4. A few children with ADA deficiency have been cured by bone marrow 
transplants from a compatible sibling or. rarely, from a parent. In these 
situations, the bone marrow cells from the donor have enough ADA to allow the 
white blood cells to mature and function to fight infection. 
5. (Explain the risks of transplantation alone, of a hapl oidentical BMT.) 
6. (Explain the In vitro T cell experiments in which cells with the 
transplanted gene survive in culture in the presence of levels of 
deoxy adenosine toxic to patient's cells prior to treatment.) 
7. Proposed delivery system with retroviral vectors: 
define retroviral vectors - ie.. recombinant-defective retroviruses with 
the genes for self replication removed and replaced with the gene(s) of 
Interest, here the ADA gene 
explain how retroviral vectors are made using a producer cell line which 
supplements the replication function but which does not allow the viral genes 
to leave the cell 
explain how bone marrow cells do not appear to be harmed or made 
Infectious because they do not receive the genes for retrovirus replication 
discuss the outcome of testing the procedures in animal s-mlce, monkeys; 
partial success but expect selective pressure in vivo (explained further in 
next section) 
KNOWLEDGE SOUGHT: 
1. Can enough cells be infected and enough enzyme be produced per cell to 
restore immunity short term, long term? Since no large animal model exists for 
ADA deficiency, the question cannot be answered other than in a patient. 
2. Will there be selective pressure by the normal factors that regulate 
growth of the white blood cells to stimulate the growth of successfully treated 
cells over those that remain defective? Again cannot answer in animal model. 
Recombinant DNA Research, Volume 12 
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