Even though the vector producing cells cannot grow and are considered harmless in humans, it is 
possible that events could occur within the cells that would permit the vector to grow and/or make the 
cells cancerous. Gene transfer using similar vectors has been used in adult and child patients. Since 
these experiments began in 1 989, none of the more than 20 people who have received cells into which 
genes have been transferred by vectors have developed any problems related to the gene transfer 
method. We believe these vectors are safe and are not a threat to other people or to society. 
This method of treatment has two major potential problems. The vector may be passed into surrounding 
normal tissue in addition to tumor tissue. We have not found any evidence of problems in mice and rats 
due to spread of vector to surrounding normal brain tissue or to other sites in the body. We believe that 
some of the surrounding blood vessel cells probably do have the vector but the number is too small to 
result in significant adverse side effects. It is possible that bleeding and neurological symptoms 
(headache, convulsions, stroke) may develop with Cytovene. 
The vector producing cells might persist in your body and cause cancer or other diseases. We expect 
your immune system to reject (kill) the vector producing cells in one to two weeks. Thus, they should 
not be able to survive and grow in your body. In addition, we expect the Cytovene therapy will kill all 
cells with the vector including the vector producing cells. Therefore, the vector producing cells should 
not survive and the insertion of the vector should not result in new cancerous cells since we think all the 
cells with the vector will be killed by Cytovene. Therefore, we feel the risk of developing a new cancer 
is very small. 
Risks of Cytovene therapy: 
Cytovene has been used extensively in humans to treat a number of infections including viral infections 
of the eye. We will be following the recommended dose for therapy that has been used to treat viral 
infections of the eye. The most commonly observed complication in people receiving Cytovene has been 
development of decreased white blood cell and platelet counts. This could result in an increased risk of 
infection and bleeding. These counts will be monitored every other day (during Cytovene treatment) and 
the drug will be discontinued if the white blood cell count or platelet count drops significantly. 
Discontinuation of the drug results in normalization of the white blood cell and platelet numbers. 
Cytovene may cause permanent or temporary infertility and may be associated with birth defects. 
Therefore, women of childbearing age should use effective contraception during Cytovene therapy and 
men should use contraception during and for at least 90 days following Cytovene therapy. Pregnant 
women are not eligible for this protocol. Cytovene can cause cancer in animals. There is no information 
available to estimate the risk of this in humans. 
Recombinant DNA Research, Volume 17 
[183] 
