When a computer won't listen, reset or initialize is often the answer. Using the same approach, researchers succeeded in returning the body's defense force, which stem cells had repeatedly turned against the body, to normal. They reset the immune system and replaced the problematic immune cells with normal ones.
A research team led by Massimo Filippi, a neurology professor at San Raffaele University Hospital in Italy, said on the 15th (local time) in the international journal Med that it confirmed two patients with neuromyelitis optica spectrum disorder (NMOSD) who received allogeneic hematopoietic stem cell transplants remained virtually cured for 15 years.
◇ Maintained normal life without medication for 15 years
Neuromyelitis optica is a very rare autoimmune disease that occurs in about 3 out of every 100,000 people. It arises when the body's immune cells cause inflammation in the optic nerve and spinal cord and strip away myelin, the protective sheath around nerves. As a result, nerve signals fail to transmit properly, the whole body stiffens, and even vision is damaged. Vomiting persists, and urination and defecation become difficult.
The researchers transplanted allogeneic hematopoietic stem cells into two male and female patients who did not respond to drugs. Hematopoietic stem cells are stem cells that produce all blood cells, including white blood cells, red blood cells, and platelets. After the procedure, the man's neurological function improved to normal and he had two children. The woman could use her previously paralyzed arm again and no longer needed drug treatment. Jiao Jiao Li, a stem cell researcher at the University of Technology Sydney, told Nature, "It may be too early to say this is a cure, but the treatment appears to have resolved the problems caused by the disease over a long period."
Filippi said this was the first time allogeneic hematopoietic stem cells were used to treat neuromyelitis optica. Put simply, allogeneic hematopoietic stem cells are another person's blood stem cells. The male patient received his younger sister's blood stem cells in 2009, and the female patient received cells the following year from an unrelated donor. Although the stem cells came from other people, they were donated by individuals whose HLA (human leukocyte antigen), the genetic trait of white blood cells, matched the patients well, so immune rejection was expected to be low.
Both received a single infusion of stem cells, yet their faulty immune systems were effectively reset. The pathogenic anti–aquaporin-4 antibodies (AQP4-IgG) that had attacked neurons in the patients disappeared. About 80% of neuromyelitis optica cases are known to be caused by AQP4-IgG. These antibodies attack aquaporin-4, a channel protein that transports water across cell membranes in the central nervous system, including the brain and spinal cord. As a result, severe inflammation develops in the optic nerve and spinal cord.
◇ Succeeded in a complete replacement of the immune system
In particular, the patients' regulatory T cells were replaced by cells from the stem cell donors. Regulatory T cells are immune cells that play a key role in suppressing excessive immune responses and preventing the immune system from attacking the body's own normal cells. This means the stem cells did not just suppress inflammation; they completely replaced the immune system.
There was also no immune rejection caused by the stem cells. When another person's stem cells mature into immune cells, they can mistake the patient's body for an invader and attack it. This complication is called graft-versus-host disease. The researchers said such immune rejection did not occur after the blood stem cell transplants.
The findings suggest stem cells could potentially cure severe autoimmune diseases. Of course, effectiveness has only been confirmed in a small number of patients, so it is not certain whether all neuromyelitis optica patients would benefit. It is also not easy to find suitable donors with no immune rejection, as in this case.
Even so, scientists called it a proof-of-concept study that demonstrates the potential of stem cell therapy and could serve as a basis for launching full-scale clinical trials. Bruce Milthorpe at the University of Technology Sydney noted that harvesting stem cells from blood, rather than from bone marrow inside bones, greatly reduced invasiveness and the risk of tissue damage to donors.
References
Med (2026), DOI: https://doi.org/10.1016/j.medj.2026.101179