The search for an ideal mesenchymal stromal cell donor in the horse : this dissertation is presented for partial fulfillment of the degree of Doctor of Philosophy in Veterinary Science, Massey University, Palmerston North, New Zealand, School of Veterinary Science

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The search for an immune privileged allogeneic mesenchymal stromal cell (MSC) line has been an interest for many biomedical researchers. This holds true for the field of equine medicine where MSCs are frequently used in research and clinical cases for the treatment of musculoskeletal disease. An ideal allogeneic MSC suppresses the immune system of the recipient leading to decreased inflammation in the face of disease. The ideal MSC also expresses the markers of a multipotent cell, retains a high level of viability and is able to perform anabolic activities to enhance repair. Our research sought to more clearly define the expression of MSC markers harvested from different equine MSC donors. Bone marrow-derived MSCs from Thoroughbreds, Standardbreds, and a subset of universal blood donor-type Standardbreds were compared. Standardbred MSCs showed significantly less MHC class II expression at early passages as compared to Thoroughbreds. When universal blood donor Standardbreds were compared to non-blood donor Standardbreds, the only significant variation was that CD90 was expressed more highly on universal blood donor MSCs as compared to non-blood donor Standardbred MSCs. The conclusion from stage one of our research was that universal blood donor-type Standardbred horses appeared less likely to cause an MHC II driven immune reaction and had the highest levels of bone marrow-derived MSC markers expressed at passage 2-4. We then compared the MSC donor cells in an in vitro trial exploring several arms of the immune system to understand the effects of the MSCs without prior activation of the immune cells, as has been done previously. Overwhelmingly, we found that MSCs of allogeneic origin cause very little to no activation of the immune system as compared to autologous MSCs. B cell and activated T lymphocyte populations were similar between the autologous and allogeneic MSCs. Those allogeneic MSCs that expressed little MHC II prior to interaction with the immune cells (MHC II-low MSCs) had reduced activation of recipient lymphocytes and neutrophils as compared to those MSCs expressing high levels of MHC II prior to interaction with immune cells (MHC II-high MSCs). MHC II-low MSCs, both of universal blood donor and non-blood donor origin, had higher expression of the genes we studied when placed in an allogeneic environment. These include both anabolic molecules known to assist in healing and some catabolic molecules. This knowledge combined with published information that ‘activated’ MSCs can be more beneficial to healing than unactivated MSCs, support the use of the more metabolically active MHC II-low MSCs as compared to MHC II-high MSCs. Based upon a wide array of testing, allogeneic MHC II-low MSCs created a low level of immune activation and an increased level of gene anabolic gene expression as compared to autologous MSCs. In conclusion passage 2-4 MHC II-low MSCs are preferred for use in allogeneic therapy.
Horses, Diseases, Treatment, Stem cell donors, Mesenchymal stem cells