On Friday 30 July 2010, the US Food and Drug Administration (FDA) lifted the clinical hold it had placed on Geron's proposed clinical trial using cells, made from human embryonic stem cells, to treat spinal cord injury. The trial was originally approved in January 2009 but before commencing it was placed on clinical hold by the FDA over concerns that mice that had been treated with the cells therapy, known as GRNOPC1, had developed microscopic cysts.

If the trial proceeds it will be the first anywhere in the world to use cells made from human embryonic stem cells. Geron plans to test its therapy on patients with complete subacute thoracic spinal cord injuries by injecting GRNOPC1 into the lesion sites between seven and 14 days after injury. The aim of this Phase 1 trial is safety and Geron has selected seven US medical centres to participate in the study which is estimated to take about two years.

GRNOPC1 contains cells known as oligodendrocyte progenitor cells which have been made from human embryonic stem cells. Those progenitor cells turn into oligodendrocytes which produce myelin, a coating that allows impulses to move along nerves. When those cells are lost due to injury, paralysis can follow. If GRNOPC1 works, the progenitor cells will produce new oligodendrocytes in the injured area of the patient's spine, potentially allowing for new movement.