The human embryonic stem cell lines eligible for federally funded research are unsuitable for use in humans because they were grown in contact with mouse cells and could conceivably infect humans with mouse viruses, a panel convened at the Johns Hopkins University said yesterday.
The group, formed last year to address "the next generation" of ethical questions associated with stem cell research, also argued that treatments derived from the limited number of approved stem cell lines would probably benefit only a limited number of Americans and could discriminate against racial minorities.
The scientists proposed a controversial long-term solution: starting a new stem cell "bank" by identifying and soliciting a diverse range of donors, creating embryos and then destroying them to get cells for theraputic use.
"We were very mindful of the implications for our conclusion," said Ruth R. Faden, a panel member and director of the Johns Hopkins Berman Bioethics Institute. "The new lines would require the destruction of human embryos."
Critics immediately assailed the plan. They included Richard Doerflinger, deputy director of pro-life activities for the U.S. Conference of Catholic Bishops, who said it would amount to creating "embryo farms."
Stem cells are the progenitor cells from which all others in the body are derived. Ultimately, scientists hope to use them to grow everything from tissue to repair damaged hearts to nerves that can regenerate damaged spinal cords.
While some scientists have experimented with stem cells derived from umbilical cords or adult bone marrow, others believe stem cells derived from embryos - initially created for in vitro fertilization but no longer required - are the most versatile.
They are also the most controversial, given that some consider the destruction of human embryos equivalent to abortion.
President Bush has prohibited federal funds from being used for research on human embryonic stem cell lines created after Aug. 9, 2001. Critics have said the ban impedes U.S. research into potential treatments.
Faden and John Gearhart, a developmental biologist at Johns Hopkins and pioneer in growing stem cells derived from human fetal tissue, said the panel wants to broaden the debate and help Americans understand the complexities of moving stem cells from the laboratory into the clinic.
One of the group's papers, published in the November issue of the journal Fertility and Sterility, touched on issues ranging from the risk of transferring genetic disorders through stem cells to the potential for tumors to form when the cells are used in treatment.
A second paper in the November/December issue of The Hastings Center Report focused on the issue of "biological access." The scientists said they're concerned that stem cell therapies might be limited to patients with a genetic makeup similar to the donors of the federally approved stem cell lines.
The issue is important because scientists believe organs grown from stem cells - and perhaps the cells themselves - could be rejected if the immune systems of a donor and recipient don't match.
The panel's recommendation for ensuring genetic diversity in stem cells used for research was more modest than its sweeping plan for the cell bank it recommended should those therapies become reality.
It proposed that a research stem cell bank include, at a minimum, the six most common genetic variations relevant to transplant rejection in all Americans - most of whom are white - as well as the two most common variations each relevant to transplant in African-Americans, Hispanics, Native Americans and Asian-Americans.
There are currently 78 samples of human embryonic material in the National Institutes of Health's stem cell registry. It is only from those samples that stem cell lines can be created for use in federally funded research.
But most of those samples have yet to be used to create lines of stem cells in the lab, said James Battey, chairman of the NIH stem cell task force.
As a result, there are only 12 lines of stem cells available today for federally funded research, he said. Those 12 lines were developed in contact with mouse cells that helped stimulate growth.
He acknowledged that the currently approved cell lines likely are limited in their genetic diversity. Even so, he said, "Until we explore all the strategies for dealing with potential immunologic rejection, we don't know what we'll need."