047 Allogeneic Transplantation of Genetically Modified Primate Embryonic Stem Cells

Aim: To examine the efficacy and safety of human embryonic stem (ES) cell-based therapies, allogeneic transplantation of monkey ES cells would be useful. We transplanted genetically marked monkey ES cells into the allogeneic fetus. Methods and Results: Cynomolgus ES cells were transduced once using a simian immunodeficiency virus-based lentivirus vector encoding the GFP gene driven by the CMV promoter at 1, 10 and 100 transducing units per cell. Five days posttransduction, 60, 80 and 90% of the cells expressed GFP, respectively, and the expression levels were stable for 5 months. GFP expression was still observed after embryoid-body formation. The gene-marked ES cells were transplanted into the cynomolgus fetus in the abdominal cavity (n = 2) or liver (n = 1) after the first trimester. The fetuses were delivered 1 month posttransplantation. Transplanted cell progeny were detected (∼1%) in multiple tissues by quantitative PCR and in situ PCR of the GFP sequence. No teratoma was found in the tissues. Conclusions: Cynomolgus ES cells can be engrafted in the allogeneic fetus. We are now trying to transplant cynomolgus ES cells differentiated to neural or hematopoietic lineage.