Eight babies born without a functioning germ-fighting system now have healthy immune systems thanks to gene therapy involving the HIV virus, the Associated Press reports. A study published Wednesday in the New England Journal of Medicine showed that using modified HIV to insert missing genes was effective at fixing the immune system of eight children with severe combined immunodeficiency syndrome—otherwise known as the “bubble boy” disease, after a boy who had the syndrome lived in a plastic bubble for 12 years to keep germs away. SCID, caused by a genetic flaw that prevents bone marrow from making proper blood cells, often kills in the first years of a child's life. Previously, the only known cure was a bone marrow transplant, a risky procedure. While “serious or lasting” side effects in the babies have popped up, scientists did say it would take more time to determine if the gene therapy was a permanent fix. “So far it really looks good,” Dr. Anthony Fauci, head of the National Institute of Allergy and Infectious Diseases, said. “To me, this looks promising.”