Advanced antibody based therapies targeting pathogenic peptide-MHCII complexes in treating Type 1 Diabetes

Background: Most pathogenic T cells in NOD mice recognize an insulin B:9-23 derived peptide bound to the I-A^g7 MHC class II molecule in the weak affinity register 3 (R3). The IA^g7/B:9-23(R3) complex contains two epitopes based on peptides with or without the native glutamate at position B21 or the core peptides termed the P8E and P8G epitopes. Previously we demonstrated that an I-A^g7/B:9-23(R3) specific monoclonal antibody mAb287 could partially protect recipient NOD mice from T1D. Our later structural analyses indicate that mAb287 only binds to p8E epitope but not the p8G epitope. Thus, we investigated if advanced antibody-based therapies with improved features are able to protect disease efficiently.

Methods: To increase therapeutic efficacy we have explored two alternative approaches. First, we have transferred redirected CD8 T cells expressing a mAb287 chimeric antigen receptor (287-CAR) to pre-diabetic mice. Second, we have treated mice with another inhibitory antibody, mAb7E, that can bind both p8E and p8G epitopes.

Results: 1) 287-CAR T cells maintain the binding specificity of mAb287, and selectively lyse antigen presenting cells expressing I-A^g7/B:9-23(R3) in vitro. In vivo, 287-CAR-T cells travel to pancreatic lymph nodes, and a single infusion of CAR-T cells can significantly delay, although not prevent, the onset of T1D. 2) MAb7E has higher binding affinities with both p8E and P8G epitopes than mAb287 and suppresses both p8E and p8G reactive T cells in vitro. In vivo, mAb7E provides greater protection from T1D than mAb287 (70% vs 35%) when administered beginning either early (4 weeks) or late (9 weeks) during pre-diabetes stages. 

Conclusion: Antibody-based immune interventions targeting I-A^g7/B:9-23(R3), with both the bi-specific antibody and antibody redirected T cells, are able to modulate the development of spontaneous T1D safely. Current studies are directed towards testing reagents recognizing orthologous HLA-DQ8/insulin complexes for the future clinical application.