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While the vaccines for Covid-19 seem to have been created in record time, the technology making them possible has been decades in development. The two vaccine candidates produced by Pfizer/BioNTech and Moderna are unlike any other vaccine that’s come before. Should they achieve commercial success, it could usher in a new era of medical science — not just for vaccines, but for cancer treatments, blood disorders, and gene therapy.
The two new vaccines are the first ever to use mRNA, which stands for “messenger RNA,” to generate immunity. Historically, vaccines have used dead or weakened viruses to imitate an infection, spurring the body to make antibodies against that virus without danger of getting sick. Measles, polio, and some seasonal flu shots are examples of vaccines made with whole virus particles.
Other vaccines use only certain fragments of the virus, called antigens, that provoke an immune response. To make this type of vaccine, the genetic code for the desired viral antigen molecule is put into yeast or bacteria cells. These microbes can be grown rapidly and inexpensively, and they can churn out massive quantities of antigen. Then the molecule must be purified to clinical standards so that it’s safe to inject into healthy people. Prevnar and Gardasil are examples of this type of vaccine.
These methods work well, but they require enormous research and development efforts. A laboratory could spend years optimizing the methods for producing one virus protein, but those methods wouldn’t automatically translate to mass-producing a different protein.
“For every new protein, you start over. It’s a brand-new procedure every step of the way,” explains immunologist Drew Weissman of the Perelman School of Medicine at the University of Pennsylvania. Weissman is one of the pioneering scientists behind the mRNA vaccine.
“The way I see it, the mRNA platform is much better, it’s much quicker, and it’s cheaper,” says Weissman. “That’s the trilogy of what you need to improve vaccines.” With mRNA, the steps are the same, no matter what virus the vaccine is targeting. This makes it easily customizable. Once an mRNA manufacturing facility is up and running, it can easily be deployed to make vaccines against any number of viral antigens.
How is that possible? Here’s how it works
A strand of mRNA carries the instructions for making one protein. Your cells normally make their own mRNA strands and use them as blueprints to manufacture all the proteins your body needs to function.
The vaccine slips a new strand of mRNA into the cell, like an extra page in the blueprint. This mRNA contains the instructions for making the coronavirus spike protein, and the cell reads it the same way it reads its own mRNAs, using it to build the viral protein. The immune system recognizes that protein as foreign, and starts making antibodies against it. Then, if you’re exposed to the actual virus, those antibodies will be available to stop the infection. Astonishingly, in animal tests, mRNA vaccines appear to induce immunity that lasts much longer than live virus vaccines.
The beauty of mRNA is that it’s temporary. Your cells won’t keep cranking out spike protein forever. Like an Instagram story, the mRNA fades away after a certain amount of time, because you don’t need to keep making coronavirus protein forever in order to maintain the protective immunity.
Another big advantage of mRNA is that it’s rapidly customizable. Once scientists know the genetic sequence of a viral protein, they can make the mRNA in the lab and package it into a vaccine in a matter of weeks.
Originally envisioned as a way to deliver gene therapy, mRNA had to overcome some serious challenges before arriving at today’s big moment. In 2005, Weissman and his colleague, Katalin Karikó, solved one of the most difficult problems facing mRNA. In its natural form, the molecule sparks an excessive immune reaction, igniting inflammation that damages the body. To avoid this, they changed the structure of the mRNA just enough to fool the immune sentries.
Similar to DNA, RNA is made up of a series of chemical “letters,” a kind of code that the cell translates to make a protein. Modifying the chemical structure of one of those letters allowed the information to remain intact, and eliminated the signal that triggered the body’s immune alarms.
Before the coronavirus pandemic hit, Weissman’s lab was working on vaccines for influenza, herpes, and HIV. “Those will all be going into phase I clinical trials within the next year,” he says. But vaccines are only the beginning of what mRNA can do.
Safer, Less Expensive Gene Therapy
Often in the case of genetic diseases, the problem is that a broken gene fails to produce a protein that the body needs for healthy function. The idea of gene therapy is simple: send in a healthy copy of the broken gene, which the cells can use to make the protein. Most times, researchers use viruses to deliver the gene, but viruses can cause problems of their own. Delivering mRNA to the cell without a virus circumvents some of these issues.
To ferry the mRNA into cells, it is encapsulated in a fatty coating called a lipid nanoparticle (LNP). Weissman’s lab has been experimenting with ways to modify the LNP so that it can home in on certain cell types.
“My lab has figured out how to specifically deliver the LNP to bone marrow stem cells,” Weissman says. This could lead to an inexpensive and practical cure for sickle cell anemia. An mRNA molecule can be programmed to encode the beta-hemoglobin gene, which is defective in sickle cell disease. That mRNA would be sent directly to the bone marrow cells using the specially targeted LNPs, enabling the bone marrow to produce healthy red blood cells that contain functioning beta-hemoglobin.
“All that would need to be done is to give people a single intravenous injection of the mRNA LNP, and you’ll cure their sickle cell anemia,” Weissman says. By contrast, the current FDA-approved gene-editing therapy for sickle cell requires the patient’s bone marrow be removed, treated, and then returned to the body—an expensive and invasive procedure. The mRNA treatment could be simple enough to deliver in lower-income countries, where sickle cell disease impacts the health of millions of people.
An up-and-coming strategy for fighting cancer is a so-called “cancer vaccine,” which uses immune cells called dendritic cells (DCs). DCs perform surveillance for the immune system. When they detect something that shouldn’t be there, whether it’s a virus, a bacteria, or even a cancer cell, the DCs chew it up, break it into its component molecules, and then show those foreign molecules to the immune cells that make antibodies.
When cancer grows slowly, though, it can slip past the DC surveillance network. To give the immune system a boost, a patient’s DCs are taken out and artificially loaded with tumor-specific proteins, or antigens. Back inside the body, the cells stimulate the generation of antibodies against the tumor.
Using mRNA to deliver the tumor antigen information to the DCs could provide a way to make this process easier, cheaper, and safer. BioNTech is currently conducting clinical trials on cancer vaccines for triple-negative breast cancer, metastatic melanoma, and HPV-positive head and neck cancers. Called FixVac, the vaccines include multiple tumor antigens that are frequently found across different patients. Early data published in September 2020 showed promise, suggesting that the mRNA therapy generates a lasting immune response, comparable to more expensive methods.
Karikó, who is now a senior vice president at BioNTech, and Weissman both speak with an air of inevitability, as if they have only been waiting patiently for the world to catch up with their discovery. The two scientists told their stories recently at the 2nd annual “mRNA Day” celebration in San Diego, hosted by Trilink BioTechnologies in honor of their recently opened facility there. After hearing the tumultuous history of the technology and seeing promising new data, one attendee asked, “what would you say was the turning point for mRNA therapeutics?”
Karikó responded simply, “When people read our  paper. We were waiting for somebody to respond, we did a lot of experiments, but we waited and waited. It was just too early for most people.”
Weissman agreed. “I think we were early,” he said. “It finally caught on, and it will hopefully change the world.”
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