Expansion and persistence of infused CD19-CAR T cells does not correlate with disease burden or cell dose. CAR T-cell expansion was determined by qPCR for the CD19-CAR transgene. CAR expansion based on (A) high (≥40% morphologic blasts in the BM) and low disease burden or (B) cell dose (DL1, dose level 1 [1 × 10⁶ CAR⁺ T cells per kg]; DL2, dose level 2, 3 × 10⁶ CAR⁺ T cells per kg]). (C and D) Peak expansion is stratified for disease burden or cell dose. (E and F) The area under the curve analysis for the first 28 days after the infusion was stratified for disease burden or cell dose. (G and H) The ratio of qPCR for the CD19-CAR transgene and the TRAC locus at 4 weeks after infusion in PB, BM, and CSF stratified for disease burden or cell dose. For patient 12 (low disease burden), qPCR data were only available until day 7 after CAR T cell infusion due to coronavirus disease 2019 (COVID-19); qPCR data are shown in panels (A and B) but not included in the analysis; t test. ns, not significant. ∗∗P < .01 and ∗∗∗P < .001.