Adult stem cells kill.

They're mass murderers, in fact. In only five years between 2000 and 2004, adult stem cells used in some 25,000 bone marrow transplant treatments have been complicit in at least 3,629 American deaths, 624 of which involved children under the age of 18, according to the National Center for Health Statistics. If the trend continues, adult stem cells will claim their 5,000th victim since 2000 this year.

Now the shocking part: To the best of my knowledge, these numbers are appearing for the first time publicly in this article. The data is scattered among some 12 million lines of text at the National Bureau of Economic Research website. No easily accessible summary report is available. I wrote a Perl script to extract the information (see below).

"I've never heard that statistic before," says John Hlinko, founder of the pro-embryonic-stem-cell lobbying group StemPac.

Arguments that adult stem cells are better than embryonic stem cells are in full swing this week as legislators debate the Stem Cell Research Enhancement Act (SB5). This politically explosive bill would overturn federal stem cell restrictions, allowing researchers to use embryos from fertility clinics that would otherwise be discarded. The senate is scheduled to vote on the bill Thursday, and conservatives have rallied opposition. Even if it passes, a veto is expected.

Stem cells of both varieties show enormous promise for seemingly miraculous medical treatments, from reversing the effects of Alzheimer's disease to repairing a damaged spinal cord. But, eager to keep embryonic stem cells out of the labs, some conservatives insist adult stem cells are so promising that embryonic stem cells need not be considered at all.

They make three common claims about adult stem cells: They already work as therapies, while embryonic stem cells are still experimental; they are derived without killing embryos; and – last but not least – they are safe compared to embryonic stem cells, which are known to cause tumors.

In fact, the risks of graft versus host disease, or GVHD, following bone marrow transplants are well documented by the National Cancer Institute. Early reports of GVHD, then known as "runt disease," were enough of a concern to merit mention in a 1960 Nobel Lecture, so the risks have been known for more than 40 years.

Complications of acute GVHD (.pdf) arise from attacks against the skin, liver and intestines. They range from mild – skin rash, nausea and cramping – to severe: blisters, bloody diarrhea and death. Chronic GVHD (.pdf) complications include attacks on the aforementioned organs, as well as any other organ.

Nevertheless, organizations including the Family Research Council, The Center for Bioethics and Human Dignity, WorldNetDaily and Do No Harm all recite the same argument: Therapies derived from embryonic stem cells will form tumors, therefore the risks are too great to justify spending the public's money to study them. Instead, they say, adult stem cells – taken from bone marrow, blood, hair follicles and various other locations without harming the human body – are a better use of taxpayer money.

That embryonic stem cell supporters haven't tallied the numbers is astonishing, given the aggressive tactics of those who attack embryonic stem cell research. David Prentice, senior fellow for life sciences at the Family Research Council, and Sen. Dave Weldon (R-Florida) have both publicly claimed that adult stem cells are inherently safe.

Bob Lanza, vice president of research and scientific development at Advanced Cell Technology, said highlighting the risks of adult versus embryonic stem cells misses the point.

Embryonic stem cell researchers "are actually at a disadvantage because the majority of scientists say we should not be pitting adult versus embryonic stem cells," Lanza said. "We need to pursue all these avenues and in the end there are going to be literally hundreds of diseases that could be treated with stem cells, and we don't know which kind will be best for which diseases."

Maybe ignoring the risks of adult stem cells is an honest mistake by adult stem cell boosters. A less charitable explanation is that they knowingly mislead the public about the safety of adult stem cells, glossing over GVHD deaths in their desire to discredit embryonic stem cell research.

Granted, the risk of GVHD is one a leukemia patient is usually willing to take. Similarly, people like me who are waiting for cures might be willing to take certain risks associated with embryonic stem cell therapies.

In the meantime, let's at least have an honest debate. Let's give scientists ample funding to solve potential complications and let the science lead the way.

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Steven Edwards is a redheaded, red-bearded, partially ventilator-dependent quadriplegic looking to trade in his wheels for the use of his legs. He hails from South Carolina.

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Author's note: Here's the Perl code in case you're curious about other causes of death that haven't been neatly tallied. T860 is the ICD-10 code for GVHD-related deaths following bone marrow transplant – the number would probably be higher if you counted cord blood transplants, but they lack an ICD-10 code. The code checks the death certificates for cause-of-death data entered (.pdf) by the doctor.

For the 2000 to 2002 gzipped datasets, I used the following command to tally the numbers: gzip -cd [filename.dat.gz] | perl -ane "s/^.{69}(.{4}).{270}(.{100})//; ($age,$cause) = ($1, $2); ++$i if ($cause =~ /T860/); BEGIN{$i=0;}END{print $i;}"

For 2003 to 2004, I used: gzip -d -c [filename.dat.gz] | perl -ane "s/^.{63}(.{3}).{274}(.{100})//; ($age,$cause) = ($1, $2); ++$i if ($cause =~ /T860/); BEGIN{$i=0;}END{print $i;}"