Survival and engraftment of mouse embryonic stem cell-derived implants in the guinea pig brain

Cells implanted at a low dose (1.5 × 103 cells per hemisphere) at 1 week of age were found to survive in very low numbers in some immunosuppressed animals out to 8 weeks. Four weeks post-implantation, cells implanted in high numbers (105 cells per hemisphere) formed teratomas in the majority of the animals implanted. Although implanted cells were found to migrate extensively within the brain and differentiate into mature cells of neural (and other) lineages, the safety issue related to uncontrolled cell proliferation precluded the use of this cell type for longer-term implantation studies. We conclude that the pluripotent cell type used in this study is unsuitable for achieving safe engraftment in the guinea pig brain.