Geron Corp (GERN.O), which is conducting the first U.S.-approved human embryonic stem cell trial, has named John Scarlett as its chief executive officer, replacing interim CEO David Greenwood, who will leave the biotech company at the end of the year.

The company's shares rose more than 4 percent after the announcement.

Scarlett, also named to Geron's board, was most recently CEO at Proteolix, a biotechnology company acquired by Onyx Pharmaceuticals Inc (ONXX.O) in 2009. Before that, he held CEO posts at Tercica, Sensus Drug Development and Covance Biotechnology Services, all of which were eventually sold to larger companies.

Geron, which is testing its stem cell therapy in patients with recent spinal cord injuries, also has experimental cancer drugs in clinical development.

Greenwood, previously Geron's chief financial officer, was named interim CEO in February after long-time CEO Thomas Okarma resigned from the job.

Geron said on Thursday that it would hold a call to discuss the latest management changes on Friday morning at 9 a.m. ET.

The company, based in Menlo Park, California, said that Greenwood, who has resigned from the company's board, would remain in his role as president and CFO during a transition period through the end of this year.

Shares of Geron, which have lost nearly 60 percent of their value so far this year, were up more than 4 percent at $2.25 in after hours trading.