Epitope promiscuity of human monoclonal autoantibodies to T-cell receptor-combining site determinants

To characterize the binding specificity and light- and heavy-chain variable region usage in monoclonal human autoantibodies (mAAbs) to T-cell receptor s, we constructed heterohybridomas from peripheral blood B cells of three r heumatoid arthritis (RA) patients. From a panel of more than 200 heterohybr idomas secreting IgM autoantibodies binding to T-cell receptor V beta chain first complementarity determining segments (CDR1), we characterized two Ig M/lambda molecules from a single patient in detail. These bound to both CDR 1 peptide epitopes and intact TCR of recombinant single-chain T-cell recept or constructs, and to T-cell surface TCR. Spectratype analysis using epitop es mimicking a set of 24 V beta genes indicated that one molecule bound onl y a few members of the set, whereas the second showed considerable epitope promiscuity by binding to more than half of the tested CDR1 peptides. Both mAAbs used variants of a V lambda 3 gene that were very similar to one anot her and to the germline gene. The epitope-promiscuous autoantibody used a V (H)4 gene identical to a germline prototype, while the other incorporated a V(H)3 sequence differing in only a single residue from its germline protot ype. The CDR3s of both were large and distinct from each other as well as f rom the corresponding segments of rheumatoid factors and "cold agglutinins" using the same or related V-H germline genes. These mAAbs offer models for deciphering the basis of epitope promiscuity, and serve as candidates for direct use in immunomodulation because they are of intrinsic human origin a nd do not require molecular engineering to adapt them for use in therapy.