T-Cell Receptor/HLA Humanized Mice Reveal Reduced Tolerance and Increased Immunogenicity of Posttranslationally Modified GAD65 Epitope

• Published in: Diabetes (New York, N.Y.) Vol. 71; no. 5; pp. 1012 - 1022
• Main Authors: Jing, Yi, Kong, Yuelin, McGinty, John, Blahnik-Fagan, Gabriele, Lee, Thomas, Orozco-Figueroa, Stephanie, Bettini, Matthew L, James, Eddie A, Bettini, Maria
• Format: Journal Article
• Language: English
• Published: United States American Diabetes Association 01.05.2022
• Subjects: Animals; Autoantigens; Beta cells; CD4 antigen; Cell activation; Cross-reactivity; Diabetes; Diabetes mellitus (insulin dependent); Diabetes Mellitus, Type 1; Effector cells; Epitopes; Epitopes, T-Lymphocyte; Histocompatibility antigen HLA; HLA-DR4 Antigen; Immunogenicity; Immunological tolerance; Immunology and Transplantation; Immunoregulation; Islets of Langerhans; Lymphocytes; Lymphocytes T; Mice; Neoantigens; Receptors, Antigen, T-Cell - genetics; Rodents; T cell receptors; Thymus
• ISSN: 0012-1797; 1939-327X
• DOI: 10.2337/DB21-0993

Accumulating evidence supports a critical role for posttranslationally modified (PTM) islet neoantigens in type 1 diabetes. However, our understanding regarding thymic development and peripheral activation of PTM autoantigen-reactive T cells is still limited. Using HLA-DR4 humanized mice, we observed that deamidation of GAD65115-127 generates a more immunogenic epitope that recruits T cells with promiscuous recognition of both the deamidated and native epitopes and reduced frequency of regulatory T cells. Using humanized HLA/T-cell receptor (TCR) mice, we observed that TCRs reactive to the native or deamidated GAD65115-127 led to efficient development of CD4+ effector T cells; however, regulatory T-cell development was reduced in mice expressing the PTM-reactive TCR, which was partially restored with exogenous PTM peptide. Upon priming, both the native-specific and the deamidated-specific T cells accumulated in pancreatic islets, suggesting that both specificities can recognize endogenous GAD65 and contribute to anti-β-cell responses. Collectively, our observations in polyclonal and single TCR systems suggest that while effector T-cell responses can exhibit cross-reactivity between native and deamidated GAD65 epitopes, regulatory T-cell development is reduced in response to the deamidated epitope, pointing to regulatory T-cell development as a key mechanism for loss of tolerance to PTM antigenic targets.