brain tumor cells by inserting the TK gene into the tumor cells. The 
way we will transport the TK gene into the tumor cells is to use a 
"vehicle" to carry the TK gene into the cells. An example is that if 
you want to move a passenger you need to put him in a car. The vehicle 
(or car) in this case is a different virus - a retrovirus that is 
found in mice - that has been inactivated so that it cannot cause 
disease. We call this vehicle a "vector". We insert the TK gene (the 
passenger) into the vector and the vector carries the gene into your 
child's brain tumor cells. The vector/gene combination is produced by 
"vector-producer" cells (little factories that make the cars containing 
the passengers) . When the vector/gene combination gets into the tumor 
cells it inserts itself into the cells' genetic material (chromosomes) 
and tells the tumor cells to begin making TK. We will also attach to 
the vector vehicle a bacterial gene that we think is harmless; this gene 
serves to mark the location of the TK gene in your child's body. When 
we give your child Cytovene, the tumor cells containing the TK gene 
produce harmful substances within themselves that cause the tumor cells 
to die. We do not expect normal brain cells to be injured because the 
vector/gene combination is attracted only to growing cells. Normal 
brain cells are not growing, but tumor cells are. The tumor cells, not 
the normal brain cells, are targets for the vector/gene combination. 
POTENTIAL BENEFITS 
This study utilizes a type of therapy that has not been used 
previously for the treatment of pediatric brain tumors. By using this 
therapy on your child, we will be learning whether the therapy is 
effective or not. If the therapy is effective, some or all of the tumor 
cells in your child's brain will be killed. If some of the cells are 
killed, your child's life may be prolonged. If all of the cells are 
killed, your child may be cured. We emphasize that we do not know if 
this therapy will be effective. It is entirely possible that the 
therapy will have no effect on your child's tumor. It is possible that 
the therapy will make your child worse. 
We believe that the information obtained from patients in this 
study may be of beneifit to future children with similar brain tumors. 
STUDY PLAN 
Pretreatment Evaluation: 
Your child may be admitted to the hospital for approximately 1 week 
for the pretreatment evaluation and the following procedures. Your 
l child will have a complete neurological and physical examination, blood 
and urine tests to determine his/her overall physical health. The 
amount of blood drawn from your child will be no more than 2 Tbs per 
day. Your child may experience some discomfort or temporary pain at the 
site of the needle entry for the routine blood studies. There is remote 
| risk of fainting and local infection. 
Your child will also have X-rays of the chest and head and any 
other areas of the body as indicated by his or her medical examination 
l and history. Additional tests may be required depending upon his/her 
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