volume of 250 /xL) 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^ B AG-transduced 3T3 cells into the left frontal 
lobe. Injections were done with a 250 /xL Hamilton syringe over 15 minutes. 
A venous port was installed in two monkeys for subsequent GCV therapy via the right 
internal jugular vein. The proximal catheter was placed in the right atrium and the distal 
access port in the interscapular subcutaneous region on the back of the monkeys. GCV was 
administered to the two monkeys with the venous access port as a slow IV. infusion of 10 
mg/Kg in 50 mL normal saline over 30 minutes for 14 days. MRI 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 day 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 nearly 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 (MRI) 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 brain up to 15 days 
and cannot be seen thereafter. This time frame is similar to what we have observed in the rat 
brain. 
b. Toxicity Evaluation : Toxicity was evaluated by clinical, radiological, and laboratory 
(chemical, bacteriological, and histological) evaluation of the monkeys. Since the xenogeneic 
cells may cause an inflammatory response by leaking into the subarachnoid space (reactive 
meningitis), cerebrospinal fluid samples were collected from all monkeys 14 days after 
injection of the cells to assess that risk. All CSF samples were obtained by cisternal puncture 
and showed normal protein and glucose levels without pleocytosis. Bacterial cultures were 
negative. Table 3, Appendix E, summarizes the CSF characteristics of the samples. 
c. Clinical evaluation : Neurologic examination of all monkeys, before or after cell injection 
and during GCV therapy was unchanged from baseline. No motor or behavioral changes 
were observed at any phase of the experiment. Two monkeys treated with HS-tk-producer 
cell injections without GCV therapy were followed for evidence of long-term toxicity. For 
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