US: The 'supercells' that cured an infant's grave genetic illness When Johan was born with a grave genetic illness called chronic granulomatous disease, he benefited from a still-experimental type of treatment known as T-cell therapy that helped his immune system fight off viruses after he received a bone marrow transplant. Johan now shows no signs of the disease that used to threaten him. "It's neat to see him processing things, and especially play outside, play in the mud," says his mother, Maren Chamorro. "You know, what a gift!"