Messenger RNA technology, so long in the wings, has leapt from understudy to main act. Its technology is deceptively simple, and its potential goes well beyond our current COVID predicament into some of our most prevalent diseases, from the flu to heart disease and even cancer.
In 1989, when Katalin Karikó submitted her first grant application to develop messenger RNA-based gene therapy, she knew she had a game-changing technology in her hands. But the Hungarian biochemist, then a professor at the University of Pennsylvania, could only dream of using mRNA in humans. In theory an almost perfect platform to make drugs and vaccines, mRNA was stacked with practical problems that would keep it away from clinical use for decades.
Then, at the end of 2019, a strange new infectious disease appeared in Wuhan and spread quickly across the planet, changing the world and sending countries and companies racing for a medical treatment that would stop the pandemic’s illness and fatalities. mRNA has become one of the saviour technologies of the COVID era; now, that success is just the first step in a transformation in how we might recognise – and cure – everything from the flu to cancer.
The concept behind mRNA technology is strikingly simple. mRNA – which stands for messenger ribonucleic acid – is a single-stranded chain of nucleotides. In an organism, it acts as a messenger, a short-lived intermediary that communicates the information contained in our genes to the ribosomes. These are the cell’s protein factories, which read the code and translate it into a protein.
Special delivery: how mRNA technology works at a cellular level
1. Uptake by endocytosis
The liposome, or nanoparticle, is swallowed by the cell through endocytosis, the process by which cells absorb external material by engulfing it in a pouch – vacuole – of cell membrane called an endosome.
2. Endosomal escape
The endosome’s membrane breaks down, and the liposome is released inside the cell.
3. Release from carrier
The presence of enzymes inside the cell degrades the liposome. The mRNA strings are released and can travel to the protein-making ribosomes.
4. Translation
In the ribosomes, the mRNA strings are read and translated into antigens – pathogen proteins. The resulting antigens are exposed to the cell surface, where immune system cells recognise them as foreign, triggering an immune response that creates a memory for the antigen. If the real pathogen appears, immune cells recognise the same antigen and attack.
Scientists have learned to transcribe a genetic sequence from a string of DNA to a string of mRNA. A synthetic mRNA sequence with the right blueprint can be turned into a drug that, like a message in a bottle, delivers instructions into a cell to turn it into a literal bodyguard through its specialised resulting protein.
In a vaccine, the mRNA string encodes the recipe to make the antigen – a protein from the pathogen we want to protect ourselves from. Once the vaccine is inside the cells, the instructions are used to synthesise the antigen, which is exposed to the cell surface. Then, a subset of immune system cells recognises the antigen as foreign, triggering an immune response. This mechanism creates a memory for this antigen. Later, when the real pathogen is present, those cells recognise the same antigen and react rapidly and strongly against the infectious agent.
After the protein has been produced, the mRNA is degraded via physiological, metabolic pathways. “It’s a transient thing,” says Associate Professor Archa Fox, a molecular biologist and mRNA expert at the University of Western Australia. This desirable trait reduces the risk of unwanted side-effects by uncontrolled protein expression.
Two main issues had hindered the advance of the technology. “One was what we call a delivery problem,” says Fox. That same transience that makes mRNA desirable is also a problem: how to protect it from degradation during its journey throughout the body and into cells. In the late 1990s, researchers were able to pack the fragile messenger into shells of fat molecules called lipid nanoparticles, which had been studied for almost two decades as a possible delivery mechanism for anti-cancer drugs. The lipidic vehicle protects mRNA from thermal degradation and shields it from destructive enzymes while shunting it to the cell.
There was another major problem. The body strongly rejects RNA from outside sources, probably to avoid being hijacked by pathogens, and in early studies the mRNA often proved so toxic that it killed the lab animals it was tested on.
It took until 2005 for Karikó, who now oversees mRNA research at BioNTech, to discover that by adding pseudouridine into the mRNA she could fool the cell into thinking that the delivered mRNA was not a foreign invader. This breakthrough laid the foundations for the apparent overnight success of today’s mRNA COVID-19 vaccines.
For over three decades, researchers across the world had been working on mRNA therapeutics that can instruct the body to make its own drugs. With COVID, that platform has reached industrial scale, and offers opportunities for cures that have eluded answers thus far.
“It’s a flexible platform,” says Professor Thomas Preiss, a molecular biologist and mRNA expert at the Australian National University.
A vaccine for plants
Just as humans can catch a cold, plants can also get viral infections. It generally starts with an insect bite. The virus only needs to reach a single cell to hijack its machinery and begin replication. Progeny viruses are released to neighbouring cells, and the infection spreads. Soon, the virus gets to the plant’s vascular system and quickly spreads to the rest of the plant.
Plants also have an immune system. When a virus infects a plant cell, it often releases RNA in the form of mRNA or double-stranded RNA to replicate. The plant immune system recognises the viral RNA and activates enzymes that chop and neutralise it to avoid the spread of the disease. Infected cells can send a signal to neighbouring cells activating antiviral defences even before the virus’ arrival.
The tactic is deadly for the virus, but not always efficient.
Viruses are part of the pest and pathogen burden that reduces global food production by 20% to 40%. With a growing global food demand and the effect of climate change on crops, new, more effective virus control is needed.
The use of insecticides, pesticides and genetic modification are the currently available methods to protect plants from viral infections. But these methods have significant drawbacks.
Insecticides and pesticides are broad-spectrum, which means they can damage the target pests and other flora and non-pest insects, while genetic modification has significant issues surrounding acceptance and regulation.
Researchers at the University of Queensland have found a way to stimulate the plant’s immune system to mount a defence against potential viruses.
Their technology, called BioClay, works very much like a vaccine. The scientists take the RNA sequence from the pathogen, load it on a clay nanomaterial and spray it on crops.
The virus RNA slowly releases on the surface of the leaves. It enters the plant and primes the immune system to recognise the invader without causing the infection.
The clay sequentially degrades in the presence of natural carbon dioxide and moisture.
Various research groups worldwide are working on RNA vaccines for plants. These vaccines represent a much simpler and faster technique than genetically engineering a plant for viral resistance and allow scientists and farmers to keep up with the quick evolution of viral pathogens.
mRNA vs the flu
The most likely next step for mRNA is as a protection against influenza. Before COVID-19 came along, many biotech companies were working on developing an mRNA flu vaccine, says Professor Damian Purcell, a virologist at the University of Melbourne and head of the Department of Microbiology and Immunology at the Peter Doherty Institute.
The flu is caused by several different strains of the influenza virus that reside in animals – zoonotic reservoirs – ready to transition and recombine with circulating human strains. Current flu vaccines suffer from a mismatch between the quickly mutating nature of the influenza virus – which requires the formulation of a new vaccine each year –and the somewhat antiquated and slow method we use to make vaccines against it. “The mRNA technology can adapt much more easily and more quickly,” says Purcell.
The first commercial flu vaccine was licensed in the US in 1945, and the method we use today has not changed much since then. Vaccine makers isolate the target flu virus strains, grow them in hen eggs, then purify them from their whites. The viruses are then chemically inactivated and injected into patients. The whole process takes several months.
In a newer method, a viral protein rather than the whole virus is grown in a laboratory – a technology called recombinant protein vaccines. If the right target is chosen, that single piece of virus can prime the immune system just as effectively as the whole virus.
But protein-based vaccines have downsides. Proteins are complex molecules, hard to handle in the laboratory, more difficult to manufacture, and purifying them is a challenge, says Purcell.
According to Purcell, manufactured proteins might not be exactly the same as those expressed in virus-infected cells. “The benefit of an mRNA vaccine is that it will almost certainly gather the same kind of modifications that would normally occur in an infected cell,” Purcell says. That means that the antibodies the vaccine generates are highly specific to the target antigen.
Currently, influenza vaccines contain three or four different strains every year. The new mRNA technology may allow even more variations to be incorporated into one vaccine formulation. According to Purcell, “mRNA might provide a way to tune to northern or southern hemisphere outbreaks specifically.”
He says scientists have collected a wealth of genomics data on circulating influenza strains in humans over the past century that could help identify parts of the virus that do not mutate. Encoding those fragments into an mRNA vaccine offers the possibility of developing a “universal flu vaccine” that takes away the need for annual boosters.
Melbourne-based Seqirus is one of the biotech companies working on next-generation mRNA influenza vaccines based on self-amplifying mRNA (sa-mRNA). This messenger gives the body instructions to amplify the mRNA, increasing protein production in the cells. Evidence shows that sa-mRNA might mount a higher immune response at the same dose level of mRNA. “The COVID-19 pandemic has accelerated global research in mRNA from what was previously a promising science to what now looks like a viable technology platform on an industrial scale,” says Ethan Settembre, vice president of Seqirus Research.
Seqirus is currently undertaking a pre-clinical trial on an sa-mRNA-based flu vaccine, and plans to commence human clinical trials next year.
Moderna and BioNTech have at least six mRNA vaccines against flu in their development pipelines.
What about other diseases?
In light of the effectiveness of the COVID-19 mRNA vaccines, numerous biotech companies around the world have turned their focus to research into mRNA vaccines against the many tropical infectious diseases we still don’t have protection for.
Both Moderna and BioNTech have several candidates in development or undergoing early clinical trials, including possible treatments for Zika, Nipah, dengue, herpes, hepatitis and malaria. There are also many candidates for HIV, probably the virus that has proved the hardest to fight.
Purcell, who has researched an HIV vaccine for the past two decades, says HIV has several levels of complexity.
Most people infected with HIV take years to develop antibodies against it. “It seems to be virtually invisible [to the immune system],” says Purcell. Only a small fraction of people with long-term HIV infections develop broadly neutralising antibodies against the virus. Most patients develop antibodies against one strain of the virus. But the virus evolves within the patient through the course of the infection, making HIV a “moving target” for a vaccine.
“There’s a genetic insufficiency in humans, and there’s a remarkable genetic evasive capability from the virus,” Purcell says.
A series of vaccinations, each showing the immune system different snapshots of HIV, might elicit broadly neutralising antibodies. But finding the right genetic components of the virus will take lots of trial and error, and fine-tuning that with traditional vaccine-making techniques could take decades. “mRNA could sidestep [HIV] lines of defence,” says Purcell. “This is 30 years of research beating our heads against the wall.”
Can you mend a broken heart?
mRNA therapies show promise in treating cardiac diseases, which affect 64 million people worldwide. Regenerative therapy aims to direct heart cells to produce proteins to regenerate damaged heart tissue. mRNA protein replacement therapies regulate basic mechanisms of cardiovascular disease, such as arterial cholesterol formation.
Another leading cause of death worldwide is heart disease, and mRNA research shows promise here as well. mRNA-based protein replacement therapies can help regulate the basic mechanisms of cardiovascular disease, including the formation of cholesterol, the build-up of plaques and cells’ death after a heart attack. One example of protein replacement therapy is the so-called localised regenerative therapy, which takes advantage of the body’s own healing mechanism.
The role of mRNA regenerative therapy is to instruct heart cells to produce proteins that help regenerate heart tissue that has been damaged by cardiovascular disease. One mRNA drug, currently being tested in a Phase 2 trial by Moderna and AstraZeneca, expresses a vascular endothelial growth factor (VEGF-A), allowing regeneration of blood vessels after an injury.
The VEGF-A encoded mRNA is injected into the heart during coronary artery bypass surgery, explains Preiss, to instruct cells to produce VEGF-A. This protein promotes angiogenesis – the formation of new blood vessels – which reduces the likelihood of a heart attack.
Such therapies could help the more than 64 million people who live with cardiovascular diseases globally, but directly injecting the mRNA drug into the heart is an invasive procedure. “A lot of progress could come from improving the targeting vehicle,” Preiss says.
One likely candidate builds on the decades-long research on nanoparticles. Nanoparticles can be engineered to target certain types of cells, so it’s possible to create one that can selectively penetrate heart cells and leave other organs alone.
Custom cancer vaccines
Perhaps the holy grail of medical science in the 21st century is a cure for cancer. In recent years, cancer vaccines and immunotherapies have promised an alternative to treating malignancies.
Preventive cancer vaccines have been approved for some cervical cancers, head and neck cancer, and liver cancer. Therapeutic cancer vaccines are clinically used for early-stage bladder cancer and prostate cancer.
To every patient their own cancer vaccine
Cancer vaccines could revolutionise treatment by encoding the recipe for cancer-specific antigens of each patient. The vaccine “wakes up” the patient’s immune system to recognise cancer cells and kills them.
1. Cancer analysis
The DNA from a single patient’s cancer cells is genomically sequenced to identify antigens specific to that patient’s cancer. The antigens’ genetic codes are transcribed into an mRNA string.
2. Vaccine delivery
A personalised vaccine is injected into the patient, whose cells are then capable of flagging the cancer’s antigen protein on their surface and triggering an immune response.
3. Immune activation
T-cells – killer cells that are part of the immune system – recognise the antigen protein as foreign and memorise it for immediate and future attacks.
4. Attacking the cancer
T-cells can now identify cancer cells as invaders and latch on to them, causing their apoptosis – cell death – without affecting other cells in the body.
Illustrations: Greg Barton. Elements: Fancy Tapis, Ttsz, Sciepro / Getty Images
Researchers at Pfizer, Moderna and a large number of other biotech companies are exploring mRNA vaccines in which the mRNA containing the recipe for cancer-specific antigens is delivered into T-cells – killer cells that are part of the immune system. These are instructed to recognise cancer cells and causes apoptosis – cell death – without affecting other cells in the body.
“Traditionally, therapeutics have targeted the tumour, but now we target the immune system,” says Professor Peter Leedman, a cancer medicine researcher at the Harry Perkins Institute in Perth. Because cancer cells differ widely between patients, the magic of the mRNA vaccine is its ability to be tailored to fit the antigen repertoire of each patient.
The theory is simple. Scientists analyse the DNA from the patient’s cancer cells to identify antigens specific to that patient’s cancer. They transcribe the antigen’s genetic code into an mRNA string and inject it back to the patient’s T-cells to direct the immune system’s attack against the cancer cells.
These personalised cancer vaccines are designed to deliver one custom-tailored therapy for one patient at a time.
It’s a revolution that could transform cancer treatment. Although chemotherapy and radiotherapy have become more and more tailored over recent decades, they’re still the equivalent of a sledgehammer compared to the potential fine artist’s chisel of personalised mRNA therapy. A fair comparison might be the design and manufacture of a prosthetic limb: a tailored, one-off piece of technology intended to give its recipient the maximum opportunity to live as “normally” as possible. It is, without exaggeration, life-changing.
The first proof-of-concept studies that proposed the idea of mRNA cancer vaccines and provided evidence of the feasibility of this approach were published more than two decades ago. Today, several cancer vaccine candidates are undergoing pre-clinical and clinical trials around the world.
Individualised cures
The ability to cure illness at a personalised level makes mRNA technology a logical choice for rare genetic diseases. In fact, research in this area of medicine has a long history, says Professor Elisabetta Tabolacci, a genetic medicine expert at the Institute of Genomic Medicine at the Catholic University of the Sacred Heart in Rome. She hopes the hype around mRNA will spark interest – and funding – towards too-often neglected rare genetic disorders.
Often life-threatening or disabling, rare genetic diseases have no cure. These conditions are caused by faulty genes that impair the expression of vital proteins.
Medications help mitigate symptoms, but replacing the missing or defective protein could be the only way to fix the problem.
That is exactly what Tabolacci is trying to achieve using mRNA-based therapy for fragile X syndrome – the most common cause of inherited intellectual disability.
Fragile X syndrome is caused by a change to a gene on the X-chromosome called the fragile X mental retardation 1 (FMR1) gene. This gene produces a protein essential for normal brain function.
Tabolacci has tested the idea in vitro using neurons from fragile X patients and found that it could restore protein synthesis.
The challenge came when she tested the treatment in mice. “In vivo, there are lots of challenges, because neurons are difficult to reach,” she says.
Nonetheless, she remains confident of the potential of the approach in fragile X syndrome: “mRNA technology is the best choice because it is long-lasting and non-toxic,” she says.
A bright future
Scientists have long known the enormous potential the mRNA technology disguises. Decades of research in various corners of medicine have allowed two biotech companies to develop COVID-19 vaccines in record time. Now, scientists want to take advantage of the surge of enthusiasm and investment to accelerate mRNA research in multiple areas of medicine. “It was a massive proof of principle,” says Preiss of the COVID vaccines.
“Who knows, one day we might have the ability to [make mRNA therapies] on a small scale at GP clinics depending on what the patient needs,” says Fox. “That’s real blue-sky thinking, but it is possible and quite exciting.”
But mRNA therapeutics– for heart disease and cancer treatment, for instance – might have a tougher road to the clinic than vaccines. These drugs face the challenges of targeting specific tissues and giving strong, long-lasting benefits without excessive side effects.
“We need to get these drugs to the right part of the body, at the right concentration,” says Leedman.
Tailoring an mRNA drug to a disease often means tweaking the structures of both the mRNA itself and the lipid nanoparticle that carries it through the body. Nanoparticle drug delivery research has an even longer history than the idea of mRNA therapy itself and has also regained momentum with the success of the COVID-19 vaccines.
Leedman sees the “delivery problem” as an opportunity rather than a challenge. “Who would have ever thought that medical research would be sexy?” he asks.
It turns out all that was needed was a global pandemic.
Originally published by Cosmos as Message in a bottle
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