Preferential V~ Gene Usage and Lack of Junctional Sequence Conservation among Human T Cell Receptors Specific for a Tetanus Toxln-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 VB region gene segment, VB2.1, 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/~ gene use by T cell receptors (TCRs) specific for this peptide. Vot gene use was more heterogeneous, with at least seven different Vc~ segments derived from five distinct families encoding ot chains able to pair with V132.1 chains to form a tt830-844/DR-specific binding site. Several cases were found of dories restricted to different DR alleles that expressed identical VI3 and (or very closely related) Vo~ 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 c~ and 13 chains, even for TCRs with identical Vol and/or VI3 gene segments and the same restriction. Among 14 anti-tt830-844 clones using the V/32.1 gene segment, 14 unique VI3-D-JI3 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, VB2.1, is that this V region plays a dominant role in the recognition of the tt830-844/DR complex.