Crf1/p41 epitope can be presented by HLA-DRB1*03, 04, and 13 and allows cross-recognition between HLA-DRB1*03 and 13. The HLA restriction of Crf1/p41-specific T-cell clones from 5 different donors was determined by stimulation with peptide-pulsed unmatched or partially matched LCLs (n = 2; for LCL DRB1*04, n = 1). (C) Crf1/p41-specific T cells are not terminally differentiated and can be rapidly expanded in vitro. 10⁷ PBMCs could be expanded to a median of 3.5 × 10⁷ cells (range, 3-4.9 × 10⁷ cells) within 14 days, and the frequency of antigen-specific cells as determined by an HLA-DRB1*04 restricted tetramer reached levels of 42% to 63% (median, 50.6%). T cells were restimulated with autologous peptide-pulsed monocytes on day 7, and culture medium was supplemented with IL-2, IL-7, and IL-15 (representative experiment, n = 8).