Pretreating mice with tafasitamab does not affect CART19 cell therapy. (A-B) The schemes of “two-step” JeKo-1 xenograft mouse model. (A) Immunocompromised NSG mice were inoculated with 1 × 10⁶ of luciferase⁺JeKo-1 via IV injection. On day −1, the mice were imaged and randomized based on the tumor burden to receive either 10 mg/kg per day of tafasitamab or PBS. Treatment was performed three times per week until the end point. The mice were euthanized when they reached the end point, and their spleens were harvested and cryopreserved. (B) NSG mice were inoculated with 1 × 10⁶ splenocytes (IV) obtained from panel A. On day −1, the mice were imaged and randomized based on the tumor burden to receive UTD or CART19. (C-D) BLI of mice engrafted with splenocytes derived from PBS (C) or tafasitamab (D) pretreated xenograft mice. (E) BLI curve for PBS-pretreated JeKo-1 xenograft model (mean ± SEM, ∗∗P < .01 at days 13, 20, and 27, t test); n = 5 in each group. (F) Kaplan-Meier curve for the PBS-pretreated JeKo-1 xenograft model (∗∗P < .01, log-rank test; hazard ratio (HR), 7.0; 95% confidence interval [CI], 1.381-35.48). (G) BLI curve for tafasitamab-pretreated xenograft mice (mean ± SEM, ∗P < .01 at days 13, 20, and 27, t test); n = 5 in each group. (H) Kaplan-Meier curve for the tafasitamab-pretreated JeKo-1 xenograft model. Mice treated with CART19 showed significantly better survival than those in the UTD group (∗∗P < .01, log-rank test; HR, 3.689; 95% CI, 0.8209-16.58). (I) BLI curves comparing CART19-administered mice engrafted with splenocytes derived from PBS- or tafasitamab-pretreated xenograft mice (mean ± SEM, ∗P < .05 at day 41, t test). (J) Kaplan-Meier curves comparing CART19-administered mice engrafted with splenocytes derived from PBS- or tafasitamab-pretreated xenograft mice (P = .05, log-rank test; HR, 5.96; 95% CI, 0.9971-35.63).