Recombinant DNA Advisory Committee - 7/31/90 
may accumulate in time, resulting in protection of the patient 
and improvement in his/her immune function. Furthermore, since 
most SCID patients do not live beyond the age of one year, the 
patients to be accessed into the study already are a subset of 
patients with a relatively mild form of this disease. Since they 
have survived for this long, they may benefit more readily than 
patients with more severe forms of the disease. 
Dr. Riley said she wanted to be sure that efficacy of the 
treatment could be measured in patients who were already on PEG- 
ADA. Dr. Parkman said that the patients who would be included in 
the protocol would not have effective protective immunity. 
Despite being able to respond to a single antigen, their T cells 
are non-functional. He said this is proved by the need to 
continue to treat them with intravenous immunoglobulin. 
Therefore, improvements in specific immunity to antigens would be 
one of the proofs that the therapy is working. 
Dr. Atlas asked whether cellular treatment would be decreased if 
the patients developed an adequate immune response. Dr. Parkman 
said the protocol did not address this issue specifically but 
that such a reduction would be a logical next step if an 
improvement in specific immunologic function is demonstrated. 
Dr. Atlas questioned whether such a reduction in therapy would 
have to be brought back to the HGTS and the RAC for approval. 
Dr. McGarrity said this would be a modification to the protocol 
and would have to be approved. However, he added that the RAC 
was going to consider a proposed addition to the "Points to 
Consider" which would expedite minor modifications to approved 
protocols and would be discussed later in the meeting. If such a 
reduction were considered to be a minor modification, and if the 
RAC approved the amendment to the "Points to Consider," then a 
minor modification could be reviewed by the local IBC and IRB. 
Then the Chair of the HGTS and the Chair of the RAC could approve 
such a modification. Dr. Miller added that the Food and Drug 
Administration (FDA) would also have to approve any such changes 
to the protocol. 
Dr. Atlas asked how many patients were likely to be eligible for 
the protocol and whether there were enough to draw a distinction 
between the existing PEG-ADA therapy and the new gene therapy. 
Dr. Parkman said the current pool of patients on PEG-ADA therapy 
was very heterogeneous in its responses to PEG-ADA, with about a 
third responding well, a third with partial responses, and a 
third who do not respond. He expected the results of the gene 
therapy protocol to be the same, noting that it might not work in 
all patients. Currently, the investigators have approximately a 
half dozen eligible patients who are interested in participating 
in the protocol. Dr. Blaese said that he felt there would be 
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