Traumatic Brain Injuries (TBI) are the leading cause of death and disability in the young population. Falls resulting in injury to the brain are also a major problem in the elderly. The rate of TBI is greater than the number of people diagnosed with brain, breast, colon, lung, and prostate cancers combined, yet nationally the US invests 95% more research dollars on cancer compared to TBI. 1.7 million new cases of TBI occur each year, at an economic cost of $60 billion. Extrapolating to California (12% of US population), there are ~210,000 new cases of TBI a year in our state, with a yearly cost that exceeds $7 billion. TBI results in permanent long-term deficits, including memory impairments and emotional disfunction, that affect both the patient and their families. There are no treatments to alleviate the long-term consequences of TBI. Yet a small reduction in damage, restoration of just some nerve fibers to their targets beyond the injury, or moderate improvement in learning, memory, or emotional outcomes could have significant implications for an individual’s quality of life. Our hypothesis was that human neural stem cells (hNCSs) might alleviate some impairments associated with TBI in a new animal model of neurotrauma. Our first goal was to grow hNSCs under cell culture conditions free from contamination of non-human products (referred to as “xenofree”), and then sort these cells based on cell surface markers known to be present in high concentrations on migratory neural stem cells (and not other byproducts of the culture conditions). Our second goal was to develop an animal model of TBI with long-lasting cognitive and emotional deficits; this animal model had to be “immuno-deficient”, or lacking a functional immune system, so that “foreign” human cells would not be rejected. Long-lasting deficits were need so that there would be a sufficient time window of dysfunction to allow the hNSCs to divide, migrate through the brain, and possibly restore function. If animals recover function too quickly on their own (as happens in some models of neurotrauma), then there would not be a large enough difference between control animals and injured animals to detect an effect of the hNSCs or not. Goal three was to test the therapeutic effects of hNSCs in this model. Finally, because a large number of people with TBI also experience seizures long after the initial injury, our forth goal was to combine “kindling” with TBI and ask whether hNSCs could alter kindling. Kindling involves implanting an electrode in the brain and very gently stimulating the brain every day until seizures occur. One can then measure how strong the seizure are and their duration (called after-discharge).
As the result of receiving CIRM Early Translation funding, we successfully generated two “xenofree” human neural stem cell lines (hNSCs) which are suitable for future therapeutic use in a variety of human neurological conditions (Goal 1). We also developed an athymic nude rat (ATN) model of controlled cortical impact TBI which exhibits sustained (2-months or longer) cognitive and emotional deficits. ATN rats lack T-cells, and thus have a sufficiently impaired immune system that they do not completely reject transplanted human cells. These ATN rats show deficits on novel place recognition (NPR), acquisition and memory of location on the Morris Water Maze, and disturbances on an Elevated Plus Maze (EPM) task in comparison to sham controls (Goal 2). We also found that sorted hNSCs survive and are not rejected in this model and that performance on the NPR task, learning on the Morris Water Maze and exploration on the EPM are all improved in the hNSC treated group compared to sham controls (Goal 3). Finally, when we repeated a therapeutic transplantation test of sorted hNSCs, but in seizure/kindled animals with TBI we found three interesting results (Goal 4). First, we replicated our earlier finding that hNSCs are efficacious in restoring memory function on the NPR task prior to kindling. Second, we found that after kindling, the improvement found with hNSCs was lost. And finally, we found that hNSCs reduce the number of After Discharge events in TBI+Kindled animals in comparison to TBI+Kindled animals that received a vehicle control injection.
In summary, we have successfully met all of our goals: (1) we generated a new human neural stem cell line suitable for future clinical trials in humans. (2) We developed an immunodeficient animal model of traumatic brain injury with sustained behavioral deficits. (3) We found very promising preclinical efficacy of our hNSCs in TBI. And (4), we have shown that hNSCs may play a role in reducing the number or severity of seizures following TBI, but if seizure activity is severe, that activity may interfere with hNSC mediated improvements on memory. With additional funding, we hope to complete the full range of preclinical studies required to translate these positive findings into an FDA approved human trial.