Single-cell systems pharmacology identifies development-driven drug response and combination therapy in B cell acute lymphoblastic leukemia.

Leukemia can arise at various stages of the hematopoietic differentiation hierarchy, but the impact of developmental arrest on drug sensitivity is unclear. Applying network-based analyses to single-cell transcriptomes of human B cells, we define genome-wide signaling circuitry for each B cell differentiation stage. Using this reference, we comprehensively map the developmental states of B cell acute lymphoblastic leukemia (B-ALL), revealing its strong correlation with sensitivity to asparaginase, a commonly used chemotherapeutic agent. Single-cell multi-omics analyses of primary B-ALL blasts reveal marked intra-leukemia heterogeneity in asparaginase response: resistance is linked to pre-pro-B-like cells, with sensitivity associated with the pro-B-like population. By targeting BCL2, a driver within the pre-pro-B-like cell signaling network, we find that venetoclax significantly potentiates asparaginase efficacy in vitro and in vivo. These findings demonstrate a single-cell systems pharmacology framework to predict effective combination therapies based on intra-leukemia heterogeneity in developmental state, with potentially broad applications beyond B-ALL.

Flow cytometric minimal residual disease measurement accounting for cytogenetics in children with non-high-risk acute lymphoblastic leukemia treated according to the ALL-MB 2008 protocol.

BACKGROUND: Quantitative measurement of minimal residual disease (MRD) is the "gold standard" for estimating the response to therapy in childhood B-cell precursor acute lymphoblastic leukemia (BCP-ALL). Nevertheless, the speed of the MRD response differs for different cytogenetic subgroups. Here we present results of MRD measurement in children with BCP-ALL, in terms of genetic subgroups with relation to clinically defined risk groups. METHODS: A total of 485 children with non-high-risk BCP-ALL with available cytogenetic data and MRD studied at the end-of-induction (EOI) by multicolor flow cytometry (MFC) were included. All patients were treated with standard-risk (SR) of intermediate-risk (ImR) regimens of "ALL-MB 2008" reduced-intensity protocol. RESULTS AND DISCUSSION: Among all study group patients, 203 were found to have low-risk cytogenetics (ETV6::RUNX1 or high hyperdiploidy), while remaining 282 children were classified in intermediate cytogenetic risk group. For the patients with favorable and intermediate risk cytogenetics, the most significant thresholds for MFC-MRD values were different: 0.03% and 0.04% respectively. Nevertheless, the most meaningful thresholds were different for clinically defined SR and ImR groups. For the SR group, irrespective to presence/absence of favorable genetic lesions, MFC-MRD threshold of 0.1% was the most clinically valuable, although for ImR group the most informative thresholds were different in patients from low-(0.03%) and intermediate (0.01%) cytogenetic risk groups. CONCLUSION: Our data show that combining clinical risk factors with MFC-MRD measurement is the most useful tool for risk group stratification of children with BCP-ALL in the reduced-intensity protocols. However, this algorithm can be supplemented with cytogenetic data for part of the ImR group.

Relevance of CD20 antigen expression among paediatric patients with B-lineage acute lymphoblastic leukaemia.

Literature regarding prognostic relevance of CD20 antigen expression among paediatric B-lineage acute lymphoblastic leukaemia (B-ALL) patients is sparse and contradictory. We analysed clinical laboratory parameters and survival characteristics pertinent to CD20 expression among 224 treatment-naïve paediatric B-ALL patients. 50% patients had CD20 expression (CD20+ B-ALL). There was no difference in the clinical & laboratory presentation and end of induction measurable residual disease (EOI-MRD) status according to CD20 expression. As compared to CD20- B-ALL patients, CD20+ B-ALL patients had two times more relapse (16% vs. 29%, p = 0.034), inferior relapse-free survival (79% vs. 66%, p = 0.025) but no difference in overall survival (75% vs. 69%, p = 0.126). Similar to high-risk NCI status and EOI-MRD positivity, CD20 expression was an independent predictor for inferior relapse-free survival (HR: 1.860, 95% CI: 1.008-3.432, p = 0.047). Compared to baseline, there was a significant increase in CD20-expressing EOI-residual blasts among CD20- B-ALL patients (5% vs. 13%, p = 0.001). EOI residual blasts of both CD20+ and CD20- patients had three times increased normalized CD20 expression intensity (nCD20), with the intensity among CD20- B-ALL patients reaching the pretreatment nCD20 of CD20+ B-ALL patients (4.9 vs. 3.6, p = 0.666). Rituximab can be considered in managing EOI-MRD-positive CD20- B-ALL patients as the residual blasts of these patients have quantitative and qualitative increases in CD20 expression.

Histidine re-sensitizes pediatric acute lymphoblastic leukemia to 6-mercaptopurine through tetrahydrofolate consumption and SIRT5-mediated desuccinylation.

Despite progressive improvements in the survival rate of pediatric B-cell lineage acute lymphoblastic leukemia (B-ALL), chemoresistance-induced disease progression and recurrence still occur with poor prognosis, thus highlighting the urgent need to eradicate drug resistance in B-ALL. The 6-mercaptopurine (6-MP) is the backbone of ALL combination chemotherapy, and resistance to it is crucially related to relapse. The present study couples chemoresistance in pediatric B-ALL with histidine metabolism deficiency. Evidence was provided that histidine supplementation significantly shifts the 6-MP dose-response in 6-MP-resistant B-ALL. It is revealed that increased tetrahydrofolate consumption via histidine catabolism partially explains the re-sensitization ability of histidine. More importantly, this work provides fresh insights into that desuccinylation mediated by SIRT5 is an indispensable and synergistic requirement for histidine combination therapy against 6-MP resistance, which is undisclosed previously and demonstrates a rational strategy to ameliorate chemoresistance and protect pediatric patients with B-ALL from disease progression or relapse.

Reduced-dose chemotherapy followed by blinatumomab in induction therapy for newly diagnosed B-cell acute lymphoblastic leukemia.

BACKGROUND: Blinatumomab early-line treatment in B-cell precursor acute lymphoblastic leukemia (B-ALL) might improve clinical outcomes. METHODS: We conducted a retrospective real-world cohort analysis in 20 newly diagnosed B-ALL patients who received reduced-dose chemotherapy (idarubicin, vindesine, and dexamethasone) for 1-3 weeks, followed by blinatumomab for 1-4 weeks as an induction therapy. RESULTS: At the end of the induction therapy, a complete remission rate of 100% was achieved; 17 (85%) patients were minimal residual disease (MRD) negative (<1 × 10-4 ). Adverse events (AEs) were reported in 12 (60%) patients-43.8% were grade 1-2 and 56.2% were grade 3-4. No incidence of neurotoxicity or grade ≥3 cytokine release syndrome was reported. CONCLUSIONS: Blinatumomab demonstrated a significant improvement in clinical outcomes in patients with newly diagnosed B-ALL irrespective of their poor-risk factor status and the pretreatment blast burden.

Dynamic evolution of bone marrow adipocyte in B cell acute lymphoblastic leukemia: insights from diagnosis to post-chemotherapy.

Adipocyte is a unique and versatile component of bone marrow microenvironment (BMM). However, the dynamic evolution of Bone Marrow (BM) adipocytes from the diagnosis of B cell Acute Lymphoblastic Leukemia (B-ALL) to the post-treatment state, and how they affect the progression of leukemia, remains inadequately explicated. Primary patient-derived xenograft models (PDXs) and stromal cell co-culture system are employed in this study. We show that the dynamic evolution of BM adipocytes from initial diagnosis of B-ALL to the post-chemotherapy phase, transitioning from cellular depletion in the initial leukemia niche to a fully restored state upon remission. Increased BM adipocytes retards engraftment of B-ALL cells in PDX models and inhibits cells growth of B-ALL in vitro. Mechanistically, the proliferation arrest of B-ALL cells in the context of adipocytes-enrichment niche, might attribute to the presence of adiponectin secreted by adipocytes themselves and the absence of cytokines secreted by mesenchymal stem cell (MSCs). In summary, our findings offer a novel perspective for further in-depth understanding of the dynamic balance between BMM and B-ALL.

Single agent subcutaneous blinatumomab for advanced acute lymphoblastic leukemia.

Blinatumomab is a BiTE® (bispecific T-cell engager) molecule that redirects CD3+ T-cells to engage and lyse CD19+ target cells. Here we demonstrate that subcutaneous (SC) blinatumomab can provide high efficacy and greater convenience of administration. In the expansion phase of a multi-institutional phase 1b trial (ClinicalTrials.gov, NCT04521231), heavily pretreated adults with relapsed/refractory B-cell acute lymphoblastic leukemia (R/R B-ALL) received SC blinatumomab at two doses: (1) 250 µg once daily (QD) for week 1 and 500 µg three times weekly (TIW) thereafter (250 µg/500 µg) or (2) 500 µg QD for week 1 and 1000 µg TIW thereafter (500 µg/1000 µg). The primary endpoint was complete remission/complete remission with partial hematologic recovery (CR/CRh) within two cycles. At the data cutoff of September 15, 2023, 29 patients were treated: 14 at the 250 µg/500 µg dose and 13 at 500 µg/1000 µg dose. Data from two ineligible patients were excluded. At the end of two cycles, 12 of 14 patients (85.7%) from the 250 µg/500 µg dose achieved CR/CRh of which nine patients (75.0%) were negative for measurable residual disease (MRD; <10-4 leukemic blasts). At the 500 µg/1000 µg dose, 12 of 13 patients (92.3%) achieved CR/CRh; all 12 patients (100.0%) were MRD-negative. No treatment-related grade 4 cytokine release syndrome (CRS) or neurologic events (NEs) were reported. SC injections were well tolerated and all treatment-related grade 3 CRS and NEs responded to standard-of-care management, interruption, or discontinuation. Treatment with SC blinatumomab resulted in high efficacy, with high MRD-negativity rates and acceptable safety profile in heavily pretreated adults with R/R B-ALL.

Tyrosine kinase inhibitor resistance in de novo BCR::ABL1-positive BCP-ALL beyond kinase domain mutations.

ABSTRACT: A better understanding of ABL1 kinase domain mutation-independent causes of tyrosine kinase inhibitor (TKI) resistance is needed for BCR::ABL1-positive B-cell precursor acute lymphoblastic leukemia (BCP-ALL). Although TKIs have dramatically improved outcomes, a subset of patients still experiences relapsed or refractory disease. We aimed to identify potential biomarkers of intrinsic TKI resistance at diagnosis in samples from 32 pediatric and 19 adult patients with BCR::ABL1-positive BCP-ALL. Reduced ex vivo imatinib sensitivity was observed in cells derived from newly diagnosed patients who relapsed after combined TKI and chemotherapy treatment compared with cells derived from patients who remained in continuous complete remission. We observed that ex vivo imatinib resistance was inversely correlated with the amount of (phosphorylated) BCR::ABL1/ABL1 protein present in samples that were taken at diagnosis without prior TKI exposure. This suggests an intrinsic cause of TKI resistance that is independent of functional BCR::ABL1 signaling. Simultaneous deletions of IKZF1 and CDKN2A/B and/or PAX5 (IKZF1plus), as well as deletions of PAX5 alone, were related to ex vivo imatinib resistance. In addition, somatic lesions involving ZEB2, SETD2, SH2B3, and CRLF2 were associated with reduced ex vivo imatinib sensitivity. Our data suggest that the poor prognostic value of IKZF1(plus) deletions is linked to intrinsic mechanisms of TKI resistance other than ABL1 kinase domain mutations in newly diagnosed pediatric and adult BCR::ABL1-positive BCP-ALL.

The influence of cytotoxic drugs on the immunophenotype of blast cells in paediatric B precursor acute lymphoblastic leukaemia.

BACKGROUND: Flow cytometry plays is important in the diagnosis of acute lymphoblastic leukaemia (ALL) and when antigen-specific immunotherapy is indicated. We have investigated the effects of prednisolone, vincristine, daunorubicin, asparaginase and methotrexate on the antigen expression on blast cells that could influence the planning of antigen-specific therapy as well as risk-based treatment assignment. PATIENTS AND METHODS: Patients aged ≤ 17 years with de novo B-cell ALL (B-ALL) were enrolled in the study. Blast cells were isolated and exposed in vitro to 5 individual cytotoxic drugs in logarithmically increasing concentrations. Then, the expression of CD10, CD19, CD20, CD27, CD34, CD45, CD58, CD66c and CD137 antigens was determined by quantitative flow cytometry. RESULTS: Cytotoxic drugs caused dose-dependent or dose-independent modulation of antigen expression. Daunorubicin caused a dose-dependent down-modulation of CD10, CD19, CD34, CD45 and CD58 and an up-modulation of CD137. Vincristine caused a dose-dependent down-modulation of CD19 and CD58 and an up-modulation of CD45. Daunorubicin also caused dose-independent down-modulation of CD27 and prednisolone down-modulation of CD10, CD19, CD27, CD34 and CD58. Down-modulation of CD20 was detected only in relation to the specific dose of daunorubicin. CONCLUSIONS: The results of the study have shown that cytotoxic drugs can alter the expression of antigens that are important for immunotherapy. Importantly, daunorubicin, prednisolone and vincristine caused down-modulation of CD19 and CD58, suggesting that these drugs are better avoided during bridging therapy prior to bispecific antibodies or CAR-T cell therapy. In addition, immunophenotypic changes on blast cells induced by different drugs could also influence risk-based treatment assignment.

Dose-Dense Mini-Hyper-CVD, Inotuzumab Ozogamicin and Blinatumomab Achieves Rapid MRD-Negativity in Philadelphia Chromosome-Negative B-cell Acute Lymphoblastic Leukemia.

BACKGROUND: The combination of low-intensity chemotherapy and inotuzumab ozogamicin (INO), with sequential blinatumomab, is highly effective in older adults with newly diagnosed B-cell acute lymphoblastic leukemia (ALL) and in relapsed or refractory B-cell ALL. Earlier, "dose-dense" administration of blinatumomab could lead to earlier and deeper measurable residual disease (MRD) responses and better outcomes. PATIENTS AND METHODS: We performed a retrospective analysis of the safety and efficacy of a dose-dense regimen of mini-hyper-CVD (mini-hyperfractionated cyclophosphamide, vincristine, and dexamethasone alternating with mini-methotrexate and cytarabine), INO, and blinatumomab in patients with B-cell ALL. RESULTS: Twenty-one patients were treated (frontline, n = 9; MRD consolidation, n = 4; relapsed/refractory, n = 8). In the frontline cohort, all patients achieved CR/CRi and MRD negativity by flow cytometry at the end of cycle 1. Across the frontline and MRD consolidation cohorts, 10/11 patients (91%) achieved next-generation sequencing MRD negativity at a sensitivity of 10-6, including 6/10 evaluable patients (60%) who achieved next-generation sequencing MRD negativity after cycle 1. The CR/CRi rate in the relapsed/refractory cohort was 63%, and all responders achieved MRD negativity by flow cytometry at the end of cycle 1. The 1-year overall survival rate for the combined cohort of the frontline and MRD-positive patients was 83%. No new safety signals were observed with the dose-dense mini-hyper-CVD, INO, and blinatumomab regimen. CONCLUSION: Dose-dense delivery of mini-hyper-CVD, INO, and blinatumomab was safe and resulted in rapid and deep MRD negativity in patients with B-cell ALL. This regimen is now being prospectively evaluated in both the frontline and relapsed/refractory settings.

CD371-positive pediatric B-cell acute lymphoblastic leukemia: propensity to lineage switch and slow early response to treatment.

ABSTRACT: In the effort to improve immunophenotyping and minimal residual disease (MRD) assessment in acute lymphoblastic leukemia (ALL), the international Berlin-Frankfurt-Münster (iBFM) Flow Network introduced the myelomonocytic marker CD371 for a large prospective characterization with a long follow-up. In the present study, we aimed to investigate the clinical and biological features of CD371-positive (CD371pos) pediatric B-cell precursor ALL (BCP-ALL). From June 2014 to February 2017, 1812 pediatric patients with newly diagnosed BCP-ALLs enrolled in trial AIEOP-BFM ALL 2009 were evaluated as part of either a screening (n = 843, Italian centers) or validation cohort (n = 969, other iBFM centers). Laboratory assessment at diagnosis consisted of morphological, immunophenotypic, and genetic analysis. Response assessment relied on morphology, multiparametric flow cytometry (MFC), and polymerase chain reaction (PCR)-MRD. At diagnosis, 160 of 1812 (8.8%) BCP-ALLs were CD371pos. This correlated with older age, lower ETV6::RUNX1 frequency, immunophenotypic immaturity (all P < .001), and strong expression of CD34 and of CD45 (P < .05). During induction therapy, CD371pos BCP-ALLs showed a transient myelomonocytic switch (mm-SW: up to 65.4% of samples at day 15) and an inferior response to chemotherapy (slow early response, P < .001). However, the 5-year event-free survival was 88.3%. Among 420 patients from the validation cohort, 27 of 28 (96.4%) cases positive for DUX4-fusions were CD371pos. In conclusion, in the largest pediatric cohort, CD371 is the most sensitive marker of transient mm-SW, whose recognition is essential for proper MFC MRD assessment. CD371pos is associated to poor early treatment response, although a good outcome can be reached after MRD-based ALL-related therapies.

Leveraging CD19CAR T cells early in the treatment of older patients with B-ALL: are we there yet?

Older adults (≥55 years old) with B-cell acute lymphoblastic leukemia (B-ALL) have dismal outcomes with standard chemotherapy as the result of low treatment efficacy and considerable risks for treatment-related morbidity and mortality. There has been a recent success with the introduction of novel therapies, such as blinatumomab and inotuzumab, in the frontline therapeutic paradigm in older adults with B-ALL. However, these agents have their own challenges including the limited durability of remission, the need for additional concurrent chemotherapy and the prolonged course of treatment, and limited efficacy in the setting of extramedullary disease. Here, we hypothesize that the incorporation of chimeric antigen receptor (CAR) T cell therapy as a consolidation treatment in older adults with B-cell ALL in their first complete remission is the ideal setting to advance treatment outcomes by reducing treatment toxicity, enhancing remission durability, and expanding the use of this effective therapy in this age population.

Severe Methotrexate Toxicity Following a Capizzi Cycle in an Obese Adolescent With Acute Lymphoblastic Leukemia and Hepatic Steatosis.

Methotrexate is a major component of pediatric leukemia treatment. While toxicities are common after high-dose methotrexate, escalating dose methotrexate (Capizzi methotrexate) is typically well-tolerated. We report an adolescent Hispanic female with pre-B acute lymphoblastic leukemia, preexisting obesity and hepatic steatosis who developed severe multiorgan failure following an escalating dose of methotrexate with delayed methotrexate excretion of 11 days. We identified one similar report in an obese adult; however, this case is the first to our knowledge involving a pediatric patient. With the rising incidence of obesity and associated comorbidities among children and adolescents with leukemia, attention to potential risks for this population is warranted.

Blinatumomab in Practice.

PURPOSE OF REVIEW: Acute lymphoblastic leukemia (ALL) is a rare hematologic neoplasm in adults, with most cases defined by pathology related to abnormal B cell proliferation known as B-cell ALL. The course is challenging, with less-than-optimal survival outcomes, even with aggressive multiagent chemotherapy and consideration for stem cell transplantation. Novel therapies focused on targetable pathways are being investigated to improve outcomes while simultaneously decreasing toxicity. In our review, we aim to evaluate the utilization of blinatumomab in B-cell ALL and provide insight on how this guides our management. RECENT FINDINGS: Blinatumomab is a bispecific T-cell engager (BiTE) immunotherapy that neutralizes malignant cells by instigating CD3-positive T cells to target CD19-positive B cells. However, this therapy targets both malignant and non-malignant lymphocytes with potentially severe side effects such as cytokine release syndrome or neurotoxicity. Evidence evaluating utilization in the relapsed or refractory setting has been most supported; however, newer trials have also indicated improved survival in the frontline treatment of B-cell ALL. As this therapy is relatively new, the treatment team may include members who are less experienced with the typical treatment course and drug mechanics. This review synthesized available data investigating the effectiveness of blinatumomab effectiveness and its adverse events in addition to providing guidance on safe administration methods utilizing a multidisciplinary healthcare team. When care is coordinated in these settings, serious side effects can be recognized early, allowing for necessary intervention leading to improved quality of life and overall survival. Future research will continue to evaluate blinatumomab in different lines of therapy and expand its way into community settings.

N-acetyl cysteine turns EPAC activators into potent killers of acute lymphoblastic leukemia cells.

Today, the majority of patients with pediatric B cell precursor acute lymphoblastic leukemia (BCP-ALL, hereafter ALL) survive their disease, but many of the survivors suffer from life-limiting late effects of the treatment. ALL develops in the bone marrow, where the cells are exposed to cAMP-generating prostaglandin E2. We have previously identified the cAMP signaling pathway as a putative target for improved efficacy of ALL treatment, based on the ability of cAMP signaling to reduce apoptosis induced by DNA damaging agents. In the present study, we have identified the antioxidant N-acetyl cysteine (NAC) as a powerful modifier of critical events downstream of the cell-permeable cAMP analog 8-(4-chlorophenylthio) adenosine-3', 5'- cyclic monophosphate (8-CPT). Accordingly, we found NAC to turn 8-CPT into a potent killer of ALL cells in vitro both in the presence and absence of DNA damaging treatment. Furthermore, we revealed that NAC in combination with 8-CPT is able to delay the progression of ALL in a xenograft model in NOD-scid IL2Rγnull mice. NAC was shown to rely on the ability of 8-CPT to activate the guanine-nucleotide exchange factor EPAC, and we demonstrated that the ALL cells are killed by apoptosis involving sustained elevated levels of calcium imposed by the combination of the two drugs. Taken together, we propose that 8-CPT in the presence of NAC might be utilized as a novel strategy for treating pediatric ALL patients, and that this powerful combination might be exploited to enhance the therapeutic index of current ALL targeting therapies.

Prognostic implications of CD9 in childhood acute lymphoblastic leukemia: insights from a nationwide multicenter study in China.

The outcomes of children with acute lymphoblastic leukemia (ALL) have been incrementally improved with risk-directed chemotherapy but therapy responses remain heterogeneous. Parameters with added prognostic values are warranted to refine the current risk stratification system and inform appropriate therapies. CD9, implicated by our prior single-center study, holds promise as one such parameter. To determine its precise prognostic significance, we analyzed a nationwide, multicenter, uniformly treated cohort of childhood ALL cases, where CD9 status was defined by flow cytometry on diagnostic samples of 3781 subjects. CD9 was expressed in 88.5% of B-ALL and 27.9% of T-ALL cases. It conferred a lower 5-year EFS and a higher CIR in B-ALL but not in T-ALL patients. The prognostic impact of CD9 was most pronounced in the intermediate/high-risk arms and those with minimal residual diseases, particularly at day 19 of remission induction. The adverse impact of CD9 was confined to specific cytogenetics, notably BCR::ABL1+ rather than KMT2A-rearranged leukemia. Multivariate analyses confirmed CD9 as an independent predictor of both events and relapse. The measurement of CD9 offers insights into patients necessitating intervention, warranting its seamless integration into the diagnostic marker panel to inform risk level and timely introduction of therapeutic intervention for childhood ALL.

Blinatumomab Therapy Is Associated with Favorable Outcomes after Allogeneic Hematopoietic Cell Transplantation in Pediatric Patients with B Cell Acute Lymphoblastic Leukemia.

Blinatumomab, a bispecific T cell engager that binds CD19 in leukemic cells and CD3 in cytotoxic T cells and leads to leukemic blast lysis, is often used in pediatric patients with relapsed/refractory (R/R) B cell acute lymphoblastic leukemia (B-ALL) prior to allogeneic hematopoietic cell transplantation (allo-HCT). Concerns about the potential risk of blinatumomab-related immune-mediated toxicities after allo-HCT have not been adequately addressed. These include graft-versus-host disease (GVHD), delayed engraftment, and graft failure or rejection. Pediatric-specific data reporting post-HCT outcomes of patients treated with blinatumomab are scarce and limited to small cohorts. We sought to investigate the clinical outcomes of pediatric patients with R/R B-ALL who received blinatumomab therapy pre-HCT, focusing on overall survival (OS), leukemia-free survival (LFS), cumulative incidence of relapse (CIR), and nonrelapse mortality (NRM), as well as the incidence of immune-mediated post-HCT complications including GVHD, delayed neutrophil or platelet engraftment, graft failure, and graft rejection. We also investigated blinatumomab's effects on B cell reconstitution based on achievement of i.v. immunoglobulin (IVIG) independence post-HCT. This single-center, retrospective study included patients with B-ALL receiving blinatumomab therapy before undergoing allo-HCT, with transplantation performed between 2016 and 2021 at our institution. Patients receiving blinatumomab for relapse after allo-HCT were excluded. Patients receiving chemotherapy alone before allo-HCT during the same period composed the control group. Seventy-two patients were included, 31 of whom received blinatumomab before allo-HCT. Survival estimates were obtained using the Kaplan-Meier method, and the log-rank test was used to analyze differences between groups. Categorical variables were compared between groups using the chi-square test or Fisher exact test, and continuous variables were compared using the Wilcoxon rank-sum test. Cumulative incidences were estimated using the competing risks method, and Gray's test was used to analyze differences between groups. A Cox proportional hazards regression model was used for univariate and multivariable analyses for OS. Landmark analysis was performed at the set time points of 30 days and 100 days post-allo-HCT. Most patients in the study cohort had high-risk relapsed B-ALL. Blinatumomab therapy induced minimal residual disease (MRD)-negative remissions in all patients, whereas 5 patients (12.2%) receiving chemotherapy alone had persistent MRD pre-allo-HCT. Time from the start of therapy to the date of allo-HCT was shorter for patients who received blinatumomab compared with those who received chemotherapy (P < .0001). Blinatumomab therapy was associated with greater LFS compared to chemotherapy alone (P = .049), but when limited to 1 year, LFS was not significantly different from control (P = .066). There appeared to be higher OS, lower CIR, and lower NRM in patients receiving blinatumomab compared to the control group; however, the differences were not significant. None of the variables assessed in multivariable analysis was associated with differences in OS. When compared to the controls, blinatumomab therapy did not result in a higher incidence of acute or chronic GVHD, delayed neutrophil or platelet engraftment, or graft failure or rejection. The time to IVIG infusion independence post-allo-HCT was similar in the 2 groups. This study supports the use of blinatumomab salvage therapy for R/R B-ALL before allo-HCT given its efficacy in inducing MRD-negative remissions and optimizing LFS, as well as its lack of association with an increased incidence of post-allo-HCT adverse immune-mediated toxicities. Larger, prospective studies are needed to confirm these findings and to investigate blinatumomab's effects in long-term post-allo-HCT events.