2 
Pr . Alters convened the meetinq of the Working Group on Human Gene Therapy at 
9:15 a.m. on December 16, 1985. He said several topics would be covered at 
this meetinq: (1) retroviral vectors; (2) the November 12, 1985, meeting of 
the RAC Working Group on Viruses; (3) transqenic animal studies; (4) the Food 
and Drug Administration (FE&) process for filing a "Notice of Claimed Investi- 
gational Exemption for a New Drug" (IND); and (5) other issues and announcements. 
Retroviral Vectors 
Dr. Anderson qave a presentation on the use of retroviral vectors to transfer 
nenes in human gene therapy. He explained that retroviruses are animal viruses 
with a glycoprotein envelope and an RNA genome that replicate through a ENA 
intermediate. The DNA intermediate is stably integrated into cellular DNA; 
the integrated DMA is termed the provirus. Dr. Anderson said at this time 
many basic retroviral functions are not fully understood. 
Dr. Anderson described the retrovirus life cycle (Attachment II). He said the 
virus recoonizes sites on the cell membrane and adsorbs to these receptor 
sites. After penetration of the cell membrane, the single-stranded RNA gencme 
is reverse transcribed in the cytoplasm to a double-stranded circular DNA 
molecule. The circular double-stranded molecule is transported into the nucleus 
and integrates into the host chromosome by a hiqhly efficient ordered process. 
The integrated provirus serves as the template for synthesis of mRNAs encoding 
the gag, pol , and env functions as well as full-length transcripts of the 
viral gencme. 
T\vo viral long terminal repeats ( LTRs ) are situated at the junctions between 
viral and cellular genomes. Functional and nucleotide sequencing studies of 
LTRs derived from a number of different retrovirus isolates suggest that LTRs 
provide a number of functions essential to the retrovirus life cycle. These 
functions include provirus integration into host DNA, viral DNA synthesis, and 
transcription of the viral gencme. The LTR on the 5' region of the provirus 
gencme contains the functional transcriptional initiation site, while the LTR 
on the 3' region contains the functional termination signal. Most retrovirus 
LTRs also include sequences that can enhance the transcriptional activity of 
flanking viral or cellular DNA. Immediately contiguous to the LTRs are 
sequences essential for virus ENA synthesis; in addition, a sequence necessary 
for packaging of the viral RNA gencme into nascent virions at the cell membrane 
is located near the 5' LTR. 
The LTRs control three major regions in the virus gencme; gag , pol , and env . 
The gag region codes for four structural proteins used in encapsidation. 
These proteins bind to 5' reqions of the gencme. The pol region codes for the 
reverse transcriptase, an endonuclease which functions in insertion of the 
provirus into the chromosome, and an endopeptidase . Fnv genes code for proteins 
involved in budding of infectious virus particles from the cell. 
The gag, pol , and env reqions represent a very intricate system with regulatory 
regions super- imposed on the structural genes. The functions of these control 
regions have not yet been fully elucidated. In a retroviral vector, some or 
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