Setting a thief to catch a thief may or may not be goodpolice strategy, but it's on the way to being tried againstAIDS.
Virologist Robert Gallo, co-discoverer of the humanimmunodeficiency virus, (HIV-1), is tooling up to pit theDNA of another retrovirus against HIV-1, primepathogen of the AIDS scourge.
"It has been shown that such a retrovirus might inhibitHIV-1 replication, said oncologist Alain Thierry of theNational Cancer Institute's (NCI) Laboratory of TumorCell Biology, which Gallo heads. "We are using ourpatented liposome delivery system to transfect thisretroviral gene into humanized mice."
Thierry is first author of a paper in the currentProceedings of the National Academy of Sciences(PNAS), dated Oct. 10, 1995. Its title: "Systemic genetherapy: biodistribution and long-term expression of atransgene in mice." He told BioWorld Today that "Geneexpression of this other retrovirus inhibits expression ofHIV-1 extremely well."
Thierry and Gallo are "also working with antisense toinhibit genes that are important for HIV replication, [and]getting good results in vitro, using our liposome deliverysystem to deliver the antisense compound." This payloadis a retroviral gene with pathogenic sequencesmutationally deleted.
Their liposomal construct for systemic gene therapy,Thierry explained, deployed multilamellar, cationicliposomes, 200 to 3,000 nanometers in diameter,containing spermine as one active ingredient. Theepisomal vector carried a firefly luciferase reporter gene,plus antigenic and promoter fragments of the humanpapova, Rous sarcoma and simian 40 viral genes.
As reported in PNAS, their team injected this plasmidinto the tail veins of mice. The luciferase gene expresseda luminescent protein that lit up a broad spectrum oforgans and tissues. Its activity persisted, with expressionon a dose-dependent basis, in lung, liver, spleen and heartfor up to three months. Control animals, which got shotsof saline, stayed in the dark.
"Results," the paper concluded, "indicated that transgenicexpression in specific tissues depended on the promoterelement used, DNA/liposome formulation, dose of DNAper injection, and route of administration."
"Spermine," Thierry pointed out, "as is very well known,vectorizes DNA naturally in cells." He added that "theepisomal vector overcomes one of the limitations ofplasmid DNA, namely that transgenes are expressed incytoplasm, and have only transient expression. Our newvector replicates independently in the cytoplasm, like aretroviral vector, but not in the chromosome, so we loseless of the gene expression." He added: "This is a hugestep."
One of France's leading biotechnology companies,Transgene SA, of Strassbourg, "is going to buy thelicense to National Institutes of Health's patent on thisliposome delivery system," Thierry said. "They plan touse the system in their gene therapy programs againstcystic fibrosis and cancer. At present," he observed,"Transgene is using an adenovirus vector construct, butits expression is limited."
He added, "We are going to collaborate heavily withTransgene, which anticipates Phase I clinical trials by theend of 1996."
Another impending collaboration awaits Gallo with amove at the end of this year from NCI to create and heada new Institute of Human Virology in Baltimore. It willbe affiliated with the University of Maryland's newBiology Center, medical school and hospital. "He willcontinue this work there," Thierry said, "together with ushere."
Meanwhile, since submitting their paper to PNAS lastJune, he and Gallo have developed several targetprograms for their systemic gene therapy system.
For one thing, they have replaced the original luciferasereporter DNA with the gene for multiple drug resistance(MDR). "This MDR gene," Thierry observed, "isselectable in vivo. We can transfer it together with atherapeutic gene at the same time."
One such is the gene for glucocerebrosidase, the enzymemissing in Gaucher's disease. "Our purpose," Thierrysaid, "is to model possible gene therapy for Gaucher's.It's difficult to select cells using the glucocerebrosidasesequence, but we can select the MDR, so the cells areexpressing both genes, one after the other."
He has tested this bicistronic (two-gene) construct in vivoin mice, "and in various organs we showed expression."
Thierry concluded: "Non-viral gene transfer offersexciting potential." n
-- David N. Leff Science Editor
(c) 1997 American Health Consultants. All rights reserved.