Viruses, Vaccines and the “Unstoppable” Ralph Tripp

University of Georgia Research Magazine | Fall/Winter 2005
By Kelli Whitlock Burton

 

Ralph Tripp arrives at his University of Georgia lab each day around 6 a.m. The place is deserted at that hour and the phones are silent. He puts on a pot of pekoe black tea, turns on his computer, scans his e-mail and then gets to work. There’s no one around to disturb this scientist in his relentless pursuit of treatments for respiratory illnesses. There’s also no one to catch this occasional practical joker if he’s in the mood to switch the chairs in his coworkers’ offices or replace boxes of essential office supplies with packets of ketchup.

Confront him about his high jinks and Tripp readily admits his guilt. There’s a method, he says, to such mischief. As he and his colleagues in the College of Veterinary Medicine ponder complicated biological problems about viruses, vaccines and therapies, their brains get befogged with whys and hows and what-ifs. Humor, says Tripp, clears the air. After a good laugh, the mind is refreshed, ready to tackle what once seemed elusive.

In much the same spirit, Tripp allows his intellectual gaze to wander every now and then. “Quite often scientists get so narrowly focused on a problem,” he said, “that it’s easy to forget there are greater issues in the world than getting a plaque assay [a lab procedure to determine the presence of viral particles] to work.”

His regularly refreshed and wide-ranging mind is apparently also a productive one. Since arriving at the university in early 2004, Tripp, a professor of infectious diseases and Georgia Research Alliance Eminent Scholar, has assembled a lab of 18 scientists and students; helped finalize preparations for the $40 million Animal Health Research Center renovation (see story on p. 20); met with representatives from Congress and the Georgia statehouse; forged a partnership with a biotech company in Cambridge, Mass., that led to a clinical drug trial; filed three patents; and facilitated the pooling of scientific talent from across campus, particularly in nanotechnology, in order to focus on such challenges as avian flu, SARS and respiratory syncytial virus, to which virtually every American child is exposed by the age of 2.

 

The Making of a Biologist

As an 18-year-old freshman at Franklin Pierce College in New Hampshire, Tripp’s interests were diverse. So he decided to major in the first class he aced. Earning his first “A” in microbiology, he indeed graduated with a degree in biology four years later. But looking back, Tripp acknowledges that his choice of path was probably not as random as it seemed. He had always leaned toward science, especially life science. Even if that first “A” were, say, in astronomy, it’s unlikely that he would have spent the past 20 years looking through a telescope instead of a microscope.

From the time Tripp started graduate school at Oregon State University, there was a good chance he’d specialize in infectious diseases. His early research subjects weren’t humans, though. He studied fish, which seemed like a good fit for someone who planned at the time to work for the U.S. Fish and Wildlife Service.

Those plans changed in 1990 when Tripp arrived at Emory University School of Medicine to do a postdoctoral fellowship in a lab that focused on adenoviruses, a family of viruses that cause respiratory infections and have developed elaborate methods to bypass the immune system. Tripp was part of the team that identified the specific regions of the virus responsible for immune evasion.

He left Emory in 1993 for a postdoc at St. Jude’s Children’s Research Hospital, working in the lab of Nobel laureate Peter Doherty. Tripp’s studies there of influenza and herpes viruses laid the foundation for research he would later do at the Centers for Disease Control and Prevention, which he joined in 1997. One of his goals at CDC was to better understand respiratory syncytial virus (RSV), which causes a serious infection in the lower respiratory tract. There was no good test or treatment for RSV, which infects hundreds of thousands of children and older adults each year. Like adenoviruses, RSV could outmaneuver the immune system, and Tripp’s goal was to figure out why.

By the time UGA hired him as an eminent scholar, Tripp had worked his way to the head of a CDC unit that studies viral immunology in respiratory viruses, authored more than 60 journal articles plus several chapters in 10 books and served as principal investigator or co-investigator on numerous projects that led to discoveries producing six patents.

What he wanted most, though, still eluded him — a better test to detect low levels of RSV, and a drug to treat it.

 

Seeking Immunity

RSV, a seasonal virus that circulates around the country each year most intensely between October and May, produces an infection that usually begins with a fever, runny nose and cough. Often misdiagnosed as the flu, RSV is the most common cause of bronchitis and pneumonia in young children, and it’s also a major pathogen in the elderly and people who are immune-compromised. A 1999 CDC study found that much of the pneumonia- and influenza-associated deaths in the United States among the elderly actually were caused by RSV.

The infection generally runs its course in a week or two. But in premature infants, the elderly, and people with compromised immune systems, RSV can lead to serious illness. Approximately 90,000 children and adults in the United States are hospitalized each year with RSV, and about 5,000 of them die. The virus does far worse damage in developing countries, where malnourished populations have little defense against infection.

The risk is not one-time-only. If a person infected with a strain of influenza virus survives the illness, the body will develop long-term immunity to that specific viral strain. Not so with RSV. A person can be infected by the same strain of RSV time and time again, and scientists don’t fully understand why. Nor, until recently, had they succeeded in developing any effective RSV treatments, and still no safe and effective RSV vaccine exists.

But in 2001, Tripp and his CDC colleagues identified a protein on the surface of RSV, called G glycoprotein, that attenuates the immune system’s normal response to infection. Their findings, published in the journal Nature Immunology, offered a much-needed peek inside the virus’s chemistry and prompted a change in direction of many labs’ vaccine-development efforts. If the G glycoprotein could somehow be turned off, after all, wouldn’t that give the immune system the boost it needed to defeat RSV?

 

Running Interference

RSV is a paramyxovirus — a virus that relies on its RNA genetic material for replication. HIV, SARS, hepatitis, mumps, influenza and polio are all examples of RNA viruses, and, unlike DNA viruses, RNA viruses are extremely prone to mutations. Creating a vaccine or drug for a virus that’s constantly changing presents a particularly difficult challenge for scientists. But a discovery in 2002 offered a potential new weapon: RNA interference, or RNAi.

First observed in 1990, but not understood until 12 years later, RNAi enables cells to control gene expression, for example to promote or deter growth or to protect the cells from viruses. When a virus invades a cell, its primary goal is to use the cell’s own mechanisms to create genetic copies of the virus as quickly as possible. The virus comes with its own RNA, which it tries to sneak into the cell. (See illustration on p. 18.) But the viral RNA is long and double-stranded while the cell’s RNA normally is single-stranded. That difference alerts the cell to the viral invasion. To protect itself, the cell switches on its RNAi machinery, a complicated network of proteins and enzymes that scientists still are trying to understand. It is thought that once the viral RNA is located, an enzyme called Dicer chops it up into smaller, more manageable pieces. A group of proteins unwinds the two RNA strands, latches onto the single strands and cleaves them. The proteins then look for other viral RNA with the same genetic sequence and destroy them. The effect is the silencing of gene expression by the virus.

During the past five years, scientists have figured out how to replicate RNAi’s defensive process synthetically in models of several organisms, including mammals. Recently, research has suggested that the double-stranded viral RNAs that prompt the host cell’s RNAi response could be used in drug development to silence targeted genes and stop viruses from spreading. At first, many scientists in the field, including Tripp, greeted the new technique with skepticism. But by the time he arrived at UGA, his doubts began to fade because several teams had demonstrated that RNAi worked.

He began organizing a team of scientists at UGA with expertise in RNAi, infectious diseases, vaccine testing and related fields. “We each have strengths in different areas and our personalities complement each other very well,” said Jeff Hogan, a professor of anatomy and radiology who came to UGA in 2004 to collaborate with Tripp. Hogan, who previously worked at the Southern Research Institute, has a background in vaccine development and testing in animal models. Another team member, Mark Tompkins, brings a knowledge of RNAi technology to the group. A professor of infectious diseases, he arrived at UGA in January 2005 after two years of working with RNAi technology at the U.S. Food and Drug Administration.

A virus’s ability to mutate gives it an ability to resist immunity induced by vaccines and drugs designed to stop it. But scientists have learned that most viruses also contain pieces of genetic sequences that are conserved and don’t mutate over time. Seeing them as possible targets for therapeutic drug development, Tripp and his colleagues identified numerous genetic sequences on RSV that seemed to be resistant to mutation.

Late last year, he was contacted by Alnylam Pharmaceuticals, a biotech company in Cambridge, Mass., interested in developing RNAi drugs for respiratory viruses. Impressed with Tripp’s work on RSV, they soon forged a partnership with UGA. Ultimately, his group whittled its list of possible targets to three genetic sequences, which Alnylam then used to develop three RNAi-based drugs, one of which is going into Phase I clinical trials.

RNAi also has potential to “self-vaccinate,” according to Tripp. RNAi treatment of an established virus infection will shut off virus replication but will still provide the host the opportunity to develop an immune response against remaining viral proteins. As a result, RNAi treatment would not only prevent the disease but also vaccinate the individual. In addition, because a virus is a parasite and contains only minimal genetic information, it must hijack an invaded cell’s reproduction machinery in order to grow and survive. Tom Hodge, a principal investigator in the veterinary college’s infectious diseases department, demonstrated in a recent publication that several host-cell genes are not necessary for cell survival but are needed for replication by some viruses. This discovery prompted Tripp and other researchers in his group to ask if a person infected with a virus could take an RNAi drug designed to silence one or more of those host genes. The virus would be unable to copy itself, and the body would gain a lifelong immunity to that particular viral strain. In effect, such a drug would be an anti-viral that works like a vaccine.

Preliminary studies suggest that this strategy would work, Tripp said, but he also foresees potential obstacles. While it may be possible to get FDA approval for RNAi drugs that silence viral genes, he speculates that the regulatory agency may be wary of approving a drug that shuts down genes in the human host. And, as is the case with RNAi drugs that target viral genes, there’s always the problem of how best to get the drug into the body.

 

To Avert the Next Pandemic

Tripp has always felt a sense of urgency about his work — his colleagues describe him as intense, determined and passionate. These days, his quest to develop an RNAi drug that works against RSV is particularly urgent. If Tripp and colleagues could realize that goal, he believes they could then develop one for combating just about any virus, including the one that now threatens the world with a new pandemic.

Between 1918 and 1919, an outbreak of Spanish flu — one of the largest influenza pandemics in history — killed approximately 50 million people worldwide, according to CDC estimates. To some present-day observers, this long-ago event is ancient history. But Tripp doesn’t see it that way. His work affords him a close view of an emerging viral strain of influenza — H5N1 influenza A virus, also known as avian flu or bird flu — that most experts say could do more damage than the flu of 1918-19.

The first human cases of avian flu were reported in Hong Kong in 1997, where 18 people were hospitalized and six died. In that outbreak, humans contracted the virus from infected poultry. But because this virus is among those known to mutate rapidly, scientists fear the avian flu virus might undergo changes in its molecular structure that would enable it to become transmissible from human to human.

“The bottom line is that we have no immunity to it, we have no vaccine for it and the only treatment option is limited and becoming ineffective,” Tripp said. “The virus is one nucleotide [away] from changing into a pathogenic human virus, and we’re sitting here pretty much naked.”

Tripp and his colleagues began working on strategies to combat H5N1 in 2005, hoping to apply what they’ve learned about RNAi drug development for RSV to this potentially devastating virus. Their idea is to use RNAi to develop a novel anti-viral drug class effective for all influenza virus strains, particularly H5N1, and applicable both to people and potentially to animals infected with avian flu. The synthetic small inhibitory RNA (siRNA) drug would be administered, most likely as an inhalant, entering cells in the lungs where the virus has set up shop. With key viral genes silenced, viruses such as H5N1 would shut down.

Another scenario would be to use the drug as a prophylactic once an influenza outbreak has been detected: People within a certain radius of the outbreak site would be medicated, thereby protecting them from the virus and stopping the outbreak from spreading.

“RNAi is certainly promising for this purpose because you can target components of the virus that traditional pharmaceuticals can’t,” Tompkins said. “It’s also universally applicable — you can target multiple viral or host genes using the same technology.”

 

Money Talks

In late spring 2005, Tripp found himself describing these possibilities to members of the House of Representatives’ Energy and Commerce Committee. It was the type of message he relays often these days. Tripp noted that a substantial portion of his time is spent talking to national and state policymakers about the promise of RNAi drug development. This is a necessary step, he believes, in doing translational science, and he’s relieved to see that policymakers are responding — particularly in taking the avian flu threat seriously.

Their interest is welcome, but what Tripp and others working on avian flu vaccines and therapies say they want most is money for ongoing research.

“We have a product that works, but we need to get the funding to help test it in the clinic and produce it on a large scale,” he said. Without government support, scientists may never overcome these obstacles, he added. “Universities, industry, even the usual National Institutes of Health grants don’t provide sufficient resources to push that through.”

If any scientist can convince government, Tripp is the one, said his former mentor, Doherty. He is “extremely dynamic, driven and adventurous in his approach.” In a word, noted Doherty, Tripp is “unstoppable.”