The first human trial of human embryonic stem cells–involving a treatment of spinal cord injury developed by Geron, a cell therapy company based in Menlo Park, CA–has been put on hold once again. The company says the trial has been halted by the Food and Drug Administration “pending the agency’s review of new nonclinical animal study data submitted by the company.”

Geron has been working on embryonic stem cells for the last decade and received approval to begin human tests of embryonic stem cells in January 2009. I described the details of the trial and the therapy in a previous blog post:

The trial is limited to eight patients with newly acquired spinal-cord injuries who will receive injections of the cell therapy, called GRNOPC1, within two weeks of their accident. GRNOPC1 is made by transforming embryonic stem cells into oligodendrocytes–a type of brain cell that wraps itself around neurons, forming a fatty insulation layer that allows electrical messages to be conducted throughout the nervous system. In many spinal-cord injuries, these cells are damaged, but the underlying nerve cells remain intact. These cells are then injected into the site of the injury, coating exposed nerves and restoring communication to the nervous system.

Scientists published the results of a successful study testing the therapy in animals in 2005, showing that paralyzed rats injected with the cells were able to walk again. Since then, Geron has been conducting numerous studies intended to show the safety of the cell-based therapy, as well as developing production methods that would make the cells as easy to use as more traditional treatments. Geron researchers have also developed a way to reliably freeze and thaw brain cells, so that they can be manufactured in a central location, and then shipped to the hospitals where they will be used.

Because embryonic-stem-cell-based therapies are so new, the FDA has had trouble deciding how to evaluate new drug applications. (Geron’s president and CEO, Thomas Okarma, thought approval was imminent when I spoke with him in 2006. See “Human Tests of Embryonic Stem Cell Treatments Planned.”) The initial trial is designed to assess safety, but doctors will also measure its effectiveness, such as improved neuromuscular control or sensation in the trunk or lower extremities.

According to a statement from the company:

Geron has been undertaking studies to enable dose escalation of its spinal cord injury product, and has been investigating application of the product to other neurodegenerative diseases. The company has also been performing additional product characterization and conducting further animal studies. Data from this work has been submitted to the FDA. Geron will work closely with the FDA to facilitate their review of the new data and to release the clinical hold. No patients have yet been treated in this study.