Biotechnology firm Geron said last night that it would discontinue its stem-cell research program and halt a pioneering clinical study in people with spinal-cord injury.

The decision brings to a halt the world's largest and longest-running program to develop medical treatments from embryonic stem cells, versatile cells able to form many other types of human tissue.

Geron's project was one of the most aggressive, controversial, and far-reaching research efforts ever undertaken by a biotechnology company. It began more than 13 years ago, when Geron financed the initial discovery of human embryonic stem cells by university researchers in Wisconsin.

Those efforts, which cost several hundred million dollars, culminated last year in a first-of-a-kind clinical study to see if lab-grown nerve cells could return movement or sensation to people with spinal-cord injury. That study, profiled in TR's July issue, was the first using embryonic stem cells ever approved by the U.S. Food and Drug Administration. 

After being paralyzed at the chest in a car crash in September 2010, a nursing student named T. J. Atchison became the first person to be treated with Geron's cells. The company says it will no longer accept patients into the study, though Atchison and others who have already been treated will continue to be monitored.

Geron plans to discontinue its work on stem cells in order to focus on cancer drugs. In a statement, John A. Scarlett, who joined Geron in September as CEO, blamed the decision on an "environment of capital scarcity and uncertain economic conditions."

The company denied it had given up on stem cells for scientific reasons. "We're not doing this because we were souring on the field, or as a result of any problems—we have not had any safety issues at all," Scarlett told Bloomberg news.