By: Scott R. King
Fetal tissue. No other topic in diabetes research is as emotionally stirring. Some say that fetal tissue is the key to progress, and perhaps that fetal tissue will even cure diabetes. Others claim that fetal tissue research is immoral because it produces an incentive for abortions. How important is fetal tissue research? Is it likely to produce a cure for diabetes? Are there alternatives that avoid ethical concerns?
First, we must understand how fetal tissue is used in diabetes research. In my last column, I discussed islet cell transplantation. The same procedure is followed for transplanting islet cells from either fetal or adult animals. The islets are transplanted into a person with diabetes, where they react to the surrounding glucose level by releasing insulin when the blood sugar is higher than normal.
Right now, islet cell transplants are always accompanied by suppression of the immune system with drugs in order to protect the cells from rejection by the body. But if implants are ever to be practical for most people with diabetes, transplantation without suppression of the immune system will be necessary.
As of today, the popular belief about fetal islet tissue is that it has two potential advantages over adult islet tissue. One advantage is that fetal tissue is less likely to be rejected by the body. The reasoning for this is that since fetal tissue is younger and less mature, the antigens that cause rejection should be present in smaller amounts, and rejection therefore less likely. While an attractive idea, this concept suffers from the fact that it is not supported by the facts. Let’s see why.
All tissues are coated with proteins that cause tissue rejection, and as it turns out, fetal cells are especially rich in these proteins. Thus, based on the likelihood of rejection, fetal tissue is less suitable than adult tissue! Therefore, the common supposition that fetal tissue is especially suitable for transplantation is opposite of the truth.
What then of the supply issue? It is true that fetal tissue grows much better than adult tissue in laboratory culture. The practical problem is that fetal islets, when grown in culture for extended periods, lose the capacity to make insulin. With today’s technology, extensively cultured fetal islets are unsuitable for transplantation into people with diabetes because they make and secrete insulin poorly. Thus most experiments with fetal tissue use tissue that has only been cultured a brief time.
The core issue is finding the cheapest and best source of islet tissue to implant into people with diabetes. At this time, the evidence strongly favors islets from mature animals: every cure of diabetes has been done with adult islets. With time fetal tissue may become useful, but it is not now. So, for the moment, practical considerations are aligned with those who oppose fetal tissue for ethical reasons.