PREFERENTIAL V-BETA-GENE USAGE AND LACK OF JUNCTIONAL SEQUENCE CONSERVATION AMONG HUMAN T-CELL RECEPTORS SPECIFIC FOR A TETANUS TOXIN DERIVED PEPTIDE - EVIDENCE FOR A DOMINANT ROLE OF A GERMLINE-ENCODED V-REGION IN ANTIGEN MAJOR HISTOCOMPATIBILITY COMPLEX RECOGNITION

To investigate the structural and genetic basis of the T cell response to defined peptide/major histocompatibility (MHC) class II complexes in humans, we established a large panel of T cell clones (61) from donors of different HLA-DR haplotypes and reactive with a tetanus toxin-derived peptide (tt830-844) recognized in association with most DR molecules (universal peptide). By using a bacterial enterotoxin-based proliferation assay and cDNA sequencing, we found preferential use of a particular V-beta-region gene segment, V-beta-2.1, in three of the individuals studied (64%, n = 58), irrespective of whether the peptide was presented by the DR6wcI, DR4w4, or DRw11.1 and DRw11.2 alleles, demonstrating that shared MHC class II antigens are not required for shared V-beta-gene use by T cell receptors (TCRs) specific for this peptide. V-alpha-gene use was more heterogeneous, with at least seven different V-alpha-segments derived from five distinct families encoding alpha-chains able to pair with V-beta-2.1 chains to form a tt830-844/DR-specific binding site. Several cases were found of clones restricted to different DR alleles that expressed identical V-beta and (or very closely related) V-alpha-gene segments and that differed only in their junctional sequences. Thus, changes in the putative complementary determining region 3 (CDR3) of the TCR may, in certain cases, alter MHC specificity and maintain peptide reactivity. Finally, in contrast to what has been observed in other defined peptide/MHC systems, a striking heterogeneity was found in the junctional regions of both alpha and beta-chains, even for TCRs with identical V-alpha and/or V-beta-gene segments and the same restriction. Among 14 anti-tt830-844 clones using the V-beta-2.1-gene segment, 14 unique V-beta-D-J-beta-junctions were found, with no evident conservation in length and/or amino acid composition. One interpretation for this apparent lack of coselection of specific junctional sequences in the context of a common V element, V-beta-2.1, is that this V region plays a dominant role in the recognition of the tt830-844/DR complex.