Background: In NOD mice, insulin B:9-23 peptide bound to I-Ag7 in an energy unfavorable register 3 (R3) forms the antigenic I-Ag7/B:9-23(R3) complex. Previously we demonstrated that I-Ag7/B:9-23(R3) specific monoclonal antibody mAb287 delayed T1D. Subsequent studies indicate that the IAg7/B:9-23(R3) complex contain two epitopes termed p8E and p8G epitopes. MAb287 binds to the p8E epitope but has a very low affinity to the p8G epitope. In the present study, we assessed whether a new antibody targeting both epitopes enhances disease protection efficacy.
Methods: We immunized young NOD mice with IAg7/B:9-23(R3) p8E and IAg7/B:9-23(R3) p8G proteins alternatively, and generated a new clone Ab757. We then tested the binding affinity of Ab757 to both epitopes and treated NOD mice with this antibody or control antibodies starting from the pre-insulitis or established-insulitis stages monitored the development of T1D.
Results: 1) MAb757 exhibits high binding affinity to both p8E and P8G epitopes, and it suppresses in vitro both p8E and p8G reactive T cells. 2). Compared to mAb287 targeting only one epitope, mAb757 shows significantly enhanced T1D protection. MAb757 injection protected 70% of recipient mice from diabetes (p<0.001 compared to control antibody treatment or mAb287) when treatment was initiated at 4 weeks (pre-insulitis) or 9 weeks of age (established insulitis stage). We previously reported that mAb287 conferred mild T1D protection (35%), but such weak protection was not observed in a repeated experiment. 3). MAb757 treatment significantly delayed the time and the severity of lymphocyte infiltrating islets assessed by immunocytochemical and flow cytometry analysis.
Conclusion: Bi-specific antibody treatment targeting two epitopes within the I-Ag7/B:9-23(R3) complex is a safe approach that significantly suppresses islet autoimmune responses and in turn protects mice from progressing to overt T1D.
J. Cepeda: None. N.S. Sekhar: None. J. Han: None. N. Zhang: None. M. Pietropaolo: None. L. Zhang: None.