Study design and CART19 RNA persistence. (A) Study schema. (B) CART19 RNA levels in peripheral blood. These were measured on each infusion day pre- and postinfusion and expressed as normalized ratio of 4-1BB/CD3ζ gene transcript copies by reverse transcription polymerase chain reaction and multiplied by a factor of 1000. Patient 1, who experienced progressive disease (PD), had the lowest CART19 RNA levels, and no CART19 RNA was detected in preinfusion samples. This was in contrast to patient 4, who achieved complete response (CR). He had CART19 RNA detected in 3 of 5 preinfusion samples, reflecting persistence for at least 48 hours from previous infusion on those days. PR, partial response; SD, stable disease.