The researchers next wanted to determine if gene-edited bone marrow cells could remain in a living organism long enough to have therapeutic benefit. Due to the difficulty of obtaining blood stem cells with the beta-globin defect, they injected normal blood stem cells that were gene-edited into mice with suppressed immune systems. They found that an average of 2% of the edited stem cells remained in the bone marrow after 4 months. One mouse maintained more than 6% of the edited stem cells. These levels could potentially be of clinical benefit.