Co-Transplantation of Hematopoietic Stem Cells and GM-CSF/G-CSF/CSF-Transfected Mesenchymal Stem Cells in SCID Mice.

Mesenchymal stem cells (MSC) are multipotent and believed to facilitate the engraftment of hematopoietic stem cells (HSC) when transplanted simultaneously in animal studies and recently even in human trials. In this study, we transfected culture-expanded MSC with GM-CSF, G-CSF, and CSF cytokine genes and then co-transplanted with HSC to further promote HSC engraftment. Mononuclear cells were harvested from the various sources and seeded in long-term culture for ex vivo MSC expansion. The phenotype and purity of MSC were assessed by flow cytometry. We transferred the above three cytokine genes into ex vivo expanded MSC, confirmed transfection by fluorescent microscope of GFP, and thereafter did co-transplantation with HSC. A total of 1x10⁷ HSC plus MSC/uL were introduced to tail vein of SCID mice. After 3–7 weeks later, with venous blood from the eyeballs, homing and engraftment of human cells were determined by flow cytometry and fluorescence in situ hybridization (FISH) studies. The total nucleated cell count and the engraftment of CD45+/CD34+ cells and XX/XY-positive human cells significantly increased in co-transplanted mice and even higher with the cytokine gene-transfected MSC in the order of GM-CSF, SCF, and G-CSF transfections (P<0.05). These results suggest that MSC transfected with hematopoietic growth factor genes are capable of enhancing the hematopoietic engraftment. Now we are planning to deliver genes involved in homing and cell adhesions, e.g., CXCR4, VLA, or TPO into ex vivo expanded MSC and do co-transplantation with HSC to further increase the efficiency of stem cell transplantation.