Co-Transplantation of Autologous Umbilical Cord Matrix Mesenchymal Stem Cells Improves Engraftment of Umbilical Cord Blood in NOD/SCID Mice.

Umbilical cord blood (UCB) is a viable source of hematopoietic stem cells for transplantation of children and adults undergoing treatment for hematological malignancies. However only 4% of adults 70kg and over have a UCB unit available which contains the widely accepted minimum cell dose of 1.5x10⁷ mononuclear cells per kilogram. Co-transplantation of hematopoietic stem cells with mesenchymal stem cells may enhance engraftment and therefore decrease transplant-related morbidity and mortality from delayed leukocyte recovery associated with a low pre-transplant cell dose. Umbilical cord matrix (UCM) cells, found in the Wharton’s Jelly, were easily and reliably extracted from minced pieces of cord by culture in RPMI + 20% fetal bovine serum at 37° and 5% humidified CO₂. UCM expand best in 20% FBS but can also be expanded in human serum, autologous serum, and X-VIVO10. Small (1–3mm) minced pieces of umbilical cord can be cyropreserved at the time of delivery in 10% DMSO solution. UCM cells exhibit a fibroblast morphology and express markers common to mesenchymal stem cells: CD73 (SH3), CD105 (SH2), CD 29, CD44, CD49b, CD117, CD166, STRO-1 and HLA-DR. UCM are negative for CD14, CD 19, CD34, and CD45.

Morphology and cell surface marker expression is stable after greater than fifteen passages. UCM cells grown in culture were shown to produce more GM-CSF and G-CSF than similar numbers of adult bone marrow mesenchymal stem cells, GM-CSF 178 pg/mL versus 77 pg/mL and G-CSF 82.6 pg/mL versus 7.9 pg/mL. NOD/SCID mice treated with anti-NK 1.1 antibodies and irradiated with 350 cGy were injected with suboptimal (1x10⁴) numbers of cord blood CD34+ cells with and without 1x10⁶ autologous UCM cells, extracted from the same umbilical cord as the cord blood CD34+ cells. Bone marrow was harvested at six weeks post transplant from both femurs and tibias and peripheral blood obtained via cardiac puncture. The percentage of human CD45+ cells in the bone marrow and the peripheral blood was assessed by flow cytometry. NOD/SCID mice transplanted with 1x10⁴ cord blood CD34+ cells alone had 3.0% human CD45+ cell engraftment in the bone marrow and 3.6% human CD45+ cells in the peripheral blood, while NOD/SCID mice transplanted with 1x10⁴ CD34+ cells and 1x10⁶ UCM cells had an average of 27.3% human CD45+ cell engraftment in the bone marrow and 3.9% human CD45+ cells in the peripheral blood. These results indicate a trend towards improved engraftment in vivo with co-transplantation of suboptimal numbers of umbilical cord blood CD34+ cells and autologous umbilical cord matrix cells versus transplantation of suboptimal numbers of umbilical cord CD34+ cells alone.