January
29, 2006
Why Revive a Deadly Flu Virus?
By Jamie Shreeve
One
morning last August, Terrence Tumpey, a research scientist at the Centers for
Disease Control and Prevention in Atlanta, walked into a room across a corridor
from his office and took off all his clothes. He pulled on cotton scrubs and a
disposable gown, two pairs of latex gloves and headgear with a clear plastic
shield enclosing his face and a tube running out the back to a set of filters
strapped to his waist. He walked through another door and down a hallway to a
large upright freezer. Mounted beside the freezer was a retinal scanner.
Tumpey, who is 6 feet tall, bent down a little to position his eyes in line
with the lens. In a digital voice, the scanner asked him to step forward. Tumpey
complied. "Identification confirmed," the scanner said, and a lock on
the freezer clicked open.
Inside
the freezer were trays and boxes containing "select agents" - highly
pathogenic microbes that under the Patriot Act cannot be handled without
special clearance from the Department of Justice. Tumpey wiped the frost off a
box. He was the only person in the C.D.C., or anywhere else, authorized to
handle this particular agent: a synthesized version of an influenza virus that, nearly a century before, killed
between 20 million and 50 million people. He placed the box in a secure
container, and after showering and dressing, carried the container through
secure corridors to another building at the C.D.C., where he entered another
suite of rooms, dressing once again according to Biosafety Level 3+ protocols,
the second most stringent level of biosecurity. For the next couple of hours,
he squirted the virus into the nostrils of laboratory mice. He was fairly
certain they would all soon die.
Getting
the flu can be a real drag. Your head pounds, your muscles ache, you lie in a
bed of misery, surrounded by clammy tufts of used Kleenex you're too tired to
pick up. Every year, 5 to 20 percent of the American population catches a flu
virus. The elderly, very young children and people with certain health
conditions are at risk for more serious complications, and annually some 36,000
of them die. Every few decades, a particularly virulent strain appears and
causes a global pandemic. In the 20th century, flu pandemics
occurred in 1918, 1957 and 1968. The last two killed two million and 700,000
people respectively - again, claiming most of their victims among the young,
the old and the weak.
The
1918 flu virus is remarkable for two reasons. First, it caused perhaps the most
lethal plague in the history of humankind. In the fall of that year it spread
across the planet, perversely striking down healthy young adults. Once
ensconced in their lungs, the virus triggered a havoc of inflammation,
hemorrhage and cell death. Trying to draw air into such lungs was like
breathing through meat. Many of the afflicted died within hours after they first
began to feel a little feverish. Others succumbed more slowly to secondary
bacterial infections. By the spring of the following year, the virus had
disappeared as mysteriously as it had come.
The
second, and in some ways even more remarkable, thing about the 1918 flu virus
is that it has literally been brought back to life. In October, a team of
scientists, Tumpey among them, announced that they had recreated the extinct
organism from its genetic code - essentially the scenario played out in the
movie "Jurassic Park," albeit on a microbial scale. In the movie, the
scientists' self-serving revivification of dinosaurs leads to mayhem and death.
Tumpey and his colleagues say they hope that their resurrected microbe will
help prevent a calamity, not cause one. They want to know what made the 1918
flu, which began as a virus native to wild birds, mutate into a form that could
pass easily from one human to another. That question has been weighing on the
minds of flu experts since 1997 - since the first fatal case in Hong Kong of
the avian flu that has since killed more than 70
people in Asia. So far, all of its victims probably caught the disease from
handling infected poultry and not from other people. How close is it to
crossing the same lethal line that the 1918 virus did? What can be learned from
the virus that caused the great pandemic that might help us avert another one?
The
risks involved in trying to answer such questions are hard to calculate,
because the experiment has no precedent. In essence, Tumpey and his colleagues
have brought one serial killer back from the grave so that it can testify
against another. How dangerous is the 1918 virus to today's population? Its
genetic code is now in public databases, where other researchers can download
it to conduct experiments. Scientists from the University of Wisconsin and the
National Microbiology Laboratory in Canada have already collaborated to
reconstruct the virus from the publicly available sequence. How easy would it
be for a bioterrorist to exploit the same information for malevolent ends?
"Give
me $100,000 and two months, and I can recreate it right here in my lab," says
Earl Brown, a flu researcher who specializes in the evolution of virulence at
the University of Ottawa. "You wouldn't be able to tell it from the real
thing that was around a hundred years ago. Would it kill at the same rate as in
1918? Probably. But you really don't want to have to find that out. You don't
want to give this thing a second time around."
Terrence
Tumpey is not moved by such talk. Even if the virus was to get out into the
population, he says he believes it would cause far less sickness than it did in
1918. And he is sure that it is not getting out, ever, at least from his lab at
the C.D.C. But whatever the danger posed by the virus in his freezer, it is
literal living proof that science has crossed into an uncertain new world,
where the drive to know life on its most fundamental level has given birth to
the means to create it.
The
resurrection of the 1918 influenza virus was a team effort engaging the
resources of the C.D.C. in Atlanta, an obscure military pathology lab outside
Washington, D.C., an esteemed group of influenza experts at Mount Sinai School
of Medicine in New York and one elderly Swede. Though the story has been told
before, it is impossible not to begin with the Swede. In 1950, Johan Hultin,
then a 25-year-old graduate student at the University of Iowa, was searching
for a Ph.D. topic when he heard a visiting virologist say that the only way to
solve the mystery of the 1918 pandemic would be to recover the virus from a
victim who had been buried in permafrost. Hultin suddenly had a topic.
After
some planning, he found what seemed like an ideal site in the remote settlement
of Brevig Mission on Seward Peninsula in Alaska. In a mere five days in
November 1918, 72 of the 80 residents of Brevig died and were later buried in a
mass grave. Hultin arrived there alone, obtained permission to dig up the grave
and after two days of hacking through frozen ground came across the preserved
body of a little girl in a blue dress, red ribbons in her hair. He and some
colleagues eventually found four more bodies and cut out samples of their
pocked and peppered lungs, keeping them frozen with dry ice exuded from fire
extinguishers.
Back
in Iowa, Hultin injected a solution of the lung tissue into fertilized chicken
eggs - a standard method for growing flu virus - and inoculated mice, rats and
finally ferrets, which have a peculiar susceptibility to human flus. Nothing
worked. If the virus was there at all, it was dead. So was Hultin's Ph.D.
thesis. He gave up, went to medical school and enjoyed a successful career as a
pathologist in San Francisco. In his spare time he traveled all over the world,
invented auto-safety equipment, restored archaeological sites, built a replica
of a 14th-century Norwegian cabin in the Sierras (it took him 36 years) and did
research on Mount Everest. But he never forgot about the one time in his life
that he failed.
Jeffery
Taubenberger, the man most responsible for resurrecting the 1918 flu virus, was
looking a little sick. His face was pale and his eyes red-rimmed, and he had
barely touched the pasta he ordered for lunch. He pulled out a handkerchief and
sneezed hard.
"There's
not a respiratory virus on earth that I don't seem to want to amplify," he
told me. "If I were alive in 1918, I'd be dead."
Taubenberger
is the chairman of the department of molecular pathology of the Armed Forces
Institute of Pathology in Rockville, Md. His department was, in the early 90's,
in the process of developing an expertise in retrieving tiny whispers of
genetic code from putrefied flesh. As Gina Kolata described in her book
"Flu," Taubenberger decided in 1995 to look for the 1918 virus in
samples of preserved lung in the A.F.I.P.'s tissue repository, which contains
about three million pathological samples dating back to the Civil War. His techniques
were far more advanced than anything Hultin had at his disposal, and his goal
was more modest. Taubenberger knew that flu particles are too unstable to
remain intact in a frozen corpse, and he wanted only to find a remnant of the
virus's genetic code, perhaps enough to reveal what made it so virulent. But
for a year and a half, he, too, failed. Finally, when Taubenberger was on the
verge of giving up, he recovered from a soldier's lung a tiny fragment of the
killer flu's identity, like the upturned edge of a sneering mouth.
"From
that moment on, I became the steward of this virus," Taubenberger said.
"Whether I liked it or not, I was obligated to get the whole thing."
Taubenberger
is a compact, attractive man in his mid-40's, with big, dark eyes and a quiet,
precise manner of speech. He looks a bit like Frodo the hobbit in the movie
version of "The Lord of the Rings," if you can imagine a middle-aged
Frodo wearing a paisley tie and an oxford shirt, a cellphone strapped to his
belt. Like Tolkein's hero, Taubenberger seems both obsessed with his quest and
a little tired of shouldering its weight. The trace of the virus in the
soldier's lung was unimaginably faint. But by using what is called the
polymerase chain reaction (P.C.R.), a common method of amplifying a signal of DNA in a sample, he and his colleague Ann Reid
were able to fish out a strand large enough to sequence; then they used that
sequence as a hook to fish out another strand, then another, gradually
overlapping pieces that matched on their ends to build increasingly longer and
more coherent pieces.
"We
had to tweak the P.C.R. method to its ultimate level of detection,"
Taubenberger said. "It wasn't simple. It was painful. Everything we did
here was painful."
Almost
immediately he and Reid ran into another problem: they were running out of raw
material. Then, out of the blue one day in 1997, he got a letter. It was from
Johan Hultin, then 72, who had read about Taubenberger's initial success in
Science magazine. He told Taubenberger about his expedition to the mass grave
in Brevig in 1951 and said he would be willing to go back and try to find the virus
again. Hultin said he would pay for the expedition himself. If he failed, no
one else need know that it had ever happened.
And
that is how Johan Hultin returned to Brevig - a tall, gray-bearded figure
arriving unannounced, carrying his wife's pruning shears to help him cut
through bone. After again obtaining permission, he reopened the grave, and on
the fourth day of digging found the body of an obese woman whose lungs were
well preserved, insulated from the occasional ground thaw by her fat. He returned
home with samples of her lungs and other organs and sent them to Taubenberger.
The entire expedition took five days.
"Ten
days later, he called me," Hultin said of the conversation with
Taubenberger. "I was in my Norwegian cabin in the mountains. 'We have the
virus,' he said. I'd been waiting 50 years to hear that."
A
flu particle is a sphere about a millionth of an inch in diameter, containing
just eight disconnected gene segments. Its surface is covered with a thicket of
spikes, like a burr. The spikes are made of a protein called hemagglutinin,
which sticks to receptors on the surface of cells in your respiratory tract,
much as the hooked spines on a burr catch fast on fibers in your trouser leg
when you're walking through high brush. In among the spikes are some other,
mushroomlike protrusions of another protein, neuraminidase. These two surface
proteins define the virus's identity - the face that your immune system sees
and attacks. Sixteen "flavors" of hemagglutinin are known, and nine
of neuraminidase. The different major families of flu are combinations of the
two, hence the designation "H5N1" for the current threat. The 1918
virus was H1N1, the mother of all flus.
Flu
viruses mutate very rapidly, and each season's version is a little different.
But your immune system preserves a memory of its previous encounters with a
flu, which are dragged up, like old photographs from the back of a closet,
every time your system responds to a new flu invasion. Very rarely, a virus
comes along bearing a surface protein that your immune system has never seen.
Often this occurs when a single host - it could be a pig, but might also be a
person - becomes infected with two strains of flu simultaneously, one from a
mammalian lineage, the other from an avian one. Inside the host, the eight gene
segments of the two strains are shuffled randomly into new configurations, like
the symbols in the window of a slot machine. If one of these configurations
happens to be both pathogenic and transmissible from human to human, jackpot: a
pandemic ensues. The 1957 and 1968 pandemics both probably occurred through
this kind of "reassortment." For a long time, most scientists
believed the same kind of gene-shuffling triggered the far more calamitous 1918
pandemic as well.
In
his hunt for the cause of the 1918 flu's virulence, Taubenberger focused first
on the hemagglutinin gene. Seasonal flus are normally confined to the
respiratory tract because before it can infect a cell, the hemagglutinin
protein needs to be split down the middle by an enzyme found there. But some
forms of avian flu - including H5N1, the one now threatening us - bear a
specific mutation in their hemagglutinin gene that allows other, more
ubiquitous enzymes to cleave apart the protein, freeing the virus to invade
cells deeper in the lungs or even in other organs. Taubenberger looked for the
same killer mutation in the 1918 virus's hemagglutinin gene, but it wasn't
there. After months of more work, he and Reid decoded the gene for
neuraminidase. It, too, gave no hint why this particular virus was so deadly.
Same
for the next gene, and the one after that. A year went by, then another.
Instead of revealing some peculiar feature that might tip off the secret of its
virulence, the genetic sequence of the virus slowly emerging seemed chillingly
ordinary. Among the chain of some 4,000 amino acids that made up its proteins,
only 25 or 30 distinguished it from a common, nonvirulent avian flu. Rather
than originating from a reassortment of genes from both an avian and mammalian
source, like the viruses that caused the later pandemics, the 1918 flu most
likely began as a bird-adapted strain that, with just a handful of mutations,
made itself at home in human beings. To flu researchers and public-health
officials, the resemblance of the 1918 sequence to those of common avian flus
underscores the stark fact that there is more than one way for a virulent
strain like H5N1 to make the jump and become transmissible person to person.
According to Taubenberger, this suggests a new strategy for surveillance, one
that would include identifying and isolating a local variant of the virus on
the verge of acquiring a complete complement of the essential mutations, after
which point it would become impossible to contain.
What
the genetic sequence of the 1918 virus did not reveal, however, was why the
virus killed so ruthlessly, or how it made that critical leap to become
transmissible. For those answers, they would have to take a more drastic step.
"Jeff spent 10 years of his life doing this, and it told us nothing about
pathogenicity," says Robert Webster, a noted flu researcher at St. Jude
Children's Research Hospital in Memphis. "That's when we realized the
sequence wasn't enough. It was necessary to put the damn thing together."
Necessary
or not, the fact that it had become possible was probably enough to ensure that
it would be done. In biology, the direction determined by what is possible has
been downward, toward the exploration of ever more reduced levels of
complexity. The progression started with the ancients, who first opened up the
human body to ponder its organs and their functions. Once microscopes were
developed in the 17th century, it became possible to observe the anatomy and
behavior of the tissues and cells making up the organs, and with later
advances, the proteins that build cells and determine their functions. In the
last century we reached the level of the genes that conjure the proteins into
being. Only in the last decade has automated sequencing made it possible to
peer beneath genes at the individual letters of DNA constituting a complex
organism's complete genome, including our own.
This
is the bottom of the biological hierarchy, the fundament, where all of life
rests upon the bedrock of inert information. Now that we have reached down this
far, it becomes possible to use that information to do a U-turn and start back
up, not just trying to understand life, but recreating and inventing it - first
simple viruses, but soon bacteria and other more complex organisms. The
resurrection of the 1918 flu incarnates this turning point. It is not the first
virus to be reconstituted from its genetic code. But it is so far the largest,
and the meanest, and the only one to be snatched back into existence from a
time when we knew so much less and were so much more at its mercy.
The
wonder is not that scientists could reconstitute the "damn thing"
from its genetic code. The wonder, and for some the fear, is that they could do
it with so little effort or expense. Biosupply companies use synthesizing machines
to build tiny pieces of DNA to order, using the sequence of letters in the
virus's code. When placed in solution, these chemical snippets naturally
assemble into longer pieces. With the help of a copying enzyme to fill in any
gaps, the DNA molecules stitch themselves together into a complete gene, which
can be inserted into a stable little circle of DNA called a plasmid - packaged
to go, so to speak. If you have plasmids containing all eight flu gene
segments, it is a fairly simple matter to inject them along with some flu
proteins into a cell and let nature take its course.
This
method of building flu-virus particles from pure code is a clever application
of the approach to understanding life called "reverse genetics" -
that is, looking at a gene to figure out its function, rather than the other
way around. But it is not one requiring some spectacular insight or
technological breakthrough. The method employs fairly routine molecular biology
and was developed independently by two different flu teams, one at Mount Sinai
School of Medicine in New York, the other at the University of Wisconsin. Peter
Palese, from the Mount Sinai team, contacted Jeffery Taubenberger and suggested
that if he would supply the blueprint for the virus, Mount Sinai would function
as the parts factory, putting together the genes. Another laboratory, one with
the biosecurity facilities required to work with highly infectious agents,
would be recruited as the final assembly plant. That role would fall to
Terrence Tumpey of the C.D.C.
The
team did not even have to wait for Taubenberger to finish the whole sequence of
the 1918 virus to begin testing its virulence. In 2001, Adolfo Garcia-Sastre
and Christopher Basler, also at Mount Sinai, reconstructed the genes for just
the two critical surface proteins and sent them on to Tumpey, at that time
working at the Southeast Poultry Research Laboratory in Athens, Ga. Taking
advantage of influenza's innate ability to mix and match genes from two
strains, he combined the two 1918 genes with others from an innocuous
laboratory strain to make a complete set. Tumpey infected some lab mice, which
are normally not affected much by human flus. Five days later, he came into the
laboratory at around 11 at night for a quick check on their progress. All the
mice were dead.
In
person, Tumpey is unnervingly imperturbable; ask him what it's like handling an
infectious agent that killed perhaps 50 million people, and he stares back at
you and gives a little shrug. But this first demonstration of the virus's power
got to him.
"I
literally felt a chill go down my spine," he told me. "I knew I had
this awesome virus, and I'd eventually be able to put the whole thing
together."
He
did not have much longer to wait. It took nearly 50 years to find a trace of
the virus in preserved tissue, and nearly 10 years for Taubenberger to sequence
its code, finishing the last of three genes driving the virus's replication
machinery early last year. From that point, it required just a few months for
the Mount Sinai group to transform the code into actual genes, and in Tumpey's
lab mere days for the genes to begin assembling themselves into viable virus
particles and come bursting out into the surrounding solution.
Tumpey
and his colleagues were well aware that bringing such a lethal pathogen back
into the world was going to cause controversy. But he was fairly certain that
he had laid the groundwork to defend the decision, obtaining approvals from the
highest levels at the C.D.C. and the National Institute of Allergy and
Infectious Diseases, which had financed the work. He had conducted experiments
showing that mice were protected from the virus by the current human flu
vaccine and by Tamiflu, the antiviral drug. In any case, because a virus
descended from the 1918 one has been circulating in the population since 1977,
Tumpey is confident that everyone carries at least partial immunity to the 1918
virus itself.
Not
everyone is as sanguine as Tumpey. "I believe that this was research that
should not have been performed," says Richard Ebright, a Howard Hughes
Medical Institute investigator at Rutgers University. "If this virus was
to be accidentally or intentionally released, it is virtually certain that
there would be greater lethality than from seasonal influenza, and quite possible
that the threat of pandemic that is in the news daily would become a
reality."
Neither
Terrence Tumpey nor Richard Ebright really knows how vulnerable the population
today would be to the resurrected virus. Nobody does. This uncertainty would
seem to limit the virus's value as a bioweapon. In theory, anyone with
nefarious intent and the requisite training in molecular biology could recreate
the virus from the sequence published on the Internet. But why would any
sensible bioterrorist go to such lengths to create a weapon that might do no
more harm than a seasonal flu bug, or, if it did prove undiminished in its
virulence, would kill his own people as indiscriminately as his enemies?
Then
again, common sense is not a prerequisite for membership in a terrorist organization.
Accidental release of the virus cannot be ruled out, either. While few question
the experience and expertise of the C.D.C. in containing dangerous microbes,
other labs will be working with the virus, and there is ample precedent for
accidents occurring under stringent biosecurity, including release of the SARS virus in the past few years from three
separate laboratories in Asia, which led to one death. In fact, the reason
those of us who were not around in 1918 still may have some immunity to that
pandemic strain is that a relatively innocuous descendant H1 type was
reintroduced into the environment in 1977, probably by accident in China or
Russia.
Given
the potential danger, Robert Webster, the esteemed flu researcher who supported
the reconstruction, is among those who say it would be better to conduct future
research on the 1918 virus under Biosafety Level 4 conditions - the maximum
degree of security, used for working with lethal microorganisms like the Ebola
virus and smallpox. But currently, only four
institutions in the U.S. have functioning BSL-4 facilities, including the
C.D.C. Imposing such restrictions would necessarily slow the progress of
research.
This
is something that Terrence Tumpey, among others, insists that we cannot afford.
Earlier this month, the H5N1 virus recorded an extraordinary rash of cases,
including four fatalities in Turkey, the first outside East Asia. All the
victims appear to have caught the virus from eating or handling infected
poultry. But most flu researchers worry that as the virus's range increases, so
does the likelihood that somewhere, sometime, some random set of mutations will
send it over the edge into transmissibility, unleashing a pandemic. Everyone
agrees that at some point, another pandemic will come - if not from this
strain, then from some other one perhaps not even yet under surveillance. The
best hope of containing its impact is to understand how it works. What are its
mechanisms of infection and replication? How does it foil the host's immune
response and jump from a conquered host to a fresh one?
In
Tumpey's view, the 1918 virus is the star witness in a murder trial, and the
interrogation should proceed without unnecessary impediments. Taubenberger's
sequence can help indicate what questions to ask. Experiments with individual
genes can suggest some possible answers. But only the living virus can reveal
the full truth. The first round of interrogation is already under way. Using
reverse genetics to test the contribution of any particular gene to the virus's
pathogenicity, Tumpey and his colleagues can replace any target gene in the
1918 virus with its complement from a harmless strain, then measure the effect
on the virus's potency. When he replaced the 1918 hemagglutinin gene with one
from a garden-variety seasonal flu, the virus replicated at less than 1100th
the rate in mice; it was definitive proof of the essential role played by that
gene in virulence. Tumpey already knew that the 1918 virus did not need one of
the host's own enzymes to turn traitor and cleave apart the hemagglutinin
protein to help the virus infect a cell. But when he created a 1918 virus
without its own neuraminidase gene, this ability was lost, revealing that the
virus toted its own cleaving mechanism into the host on that gene, like a
butcher who brings his own knife. Meanwhile, Peter Palese's group has shown
that another gene in the 1918 virus is especially good at blunting the human
immune system's initial counterattack.
"It
was perfect genes, working together, that made this virus what it was,"
Palese said. Then he gave a little laugh. "Or what it is."
Scientists
can also examine the role in virulence and transmission of particular mutations
on the virus's genes. Taubenberger's sequence again offers guidance. One of the
large genes driving replication, for instance, bears a single mutation that is
found not only in the 1918 virus, but also in all human flus. But no bird flus
have this mutation - not even H5N1. Is this mutation perhaps necessary for an
avian virus to become transmissible from human to human? Combining reverse
genetics with some other molecular tricks, you could insert that mutation into
the gene of a nonvirulent avian flu, construct the virus and see how it
behaves. The ultimate hope of such experiments is to uncover a clue to how the
virus spreads or kills, and possibly a way to cripple it. Terrence Tumpey is
already planning experiments with several research groups and companies that
will use the 1918 virus to test possible antiviral drugs to block some
universal mechanism of virulence, like the binding of hemagglutinin to the host
cell. That work has added urgency, since the H5N1 flu appears to have developed
resistance to one of two flu drugs currently on the market.
What
may be the most informative research he intends to conduct must surely be the
most dangerous as well. Tumpey's freezer contains the resurrected 1918 virus,
which is lethal and highly transmissible. It also contains samples of the H5N1
virus, which is lethal but not yet transmissible. Using reverse genetics, he
imagines "a great set of experiments" combining the genes of these
two killers in various combinations, seeing if one might have the capacity to
transmit from an infected animal model, like a ferret, to an uninfected one.
This would create in the laboratory the very pandemic strain that researchers
most fear may emerge at any time in nature. According to Tumpey, plans for
these experiments are already "on paper." Needless to say, they will
require complete approval first, and may have to be performed under Biosafety
Level 4 conditions, since we would have no immunity to the recombinant
organism.
For
Richard Ebright, the prospect that the C.D.C. or some other lab would
"jump the gun on nature" is worrisome under any circumstances. Other
scientists and bioethicists are also calling for more independent,
international review and control of further research on the 1918 virus and
other synthetic pathogens yet to be concocted. It all comes down, of course, to
whether what we can learn justifies the risk of bringing them into existence.
While that debate moves forward, nature will go on conducting its own creative
experiments, indifferent as always to our abilities to defend ourselves against
them.
Jamie
Shreeve is the author of "The Genome War: How Craig Venter Tried to
Capture the Code of Life and Save the World." His last article for the
magazine was about chimeras.