PSI in conjunction with CAR T-cell expansion in vivo or in conjunction with conditioning-driven IL-15 pre–CAR T-cell infusion correlates with OR. CAR T-cell levels in blood measured by quantitative PCR were correlated with clinical outcome. A composite index integrating PSI and CAR T-cell expansion in vivo was developed as detailed in the supplemental Methods and was associated with OR. The metrics were added to each other after each was first standardized to have unit variance. This standardization was achieved by dividing the metrics by their respective standard deviation to bring them to a common magnitude/scale. Whole product PSI alone (A), peak CAR levels in blood alone (B), and product PSI in conjunction with peak CAR levels (C) are shown in association with OR. Pre–CAR T-cell infusion (day 0) IL-15 serum levels alone (D) or in conjunction with product PSI (E) are shown in association with OR. Statistical values were computed using the Mann Whitney U test (P values were not adjusted for multiplicity).