PRECLINICAL SAFETY STUDIES

Animal Toxicology Testing of GRNOPC1
Geron has developed a manufacturing process to produce GRNOPC1 to standards required to begin human clinical trials. GRNOPC1 produced by this process was subjected to extensive toxicology testing to support the IND (Investigational New Drug) application and begin human clinical trials.

The IND application detailed more than 24 separate studies in rats and mice that required more than five billion GRNOPC1 cells. The IND application contained more than 21,000 pages of data from the animal and in vitro testing of the cells to ensure the highest possible degree of safety of the product before initiating human clinical trials.

Absence of Teratoma Formation
A major concern for hESC-based therapies is the possible formation of teratomas (benign growths of unwanted cells) that may result from the injection of the therapeutic cells. Teratomas are thought to arise from contaminating, live, undifferentiated hESCs that may reside in the population of therapeutic cells.

Twelve-month in-life teratoma studies were undertaken to determine if clinical grade GRNOPC1 preparations could form teratomas in vivo. Uninjured and spinal cord-injured animals were maintained for up to 12 months after a single injection of clinical grade GRNOPC1. After sacrifice, animals were carefully examined histologically by trained neuropathologists for the presence of teratomas within the spinal cord. No teratomas were found in any animal injected in the spinal cord with clinical grade GRNOPC1. Positive control animals in which teratomas were found included animals that received pure, undifferentiated hESCs or GRNOPC1 preparations that were intentionally contaminated with at least 5% of live, undifferentiated hESCs. These data demonstrate the absence of teratoma formation one year after the injection of clinical grade GRNOPC1.

Absence of Significant Acute or Chronic Systemic Toxicity and
Absence of Systemic Migration of GRNOPC1 Outside the Nervous System
A standard panel of acute and chronic toxicology studies was performed in rats and mice receiving injections of GRNOPC1. These studies examined both the GRNOPC1 product and the effects of its delivery to the injured spinal cord. Multiple hematology, clinical chemistry, urinalysis, and gross and microscopic pathology tests were performed on the spinal cord-injured rats that received GRNOPC1. No significant systemic toxicity was found. GRNOPC1 was not detected outside of the central nervous system in spinal cord-injected animals. In some animals, human non-neural differentiated cell types were observed in the injury site, which did not lead to adverse consequences.

Absence of Allodynia
Injured rats injected with GRNOPC1 were tested for allodynia (pain induced by normally non-noxious stimuli). In these studies, control and GRNOPC1-treated animals were tested for abnormal behavioral responses to cold and mechanical stimuli placed at, above or below the area of injury. No evidence for allodynia was detected.

Absence of Direct Allogeneic Immune Response to GRNOPC1
GRNOPC1 is intended for implantation in the lesion site after spinal cord injury and will be an allograft in human subjects. Because of the potential for allograft rejection, studies were performed to determine the ability of GRNOPC1 to stimulate or be the target for humoral or cell-mediated immune responses. In vitro studies were performed to test human allogeneic antibody, T cell and NK cell responses to GRNOPC1. In these studies, GRNOPC1 was incubated with serum and cell samples from normal healthy volunteers and analyzed for either GRNOPC1 lysis or T cell proliferation (Journal of Neuroimmunology, Vol. 192, 2007). The collective in vitro immunological data suggest that GRNOPC1 does not have major susceptibility to direct humoral or cell-mediated alloimmune attack. These results serve as the rationale for short-term administration of low-dose immunosuppression in the clinical protocol.