Purified MHC-Matched Hematopoietic Stem Cell Transplantation Following Total Lymphoid Irradiation and Anti-Thymocyte Globulin (TLI+ATG) Blocks EAE Pathogenesis.

In prior studies, we demonstrated that transplantation of major histocompatibility complex (MHC) matched and mismatched purified hematopoietic cells (HSCs) can block diabetes pathogenesis in pre-diabetic NOD mice. Here we applied this treatment to experimental allergic encephalomyelitis (EAE), an animal model for the human autoimmune disease multiple sclerosis (MS). C57BL/6 (B6) strains congenic for the CD45 locus were immunized with MOG 35–55 to induce disease. Similar to our studies in NOD mice we observed that disease response after transplantation of MHC-mismatched hematopoietic cells in EAE affected mice was superior to those that received congenic cells. Importantly, mice transplanted with MHC-matched HSC or BM showed no significant improvement in disease symptoms when compared with congenic recipients or disease controls. This result was markedly different from the positive response observed in NOD mice transplanted with MHC-matched HSC. We then sought to optimize translation of this approach by giving total lymphoid irradiation (TLI) plus anti-thymocyte globulin (ATG), a non-myeloablative regimen and permits allogeneic hematopoietic cell engraftment with significant protective effect against GVHD. We found that TLI/ATG treatment in wild type C57BL/6 mice permit engraftment of purified HSC isolated from MHC-matched AKR/B donors and improve disease severity significantly. The level of stable mixed chimerism correlated with the clinical score. While the prior studies demonstrated that a class of regulatory cells that express both nature killer cell and T cell markers (NK-T) are present at high levels in TLI/ATG treated mice, we determined that regulatory CD4+CD25+Foxp3+ cells are also present at a disproportionately high levels as compared to wild type animals. To study the role of regulatory T cell in disease protection, a flexible lentiviral vector platform supporting constitutive expression of a Tet-transactivating component with a selection marker and coordinated conditional expression of miR-shRNA targeting Foxp3 gene products in stem cells is being developed. The detailed mechanism will be discussed. We hope a MHC-matched hematopoietic graft in conjunction with TLI/ATG conditioning shown here to successfully ameliorate EAE can be translated to the treatment of human autoimmune disease.