Gene Therapy Sprouts New Neurons in Alzheimer’s Patients’ Brains


The journal JAMA Neurology has published a new study that describes an experimental gene therapy that reduces the rate at which nerve cells in the brains of Alzheimer’s patients degenerate and die. See Tuszynski, M. H., et al. (2015). Nerve Growth Factor Gene Therapy: Activation of Neuronal Responses in Alzheimer Disease. JAMA Neurology, published online August 24, 2015. DOI: 10.1001/jamaneurol.2015.1807.

In this study, targeted injections of a growth factor called “nerve growth factor” or NGF into the brain of patients rescued dying cells around the injection site, enhanced the growth of these cells and induced them to sprout new nerve fibers. Surprisingly, in some cases, these beneficial effects persisted for 10 years after the therapy was first delivered.

Alzheimer’s disease (AD) is the world’s leading form of dementia. It affects approximately 47 million people worldwide, and this number is expected to almost double every 20 years. Despite the huge amounts of time, effort, and money devoted to developing an effective cure, the vast majority of new drugs for AD have failed in clinical trials.

While these new results are preliminary findings, they come from the first human trials designed to test the potential benefits of NGF gene therapy for AD patients.

NGF was discovered in the 1940s by Rita Levi-Montalcini, who demonstrated, quite convincingly, that a small protein that she had isolated and purified promoted the survival of certain sub-types of sensory neurons during development of the nervous system. Since that time, others have shown that it also promotes the survival of neurons that produce acetylcholine in the basal forebrain; these cells die off at an alarming rate in AD patients.

In 2001, Mark Tuszynski and his coworkers at the University of California, San Diego School of Medicine initiated a clinical trial based on these laboratory findings. This trial was the first of its kind, and it was designed to investigate the ability of NGF gene therapy to slow or prevent the neuronal degeneration and cell death characteristic of AD.

In phase I of this trial, eight patients with mild AD received so-called “ex vivo” therapy to deliver the NGF gene directly into the brain. This trial extracted skin fibroblasts from the skin on the patient’s backs, and then genetically engineered those cells to express the NGF genes. These NGF-expressing cells were then implanted into the patients’ basal forebrain. Since NGF is too large to cross the blood-brain barrier, it had to be administered directly into the brain. Also, outside the brain, exogenous NGF can stimulate other nerve cells can cause unwanted side-effects such as pain and weight loss.

One of these patients died just 5 weeks after receiving the therapy. Tuszynski’s team secured permission to perform an autopsy of this patient, and in 2005 they reported that the treatment led to robust growth responses, and did not cause any adverse effects (Tuszynski, M. H., et al. (2005). A phase 1 clinical trial of nerve growth factor gene therapy for Alzheimer disease. Nature Medicine, 11: 551 – 555).

The latest results come from postmortem examination of these patients’ brains, all of whom had also been recruited in a safety trial between March 2001 and October 2012. Additionally, two other were included who had received in vivo therapy that included injecting a modified virus that carried the NGF gene into the basal forebrain.

Some of the participants died about one year after undergoing therapy, and others survived for 10 years after the treatment. These autopsies showed that all of them had responded to the treatment.

Essentially, all the brain tissue samples taken from around the implantation sites contained diseased neurons, as expected, but the cells were overgrown, and had sprouted axonal fibers that had grown towards the region into which NGF had been delivered. In contrast, samples taken from the untreated side of the brain exhibited no such response.

This trial was conducted to test the safety of the treatment and it did confirm that none of the patients experienced long-term adverse effects from the treatment, even after long periods of time. These results also suggest that NGF is successfully taken up by nerve cells following targeted delivery. Also the cells synthesize NGF protein so that its concentration dramatically increases in and around the delivery site. Probably the most exciting part of these findings is that the responses to NGF can persist for many years after the gene has been delivered into the brain.

Cholinergic Neuronal Hypertrophy and Sprouting Shown is labeling for p75, a neurotrophin receptor expressed on cholinergic neurons of the nucleus basalis of Meynert. Images were obtained 3 years after adeno-associated viral vectors (serotype 2)–nerve growth factor (AAV2-NGF) delivery (A-C) and 7 years after ex vivo gene transfer (D-F). A-C, Cholinergic neurons are labeled for p75 within the zone of transduction (A), 3 mm from the zone of transduction (B), and in a control Alzheimer disease (AD) brain of the same Braak stage (C). Cells near the NGF transduction region appear larger. The inset shows higher-magnification views of a typical neuron from each region. D, Shown is a graft of fibroblasts transduced to secrete NGF (yellow arrowhead) adjacent to the nucleus basalis of Meynert (red arrowheads). E, The graft (G) at higher magnification is densely penetrated by p75-labeled axons arising from the nucleus basalis of Meynert. These axons are sprouting toward the graft, a classic trophic response. F, Shown are p75-labeled axons from the nucleus basalis of Meynert sprouting toward the graft. Individual axons coursing toward the graft are evident (arrowheads). The bar represents 125 µm in A through C, 500 µm in D, and 100 µm in E and F.
Cholinergic Neuronal Hypertrophy and Sprouting
Shown is labeling for p75, a neurotrophin receptor expressed on cholinergic neurons of the nucleus basalis of Meynert. Images were obtained 3 years after adeno-associated viral vectors (serotype 2)–nerve growth factor (AAV2-NGF) delivery (A-C) and 7 years after ex vivo gene transfer (D-F). A-C, Cholinergic neurons are labeled for p75 within the zone of transduction (A), 3 mm from the zone of transduction (B), and in a control Alzheimer disease (AD) brain of the same Braak stage (C). Cells near the NGF transduction region appear larger. The inset shows higher-magnification views of a typical neuron from each region. D, Shown is a graft of fibroblasts transduced to secrete NGF (yellow arrowhead) adjacent to the nucleus basalis of Meynert (red arrowheads). E, The graft (G) at higher magnification is densely penetrated by p75-labeled axons arising from the nucleus basalis of Meynert. These axons are sprouting toward the graft, a classic trophic response. F, Shown are p75-labeled axons from the nucleus basalis of Meynert sprouting toward the graft. Individual axons coursing toward the graft are evident (arrowheads). The bar represents 125 µm in A through C, 500 µm in D, and 100 µm in E and F.

Now, does the observed cellular response to NGF alleviate disease symptoms? Although phase II trials testing the efficacy of the treatment are ongoing, preliminary findings from the initial study suggest that the therapy did indeed slow the rate at which mental function declined in one of the patients involved. These new results indicate that gene therapy is a viable strategy for treating Alzheimer’s and other neurodegenerative diseases, and warrants further research and development.

Stem Cells from Human Placenta Repair Damaged Lungs


The placenta does more than provide yet unborn babies with oxygen from the mother’s blood supply; they are also a rich source of stem cells. Vladamir Serikov from the Children’s Hospital Oakland Research Institute in Oakland, California first isolated and characterized “chorionic mesenchymal stem cells” from human placenta in 2009 (see Exp Biol Med 2009 234:813-23), and since that time, his work has been conformed by several other research labs (Cell Stem Cell 2009 5:385-95 & Dev Biol 2009 327:24-33). Now Serikov and his research team have used his hCMSCs to repair damaged lungs in laboratory animals.

In this present publication, the Serikov team grew placenta-derived hCMSCs in culture and discovered that these grew like gangbusters. After 100 doublings, the cells showed no signs of giving up and their chromosomes show no signs of shortening, which is a symptom of aging when cells are grown in culture. Stem cells, have the ability to properly maintain the ends of their chromosomes and not show these signs of aging. Serikov’s hCMSCs have this definitive stem cell ability.

Next, the Oakland-based team tried to get these hCMSCs to differentiate into various cell types using published protocols. The hCMScs formed fat cells, bone cells, blood vessel-like cells, and liver cells in culture. When treated with a molecule called nerve growth factor, hCMSCs even sprouted nerve cell-like extensions and expressed genes common found in neurons (the cells that make a propagate nerve impulses).

To determine if these cells had the capacity to heal damaged tissue, Serikov and co-workers treated human lungs that were donated by a deceased individual but were denied for transplantation with a bacterial toxin that tends to really screw up the lungs. One lobe of the lung was treated with toxin only but the other side was treated with the toxin and five million hCMSCs. The side that received only the toxin showed damage to the lining of the lungs that was reflected in poor gas exchange and high fluid uptake by the lung tissue, but the side that received the hCMSCs was able to properly pump out the liquid and maintain the structure of the lung. When this same assay was applied to cultured lung tissue from humans, it was clear that the hCMSCs helped repair the columns of lung cells through the modicum of growth factors that they secrete. Certainly, hCMSCs have the capacity to heal the lungs after they are ravaged by a deadly bacterial toxin.

Two other experiments underscored the therapeutic capacity of these cells. When hCMSCs were infused into mice after the animals have been hit with high doses of radiation, they took up residence in multiple tissues, including the intestine, lungs, brain, and liver. Therefore, hCMSCs can not help heal tissues by means of what they secrete (so-called paracrine mechanisms), but by incorporating into tissues and becoming an integral part of it. Finally, when hCMSCs were implanted into mice and examined one year later, none of the mice showed any signs of tumors. There were also no signs of pain, heart problems, distress, fever, or weight loss. Therefore, these cells seem to be well tolerated, and do not have a high capacity for tumor formation.

These preclinical studies should give way to studies in larger animals, and if those are successful, hopefully, the first human clinical trials with these amazing stem cells that come from an abundant source, the human afterbirth.

See Igor Nazarov et al., “Multipotential Stromal Stem Cells from Human Placenta Demonstrate High Therapeutic Potential,” Stem Cells Translational Medicine 2012 1:359-72.