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The use of UCB for transplantation in adults is limited due to the low cell number in each unit. Engraftment rates are lower and the time for neutrophil and platelet recovery is longer following CBT compared to bone marrow (BM) transplants. Co-transplantation of human hematopoietic stem/progenitor cells (HSC) with mesenchymal stromal cells in an irradiated NOD/SCID mice model has been demonstrated to promote HSC engraftment. Using PluriX technology, we expanded human placental derived MSC on 3D-carriers in a bioreactor (PLX-I) and evaluated its potential to promote UCB engraftment in the NOD/SCID mice model. Flow cytometer analysis detected high rates of expression of CD105, CD73, CD90 and CD29 and lacked expression of CD45, CD34 and CD19 surface markers in the PLX-I cells. PLX-I cells were capable of differentiation into bone, adipose tissue and cartilage under specific inductive conditions. Additionally, they possess both immune privileged and immune suppressive characteristics in a mixed lymphocyte reaction (MLR) assay. In this study 60 – 100x103 hUCB derived CD34+ cells were injected into the tail vein of 7–8 week old NOD/SCID mice along with 0.5x106 PLX-I cells. Human cell engraftment was tested in both sublethally irradiated (350 rad) and chemotherapy (50 mg/kg busulfan) treated NOD/SCID mice. Following 5–6 weeks, mice BM FACS analysis showed a significant increase in % hCD45+ rate in mice transplanted with PLX-I cells compared to mice transplanted with CD34+ cells alone: 13.6 vs. 31.7, p=0.01, (n=6) in the irradiation setting and 28.8 vs 6.3, p<0.05 (n=7) in the chemotherapy setting. These preclinical results demonstrate the potential of human placental-derived MSCs, grown as a 3D culture (PLX-I), to promote hUCB CD34+ cell engraftment in BM. Co-transplantation of PLX-I may be considered for improving the delayed engraftment using CB as the source of HSC.

Pluristem Therapeutics, Inc., based in Haifa, Israel, is a regenerative, biotherapeutics Company dedicated to the commercialization of nonpersonalized (allogeneic) cell therapy products. The Company is expanding noncontroversial placental-derived mesenchymal stem cells via a proprietary 3D process, named PluriX, into therapeutics for a variety of degenerative, malignant and autoimmune disorders. Pluristem will be conducting Phase I trials in the USA with its first product, PLX-I, which addresses the global shortfall of matched tissue for bone marrow transplantation by improving the engraftment of hematopoietic stem cells contained in umbilical cord blood.

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