we  must be able to manipulate stem cells so that they possess the necessary characteristics for successful differentiation, transplantation, and engraftment.

The following is a list of steps in successful cell-based treatments that scientists will have to learn to control to bring such treatments to the clinic.

To be useful for transplant purposes, stem cells must be reproducibly made to:

• Proliferate extensively and generate sufficient quantities of tissue.
• Differentiate into the desired cell types.
• Survive in the recipient after transplant.
• Integrate into the surrounding tissue after transplant.
• Function appropriately for the duration of the recipient’s life.
• Avoid harming the recipient in any way.

Graft rejection is a major problem and the methods need to be designed  to avoid the problem. Scientists are experimenting different strategies to overcome the problem.