UC Irvine

Traumatic brain injury (TBI) in humans can result in permanent tissue damage and has been linked to cognitive impairment that lasts years beyond the initial insult. Clinically effective treatment strategies have yet to be developed. Transplantation of human neural stem cells (hNSCs) has the potential to restore cognition lost due to injury, however, common methods for the generation of human embryonic stem cell (hESC) derived neural stem cells result in cells with potentially compromised safety profiles due to maintenance of cells in conditions containing non-human proteins (e.g. in bovine serum or on mouse fibroblast feeders) as well an increased risk of teratoma formation. Additionally, the vast majority of rodent TBI/hNSC studies to date have evaluated cognition only at early time points, typically less than 1 month post-injury and cell transplantation, and human cell engraftment and long-term survival in rodent models of TBI has been difficult to achieve due to host immunorejection of the transplanted human cells. To overcome these shortfalls, we have generated hNSCs in completely “Xeno-Free” (human only) culture conditions. Furthermore, we have enriched the hNSCs for the cell surface marker CD133 via magnetic sorting, which has led to an increase in the expansion rate and neuronal fate specification of the hNSCs in vitro, and we have confirmed neural lineage specificity and a lack of teratoma formation upon sorted hNSC transplantation into the immunodeficient NOD-scid mouse brain. We then developed a novel TBI xenotransplantation model that utilizes immunodeficient athymic nude (ATN) rats as the host recipient for the post-TBI transplantation of human embryonic stem cell (hESC) derived NSCs and have furthermore evaluated cognition in these animals at long-term (≥2 months) time points. We report that immunodeficient ATN rats demonstrate hippocampal-dependent spatial memory deficits at 2-3 months post-TBI, confirming that ATN rats recapitulate some of the cognitive deficits found in immunosufficient animal strains. hNSCs survived for at least 5 months post-transplantation and differentiated into cells from all three neural cell lineages. Furthermore, hNSC transplantation facilitated cognitive recovery after TBI, even in the absence of gross histological modulation of lesion or total spared hippocampal tissue volume. Importantly, we have found an overall increase in host hippocampal neuron survival in hNSC transplanted animals and demonstrate that a correlation exists between hippocampal neuron survival and cognitive performance. Together, these findings support the use of immunodeficient rodents in models of TBI that involve the transplantation of human cells, and suggest that hNSC transplantation may be a viable, long-term therapy to restore cognition after TBI.