IL3RA and neoplasm: Since relapses at a low UCART123 dose level were associated with CD123 + disease recurrence, we injected secondary recipient mice with 2 × 106 relapsed BPDCN tumor cells (CD123+ tumor cells collected from the spleen of a mouse from the group treated with 1 × 106 UCART123 in the initial PDX-3 experiment), and randomized upon engraftment into vehicle or 1 × 106 UCART123 treatment cohorts (Supplementary Fig. 12a).