Money for stem cells: Bush may veto another attempt to expand funding options.STEVE GSCHMEISSNER / SPL

For the second time in nine months, the US Senate has voted to lift restrictions on federal funding for human embryonic stem-cell research. But once again, the measure is expected to be vetoed by President Bush.

"This bill crosses a moral line that I and many others find troubling. If it advances all the way through Congress to my desk, I will veto it," the president said in a statement issued shortly after the Senate vote.

Senator Tom Harkin (Democrat, Iowa), the bill's leading proponent, urged the president to reconsider. "Tonight I am appealing to President Bush to re-examine the substance of this bill, and to reconsider his threat to veto it."

The vote, which came in at 63 (for) to 34 (against) on 11 April, was similar to the vote last summer on a largely similar bill (see 'US Senate passes stem cell bill'). Neither vote reached the two-thirds majority required to override a presidential veto.

Advocates for the bill had hoped that election gains in November that put the chamber in Democratic control would produce a veto-proof majority for the bill. The three Democrats who missed this week's vote would almost certainly have voted in favour, bringing the total to 66 — one vote shy of the two-thirds majority goal.

Last summer the Senate voted 63 (for) to 37 (against), and Bush vetoed the measure.

Leftovers

The bill, the Stem Cell Research Enhancement Act, allows federal funding for research on stem cells derived from embryos left over at fertility clinics and already slated for destruction. It requires that couples be approached about donating leftover embryos only after they have independently decided to discard them. They may not be offered financial or other inducements to donate.

The current Bush policy, in place since August 2001, only allows federal funding for research on stem-cell lines derived before that date; the number of such lines has dwindled to 21.

It is hoped that stem cells may one day lead to cures for a wide range of diseases, from Alzheimer's to juvenile diabetes. Opponents of the bill argue that stem cells derived from adult sources offer plenty of promise and don't involve the destruction of human embryos.

John Gearhart, director of the Stem Cell Program at the Johns Hopkins Institute for Cell Engineering, estimated on Tuesday that, conservatively, at least 50 or 60 new lines would immediately become available to federally funded researchers were the new legislation enacted. "There are probably three times that many that are in the process" of being made, he added.

Take two

Confusingly, the Senate also passed another stem-cell bill on Wednesday — this one backed by the White House. It seems to allow federal funding for research on stem cells derived from embryos that the bill terms "naturally dead". However, the bill also states that nothing within it should be construed as altering the president's current policy. It passed by a vote of 70 to 28, with Republicans the main supporters

Sponsored by Norm Coleman (Republican, Minnesota), the bill defines "naturally dead" as "having naturally and irreversibly lost the capacity for integrated cellular division, growth, and differentiation".

Critics note that there is no scientific standard for determining what is a viable embryo. In practice, fertility doctors use microscopes to identify, as much by art as by science, which embryos look healthiest and therefore are the best bets for implantation.

The Stem Cell Research Enhancement Act will not reach Bush's desk until after the House of Representatives returns from a spring recess next week. The House passed a similar bill in January, but again not by enough to prevent a veto.

The two chambers may work out differences between the two bills and then vote on that compromise measure. Alternatively, the House may vote on the bill exactly as passed by the Senate. Either way, if the president vetoes the bill, Harkin says, backers may try attaching it to must-pass spending legislation later this year. "Momentum is building," Harkin says. "One way or another, we are going to lift these arbitrary restrictions this year."

Visit our senatepassesstemcellbill.html">newsblog to read and post comments about this story.