Adenovirus-mediated transgene expression in nonhuman primate brain

Transgene expression in the brain of St. Kitts green monkey, Cercopithecus aethiops sabeus, was studied following injection of a serotype 5 adenoviral vector deleted in E1 and E3, The vector harbored the transgene for Escherichia coli beta-galactosidase (beta-Gal) with the simian virus 40 (SV40) nuclear localization signal under control of the Rous sarcoma viral (RSV) long terminal repeat. Several titers ranging from 5 x 10(7) to 2 x 10(9) plaque-forming units (PFU) in volumes ranging from 5 to 250 mu l were injected into the caudate nuclei of 18 monkeys. Monkeys were treated with dexamethasone for 9 days, beginning the day prior to surgery, and were sacrificed at 1 week or at 1, 2, or 3 months. At 1 week, beta-Gal was expressed in thousands of cells, including both neurons and astrocytes. In addition, some dopaminergic neurons in the substantia nigra expressed transgene, suggesting retrograde transport of the vector. At 1 month 162,000 +/- 68,000 (SEM) or 65,000 +/- 29,000 beta-Gal-expressing cells persisted in striatum injected with 6 x 10(8) PFU in 30 mu l or 5 x 10(7) PFU in 5 mu l, respectively, Transgene expression was also observed in one of two monkeys sacrificed at 2 months and in a single monkey sacrificed at 3 months, No transgene expression was observed at 1 month in striatum injected with a higher titer (2 x 10(9) PFU in 100 mu l) or more dilute vector (5 x 10(7) PFU in 30 mu l), Staining for the major histocompatibility complex II (MHC II) subtype DR showed intense staining in sites injected with a higher vector titer, in which no transgene persisted at 1 month, whereas low to moderate staining was present in sites with high transgene expression. These observations suggest that there is an optimal range of vector titers for obtaining persistent transgene expression from E1E3-deleted adenovirus in primate brain, above which host responses limit transgene stability.