If the person's own cells can be used to generate stem cells, there would be no risk of rejection. Similarly, cloned stem cells could generate organs for transplantation. This would not only solve the same problem of immune system rejection, but also the overall shortage of donated organs. Roslin Institute scientists didn't make Dolly so they could get on The Tonight Show . Rather, they wanted a way to make transgenic animals to produce medicinally useful proteins in their milk.
Scientists create transgenic animals by incorporating genes from one animal into another.
The resulting transgenic animals can then express the protein that the new gene encodes. In normal breeding, successive generations often lose the incorporated gene, and making new transgenic animals is very difficult. Once a transgenic animal is made, cloning makes sure that its genetic makeup remains the same through successive generations. In the same way that cloning copies transgenic animals that produce medicines, cloning can also copy animals bred to provide organs for people. The recently announced pig clones may help solve this problem, if the cloned pigs have been genetically modified to prevent rejection.