A new gene therapy has been discovered that could help rebuild immune systems of older children and young adults that have a rare disorder.

The discovery was made by researchers at the National Institute of Allergy and Infectious Diseases (NIAID), and involved mutations in the IL2RG gene, according to a Medical Daily report.

These mutations appear to cause X-linked severe combined immunodeficiency (SCID-X1), an important finding that could lead to a breakthrough in how scientists develop treatments for this disease.

Stem cell transplants are currently the only known way to tread infants who have SCID-X1, meaning stem cells from a sibling or the parents will be needed and even then it will only partially restore the immune system. They’ll still need treatment throughout their lives and will have to battle with medical problems along the way.

So researchers have been looking for a better way to treat this disease, and so they took a closer look at gene therapy in combination with low-dose chemotherapy in five SCID-X1 patients between 7 and 24 years of age. The scientists started removing stem cells from the bone marrow of participants and then delivered a normal IL2RG gene to the cells and reinserting them back into the body.

The treatment was surprisingly successful, with two of them showing significant improvements in immunity, and one showing improvement three years later. Another patient died two years later, but not before showing some improvement that indicates had it been started earlier, it may have saved that person’s life.