replication-competent human retrovirus. Again, the probability of this 
occurring appears small. No replication-competent human endogenous 
retrovirus has ever been isolated and all known sequences have deletions and 
frame-shift mutations in the viral genes. The sequences defective in human 
endogenous retroviruses (namely gag, pol, and env), are the sequences deleted 
from the LNL-6 vector, so LNL-6 is unable to provide the needed sequences 
to restore function to human endogenous retroviral sequences. Also, there is 
no homology known between the LNL-6 vector and the human retroviral 
sequences, so that homologous recombination is not expected. In addition, 
variation in the structure of these human and murine viral sequences, such as 
tRNA binding sites, make the likelihood of successful recombination extremely 
small. 
These expectations have been borne out in preclinical and clinical practice. 
Recombination between MLV and human endogenous retroviral sequences 
has not been detectable in primate cells in vitro or in vivo. This question was 
specifically addressed in the LNL-6 TIL human gene transfer clinical trial. 
After retroviral insertion, reverse transcriptase (RT) assays have never 
detected RT activity. 
4.6 Introduction of the neo^ Gene 
The neo^ gene product, neomycin phosphotransferase, phosphorylates the 3’- 
hydroxyl group of the aminohexose I of neomycin and its analogues, thereby 
inactivating the antibiotic. While amikacin may be inactivated by this enzyme, 
gentamicin and tobramycin and other aminoglycosides do not contain a 
hydroxyl ^it the 3’ position and are not inactivated. Therefore, introduction of 
the neo^ gene would not exclude the use of aminoglycosides or any other 
conventional antibiotic that may be needed in the clinical management of 
these patients. 
In short, the vectors to be used in this study are currently in clinical trial, and 
have not been associated with any adverse effects. 
5.0 PLAN OF CLINICAL STUDY 
5.1 Specific Inclusion and Exclusion Criteria for Gene Transduction (Eligibility see 
section 10). 
To ensure that a sufficient aliquot of marrow can be removed for transduction 
without potentially compromising the rate of reconstitution, the minimum 
quantity of marrow mononuclear cells to be obtained at harvest will be raised 
by 30% above the minimum value quoted in previous AML ABMT protocols 
[514] 
Recombinant DNA Research, Volume 14 
