title: Glutamic acid decarboxylase-derived epitopes with specific domains expand CD4(+)CD25(+) regulatory T cells.
abstract: BACKGROUND
  CD4(+)CD25(+) regulatory T cell (Treg)-based immunotherapy is considered a promising regimen for controlling the progression of autoimmune diabetes. In this study, we tested the hypothesis that the therapeutic effects of Tregs in response to the antigenic epitope stimulation depend on the structural properties of the epitopes used.
  
  
  RESULTS
  Splenic lymphocytes from nonobese diabetic (NOD) mice were stimulated with different glutamic acid decarboxylase (GAD)-derived epitopes for 7-10 days and the frequency and function of Tregs was analyzed. We found that, although all expanded Tregs showed suppressive functions in vitro, only p524 (GAD524-538)-expanded CD4(+)CD25(+) T cells inhibited diabetes development in the co-transfer models, while p509 (GAD509-528)- or p530 (GAD530-543)-expanded CD4(+)CD25(+) T cells had no such effects. Using computer-guided molecular modeling and docking methods, the differences in structural characteristics of these epitopes and the interaction mode (including binding energy and identified domains in the epitopes) between the above-mentioned epitopes and MHC class II I-A(g7) were analyzed. The theoretical results showed that the epitope p524, which induced protective Tregs, possessed negative surface-electrostatic potential and bound two chains of MHC class II I-A(g7), while the epitopes p509 and p530 which had no such ability exhibited positive surface-electrostatic potential and bound one chain of I-A(g7). Furthermore, p524 bound to I-A(g7) more stably than p509 and p530. Of importance, we hypothesized and subsequently confirmed experimentally that the epitope (GAD570-585, p570), which displayed similar characteristics to p524, was a protective epitope by showing that p570-expanded CD4(+)CD25(+) T cells suppressed the onset of diabetes in NOD mice.
  
  
  CONCLUSIONS
  These data suggest that molecular modeling-based structural analysis of epitopes may be an instrumental tool for prediction of protective epitopes to expand functional Tregs.
authors.affiliation: Department of Molecular Immunology, Institute of Basic Medical Sciences, Beijing, PR China.
authors.forename: Guojiang
authors.initials: G
authors.lastname: Chen
authors.forename: Gencheng
authors.initials: G
authors.lastname: Han
authors.forename: Jiannan
authors.initials: J
authors.lastname: Feng
authors.forename: Jianan
authors.initials: J
authors.lastname: Wang
authors.forename: Renxi
authors.initials: R
authors.lastname: Wang
authors.forename: Ruonan
authors.initials: R
authors.lastname: Xu
authors.forename: Beifen
authors.initials: B
authors.lastname: Shen
authors.forename: Jiahua
authors.initials: J
authors.lastname: Qian
authors.forename: Yan
authors.initials: Y
authors.lastname: Li
mesh_terms: D000818:Animals; D015496:CD4-Positive T-Lymphocytes / Q000378:metabolism*; D016207:Cytokines / Q000378:metabolism; D003922:Diabetes Mellitus, Type 1 / Q000276:immunology; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D000939:Epitopes / Q000737:chemistry*; D005260:Female; D005968:Glutamate Decarboxylase / Q000737:chemistry* / Q000378:metabolism; D007167:Immunotherapy / Q000379:methods; D053645:Interleukin-2 Receptor alpha Subunit / Q000378:metabolism*; D051379:Mice; D016688:Mice, Inbred NOD; D008958:Models, Molecular; D013154:Spleen / Q000166:cytology; D050378:T-Lymphocytes, Regulatory / Q000166:cytology* / Q000276:immunology
chemical_list: D016207:Cytokines; D000939:Epitopes; D053645:Interleukin-2 Receptor alpha Subunit; D005968:Glutamate Decarboxylase