Neuronal replacement strategies for spinal cord injury.

Functional recovery following central nervous system (CNS) trauma or neurodegenerative disease is likely to require the transplantation of exogenous neurons. Given the logistical constraints of the potential widespread use of fetal human CNS tissues for therapeutic treatment, alternative sources of exogenous neurons for grafting will likely be necessary. Described here are studies examining the use of an immortalized, CNS-derived, neuronal precursor cell line, RN33B, as such a source. Results demonstrate that RN33B cells show remarkable plasticity to respond to local microenvironmental cues to differentiate in a direction that is morphologically indistinguishable from endogenous neurons at the site of transplantation. Concomitantly, the adult CNS retains the capacity to direct very specific differentiation of those engrafted precursor cells. However, the type and extent of site-specific appropriate differentiation is influenced by the type and extent of the lesion at the graft site. Attempts at immortalizing human CNS cells wtih similar approaches led to significant chromosomal aberrations, obviating such a strategy for therapeutic treatment. Thus, we utilized mitogen expansion of fetal human spinal cord cells as a means to generate populations of undifferentiated human neural precursor cells. Cells were expanded in the presence of epidermal growth factor and fibroblast growth factor 2, were readily passaged, and retained a pluriopotential to differentiate into neurons and astrocytes through at least 4 passages, after which the proliferating precursors became restricted to the astrocytic lineage. Further delineation of the variable needed to maintain these cells as undifferentiated, pluripotent precursor cells should ultimately enable examination of the ability of these cells to restore function in the damaged CNS.