Brexucabtagene autoleucel (Brexu-cel) as consolidation treatment in adults with B-cell acute lymphoblastic leukemia.

6543 Background: Brexu-cel is a CD19 CAR T cell approved for adult patients with R/R B-cell ALL. We aimed to evaluate toxicity/efficacy in adult pts with marrow blasts <5%. Methods: We retrospectively analyzed pts (≥18y) with B-ALL who received brexu-cel (not on clinical trials) at MDACC, Houston. Pts were included if they had marrow blasts <5% and without any clinical (and imaging) evidence of extra-medullary disease (EMD) at the time of LD. CAR T levels were monitored post infusion in PB using flow cytometry. Results: 46 pts received Brexu-cel from Feb 2022 to Dec 2024. Baseline characteristics are as in table 1. 36/46 pts were NGS MRD negative (30 had undetectable disease at 10 -6 sensitivity and 6 had disease detectable < LLOD of the assay; clonoSEQ). 10/36 pts were positive at values ranging from 3-3283 cells/million. Post infusion peak CAR T expansion was noted at a median of 8 days from infusion and the median peak expansion was 13.5 cells/µL [range <1-2222]. A peak CAR T expansion threshold of 15 cells/µL was identified as an optimal predictor for RFS with a neg predictive value of 97%. 23/46 (50%) pts of the whole cohort had a peak CAR T expansion of ≥15 cells/µL. Amongst the 10 pts who were NGS MRD positive at the time of CAR T infusion, the median peak CAR T expansion was 77.5 cells/µL [range 3-573] and 7/10 (70%) had a peak expansion of ≥15 cells/µL. Amongst those (n=36) who were NGS MRD negative at the time of CAR T infusion, the median peak CAR T expansion was 10 cells/µL [range <1-2222] and 16/36 (44%) had a peak expansion of ≥15 cells/µL.Among the 23 pts who had a peak expansion of ≥15 cells/µL, 1 had a relapse, 1 died while in MRD negative remission and the remaining 21 (91%) are alive in remission. In contrast, among the 23 pts with a peak expansion of <15 cells/µL, 8 pts had a molecular/clinical relapse while 15/23 (65%) were alive in remission. With a median follow-up of 12.8 mos (range 1-27), the 12-mo RFS is 71% for the whole cohort (86% in the CAR T expansion ≥15 cells/µL; 58% in the peak CART expansion <15 cells/µL). The 12-mo OS is 94% for all pts. 6 pts had a subsequent allo-SCT after the CAR T infusion at the treating physician’s discretion at a median of 3.6 mos (range 2.8-8.8) from the cell infusion. Among the 3 pts with G3-4 CRS/ICANS, (table1) the peak CAR T expansion was 102, 1270 and 2222 cells/µL. Conclusions: Brexu-cel CAR T expansion was observed even in pts with no morphologic disease. CAR T expansion threshold of ≥15 cells/µL could identify pts with durable RFS. Rates of G3-4 CRS/ICANS were low when brexu-cel was used as consolidation. Parameters N (%), median [range]N=46 Age 38 [20-84] ≥60 years 9 (20) Gender Male 29 (63) Disease / Prior Therapy Median lines of therapy 2 [1-4] CART infusion in CR1 12 (26) Prior blinatumomab 44 (94) Prior inotuzumab 35 (76) Prior allo-SCT 7 (15) Ph positive ALL 15 (33) Ph like ALL 10 (28) Post CAR T complications G3 CRSG4 CRS 3 (7) 0 G3 ICANSG4 ICANS 1 (2)1(2)