1.   Adult stem cells, if they could be extracted from each patient as need arose, could be used without any risk of immune rejection.

2.   But embryonic stem cells grow much more prolifically than adult stem cells and biologists have in mind several ways of handling the problem of immune rejection.

3.   But scientists must figure out a way to overcome the problem of immune rejection before using stem cells as treatment, experts say.

4.   Many serious technical problems remain to be resolved, including finding ways to guide the stem cells down desired paths of development and ways to prevent immune rejection.

5.   Second, transplant experts expect to face other problems involving immune rejection, although less daunting ones.

6.   The hope is that those stem cells can generate organs that will not provoke immune rejection when transplanted into the patient who provided the cells for cloning.

7.   The treated cells would then be returned to the patient without danger of immune rejection.

8.   Treating patients with cells derived from their own stem cells would avoid any problems of immune rejection.

9.   When such tissues were placed back into the cow, researchers were surprised to find there were no immune rejection problems.

10.   Immune rejection remains a key stumbling block.