A Phase I Study of Ex Vivo Nerve Growth Factor Gene Therapy for Alzheimer's Disease

Although the precise pathogenesis of AD is unknown, certain pathological features accompany the disease. These pathological features include the abnormal accumulation of extracellular amyloid, the formation of intraneuronal neurofibrillary tangles, synapse loss, and cellular degeneration. Cellular degeneration occurs in several neuronal populations in the central nervous system. Among the neuronal populations that degenerate in AD, loss of basal forebrain cholinergic neurons is particularly severe. Loss of cholinergic neurons in AD correlates best with severity of dementia, the density of amyloid plaques in the brain, and the amount of synapse. To date, the only FDA-approved therapies for Alzheimer's Disease focus on augmenting the function of degenerating cholinergic neurons.

The present trial will move beyond compensating for cholinergic neuronal degeneration by attempting to 1) protect cholinergic neurons from degeneration, and 2) augment the function of remaining cholinergic neurons by directly elevating choline acetyltransferase (ChAT) function in neurons. These two therapeutic interventions will be brought about by the delivery of human NGF to the brain.

NGF has been shown to prevent both lesion-induced and spontaneous, age-related degeneration of basal forebrain cholinergic neurons. Further, NGF infusions reversed both lesion-induced memory loss and spontaneous, age-related memory loss in rodents. Based on these findings, NGF administration offers significant potential as a neuroprotective strategy in Alzheimer's disease.

Grafts of primary fibroblasts transduced to express human nerve growth factor have been shown to sustain NGF in vivo gene expression for at least eighteen months in the rodent central nervous system. In addition, these grafts sustain NGF messenger RNA production for at least 14 months in vivo. In primate systems, ex vivo NGF gene therapy has been demonstrated to sustain NGF protein production in the brain in the rhesus money for at least one year.

Thus, the available data suggests that ex vivo NGF gene therapy is an effective means of preventing loss of basal forebrain cholinergic neurons and of augmenting cholinergic function in the primate brain. In animals, this procedure is safe and well tolerated. Based on these data, clinical trials of ex vivo NGF gene therapy in Alzheimer's disease has begun.