TWiV 459: Polio turns over a new leaf

The TWiV team reviews the first FDA approved gene therapy, accidental exposure to poliovirus type 2 in a manufacturing plant, and production of a candidate poliovirus vaccine in plants.

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The $475,000 drug

KymriahThe US Food and Drug Administration recently approved the first gene therapy, Kymriah, to treat B-cell acute lymphoblastic leukemia. It uses a lentivirus to modify the patient’s T cells to kill tumor cells.

Acute lymphoblastic leukemia, or ALL, is caused by uncontrolled growth of B cells, which normally produce antibodies to fight off infections. It is the most common cancer in children. The uncontrolled production of these cells by the bone marrow causes a shortage of blood cell production, leading to fever, increased risk of infection, and anemia. These B cells have on their surfaces a protein called B19 – which is the key to understanding how Kymriah works.

The therapy begins with drawing blood from the patient, from which T cells are purified. These T cells are then infected with a lentivirus vector that encodes the gene for a chimeric antigen receptor (CAR) that recognizes the B19 protein. The CAR protein is synthetic – it doesn’t exist in any cell. The extracellular domain consists of a single-chain antibody directed against the B19 protein (pictured). The cytoplasmic domain of the protein contains sequences that stimulate the T cells to proliferate.

After the T cells are infected with the CAR-encoding lentivirus, they are infused back into the patient. Upon encountering a B cell producing B19, the T cells bind to the protein and kill the cells, thus eliminating the cancer.

Kymriah was licensed by the FDA after testing showed it was effective, leading to remission of cancers in the majority of children treated. But the price tag is steep – $475,000 for a treatment, and other similar drugs in the pipeline could be even more expensive. The drug makers justify the high price by arguing that it reflects the value to the patient – it saves their lives.

But vaccines also save lives, and they cost much less than Kymriah. The difference, of course, is that vaccines are given to millions of people. Kymriah, in contrast, would be given to thousands in the US.

In other words, the high cost of Kymriah reflects the need of drug companies to recoup their high investment in developing and testing the drug – not the value to the patient.  Rather than spinning a false story about the value of a drug to a patient, the drug companies should be honest about the pricing of their products. No wonder the public has a negative image of the industry.

TWiV 458: Saliva of the fittest

The TWiVians present an imported case of yellow fever in New York City, and explain how a dengue virus subgenomic RNA disrupts immunity in mosquito salivary glands to increase virus replication.

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Roger W. Hendrix, 74

Virologist Roger W. Hendrix died on 15 August 2017. I only met Roger once, at the 2011 ASM meeting in New Orleans where we recorded an episode of This Week in Virology. The video of that episode is below, starting at my conversation with Roger at 30:34. Harmit Malik and Rachel Katzenellenbogen were my other guests on TWiV 135.

Thirty-five years later

Thirty-five years ago this month, in September 1982, I arrived at Columbia University College of Physicians & Surgeons to open my virology laboratory. I brought with me an infectious DNA copy of the poliovirus RNA genome, the first of its kind, and a lot of enthusiasm. Over the years we used this infectious DNA to study poliovirus neurovirulence, pathogenesis, and translation, among other topics; I wrote grant applications, published papers, and trained new scientists. In short, I was a typical academic scientist.

My career forked in 2000 with the publication by the American Society for Microbiology of the textbook Principles of Virology. Because this book was written by process, not by virus, each of the authors learned far more virology than ever before. As a consequence of writing this book, I became interested in disseminating virology to the public. Beginning with virology blog in 2004, I began to use social media to communicate science. This interest has lead to a collection of blogs, podcasts, lectures, and videos, in addition to four editions of Principles of Virology.

Recently virologist Islam Hussein, founder of Virolvlog and an avid science communicator, decided to summarize my modest scicomm career with an infographic. I’m grateful to Islam for this lovely chart, which was produced by Mohamed Gaawan. Here’s to the next 35 years.

Dr.-Vincent-Racaniello

TWiV 457: The Red Queen meets the White Rabbit

Brianne returns to the TWiV Gang to discuss the distribution of proteins on the influenza viral genome, and the evolution of myxoma virus that was released in Australia to control the rabbit population.

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A plasmid on the road to becoming a virus

Origin of virusesPlasmids have been discovered that can move from cell to cell within membrane vesicles in a species of Archaea (link to paper). They provide clues about the origin of virus particles.

Electron microscope analysis of the culture medium from Halobrum lacusprofundi R1S1, an Archaeal strain from Antarctica, revealed spherical particles which were subsequently shown to contain a 50,000 base pair circular double-stranded DNA molecule. When added to H. lacusprofundi, the purified membrane vesicles entered the cells and the DNA replicated.

Nucleotide sequence analysis of the plasmid within the membrane vesicles revealed 48 potential protein coding regions and an origin of DNA replication. None of these proteins showed any similarity to viral stuctural proteins, leading the authors to conclude that these particles are not viruses.

Many of the proteins encoded in the plasmid DNA were found in the membrane vesicles. Some of these are similar to cell proteins known to be involved in the generation of membrane vesicles. However no DNA polymerase-like proteins are encoded in the plasmid. These data suggest that the plasmid encodes proteins that generate, from the membranes of the cell, the vesicles needed for their transport to other cells. However, replication of the plasmid is carried out by cellular DNA polymerases.

It is likely that the plasmid-containing membrane vesicles are precursors of what we know today as virus particles. It is thought that viruses originated from selfish genetic elements such as plasmids and transposons when these nucleic acids acquired structural proteins (pictured; image credit). Phylogenetic analyses of the structural proteins of many enveloped and naked viruses reveal that they likely originated from cell proteins on multiple occasions (link to paper).

The membrane-encased Archaeal plasmid seems well on its way to becoming a virus, pending acquisition of viral structural proteins. Such an early precursor of virus particles has never been seen before, emphasizing that science should not be conducted only under the streetlight.

TWiV 456: Be careful of canons

Brianne joins the TWiVMasters to explain how mutations in genes encoding RNA polymerase III predispose children to severe varicella, and detection of an RNA virus by a DNA sensor.

 

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Phage synergy with the immune system

bacteriophage modelNot long after their discovery, viruses that infect bacteria – bacteriophages – were considered as therapeutic agents for treating infections. Despite many years of research on so-called phage therapy, clinical trials have produced conflicting results. They might be explained in part by the results of a new study which show that the host innate immune system is crucial for the efficacy of phage therapy.

When mice are infected intranasally with Pseudomonas aeruginosa (which causes pneumonia in patients with weak immune systems), the bacterium multiplies in the lungs and kills the animals in less than two days. When a P. aeruginosa lytic phage (i.e. that kills the bacteria) is instilled in the nose of the mice two hours after bacterial infection, all the mice survive and there are no detectable bacteria in the lungs. The phage can even be used prophylactically: it can prevent pneumonia when given up to four days before bacterial challenge.

The ability of phage to clear P. aeruginosa infection in the mouse lungs depends on the innate immune response. When bacteria infect a host, they are rapidly detected by pattern recognition receptors such as toll-like receptors. These receptors detect pathogen-specific molecular patterns and initiate a signaling cascade that leads to the production of cytokines, which may stop the infection. Phage cannot clear P. aeruginosa infection in mice lacking the myd88 gene, which is central to the activity of toll like receptors. This result shows that the innate immune response is crucial for the ability of phages to clear bacterial infections. In contrast, neither T cells, B cells, or innate lymphoid cells such as NK cells are needed for phage therapy to work.

The neutrophil is a cell of the immune system that is important in curtailing bacterial infections. Phage therapy does not work in mice depleted of neutrophils. This result suggests that humans with neutropenia, or low neutrophil counts, might not respond well to phage therapy.

A concern with phage therapy is that bacterial mutants resistant to infection might arise, leading to treatment failure. In silico modeling indicated that phage-resistant bacteria are eliminated by the innate immune response. In contrast, phage resistant bacteria dominate the population in mice lacking the myd88 gene.

These results demonstrate that in mice, successful phage therapy depends on a both the innate immune response of the host, which the authors call ‘immunophage synergy’. Whether such synergy also occurs in humans is not known, but should be studied. Even if observed in humans, immunophage synergy might not be a feature of infections in other anatomical locations, or those caused by other bacteria. Nevertheless, should immunophage synergy occur in people, then clearly only those with appropriate host immunity – which needs to be defined – should be given phage therapy.

TWiV 455: Pork and genes

Erin Garcia joins the TWiVirions to discuss a computer exploit encoded in DNA, creation of pigs free of endogenous retroviruses, and mutations in the gene encoding an innate sensor of RNA in children with severe viral respiratory disease.

 

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