Introduction of Rab5 into CARTs isolated from patients improves CART function. (a–c) Primary human T cells were activated and transduced with BCMABBz-CAR expressing either tEGFR or Rab5. After 11 days of culture, 1 × 10⁶ CAR⁺ T cells were co-cultured with 2 × 10⁶ H929-GFP cells. Flow cytometry measuring the persistence of GFP-expressing H929 cells and BCMA-specific CARTs before start of CAE assay and after the third tumor challenge (a), BCMA antigen on T cells (b), and surface CAR expression (c). Data are representative of three independent experiments with samples from different healthy donors. (d and e) Representative flow cytometry plots (d) and summary data (e) of BCMA CAR expression in T cells from BCMA-CART–treated MM patients, electroporated with Rab5 or tEGFR encoding mRNA. (f–h) T cells isolated from MM patients previously treated with BCMA-CART therapy were electroporated with tEGFR or Rab5 mRNA, then co-cultured with H929-GFP or KMS-27-GFP tumor cells for 48 h. Tumor elimination capability (f), BCMA expression level (g), and surface BCMA-CAR expression level (h) of patients-derived CARTs, measured by flow cytometry. Experiments in d–h are reproducible with three different donors. Error bar show mean ± SEM. Statistical comparisons were made using unpaired t tests. **P < 0.01.