It works by editing the patients' own hematopoietic stem cells with the functional ADA gene. The cells are then transferred back into the patient's bone marrow to mature and produce the normal ADA protein. FDA approval has so far evaded Orchard, although the agency has accepted a request to run a trial for Libmeldy and granted it a regenerative medicine advanced therapy designation. Investors have peppered Orchard executives with questions during recent earnings calls on when the FDA might give a nod to any one of the company's therapies.