Safety Implications of Epigenetic and Genetic Adaptation of Human Embryonic Stem Cells to Culture In Vitro
Ten years after the discovery of human embryonic stem (ES) cells, we are on the verge of the first clinical trials of products derived from this unique, remarkable and renewable source of healthy human tissue for transplantation therapies. However, safety concerns around the use of ES cell grafts are holding back clinical applications. A key issue is the known potential for formation of tumors or other inappropriate growths in ES cell derived grafts. This concern is amplified by the known propensity for ES cells to develop genetic alterations during their growth in the laboratory; these genetic changes resemble those associated with various forms of human cancers. Also, ES cells can undergo what are known as epigenetic alterations, or heritable changes in the way the cell reads out its genetic code. These epigenetic alterations may also predispose affected cells to form cancers. Although there is concern, in fact there have been few studies to assess how these epigenetic and genetic changes might arise, how best to detect them, and what their implication is for cell behavior in vivo. It is imperative for the future of regenerative medicine that we understand this area better: concern certainly is warranted, but an overly cautious approach will delay the implementation of therapies that have great potential to alleviate suffering. This study aims to provide a scientific basis for assessing and monitoring the process of how ES cells acquire cancer-like properties during propagation in the laboratory, and for understanding the implication of changes in the cell for the safe use of ES products in the clinic. We will examine carefully how the cells change in terms of their growth properties, and how this affects their ability to turn into specialised cells that would be used in treating patients. We will see what genetic and epigenetic changes in the cells occur, and we will monitor several key pathways in cancer development that might be expected to affect ES cells. Using this information, we will design sensitive tests that can detect small numbers of abnormal cells in a culture population. We will then see how the process of genetic and epigenetic change affects the behavior of cells in vivo, whether the changes cause tumor formation or disturbances in the formation of specialized tissues like nerve cells. We will also assess how sensitive current animal assays are for detection of abnormal cells. The results of this work will provide a strong basis for preclinical assessment of ES cell safety. This is an essential step on the road to therapy.
Cell products derived from embryonic stem cells are rapidly moving towards clinical trials for several devastating medical conditions. However, there are safety concerns that surround the use of these products, in particular, the possibility that ES derived cells might form tumors or other inappropriate growths following transplantation. There is little scientific data in the public domain to guide regulatory decisions in this area, but much at stake: excessive haste could result in adverse outcomes that could hold back progress for years, whilst an overly conservative approach likewise could needlessly delay the implementation of new therapies of great potential. This study will provide a scientific basis for safety assessment of stem cell based therapeutics. By putting the process of safety assessment on a stronger scientific foundation, we will ensure that patients in California and elsewhere see the benefits of stem cell based therapies as soon as possible and with the minimum of risk. If the State is to take the lead in translating stem cell research into clinical benefit, we must address this critical area in a timely fashion.