Deletions occurred during the ex vivo production of GMCs. Using nested PCR assays with a second run using a specific primer spanning the junction sequence, no deletions within packaging cell line DNA (PC) were detected. PCR products were detected within GMC products before infusion (D0), as well as 1, 3, 6, and 9 years (Y) after infusion. Specific PCR was applied to GMC samples of the 4 patients, enabling demonstration that deletions were patient specific. ND indicates not done. Vertical lines have been inserted to indicate a repositioned gel lane.