Comparison of TCR-alpha beta sequences of cross-reactive anti-DR alloreactive T-cell clones: identification of possible contact residues based on charge complementarity between TCR chains and DR determinants.

We analysed alloreactive T-cell clones selected for their differential recognition of DR variants differing in the third hypervariable region (hvr) of the DRB1 gene (amino acid positions 67-70-71). This polymorphism leads to two main hvr3 types: a basic form (Leu67-Gln70-Arg/Lys71) and an acidic form (Ile67-Asp70-Glu71) where residue 70 is probably directly accessible to the TCR on DR beta chains. The TCRs have been sequenced. Three DRw13-reactive clones use similar V alpha 2 and V beta 13 gene family members but differ mainly by their cross-reactivity towards acidic or basic DR4 variants and by the sequence of CDR3 on their TCR alpha and/or beta chains. One anti-DRw13 clone cross-reacts with most specificities sharing the DRw13 type of hvr3 and reciprocally one anti-DRBon (DRB1*0103) clone cross-reacts with DRw13. These two clones use similar V beta genes and share negative charges in CDR2 alpha at position 56. They also share these negative charges in CDR2 alpha with two other clones reacting specifically with DRBon, the acidic variant of DR1. We hypothesized that the selective recognition of positively or negatively charged residues on the DR beta chain would necessitate reciprocal charges on the TCR complementarity determining regions (CDRs) responsible for this interaction. This facilitated identification of those residues of the TCR that possibly interact with the hvr3 determinant of HLA-DR. From these observations the mechanisms allowing the recognition of alloantigens by these T-cell clones are discussed.