New strains for modeling and for hosting human autoimmune diseases
Project Leader: David Serreze, Ph.D.
Co-Investigator: Dale Greiner, Ph.D. (U Mass Med Sch)
The overall objective of this project is to model autoimmune disease in mice by humanizing genes important for enabling immune responses against pathogens, but not "self." This will be accomplished by systematic deletion of key Major Histocompatibility Complex (MHC) genes in host mouse strains – NOD for study of autoimmune Type 1 Diabetes, and immunodeficient NSG mice for human transplants – to create all-purpose “recipient” strains. These new models will then be examined for ability to host diabetogenic autoimmune responses – spontaneously in NOD mice, and following human T-cell transplant in NSG mice. Because many human disease conditions have autoimmune and immune/inflammatory components, these new tools will likely have broad applications for modeling other diseases.
Background & Rationale
Type 1 Diabetes (T1D) in both humans and NOD mice is an autoimmune disease resulting from interactions between multiple susceptibility (Idd) genes, but with certain major histocompatibility complex (MHC) haplotypes providing the primary disease risk factor. It has long been known that within the MHC, particular combinations of class II variants determine a large component of T1D susceptibility in humans by mediating pathogenic CD4 T-cell responses. Similarly, in the NOD mouse, the presence or absence of certain MHC class II gene products is critical to T1D development. However, because MHC class II expression is largely limited to hematopoietically derived antigen presenting cells (APCs-including dendritic cells, macrophages, and B-lymphocytes) the effects of autoreactive CD4 T-cells on insulin producing pancreatic β-cells and T1D development are indirect. In contrast, like most other cell types, pancreatic β-cells do express MHC class I molecules. Epidemiological studies now indicate that in addition to class II effects, class I variants provide an independent T1D risk factor. Together, these observations indicate that due to an ability to directly engage and destroy pancreatic β-cells, MHC class I restricted autoreactive CD8 T-cells are likely the ultimate mediators of T1D development in both humans and NOD mice. Subsequent studies indicated T1D development in NOD mice depends on expression of the particular class I alleles within the H2g7 MHC haplotype. Similarly, epidemiological, clinical, and transgenic mouse studies have indicated that when expressed in the proper genomic context certain common human class I molecules, such as HLA-A2.1 present in ~40% of Caucasians, can mediate diabetogenic CD8 T-cell responses. Approximately 60% of human T1D patients express the HLA-A2.1 class I variant. Thus, identifying a means to attenuate the generation or functional activity of CD8 T-cells mediating MHC class I restricted autoimmune destruction of pancreatic β-cells may ultimately be of great clinical significance for effective T1D intervention. The full functional activation of CD8 T-cells usually requires cytokine-induced signaling events derived from CD4 helper T-cells. Therefore, it may also be important to identify a means to specifically attenuate pathogenic CD4 T-cells either independently or in conjunction with CD8 effectors.
We have used mice expressing human HLA-A2.1 class I molecules in the absence of any murine counterparts (designated NOD.B2mnull.HHD) to identify autoreactive CD8 T-cell populations of pathogenic significance in a sizeable proportion T1D patients and to develop potentially clinically translatable means to functionally attenuate these effectors. However, mice carrying an inactivated β2m gene are poor breeders which can limit their ability to be produced in sufficient numbers for experimental purposes. Intact ß2m molecules are also required for the stable expression of FcRn that limits the catabolism of IgG. Thus, a lack of ß2m expression also limits the ability to test possible antibody-based interventions for T1D in NOD.B2mnull.HHD mice. Thus, it is critical to develop new NOD and NSG stocks in which murine MHC genes have been directly eliminated and that then can serve as platforms for introduction of transgenes encoding various human HLA molecules, allowing these mice to be employed in a pipeline model to test potentially clinically applicable T1D interventions.