Editing Ebola – how to tame one of the world’s deadliest viruses

Blogging on Peer-Reviewed ResearchIn a list of the most dangerous jobs in the world, ‘Ebola researcher’ must surely rank near the top. But if new research is anything to go by, it may soon fall several places. An international team of scientists have recently found a way to neuter the virus, making it easy to study without risking your life. The altered virus looks like Ebola and behaves like Ebola, but it can’t kill like Ebola. It should make studying the virus easier and most importantly, safer.

Ebola virusThe Ebolaviruses and their cousins, the closely related Marburg family, have a chilling and deserved reputation. In some outbreaks, 90% of those infected die from massive blood loss. There is no approved antiviral treatment. There is no vaccine. And given that it’s almost a rite du passage for infectious disease scientists to contract the contagion they study, working with Ebola is a delicate affair.

Maximum protection

Ebola research requires the highest level of safety possible – the “Biosafety Level-4” laboratory. The stand-alone facilities are designed to be easily sealed and impervious to animals and insects. All routes in and out, including all pipes and ventilation, are peppered with multiple airlocks, showers and rooms designed to prevent any chance of escaping viruses.

There are very few people who are qualified to work in such a prohibitive environment and those that do have to wear a Hazmat suit at all times and breathe from a self-contained oxygen supply. No wonder then that the majority of Ebola research doesn’t actually use live, infectious viruses.

Scientists must instead settle with isolated proteins, proteins shoved into other, less harmful viruses or even “virus-like particles”. But these artificial systems are different to the virus proper, and using them is like staring at a complex machine through a cobweb-covered keyhole. Peter Halfmann from the University of Wisconsin has found a way around this, opening the door for scientists to get a proper look at the virus.

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Sickle cell mice cured by stem cells reprogrammed from their own tails

Blogging on Peer-Reviewed ResearchSickle cell mice cured by stem cells reprogrammed from their own tailsStem cells have long been hyped as the shiny future of medicine. Their ability to produce to every type of cell in the body provided hope for treating diseases from Alzheimer’s, to Parkinson’s to stroke, by providing a ready supply of replacement cells. Despite years of slow progress, we are now tantalisingly close to turning this hype into reality and a new study suggests that the dawn of promised stem cell treatments is getting closer.

For the first time, scientists have cured mice of a genetic disorder called sickle cell anaemia using personalised stem cells reprogrammed from cells in their tails. The study is a powerful ‘proof-of-principle’ that reprogrammed stem cells could one day fulfil their potential in fighting human disease.

The personal touch is of the utmost importance. It’s no good just giving someone any old stem cells. Genetic differences between the donor and recipient could cause problems in the long-term and trigger attack and rejection from the hosts’ immune system in the short-term. The trick is to convert a patient’s own cells into personalised stem cells for their own private use.

Last year, a group of Japanese scientists found a way to do this in mice and produced “induced pluripotent stem cells” (iPSCs) that were very similar to embryonic stem cells. And just last month, I blogged about two breakthrough papers which showed that human cells could also be reprogrammed into iPSCs.

Now, Jacob Hanna and colleagues from the Whitehead Institute for Biomedical Research, the University of Alabama and MIT, have used these reprogrammed cells to cure a genetic disease – sickle cell anaemia.

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Human skin cells reprogrammed into stem cells

Blogging on Peer-Reviewed ResearchPotential is a sad thing to lose. Have you ever thought that it would be great to return to your childhood, when your options seemed limitless and life hadn’t taken you down increasingly narrow corridors of possibility? Wouldn’t it be great to rewind the clock and have the choice to start over?

Human skin cells are reprogrammed into stem cellsWhile that’s still the stuff of science-fiction, for some cells in your body it may soon be science fact. In one of the most exciting scientific breakthroughs of the year, two groups of scientists have found a way of turning adult human cells back into the stem cells of embryos.

Creating embryonic stem cells

Embryonic stem cells are the embodiment of potential. Armed with a trait called ‘pluripotency‘, they can give rise to every single type of cell and tissue in the body, renewing themselves indefinitely while their daughters take up the mantle of nerves, muscles, blood and more.

For years, stem cells have been touted as the Holy Grail of modern medicine. Within their membranes lies the potential to understand how we develop, test new drugs and most importantly, provide replacement cells to treat Alzheimer’s, Parkinson’s, spinal cord injuries, diabetes, stroke and more.

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Drugs and stimulating environments reverse memory loss in brain-damaged mice

Scientists have restored lost memories in brain-damaged mice by giving them an experimental group of drugs, or by placing them in a stimulating environment. Their remaining neurons re-wired themselves and retrieved memories that had been misplaced, not lost, providing hope for treating human conditions like dementia and Alzheimer’s disease.

Dementia results in massive neuron loss, but that doesn’t mean memories are destroyed.You swallow the pill. As it works its way through your digestive system, it slowly releases its chemical payload, which travels through your bloodstream to your brain. A biochemical chain reaction begins. Old disused nerve cells spring into action and form new connections with each other. And amazingly, lost memories start to flood back.

The idea of a pill for memory loss sounds like pure science fiction. But scientists from the Massachussetts Institute for Technology have taken a first important step to making it a reality, at least for mice.

Andre Fischer and colleagues managed to restore lost memories of brain-damaged mice by using a group of drugs called HDAC inhibitors, or by simply putting them in interesting surroundings.

They used a special breed of mouse, engineered to duplicate the symptoms of brain diseases that afflict humans, such as Alzheimer’s. The mice go about their lives normally, but if they are given the drug doxycycline, their brains begin to atrophy.

The drug switches on a gene called p25 implicated in various neurodegenerative diseases, which triggers a massive loss of nerve cells. The affected become unable to learn simple tasks and lose long-term memories of tasks they had been trained in some weeks earlier.

A richer environment

Lost memories can be recovered by encouraging surviving neurons to re-wire themselves.Fischer moved some of the brain-damaged mice from their usual Spartan cages, to more interesting accommodation. Their new cages were small adventure playgrounds, replete with climbing frames, tunnels and running wheels, together with plentiful food and water.

In their new stimulating environments, the mice returned to their normal selves. Their ability to learn improved considerably, and amazingly, seemingly lost memories were resurrected.

They didn’t grow any new neurons, and their brains remained the same size. But Fischer found that they did have many more synapses – the connections between nerve cells – than brain-damaged peers. Even though they had lost a substantial number of neurons, their enriched environments triggered the surviving cells to re-wire themselves.

These experiments suggest that lost memories are in fact not lost at all, but misplaced. The dead neurons take important connections with them and the survivors, though incommunicado, still retain latent traces of memory.

When they are jolted into action and form new networks, these trace memories are reinstated. And that provides genuine hope for people affected by dementia, Alzheimer’s and other conditions.

Memory-restoring drugs

Brain damage from Alzheimer’s disease could potentially be reversed by HDAC inhibitors.It would be a touch silly to suggest putting such people in the equivalent of a large playpen. But Fischer also found a group of drugs called HDAC inhibitors that have the same effect – the molecular equivalent of a stimulating environment.

HDACs or histone deacetylases control whether genes are switched on or off by altering other proteins called histones. DNA winds around histones like spools, which serves to package this long and unwieldy molecule into a compact and more manageable form.

HDACs change the histones so that they wrap more tightly around DNA and render its genetic code unreadable. Any genes contained in these stretches of DNA are silenced. Drugs like sodium butyrate (SB) neutralise HDACs, freeing DNA from the repressive grip of histones.

Any silenced genes can now be freely switched on and among these, are genes that allow the brain’s neurons to sprout new synapses. The details still need to be ironed out, but the results are clear – just like mice housed in fun cages, those treated with SB regained lost memories.

The next steps

Naysayers might point out that these results are all very good for mice, but are a long way off benefiting people. But while our brains outclass those of mice, we appear to store memories in very similar ways. New experienced are initially encoded among the neurons of the hippocampus, only to be transferred into deeper and long-term stores about three or four weeks later.

Four years ago, a man who had been barely conscious for almost 20 years began to move and speak again. His nerves, badly damaged by a car crash, had started to re-wire themselves and form new connections, in the same way that Fischer’s rats did. The possibilities are there; it’s just the method that needs refinement.

At the moment, the biggest problem with Fischer’s approach is that it’s akin to shooting at a fly with a shotgun. HDAC inhibitors have far-reaching effects on a multitude of different genes. It’s fortunate that these include genes that lead to brain re-wiring, but such a scattershot approach is prone to collateral damage.

Documenting the full actions of HDAC inhibitors is vital. It will allow scientists to understand what side effects such treatments would have in people, while designing more sophisticated drugs with a narrower range of targets.

Reference: Fischer, Sananbenesi, Wang, Dobbin & Tsai. 2007. Recovery of learning and memory is associated with chromatin remodelling. Nature doi:10.1038/nature05772

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Sneaking medicines past the brain’s defences

The brain is surrounded by a protective barrier designed to keep infections out. But it can also block out medicines intended to treat brain diseases. Now, scientists have developed a way of sneaking helpful proteins across the barrier by giving them fake molecular ID.

Using genetic engineering, a group of scientists have developed a way of sneaking a virus past the brain’s defences. Don’t panic – this isn’t some nightmare scenario. It could be the first step to curing a huge number of brain diseases.

The brain needs to be protected from incoming infections.The brain seems incredibly well protected amid its shell of bone and cushioning fluid. But even the strongest of forts needs supply lines, and brain is no exception.

A dense network of blood vessels carries vital oxygen to its cells. These vessels are a potential vulnerable spot, providing access for bacteria and other disease-causing organisms to migrate in from other body parts.

But even these weak spots are heavily guarded. The blood vessels in the brain are lined with a tightly packed layer of cells that restrict the flow of molecules from blood to brain. These cells form a protective shield called the blood-brain barrier, or BBB.

It is a superb defence but it can do its job too well. Not only does it block out dangerous microbes, but it can also exclude large proteins and drugs designed to treat brain diseases. Usually, these large molecules need to be distributed throughout the entire brain to be effective. With the BBB in the way, they don’t stand a chance.

Now, Brian Spencer and Inder Verma from the Salk Institute of Biological Studies have come up with a way to disguise helpful molecules to sneak them past the brain’s defences.

The blood brain barrier controls the import of molecules into the brain with the tight security of airport immigration.Their method exploits special gates in the barrier that control the import of essential nutrients and molecules like cholesterol into the brain. These molecules are escorted by a large protein called apoliprotein B (apoB), and are presented to sentinel proteins that guard the gates.

One of these guardians, called LDLR, is designed to recognise a specific segment of apoB. Once it has confirmed the visitor’s identity, it escorts apoB and the molecules it accompanies through the barrier. The whole system works with the tight control of a maximum security prison.

Spencer and Verma managed to fool the system. They took the part of apoB that is recognised by LDLR and stuck it to various proteins, giving them the molecular equivalent of a fake pass.

First, they tested their method in mice. They injected the animals with a harmless virus designed to travel to its liver and spleen. There, the virus sets about building the disguised protein, which is secreted en masse into the bloodstream.

The beauty of this method is that it works after a single injection that transforms the liver and spleen into factories for the protein of choice.

Spencer and Yerma’s method works for glucocerebrosidaseTheir first candidate was GFP, a jellyfish protein that glows in the dark with a greenish hue, allowing it to be easily tracked. Sure enough, the injected mice soon gave off a greenish glow from their brains and the rest of their central nervous systems.

Better still, their method showed real practical potential by sneaking an enzyme called glucocerebrosidase (right) into the brain. Glucocerebrosidase is vital for the storage of fats. People who lack it suffer form a condition called Gaucher’s disease, where fatty desposits collect on various organs and cause brain damage, among other symptoms.

The disease is relatively easy to fix using regular injections, but the resulting brain damage is not for the injected enzyme is usually repelled by the blood-brain barrier. But Spencer and Verma’s method may change all that.

The duo fully admit that their work is merely a first step, but it is an important one nonetheless. The technique must first be refined and tested in people before it can be widely used. Developing drugs and proteins for treating brain disorders is pointless if those new medicines just congregate uselessly outside the blood-brain barrier. Spencer and Verma may have given them a way in.


Reference: Spencer & Verma. 2007. Targeted delivery of proteins across the blood-brain barrier. PNAS 104: 7594-7599.

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Genetically-modified mosquitoes fight malaria by outcompeting normal ones

Genetically-engineered mosquitoes that are resistant to the malarial parasite could be the key to reducing the burden of malaria. In laboratory experiments, they are stronger and fitter than their normal peers and rapidly dominate the population.

Fighting malaria with mosquitoes seems like an bizarrely ironic strategy. But that’s exactly what many scientists are trying to do.

The Anopheles mosquito carries the malaria parasite Plasmodium, but at a cost to its own health.Malaria kills one to three million people every year, most of whom are children. Many strategies for controlling it naturally focus on ways of killing the mosquitoes that spread it, stopping them from biting humans, or getting rid of their breeding grounds.

But the mosquitoes themselves are not the real problem. They are merely carriers for the true cause of malaria – a parasite called Plasmodium. It suits neither mosquitoes nor humans to be infected with Plasmodium, and by helping them resist it, we may inadvertently help ourselves.

With the power of modern genetics and molecular biology, scientists have produced strains of genetically engineered mosquitoes that cannot transmit the malarial parasite.

These ‘GM-mosquitoes’ carry a modified gene – a transgene – that produces chemicals which interfere with Plasmodium’s development. Rather than becoming suitable carriers, the modified mosquitoes are death for any invading Plasmodium.

But scientists can’t very well change the genes of every mosquito in the tropics. To actually reduce the burden of malaria, the genetic changes that induce malaria resistance need to be spread throughout the mosquito population. The easiest way to do this is, of course, to let the insects do it themselves.

And Mauro Marrelli and colleagues from the Johns Hopkins University have found that they are more than up to the task.

The Plasmodium parasite causes malaria but can’t survive in genetically modified mosquitoes.They kept cages full of equal numbers of engineered and normal mosquitoes and fed them on the blood of mice infected by Plasmodium. After nine generations, they found that the engineered insects had become proportionally more common, making up about 70% of the total population.

Like most parasites, Plasmodium affects the health of its host. So mosquitoes that are parasite-resistant are stronger and fitter than their infected peers. Marrelli found that they were about 25% less likely to die early, and had more young, with every female laying an average of 60 eggs compared to 43.

With these advantages, the transgenic mosquitoes outlasted and out-bred normal ones, and quickly established a majority in the population.

But if the advantages to resistance are so great, why haven’t naturally-resistant mosquitoes replaced non-resistant ones? Other studies have shown that resistant mosquitoes fight off Plasmodium with the help of hyperactive immune systems, but have no evolutionary advantages over carriers.

Marrelli thinks that because chronic immune responses produce health problems of their own, that cancel out the advantage of not carrying Plasmodium. In contrast, the transgenic mosquitoes are simply expressing a gene that is mostly harmless. The gene also kills Plasmodium early on in its life cycle, well before it triggers the body’s own immune system.

Even though a single transgene copy does not affect the modified insects’ health, it appears that two copies might have some as-yet-unknown health consequences. This may explain why the resistant mosquitoes in Marrelli’s experiments did not totally dominate the population, but plateaued at 70%. The strongest mosquitoes are those with just one copy of the gene.

Malaria affects tropical countries around the world.This means that introducing the engineered mosquitoes into the wild would not completely wipe out their disease-spreading cousins. But it would still drastically cut their numbers. Considering that malaria infects over 400 million people a year, reducing this number by 70% would be a monumental victory for international health.

Nonetheless, Marrelli is cautious about the future of malaria-resistant strains. These experiments are a proof-of-principle and their results may not bear out as planned in practice.

In the field, only a relatively small proportion of mosquitoes become infected, and he expects the spread of the transgene to be slower. But if it becomes established, it could complement other programmes for controlling malaria, by making it very hard for the parasite to re-colonise a cleared area after it has been eradicated.

 

Reference: Marrelli, Li, Rasgon & Jacobs-Lorena. 2007. Transgenic malaria-resistant mosquitoes have a fitness advantage when feeding on Plasmodium-infected blood. PNAS 104: 5580-5583.

Images: Plasmodium image by Ute Frevert

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Magnifection: mass-producing drugs in record time

Monoclonal antibodies are a rapidly emerging group of drugs with the potential for treating diseases from arthritis to cancer. Now, a new technique called ‘magnifection’ is set to drastically reduce the time and expense needed to make these molecules, ensuring that enough can be made to treat patients at a reasonable cost.

Developing new drugs is a very expensive process.

Imagine reading the paper to find that a new wonder drug has been created that could save your life, if only you could afford it. Alternatively, put yourself in the shoes of the authorities that must decide not to offer powerful new drugs on the NHS because they simply aren’t cost-effective enough. These situations are all too common-place and are largely a result of the extremely high costs of drug development. But recently, scientists at Icon Genetics and Bayer Bioscience have made a tremendous step toward lowering these costs for some of the most promising new treatments.

The treatments in question are called ‘monoclonal antibodies’ or ‘MAbs’, synthetic versions of the natural antibodies that our immune systems use to identify and neutralise infectious agents. MAbs are specially shaped to act like molecular gloves, sticking onto a target of choice and inactivating it by blocking interactions with other molecules.

The most famous member of this group, the breast cancer drug Herceptin, is one of a handful of currently available MAbs. But they are about to be joined by many more – over 150 MAbs are in development and the market for them is likely to exceed £10 billion.

But no matter how good these new biotechnological wunderkinds are, they will be worthless unless they reach the patients they are designed to benefit. And with the cost of treatment courses exceeding tens of thousands of pounds, that is looking unlikely. Every stage of the manufacturing process from raw materials to equipment is exorbitantly expensive and drives the inflated prices of the end product. As such, only better, cheaper and more effective production methods will enable scientists to fully realise the potential of these designer molecules.

Manufacturing monoclonal antibodies takes a lot of time and money. Currently, all MAbs are grown using mammalian cells and over the past twenty years, a variety of other hosts from insects to bacteria to yeast have been considered as replacements in the search for efficiency. But all these choices have crippling flaws, with the most significant being massively lengthened development times.

Plants, one of the many possible host options, are no exception to this. While mammalian cells take at most a year to produce a gram of antibodies, plants require at least two.

Combined with complex genetics, long life-spans, the need for land and the threat of contaminating wild stocks, plants seem to be a dead end as far as antibodies go. But Anatoli Giritch and colleagues have revived their potential in spectacular fashion.

Their technique, called ‘magnifection’ uses infectious agents like bacteria and viruses to carry the instructions for making antibodies throughout the plant’s cells, hidden under multiple layers of encryption. Each antibody is a union of different molecules and the recipes for making these separate components are encoded in two different viruses – one that usually infects tobacco and another that targets potatoes. Each virus is then split into different segments and loaded into a type of bacteria called Agrobacterium.

Once Agrobacterium infects the plant, it spreads rapidly and eventually reaches about 95% of its leaf cells. The addition of a specific enzyme then acts as a trigger, causing the bacteria to begin assembling viruses. These spread locally across neighbouring cells and begin churning out antibody components, turning the plant into a monoclonal antibody factory.

The result is MAb production on a scale completely unheard of. It took this system just two to three weeks to churn out a gram of antibodies, utterly smashing the current record of 6 months. And each kilogram of host leaves were yielding 10-100 times more raw product than any other production system.

The key to magnifection’s success lies in the choice of viruses. While many virus combinations compete with each other for a host’s resources, the tobacco mosaic virus and potato virus X seem to co-exist harmoniously. Giritch et al. believe that they use different host proteins to replicate themselves and so never draw upon the same pool of resources.

The duo are now trying to tweak the magnifection protocol to achieve even better results. They will consider different virus combinations and will try to add chaperone molecules that help antibody components to combine with greater efficiency. Regardless of any further improvements, the implications for magnifection are tremendous. The technique is rapid, versatile and can be easily scaled-up. The result will be more drugs at lower prices leading, hopefully, to a better deal for patients.

Magnifection is particularly suited to situations where we might need to manufacture vast quantities of antibodies or other complex molecules in a short amount of time. A viral pandemic, or a biological terror attack, are just two examples of such emergencies.

Giritch, Marillonnet, Engler, van Eldik, Botterman, Klimyuk & Gleba. 2006. PNAS 103: 14701-14706.