Negative signaling by anti-HLA class I antibodies is dependent upon two triggering events.
mAb with specificity for the alpha3 domain of HLA class I antigens, such as mAb TP25.99 and W6/32, are capable of inhibiting the proliferation of stimulated T cells in vitro by binding to their surface HLA class I antigens. The inhibitory potential of another HLA class I alpha3 domain-specific mAb, A1.4, was evaluated. In contrast to mAb TP25.99 and W6/32, which routinely inhibited superantigen (SEB) stimulation of T cells by >90%, mAb A1.4 at equivalent concentrations demonstrated only 20-50% inhibition. Univalent Fab fragments of all three mAb lacked inhibitory activity. Interestingly, however, by combining univalent W6/32 (or TP25.99) Fab fragments with intact, bivalent mAb A1.4 (at a non-inhibitory, sub-threshold concentration of 1 microg/ml), significant inhibition of SEB-driven T cell proliferation was obtained. Inhibition by the anti-HLA class I mAb W6/32 and TP25.99 was evident even when SEB was used in conjunction with paraformaldehyde-fixed HLA class I-, class II+ Daudi cells, suggesting that the inhibitory activity of these mAb results from direct HLA class I epitope engagement on the T cell. These findings suggest that effective antibody-mediated induction of the HLA class I inhibitory pathway within T cells is dependent upon two separable molecular triggers at the T cell surface. The first can be delivered by univalent mAb derivatives that engage one or more critical HLA class I epitope(s). The second requires intact mAb, though seems to be less selective as to the HLA class I specificity. This model may explain why some, but not all, anti-HLA class I mAb are inhibitory when used singly. Achieving synergies between a wider array of anti-HLA class I mAb and their derivatives may provide a path for more effectively tapping into the HLA class I inhibitory pathway in a therapeutic context.
Fayen
J
J
Institute of Pathology, Case Western Reserve University, Cleveland, OH 44106-4943, USA.
Huang
J H
JH
Ferrone
S
S
Tykocinski
M L
ML
D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism / Q000494:pharmacology*; D000918:Antibody Specificity; D004768:Enterotoxins / Q000494:pharmacology; D000939:Epitopes / Q000276:immunology; D015789:HLA-A2 Antigen / Q000235:genetics / Q000378:metabolism; D015395:Histocompatibility Antigens Class I / Q000276:immunology* / Q000378:metabolism; D007128:Immunoglobulin Fragments / Q000494:pharmacology; D008213:Lymphocyte Activation / Q000187:drug effects / Q000276:immunology; D051379:Mice; D008807:Mice, Inbred BALB C; D015398:Signal Transduction / Q000502:physiology*; D013268:Stimulation, Chemical; D013601:T-Lymphocytes / Q000276:immunology; D014162:Transfection
D000911:Antibodies, Monoclonal; D004768:Enterotoxins; D000939:Epitopes; D015789:HLA-A2 Antigen; D015395:Histocompatibility Antigens Class I; D007128:Immunoglobulin Fragments; C031818:enterotoxin B, staphylococcal