did not show evidence of inflammation or destructive changes in 
either group. Dexamethasone was administered to the rats as an 
oral dose of 0.5 mg/Kg/day, starting on the third day post 
injection of the VPC. It appeared that dexamethasone pretreatment 
diminishes the non-specific symptoms related to the surgery and 
implantation of cells in the brain. 
4. Toxicity studies in non-human primates. Five rhesus monkeys were 
used for the primate experiments. The study was designed to 
address 2 major issues: 1. What is the fate (survival time, 
proliferation potential) of the murine VPC within the brain? 2. 
Is there significant toxicity from the intracerebral injection of 
HS-tk vector-producer cells, alone or with subsequent GCV therapy? 
As is in standard neurosurgical practice, the monkeys were 
treated with high-dose steroids (dexamethasone, 2 mg/Kg IM/day) 
starting 7 days before surgery and continued for 3 weeks at which 
point the dose was gradually tapered during one week and 
discontinued. Antibiotic therapy (Cefotaxime, 30 mg/Kg, IM BID) 
was administered starting on the day of surgery and continued for 
10 days. Using general anesthesia under aseptic conditions, 
monkeys received stereotaxic intracerebral injection of 10 7 HS-tk 
VPC mixed with 10 6 B-GAL VPC (total volume of 250 uL) into the deep 
white matter of the right frontal lobe. One monkey received 
bilateral injections of an HS-tk/B-GAL vector-producer cell mixture 
(10:1), as described, into the right frontal lobe and 10 7 BAG- 
transduced 3T3 cells into the left frontal lobe. Injections were 
done with a 250 uL Hamilton syringe over 15 minutes. 
GCV was administered to the two monkeys through a venous 
access port as a slow IV, infusion of 10 mg/Kg in 50 mL normal 
saline over 30 minutes daily for 14 days. MR scans, including T1 
and T2 weighted images and gadolinium-enhanced T1 weighted studies 
were obtained before GCV treatment (day 5 after cell injections) , 
7 days after initiation of GCV therapy (14 days after cell 
injection) , and 90 days after cell injection in non GCV-treated 
monkeys. Physical and neurological examinations were performed 
twice a day on each monkey. Repeat blood samples were obtained 
from all animals before and during the experiment for routine 
chemistry and CBC. Cerebrospinal-fluid (CSF) samples were taken 
by cisternal puncture from all monkeys on the tenth post-operative 
days and were assayed for routine chemistry and bacteriological 
analysis. Two monkeys who received intracerebral injections of the 
HS-tk producer cells without GCV have now been followed more than 
one year without evidence of adverse effects. These results are 
summarized in table 2, Appendix E. 
a. Fate of the producer cells: To address this question, histologic 
examination was carried out on the brains of 3 monkeys. No 
proliferation of the VPC within the brain was observed in either 
the GCV-treated (2) or non-treated (1) monkeys. This was 
determined on the basis of histological and radiological (MR) 
examination of the brains. In one GCV treated animal examined 15 
days after cell injection, some residual murine cells (using the 
B-GAL-producer cells as a marker) were found among the injected HS- 
tk VPC. No B-GAL positive murine cells were found in the 2 animals 
examined 3 weeks after cell injection, regardless if GCV was or was 
not administered. It is concluded that the VPC survive in the 
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