Out of severe combined immunodeficiency, Leber's congenital amaurosis 2, spinal muscular atrophy, Duchenne muscular dystrophy, sickle cell anemia, beta-thalassemia, and cystic fibrosis, which can be treated successfully with ex vivo therapy and what do those have in common that makes them amenable to ex vivo therapy? Consider the cells/tissues affected by each disease in relation to the requirements for a successful ex vivo therapy.