Tuesday, March 14, 2006

The Knowledge -- Part 2

Continued from page 2

By Mark Williams

There is some evidence that the Russians discovered the effects of inserting the IL-4 gene into a poxvirus. Those effects are deadly. In 2001, Ian Ramshaw and a team of virologists from the Australian National University in Canberra spliced IL-4 into ectromelia, a mousepox virus, and learned that the resulting recombinant mousepox triggered massive overproduction of the IL-4 peptide. Even the immune systems of mice vaccinated against mousepox could not control the growth of the virus: a 60 percent mortality rate resulted. Other experiments have confirmed the lethality of the recombinant pathogen. The American poxvirus expert Mark Buller, of Saint Louis University in Missouri, engineered various versions of the recombinant, one of which maintained the mousepox virus's full virulence while generating excessive interleukin-4. All the mice infected with this recombinant died. The BBC reported that when asked about the Australian experiment, Sandakhchiev, Vector's director, remarked, "Of course, this is not a surprise."

Because vaccinia is universally available, it is fortunate that a vaccinia-IL-4 hybrid would not be an effective biological weapon: vaccinia has limited transmissibility between humans. Still, there are other viruses that are transmissible. Smallpox, the most infamous, is nearly impossible for aspiring bioterrorists to acquire. But a herpesvirus named varicella-zoster, or common chickenpox, is easily acquired and even more infectious than smallpox.*

What would happen if bioterrorists spliced IL-4 into chickenpox and released the hybrid into the general population? Perhaps nothing. Very often, the Soviet bioweaponeers successfully spliced new genes into pathogens, only to find that infected test animals showed no symptoms. One reason was that the genetically engineered microbes were often "environmentally unstable" -- that is, they did not retain the added genes. Engineering recombinant pathogens can be ineffective for other reasons, too: the foreign gene might be expressed in the "wrong" organ. But according to several virologists with knowledge of biological weapons, the result of splicing IL-4 into chickenpox might be to suppress the immune response to the disease. According to these virologists, the effect would be similar to what happens to cancer patients when they catch chickenpox. They often die -- even when treated with antiviral therapies. For healthy children or adults, chickenpox is usually a superficial disease that mainly affects the skin; but depending on the immunosuppressive state of an infected cancer patient, chickenpox lesions can be slow to heal, and the viscera -- that is, the lungs, the liver, and the central nervous system -- become progressively diseased.

Bioterrorists could create a varicella-IL-4 recombinant virus more easily than they could acquire or manufacture the pathogens that top the select-agents list. IL-4 is one of the standard genes used in medical research; a plasmid of human IL-4 could be ordered from one of the DNA synthesis jobbing companies and delivered via FedEx for $350. If our hypothetical bioterrorists were worried about detection, they might avoid the DNA synthesis companies altogether. Conveniently, without its junk DNA, IL-4 is only about 462 base pairs long. It's possible to download IL-4's genetic sequence from the Internet, use a basic synthesizer to construct it in five segments, and then assemble those segments "manually," as Popov's scientists did. The other principal tools needed would be a centrifuge -- like the $5,000 DNA synthesizer, cheaply available via Internet sites -- and a transfection kit, a small bottle filled with reagent that costs less than $200 and which would be necessary to introduce the IL-4 gene into chickenpox. Finally, the terrorists would also require an incubator and the media in which to grow the resulting cells. The total costs, including the DNA synthesizer: probably less than $10,000.

*Correction: an earlier version of this story misidentified varicella-zoster, a herpesvirus, as an orthopoxvirus.

Conscious of the controversial nature of this article, Technology Review asked Allison Macfarlane, a research associate in the Science, Technology, and Global Security Working Group in MIT's Program in Science, Technology, and Society, to rebut its argument: see "Assessing the Threat." We were also careful to elide any recipes for developing a biological weapon. Such details as do appear have been published before, mainly in scientific journals.

Mark Williams is a contributing writer to Technology Review.