Fig. 3

MC-dependent basal expression results in potent antitumor activity and the associated toxicity. a, b NSG mice engrafted with CD19⁺ Raji-EGFPluc tumor cells were treated with 5 × 10⁶ non-transduced (NT) or 1 × 10⁶ or 5 × 10⁶ iC9-CD19.ζ-MC-modified T cells via i.v. injection after 7 days. Tumor growth was assessed by bioluminescence imaging (BLI) on a weekly basis for 70 days post-tumor challenge. c Weight of control (NT) and CAR-T-treated animals was measured to assess CAR-related toxicities. Mice exhibited a >20% reduction in weight on days 6 and 13 after receiving 5 × 10⁶ and 1 × 10⁶ iC9-CD19.ζ-MC-modified T cells, respectively. At this time, a single injection of 5 mg/kg rimiducid was administered i.p., which promptly resolved the toxicity. d Serum cytokine levels were assessed in naive (untreated), NT, and CAR-treated animals before and 24 h after rimiducid injection, showing high levels of hIFN-γ and hIL-6 prior to drug administration and returning to background levels following the activation of the iC9 safety switch. e, f Naive mice and mice that received CAR-T cells and rimiducid were subsequently rechallenged with Raji-EGFPluc tumor cells, demonstrating that residual iC9-CD19.ζ-MC-modified T cells can effectively control tumor outgrowth. g, h Twenty-five days post-tumor rechallenge, mice were euthanized and the splenocytes were analyzed for the presence of CAR-T cells (CD3⁺CD34⁺) by flow cytometry and compared with the original product for frequency and CAR expression (mean fluorescence intensity, MFI). *** represents a P-value < 0.005