They discover a mechanism of the dengue virus that deactivates the natural defense of cells

In a year in which dengue was once again in the news because Argentina faces an outbreak with record cases and deaths, and other nations also see their populations threatened by this disease, some scientists have made a pioneering discovery that opens the door to design of more effective vaccines against dengue.

The team that made this finding was led by virologist Andrea Gamarnik, a researcher at the National Council for Scientific and Technical Research (CONICET) at the Leloir Institute Foundation, both entities in Argentina.

The study reveals a new pathway that dengue virus uses to control the antiviral response of human cells in order to successfully infect them. But not only that; the researchers also determined that this viral defense pathway is different depending on the strain of virus causing the infection (DEN1, DEN2, DEN3, or DEN4).

“This finding on how dengue virus and human cells interact also explains why different viral types can cause different clinical manifestations,” Gamarnik told the CyTA-Leloir Agency. And he added: “Although from the point of view of virology we knew that there were differences, we did not know in detail the molecular causes of them and that is one of the reasons why it is difficult to make vaccines that generate good immunity for the four viruses at Same time”.

An important characteristic of the dengue virus is that previous exposure to any of the four serotypes can cause a more severe clinical manifestation if the new infection is with a variant different from the previous one. That is why it is so important to have quadrivalent vaccines equally effective against all four serotypes, something that none of the existing vaccines has yet achieved.

“When a virus enters a cell, a kind of silent pitched battle begins: the pathogen seeks to infect in order to multiply and it defends itself by triggering its first defense, which are the innate antiviral systems. But the virus also protects itself and unleashes responses to counter cellular attacks. If the virus wins this first two-way battle, the infection progresses, the person can become ill and show symptoms. On the other hand, if the one that triumphs is the immune system of the cell, the virus disappears and the fight ends”, described the infection process María Mora González López Ledesma, co-author of the study. “We determined the way in which the dengue virus counteracts the antiviral attack of the cell, and the most interesting thing is that this mechanism is active in type 2 DEN but not in type 4,” specified González López Ledesma.

Why is that so interesting? “The approved dengue vaccines – and those that are in the process of approval – are known as ‘attenuated tetravalent’, that is, their formula contains the four viruses (hence quadrivalent) and also does not include only a part of it , as in the case of the vaccines that were used against COVID-19 based on the Spike protein, but use the entire but weakened virus. This seeks to protect against the four serotypes at the same time”, responded Gamarnik, whose Molecular Virology laboratory at the FIL has been working on dengue for 20 years. Since the virus is weakened in these vaccines, it cannot cause disease, but it can awaken the antiviral immune response that will protect the body against contact with the real pathogen.

According to the specialist, in the development of vaccines it is observed that attenuated type 4 viruses generate high immunity, while those of DEN2 do not do so well and that, now they know, is related to the discovery that they have just published: the type 2 is more effective in turning off the cell’s antiviral response.

“If we know the changes that we can make at the molecular level so that the type 2 virus cannot counteract the action of the immune system, we can, through genetic engineering, design better vaccines,” Gamarnik specified. And he added: “In our work we found that by changing just one amino acid of the DEN2 NS5 protein (it would be equivalent to removing a brick in the entire building of the viral protein) we can simulate what happens in DEN4. With that information, better vaccines could be obtained.”

According to the latest data from the National Ministry of Health, in Argentina this year 100,675 cases of dengue were registered, with predominant circulation of DEN2 (81.37%). “This data is relevant, since in the three previous outbreaks (2009, 2016 and 2020) the dominant serotype was DEN1. This serotype change could represent a risk in terms of the development of cases of severe dengue. In fact, the four serotypes have circulated in our country in different years and in different proportions. This highlights the importance of having vaccines that are equally effective against the four serotypes of dengue,” explained González López Ledesma.

Andrea Gamarnik (left) and María Mora González López Ledesma. (Photo: CyTA-Leloir Agency)

surprise in the lab

The Royal Spanish Academy defines the word “serendipity” as “a valuable finding that occurs accidentally or casually”. That was exactly what happened with this newly revealed mechanism of the dengue virus.

“The truth is that we were not looking for what we found. If we had set our minds to it, we would not have succeeded because it was like finding a needle in a haystack,” Gamarnik confessed and said that they were actually carrying out a basic research project to generate knowledge about how the virus proteins interact with those of the virus. human cell.

“We used proteomics technology and we were able to measure thousands and thousands of interactions. Suddenly our attention was drawn to the fact that a virus protein, called NS5, attached itself to another present in the cell and deactivated it, eliminating it. Then the question arose as to what the virus does to eliminate that cellular protein. It was thus that we entered an unexpected path of investigations that took us about three years,” said Gamarnik.

The work began before the outbreak of the pandemic, but in March 2020 the team decided to interrupt it to focus on developing tools that could help fight the new coronavirus, such as the COVIDAR kits. In mid-2022, the investigations on dengue were resumed and they made the discovery that has now been made public.

“After more than 20 years of working with the dengue virus, I could say that, by the way, this is one of the most elegant and beautiful advances we have made: we started with a very general question and discovered something very useful”, Gamarnik summarized, before concluding: “It was like filming a suspense movie without knowing the end until the last moment. This is what is so exciting about basic science, one generates questions based on curiosity and when answered rigorously they take us to unexpected places”.

The vaccine challenge

So far there are two approved dengue vaccines in Argentina: since 2017, the one from the Sanofi Pasteur laboratory, which is indicated only for people between the ages of 6 and 45 with confirmed previous dengue infection and which is currently not on the market; and the recently authorized Takeda company, which acts against the four serotypes of dengue, uses DEN2 as a base and will be available soon.

To fully understand what the design of this new vaccine is like, it is important to know that a virus has two main components, an envelope and a genetic material with the necessary information to produce new viruses (just like SARS-Cov-2, the genetic material of the dengue virus is a single RNA molecule).

“Takeda’s vaccine contains the shell of the four types of the virus, but inside they all have the genetic material of DEN2. In other words, the composition of the vaccine is the complete DEN2 and a simulation of the other three types of dengue. In the vaccine, these four viruses are attenuated, which means that they do not have the capacity to cause disease”, explained Andrea Gamarnik, who added: “Although Takeda’s vaccine protects against all serotypes because by having the four covers the The body’s immune system generates antibodies against each of them, it was found to work very well against DEN2 and DEN1, but there is not much information about what happens with the other two types.”

In this sense, María Mora González López Ledesma emphasized: “You have to be careful because the immune response that is generated with the vaccine remains in the cellular memory and if we do not have sufficient evidence about how it acts in the cases of DEN3 and DEN4, we will not we know what can happen in the event of eventual exposure to these viruses in the future. So far, the safety studies have yielded encouraging data, but there is still pending data being collected. We have to think that these vaccines are very difficult to develop; in this case, it has already been more than 15 years”.

The study is titled “Dengue virus NS5 degrades ERC1 during infection to antagonize NF-kB activation”. And it has been published in the academic journal Proceedings of the National Academy of Sciences (PNAS), of the National Academy of Sciences of the United States. (Source: CyTA-Leloir Agency)