undergo a brain scan to estimate the volume of the tumor fossa. On day 8 the skin overlying 
the Ommaya will be cleansed with betadine. A needle will be inserted through the overlying 
skin into the reservoir with the patient awake. VPC will be slowly injected into the reservoir 
until the tumor fossa has been filled based on brain scan estimates of the tumor fossa 
volume. GCV will be administered starting on the 15th post-operative day for 14 days (days 
15-28). Repeat administration of producer cells will be done on day 42, followed by another 
cycle of GCV administration 7 days later (days 49-63). 
C. Volume and number of injected cells: Factors such as tumor size, location, and the 
preoperative neurological condition of the patient will determine the injectable volume. The 
final cell concentration will be adjusted to 1-2X10^ cells/mL. 
D. Peri-operative medications: 
1. Antibiotics : All patients will receive a single dose of Ceftriaxone or the equivalent just prior 
to the initial surgical procedure and prior to the injection of the Ommaya reservoir. 
2. Steroids : All patients will receive dexamethasone at 32 mg/day starting 7 days prior to each 
VPC injection and treatment will be continued until GCV is discontinued. Dexamethasone 
will then be tapered. As experience is gained, the need for high dexamethasone dosing may 
be modified. 
3. Mannitol : Patients may receive mannitol during the surgical procedure at lg/kg and the dose 
repeated TID for 24 hours following the procedure, as clinically indicated. 
4. Anticonvulsants : Anticonvulsive therapy will be administered according to the usual 
neurosurgical guidelines. 
5. Analgesics : Pain medications will include Acetominophen 650-1000 mg Q 4 hours. 
E. The GlTkSvNa.29 Retroviral Vector (Appendix G). GlTkSvNa.29 is a retroviral vector 
derived from the Moloney murine leukemia virus (MoMLV). This vector contains a Herpes 
simplex type I thymidine kinase (HS-tk) gene cDNA that is transcribed from the viral LTR 
and a bacterial neomycin resistance (NeoR) gene transcribed from an internal SV40 (simian 
virus 40) early promoter (LTR— HS-tk-SV--NeoR-LTR) in the G1 vector backbone 
(Genetic Therapy Inc., Gaithersburg, Md). This Gl-based vector has been modified for 
increased safety by alteration of the gag start codon to a stop codon, and by elimination of 
viral sequences needed in trans for the formation of the virus particle. This has been shown 
to minimize the potential for the development of replication-competent virus production 
from producer cells which contain the vector. The HS-tk gene is a negative selectable 
marker or “suicide” gene. When a HS-tk transduced cell is exposed to GCV, the GCV 
acts as a substrate for phosphorylation by HS-tk resulting in a monphosphate (MP) form of 
the drug. Cellular phosphorylases convert this GCV-MP to GCV-triphosphate (GCV-TP) 
that inhibits DNA polymerase and is incorporated into DNA resulting in an inability of the 
cell to proliferate. The end result is cell death for the HS-tk transduced cells (21-25). The 
NeoR gene is a positive selectable marker. The bacterial NeoR gene encodes for NPT II 
(neomycin phosphotransferase II), an enzyme that will protect GlTkSvNa.29 expressing 
cells from the toxic effects of G418 (a neomycin analog). NeoR has been used in many 
human clinical trials to date without adverse effect. NPT-II inactivates the antibiotic 
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Recombinant DNA Research, Volume 17 
