Genome Replacement in Human Embryonic Stem Cells
Embryonic stem cells have tremendous potential value for the treatment of many diseases and injuries, but like other transplants their use is likely to be limited because the immune system of the recipient will probably reject the transplant unless there is a good genetic match between donor and recipient. The ideal solution to this problem would be to replace the genetic material of stem cells with genetic material from the prospective patient, and to use the genetically modified stem cells in therapy. Work on experimental animals has shown that it is possible to do this by implanting a nucleus from one of the patient’s body cells into an oocyte from which the nucleus is removed. The oocyte is then allowed to grow into an embryo, and stem cells are derived from the embryo when it reached the appropriate stage. This method suffers from several drawbacks, the most significant being the need for oocyte donors, the technical difficulty of performing the nuclear replacement, and ethical objections to the production of embryos which are later to be destroyed for the benefit of the patient.
We have devised an alternative strategy in which the nuclei of existing stem cell lines will be replaced by nuclei from cells of the prospective patient, by physically fusing together the stem cell with a body cell from the patient under condition preventing the survival of the stem cell nucleus. The resulting cell lines, with the genetic material from the patient in stem cell cytoplasm, will then be grown up and should be suitable for use in cellular therapy. In the proposed research we will compare several methods for incapacitating or removing the stem cell nucleus from the fused cells, and we will rigorously test the resulting cell lines for the correct genetic makeup as well as the retention of developmental properties characteristic of stem cells.
California has taken the lead in the nation in providing support for stem cell research and especially in support for developing the use of human embryonic stem cells in cellular therapy for many diseases and disorders. Many laboratories are investigating methods to control the differentiation of these cells, so that they will no longer be likely to produce tumors in the patient, and they will be more suited to regenerative therapy in specific organs. But the full potential of these cells cannot be met until a solution is found to the problem of immune rejection by the patient. Claims made outside the U.S. for success in generation of stem cell lines that are genetically tailored to the patient turned out to be fraudulent, so the field still awaits a solution to this problem.
The conventional approach to generating patient-specific stem cell lines would be to transplant a somatic cell nucleus into an oocyte obtained from a donor, then allow the oocyte to develop into an embryo and recover stem cells from that embryo. However, this has several drawbacks as stated elsewhere in this proposal.
California could continue to lead the nation in embryonic stem cell research and in developing the use of these cells in cellular therapy if a solution cold be found to the problem of immune rejection. Here we propose a novel but feasible method of generating patient-specific embryonic stem cells from existing stem cell lines, avoiding the problems of obtaining egg donors, and of generating embryos for later destruction. If this method could be developed in California it would allow the state to continue the momentum that has built up in stem cell research, and to continue to build upon it by moving to the next stage where these cells are actually used in the clinic to treat some of the most devastating injuries and diseases affecting our people.