Embryonic Stem Cells Stimulate Immune Rejection in Mice

This shouldn’t be a surprise because scientists have worried about it all along, but ES cells injected in mice clearly stimulated the kind of immune rejection seen with transplanted organs. From the Scientific American story:

The much-ballyhooed human embryonic stem cell apparently may share a problem with transplanted organs: a high probability of rejection.

Researchers at Stanford University School of Medicine found that mice mounted an immune response after being injected with human embryonic stem cells (hESCs). The result: all the transplanted stem cells—which hold the promise of maturing into several different types of tissue—were dead within a week.

Wu says that the fact that the hESCs could not survive in the mouse, coupled with previous work showing that the animals also reject mice ESCs, suggests that if human stem cells were transplanted to a patient, they would very likely provoke an immune response. The U.S. Food and Drug Administration, however, has not approved the injection of hESCs into patients because the raw cells have the potential to become cancerous...

The new study not only showed that these cells are not invisible to the immune system, but using a noninvasive molecular imaging technique, the scientists could see when exactly the cells were dying off. The finding means that people who may one day be treated using pools of stem cells taken from many lines could reject them, making the therapy useless.

This is a real problem for proponents of ESCR as a therapy that will make it difficult to permit human trials. Moreover, when added to the tumor problem, the very pronounced difficulties with ESCR should color our thinking about where we want to put public money in research—even without cosidering the ethical objections that have raised such a fuss for the last ten years. It seems clear to me that based on the emerging science alone, public funding should favor IPSCs—which will not have the immune response problem (but as pluripotent cells, still have tumor issues)—and adult/umbilical cord blood stem cells.