Sequence-specific analysis of microchimerism by real-time quantitative polymerase chain reaction in same-sex nonhuman primates after islet and bone marrow transplantation

Transplantation tolerance

Tolerance has been defined as graft-specific survival in the absence of continued immunosuppression. The mechanisms of central and peripheral tolerance are discussed in this review, as well as the barriers and limitations in achieving graft-specific tolerance. The need remains for definitive laboratory assays to determine the presence of a tolerant state. Genetic biomarker analysis pre-transplant may allow for better donor: recipient matching, lessening the need for immunosuppression, while post-transplant analysis of biomarkers, certain cytokines, and regulatory leukocytes may permit minimally invasive assessment of graft function and potentially, of graft-specific tolerance.

Mesenchymal stem cells enhance allogeneic islet engraftment in nonhuman primates

OBJECTIVE

To test the graft-promoting effects of mesenchymal stem cells (MSCs) in a cynomolgus monkey model of islet/bone marrow transplantation.

RESEARCH DESIGN AND METHODS

Cynomolgus MSCs were obtained from iliac crest aspirate and characterized through passage 11 for phenotype, gene expression, differentiation potential, and karyotype. Allogeneic donor MSCs were cotransplanted intraportally with islets on postoperative day (POD) 0 and intravenously with donor marrow on PODs 5 and 11. Recipients were followed for stabilization of blood glucose levels, reduction of exogenous insulin requirement (EIR), C-peptide levels, changes in peripheral blood T regulatory cells, and chimerism. Destabilization of glycemia and increases in EIR were used as signs of rejection; additional intravenous MSCs were administered to test the effect on reversal of rejection.

RESULTS

MSC phenotype and a normal karyotype were observed through passage 11. IL-6, IL-10, vascular endothelial growth factor, TGF-β, hepatocyte growth factor, and galectin-1 gene expression levels varied among donors. MSC treatment significantly enhanced islet engraftment and function at 1 month posttransplant (n = 8), as compared with animals that received islets without MSCs (n = 3). Additional infusions of donor or third-party MSCs resulted in reversal of rejection episodes and prolongation of islet function in two animals. Stable islet allograft function was associated with increased numbers of regulatory T-cells in peripheral blood.

CONCLUSIONS

MSCs may provide an important approach for enhancement of islet engraftment, thereby decreasing the numbers of islets needed to achieve insulin independence. Furthermore, MSCs may serve as a new, safe, and effective antirejection therapy.