Perspectives and future directions of human pluripotent stem cell-based therapies: lessons from Geron's clinical trial for spinal cord injury.

Halting the first clinical trial on the use of embryonic stem cell derivatives for spinal cord injury resulted in disappointment and created concerns about the future use of pluripotent stem cell-based therapy in the treatment of human diseases. This article presents reflections and concerns related to the halted embryonic stem cell-based clinical trial and discusses some important and controversial issues for achieving safe and successful cell therapy. This manuscript highlights two important points for successful translation of pluripotent stem cell-based therapy in clinics: (i) reproducible xeno-free growth and differentiation of pluripotent stem cells in good manufacturing practice conditions as the prerequisites to ensure a defined and controlled cell source and (ii) extensive studies in small and large animal models and comprehensive basic studies to determine any adverse or toxic effects of transplanted cells, especially teratoma formation, in addition to improving surgical procedure and cell delivery system.