INSERTION OF 2 INDEPENDENT ENHANCERS IN THE LONG TERMINAL REPEAT OF ASELF-INACTIVATING VECTOR RESULTS IN HIGH-TITER RETROVIRAL VECTORS WITH TISSUE-SPECIFIC EXPRESSION
A. Fassati et al., INSERTION OF 2 INDEPENDENT ENHANCERS IN THE LONG TERMINAL REPEAT OF ASELF-INACTIVATING VECTOR RESULTS IN HIGH-TITER RETROVIRAL VECTORS WITH TISSUE-SPECIFIC EXPRESSION, Human gene therapy, 9(17), 1998, pp. 2459-2468
Citations number
41
Categorie Soggetti
Genetics & Heredity","Biothechnology & Applied Migrobiology","Medicine, Research & Experimental
The use of retroviral vectors (RVs) derived from the murine oncoretrov
iruses for gene therapy is associated with the risk of malignant trans
formation of infected cells and ectopic expression of the proteins of
interest. Targeting retroviral vectors to specific tissues would incre
ase their safety and clinical applicability. To explore the potential
of targeting vector expression to skeletal muscle, the murine leukemia
virus broad transcriptional tropism was modified by substituting the
viral promoter and/or enhancer with a transcriptional cassette contain
ing the human T cell leukemia virus type I Tax-responsive element and
the minimal muscle creatine kinase enhancer and promoter. The resultin
g retroviral vectors could be transcriptionally trans-activated by tax
. In the absence of Tax, however, the viruses showed muscle-specific e
xpression. Trans-complementing packaging and indicator cells stably ex
pressing Tax were used to isolate high-titer producer cell clones (10(
6) CFU/ml). In vitro, the levels of expression of these RVs in Tax-exp
ressing fibroblasts were 10,000-fold higher than in normal fibroblasts
and 1000-fold higher in C2C12 myotubes than in C2C12 myoblasts. Expre
ssion of the vectors and the endogenous muscle creatine kinase gene wa
s similarly dependent on the maturity of the muscle cultures. One vect
or with modified LTRs was also tested in vivo in regenerating muscle a
nd showed a delayed pattern of expression in myofibers compared with t
he vector containing the wild-type LTRs, These vectors can be easily m
odified to contain different tissue-specific enhancer and promoter ele
ments and the availability of complementing packaging and indicator ce
lls expressing Tax should allow their application in a variety of gene
therapy settings.