Two-year follow-up of KTE-X19, an anti-CD19 chimeric antigen receptor (CAR) T-cell therapy, in adult patients (Pts) with relapsed/refractory B-cell acute lymphoblastic leukemia (R/R B-ALL) in ZUMA-3.

7010 Background: Brexucabtagene autoleucel (KTE-X19) is an autologous anti-CD19 CAR T-cell therapy approved in the US to treat adult R/R B-ALL based on the ZUMA-3 study. The overall complete remission (CR) rate (CR + CR with incomplete hematologic recovery [CRi]) was 71% (95% CI, 57-82) after 16.4 mo median follow-up (N = 55; Shah et al. Lancet 2021). Here, we report updated outcomes with longer follow-up in these pts and in a larger pooled analysis of Phase (Ph) 1 and 2 pts who received the pivotal dose of KTE-X19. Methods: Eligible adults (≥18 years) had R/R B-ALL and received a single infusion of KTE-X19 at the pivotal dose (1×106 CAR T cells/kg) following leukapheresis and conditioning chemotherapy. The primary endpoint was CR/CRi rate by central review. Results: As of 23 July 2021, median follow-up was 26.8 mo (range, 20.7-32.6) for treated Ph 2 pts (N = 55). The CR/CRi rate per central review was 71% (95% CI, 57-82; 56% CR; 15% CRi). Eleven pts (20%; 8 CR and 2 CRi) proceeded to subsequent allogeneic stem cell transplant (alloSCT). Median duration of remission (DOR) censored at subsequent alloSCT was 14.6 mo (9.4-not estimable [NE]); not censored: 18.6 mo (9.6-NE); 6/39 responders (15%) had ongoing responses at data cutoff. Median (95% CI) relapse-free survival (RFS) was 11.6 mo (2.7-20.5) censored at subsequent alloSCT and 11.7 mo (2.8-20.5) not censored at subsequent alloSCT; 18-mo RFS rates (95% CI) were 35% (20.5-50.6) and 42% (28.0-55.0), respectively. Median (95% CI) overall survival (OS) was 25.4 mo (16.2-NE) among all KTE-X19-treated pts and not reached (25.4-NE) in pts with CR (n = 31). For Ph 1/2 pts (N = 78) who received the pivotal KTE-X19 dose (median follow-up: 29.7 mo; range 20.7-58.3), the CR/CRi rate by independent review was 73% (95% CI, 62-82). Medians (95% CI) for DOR, RFS, and OS were 18.6 mo (9.6-NE), 11.7 mo (6.1-20.5), and 25.4 mo (16.2-NE), respectively. A subgroup analysis revealed that in pts aged 18-39 (n = 36), 40-59 (n = 27), and ≥60 (n = 15) years, the CR/CRi rates (95% CI) were 69% (52-84), 70% (50-86), and 87% (60-98); 24-mo OS rates (95% CI) were 48% (30-64), 54% (33-71), and 57% (28-78), respectively. In pts with pre-KTE-X19 infusion marrow blast percentages > 25 to ≤50 (n = 12), > 50 to ≤75 (n = 14), and > 75 to 100 (n = 30), CR/CRi rates (95% CI) were 83% (52-98), 86% (57-98), and 57% (37-75); 24-mo OS rates (95% CI) were 58% (27-80), 55% (26-77) and 37% (19-55), respectively. There were no new safety signals; the proportion of treated Ph 2 pts with Gr ≥3 treatment emergent adverse events was unchanged since prior data cutoff. One pt had an ongoing neurologic event of Gr 1 finger numbness. Conclusions: With longer follow-up and an expanded data set by independent review, outcomes remain durable in adults with R/R B-ALL, most of whom were heavily pretreated, with median OS not yet reached in pts with CR. Long-term safety was favorable. Clinical trial information: NCT02614066.