title: Fab antibodies capable of blocking T cells by competitive binding have the identical specificity but a higher affinity to the MHC-peptide-complex than the T cell receptor.
abstract: In transplant rejection, graft versus host or autoimmune diseases T cells are mediating the pathophysiological processes. Compared to unspecific pharmacological immune suppression specific inhibition of those T cells, that are involved in the disease, would be an alternative and attractive approach. T cells are activated after their T cell receptor (TCR) recognizes an antigenic peptide displayed by the Major Histocompatibility Complex (MHC). Molecules that interact with MHC-peptide-complexes in a specific fashion should block T cells with identical specificity. Using the model of the SSX2 (103-111)/HLA-A*0201 complex we investigated a panel of MHC-peptide-specific Fab antibodies for their capacity blocking specific T cell clones. Like TCRs all Fab antibodies reacted with the MHC complex only when the SSX2 (103-111) peptide was displayed. By introducing single amino acid mutations in the HLA-A*0201 heavy chain we identified the K66 residue as the most critical binding similar to that of TCRs. However, some Fab antibodies did not inhibit the reactivity of a specific T cell clone against peptide pulsed, artificial targets, nor cells displaying the peptide after endogenous processing. Measurements of binding kinetics revealed that only those Fab antibodies were capable of blocking T cells that interacted with an affinity in the nanomolar range. Fab antibodies binding like TCRs with affinities on the lower micromolar range did not inhibit T cell reactivity. These results indicate that molecules that block T cells by competitive binding with the TCR must have the same specificity but higher affinity for the MHC-peptide-complex than the TCR.
authors.affiliation: I. Med. Klinik, Saarland University Medical School, 66421 Homburg/Saar, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Neumann
authors.forename: Christine
authors.initials: C
authors.lastname: Sturm
authors.forename: Martin
authors.initials: M
authors.lastname: Hülsmeyer
authors.forename: Nina
authors.initials: N
authors.lastname: Dauth
authors.forename: Philippe
authors.initials: P
authors.lastname: Guillaume
authors.forename: Immanuel F
authors.initials: IF
authors.lastname: Luescher
authors.forename: Michael
authors.initials: M
authors.lastname: Pfreundschuh
authors.forename: Gerhard
authors.initials: G
authors.lastname: Held
mesh_terms: D019138:Antibodies, Blocking / Q000276:immunology*; D000915:Antibody Affinity; D000951:Antigens, Neoplasm / Q000276:immunology* / Q000378:metabolism; D001667:Binding, Competitive; D002999:Clone Cells; D000939:Epitopes; D006086:Graft vs Host Disease / Q000276:immunology* / Q000473:pathology / Q000517:prevention & control; D015234:HLA-A Antigens / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D015789:HLA-A2 Antigen; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000276:immunology*; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009363:Neoplasm Proteins / Q000276:immunology* / Q000378:metabolism; D010446:Peptide Fragments / Q000276:immunology* / Q000378:metabolism; D019151:Peptide Library; D011485:Protein Binding; D011948:Receptors, Antigen, T-Cell / Q000276:immunology / Q000378:metabolism; D012097:Repressor Proteins / Q000276:immunology* / Q000378:metabolism; D037182:T-Cell Antigen Receptor Specificity; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology / Q000378:metabolism
chemical_list: D019138:Antibodies, Blocking; D000951:Antigens, Neoplasm; D000939:Epitopes; D015234:HLA-A Antigens; C435939:HLA-A*02:01 antigen; D015789:HLA-A2 Antigen; D007140:Immunoglobulin Fab Fragments; D009363:Neoplasm Proteins; D010446:Peptide Fragments; D019151:Peptide Library; D011948:Receptors, Antigen, T-Cell; D012097:Repressor Proteins; C093962:synovial sarcoma X breakpoint proteins