January 15, 2003
Shift Emerges In Debate On Therapeutic Cloning

Some ethicists are drawing an ethical line at the point where the cells in an embryo start to organize into some sort of 3 dimensional shape.

Cynthia Cohen, senior research fellow at the Kennedy Institute of Ethics at Georgetown University and member of a national Episcopal task force on ethics and genetics, said the moral status of the embryo "arouses the most vehement discussion" when she addresses church and civic groups.

Cohen said she believes, as do many scientists and religious leaders, that "very early embryos" -- those younger than 14 days -- cannot be considered human because cells have not formed a single, individualized entity.

The argument of ethicists who make the 14 day distinction is that cells that are not yet organized 3 dimensionally into shapes haven't really started to create a life. They argue therefore that it is ethical to take cells from an embryo that is less than 2 weeks old and starting doing things to those cells to induce them to change into a more differentiated (i.e. specialized, less general purpose) state in order to grow organs or to make non-embyronic stem cells for stem cell therapeutic uses.

If the 14 day dividing point was legally adopted this would not move us that much closer to being able to grow replacement organs. Cells from the first two weeks of embryo development would not immediately be usable for, say, growing organs. As was demonstrated recently with mini human kidneys grown in mice it is not until the later stages of embryo development (7-8 weks in the case of kidney progenitor cells) that cells change into progenitor cells that are suitable for growing organs. Without the larger developing embryo to use as a context that interacts with organ progenitor cells to bring them to the point where they are readly to become organs scientists would have to figure out how to make early embryo cells turn into cells that are for growing particular organ types. That may turn out to be a fairly difficult problem to solve.

The strong opponents of therapeutic cloning in the United States are not going to find the 14 day development point an acceptable boundary for the last point to which human embryos can be grown to for the purpose of extracting cells for therapeutic cloning. In cloning an adult cell nucleus is placed in an unfertilized egg in place of the egg's nucleus. This is done to make the regulatory state of the adult nucleus (which has a full genetic complement whereas the egg has only half a genetic complement and normally gets the other half by fertilization by a sperm) revert back into the state close to that of a freshly fertilised egg.

Any technique is going to elicit religiously motivated ethical objections as long as the technique causes a nucleus to revert to the state that is the same as that of a freshly fertilized egg's nucleus. If one could get an adult nucleus to convert directly into the genetic state of an organi progenitor cell (e.g. the genetic state of a kidney progenitor cell between the 7th and 8th week of embryonic development) then one would effectively avoid the main ethical objection raised against the technique of therapeutic cloning.

Share |      Randall Parker, 2003 January 15 02:23 AM  Biotech Organ Replacement


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