Canine Bone Marrow Derived Mesenchymal Stromal Cells Suppress Allo-Reactive Lymphocyte Proliferation in Vitro but Fail to Enhance Engraftment in Canine Bone Marrow Transplantation

摘要

Stable mixed hematopoietic chimerism has been consistently established in dogs mildly immunosuppressed by 200 cGy of total body irradiation (TBI) before and given a brief course of immunosuppression with mycophenolate mofetil (28 days) and cyclosporine (35 days) after dog leukocyte antigen (DLA)-identical marrow transplantation. However, when TBI was reduced from 200 to 100 cGy, grafts were nearly uniformly rejected within 3 to 12 weeks. Here we asked whether stable engraftment could be accomplished after a suboptimal dose of 100 cGy TBI with host immunosuppression enhanced by donor-derived mesenchymal stromal cells (MSC) given after transplantation. MSC were cultured from marrow cells and evaluated in vitro for antigen expression. They showed profound immunosuppressive properties in mixed leukocyte reactions (MLR) in a cell dose-dependent manner not restricted by DLA. MSC and lymphocyte contact was not required, indicating immunosuppression was mediated by soluble factors. Prostaglandin E2 was increased in culture supernatant when MSC were co-cultured in MLR. Adding indomethacin restored lymphocyte proliferation in cultures containing MSC. MSC expressed CD10, CD13, CD29, CD44, CD73/SH-3, CD90/Thy-1, and CD106/VCAM-1. For in vivo studies, MSC were injected on the day of marrow grafting and on day 35, the day of discontinuation of postgrafting cyclosporine. MSC derived from the respective marrow donors failed to avert marrow graft rejection in 4 dogs given DLA-identical grafts after nonmyeloablative conditioning with 100 cGy in a time course not significantly different from control dogs not given MSC. While MSC displayed in vitro characteristics similar to those reported for MSC from other species, their immunosuppressive qualities failed to sustain stable marrow engraftment in vivo in this canine model.