Stanford researchers have published results that verify, yes, human embryonic stem cells are rapidly rejected by the immune system, considered foreign enemies when injected into the body. When transplanted into mice with normal immune systems, the cells were dead within a week. In subsequent transplant attempts the embryonic stem cells were eliminated even faster, showing that the immune system had been primed to reject the cells, similar to a vaccination.

The current paper is no surprise. Earlier reports showed the same rejection using mouse embryonic stem cells injected into the heart, with increasing rejection potential as the cells differentiated. With other differentiated embryonic stem cells similar rejection has been observed.

Of course, the FDA has yet to approve any clinical trial with embryonic stem cells because these cells (whether growing or even pre-differentiated) have a nasty tendency to form cancerous tumors. But the current findings show there are multiple problems with potential application of embryonic stem cells for humans.