By the time Fabian Müller met the patient in the middle of his station new research paperhe was absolutely convinced that experimental treatment was his last hope. The patient, a 47-year-old mother of two, had for many years been battling three severe autoimmune diseases, all of which were causing her body to attack parts of her blood. His doctors had made nine different attempts to treat his condition, but none of them worked. By early 2025, he had been hospitalized in Dresden, Germany, for more than two months, given multiple immunosuppressive drugs and receiving up to three red blood cell transfusions daily, as his care team tried and failed to contain the massive outbreak.
In desperation, the woman’s care team went to Müller, a blood-oncologist at Erlangen University Hospital, about three hours away by ambulance. In recent years, he and his colleagues have earned a reputation as pioneers in experimental CAR-T cell therapy—a type of personalized immunotherapy originally developed for cancer—against a variety of autoimmune diseases, with promising early results. Small CAR-T studies, including early results from several ongoing clinical trialsshow that most people with autoimmune disease go into remission after treatment; some patients have now stopped CAR-T cell therapy for years and continue to be healthy without the help of any drugs. Müller hopes that this latest patient—the most complex immunodeficiency patient to receive treatment to date—will soon be able to say the same. He underwent CAR-T treatment early last year and has returned to a normal life. After years of constant beatings on machines and tubes, he hasn’t needed to be hospitalized in months. (The patient has requested anonymity to protect her privacy, Müller told me.)
Müller and other CAR-T researchers are cautious about predicting the future of their technology. CAR-T is new to autoimmune disease – it was tested on a patient in 2021 – and scientists are not yet sure how long remission can last or if patients can experience long-term effects. But for the first time, patients with some of the world’s worst autoimmune conditions are experiencing long-term remission after a single treatment. And many researchers are beginning to think that CAR-T could offer people with autoimmune disease a new kind of hope: the possibility of a full recovery.
Diseases of the immune system—a broad and complex spectrum of ailments including rheumatoid arthritis and type 1 diabetes—have long puzzled researchers. For reasons that are still not well understood, the body’s immune system, which is normally programmed to root out and destroy pathogens or diseased cells, starts attacking healthy cells instead. Although the conditions can be controlled, usually with immunosuppressant drugs, scientists have never thought of a way to boost the immune system in line.
CAR-T therapy may be exactly the kind of reset the immune system needs. The treatment involves reprogramming T cells—a type of immune protector—into chimeric antigen receptor T cells (hence, CAR-T) that can kill other cells that scientists have chosen. In the case of many autoimmune diseases, that means targeting B cells, another type of immune cell that’s normally responsible for the body turning itself upside down. CAR-T treatment eliminates the misbehaving cells, allowing the body, in theory, to replace its own B cells with those that leave only healthy tissue.
Until now, the theory has spread. Early trials—many of them led by Müller’s team—suggest that CAR-T therapy can treat several different autoimmune diseases, including myositis, systemic sclerosis, ulcerative colitis, and myasthenia gravis, with few side effects. In experiments, including several soon lessons from Müller and colleagues, many of the several lupus patients that researchers have injected with CAR-Ts have gone into remission, and stayed there for many months. Overall, CAR-T has been surprisingly successful against autoimmune disease, Marcela Maus, director of the Cellular Immunotherapy Program at Massachusetts General Hospital, told me, especially given CAR-T’s track record against certain cancers. These experimental treatments also offer significant lifestyle improvements over traditional management of severe and complex autoimmune disease, which may include a lifetime of each dose of immunosuppressive drugs. And while CAR-T can cause a severe inflammatory response in some cancer patients, those risks do not appear to be common in people with autoimmune disease.
Müller’s recent patient presented yet another puzzle—not least because he suffered from three different autoimmune diseases. In 2014, when she had her first son, she was diagnosed with autoimmune hemolytic anemia, in which the body destroys its own red blood cells. Soon after, she developed two more autoimmune diseases: one that caused her blood to clot excessively, and another that damaged her blood cells, putting her at greater risk of uncontrolled bleeding. Before he got sick, the patient was active, energetic, “always doing a million things at once,” Müller told me. Within a few years of her diagnosis, though, she was struggling to get through everyday tasks, unable to work, hospitalized for months each year. Her youngest son, who is 8 years old, knew his mother “only as a sick person,” Müller said. As early as 2025, the patient told Müller that he was willing to try anything he and his colleagues had to offer. With each additional day of intensive, unsuccessful treatment, her risk of serious complications was increasing as her chances of survival decreased rapidly.
Earlier last year, Müller and his colleagues took a patient’s T cells, programmed them to destroy most of his body’s B cells, and then put the modified T cells back into his body. His B cells began to disappear quickly, and after a few weeks, his blood began to look normal. A year on from the treatment, he is still very tired, and has to have blood drawn every week to clear the iron build-up in his body after receiving many blood transfusions. But her outpatient care is overseen, and she no longer relies on drugs or blood transfusions. He spends time with his children in ways he never did before. As far as Müller’s team can tell, the treatment accomplished the immune reactivation they had hoped for: His body has produced new B cells, and so far they don’t seem to be irritated by any of the components of his blood, as immune cells should be.
Not everyone will be so lucky. CAR-T therapy can cost hundreds of thousands of dollars or more. Germany allows people with severe immune conditions to receive treatment on a compassionate use basis, and it covers it through a nationwide health system. But in the United States, the only reliable way to get CAR-T to those patients comes through limited clinical trials. Some researchers worry that some patients will not remain in remission, perhaps because they have some kind of tendency to produce immune cells. And certain autoimmune diseases—especially those that may not be dependent on poorly functioning B cells—may be difficult to treat with CAR-T. Deleting too many T cells, for example, carries a high risk of pushing a person into a state of immunodeficiency, similar to AIDS, Avery Posey, a CAR-T expert at the University of Pennsylvania, told me. But new developments are in the works that could address some of those issues, Posey said. Scientists are excited about new ways to make CAR-T cells more efficiently and cheaply, including through injections, somewhat similar to vaccines, that can induce patients’ bodies to reprogram some of their own T cells—that is, to produce their own CAR-Ts at home. In some cases, the subset of cells that CAR-Ts target can also be reduced, so that the body’s most problematic cells are taken out of action, while healthy immune cells remain.
Müller remains encouraged by the fact that his first antibody patient, a young woman with lupus, is still doing well more than five years after his CAR-T treatment. Since he got his master’s degree and now he works in his hospital, conducting clinical trials; they wave as they look at each other in the cafe. For now, his immune system seems to be behaving as it should.
