Geron's ( GERN) upcoming and widely publicized stem cell trial involving patients with spinal cord injuries was criticized as risky and clinically dubious because the entire rationale for the study is "based on a single experiment in eight rats." The negative view of Geron's research effort came from a spinal surgeon and stem cell researcher during a conference call for institutional investors held Monday by Summer Street Research Partners, an independent health care research firm. A recording of the conference call was obtained by TheStreet.com, which chose not to disclose the doctor's name out of privacy concerns since the call was not intended for public dissemination. At the beginning of the call, the doctor said he had no financial ties to Geron, nor did he own or short Geron stock. In January, the Food and Drug Administration granted Geron permission to launch a small safety study of its human embryonic stem cell-derived therapy in patients paralyzed from the waist down due to severe spinal cord injury. Geron and other stem cell advocates hailed the study's start as a landmark achievement in the nascent field of regenerative medicine. But investors have had a less enthusiastic reaction to the news. The price of Geron shares rose from $5 to more than $8 in the days immediately after the Jan. 23 announcement, but the gains were quickly sold. Geron's stock has fallen steadily since then, hitting a low of $3.79 on March 5, hurt in part by a $43 million spot financing deal and a sharp downturn in the broader market.