Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Scientists force viruses to evolve as better delivery vehicles for gene therapy


Viruses and humans have evolved together over millions of years in a game of one-upmanship that, often as not, left humans sick or worse.

Now, a University of California, Berkeley, researcher has shown that viruses - in this case, a benign one - can be forced to evolve in ways to benefit humans.

The adeno-associated virus, or AAV, is a common, though innocuous, resident of the body that has received a lot of attention in recent years as a possible carrier for genes in gene therapy. Because as many as 90 percent of people already have the virus, however, their immune systems are primed with antibodies to quickly tackle and neutralize it, thwarting any attempt at gene therapy.

UC Berkeley’s David Schaffer, associate professor of chemical engineering and a member of the Helen Wills Neuroscience Institute, with colleagues Narendra Maheshri, James T. Koerber and Brian Kaspar, decided to speed up the process of viral evolution and direct the change in a way that would allow the virus to slip past the body’s immune defenses, making it a more viable vehicle for gene therapy. In essentially two generations of accelerated evolution, requiring about two months of lab work, they succeeded.

Schaffer and his team at UC Berkeley and at Ohio State University report their success in the current issue of Nature Biotechnology.

"Directed evolution has mainly been done to change the activity of an enzyme - to make it more effective toward a new substrate or better able to catalyze a reaction, for example - or to make antibodies better binders against specific targets," said Schaffer, who also is an affiliate of the UC Berkeley wing of the California Institute for Quantitative Biomedical Research (QB3). "In the viral realm, this approach is essentially untapped."

This technique could be used to improve many other characteristics of AAV to make it a better delivery vector for genes.

"We think there are a huge variety of new problems we could address as well, such as targeting the virus to cells it is ordinarily not good at getting into, or speeding its transport through the body," he said.

Though Schaffer acknowledges that the technique could be used to help pathogenic viruses evade the human immune system, potentially making them more virulent, he said that other and easier techniques already allow this frightening possibility.

AAV consists of two genes enclosed within a ball, or capsid, of proteins. The capsid proteins are what antibodies recognize, and as a result were the target of directed evolution. To provide the raw material for evolution - the genetic variation from which nature selects the best-adapted organism - the researchers created mutant viruses by introducing small variations in the genes through an error-prone polymerase chain reaction (PCR) coupled with a test tube recombination technique. After reassembling the mutant viruses inside their capsids, they introduced them to blood serum pooled from rabbits immunized against AAV, and thus containing many types of antibodies to AAV. Only the mutant viruses good at evading antibodies to AAV survived the serum.

After passing the viruses three times through increasingly more potent serum, they isolated the survivors and subjected them to another round of PCR that introduced more mutations. After passing this second generation through serum three times, they isolated viruses that could survive AAV antibodies much better than the original strain of AAV. One strain of virus was 96 times more effective than the wild AAV, and two evolved strains survived injection into mice with nearly 1,000 times the level of antibodies required to neutralize the wild virus.

By sequencing the survivor strains, the researchers discovered that the capsid proteins of the survivors differed from those of the original strain by only seven amino acid building blocks, two of which were responsible for most of the altered interaction with antibodies.

"Starting from scratch, just trying to rationally decide which two amino acid changes to make on the virus, there is no way you would have guessed those two," Schaffer said. "Using the same algorithm as nature came up with - evolution - to solve the problem, is the best way to do it."

Since each generation takes about a month, Schaffer predicted that many types of new and improved strains could be created in a few months’ time, and certainly in less than a year. He is pursuing experiments now using pooled human blood serum.

"This virus is kind of a gift from nature, a very safe and efficient virus, but nature never evolved it to be a human therapeutic. So, in a sense, we have to re-evolve it for that purpose," he said.

Robert Sanders | EurekAlert!
Further information:

More articles from Life Sciences:

nachricht Don't Give the Slightest Chance to Toxic Elements in Medicinal Products
23.03.2018 | Physikalisch-Technische Bundesanstalt (PTB)

nachricht North and South Cooperation to Combat Tuberculosis
22.03.2018 | Universität Zürich

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Space observation with radar to secure Germany's space infrastructure

Satellites in near-Earth orbit are at risk due to the steady increase in space debris. But their mission in the areas of telecommunications, navigation or weather forecasts is essential for society. Fraunhofer FHR therefore develops radar-based systems which allow the detection, tracking and cataloging of even the smallest particles of debris. Satellite operators who have access to our data are in a better position to plan evasive maneuvers and prevent destructive collisions. From April, 25-29 2018, Fraunhofer FHR and its partners will exhibit the complementary radar systems TIRA and GESTRA as well as the latest radar techniques for space observation across three stands at the ILA Berlin.

The "traffic situation" in space is very tense: the Earth is currently being orbited not only by countless satellites but also by a large volume of space...

Im Focus: Researchers Discover New Anti-Cancer Protein

An international team of researchers has discovered a new anti-cancer protein. The protein, called LHPP, prevents the uncontrolled proliferation of cancer cells in the liver. The researchers led by Prof. Michael N. Hall from the Biozentrum, University of Basel, report in “Nature” that LHPP can also serve as a biomarker for the diagnosis and prognosis of liver cancer.

The incidence of liver cancer, also known as hepatocellular carcinoma, is steadily increasing. In the last twenty years, the number of cases has almost doubled...

Im Focus: Researchers at Fraunhofer monitor re-entry of Chinese space station Tiangong-1

In just a few weeks from now, the Chinese space station Tiangong-1 will re-enter the Earth's atmosphere where it will to a large extent burn up. It is possible that some debris will reach the Earth's surface. Tiangong-1 is orbiting the Earth uncontrolled at a speed of approx. 29,000 km/h.Currently the prognosis relating to the time of impact currently lies within a window of several days. The scientists at Fraunhofer FHR have already been monitoring Tiangong-1 for a number of weeks with their TIRA system, one of the most powerful space observation radars in the world, with a view to supporting the German Space Situational Awareness Center and the ESA with their re-entry forecasts.

Following the loss of radio contact with Tiangong-1 in 2016 and due to the low orbital height, it is now inevitable that the Chinese space station will...

Im Focus: Alliance „OLED Licht Forum“ – Key partner for OLED lighting solutions

Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP, provider of research and development services for OLED lighting solutions, announces the founding of the “OLED Licht Forum” and presents latest OLED design and lighting solutions during light+building, from March 18th – 23rd, 2018 in Frankfurt a.M./Germany, at booth no. F91 in Hall 4.0.

They are united in their passion for OLED (organic light emitting diodes) lighting with all of its unique facets and application possibilities. Thus experts in...

Im Focus: Mars' oceans formed early, possibly aided by massive volcanic eruptions

Oceans formed before Tharsis and evolved together, shaping climate history of Mars

A new scenario seeking to explain how Mars' putative oceans came and went over the last 4 billion years implies that the oceans formed several hundred million...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

New solar solutions for sustainable buildings and cities

23.03.2018 | Event News

Virtual reality conference comes to Reutlingen

19.03.2018 | Event News

Ultrafast Wireless and Chip Design at the DATE Conference in Dresden

16.03.2018 | Event News

Latest News

For graphite pellets, just add elbow grease

23.03.2018 | Materials Sciences

Unique communication strategy discovered in stem cell pathway controlling plant growth

23.03.2018 | Agricultural and Forestry Science

Sharpening the X-ray view of the nanocosm

23.03.2018 | Physics and Astronomy

Science & Research
Overview of more VideoLinks >>>