It's vacation time. You and your family visit a country where you've never been and, in fact, your parents or grandparents had never been. You find yourself hiking beside a beautiful lake. It's a gorgeous day. You dive in. You are not alone.
How can your T cells and B cells react to a pathogen they've never seen?
In the water swim parasites, perhaps a parasite called giardia. The invader slips in through your mouth or your urinary tract. This bug is entirely new to you, and there's more. It might be new to everyone you've ever met or come into contact with. The parasite may have evolved in this setting for hundreds of thousands of years so that it's different from any giardia bug you've ever come into contact with before or that thrives in the region where you live.
How can your T cells and B cells react to a pathogen they've never seen, never knew existed, and were never inoculated against, and that you, or your doctors, in all their wisdom, could never have foreseen?
This is the infinity problem.
For years, this was the greatest mystery in immunology.
As I reported An Elegant Defense -- my book about the science of the immune system told through the lives of scientists and medical patients -- I was repeatedly struck by the profundity of this question. It is hard to overstate: how can we survive in a world with such myriad possible threats?
Matt Richtel's new book about the science of the immune system, An Elegant Defense, was published this month.
To further underscore the quandary, the immune system has to neutralize threats without killing the rest of the body. If the immune system could just kill the rest of the body too, the solution to the problem would be easy. Nuke the whole party. That obviously won't work if we are to survive. So the immune system has to be specific to the threat while also leaving most of our organism largely alone.
"God had two options," Dr. Mark Brunvand told me. "He could turn us into ten-foot-tall pimples, or he could give us the power to fight 10 to the 12th power different pathogens." That's a trillion potential bad actors. Why pimples? Pimples are filled with white blood cells, which are rich with immune system cells. In short, you could be a gigantic immune system and nothing else, or you could have some kind of secret power that allowed you to have all the other attributes of a human being—brain, heart, organs, limbs—and still somehow magically be able to fight infinite pathogens.
Dr. Brunvand is a retired Denver oncologist, one of the many medical authorities in the book – from wizened T-cell innovator Dr. Jacques Miller, to the finder of fever, Dr. Charles Dinarello, to his eminence Dr. Anthony Fauci at the National Institutes of Health to newly minted Nobel-Prize winner Jim Allison.
In the case of Dr. Brunvand, the oncologist also is integral to one of the book's narratives, a remarkable story of a friend of mine named Jason. Four years ago, he suffered late, late stage cancer, with 15 pounds of lymphoma growing in his back, and his oncologist put him into hospice. Then Jason became one of the first people ever to take an immunotherapy drug for lymphoma and his tumors disappeared. Through Jason's story, and a handful of other fascinating tales, I showcase how the immune system works.
There are two options for creating such a powerful immune system: we could be pimples or have some other magical power.
Dr. Brunvand had posited to me that there were two options for creating such a powerful and multifaceted immune system: we could be pimples or have some other magical power. You're not a pimple. So what was the ultimate solution?
Over the years, there were a handful of well-intentioned, thoughtful theories, but they strained to account for the inexplicable ability of the body to respond to virtually anything. The theories were complex and suffered from that peculiar side effect of having terrible names—like "side-chain theory" and "template-instructive hypothesis."
This was the background when along came Susumu Tonegawa.
Tonegawa was born in 1939, in the Japanese port city of Nagoya, and was reared during the war. Lucky for him, his father was moved around in his job, and so Tonegawa grew up in smaller towns. Otherwise, he might've been in Nagoya on May 14,1944, when the United States sent nearly 550 B-29 bombers to take out key industrial sites there and destroyed huge swaths of the city.
Fifteen years later, in 1959, Tonegawa was a promising student when a professor in Kyoto told him that he should go to the United States because Japan lacked adequate graduate training in molecular biology. A clear, noteworthy phenomenon was taking shape: Immunology and its greatest discoveries were an international affair, discoveries made through cooperation among the world's best brains, national boundaries be damned.
Tonegawa wound up at the University of California at San Diego, at a lab in La Jolla, "the beautiful Southern California town near the Mexican border." There, in multicultural paradise, he received his PhD, studying in the lab of Masaki Hayashi and then moved to the lab of Renato Dulbecco. Dr. Dulbecco was born in Italy, got a medical degree, was recruited to serve in World War II, where he fought the French and then, when Italian fascism collapsed, joined the resistance and fought the Germans. (Eventually, he came to the United States and in 1975 won a Nobel Prize for using molecular biology to show how viruses can lead, in some cases, to tumor creation.)
In 1970, Tonegawa—now armed with a PhD—faced his own immigration conundrum. His visa was set to expire by the end of 1970, and he was forced to leave the country for two years before he could return. He found a job in Switzerland at the Basel Institute for Immunology.
Around this time, new technology had emerged that allowed scientists to isolate different segments of an organism's genetic material. The technology allowed segments to be "cut" and then compared to one another. A truism emerged: If a researcher took one organism's genome and cut precisely the same segment over and over again, the resulting fragment of genetic material would match each time.
When you jump in that lake in a foreign land, filled with alien bugs, your body, astonishingly, well might have a defender that recognizes the creature.
This might sound obvious, but it was key to defining the consistency of an organism's genetic structure.
Then Tonegawa found the anomaly.
He was cutting segments of genetic material from within B cells. He began by comparing the segments from immature B cells, meaning, immune system cells that were still developing. When he compared identical segments in these cells, they yielded, predictably, identical fragments of genetic material. That was consistent with all previous knowledge.
But when he compared the segments to identical regions in mature B cells, the result was entirely different. This was new, distinct from any other cell or organism that had been studied. The underlying genetic material had changed.
"It was a big revelation," said Ruslan Medzhitov, a Yale scholar. "What he found, and is currently known, is that the antibody-encoding genes are unlike all other normal genes."
The antibody-encoding genes are unlike all other normal genes.
Yes, I used italics. Your immune system's incredible capabilities begin from a remarkable twist of genetics. When your immune system takes shape, it scrambles itself into millions of different combinations, random mixtures and blends. It is a kind of genetic Big Bang that creates inside your body all kinds of defenders aimed at recognizing all kinds of alien life forms.
So when you jump in that lake in a foreign land, filled with alien bugs, your body, astonishingly, well might have a defender that recognizes the creature.
Light the fireworks and send down the streamers!
As Tonegawa explored further, he discovered a pattern that described the differences between immature B cells and mature ones. Each of them shared key genetic material with one major variance: In the immature B cell, that crucial genetic material was mixed in with, and separated by, a whole array of other genetic material.
As the B cell matured into a fully functioning immune system cell, much of the genetic material dropped out. And not just that: In each maturing B cell, different material dropped out. What had begun as a vast array of genetic coding sharpened into this particular, even unique, strand of genetic material.
This is complex stuff. But a pep talk: This section is as deep and important as any in describing the wonder of the human body. Dear reader, please soldier on!
Researchers, who, eventually, sought a handy way to define the nature of the genetic change to the material of genes, labeled the key genetic material in an antibody with three initials: V, D, and J.
The letter V stands for variable. The variable part of the genetic material is drawn from hundreds of genes.
D stands for diversity, which is drawn from a pool of dozens of different genes.
And J is drawn from another half dozen genes.
In an immature B cell, the strands of V, D, and J material are in separate groupings, and they are separated by a relatively massive distance. But as the cell matures, a single, random copy of V remains, along with a single each of D and J, and all the other intervening material drops out. As I began to grasp this, it helped me to picture a line of genetic material stretching many miles. Suddenly, three random pieces step forward, and the rest drops away.
The combination of these genetic slices, grouped and condensed into a single cell, creates, by the power of math, trillions of different and virtually unique genetic codes.
In anticipation of threats from the unfathomable, our defenses evolved as infinity machines.
Or if you prefer a different metaphor, the body has randomly made hundreds of millions of different keys, or antibodies. Each fits a lock that is located on a pathogen. Many of these antibodies are combined such that they are alien genetic material—at least to us—and their locks will never surface in the human body. Some may not exist in the entire universe. Our bodies have come stocked with keys to the rarest and even unimaginable locks, forms of evil the world has not yet seen, but someday might. In anticipation of threats from the unfathomable, our defenses evolved as infinity machines.
"The discoveries of Tonegawa explain the genetic background allowing the enormous richness of variation among antibodies," the Nobel Prize committee wrote in its award to him years later, in 1987. "Beyond deeper knowledge of the basic structure of the immune system these discoveries will have importance in improving immunological therapy of different kinds, such as, for instance, the enforcement of vaccinations and inhibition of reactions during transplantation. Another area of importance is those diseases where the immune defense of the individual now attacks the body's own tissues, the so-called autoimmune diseases."
Indeed, these revelations are part of a period of time it would be fair to call the era of immunology, stretching from the middle of the 20th century to the present. During that period, we've come from sheer ignorance of the most basic aspects of the immune system to now being able to tinker under the hood with monoclonal antibodies and other therapies. And we are, in many ways, just at the beginning.
In November 2020, messenger RNA catapulted into the public consciousness when the first COVID-19 vaccines were authorized for emergency use. Around the same time, an equally groundbreaking yet relatively unheralded application of mRNA technology was taking place at a London hospital.
Over the past two decades, there's been increasing interest in harnessing mRNA — molecules present in all of our cells that act like digital tape recorders, copying instructions from DNA in the cell nucleus and carrying them to the protein-making structures — to create a whole new class of therapeutics.
Scientists realized that artificial mRNA, designed in the lab, could be used to instruct our cells to produce certain antibodies, turning our bodies into vaccine-making factories, or to recognize and attack tumors. More recently, researchers recognized that mRNA could also be used to make another groundbreaking technology far more accessible to more patients: gene editing. The gene-editing tool CRISPR has generated plenty of hype for its potential to cure inherited diseases. But delivering CRISPR to the body is complicated and costly.
"Most gene editing involves taking cells out of the patient, treating them and then giving them back, which is an extremely expensive process," explains Drew Weissman, professor of medicine at the University of Pennsylvania, who was involved in developing the mRNA technology behind the COVID-19 vaccines.
But last November, a Massachusetts-based biotech company called Intellia Therapeutics showed it was possible to use mRNA to make the CRISPR system inside the body, eliminating the need to extract cells out of the body and edit them in a lab. Just as mRNA can instruct our cells to produce antibodies against a viral infection, it can also teach them to produce the two molecular components that make up CRISPR — a guide molecule and a cutting protein — to snip out a problem gene.
"The pandemic has really shown that not only are mRNA approaches viable, they could in certain circumstances be vastly superior to more traditional technologies."
In Intellia's London-based clinical trial, the company applied this for the first time in a patient with a rare inherited liver disease known as hereditary transthyretin amyloidosis with polyneuropathy. The disease causes a toxic protein to build up in a person's organs and is typically fatal. In a company press release, Intellia's president and CEO John Leonard swiftly declared that its mRNA-based CRISPR therapy could usher in a "new era of potential genome editing cures."
Weissman predicts that turning CRISPR into an affordable therapy will become the next major frontier for mRNA over the coming decade. His lab is currently working on an mRNA-based CRISPR treatment for sickle cell disease. More than 300,000 babies are born with sickle cell every year, mainly in lower income nations.
"There is a FDA-approved cure, but it involves taking the bone marrow out of the person, and then giving it back which is prohibitively expensive," he says. It also requires a patient to have a matched bone marrow done. "We give an intravenous injection of mRNA lipid nanoparticles that target CRISPR to the bone marrow stem cells in the patient, which is easy, and much less expensive."
Meanwhile, the overwhelming success of the COVID-19 vaccines has focused attention on other ways of using mRNA to bolster the immune system against threats ranging from other infectious diseases to cancer.
The practicality of mRNA vaccines – relatively small quantities are required to induce an antibody response – coupled with their adaptable design, mean companies like Moderna are now targeting pathogens like Zika, chikungunya and cytomegalovirus, or CMV, which previously considered commercially unviable for vaccine developers. This is because outbreaks have been relatively sporadic, and these viruses mainly affect people in low-income nations who can't afford to pay premium prices for a vaccine. But mRNA technology means that jabs could be produced on a flexible basis, when required, at relatively low cost.
Other scientists suggest that mRNA could even provide a means of developing a universal influenza vaccine, a goal that's long been the Holy Grail for vaccinologists around the world.
"The mRNA technology allows you to pick out bits of the virus that you want to induce immunity to," says Michael Mulqueen, vice president of business development at eTheRNA, a Belgium-based biotech that's developing mRNA-based vaccines for malaria and HIV, as well as various forms of cancer. "This means you can get the immune system primed to the bits of the virus that don't vary so much between strains. So you could actually have a single vaccine that protects against a whole raft of different variants of the same virus, offering more universal coverage."
Before mRNA became synonymous with vaccines, its biggest potential was for cancer treatments. BioNTech, the German biotech company that collaborated with Pfizer to develop the first authorized COVID-19 vaccine, was initially founded to utilize mRNA for personalized cancer treatments, and the company remains interested in cancers ranging from melanoma to breast cancer.
One of the major hurdles in treating cancer has been the fact that tumors can look very different from one person to the next. It's why conventional approaches, such as chemotherapy or radiation, don't work for every patient. But weaponizing mRNA against cancer primes the immune cells with the tumor's specific genetic sequence, training the patient's body to attack their own unique type of cancer.
"It means you're able to think about personalizing cancer treatments down to specific subgroups of patients," says Mulqueen. "For example, eTheRNA are developing a renal cell carcinoma treatment which will be targeted at around 20% of these patients, who have specific tumor types. We're hoping to take that to human trials next year, but the challenge is trying to identify the right patients for the treatment at an early stage."
Repairing Damaged mRNA
While hopes are high that mRNA could usher in new cancer treatments and make CRISPR more accessible, a growing number of companies are also exploring an alternative to gene editing, known as RNA editing.
In genetic disorders, the mRNA in certain cells is impaired due to a rogue gene defect, and so the body ceases to produce a particular vital protein. Instead of permanently deleting the problem gene with CRISPR, the idea behind RNA editing is to inject small pieces of synthetic mRNA to repair the existing mRNA. Scientists think this approach will allow normal protein production to resume.
Over the past few years, this approach has gathered momentum, as some researchers have recognized that it holds certain key advantages over CRISPR. Companies from Belgium to Japan are now looking at RNA editing to treat all kinds of disorders, from Huntingdon's disease, to amyotrophic lateral sclerosis, or ALS, and certain types of cancer.
"With RNA editing, you don't need to make any changes to the DNA," explains Daniel de Boer, CEO of Dutch biotech ProQR, which is looking to treat rare genetic disorders that cause blindness. "Changes to the DNA are permanent, so if something goes wrong, that may not be desirable. With RNA editing, it's a temporary change, so we dose patients with our drugs once or twice a year."
Last month, ProQR reported a landmark case study, in which a patient with a rare form of blindness called Leber congenital amaurosis, which affects the retina at the back of the eye, recovered vision after three months of treatment.
"We have seen that this RNA therapy restores vision in people that were completely blind for a year or so," says de Boer. "They were able to see again, to read again. We think there are a large number of other genetic diseases we could go after with this technology. There are thousands of different mutations that can lead to blindness, and we think this technology can target approximately 25% of them."
Ultimately, there's likely to be a role for both RNA editing and CRISPR, depending on the disease. "I think CRISPR is ideally suited for illnesses where you would like to permanently correct a genetic defect," says Joshua Rosenthal of the Marine Biology Laboratory in Chicago. "Whereas RNA editing could be used to treat things like pain, where you might want to reset a neural circuit temporarily over a shorter period of time."
Much of this research has been accelerated by the COVID-19 pandemic, which has played a major role in bringing mRNA to the forefront of people's minds as a therapeutic.
"The pandemic has really shown that not only are mRNA approaches viable, they could in certain circumstances be vastly superior to more traditional technologies," says Mulqueen. "In the future, I would not be surprised if many of the top pharma products are mRNA derived."
"Making Sense of Science" is a monthly podcast that features interviews with leading medical and scientific experts about the latest developments and the big ethical and societal questions they raise. This episode is hosted by science and biotech journalist Emily Mullin, summer editor of the award-winning science outlet Leaps.org.