The Derivation of New Human Embryonic Stem Cell Lines for Clinical Use

Embryonic stem (ES) cell lines are derived from the pluripotent cells of the early embryo. The key properties of ES cells are their ability to proliferate indefinitely in vitro without differentiation, and their capability to give rise to all cells of the body. The recent derivation of ES cell lines from human embryos (Thomson et al., 1998, Reubinoff et al., 2000) attracts significant attention due to the remarkable potential of these cells for basic scientific research, drug development, and regenerative medicine.

Since human embryonic stem cells (hESCs) are capable of unlimited self-renewal and can give rise to any specialized cell via differentiation, they can potentially be used as an unlimited donor source of cells for transplantation in a variety of disorders that result from the loss of cells or cellular dysfunction. Among these conditions is Parkinson's disease, multiple sclerosis, traumatic spinal cord injury, diabetes, heart failure, liver failure, etc.

It has been proposed that the essential characteristics of primate ES cells should include (i) derivation from the preimplantation or periimplantation embryo, (ii) prolonged undifferentiated proliferation, and (iii) stable developmental potential to form derivatives of all three embryonic germ layers even after prolonged culture (Thomson, 1996). The investigators have derived stem cell lines from early human embryos that meet these criteria (Reubinoff et al., 2000). Our group was second in the world to derive hESC lines, and the first to show their potential to undergo somatic differentiation in vitro (Reubinoff et al., 2000).

To exploit the remarkable potential of hESCs, improvement of currently used methods for culturing and manipulating the cells as well as controlling their differentiation are required. In this context, the investigators have developed novel approaches to cryopreserve (Reubinoff et al., 2001), to genetically modify (Gropp et al., 2003; Ben-Dor et al., 2006) and to control the differentiation of hESCs cells (Reubinoff et al., 2001, Itsykson et al., 2005).

Human ES cell lines are derived from embryos produced by in vitro fertilization (IVF) for clinical purposes. Surplus frozen embryos that are no longer required for infertility treatment are recruited for this purpose after donor informed consent and institutional/national review board approvals are obtained. The embryos are thawed and cultured to the blastocyst stage (5-6 days), the inner cell mass (ICM) comprised of pluripotent cells is isolated, and the stem cells are most commonly cultured on mouse embryonic fibroblast feeder cell layer. The feeder layer is required to prevent differentiation and to promote the proliferation of the stem cells.