Human embryonic stem cells leap the barrier

To the Editor: The recent editorial by Penington and Mitchell1 unreservedly supports the Victorian Government’s legislation allowing “therapeutic cloning” by somatic cell nuclear transfer (SCNT) — generating an embryo by transferring an adult somatic cell nucleus (skin, muscle, etc) from an individual into a donated ovum from which the nucleus has been removed. State and federal support for therapeutic cloning has clearly been dependent upon belief in the therapeutic benefits to be obtained — a belief that the editorial does nothing to dispel.

Since the licensing system for embryo research (Research Involving Human Embryos Act 2002 [Cwlth]) was introduced, there have been no discoveries in animal or human embryonic stem (ES) cell research that support an urgent need for therapeutic cloning. This includes references 3–8 in Penington and Mitchell’s editorial, all of which fall far short of providing proof of concept of efficacy of ES cells in treatment.

A number of major problems need to be resolved before any remotely credible scientific case could be made for the need for therapeutic cloning. These include achieving prolonged, effective, safe therapy in an animal model of disease, and safe transplantation of ES cells in animals, without any tumour formation — a problem that occurs commonly,2,3 not on the “rare occasions” claimed in the editorial. We need to understand how stable the fully differentiated phenotype is when ES cells are used to generate specialised cells. This can be explored in animal ES cells, but also in human ES cells that do not need to be prepared by therapeutic cloning. If stability is indeed shown, these cells must die eventually — how will they then be replaced? Will this require a compromise of using less “mature” cells and incurring an even greater risk of tumour formation?

If cells derived by SCNT are to be used to find “new approaches to ... hitherto unyielding diseases”, proof of this concept could readily be provided by studying animal examples. Crucially though, that will require resolution in animal studies of the effect of SCNT on genetic controls and epigenetic effects in the derived ES cells.

These are all scientific requirements. Proceeding to therapeutic cloning provides no scientific advance without them — and of course it should be noted that no one anywhere in the world has ever made human ES cells by SCNT.

Penington and Mitchell’s editorial provides a limited view of these matters. It acknowledges the long lead times required if there is ever to be success in ES cell therapies, but does not advance even a single compelling argument in support of SCNT now.