The Coming Plague

by Laurie Garrett

  Reflecting thirty years later on the revolution that had transpired since, Watson said, “None of this could have been predicted. Now it’s hard to imagine things going any faster. But it will be faster. Mysteries will tumble. All is now open to experimental attack, and problems we can’t even foresee today will be identified and solved within less than a decade.”

  His prophesy would prove remarkably accurate, as massive global computer interconnections and fax machines would become the preferred method of sharing the excitement of biological discovery, the pace becoming so furious that by the mid-1980s most researchers would consider journal publication of their findings a matter of historic obligation, rather than a primary method for informing their colleagues. By the time results were published, most molecular biologists would already be two or three experiments further along in their laboratories.

  Since the early 1970s, biologists had been working on ways to chop up DNA and RNA in order to figure out what various pieces of the genetic code actually controlled. It had been determined that nearly all living systems had repair mechanisms to fix damaged DNA. In addition, they knew that something in the DNA regulated when the genes for, say, growing fingers were turned on and when they were switched off. There was also a sense that the malfunctioning of such genetic signals lay at the core of the causation of cancer, because tumor cells seemed to behave as if all their internal policing mechanisms were out of control.

  Scientists soon realized that the world of DNA was replete with specialized proteins that busily moved up and down the vital molecule’s lengthy sequence performing a myriad of tasks, ranging from snipping out a single defective nucleotide to making a copy of an entire DNA molecule, or chromosome. These proteins, which were themselves made according to instructions inside the DNA, were the key to regulation of the massive genetic code. Like switching signals in a vast computer data base that ensured desired bits of information were displayed on the VDT screen when—and only when—the human user wanted to see them, these proteins, particularly a group known as restriction enzymes, made sure that genes were expressed only when necessary, cut out if troublesome, inserted if needed, and remained silent information stored in the DNA data banks at all other times.

  The world’s top molecular biologists concluded that the best way to decipher DNA was to manipulate these regulatory proteins and see what effect removal of this or that piece of DNA might have on the virus, bacteria, or cell it controlled. Scientists like Stanley Cohen and Paul Berg at Stanford University made batches of these proteins, mixed them with DNA, and watched the results. Berg and Cohen soon figured out how to excise minute, discrete pieces of DNA with the precision of molecular surgeons. They also learned how to insert genes into DNA sequences by opening up the DNA, attaching the desired segments, and then allowing the DNA to recombine, the new gene now having been incorporated.2

  In late 1973, Berg hit on an idea: put genes into harmless viruses, let the viruses infect cells, thereby carrying the genes inside. The genes might then be recombined into the cellular DNA. This was especially easy to achieve by using bacteriophages—viruses that infect bacteria—to carry experimental genes into well-understood, simple organisms, such as the Escherichia coli bacterium. Berg envisioned treating genetic deficiency diseases one day through just such a mechanism.

  Berg’s idea not only worked but caused an international upheaval in biology. Within a year every molecular biologist who could get her or his hands on the proper chemicals and viruses was using the genetic engineering technique to study life in a test tube. But Berg worried that his own experiments, using monkey virus SV40 to carry genes inside E. coli bacteria, could be dangerous, and in 1974 convened a meeting of the world’s preeminent biologists to establish safety rules for their enterprise.

  While some critics would attack genetic engineering research as ungodly or risky, the field was as unstoppable as a speeding locomotive. What was considered experimental in 1976 was routine by 1979. The SV40 experiments Berg and Cohen fretted over in 1974 were graduate student training exercises by 1980. And the term “genetic engineering” was transformed from an almost whimsical description of a handful of experiments performed in a few select laboratories during the mid-1970s to a label applied to a global multibillion-dollar industry in the 1980s.

  For the disease detectives the revolution was a mixed blessing: on one hand it offered new tools for solving microbial mysteries, but it was also immediately obvious that funding—never generously available to parasitologists or infectious disease researchers—was becoming even scarcer as resources shifted toward molecular pursuits.

  Bright, young scientists followed the excitement—and the money. And why not? Clearly, in 1976 the opportunity to work, for example, as one of twenty-four postdoctoral fellows in the MIT laboratory of Nobel laureate Har Gobind Khorana manufacturing the first fully functional man-made gene was a great deal more seductive pursuit than joining a team that used old-fashioned light microscopes to count the number of malarial sporozoites in a mosquito.

  Yet what the microbe hunters learned when they applied their newly honed genetic manipulation skills to the task only heightened their sense of concern. They soon discovered that microbes could share genes with one another that made them more formidable human enemies; many viruses not previously thought to do so could cause cancer; some microbes possessed the ability to chemically manipulate the human immune system to their advantage; and there were viruses that could hide for years on end inside human DNA.

  It was Barbara McClintock who first suggested that genetic signals could move about, be mobile, producing changes in the fated appearance of an organism. During the 1940s and 1950s, well before Watson and Crick discovered the link between genes and the structure of DNA, McClintock studied maize plants at the Cold Spring Harbor Laboratory on Long Island, New York. She showed that genes could move from one position to another on maize chromosomes, causing radical changes in the appearance of corn kernels. The cause of these differences would not be inherited genes per se, but the movement or transpositioning of those genes. The movable genes were dubbed transposons.3 Only years later would the full impact of her pioneering efforts finally be evident, and McClintock would be awarded the 1990 Nobel Prize in Medicine.

  A decade after McClintock discovered transposons in maize, Joshua Lederberg showed that bacteria had movable bits of DNA that conferred the ability to resist antibiotics. And by the 1970s, when Berg and Cohen invented the techniques of genetic manipulation, scientists all over the world realized that certain bacterial genetic traits commonly jumped about from place to place within a cell’s chromosome, or between bacteria. These were not rare events. In fact, it seemed that at the bacterial level, genetics, far from being the rigid blueprint envisioned less than a decade earlier, was more akin to a game of Scrabble in which each organism came into existence with a finite set of letter tiles, or genes, but jumbled those tiles around according to a set of rules creating a vast variety of different words.4

  These Scrabble tiles of movable genes could be in the form of discrete packages of DNA that moved about along the bacterial genome—Mc-Clintock’s transposons. They could be singular genes that appeared to leap about almost at random, designated “jumping genes.” Or they could be highly stable rings of DNA, called plasmids, that sat silently in the bacterial cytoplasm waiting to be stimulated into biochemical action.

  It became alarmingly obvious that microbes used this constant game of genetic Scrabble to their advantage in a variety of ways. Bacteria could occasionally undergo a process called sexual conjugation, stretching out portions of their membranes to meet one another and passing plasmids, transposons, or jumping genes—including genes that conferred resistance to antibiotics.

  Naturally, if humans could manipulate the Scrabble game to their advantage in the laboratory, so could the microbes in the real world. It wasn’t a long intellect
ual leap from jumping bacterial genes, for example, to viewing viruses as well-packaged transposons capable of corralling the genetic resources of the bacterial, or even human, cells they invaded.

  The quintessential example of Lederberg’s notion of genetic entanglement was discovered by Howard Temin at the University of Wisconsin in Madison and David Baltimore at Massachusetts Institute of Technology: retroviruses. These tiny RNA viruses were unique in that they gained entry into cells and made reverse mirror-image copies of their RNA (running backward compared with the normal course of events) to produce a DNA version of their genes. And then they exploited vulnerable locations along the host’s DNA to insert themselves, like a transposon, into the cell’s genetic material. The retroviruses accomplished this feat through the use of a unique enzyme called reverse transcriptase, which performed the mirror-image flip of viral RNA genes into DNA.

  Shortly after the discovery of retroviruses, National Cancer Institute scientists Robert Huebner and George Todaro proposed a theory to explain the ability of these viruses to cause cancer. They suggested that there were places along animal chromosomes where transposons rarely went, and into which a viral insertion could spell cellular disaster. According to their hypothesis, if a retrovirus inserted itself near certain host genes, those cellular segments of DNA would be switched on, and they, in turn, would cause wild cell growth and misbehavior—the hallmarks of cancer. Driving their theoretical point home, Huebner and Todaro named these cellular DNA sites of special viral vulnerability “oncogenes.”

  Baltimore believed in oncogenes. He also believed that retroviruses were capable of inserting themselves permanently in animal germ line DNA, right alongside these oncogenes, and being passed on in that form via sperm or eggs to the next animal generation. In this way, he reasoned, virally induced cancers could be inherited. Baltimore cautiously predicted that human retroviruses would be found that, as theorized by Huebner and Todaro, triggered cellular oncogenes.

  Having shared the 1975 Nobel Prize with Howard Temin and another leading microbiologist, Renato Dulbecco, Baltimore turned his attention broadly to the role of retroviruses and the more traditional RNA viruses in cancer.

  “What is cancer?” he asked in 1978.5 “This question is at the heart of present efforts to control this disease, and the most manipulable model systems for studying it have been virus-induced cancers. That viruses cause cancer in animals is a certainty; that they do so in humans is less certain but probable.”

  Temin and Baltimore, working independently, had already shown that two retroviruses caused cancer in animals: Rous sarcoma (in chickens) and Rauscher mouse leukemia viruses. Other animal retroviruses, by virtue of their ability to get inside and disrupt cellular DNA, were shown to be associated with cancer: avian leukosis virus (leukemia in chickens), Moloney leukemia virus (in mice), Kirsten sarcoma virus (in mice), Gibbon ape leukemia virus, cow and feline leukemia viruses, visna virus (in sheep), mammary tumor virus (in mice), and a host of so-called foamy viruses (found in monkeys, cats, and cattle).

  Faced with these discoveries, Joshua Lederberg said that the only reasonable way to look at viruses was to recognize that “the very essence of the virus is its fundamental entanglement with the genetic and metabolic machinery of the host.”6

  During the early 1980s, the genetic engineers discovered that those genetic entanglements could be deliberately manipulated in hundreds of different ways, allowing scientists to learn what tasks a given gene sequence normally performed by moving, switching off, turning on, or mutating that sequence. This could be done by inserting artificially constructed plasmids into cells, or by attaching genes to bacteriophages—minuscule viruses that infect bacteria.7

  In California, Michael Bishop and Harold Varmus were in pursuit of oncogenes. In their laboratories at the University of California, San Francisco, long-haired, bearded Michael Bishop and his taller, leaner bespectacled counterpart Harold Varmus formed a Mutt-and-Jeff team that zeroed in on the Rous sarcoma virus. It was such a potent cancer-causing agent that all chicken muscle cells in petri dishes could be transformed to cancer cells within twenty-four hours of infection. Researchers at Rockefeller University had previously discovered that the virus contained a gene they called src (for “sarcoma”) that seemed to cause the tumor transformation of infected cells.

  Between 1976 and 1983, Bishop and Varmus discovered that src was, indeed, a potent cancer-causing virus product that was a near-duplicate of a gene normally present in chickens. To differentiate between the two, Bishop and Varmus designated the viral oncogene v-src and the normal cellular oncogene c-src.8 The pair of energetic young researchers then asked just how widespread was the c-src oncogene in the animal world. To the surprise of many, they quickly discovered c-src in the DNA of other birds, animals, insects, and humans.9

  Why would humans and chickens share a common gene—one that caused cancer, no less? Varmus and Bishop quickly discovered that c-src was the genetic blueprint for the manufacture of a protein that ended up nestling on the inner lining of the cell membrane. There, it acted as a kinase, chemically altering passing proteins by adding phosphate ions to specific amino acids. This radically changed the biochemical reactivity of the proteins, and the impact was so profound that nearly every aspect of cell structure and activity was adversely affected. The discovery “sent the thrill of recognition down the spines of biochemists,” Bishop said,10 because they had long recognized that nearly every essential activity inside a human or animal cell was affected by phosphorylation.

  Other researchers quickly discovered that the same pattern held true for a variety of cancer-causing retroviruses: the viruses carried genes that mimicked oncogenes that were commonly found in the DNA of all animals, humans, even insects. And those oncogenes controlled very powerful enzymes that could alter hundreds of different essential proteins inside cells, causing the cells to transform into cancer.

  “The genes of retroviruses assume principles that are very similar to what we call jumping genes,” Varmus explained. “And they, too, have evolved mechanisms for getting around, for picking up new genes, for making mutations. And carrying out evolutionary changes.”

  The retroviral genes “jumped” better along the cellular genome than did the “garden-variety oncogenes” inside the cell, Varmus asserted. And they had the ability to insert themselves into host DNA, reproduce right along with the host cell, and, as Varmus put it, “carry out God-knows-what.”

  Scientists hypothesized that normally oncogenes were switched on only at given times in an animal’s development. For example, as a fetus grew, such wild cellular activity might be key to its development from a fertilized egg to a baby.11

  Bishop hypothesized that these oncogenes acted “as a keyboard on which many different carcinogens can play, whether they be chemicals, x-rays, the ravages of aging, even viruses themselves. With the revelation that there were a limited number of genes in cells that were affected, it became natural to see them as a keyboard on which many different causes of cancer play. It’s not an endless keyboard—it’s a keyboard of perhaps less keys than a standard piano keyboard. And out of this comes the manifestation of cancer—the melody, if you wish. An enemy has been found—it is part of us—and we have begun to understand its lines of attack.”

  The discovery of oncogenes would cause a shift in thinking among cancer experts worldwide, prompting many to wonder for the first time just how many human tumors were started by microbes.

  And, sure enough, in 1979 researchers at the U.S. National Cancer Institute, the Tokyo Cancer Institute, and Kyoto University discovered a retrovirus that caused cancer in human beings. Dr. Robert Gallo and his NCI colleagues found evidence of a virus inside the T cells (disease-fighting white blood cells) of a twenty-eight-year-old African-American man who had come to Bethesda, Maryland, in 1979 from his Alabama home for expe
rimental cancer treatment. The NCI group quickly found two other individuals who suffered T-cell lymphomas and seemed to be infected with a virus: an immigrant woman from the Caribbean and a Caucasian man who had traveled extensively in the Caribbean and Asia.

  Two years earlier Kiyoshi Takatsuki, an epidemiologist with the Tokyo Cancer Institute, had discovered groups of people living on outer Japanese islands who apparently had cancer involving their immune systems’ T cells.12 The Japanese researchers dubbed the disease adult T-cell leukemia or ATL. Gallo’s laboratory isolated their virus and named it HTLV, or human T-cell leukemia virus.13 The Gallo group also identified the existence of an oncogene in the HTLV virus that gave the microbe the ability to produce leukemia.14 Attempts at collaboration between the Japanese and American researchers went awry and Yorio Hinuma and Mitsuaki Yoshida of Kyoto University announced discovery of a different virus in the Japanese leukemia patients, named ATLV, or adult T-cell leukemia virus.15

  Ultimately, Mitsuaki Yoshida led a Tokyo Cancer Institute study in 1980 that compared ATLV and HTLV and found them identical. They furthermore showed that Japanese monkeys (Macaca fuscata), Indonesian rhesus monkeys, and African green monkeys captured in Kenya and held in captivity in Germany had antibodies to ATLV/HTLV, and that the virus—or a monkey version of the human virus—could be transmitted from one cocaged animal to another.16 The finding posed several questions, the researchers wrote, including “Are monkeys the natural reservoir of ATLV? Is ATLV transmissible from monkeys to humans through a certain vector? What is the mode of infectious transmission of ATLV in monkeys?”17 The finding, and questions it posed, would be echoed with other diseases in coming years.