Transgene expansion and persistence and response in patients with B-ALL. Tisagenlecleucel transgene levels over time among patients who achieved ongoing CR and among patients who experienced CD19⁻ and CD19⁺ relapses. The solid transgene curves represent profiles with persistent transgene levels, whereas the profiles with loss of persistence, at some point during follow-up after CAR T-cell therapy, are represented by dashed lines. The thick horizontal black dashed line represents the lower limit of quantification. The geometric mean expansion (n, geometric mean % coefficient of variation) in ongoing CR with persistence, ongoing CR without persistence, CD19⁻ relapse, patients with CD19⁺ transgene persistence, and patients with CD19⁺ relapse with no persistence were observed to be 49 800 (n = 23, 95%), 43 600 (n = 24, 204%), 49 300 (n = 25, 110%), 5250 (n = 2, 212%), and 12 000 copies per μg (n = 12, 190%), respectively.