Genetically Modified Astrocytes Secreting Beta-Nerve Growth Factor (β-NGF) Support Adrenal Chromaffin Cells Grafted into the Striatum

Intracerebral transplantation of genetically engineered cells is a useful method for delivering recombinant growth factors to the brain. Despite the clear experimental and therapeutic potential of this technique, relatively few cell types have been studied as targets for genetic manipulation and transplantation. Our interest has been to determine whether primary type I astrocytes, the normal support cell of the CNS, are suitable for this purpose. For these studies, type I astrocytes purified from newborn rat cerebral cortex were genetically modified in culture to constitutively express a mouse/3-NGF transgene, by infection with a replication-defective retroviral vector as previously described (Cunningham et al., Brain Res 561: 192-202). Infected astrocytes were found to release NGF into the culture medium at a rate that is > 10-fold higher than that of sister cultures of uninfected astrocytes (9.3+_2.9 pg/10 s cells/h vs. <0.8 pg NGF/10 cells/h). To evaluate the potential of these transgenic astrocytes to provide trophic support to brain grafts, their effects on the survival and neuronal transdifferentiation of intrastriatal adrenal chromaffin cell co-grafts were evaluated in the unilateral 6-hydroxydopamine-lesioned rat (an animal model of Parkinson's disease). NGF-producing transgenic astrocytes (AsN.8) were fluorescently labeled with DiI, mixed 1:1 with suspensions of postnatal day 12 adrenal chro