In a clinical trial, about a third of the patients who received Onasemnogene abeparvovec, an FDA approved AAV9 vector therapy for SMA, showed liver damage associated with an inflammatory reaction comprised mainly of CD8+ T cells, but all patients recovered after treatment with steroids, which broadly suppress immune activity and are especially effective in controlling CD8+ T cell-mediated cytotoxicity (116). The gene discussed is CD8A; the disease is proximal spinal muscular atrophy.