By David N. Leff
Editor's note: Science Scan is a roundup of recently published, biotechnology-relevant research.
Adenovirus (AV) is short for "Adenoidal-pharyngeal-conjunctival." As that moniker implies, AV is high on the most-wanted rap sheet of viruses that cause the common cold. That word "common" is key. Essentially 100 percent of human children, as they grow up, have sustained an AV infection, usually mild. The smoking gun is the presence in their blood of antibodies against AV virion antigens.
These lifelong pre-existent antibodies come in two flavors: "total" (TAb) and "neutralizing" (NAb). Almost all adults carry TAb to adenovirus type 5 (AV5) - one of some 40 viral variants. Only 57 percent have NAb against AV5. "These antibodies," observes a report in the July 20, 2000, issue of Human Gene Therapy, "are of significant interest in the design of therapeutic strategies based on adenoviruses."
That paper's title sums up its in vivo trials in these terms: "Pre-existent adenovirus antibody inhibits systemic toxicity and antitumor activity of CN706 in the nude mouse LNCaP xenograft model: Implications and proposals for human therapy." Its senior author is Daniel Henderson, president and CEO of Calydon Inc. in Sunnyvale, Calif.
CN706 is a proprietary AV5 construct, engineered to replicate in, and kill, LNCaP metastatic prostate cancer cells. To simulate the human situation, the co-authors generated hyperimmune AV5 antibodies in rabbits, and injected them into the tail veins of nude mice in which xenografted LNCaP human prostate tumors were growing. A day later, they injected a dose of the CN706 virus. When mice carrying those pre-existing adenovirus antibodies were treated with a massive dose of virus that should have killed 100 percent of the animals, not one of the mice was affected.
"Pre-existent anti-adenovirus antibody," the journal paper reported, "protected mice from virus-induced toxicity and significantly reduced antitumor activity." That bad news reflects what too often happens in human patients treated with AV-based gene therapy, when ubiquitous pre-existing antiviral antibodies vitiate the vector's efficacy, and may induce toxicity.
As part of a Phase I clinical trial protocol that Calydon has reviewed with FDA, the company's rapid immunoassay will be used to screen prostate cancer patients being considered for intravenous treatment with an experimental, adenovirus-based therapeutic drug. Patients are currently being recruited at three academic medical centers.
"This immunoapheresis technology," Calydon's Henderson concluded, "will create a window of therapeutic opportunity by transiently removing high levels of pre-existent antibody, thus allowing safe and predictable human clinical trials of intravenously administered adenovirus for human gene and anti-cancer therapies."
Virulence Factor Of Layabout Tropical Disease Bug - Leishmania - Unmasked In Knockout Mice
Leishmania is not a mania. It's an infectious microbe - specifically, a protozoan parasite. It infects more than 10 million people in the tropics, and often is fatal. Just as mosquito bites inflict malaria, biting sand flies inject Leishmania major into their victims. Then, like the TB pathogen, Mycobacterium tuberculosis, L. major holes up in macrophages of the immune system. (See BioWorld Today, March 22, 1999, p. 1.)
The only drug therapies for leishmaniasis are based on heavy metals, such as arsenic and antimony, which, besides being expensive, can themselves kill the patient. And vaccine there is none - so parasitologists are turning to genetic approaches.
"Anything we can find out about how the Leishmania parasite survives may be useful in combating it," observed molecular microbiologist Stephen Beverley, at Washington University School of Medicine in St. Louis. He is senior author of a paper in the Proceedings of the National Academy of Sciences (PNAS), dated August 1, 2000. Its title: "Lipophosphoglycan [LPG] is a virulence factor distinct from related glycoconjugates in the protozoan parasite Leishmania major."
The co-authors asked the question: What role does LPG play in survival of the parasite in its human host, the macrophage? These white blood cells normally ingest and terminate invading microorganisms and other foreign invaders. Because LPG coats much of L. major's surface, Beverley speculated that macrophages possibly shield the pathogen from toxins it produces, or turn off host genes that might destroy it.
Using homegrown gene-modifying techniques, the co-authors inoculated mice with a mutant L. major that did not produce LPG. Macrophages eliminated 75 percent of this faux parasite in two days, and the mice didn't develop L. major's typical skin lesions until 60 days later.
"This study proves for the first time," Beverley concluded, "that LPG is required for virulence." He now hopes to find genes to serve as targets for drug or vaccine development.
Monoclonal Antibody To Transforming Growth Factor-Beta Cures Kidney Disease In Diabetic Mice
Kidney disease is a hallmark and handmaid of diabetes mellitus - both types I and II. Diabetic nephropathy is a leading cause of end-stage renal disease in the industrialized world. Almost 40 percent of all new applicants for a kidney transplant in the U.S. have diabetic kidney disease. Caring for these patients costs some $7 billion annually.
Recent research indicts renal transforming growth factor-beta (TGF-b) as complicit in this pathology. The db/db diabetic mouse models that condition exquisitely. Scientists at Jefferson Medical College and the University of Pennsylvania, both in Philadelphia, treated these animals, and their non-diabetic control littermates, with a neutralizing monoclonal antibody to TGF-b thrice weekly for eight weeks. As they report in the Proceedings of the National Academy of Sciences (PNAS) Early Edition, released July 4, 2000, "These findings strongly suggest that overt nephropathy was prevented."
Their article bears the title: "Long-term prevention of renal insufficiency, excess matrix gene expression, and glomerular mesangial matrix expansion by treatment with monoclonal antitransforming growth factor-b antibody in db/db diabetic mice."