Implants of polymer‐encapsulated human NGF‐secreting cells in the nonhuman primate: Rescue and sprouting of degenerating cholinergic basal forebrain neurons

Abstract

Baby hamster kidney (BHK) cells were genetically modified to secrete high levels of human nerve growth factor (BHK-hNGF). Following polymer encapsulation, these cells were implanted into the lateral ventricle of four cynomolgus monkeys immediately following a unilateral transection/aspiration of the fornix. Three control monkeys received identical implants, with the exception that the BHK cells were not genetically modified to secrete hNGF and thus differed only by the hNGF construct. One monkey received a fornix transection only. All monkeys displayed complete transections of the fornix as revealed by a comprehensive loss of acetylcholinesterase-containing fibers within the hippocampus ipsilateral to the lesion. Control monkeys that were either unimplanted or received BHK-control (non-NGF secreting) cell implants did not differ from each other and displayed extensive losses of choline acetyltransferase and p75 NGF receptor (NGFr)-immunoreactive neurons within the medial septum (MS; 53 and 54%, respectively) and vertical limb of the diagonal band (VLDB; 21 and 30%, respectively) ipsilateral to the lesion. In contrast, monkeys receiving implants of BHK-hNGF cells exhibited a only a modest loss of cholinergic neurons within the septum (19 and 20%, respectively) and VLDB (7%). Furthermore, only implants of hNGF-secreting cells induced a dense sprouting of cholinergic fibers within the septum, which ramified against the ependymal lining of the ventricle adjacent to the transplant site. Examination of the capsules retreived from monkeys just prior to their death revealed an abundance of cells that produced detectable levels of hNGF in a sufficient concentration to differentiate PC12A cells in culture. These findings support the use of polymer-encapsulated cell therapy as a potential treatment for neurodegenerative diseases such as Alzheimer disease where basal forebrain degeneration is a consistent pathological feature. Moreover, this encapsulated xenogeneic system may provide therapeutically effective levels of a number of neurotrophic factors, alone or in combination, to select populations of neurons within the central nervous system.

The aged monkey basal forebrain: rescue and sprouting of axotomized basal forebrain neurons after grafts of encapsulated cells secreting human nerve growth factor.

“…At the time of their retrieval just prior to sacrifice, numerous BHK cells were observed within the capsules, which now produced hNGF at a rate of 9.6 ng per 24 h per animal. This level of NGF production was biologically relevant, as media obtained from these capsules after grafting for 1 NGFr-ir in parallel (15)(16)(17)(18). The present data suggest that these cholinergic markers may be differentially regulated in the aged primate brain in response to pertubations in the cholinergic basal forebrain system.…”

“…Toward this end, intraventricular infusion of NGF has recently been demonstrated to prevent the degeneration of CBF neurons after unilateral fornix transection in young adult nonhuman primates (15,16). We have recently demonstrated that grafts ofpolymer-encapsulated NGF-secreting cells can rescue degenerating basal forebrain neurons in nonhuman primates as well (17). However, AD is a disease of the elderly and no data exist that demonstrate the ability of NGF to provide trophic influences for degenerating CBF neurons in the aged primate brain.…”

“…USA 91 (1994) 10899 fine forceps between the head of the caudate and the septum. The methods for transfecting BHK cells with the hNGF construct and encapsulating the cells within polymer capsules have been detailed (17,19,20). A total of five capsules were implanted in each animal oriented in a row in the rostrocaudal direction.…”

Selectivity of Cell Signaling in the Neuronal Response Based on NGF Mutations and Peptidomimetics in the Treatment of Alzheimers Disease

“…Briefly, eight individuals with early-stage, probable AD were administered primary autologous fibroblasts, which had been genetically modified to synthesize and secrete NGF, via stereotaxic injections to the CBF. This approach was shown to survive grafting into the brain and provided stable NGF secretion for up to 18 months in animal studies with improvement of cholinergic function and memory (Emerich et al, 1994;Tuszynski et al, 2002;Tuszynski et al, 2005). At 22 months of follow up, no adverse side effects were reported in the clinical trial.…”

Experimental strategies to promote axonal regeneration after traumatic central nervous system injury

“…However, one major obstacle that arises using this approach is the continued growth of ®broblasts after implantation leading to varying degrees of tumor formation (Homan et al, 1993;Tuszynski et al, 1994). Polymer encapsulation may help to overcome this problem since it prevents the inherent risk of tumor formation and protects the genetically modi®ed cells from immune destruction, while permitting the diffusion of molecules into the surrounding tissue for >1 year after implantation in adult rat ventricles (Emerich et al, 1994;Winn et al, 1996). Recently, X-ray treated genetically modi®ed Schwannoma cells stimulated axonal regeneration in the nigrostriatal pathway (Brecknell et al, 1996), genetically modi®ed rat astrocytes have been shown to survive well after transplantation and express the desired protein (Lundberg et al, 1996) human astrocytes have been eciently infected with a retrovirus harbouring the NGF gene (Lin et al, 1997) and rat Schwann cells genetically modi®ed to secrete BDNF increased axonal regeneration in spinal cord (Menei et al, 1998).…”