ACAR-H mediated clearance of BCMA negative tumor. (A) BCMA-3 (5807 ABC) and TACI-2 (2229 ABC) SUPT1 targets were transduced with RQR8.2A.Fluc and HA.2A.Fluc, respectively, and used in an in vivo tumor escape model. Twenty-one NSG mice were intravenously injected with a total of 3.5 × 106 BCMA- and TACI-expressing SUPT1 cells at a ratio of 4:1. At D+4, mice were intravenously injected with NT PBMCs, and T cells transduced with ACAR-H or a CAR construct targeting BCMA alone (BCMA CAR) at a dose of 5 × 106 CAR cells/animal (n = 7 per cohort). Tumor burden was monitored by BLI at different time points (dorsal views shown). (B) Average radiance (p/s/cm2/sr) of whole mice in the 3 groups at different time points. (C) Nine days post-CAR T cells, the experiment was terminated, and FACS of BM MNCs showed persistent engraftment of BCMA and TACI SUPT1 cells following NT T cells, clearance of both cell populations by ACAR-H T cells, and eradication of BCMA expressing tumor only by BCMA CAR (single example from 3 cohorts shown). (D) SUPT1 cells were identified as live/single/muCD11b−/CD2−/CD4+/CD8+ and BCMA (i) and TACI (ii) expression determined by RQR8 and HA staining, respectively, with numbers normalized to Flow-Check beads to calculate relative engraftment. Mean ± SEM shown. **P < .01, ***P < .001 by t test.
