Since their discovery eleven years ago, there has been steady progress towards the application of human embryonic stem (ES) cells in medicine. Now, the field is on the threshold of a new era. Recent results from several laboratories show that human skin cells can be converted to cells resembling ES cells through simple genetic manipulations in the laboratory. There is currently much excitement about these induced pluripotent stem (iPS) cells, which might have advantages over ES cells in studying and treating disease. However, we do not yet sufficiently understand their nature and potential to be certain that they can replace (ES) cells in research and therapy. Because of this, it is important to continue to develop new ES cell lines, and to compare their properties with those of iPS cells. Technological advances in ES cell research now enable us to grow stem cells under conditions that are much more suitable for future patient use than those used to develop the first ES cell lines.
In the second year of this grant, we have refined and validated new technologies for deriving and propagating ES and iPS cell lines. One of our goals was to derive these lines under defined conditions (where all the chemical and protein additives used in the cell cultures are known) and without the use of animal products. The use of defined culture systems means that cells can be produced in a standardized consistent fashion and that no unknown and potentially hazardous components are present. Elimination of animal products reduces the possibility that additives like animal serum or animal helper cells could transmit disease causing agents like viruses to the stem cells. Our culture system is fully defined, and is based on a totally new molecular pathway for maintaining stem cell propagation that we have discovered. We have now fully validated the system for long-term support of human pluripotent stem cells.
Deriving new ES cell lines from embryos can be more demanding than maintaining existing lines. We are in the process of deriving new ES cell lines using another system that still employs helper cells (feeder cells) but has no animal products (xeno-free conditions). We have successfully used this system to derive iPSC (below).
Current techniques for deriving iPS cells require genetic modification of the adult cells, a procedure that carries a risk of inducing changes in the stem cells that cause them to form tumors when injected into a host. We have successfully used these techniques to make iPS cell lines in our laboratory and have developed four new iPSC lines that are being distributed through our CIRM Shared Laboratory Facility. However, because of the risks associated with genetic modification, we have explored alternative methods for making iPS cells. We have now made 5 iPSC lines using technology that enables us to remove the genetic modification after the reprogramming event. These cell lines were derived under xeno-free conditions.
In the final year of this grant, we will complete the derivation and characterization of ES and iPS cell lines under identical conditions, and we will carefully compare the properties of these two types of pluripotent stem cell.