T cell receptor diversity in CTLs specific for the CTT-1 and CTT-2 minor histocompatibility antigens.

Minor histocompatibility Ags (HA) and their associated immunogenic peptides provide a formidable barrier for successful transplantation, but there is virtually no information regarding the diversity of minor HA-specific TCRs. We have investigated the diversity of alpha- and beta-chains in TCRs specific for the CTT-1 and CTT-2 peptides that are immunodominant in CTL responses to multiple minor HA. CTLs were cloned after in vitro stimulation, and alpha- and beta-chain transcripts were amplified and sequenced to identify utilized V genes, complementarity-determining regions 3 (CDR3s), and joining region genes. Twenty-one unique CTT-2-specific TCRs were identified in 31 clones, and 22 CTT-1-specific TCRs were identified in 29 clones. A relatively limited number of V beta subfamilies were represented in these panels of TCRs, with Vbeta 5 and V beta8 genes expressed in multiple TCRs in each panel. Similar diversity was observed with V alpha usage, and V alpha4 subfamily usage was more prominent in CTT-2-specific TCRs than in CTT-1-specific TCRs. Neither alpha nor beta CDR3 regions exhibited prominent motifs or length restriction. However, CTT-1- and CTT-2-specific beta CDR3 regions included an excess of negatively over positively charged residues that were bimodally distributed among CDR3 positions. In fact, 50% of CTT-1-specific CDR3 regions included two negative charges separated by three to five amino acids. Despite the similarities in net charge of beta CDR3 regions, TCRs specific for these two minor HA peptides are relatively diverse and would expectedly withstand attempts at anti-TCR Ab-mediated immunosuppression.