J Virol, February 1998, p. 1115-1121, Vol. 72, No. 2
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Department of Gene
Regulation1 and
Laboratory of Molecular
Genetics,
Received 16 June 1997/Accepted 21 October 1997
We report here on stable prepackaging cell lines which can be
converted into packaging cell lines for high-titer vesicular stomatitis
virus G protein (VSV-G)-pseudotyped retrovirus vectors by the
introduction of Cre recombinase-expressing adenovirus. The generated
prepackaging cell lines constitutively express the gag-pol
genes and contain an inducible transcriptional unit for the VSV-G gene.
From this unit, the introduced Cre recombinase excised both a neomycin
resistance (Neor) gene and a poly(A) signal flanked by a
tandem pair of loxP sequences and induced transcription of
the VSV-G gene from the same promoter as had been used for
Neor expression. By inserting an mRNA-destabilizing signal
into the 3' untranslated region of the Neor gene to reduce
the amount of Neor transcript, we were able efficiently to
select the clones capable of inducing VSV-G at high levels. Without the
introduction of Cre recombinase, these cell lines produce neither VSV-G
nor any detectable infectious virus at all, even after the transduction of a murine leukemia virus-based retrovirus vector encoding
-galactosidase. They reproducibly produced high-titer virus stocks
of VSV-G-pseudotyped retrovirus (1.0 × 106 infectious
units/ml) from 3 days after the introduction of Cre recombinase. We
also present evidence that VSV-G-producing cells are still fully
susceptible to transduction by VSV-G pseudotypes. However, in this
vector-producing system, which regulates VSV-G pseudotype production in
an all-or-none manner, the integration of vector DNA into packaging
cell lines would be minimized. We further show that heparin
significantly inhibits retransduction of VSV-G pseudotypes in the
culture fluids of packaging cell lines, leading to a two- to fourfold
increase in the yield of the pseudotypes after induction. This
vector-producing system was very stable and should be advantageous in
human gene therapy.
*
Corresponding author. Mailing address: Department of
Gene Regulation, Institute of Medical Science, University of Tokyo,
4-6-1 Shirokanedai, Minato-ku, Tokyo 108, Japan. Phone: 81-3-5449-5730. Fax: 81-3-5449-5449. E-mail:
iba{at}hgc.ims.u-tokyo.ac.jp.
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