I don’t think there are any magic bullets.
Having said that, it seems hard for me to believe that stem cells will not have some future role to play in medicine.
What we can do now (I’ve done some of this myself) is grow them, manipulate them genetically, differentiate them into various types (neurons, cardiac myocytes, hepatocytes, and all kinds of other things), and implant them.
Getting stem cells, or the progeny of stem cells, to go right where we want, stay alive, and do just what we want has proven to be an enormously difficult task. The initial hopes that one could simply introduce totipotent or pleuripotent cells into sites of injury and regenerate healthy tissue without much manipulation have been dashed almost completely. We know now that approach can yield all kinds of unwanted results, like a taratoma (in the case of ES cells); and often the grafted cells simply die because they fail to integrate properly, and hence self-destruct. Some of the most troubling disappointments recently have been in the area of cardiovascular research; most notably relating to the research of Piero Anversa’s group, which claimed to see functional regeneration of myocardium following infarct using autologous hematopoietic stem-cell grafts in animal models. Several other well-respected groups have not been able to replicate such results (two articles and a rather stinging editorial were just published on the subject in the journal Nature), and have questioned the finding that stem cells derived from bone marrow can differentiate into cardiac muscle. Rather, it appears some of the grafted stem cells may fuse with remaining muscle cells in the myocardium. This may still provide some functional improvement, but the phenomena falls far short of the promise of rebuilding lost tissue good as new by replacing lost cells with new ones of the desired type. We’re just not there yet.
But again, with more time and research, I think a combined approach of stem cells, plus some genetic manipulation of those cells to make it somehow easier for them to incorporate post-grafting, will be the way of the future. We’ll also develop better techniques to differentiate stem cells in vitro, and to provide them with various kinds of scaffolding, to perhaps engineer replacement organs, or parts of organs, which can then be grafted to treat conditions like diabetes or liver disease.
As is true of all tissue grafts, if the cells are not derived somehow from the patient, they will almost certainly lead to graft-versus-host disease and graft failure. So, for instance, ES cells hold the promise of being more versitile than, say, mesenchymal stem cells, but rejection is still an issue. Some exciting new research in cloning has shown us that it may be possible to derive ES cells from adult somatic cells by injecting nuclei from those cells into denucleated oocytes, in much the same manner as was used to generate Dolly the sheep. If this proves to be a viable source of stem cells in humans, that could revolutionize the field.
So, there’s lots to look forward too, but many hurdles to get over in the mean time. There will probably be other issues that we haven’t even thought of yet, and we always have to be ready for disappointment. I think, based on what I’ve seen and read, though, that some modest strides in stem cell therapies will probably lead to new clinically-approved treatments in a decade or so, twenty years at the latest. I’m not sure we’re going to be growing new hearts or brains any time in the forseeable future; and we can’t forget our friends in the cybernetics field who are taking a different, perhaps more practical approach to building spare parts.
It’s an interesting future in store, there’s no question. But, like I said, don’t expect many, if any, magic bullets. Such discoveries are few and far between, and never seem as wonderful in retrospect (thinking specifically of antibiotics and drug-resistance) as they do at first blush.