Tolerance to stem cell grafts
The research of this proposal outlines a new strategy for improving transplantation tolerance in combinations of mismatch donor/recipient combinations such as parent/child, non-identical sibling combinations, and most combinations of unrelated donors. It has been shown in the past that a transfer of adult stem cells (hematopoietic stem cell) from a prospective organ donor in some cases have been able to establish a new parallel immune system (chimerism), which have made the transplant patient tolerant to the new organ graft.
In connection with research on the autoimmune disease type 1 diabetes in humans, we have over the past 15 years developed a humanized mouse model that exclusively expresses human transplantation antigens (HLA-DR and DQ genes). The immune function of these mice have over these years been optimized with several new human transgenes to better reflect the function of the original immune and autoimmune responses that these HLA genes control in humans. Thus, we have transgenic mice that represent diabetes susceptible human HLA genes and other mice with HLA genes with known protective effects against development of type 1 diabetes.
The proposal promotes the idea to manipulate and engineer the adult stem cell graft before transfer with a particular transient/short-lived defective virus infection, which boosts the capacity of these stem cells to survive in the recipient organism to further preserve donor specific tolerance in the future and allow for long-term survival of the "second graft" for example a kidney graft or new beta islets in diabetes.
The humanized HLA class II transgenic mice will be used to evaluate the tolarizing function of the manipulated/engineered stem cell graft to protect and prolong graft survival after established immune chimerism followed by a new transplantation challenge of the mice with a donor specific fetal heart grafts or donor specific beta-islets transplantation of the mice.
This re-education of the immune system may then allow us to transfer new donor beta cells from mice that carry transplantation antigens that are protective to the development diabetes into mice, where the insulin producing beta cells of the pancreas have been completely eliminated by means of high dose streptozotocin treatment.
Since we are dealing with human transplantation antigens, we hope that our findings will inform the use of similar approaches to allow for transplantation of human stem and beta cells into patients with diabetes.
This proposal is beneficial to the State of California because it will establish an unique method to establish chimerism with human MHC class II molecules in the mouse. At the same time, it will investigate the possibility that improving antigen processing and presentation (APP) in the context of forced expression of tissue-restricted antigens (TRAs) by Aire and lack of co-stimulation, we will create a situation analogous to central tolerance in the thymus with cells in the periphery. A precedent for this notion exists already with extra-thymic Aire-expressing cells (ETACs) in the spleen. With subsequent tranplantation of allogeneic beta cells into diabetic mice, we will have established a paradigm for how to treat human T1D in the future. All systems that will be investigated in the mouse can be adapted directly to humans and we have all human transcription factors already. Thus, our humanized mice will inform directly how to approach chimerism and organ transplantation in humans, using stem cells and/or more mature organs.