In political debates, one rap on human embryonic stem cells is that no practical therapies have come from the research.

The world’s first clinical trial of using the cells to treat a human disease was suspended last year by the U.S. Food and Drug Administration.

Now the cells are inching toward the clinic again.

The FDA has renewed its approval for the clinical trial involving a treatment for spinal cord injuries, Geron Corporation announced on Friday. California-based Geron and the University of California Irvine developed the cells to be used in the therapy called GRNOPC1.

The first phase of the trial is to establish the safety of the therapy. The FDA had halted the trial after lab mice injected with the stem cells in one study developed small cysts at the injury site. Geron says it satisfied those concerns through further animal studies with stepped up methods for testing and monitoring its cells.

Geron says it has lined up seven U.S. medical centers to participate in the trial which initially will involve treatment of patients with spinal cord injuries up to 14 days old. The centers will be identified as they are ready to enroll patients in the study, it said.

The potential medical use of human embryonic stem cells has been controversial since the first of them were isolated at the University of Wisconsin in 1998. The discovery involved the destruction of human embryos that a fertility clinic had planned to discard.

But while controversy raged, animal studies at the University of Minnesota and elsewhere have shown such stem cells to have remarkable restorative powers. They can be transformed into any type of cell in the body and adapted to help treat maladies from diabetes to heart disease.

In this case, a target is damaged nerve cells.  In animal studies, neural cells derived from embryonic stem cells and injected into the spinal cord injury site have led to significant recovery of the ability to move and bear weight, Geron says.

The cells produce a natural insulating membrane called myelin which wraps around the damaged neurons and enables them to conduct electrical impulses. Without such impulses, nerve networks short circuit and fail to do their jobs, leaving parts of the brain and the spinal cord unable to function.

Eventually, Geron plans to deploy similar cells for treating degenerative disorders of the central nervous system, including Alzheimer’s and multiple sclerosis.

Those applications likely are years away.

The point for now is that movement toward them has resumed.