Recombinant DNA Advisory Committee - 2/10-11/92 
transduced fraction after the three-day incubation and re-sort by FACS for CD34(+) cells. 
Then, PCR analysis can be performed to detect ADA gene expression in these cells. Gene 
expression needs to be examined in the T lymphocyte progeny, not the CD34( + ) cells. 
The only way to answer that question would be to readminister the selected cells to SCID 
mice, examine their thymuses in six months, and observe if there was expression of human 
ADA. There is difficulty in performing experiments to determine if the T lymphocyte 
progeny expresses ADA. Currently, granulocytes from two patients are being examined by 
PCR, and there are plans to assay for this activity. 
Dr. Haselkom had a concern about the biotin and avidin dissociating under the 
experimental conditions being described. He suggested measuring how much avidin 
remains after the final stage of the purification procedures when cells are reinserted into 
the patient. Dr. Nienhuis responded by clarifying that since 12-8 is a relatively low-affinity 
antibody, it is probably the antibody-antigen bond that is disrupted. Since CD34 is a 
transmembrane protein, it is unlikely that it would detach from the cell unless the avidin 
binds and affinity is extremely high. When the cells are ready to administer to the 
patients, the investigators will monitor for avidin. 
Dr. Mclvor asked whether there is a mechanism in place for determining whether the 
proposed experiments should be a modification to an existing protocol or a separate 
protocol. Dr. Wivel responded that there is a mechanism described in the Points to 
Consider in the Design and Submission of Protocols for the Transfer of Recombinant DNA 
Into the Genome of Human Subjects that calls for consultation of the Chairs of the RAC 
and HGTS to determine if a modification is major or minor. There was a determination 
that this particular protocol is considered a major modification, not a new protocol. This 
amendment involves adding additional therapy for patients already involved in the protocol 
rather than starting a new set of patients. In any event, RAC's normal standards for 
approving protocols will have to be satisfied. Dr. Mclvor stated, and Mr. Barton agreed, 
that the standard should not be whether or not there is a new patient population, but 
whether there are fundamentally new scientific issues involved. Dr. Mclvor stated that 
scientifically this proposed amendment should be considered a separate protocol. Dr. Post 
commented that if there are no new risks associated with adding this component to the 
protocol, it would be more advantageous to use the same patient population than to 
expose a new patient population to a protocol where there is not as much efficacy data. 
Dr. Krogstad stated that questions of efficacy and safety should be separated. There is a 
major issue over the safety of the new vector. 
Ms. Buc posed several procedural questions, one relating to the relationship between the 
HGTS and the RAC. Dr. Wivel replied that the HGTS has the same standing as that of 
any of the RAC subcommittees that have been created. Historically, subcommittees were 
created in response to a perceived need. These subcommittees were created and dissolved 
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Recombinant DNA Research, Volume 15 
