Diabetogenic Role of MHC Class I Alleles in NOD Mice

Jackson Laboratory, Bar Harbor ME

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Abstract

DESCRIPTION (provided by applicant): In addition to long known contributions from particular MHC class II molecules, there is growing appreciation that in both humans and NOD mice some MHC class I variants also play an essential role in autoimmune type 1 diabetes (T1D) development by mediating pathogenic CD8 T-cell responses. The overall goal of this renewal application continues to be dissection in NOD based mouse models of the mechanistic basis for MHC class I restricted diabetogenic CD8 T-cell development, and use of this information to identify potentially clinically translatable means to attenuate such effectors. While the H2g7 MHC haplotype encoded Kd and Db class I molecules are essential to T1D development in NOD mice, they are common variants also characterizing many non-autoimmune prone strains. This suggested H2g7 MHC class I molecules aberrantly mediate diabetogenic CD8 T-cell responses in NOD mice through interactions with some of the many other disease susceptibility (Idd) genes characterizing this strain. Aim 1 will test the hypothesis based on preliminary mRNA transcript profiling and congenic truncation analyses that a hyper-expression variant of the NFkB inhibitory Nfkbid gene located within the previously identified Idd7 locus is an important contributor to the failure of diabetogenic CD8 T-cells to undergo thymic negative selection in NOD mice. Similarly, epidemiological studies indicate that in humans certain common class I molecules such as HLA-A2.1 can aberrantly contribute to T1D development also likely through a genetically contextual process. Indeed, we found that when expressed in the context of the NOD genome, human HLA-A2.1 molecules mediate diabetogenic CD8 T-cell responses. HLA-A2.1 restricted diabetogenic CD8 T-cells in this NOD background stock primarily recognize two peptides each derived from the pancreatic ss cell proteins insulin (INS) and islet specific glucose-6-phosphatase catalytic subunit related protein (IGRP). Immunological tolerance can be efficiently induced to antigens bound to autologous leukocytes by the cross-linking agent ethylene carbodiimide (ECDI), and such an approach is in a clinical trial as a possible multiple sclerosis intervention. However, there are many hurdles to cell based therapies, and possible T1D intervention approaches can only be considered in humans already at a late prodromal stage of disease development. Therefore, to broaden potential clinical translation, Aim 2 will test the possibility supported by new preliminary data that treatment with synthetic microparticles bearing appropriate ECDI coupled INS and/or IGRP autoantigenic peptides can exert late disease stage T1D protective effects in NOD-HLA-A2 mice, and/or enables reversal of established disease by pancreatic islet transplantation. Finally, epidemiological evidence implicates B39 as a potentially highly potent diabetogenic HLA class I variant in humans. Thus, Aim 3 will assess whether transgenically expressed B39 molecules mediate diabetogenic CD8 T-cell responses in NOD mice, and if so, identify ß cell autoantigens displayed by this class I variant, and test their capacity to serve as broadened disease intervention reagents.