Transfectable and Transplantable Postmitotic Human Neurons: A Potential “Platform” for Gene Therapy of Nervous System Diseases

We have characterized a human embryonal carcinoma cell line (NTera-2 or NT2 cells) that is transfectable and capable of differentiating into postmitotic neuron-like cells (NT2N cells) following treatment with retinoic acid in order to identify a human neuronal cell line that might serve as a "platform" for gene therapy of human neurological diseases. Studies of NT2N cells transplanted into the brain or spinal cord of immunecompetent and immunodeficient rodents show that NT2N cells integrate into the host central nervous system (CNS) and establish the molecular and structural polarity of authentic neurons in vivo. Further, grafted NT2N cells acquire the molecular phenotype of fully mature neurons within 6 months postimplantation and the grafts survive > 1 year in immunodeficient mice without reverting to a neoplastic state. Although grafts of the retinoic acid-naive NT2 cells can form lethal tumors in the CNS, these cells differentiate into postmitotic neuron-like cells and do not form tumors when the grafts are confined to the caudoputamen. Based on the studies reviewed here, we conclude that grafted NT2N cells could serve as a suitable platform for the delivery of exogenous proteins into the CNS for gene therapy of human nervous system diseases.