possible to detect one infected cell in 10,000 unmarked cells. 
He concluded by saying, "if we ever find a human TIL which has an 
infectious viral particle, we simply won't use it." 
Describing data on the reverse transcriptase assays. Dr. Anderson 
commented that it is not very sensitive past dilutions of lCT 3 . 
In conclusion. Dr. Anderson listed the following assays for 
replication competent retrovirus: S+/L-, 3T3 amplification at 1 
and 3 weeks, PCR for envelope sequences and viral genome, and, in 
addition, S+/L- performed by a commercial laboratory. 
Dr. Mulligan asked if in the helper assay, which can detect a 
titer of 3X10% whether the presence of a recombinant at a titer 
10-fold higher did not present problems with assay sensitivity. 
Dr. Anderson replied that in such a case, 1: 10-fold dilutions 
could be made to bring the test sample into the proper 
sensitivity range for the assay. Further, in response to 
continued questioning. Dr. Anderson said the point was that they 
were testing human TIL which have titers of zero, 1, 5, or 10. 
Dr. Mulligan said that he felt it necessary to see confirmatory 
data on the sensitivity of the helper assay, to which 
Dr. Anderson replied that the assay was sensitive and could 
detect one viral particle up to as high as one could go and, 
therefore, was a non-issue. He said he, as well as other cancer 
researchers, feel that the added risk to cancer patients of using 
marked cells was slight. He noted that in many cases, these same 
patients were enrolled in Phase I trials of new chemotherapeutic 
agents with no greater problems or benefit but with far greater 
risk. He said, "This is a safe procedure. It is a 
straightforward procedure." 
Dr. Mclvor pointed out that the Human Gene Therapy Subcommittee 
had not seen much of the data that had been presented at today's 
meeting. Dr. Anderson confirmed that the Subcommittee had been 
told the data would be supplied but, as he pointed out earlier, 
that was prior to the conversation over publication. He noted 
that this was the first time the bulk of this data had been 
presented. 
Dr. Anderson continued by presenting data on in vivo safety 
studies in monkeys that were inoculated with large amounts of 
murine amphotropic retroviral particles after being 
immunosuppressed with no evidence of clinical illness as a 
result. 
Insofar as infection of healthcare workers. Dr. Anderson said 
there was some concern over possible needlesticks . He said 
experiments were done, again in immunosuppressed monkeys, taking 
skin fibroblasts and chronically infecting them so they were 
shedding virus and reinserting them in the animal until a 
retroviremic state could be achieved. Virus could be 
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