Technical advances to genetically engineering human embryonic stem cells

Human embryonic stem cells (hESC) are important to basic scientific research as an in vitro model system for the study of human development and to clinical research as an invaluable cell source for regenerative medicine. The ability to genetically engineer hESC is a critical resource as it facilitates many fundamental studies to understand gene regulation and cell development. These techniques include (1) unidirectional or reversible; (2) non-, pseudo- or completely site-specific; and (3) endogenous and/or pre-engineered DNA sequences modification; where each has its own strengths and limitations. This article reviews the various methodologies to genetically engineer hESC to achieve a stable gene insertion or deletion. We discuss the existing challenges of the well-established methodologies (lentivirus and Cre/loxP system), and further examine recent advances in this field, such as the latest genetic modifying tools (phiC31 integrase, PiggyBac transposase and zinc finger nucleases). We also propose new opportunities for future developments to aid genetic modifications of hESC, and new applications for future basic and therapeutic research in hESC.