Fighting the flu virus

Last Updated 12 July 2010, 10:24 IST

With a dangerous type of influenza setting off the latest global pandemic killing thousands, researchers are now scrambling to develop new drugs and vaccines to prevent and treat the infection. A group in Bangalore with its US collaborators has reported an early success.

The scientists have designed a protein molecule which when injected in mice give the animals protection from one of the fatal influenza strains. They were also able to produce the protein in sufficient quantity in one of the common bacteria – one of the key criteria to make the product a commercial success at a later stage.

“It is a protein molecule (immunogen), which is a fragment of a conserved region of the HA (Hemagglutinin) protein from the H3N2 subtype. Injection of this molecule into mice protects them from death when exposed to virus,” Raghavan Varadarajan, professor at molecular biophysics unit of the Indian Institute of Sciences, Bangalore told Deccan Herald.

Varadarajan with students and colleagues from Jawaharlal Nehru Centre for Advanced Scientific Research and Merck Research Laboratories in the USA tweaked the protein molecule in such a way as to clear the infection by generating antibodies which prevent the virus from releasing its genetic material inside a cell and multiplying. The findings were published in the Proceedings of National Academy of Sciences on July 5.  But, how close are these researchers to creating a new vaccine against influenza that results in 20,000-40,000 deaths annually in the USA alone and killing millions in a pandemic year? “We are a long way from the market. We have to first try and improve the molecules so that it elicits more neutralising antibodies that prevents the virus’ entry into cells. Several improvements and tests are needed before such a molecule can be considered for human use,” he said.

In the last five years, the world witnessed two major influenza outbreaks. In the first case, the virus came from birds and in the second case, it spread from pigs. While the avian flu does not seem to be a risk at the moment, swine flu continues to be a major health issue for India killing more than 1600 since last year and affecting thousands. The scientists witnessed protection for H3N2, which is one of the major sub types responsible for human influenza infection. “The immunogen based on H3 sequence does not protect against H1N1 viruses (seasonal or pandemic flu). However, it is possible that similar immunogens based on H1N1 sequence may confer protection against this subtype,” he said.

India does not have a registry on influenza count. But undoubtedly, it is one of the major respiratory illnesses with a high death count.

Even though the virus has different subtypes, only H1N1, H3N2 subtypes and the B-type viruses circulate in human population. The global panic was triggered by the highly pathogenic avian influenza strain (H5N1), which has been identified as the causative agent of a severe form of flu in human. Conventional influenza vaccines consist of inactivated virus. These vaccines produce antibodies against the HA surface protein. Neutralising antibodies are those that bind to virus and prevent infection. They can target two sub-units in the spike-shaped HA – one for binding to specific human cell surface sugar (HA1) and a second one for triggering the infection (HA2).

The HA1 binds to sialic acid on the surface of the cells. After entering the cell, HA2 through a chain of complicated biochemical processed releases the viral proteins and genetic material into the cell completing the infection process.

While most of the available vaccines target the HA1 portion, a key problem is that the virus is able to evade the binding in a few years because of its natural mutation. The composition of common flu vaccines, therefore, needs to be changed in every few years.

Targetting the HA2 portion
The Bangalore-US team targeted the HA2 portion, which is more conserved thereby eliminating the need of changing the vaccine composition in every few years. But since this subunit is less accessible to the immune system, such antibodies are less common. Moreover, other researchers in the past found it difficult to produce HA2 in the shape it adopts at neutral pH.

The scientists introduced designated mutations in HA2 as well as include fragments of HA1 that normally binds to HA2 to express HA2 in its neutral pH conformation. The protein was expressed in the bacterium Escherichia coli. Another key step was to fold the protein in right orientation to elicit proper immune response.
While the protein construct gave encouraging results in mice model, the scientists observe a temporary weight loss in animals.

“This means infection is not prevented, but it is cleared. We have to improve the molecule so that the mice will not suffer from a weight loss,” Varadarajan said, making it aptly clear that the new vaccine is still many years away.

(Published 12 July 2010, 10:24 IST)

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