When I was taking German in college in the early years of this millennium, I once stumbled upon a word that appeared foreign even when translated into English: Diphtherie, or diphtheria. “What’s diphtheria?” I wondered, having never encountered a single soul afflicted by this disease.

Diphtheria, once known as the “strangling angel,” was a leading killer of children into the early 20th century. The bacterial infection destroys the lining of the throat, forming a layer of dead, leathery tissue that can cause death by suffocation. The disease left no corner of society untouched: Diphtheria killed Queen Victoria’s daughter, and the children of Presidents Lincoln, Garfield, and Cleveland. Parents used to speak of their first and second families, an elderly woman in Ottawa recalled, because diphtheria had swept through and all their children died.

Today, diphtheria has been so thoroughly forgotten that someone like me, born some 60 years after the invention of a diphtheria vaccine, might have no inkling of the fear it once inspired. If you have encountered diphtheria outside of the historical context, it’s likely because you have scrutinized a childhood immunization schedule: It is the “D” in the DTaP vaccine.

Vaccine breakthroughs over the past two centuries have cumulatively made the modern world a far more hospitable place to be born. For most of human history, half of all children died before reaching age 15; that number is down to just 4 percent worldwide, and far lower in developed countries, with vaccines one of the major drivers of improved life expectancy. “As a child,” the vaccine scientist Stanley Plotkin, now 92, told me, “I had several infectious diseases that almost killed me.” He ticked them off: pertussis, influenza, pneumococcal pneumonia—all of which children today are routinely vaccinated against.

But the success of vaccines has also allowed for a modern amnesia about the level of past human suffering. In a world where the ravages of polio or measles are remote, the risks of vaccines—whether imagined, or real but minute—are able to loom much larger in the minds of parents. This is the space exploited by Robert F. Kennedy Jr., one of the nation’s foremost anti-vaccine activists and now nominee for secretary of Health and Human Services. It is a stunning reversal of fortune for a man relegated to the fringes of the Democratic Party just last year. And it is also a reversal for Donald Trump, who might have flirted with anti-vaccine rhetoric in the past but also presided over a record-breaking race to create a COVID vaccine. Kennedy has promised that he would not yank vaccines off the market, but his nomination normalizes and emboldens the anti-vaccine movement. The danger now is that diseases confined to the past become diseases of the future.

Walt Orenstein trained as a pediatrician in the 1970s, when he often saw children with meningitis—a dangerous infection of membranes around the brain—that can be caused by a bacterium called Haemophilus influenzae type b or Hib. (Despite the name, it is not related to the influenza virus.) “I remember doing loads of spinal taps,” he told me, to diagnose the disease. The advent of a Hib vaccine in the 1980s virtually wiped these infections out; babies are now routinely vaccinated in the first 15 months of life. “It’s amazing there are people today calling themselves pediatricians who have never seen a case of Hib,” he says. He remembers rotavirus, too, back when it used to cause about half of all hospitalizations for diarrhea in kids under 5. “People used to say, ‘Don’t get the infant ward during diarrhea season,’” Orenstein told me. But in the 2000s, the introduction of rotavirus vaccines for babies six months and younger sharply curtailed hospitalizations.

To Orenstein, it is important that the current rotavirus vaccine has proved effective but also safe. An older rotavirus vaccine was taken off the market in 1999 when regulators learned that it gave babies an up to one-in-10,000 chance of developing a serious but usually treatable bowel obstruction called intussusception. The benefits arguably still outweighed the risks—about one in 50 babies infected with rotavirus need hospitalization—but the United States has a high bar for vaccine safety. Similarly, the U.S. switched from an oral polio vaccine containing live, weakened virus—which had a one in 2.4 million chance of causing paralysis—to a more expensive but safer shot made with inactivated viruses that cannot cause disease. No vaccine is perfect, says Gregory Poland, a vaccinologist and the president of the Atria Academy of Science & Medicine, who himself developed severe tinnitus after getting the COVID vaccine. “There will always be risks,” he told me, and he acknowledges the need to speak candidly about them. But vaccine recommendations are based on benefits that are “overwhelming” compared with their risks, he said.

The success of childhood vaccination has a perverse effect of making the benefits of these vaccines invisible. Let’s put it this way: If everyone around me is vaccinated for diphtheria but I am not, I still have virtually no chance of contracting it. There is simply no one to give it to me. This protection is also known as “herd immunity” or “community protection.” But that logic falls apart when vaccination rates slip, and the bubble of protective immunity dissolves. The impact won’t be immediate. “If we stopped vaccinating today, we wouldn’t get outbreaks tomorrow,” Orenstein said. In time, though, all-but-forgotten diseases could once again find a foothold, sickening those who chose not to be vaccinated but also those who could not be vaccinated, such as people with certain medical conditions and newborns too young for shots. In aggregate, individual decisions to refuse vaccines end up having far-reaching consequences.

Evolutionary biologists have argued that plague and pestilence rose in tandem with human civilization. Before humans built cities, back when we still lived in small bands of hunter-gatherers, a novel virus—say, from a bat—might tear through a group only to reach a dead end once everyone was immune or deceased. With no one else to infect, such a virus will burn itself out. Only when humans started clustering in large cities could certain viruses keep finding new susceptibles—babies or new migrants with no immunity, people with waning immunity—and smolder on and on and on. Infectious disease, you might then say, is a necessary condition of living in a society.

But human ingenuity has handed us a cheat code: Vaccines now allow us to enjoy the benefits of fellow humanity while preventing the constant exchange of deadly pathogens. And vaccines can, through the power of herd immunity, protect even those who are too young or too sick to be effectively vaccinated themselves. When we get vaccinated, or don’t, our decisions ricochet through the lives of others. Vaccines make us responsible for more than ourselves. And is that not what it means to live in a society?

Lupus, doctors like to say, affects no two patients the same. The disease causes the immune system to go rogue in a way that can strike virtually any organ in the body, but when and where is maddeningly elusive. One patient might have lesions on the face, likened to wolf bites by the 13th-century physician who gave lupus its name. Another patient might have kidney failure. Another, fluid around the lungs. What doctors can say to every patient, though, is that they will have lupus for the rest of their life. The origins of autoimmune diseases like it are often mysterious, and an immune system that sees the body it inhabits as an enemy will never completely relax. Lupus cannot be cured. No autoimmune disease can be cured.

Two years ago, however, a study came out of Germany that rocked all of these assumptions. Five patients with uncontrolled lupus went into complete remission after undergoing a repurposed cancer treatment called CAR-T-cell therapy, which largely wiped out their rogue immune cells. The first treated patient has had no symptoms for almost four years now. “We never dared to think about the cure for our disease,” says Anca Askanase, a rheumatologist at Columbia University’s medical center who specializes in lupus. But these stunning results—remission in every patient—have fueled a new wave of optimism. More than 40 people with lupus worldwide have now undergone CAR-T-cell therapy, and most have gone into drug-free remission. It is too early to declare any of these patients cured for life, but that now seems within the realm of possibility.

Beyond lupus, doctors hope CAR-T portends a bigger breakthrough against autoimmune diseases, whose prevalence has been on a troubling rise. CAR-T has already been used experimentally to treat patients with other autoimmune diseases, including multiple sclerosis, myositis, and myasthenia gravis. And the success of CAR-T has inspired researchers to borrow other—cheaper and simpler—strategies from cancer therapy to kill immune cells gone awry. Not all of these ideas will pan out, but if any do, the next few years could bring an inflection point in treating some of the most frustrating and intractable diseases of our modern era.

CAR-T-cell therapy was originally developed as a way to kill malignant cells in blood cancer. It could, scientists later reasoned, also be used to kill specific white blood cells, called B cells, that go haywire with certain autoimmune diseases. One group tried a CAR-T-like therapy against an autoimmune disease called pemphigus vulgaris, and another CAR-T against lupus. It worked—but these experiments were only in mice.

This was the sum total of available scientific evidence when a 20-year-old woman came to her doctors in Erlangen, Germany, asking to try anything for her severe and uncontrolled lupus. None of the long-term medications typically used to manage lupus were working. Her kidneys, heart, and lungs were all failing, and she could walk only 30 feet by herself. CAR-T was risky, her doctor agreed, but lupus was killing her.

CAR-T-cell therapy could essentially turn her immune system against itself. First, doctors extracted from her blood a class of immune cells, called T cells, which they then engineered into chimeric antigen receptor T (CAR-T) cells that could recognize and destroy the B cells driving her lupus. CAR-T cells can cause dangerous and overwhelming inflammatory responses in cancer patients, and her doctors did worry that CAR-T could do the same for someone with autoimmune disease, whose immune system is already in overdrive. “We take the T cells out, activate them like crazy, and then shoot those massively overactivated T cells in an activated autoimmune disease. So if you think about it, that's kind of crazy to do that, right?” says Fabian Müller, a hematologist-oncologist at the University Hospital of Erlangen and one of the doctors on the German team that pioneered the treatment. But fortunately, the woman with lupus did not have any serious side effects, nor did any of the other patients the German group has since dosed. They are all living their everyday lives, free of lupus symptoms and medications. The woman who could walk a mere 30 feet now runs five times a week, Müller told me. She’s gone back to school and is considering studying for a master’s in immunology.

Müller and his colleagues believe that CAR-T-cell therapy works by wiping out enough B cells to trigger a “deep reset” of the immune system. CAR-T cells are dogged little assassins; they are able to find and destroy even the B cells hiding deep in the body’s tissues. A patient’s B-cell count eventually recovers, but the new ones no longer erroneously attack the body itself. Cancer patients are sometimes considered “cured” after five years of remission, and the first lupus patient to receive CAR-T is not so far off from that milestone. But the therapy cannot erase the genetic predisposition many patients have for the disease, says Donald Thomas, a rheumatologist in Maryland. Whether remission is actually durable enough to be a “cure” will take time to find out.

Still, these extraordinary results have set off a gold rush among biotech companies eager to solve autoimmune diseases. CAR-T start-ups founded to treat cancer are pivoting to target autoimmune diseases. And large pharmaceutical companies such as Bristol Myers Squibb, AstraZeneca, and Novartis are developing their own therapies. Columbia’s Askanase is now an investigator on five separate trials, all using CAR-T or a similar cellular therapy, and she hears from more companies all the time. There’s so much interest, she told me, “I don’t even know there are enough patients” to test new treatments. About 1.5 million Americans have lupus, but only a minority of them—those sick enough to justify experimental treatment but not so sick that they’ve suffered too much irreversible organ damage—are eligible for trials.

For now, CAR-T for lupus and other autoimmune diseases is pretty much only accessible in the U.S. through clinical trials—which, in effect, means it’s inaccessible to almost all lupus patients. Jonathan Greer, a rheumatologist in Florida, works in a seven-doctor practice that treats hundreds of people with lupus; not a single one has received CAR-T. He doesn’t know of a single center in Florida that is up and running to do these studies, so interested patients would have to travel out of state.

Even if it becomes FDA approved for autoimmune diseases, CAR-T is a long and expensive process. Because each patient’s own cells are reengineered, it cannot be easily scaled up. The cost of CAR-T for cancer runs about $500,000. Patients also need chemotherapy to kill existing T cells to make room for CAR-T, which adds risk, and in lupus, they usually need to taper off any medications keeping their disease in check, which can cause flare-ups. All these complications make the current iteration of CAR-T suitable only for lupus patients with severe disease, who have run out of other options.

The practical limitations of CAR-T have dogged the cancer field for a long time now, and researchers have already come up with ideas to get around it. A number of simpler strategies for killing B cells are now making their way from blood cancer to autoimmune disease. They include using donor T cells, a different type of immune cell called natural killer cells, or a molecule that binds a T cell to the B cell it’s meant to destroy. Those molecules, called bispecific T-cell engagers, or BiTEs, are “cheap, fast, uncomplicated,” Müller said, but they may not penetrate as deeply into the tissues where B cells reside. Nevertheless, in September, The New England Journal of Medicine published two successful case reports describing successful treatment in a handful of autoimmune diseases, including lupus, with a BiTE called teclistamab. Similar BiTES on the market could be repurposed for autoimmune disease too.

These simpler therapies may ultimately be “good enough,” Askanase said. And their ease of use could ultimately beat out custom CAR-T therapy, which is unlikely to reach all of the millions of people with lupus worldwide. It’s simply too expensive and too cumbersome, a problem that has held back other cutting-edge therapies that were approved to much initial fanfare. Even if CAR-T itself is never widely adopted for autoimmune diseases, it has opened the door to new ideas that could one day revolutionize their treatment.