A phase II/III trial has been undertaken with intravitreal implants of encapsulated human RPE cells engineered to continuously secrete ciliary neurotrophic factor (CNTF) protein in patients with early-stage and late-stage RP.74 Patients were randomly assigned to receive a high-dose or low-dose implant in one eye and sham surgery in the fellow eye. The gene discussed is CNTF; the disease is retinitis pigmentosa 1.