TRANSPLANTED HUMAN NEURONS DERIVED FROM A TERATOCARCINOMA CELL-LINE (NTERA-2) MATURE, INTEGRATE, AND SURVIVE FOR OVER 1 YEAR IN THE NUDE-MOUSE BRAIN

Retinoic acid (RA) induces a human teratocarcinoma cell line (NTera-2 or NT2) to give rise exclusively to post-mitotic neuron-like (NT2N) ce lls, but NT2N cells never acquire a fully mature neuronal phenotype in vitro. To determine whether NT2N cells can mature into adult neuron-l ike cells in vivo, purified NT2N cells were grafted into different reg ions of the central nervous system (CNS) of adult and neonatal athymic mice, and the grafts were examined immunohistochemically by light, co nfocal, and electron microscopy using antibodies to a panel of develop mentally regulated neuronal polypeptides. NT2N grafts were distinguish ed from endogenous mouse neurons with antibodies that recognize human or murine specific-epitopes in selected neuronal polypeptides. Viable NT2N cells were identified in > 89% of graft recipients (N = 90), and some grafts survived 14 months. Within 3 weeks of implantation, grafte d NT2N cells re-extended their processes, and the location of the graf ts (e.g., septum versus neocortex) appeared to determine the extent to which processes were elaborated. Within the early post-transplantatio n period, grafted NT2N cells expressed the same neuronal polypeptides as their in vitro counterparts. However, between 6 weeks and 4-6 month s post-implantation, the grafted NT2N cells progressively acquired the molecular phenotype of fully mature in vivo neurons as evidenced by d ramatically increased expression of the most highly phosphorylated iso forms of the heavy neurofilament subunit, and the de novo expression o f adult CNS tau. Notably, the time course for the extension of process es and the expression of neuronal polypeptides by NT2N grafts was simi lar in neonatal and adult mice. Although grafted NT2N cells formed syn apse-like structures and elaborated dendrites and axons, these axons r emained unmyelinated. Finally, none of the transplanted NT2N cells rev erted to a neoplastic state. These studies demonstrate that pure popul ations of grafted human NT2N cells acquire a fully mature neuronal phe notype in vivo, and that these cells integrate and survive for > 1 yea r post-implantation in the mouse CNS. These human neuron-like cells ar e an attractive model system for studies of neuronal development, pola rity and transplantation. (C) 1995 Wiley-Liss, Inc.