TWiV 421: Like flies on shot

The TWiVnauts present another example of an infectious but replication incompetent vaccine, an insect specific arborvirus bearing chikungunya virus structural proteins.

You can find TWiV #421 at, or listen below.

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Paradoxical vaccines

gene stops hereA new breed of vaccines is on the horizon: they replicate in one type of cell, allowing for their production, but will not replicate in humans. Two different examples have recently been described for influenza and chikungunya viruses.

The influenza virus vaccine is produced by introducing multiple amber (UAG) translation stop codons in multiple viral genes. Cloned DNA copies of the mutated viral RNAs are not infectious in normal cells. However, when introduced into specially engineered ‘suppressor’ cells that can insert an amino acid at each amber stop codon, infectious viruses can be produced. These viruses will only replicate in the suppressor cells, not in normal cells, because the stop codons lead to the production of short proteins which do not function properly.

When inoculated into mice, the stop-codon containing influenza viruses infect cells, and although they do not replicate, a strong and protective immune response is induced. Because the viral genomes contain multiple mutations, the viruses are far less likely than traditional infectious, attenuated vaccines to sustain mutations that allow them to replicate in normal cells. It’s a clever approach to designing an infectious, but replication-incompetent vaccine (for more discussion, listen to TWiV #420).

Another approach is exemplified by an experimental vaccine against chikungunya virus. The authors utilize Eilat virus, a virus that only replicates in insects. The genes encoding the structural proteins of Eilat virus were replaced with those of chikungunya virus. The recombinant virus replicates in insect cells, but not in mammalian cells. The virus enters the latter cells, and some viral proteins are produced, but genome replication does not take place.

When the Eilat-Chikungunya recombinant virus in inoculated into mice, there is no genome replication, but a strong and protective immune response is induced. The block to replication – viral RNA synthesis does not occur – is not overcome by multiple passages in mice. Like the stop-codon containing influenza viruses, the Eilat recombinant virus is a replication-incompetent vaccine.

These are two different approaches to making viruses that replicate in specific cells in culture – the suppressor cells for influenza virus, and insect cells for Eilat virus. When inoculated into non-suppressor cells (influenza virus) or non-insect cells (Eilat virus), a strong immune response is initiated. Neither virus should replicate in humans, but clinical trials have to be done to determine if they are immunogenic and protective.

The advantage of these vaccine candidates compared with inactivated vaccines is that they enter cells and produce some viral proteins, likely resulting in a stronger immune response. Compared with infectious, attenuated vaccines, they are far less likely to revert to virulence, and are easier to isolate.

These two potential vaccine technologies have been demonstrated with influenza and chikungunya viruses, but they can be used for other virus. The stop-codon approach is more universally applicable, because the mutations can be introduced into the genome of any virus. The Eilat virus approach can only be used with viruses whose structural proteins are compatible with the vector – probably only togaviruses and flaviviruses. A similar approach might be used with insect-specific viruses in other virus families.

Why do I call these vaccines ‘paradoxical’? Because they are infectious and non-infectious, depending on the host cell that is used.

Note: The illustration is from a t-shirt, and the single letter code of the protein spells out a message. However the title, ‘the gene stops here’, is wrong. It should be ‘the protein stops here. The 3’-untranslated region, which continues beyond the stop codon, is considered part of the gene.

TWiV 420: Orthogonal vectors

The TWiV gurus describe how to use an orthogonal translation system to produce infectious but replication-incompetent influenza vaccines.

You can find TWiV #420 at, or listen below.

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Fake news and fake science

The Cow PockIn a recent editorial, the New York Times wrote about ‘the breakdown of a shared public reality built upon widely accepted facts’. As a scientist, I am appalled by the disdain for facts shown by many in this country, including the President-Elect. Unfortunately, science is not without its share of fake information.

The Times argues that at one time, nearly everyone had a unified source of news – the proverbial Walter Cronkite. Social media and the internet changed all that, allowing people to have their own sources of news, whether they be real or fake. The web developers in Macedonia who are paid $30,000 a month to spew out fake news are just part of the problem.

The goal of science is to discover how our world works. It’s about finding facts, not fake answers. Yet fake science has always been with us. Not long after Edward Jenner demonstrated vaccination against smallpox using pustules from milkmaids with cowpox, skeptics thought that this process would lead to the growth of cow-parts from the inoculated areas (see illustration). To this day anti-vaxers spew fake science which they claim shows that vaccines are not safe, do not work, or cause autism.

Fake science does not stop with anti-vaxers. There are people who deny climate change (including our President-Elect), despite easily accessible data showing that the trend is real. There are people who, bafflingly, claim that HIV does not cause AIDS, or that Zika virus does not cause birth defects, or that genetically modified plants will cause untold harm to people who consume them. The list of fake science goes on and on. The situation is appalling to any scientist who examines the data and finds clear proof that HIV does cause AIDS, and that Zika virus does cause birth defects.

There is also fake science perpetrated by scientists – those who publish fake data to advance their career. There are so many examples of such science fraud that there is a website to document the inevitable retractions – called RetractionWatch, of course. I find the existence of such a site lamentable.

That fake news can play such a large part in the operation of our society was something I only recognized recently. My initial reaction, as a scientist, was outrage that anyone would want to believe in, and adopt, lies. But this is a naive reaction, not only because bad behavior should always be expected of some humans, but because fake science has surrounded me for my entire career.

Nevertheless, I am a scientist who looks for the truth, and I simply cannot tolerate fabrication, whether in science or politics or in any field.

I don’t know how to solve the fake news and fake science problems. But the Times has a suggestion:

Without a Walter Cronkite to guide them, how can Americans find the path back to a culture of commonly accepted facts, the building blocks of democracy? A president and other politicians who care about the truth could certainly help them along. In the absence of leaders like that, media organizations that report fact without regard for partisanship, and citizens who think for themselves, will need to light the way.

I’m not sure that today’s profit-driven media organizations are the answer to the fake news problem. But I’ve always felt that scientists can help counter fake science. We all need to communicate in some way so that the public sees us as a single voice, advocating the huge role that science plays in our lives. That’s why here at virology blog, and over at MicrobeTV, you’ll always find real science.

TWiV 419: The selfless gene

The TWiVrific gang reveal how integration of a virophage into the nuclear genome of a marine protozoan enhances host survival after infection with a giant virus.

You can find TWiV #419 at, or listen below.

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Altruistic viruses

Cafeteria roenbergensisVirophages (the name means virus eater) were first discovered to replicate only in amoeba infected with the giant mimiviruses or mamaviruses.  They reduce yields of the giant viruses, and also decrease killing of the host cell. Another virophage called mavirus has been found to integrate into the genome of its host and behaves like an inducible antiviral defense system (link to paper).

The host cell of the virophage mavirus is Cafeteria roenbergensis, Cro (pictured), a marine phagotropic flagellate, that is infected with the giant virus CroV (Cafeteria roenbergensis virus). When Cro cells are infected with a mixture of mavirus and CroV, the virophage integrates into the host cell genome. There it remains silent; the cells survive, and no virophage particles are produced. Such cells can be called lysogens, a name applied to bacteria containing integrated bacteriophage genomes, or prophages.

How does the mavirus genome integrate into the Cro cell? The viral genome encodes an integrase, an enzyme that cuts host DNA and inserts a copy of the viral genome. Retroviruses achieve the same feat via an integrase.

When Cro-mavirus lysogens are infected with CroV, the integrated mavirus genome is transcribed to RNA, the viral DNA replicates, and new virus particles are formed. These virophages inhibit the replication of CroV by 100-1000 fold. As a consequence, the host cell population survives.

These findings suggest that the virophage mavirus is altruistic: induction of the integrated genome leads to killing of the host cell, but other members of the cell population are protected. Altruism is not unknown in Nature, but how it evolved is an intriguing question.

All this work was done in a laboratory. It will be necessary to determine if integration of mavirus into Cro cells in the wild has any influence on the ecology of these organisms.

TWiV 418: Of mice and MERS

The TWiVsters describe a new animal model for MERS coronavirus-induced acute respiratory distress syndrome, produced by CRISPR/Cas9 editing of the mouse gene encoding an ortholog of the virus receptor.

You can find TWiV #418 at, or listen below.

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TWiM 140: Small town, big science

At the Hamilton, Montana Performing Arts Center, Vincent speaks with three local high school graduates and two high school teachers about how Rocky Mountain Laboratories influenced school science programs and opened up career opportunities.

You can find TWiM #140 at, or listen and watch here.

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TWiV Special: Gary Nabel on World AIDS Day 2016

For World AIDS Day 2016, Vincent speaks with Gary Nabel, Chief Scientific Officer at Sanofi and former Director of the Vaccine Research Institute of NIAID, about his career and his work on HIV vaccines.

You can find this TWiV Special at, or listen and watch here.

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TWiV 417: O is the loneliest letter

The Fellowship of the Virus trace the early history of HIV in North America, based on genome sequences obtained from late 1970s archival sera, which also reveal that Gaetan Dugas was not Patient Zero.

You can find TWiV #417 at, or listen below.

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