Adult stem cells obtained from bone marrow have been used clinically for decades to treat leukaemia. Since no ethnic issues are associated with adult stem cells, people are trying to isolate more stem cells lines in adult tissues. However, the major limitation of using adult stem cells is they tend to lose their stem cell properties and become more specialized during ex vivo
Embryonic stem cells are capable of unlimited self renewal without difficulties to maintain their stem cell state. So they provide a great potential for transplantation therapies of a wide range of degenerative diseases. The derivation of first human stem cell line was reported in 1998, when a group led by Dr. James Thompson at the University of Wisconsin developed a technique to isolate and grow the cells. Clinical trials with cells derived from embryonic stem cells are likely to commence within the next few years.