Solh, Melhem

Abstract BMT CTN (Blood and Marrow Transplant Clinical Trials Network) 1506 (“MORPHO”) was a randomized study of gilteritinib compared with placebo as maintenance therapy after hematopoietic cell transplantation (HCT) for patients with FLT3-ITD–mutated acute myeloid leukemia (AML). A key secondary end point was to determine the impact on survival of before and/or after HCT measurable residual disease (MRD), as determined using a highly sensitive assay for FLT3-ITD mutations. Generally, gilteritinib maintenance therapy was associated with improved relapse-free survival (RFS) for participants with detectable peri-HCT MRD, whereas no benefit was evident for those lacking detectable MRD. We conducted a post hoc analysis of the data and found that the level of MRD detected with this approach correlated remarkably with RFS and relapse risk, and that MRD detectable at any level negatively affected RFS. In the placebo arm, 42.2% of participants with detectable FLT3-ITD MRD relapsed compared with 13.4% of those without detectable MRD. We found that 14.8% of participants had multiple FLT3-ITD clones detected as MRD and had worse survival irrespective of treatment arm. Finally, we examined the kinetics of FLT3-ITD clonal relapse or eradication and found that participants on the placebo arm with detectable MRD relapsed rapidly after HCT, often within a few weeks. MRD-positive participants on the gilteritinib arm relapsed either with FLT3 wild-type clones (assessed by capillary electrophoresis), after cessation of gilteritinib with persistent MRD, or on progression of multiclonal disease. These data demonstrate the potential of FLT3-ITD MRD to guide therapy with gilteritinib for this subtype of AML. This trial was registered at www.clinicaltrials.gov as #NCT02997202.

Introduction: Brexucabtagene autoleucel (brexu cel) is a CD19-targeted chimeric antigen receptor (CAR) T cell therapy approved for the treatment of adults with relapsed/refractory (R/R) acute lymphoblastic leukemia (ALL). Some patients (pts) proceed with a consolidative allogeneic hematopoietic cell transplant (HCT) after breux cel. We do not know which pts can safely avoid a consolidative HCT and its associated morbidity. Methods: We conducted a retrospective cohort study utilizing the Real-World Outcomes Collaborative of CAR-T in Adult ALL (ROCCA) dataset. ROCCA is a registry of brexu cel pts in 32 centers in North America. We defined complete remission (CR) as < 5% blasts in the bone marrow and no central nervous system (CNS) or extramedullary (EM) disease on or around D28 after brexu cel. We defined measurable residual disease negative (MRD-) CR as CR and no abnormal blasts in the bone marrow by multiparameter flow cytometry, quantitative polymerase chain reaction, ClonoSeq next generation sequencing (NGS), or other sequencing modalities with lower sensitivity. ClonoSeq NGS has a sensitivity of 10-6, while the other modalities have a sensitivity of at least 10-4. We defined progression free survival (PFS) as the time from CAR-T infusion to relapse or death, censored at the date of last follow-up. Statistical analyses were performed in R. Univariable Cox proportional hazards regression analyses were performed to determine the association of pre-specified variables with PFS. Variables known to be associated with CAR T outcomes in ALL were entered into a multivariable model. HCT was incorporated as a time-varying covariate. Results: During the study period, 281 pts were infused with brexu cel. We focused our analysis on 172 (61%) pts with confirmed MRD- CR on D28, as that is the group with clinical equipoise regarding maintenance strategy. 38 (22%) of those pts received a consolidative HCT, 30 (17%) received another form of maintenance therapy (primarily tyrosine kinase inhibitors for Philadelphia (Ph)-chromosome positive ALL), and 104 (60%) pts received no maintenance therapy. Pts who underwent consolidative HCT were younger (median age 35 years) than those who received no maintenance (42y) (p = 0.023) and were less likely to have a history of prior HCT (13% vs. 47%, p < 0.001). No differences were observed with respect to sex, TP53 mutation status, prior inotuzumab (ino) or blinatumomab (blina) exposure, disease burden prior to CAR, or development of any cytokine release syndrome (CRS) or any neurotoxicity with brexu cel. We performed univariable Cox proportional hazard regression analyses among pts in MRD- CR on D28, excluding those who received other maintenance therapy besides HCT; the median follow up was 8.1 months. In univariable analyses, D28 MRD negativity by ClonoSeq NGS (versus MRD negativity by other, less sensitive methods), development of CRS, and pre-CAR BM blasts < 5% were associated with improved PFS; prior ino exposure was negatively associated with PFS (p < 0.05). Age, sex, Ph status, TP53 status, and neurotoxicity development were not associated with PFS. In a multivariable model incorporating ALL type, prior HCT, prior ino/blina, and pre-CAR blast burden, as well as consolidative HCT as a time-varying covariate, only MRD negativity by ClonoSeq NGS with at least 10-6 sensitivity retained statistical significance (PFS hazard ratio 0.34, 95% confidence interval (CI) 0.15-0.77, p = 0.005). Pts who were MRD- by ClonoSeq NGS on D28 and received no maintenance had favorable 6m PFS of 76% (95% CI: 59-98%) and OS of 100% with a median follow up of 6.3 months in this subgroup. Among those in MRD- CR by NGS, HCT as a time-varying covariate was not associated with improved PFS (HR 0.6, p = 0.6). Conclusions: In a large real-world cohort of adults with R/R B-ALL infused with brexu cel, we identified practice variation regarding the use of consolidative HCT. Among brexu cel recipients who entered an MRD- CR, we identified ClonoSeq NGS MRD negativity as a novel predictive factor of favorable oncologic outcomes, even without a consolidative HCT. Similar results have been obtained in pediatric ALL patietns ftreated with 41BB-based tisagenleucleucel (Pulsipher et al., Blood Cancer Discovery 2022). Longer follow-up is needed to validate the safety of omitting consolidative HCT in such pts, but these results encourage the potential for definitive therapy with brexu cel when D28 ClonoSeq NGS MRD is negative.

Introduction: Brexucabtagene Autoleucel (brexu-cel) is the first CD19-targeting chimeric antigen receptor (CD19.CAR) T-cell therapy approved for the treatment of relapsed/refractory (r/r) B-cell acute lymphoblastic leukemia (B-ALL) in adult (≥18 yo) patients (pts) based on results from the ZUMA-3 trial. However, data on the safety and efficacy of CAR-T cells in older pts (≥60 yo) remains limited, with only 8 pts >65 yo enrolled in the ZUMA-3 trial. We evaluated the treatment characteristics and outcomes with use of brexu-cel amongst patients ≥60 yo in the Real-World Outcomes Collaborative for CAR-T in ALL (ROCCA) consortium database. Methodology: ROCCA is a consortium of over 30 U.S.-based institutions with a database of adult pts with B-ALL who received brexu-cel as standard of care therapy. We identified pts ≥60 yo and further stratified them into two cohorts: 60-69 yo and ≥70 yo. Outcomes of interest included OS, PFS, ORR, and toxicities (CRS and ICANS). Both OS and PFS were calculated from the day of brexu-cel infusion. Response assessment occurred on day +28, and MRD evaluation was per institutional practices. CRS and ICANS were graded according to the American Society for Transplantation and Cellular Therapy criteria. Results: Of 280 brexu-cel recipients in the ROCCA database, 73 (26%) were ≥60 yo, of which 58 (79%) were between 60-69 yo and 15 (21%) were ≥70 yo. Among pts ≥60 yo, the median age at infusion was 65 (range 60-81). Pts were heavily pretreated with a median of 3 prior lines of therapy (range 2-9). Prior therapies included: allogeneic HSCT (38%), inotuzumab ozogamicin (41%), and blinatumomab (62%). Forty pts (55%) had Ph-negative B-ALL, 24 (33%) had Ph+ B-ALL and 9 (12%) had Ph-like B-ALL. When grouped by HCT-CI equal to 0, 1-2 or ≥3, a higher proportion of pts ≥60 yo had HCT-CI ≥3 (19% vs. 7% in <60 yo; p=0.004). Pre-apheresis, 33 pts (45%) had active disease (>5% marrow blasts or extramedullary disease), 34 (47%) were in CR (of whom 14 were MRD-negative) and 6 had unknown disease status. Following brexu-cel, 43 (59%) achieved MRD-negative CR, 20 (27%) had MRD + or CR with unknown MRD status, 6 (8%) had refractory disease and 5 had no disease evaluation available. The ORR was similar between pts 60-69 and ≥70 yo (MRD-negative CR rate: 58% vs 61%, r/r to brexu-cel: 9% vs 6%) and was comparable to pts <60 yo (MRD-negative CR 66%; r/r disease of 9%). The rate of all grade ICANS was higher in pts ≥70 (77%) than in pts 60-69 (47%) or pts <60 (49%), with grade 1-2 ICANS occurring at a significantly higher rate in pts ≥70 (44% vs. 20% in 60-69 and 20% in <60, p=0.049). Grade 3-4 ICANS were similar between the groups: 33%, 27% and 29% in the ≥70, 60-69, and <60 groups, respectively. Conversely, rates of CRS were similar across age groups (80-84%). There was no statistically significant difference in the rate of grade 3-4 CRS which was 17% in pts ≥70, 4% in pts 60-69, and 11% in pts <60 yo. With a median follow-up of 332 days (range 8-936 days) from infusion, pts ≥60 yo had a median PFS of 395 days compared to 547 days in pts <60 yo. Median PFS was lower in the ³70 yo (231 days) compared to 677 in the 60-69 yo cohort. No statistically significant difference was found between the <60 and ≥60groups in 6- and 12-month PFS rates (6 months PFS: 66% vs 64%, p=0.77 and 12 months PFS: 57% vs 57%, p=1.00). When pts ≥60 yo were stratified by age, pts ≥70 yo had similar 6-month PFS compared to other age groups but significantly lower 12-month PFS (38%; vs. 64% in pts 60-69and 57% in pts <60, p=0.001). Median OS was not reached in any of the age groups, and there was no statistically significant difference in 6-month OS (72% in ≥ 70 vs. 82% in the 60-69 vs. 82% in <60, p=0.14) or 12-months OS (61% in ≥ 70 vs. 69% in 60-69 vs. 73% in <60, p=0.18). Conclusion: This is the largest study to date of older B-ALL pts receiving CAR-T cells. We observed that older pts, particularly those aged 60-69, have similar outcomes to younger pts. However, pts ≥70 yo had lower median and 12-month PFS when compared to younger patients. Additionally, pts ≥70 yo had higher rates of grades 1-2 ICANS. An important limitation of this analysis is the potential selection bias among clinicians when selecting older patients for this treatment. Longer follow-up, including inclusion of additional pts ≥70 yo is needed to confirm these results, and further studies are needed to identify the optimal approach for use of CAR T-cell therapy in patients in this age group.

PURPOSE On the basis of the results of the ZUMA-3 trial, brexucabtagene autoleucel (brexu-cel), a CD19-directed chimeric antigen receptor T-cell therapy, gained US Food and Drug Administration approval in October 2021 for adults with relapsed/refractory (R/R) B-cell ALL (B-ALL). We report outcomes of patients treated with brexu-cel as a standard therapy. METHODS We developed a collaboration across 31 US centers to study adults with B-ALL who received brexu-cel outside the context of a clinical trial. Data were collected retrospectively from October 2021 to October 2023. Toxicities were graded per American Society for Transplantation and Cellular Therapy guidelines for cytokine release syndrome (CRS) and immune effector cell–associated neurotoxicity syndrome (ICANS). RESULTS At the time of data lock, 204 patients had undergone apheresis and 189 were infused. Median follow-up time was 11.4 months. Forty-two percent of patients received brexu-cel in morphologic remission and would have been ineligible for participation in ZUMA-3. After brexu-cel, 151 achieved complete remission (CR), of which 79% were measurable residual disease (MRD) negative remissions. Median progression-free survival (PFS) was 9.5 months and median overall survival was not reached. Grade 3-4 CRS or ICANS occurred in 11% and 31%, respectively. In multivariable analysis, patients receiving consolidative hematopoietic cell transplantation (HCT; hazard ratio, 0.34 [95% CI, 0.14 to 0.85]) after brexu-cel had superior PFS compared with those who did not receive any consolidation or maintenance therapy. CONCLUSION Similar to ZUMA-3, high rates of MRD-negative CR were observed after brexu-cel treatment for R/R B-ALL. The use of HCT as consolidation after brexu-cel resulted in improved PFS.

Abstract The effect of prior inotuzumab ozogamicin (InO) treatment on brexucabtagene autoleucel (brexu-cel) outcomes remains unclear in adults with acute lymphoblastic leukemia (ALL). We conducted a retrospective multicenter analysis of 189 patients with relapsed/refractory ALL treated with brexu-cel. Over half of the patients received InO before brexu-cel (InO exposed). InO-exposed patients were more heavily pretreated (P = .02) and frequently had active marrow disease before apheresis (P = .03). Response rate and toxicity profile after brexu-cel were comparable for InO-exposed and InO-naïve patients; however, consolidation therapy after brexu-cel response was used at a higher rate in InO-naïve patients (P = .005). With a median follow-up of 11.4 months, InO-exposed patients had inferior progression-free survival (PFS; P = .013) and overall survival (OS; P = .006) in univariate analyses; however, prior InO exposure did not influence PFS (hazard ratio, 1.20; 95% confidence interval, 0.71-2.03) in multivariate models. Within InO-exposed patients, InO responders had superior PFS (P = .002) and OS (P < .0001) relative to InO-refractory patients. The timing of administering InO did not affect brexu-cel outcomes, with comparable PFS (P = .51) and OS (P = .86) for patients receiving InO as bridging therapy or before apheresis. In conclusion, although InO exposure was associated with inferior survival outcomes after brexu-cel in unadjusted analyses, these associations were no longer significant in multivariate analyses, suggesting it is unlikely that InO negatively affects brexu-cel efficacy. Our data instead imply that InO-exposed recipients of brexu-cel tend to be higher-risk patients with intrinsic adverse leukemia biology.

Abstract We evaluate the impact of donor types on outcomes of hematopoietic cell transplantation (HCT) in myelofibrosis, using the Center for International Blood and Marrow Transplant Research registry data for HCTs done between 2013 and 2019. In all 1597 patients, the use of haploidentical donors increased from 3% in 2013 to 19% in 2019. In study-eligible 1032 patients who received peripheral blood grafts for chronic-phase myelofibrosis, 38% of recipients of haploidentical HCT were non-White/Caucasian. Matched sibling donor (MSD)–HCTs were associated with superior overall survival (OS) in the first 3 months (haploidentical hazard ratio [HR], 5.80 [95% confidence interval (CI), 2.52-13.35]; matched unrelated (MUD) HR, 4.50 [95% CI, 2.24-9.03]; mismatched unrelated HR, 5.13 [95% CI, 1.44-18.31]; P < .001). This difference in OS aligns with lower graft failure with MSD (haploidentical HR, 6.11 [95% CI, 2.98-12.54]; matched unrelated HR, 2.33 [95% CI, 1.20-4.51]; mismatched unrelated HR, 1.82 [95% CI, 0.58-5.72]). There was no significant difference in OS among haploidentical, MUD, and mismatched unrelated donor HCTs in the first 3 months. Donor type was not associated with differences in OS beyond 3 months after HCT, relapse, disease-free survival, or OS among patients who underwent HCT within 24 months of diagnosis. Patients who experienced graft failure had more advanced disease and commonly used nonmyeloablative conditioning. Although MSD-HCTs were superior, there is no significant difference in HCT outcomes from haploidentical and MUDs. These results establish haploidentical HCT with posttransplantation cyclophosphamide as a viable option in myelofibrosis, especially for ethnic minorities underrepresented in the donor registries.

PURPOSE Allogeneic hematopoietic cell transplantation (HCT) improves outcomes for patients with AML harboring an internal tandem duplication mutation of FLT3 ( FLT3-ITD) AML. These patients are routinely treated with a FLT3 inhibitor after HCT, but there is limited evidence to support this. Accordingly, we conducted a randomized trial of post-HCT maintenance with the FLT3 inhibitor gilteritinib (ClinicalTrials.gov identifier: NCT02997202 ) to determine if all such patients benefit or if detection of measurable residual disease (MRD) could identify those who might benefit. METHODS Adults with FLT3-ITD AML in first remission underwent HCT and were randomly assigned to placebo or 120 mg once daily gilteritinib for 24 months after HCT. The primary end point was relapse-free survival (RFS). Secondary end points included overall survival (OS) and the effect of MRD pre- and post-HCT on RFS and OS. RESULTS Three hundred fifty-six participants were randomly assigned post-HCT to receive gilteritinib or placebo. Although RFS was higher in the gilteritinib arm, the difference was not statistically significant (hazard ratio [HR], 0.679 [95% CI, 0.459 to 1.005]; two-sided P = .0518). However, 50.5% of participants had MRD detectable pre- or post-HCT, and, in a prespecified subgroup analysis, gilteritinib was beneficial in this population (HR, 0.515 [95% CI, 0.316 to 0.838]; P = .0065). Those without detectable MRD showed no benefit (HR, 1.213 [95% CI, 0.616 to 2.387]; P = .575). CONCLUSION Although the overall improvement in RFS was not statistically significant, RFS was higher for participants with detectable FLT3-ITD MRD pre- or post-HCT who received gilteritinib treatment. To our knowledge, these data are among the first to support the effectiveness of MRD-based post-HCT therapy.

Cellular Immunotherapies: Late Phase and Commercially Available Therapies The Impact of Inotuzumab Ozogamicin (InO) Treatment on Brexucabtagene Autoleucel (Brexu-cel) Outcomes in Adults with Relapsed/Refractory B-cell Acute Lymphoblastic Leukemia (B-ALL) Introduction: Brexu-cel is the first approved CD19-directed chimeric antigen receptor (CAR) T-cell therapy for adult patients (pts) with relapsed/refractory (r/r) B-ALL. InO, an anti-CD22 antibody drug conjugate, is also approved for the same indication. With the accessibility to several targeted therapies in r/r B-ALL, the optimal sequence remains uncertain. The effect of prior treatment with InO on brexu-cel outcomes remains underreported, especially as a bridging therapy, as well as the effect of previous response to InO on post brexu-cel outcomes. Methods: This is a retrospective multicenter analysis from 25 U.S. institutions of adults (≥18 years) with r/r B-ALL treated with commercial brexu-cel from 2021 to 2023 post FDA approval. Methodologies for assessing minimal residual disease (MRD) (minimal threshold of 10 -4) included flow cytometry, NGS, or qPCR depending on institutional practice. Progression-free survival (PFS) and overall survival (OS) were calculated from day of brexu-cel infusion and were not censored for hematopoietic cell transplant (HCT) or maintenance. All living patients were censored at the time of last follow-up prior to data lock, which occurred on June 30, 2023. Results: Among 152 infused, 83 (54.6%) had pre-CAR InO therapy (InO-exposed), with a median of 3 administered doses (range: 1-22). Within the InO-exposed cohort, 23 (28%) pts received InO as a CAR T-cell bridging therapy (ie, between apheresis and lymphodepletion) with or without pre-apheresis and 60 (72%) pts received InO only during pre-apheresis. Baseline characteristics for InO exposed and InO-naïve pts are shown in Table 1. InO-exposed pts had higher median prior lines of therapies (4 vs. 3; p= 0.05), more frequently had active disease (≥5% marrow blasts) at the time of apheresis (67% vs. 44%, p= 0.02), and had lower incidence of Ph+ disease (19% vs. 45%, p=0.003), compared to InO-naïve pts, respectively. The incidences of cytokine release syndrome (CRS) (85% vs. 85%, p= 0.26) and ICANS (58% vs. 57%, p= 0.36) post infusion were similar, and post-infusion death in remission occurred in 17% and 12% among InO-exposed and InO-naïve pts, respectively. Morphological complete remission (CR) and MRD- rates following brexu-cel infusion were 89% and 77% for InO-exposed pts, and 92% and 70% for InO-naive pts, respectively. Post CAR therapy, more InO-naïve pts underwent consolidation/maintenance therapy (transplant, chemotherapy, or TKIs) compared to InO-exposed pts (41% vs. 19%, p= 0.004). The median follow-up after brexu-cel was 8.4 (range) months. Median OS (not reached (NR) vs. 12 months; p= 0.033) and median PFS (NR vs. 7 months; p= 0.029) were superior in InO-naïve pts compared to InO-exposed pts, respectively. However, after adjusting for pre-apheresis disease burden and post-CAR maintenance therapy, there were no longer significant differences in OS (HR= 1.25;95%CI: 0.62-2.53; p= 0.53) or PFS (HR= 1.24;95%CI:0.71-2.16, p=0.45) based on pre-CAR InO exposure. When InO-exposed pts were stratified based on prior InO-response (CR vs. no response), InO-responsive pts had superior estimated 12-month OS (64%) and PFS (38%) relative to InO-refractory pts (OS: 33%; PFS: 34%), but inferior to InO-naïve pts (OS: 75%; PFS 56%), with p-values of 0.0001 and 0.021 for OS and PFS, respectively (Figure 1). The timing of pre-CAR InO therapy did not impact brexu-cel survival outcomes, with comparable estimated 12-month OS (43% vs. 58%, p= 0.35) and PFS (46% vs. 38%, p= 0.57) for InO-exposed pts during bridging therapy and patients who received InO as a therapy prior to apheresis. Conclusion: After adjusting for pre-CAR disease burden and post-CAR consolidation/maintenance, we found that prior InO exposure does not significantly associate with PFS or OS following brexu-cel. However, relative to InO-responsive patients, patients who were InO-refractory appear to have worse post-CAR survival outcomes. Finally, timing of InO administration (ie as a prior line of therapy or as CAR bridging) did not influence outcomes brexu-cel outcomes.

Background: BMT CTN 1506/MORPHO was a randomized study of the FLT3 inhibitor gilteritinib versus placebo as post-transplant (HCT) maintenance therapy for patients (pts) with FLT3-ITD acute myeloid leukemia (AML). Patients with FLT3-ITD AML in first remission underwent HCT and then were randomized, in double-blind fashion, to either gilteritinib or placebo for 24 months. The primary endpoint was relapse-free survival (RFS), and a pre-specified secondary endpoint was the effect of measurable residual disease (MRD) on survival as detected by a highly sensitive assay for FLT3-ITD mutations. In the primary analysis, while RFS was higher for pts randomized to gilteritinib, the difference did not reach the pre-determined threshold for significance (HR: 0.679; 95% CI: 0.459, 1.005; 2-sided p-value: 0.0518). However, in the secondary analysis, the 50.6% of pts who had MRD detectable pre- or post-HCT had significantly higher RFS with gilteritinib (HR of relapse or death=0.515, 95% CI: 0.316, 0.838, p = 0.0065). In this post-hoc analysis, we examined 1) the impact on RFS of different levels of FLT3-ITD variant allele frequency (VAF) pre-randomization (immediately before or after HCT but prior to randomization to gilteritinib or placebo); 2) the impact of the presence of multiple mutations detected as MRD pre-HCT; and 3) the eradication of FLT3-ITD clones detected post-HCT during follow up on gilteritinib or placebo. Methods: First-pull marrow aspirates were collected from pts at two time points pre-randomization (pre-HCT and between 30-90 days post-HCT), as well as at 3, 6, 12, 18, and 24 months post-randomization. For MRD detection (performed at Invivoscribe; San Diego, CA), 700 ng input DNA was amplified by polymerase chain-reaction (PCR) using 25 cycles and primers flanking exons 14 and 15 of FLT3, followed by next-generation sequencing (NGS) analysis of the amplicons. Variant allele frequency (VAF) was calculated as FLT3 mutant reads/total FLT3 reads. For pts with multiple FLT3-ITD mutations, the VAF used in analysis was the sum of the VAFs for each FLT3-ITD variant. The lower limit of blank (LOB) of the assay is estimated to be 1 x 10 -6 VAF. For terminology, VAF > 1 x 10 -6 and < 1 x 10 -5 is referred to as MRD6, VAF > 1 x 10 -5 and < 1 x 10 -4 is MRD5, VAF > 1 x 10 -4 or greater is MRD4, and MRD0 equals no detectable MRD. Results: MRD was evaluated in 350/356 (98.3%) pts pre-HCT and 347/356 (97.5%) pts post-HCT. MRD was detected in 46% of pts pre-HCT and 19.9% prior to randomization, including 4.5% who did not have detectable MRD pre-HCT. The variant allele frequency (VAF) of detectable MRD ranged from a low of 1.09 x 10 -6 to a high of 3.0 x 10 -1. More than a single mutation was detected in 51 pts pre-HCT. Most of these 51 pts had 2 clones, but the total ranged from 2-9. The presence of more than one mutation detected as MRD immediately pre-HCT was associated with worse RFS compared with all other pts (MRD-positive with only one clone and MRD-negative), irrespective of treatment arm (Figure 1A; HR=2.428, 95% CI: 1.555, 3.792, P < 0.001). There was no significant difference in age, mutation length, VAF, or karyotype between pts with more than one mutation and those with single mutations. However, if the VAFs of pts with multiple FLT3-ITD mutations were summed and treated as a single value, then the median VAF for pts with multiple mutations was higher than for those with single mutations (2.14 x 10 -4 vs. 3.12 x 10 -5). The VAF (including the summed VAFs of pts with multiple mutations) at multiple levels correlated very closely with RFS after HCT. To illustrate this quantitative effect of peri-HCT FLT3-ITD VAF on RFS, Kaplan-Meier analysis of pts on the placebo arm grouped by MRD level is displayed in Figure 1B. In the 71 pts with MRD detectable post-HCT, the MRD was eradicated in 69% of pts on gilteritinib versus 44% of pts on placebo. Conclusions Pts with multiple FLT3-ITD mutations have a worse prognosis, which may simply be a reflection of increased disease burden (VAF). The quantity of FLT3-ITD MRD appears to highly correlate with outcome. Gilteritinib appears to augment the effect of HCT, as evidenced by increased eradication of MRD post-HCT. These data illustrate the potential utility of the PCR-NGS FLT3-ITD MRD assay in the management of pts with FLT3-ITD AML.

Introduction: In October 2021, the FDA approved brexu-cel for the treatment of adults ≥ 18 years old with R/R B-ALL. Following this approval, a consortium of cancer centers was formed across the US to investigate outcomes following commercial brexu-cel use for adults with R/R B-ALL. One area of interest is the toxicity profile of brexu-cel when given in the real-world context, including the respective incidences and severity of cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity (ICANS). Methods: Eligible pts included adults ≥ 18 years old who received commercial brexu-cel starting in October 2021 onward at a participating center in the US (N = 25). Retrospective patient data were collected across participating institutions, with the most recent data lock occurring on June 30, 2023. Criteria from the ASTCT were used to grade CRS and ICANS severity. Statistical methods included the use of medians and simple ratios for descriptive outcomes; univariate logistic regression models were used to assess the association of various factors with the probability of CRS and ICANS, and Cox regression was used to examine the association of each with the hazards of mortality and failure for event-free survival (EFS; earliest of progression, relapse, or death). Results: Key demographics and toxicities are described in Tables 1 and 2 (respectively). Of the 152 pts infused with brexu-cel, 82% (N = 125) developed CRS and 56% (N = 85) developed ICANS. CRS and ICANS did NOT develop in 12% (N = 19). Twenty percent of all pts (N = 31) required ICU-level care for management of CAR-related toxicities, with a median LOS in ICU of 4 days (range 1-79). In univariate models, grade 3+ ICANS was most likely to occur in pts with active disease (≥ 5% marrow blasts and/or EMD) at the time of apheresis (OR 2.63, 1.28-5.38, p = 0.008); a numerical increase for grade 3+ CRS (OR 2.35, 0.69-8, p = 0.17) was seen in pts with active disease at apheresis. Therapies received for these CAR-related toxicities included steroids, tocilizumab (toci), and anakinra (Table 2). Among pts who received steroids (N = 94), 37% (N = 34) achieved a sufficient response to the first steroid trial and did not require subsequent therapies; otherwise, toxicities improved with the first steroid course but later worsened in 16% (N = 15); the first trial of steroids was not effective but improved when further steroids were given in 31% (N = 29); there were no responses to any doses of steroids in 10% (N = 9). In pts receiving toci (N = 103), 31% (N = 32) achieved a sufficient response to the first dose and did not require any further therapy; toxicities improved with the first dose but later worsened in 31% (N = 32); the first dose was ineffective but improvement was seen with subsequent doses in 21% (N = 22); 9% (N = 9) did not respond at all to toci. The rate of death within day +28 was 6% (N = 9), and the respective causes were typically multifactorial: CRS was implicated in 3 cases, ICANS in 3, infection in 5, disease relapse/progression in 2, and HLH in 1 case. In total, uncontrolled ICANS was implicated in the death of 6 pts (between day +9 to day +106). HLH was reported in 6 pts: in most cases, this was a biochemical diagnosis, and it either overlapped with concurrent CRS or infection or occurred following CRS/ICANS. The most common infections between day 0 and day +28 included bacteremia in 8% of pts (N = 12), fungal infections in 4% (N = 6), pneumonia in 3% (N = 5), and CMV infections in 3% (N = 4). The fungal infections included 4 instances of invasive sinopulmonary infections (2 due to aspergillus; 2 due to mucormycosis) and 2 cases of candidemia. With both CRS and ICANS treated as a time-varying covariate, the development of grade 3+ CRS was associated with a higher hazard of death (HR 2.38, 1.00-5.66, p = 0.05); grade 3+ ICANS was not associated with a demonstrably higher risk of death (HR 1.11, 0.60-2.05, p = 0.74). The HR of EFS failure for Grade 3+ CRS was 1.81 (0.87-3.79, p = 0.12) and for grade 3+ ICANS HR = 0.93 (0.56-1.53, p = 0.77). Conclusions: In this real-world study of toxicities from brexu-cel use for adults with R/R B-ALL, we observed CRS and ICANS in the majority of pts, and no new safety signals were observed. Rates of severe CRS and ICANS were more common with active disease. Interestingly, though CRS-related mortality was rare, grade 3+ CRS was associated with a higher risk of death. Efforts to identify mechanisms and mitigable risk factors for these toxicities are warranted.