High efficiency and high fidelity somatic cell nuclear reprogramming
Embryonic stem (ES) cells possess a remarkable property of pluripotency to give rise to all cells of the organism; therefore holding great promise for regenerative medicine. ES cells are envisioned as potential sources for use in cell replacement therapies. However, as with any allogeneic material, ES cells generated from fertilized embryos, and derivatives of such cells, inevitably face risks of immunorejection when transplanted into a host. A solution to the problem of rejection is to derive ES cells from embryos cloned from a host patient’s own cells, because any replacement cells would be genetically identical to the host.
ES-like cell lines have been generated from somatic cells via somatic cell nuclear transfer (SCNT) technology. By this technique the developmental fate of a somatic cell nucleus can be reprogrammed following transfer into an enucleated oocyte, resulting in a cloned embryo that can be used to derive novel ES cells. The nuclear transferred ES cell lines have been shown to possess the same characteristics for self-renewal and unlimited differentiation capacity as those of conventional ES cell lines derived from normal embryos produced by fertilization. Although these cloning experiments are direct evidence that a terminally differentiated cell can be fully reset to a pluripotent ES cell state, the fidelity of reprogrammed nuclei is very inefficient as evidenced by the extremely low frequency (<5%) of producing healthy offspring in animals. Thus, the current available SCNT technique makes ES cell related therapies only an academic possibility at this time.
Alternative approaches in deriving stem cells are based on genome-wide analysis on genes that are involved in the molecular control of pluripotency. Takahashi and Yamanaka (2006) have recently reported the induction of pluripotent stem cells from mouse embryonic and adult fibroblast cells by introducing four factors (Oct3/4, Sox2, c-Myc and Klf4) under ES cell culture conditions. All four factors play a crucial role in maintaining the undifferentiated state and proliferation of ES cells in culture. The resultant induced pluripotent stem (iPS) cells are similar but not identical to bona fide ES. The iPS cells are not fully reprogrammed and have a limited capacity to stably integrate into normal tissues in vivo. Thus, this approach is unlikely to sufficiently reprogram somatic cells to a state that will be optimal for human therapeutic cloning.
The proposed research is to develop a new high-efficiency nuclear transfer (HENT) approach to obtain high fidelity ES cells. The approach is based on the current existing SCNT method in combination with transcription factors that are known to be required for ES cell renewal and pluripotency. The long-term goal of the proposed research is to apply HENT to derive high fidelity human ES cells and subsequently for cell replacement therapies.
Efficient derivation of host patient-specific embryonic stem (ES) cells is a fundamental step, currently a bottleneck, for cell replacement therapies and regenerative medicine. The proposed research aims to increase the efficiency of ES cell derivation from somatic cells through a modified nuclear transplantation technique. The result of such work will potentially benefit the state of California and its citizens in many aspects including health, life, costs, and leadership in biomedicine.
∑ About half of California families have a child or adult who suffers or will suffer from devastating medical conditions that could potentially be treated or cured with stem cell therapies.
∑ Development of ES cell therapies that treat diseases and injuries with the ultimate goal to cure them will improve the California health care system and reduce the long-term health care cost burden on California.
∑ Intellectual property resulted from the research will provide an opportunity for the state to benefit from royalties, patents, and licensing fees.
∑ The research will contribute to the advancement of the biomedical research in California to world leadership.