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 more than 12 months following cell 
injection, no ill-effects or any changes from baseline neurological 
status have been observed. 
d. Radiological evaluation - MR Studies: Both GCV-treated and non- 
treated monkeys' MR scans showed the localized injection site as 
an isointense lesion (7 days after cell injection) or hypointense 
lesion (7 days after start of GCV) measuring a few mm in diameter 
with enhancement of the surrounding rim following IV injection of 
gadolinium. No edema or mass effect were noted in any of the 
monkeys. This appearance is compatible with a local breakdown of 
the blood-brain barrier, as is expected from the cell injection 
alone . 
e. Histologic Studies; Mild reactive gliosis was seen in the vicinity 
of the cell injection site without evidence of edema or 
pathological changes in neighboring brain tissue. This was true 
for both the GCV-treated and non-treated animals. Specimens 
stained for myelin showed localized demyelination limited to the 
injection site which did not increase in size when GCV was given. 
A few endothelial cells adjacent to the injection site showed B- 
galactosidase activity as evidence of transduction with the B-GAL 
vector. 
f. Complications : The only complications observed were 2 septic 
complications related to the profound immunosuppression induced in 
the monkeys by high-dose steroids. One monkey (number 1) , which 
had undergone implantation of the venous access port into the right 
heart developed, acute bacterial endocarditis with resultant 
Staphylococcus aureus septicemia and septic shock that led to its 
death 3 days after cessation of the prophylactic antibiotic 
therapy. This occurred 7 days after starting GCV therapy. An MR 
study that was obtained 24 hours before death as well as 
macroscopic appearance of the brain and histology showed no 
evidence of CNS-related toxicity. Another monkey, which received 
bilateral injections (HS-tk-producer on one side and B-GAL- 
transduced 3T3 cells on the other side) and no GCV therapy, died 
on the 21st post-operative day (one day before planned sacrifice) . 
Necropsy revealed bilateral interstitial pneumonia due to 
cytomegalovirus as well as systemic mycosis (Candida albicans 
cultured from all harvested organs) as cause of death. Again, no 
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Recombinant DNA Research, Volume 18 
