Only eight people will take part in the first known clinical trial testing the safety of embryonic stem cells in humans and each patient will go through a very stringent selection process, the lead researcher of the study said on Monday.

“I think it’s likely that 50 percent or even 75 percent of patients we evaluate will not meet the criteria,” Dr. Richard Fessler of Northwestern University and Northwestern Memorial Hospital, who is leading the trial sponsored by Geron Corp.

Geron has the first U.S. Food and Drug Administration license to use the controversial embryonic stem cells to treat people — in this case patients with new spinal cord injuries.

The company announced on Monday that the first patient had started treatment at a rehabilitation hospital in Atlanta. Northwestern is the only other site ready to enroll patients.

“What will happen is some individuals will experience some kind of spinal cord injury,” Fessler said in a telephone interview.

If the injury is the right kind — the spine is crushed but not severed, the patient does not have an infection or a history of cancer and if the injury occurs in the right spot in the middle of the back — the patient’s doctor might recommend they be included in the trial.

From there, people will be evaluated to see if any metal rods or screws used to stabilize the spine obstruct the view of the spinal cord on an advanced type of scanner called a magnetic resonance imaging or MRI machine.

Patients offered a chance to be in the trial have only 11 days from the time of their injury to decide, Fessler said.

“We have to transplant them within 14 days of the injury,” Fessler said. “We have three days of preoperative testing we have to do before we can do the transplant. They have to be given the offer and make their decision by day 11.”

OFFERING ADVICE

All patients will have an independent patients’ advocate standing by to make sure they are not pressured to take part in the study.

And in many cases, patients may want to seek the advice of clergy to help them think through any ethical concerns they may have in being injected with human embryonic stem cells, Fessler said.

Embryonic stem cells come from days-old embryos and can produce any type of cell in the body.

Opponents of their use say it is wrong to make the cells because they involve the destruction of an embryo. Geron’s cells are made from embryos left over after in-vitro fertilization attempts at fertility clinics.

Supporters believe it is equally wrong to let the embryos be destroyed.