Editor's note: Science Scan is a roundup of recently published biotechnology-relevant research.
Human fertility is a numbers game. To wit: Worldwide, 20 percent of couples are infertile. Of this proportion, the unmacho fact is that 30 percent to 50 percent of that infertility is due to the inability of the male partner to fulfill the sperm-cell side of the bargain. In 70 percent to 90 percent of those cases, that spermatic insufficiency can be diagnosed as azoospermia (absence of living spermatozoa in the semen) or oligospermia (not enough sperm in the penile ejaculate). That disruption of spermatogenesis is considered primarily of genetic origin.
At the Salk Institute in La Jolla, Calif., molecular geneticists wondered whether gene therapy could correct those inherited male deficits. The in vivo experiments they mounted are reported in the Proceedings of the National Academy of Sciences (PNAS), dated May 28, 2002, under the title: "Restoration of spermatogenesis by lentiviral gene transfer: Offspring from infertile mice."
The co-authors began their gene therapy experiments by recruiting a strain of mutant mice that lack c-kit gene expression on the surface of somatic Sertoli cells, testicular cells that provide a microenvironment that supports spermiogenesis. Next, the team tested the relative efficacy of four leading viral vectors - adenovirus, adeno-associated virus, retrovirus and lentivirus - in introducing genes into the Sertoli cells of mice. Only the last, a vector derived from lentivirus - which is related to HIV - passed muster. They effectively added genes specifically into Sertoli cells without causing toxicity or undesired transmission of viral DNA to offspring. That successfully restored sperm production in the mutant mice.
Initially, the treated animals could not produce enough viable sperm to inseminate a female via copulation or standard in vitro fertilization. Instead, the co-authors resorted to intracytoplasmic sperm injection, a common technique used in infertility clinics. It consists of injecting a single sperm directly into an ovum. Subsequently, after a few days, copulation became possible, and the recipient mice produced a total of 390 pups over a period of three months.
"Gene therapy approaches," the PNAS paper concluded, "along with germ cell transplantation and assisted fertilization techniques, offer a potential novel treatment for male infertility."
When Bacterium Meets Fungus, Infective Virulence Factors Act Up - But Not Always
Bacterial-fungal interactions have great environmental, medical and economic importance, yet few have been characterized at the molecular level. Take Pseudomonas aeruginosa and Candida albicans, two virulent, opportunistic pathogens that grievously infect people. When P. aeruginosa meets up with C. albicans, it kills the fungus by throwing a dense biofilm over Candida's filaments. Several of the bacterial virulence genes, of importance to human diseases, are involved in terminating those fungal filaments with extreme prejudice. Paradoxically, the same P. aeruginosa spares yeast-form C. albicans, which it neither binds nor kills.
A microbiologist and a molecular geneticist at Harvard Medical School in Boston propose that "many virulence factors studied in the context of human infection may also have a role in bacterial-fungal interactions. Their paper in Science dated June 21, 2002, bears the title: "Pseudomonas-Candida Interactions: An ecological role for virulence factors."
The co-authors point out, "Interactions between prokaryotes and eukaryotes are ubiquitous. Although the pathogenic and symbiotic relationships bacteria have with plants and animals have garnered the most attention, the prokaryote-eukaryote encounters that occur among microbes are likely far more common. Many of the virulence factors that we study in the context of human disease," they add, "may also have an ecological role within microbial communities."
In immune-compromised human hosts, they point out, P. aeruginosa "uses an arsenal of virulence factors to cause serious infections associated with burns, catheters and implants. C. albicans is also a benign member of the skin and mucosal flora" - until infectivity kicks in. Their PNAS paper recounts the assays and analyses conducted on the virulence factors of both organisms. It concludes: "We speculate that antagonisms between bacteria and microscopic fungi have contributed to the evolution and maintenance of many pathogenesis-related genes. "
Count All The Gotchas: Pluses And Minuses Of Anthrax As A Bioweapon
"Antibiotics are typically so successful at combating bacteria that we do not easily comprehend how a person can walk into a hospital with flu-like symptoms, and yet die of a bacterial infection after days of aggressive drug treatment even though the bacterium is not resistant to antibiotics. Yet, this is what happened during last year's bioterrorism incident in the U.S. when five people died after inhaling spores of Bacillus anthracis, the bacterium that causes anthrax."
This brief but counterintuitive passage leads a "Perspective" in Science, released online July 2, 2002. Its title: "A binding contract for anthrax." Its authors are cellular and molecular biologists at the University of Texas at Austin. Their article covers a sampling of the numerous Catch-22s up the sleeve of potentially weaponized B. anthracis:
Symptoms appear only after the bacillus has already multiplied inside its host, and begun to produce large amounts of the tripartite toxin - protective antigen (PA), lethal factor (LF), edema factor (EF) - that eventually will kill its human patient.
One possible countermeasure: Passively immunize infected patients with an antitoxin antibody, while also aggressively treating them with antibiotics.
An antitoxin vaccine must have several properties. It should not be cleared too quickly from the blood; it must bind with high affinity to its target toxin.
If an antibiotic-resistant form of B. anthracis were deployed as a bioweapon, an antitoxin antibody might not be protective, as bacteria would continue to proliferate unchecked, and release large amounts of toxin that would eventually overwhelm its host.
One big advantage of an antitoxin vaccine is that it would be administered to people showing symptoms of anthrax poisoning, so the general population could be spared receiving the antibody.
The biggest hurdles to bringing a new anthrax therapeutic to market are likely to be financial and legal. First, there is no assurance of a market as the very existence of an effective therapeutic might help dissuade a future attack, and contribute to a lack of demand.