3D Grown Human Placental-Derived Mesenchymal Stromal Cells (PLX-I) Support and Potentiate the Engraftment of Human Cord Blood Unfractionated (UFCBC) and Fractionated CD34+ Cells (hCD34+) in Irradiated NOD/SCID Mice.

The use of human umbilical cord blood (hUCB) for transplantation (CBT) in adults is limited due to the low cell number in each unit. Engraftment rates are lower and the time to neutrophils and platelet recovery is longer following CBT compared to bone marrow (BM) transplantation (28 vs 14 days, respectively). Co-transplantation of human hematopoietic stem/progenitor cells (hHSC) with mesenchymal stromal cells in an irradiated NOD/SCID mice model has been demonstrated to promote HSC engraftment. In a typical clinical setting of CBT, unfractionated cord blood cells (UFCBC) are usually used. On the other hand, in the irradiated NOD/SCID mice model, the CD34+ enriched fraction is usually used. Therfore, performing pre-clinical studies using UFCBC would better reflect the outcome in the clinical setting. Using PluriX technology, we expanded human placental derived mesenchymal stromal cells on 3D carriers in a bioreactor (PLX-I) and evaluated their potential to promote the engraftment of UFCBC or hUCB derived fractionated CD34+ cells (hCD34+) in NOD/SCID mice. UFCBC (10⁷) or hCD34+ (5×10⁴) were injected into the tail vein of 7–8 week old NOD/SCID mice along with 0.5×10⁶ or 1×10⁶ PLX-I cells. Following 5–6 weeks, FACS analysis of % human CD45+ cells in mice BM demonstrated that in the PLX-I untreated mice, the 10⁷ UFCBC engrafted in a lower rate compare to 5*10⁴ hCD34+ (6.28% vs. 14.43% respectively, n=10). Furthermore, in both settings, hCD34+ and UFCBC, the addition of PLX-I enhanced the hHSC engraftment 1.7 and 2 fold respectively compared to PLX-I untreated mice (24.13% vs. 14.43% in hCD34+ setting and 12.85% vs. 6.28% in UFCBC setting, n=10). We conclude that UFCBC can be used for hHSC engraftment in NOD/SCID mice model and co-transplantation of these cells with PLX-I may serve as a promising approach for the improvement of the hitherto delayed engraftment following cord blood transplantation.