Defibrotide plus best standard of care compared with best standard of care alone for the prevention of sinusoidal obstruction syndrome (HARMONY): a randomised, multicentre, phase 3 trial

Classical and Late-Onset SOS/VOD After Allogeneic HSCT: A Japanese Transplant Registry Analysis

Sinusoidal obstruction syndrome/veno-occlusive disease (SOS/VOD) is a lethal complication of allogeneic hematopoietic stem cell transplantation (allo-HSCT). According to the 2016 European Society for Blood and Marrow Transplantation criteria, SOS/VOD is classified into classical SOS/VOD and late-onset SOS/VOD, but their similarities and differences remain unclear. Here we retrospectively investigated the incidence, risk factors, and impact on transplant outcomes of classical and late-onset SOS/VOD in 16 518 allo-HSCT recipients using the Japanese nationwide registry data. The cumulative incidences of classical and late-onset SOS/VOD were 2.5% and 2.2%, with a median onset of 13 and 42 days after transplantation, respectively. Both patients with classical (hazard ratio [HR], 3.45; 95% CI, 3.07-3.87) and late-onset (HR, 3.98; 95% CI, 3.51-4.51) SOS/VOD had a significantly worse overall survival compared with those without. The risk factors for classical and late-onset SOS/VOD are different. Hepatic comorbidities, high-risk diseases, use of melphalan (MEL), and myeloablative conditioning are associated with both types of SOS/VOD. Whereas poor performance status, a prior history of transplantation, and positive hepatitis C virus are associated with only classical SOS/VOD, allo-HSCT from cord blood or related human leukocyte antigen-haploidentical donors, use of total body irradiation and busulfan (BU), and tacrolimus-based graft-versus-host disease prophylaxis are associated with only late-onset SOS/VOD. In particular, the incidence of late-onset SOS/VOD is much higher in patients receiving both BU- and MEL-containing conditioning regimens. These findings suggest that different monitoring and treatment approaches are necessary for allo-HSCT recipients at high risk for classical and late-onset SOS/VOD.

Evolution of Allogeneic Stem Cell Transplantation: Main Focus on AML

In recent years, treatments in the field of hematologic malignancies have undergone significant evolution; allogeneic hematopoietic stem cell transplantation (allo-HSCT) has shifted from an "ultimate" therapy to becoming a component of a comprehensive therapeutic strategy for acute myeloid leukemia (AML). Advances in risk stratification (including molecular profiling and measurable residual disease assessment), conditioning regimens, and graft-versus-host disease (GVHD) prophylaxis-such as post-transplant cyclophosphamide-have improved outcomes and expanded donor selection and transplant eligibility. We should not only focus on the transplantation procedure but also consider various therapeutic components, including chemotherapy, targeted therapy (possibly including chimeric antigen receptor T-cell therapy), and post-transplant maintenance therapy, which need to be orchestrated within the broader context of leukemia treatment. In this review, we summarized key developments in allo-HSCT for AML and aim to "decipher" each component of transplantation.

Operational procedure sharing pathway in veno-occlusive disease: a Delphi consensus-based recommendations

Background

The hepatic Veno-Occlusive Disease (VOD), also known as Sinusoidal Obstruction Syndrome (SOS), is a serious complication that can occur after high-dose chemotherapy and hematopoietic stem cell transplantation (HSCT). In Italy, the approach to VOD varies due to differences in healthcare practices and diagnostic criteria among different regions.

Aim and methods

To address this issue, a structured, multi-step Delphi consensus project was undertaken with the aim of standardizing the diagnostic and therapeutic pathways for VOD in Italian clinical practice. The project involved a methodologist, a scientific board of 10 experts, and an expert panel of 45 specialists from Italian hospital centers. This 12-month process included independent contributions, harmonization by a methodologist, and discussions through web meetings.

Results

The survey identified 15 clinical topics divided into five key areas, including pre-HSCT patient evaluation, clinical-laboratory aspects for diagnosis and therapy, integration of clinical evaluations with EBMT criteria, monitoring with imaging techniques, and adherence to guidelines for managing defibrotide therapy. Key findings include the recommendation of weekly imaging even when VOD is not clinically suspected, the importance of early diagnosis and treatment with defibrotide, and the need for a standardized approach across different centers.

Conclusion

The Delphi consensus revealed significant variability in the management of VOD across Italian centers and emphasized the necessity of a multidisciplinary approach involving hematologists, hepatologists, and radiologists. Establishing a national network for sharing best practices and utilizing advanced imaging technologies is essential for improving VOD diagnosis and treatment. The findings indicate the importance of implementing standardized protocols and continuous education to enhance patient outcomes in HSCT settings.

Drug-induced hepatic sinusoidal obstruction syndrome: current advances and future perspectives

Hepatic sinusoidal obstruction syndrome (HSOS) has gained recognition as a rare form of drug-induced liver injury (DILI) in recent years. Although extensively studied in the context of hematopoietic stem cell transplantation (HSCT), the applicability of this knowledge to drug-induced HSOS remains limited due to distinct etiological factors. The primary causes of drug-induced HSOS include the ingestion of pyrrolizidine alkaloid (PA)-containing plants, as well as the use of chemotherapeutic agents and immunosuppressive drugs. The underlying pathogenesis is not yet fully understood. Noninvasive diagnostic imaging modalities such as ultrasonography, computed tomography, and magnetic resonance imaging play a valuable role in diagnosis. Further research is essential to develop standardized severity grading systems and optimize treatment strategies. This review summarizes the key etiologies, pathological mechanisms, clinical features, diagnostic approaches, severity assessment, and therapeutic options for drug-induced HSOS.

Kidney Disease and Hematopoietic Stem Cell Transplantation

Hematopoietic stem cell transplantation (HSCT) is a potentially curative therapy for patients with hematologic malignancies and certain solid tumors and nonmalignant hematologic conditions. Both AKI and CKD occur commonly after HSCT and are associated with significant morbidity and mortality. AKI and CKD in this setting may result from direct effects of the transplant or be caused by pretransplant bone marrow conditioning regimens and/or nephrotoxic agents administered in the post-transplant period. In this article, we review the epidemiology, risk factors, etiologies, pathophysiology, diagnosis, prevention, and treatment of post-HSCT AKI and CKD, with special attention to recent advances in this fast-moving and evolving field.

How I treat postimmunotherapy relapsed B-ALL

ABSTRACT

Despite significant advancements in single-antigen targeted therapies for B-cell acute lymphoblastic leukemia (B-ALL), nonresponse and relapse persist as major challenges. Antigen escape after blinatumomab or CD19-directed chimeric antigen receptor (CAR) T cells (CD19-CAR), as CD19-negative B-ALL or lineage switch (LS) to acute myeloid leukemia, present diagnostic and treatment complexities. Given the poor outcomes for patients experiencing a postinfusion relapse, particularly those with loss of the target antigen, a strategic approach to diagnosis and treatment is imperative. In this discussion, we outline a systematic approach to managing postimmunotherapy events, categorized by CD19-positive relapse, CD19-negative relapse, and LS. We explore treatment modalities including CD19-CAR reinfusions, humanized CAR constructs, combinatorial strategies, and alternative antigen-targeted therapies, such as blinatumomab and inotuzumab. Challenges in diagnosis, particularly with antigen-escape, are addressed, highlighting the role of next-generation sequencing and multiparameter flow cytometry for myeloid marker monitoring.

Early defibrotide therapy and risk factors for post-transplant veno-occlusive disease/sinusoidal obstruction syndrome in childhood

BACKGROUND

Veno-occlusive disease (VOD), also known as sinusoidal obstruction syndrome (SOS), is a life-threatening complications of hematopoietic cell transplantation (HCT).

METHODS

We studied the impact of early defibrotide (DF) therapy on the outcomes of pediatric patients with VOD/SOS after transplantation, focusing on recent immunotherapies. A total of 111 pediatric patients who underwent HCT for malignant disease between February 2017 and March 2023 at Kyushu University Hospital were included.

RESULTS

Among 111 patients of less than 20 years of age who underwent HCT for malignancy at a single institution between 2017 and 2023, VOD/SOS occurred in 25 (23%) patients. VOD/SOS developed more frequently in the post-DF era (2020-2023, n = 58) than in the pre-DF era (31% vs. 13%, p = .04). The proportion of patients with relapsed/refractory acute lymphoblastic leukemia (ALL) was higher in the post-DF era than in the pre-DF era (44% vs. 8%, p = .04). Early DF therapy that was started at two European Society for Blood and Marrow Transplantation diagnostic criteria reduced the severity of VOD/SOS (p < .01) in comparison to non-early therapy started at less than two criteria. A multivariate analysis indicated that a history of cytokine release syndrome (odds ratio [OR] = 10.4, p = .01) and juvenile myelomonocytic leukemia (OR = 8.98, p = .04), but not an endothelial activation and stress index (EASIX) score of greater than 0.85, were independent risk factors for VOD/SOS.

CONCLUSIONS

Early DF therapy improves the severity and survival outcomes of post-transplant VOD/SOS in children. However, its incidence is increasing in the era of immunotherapy for progressive diseases.

Hepatic Sinusoidal Obstruction Syndrome/Veno-Occlusive Disease (SOS/VOD) Primary Prophylaxis in Patients Undergoing Hematopoietic Stem Cell Transplantation: A Network Meta-Analysis of Randomized Controlled Trials

Introduction: Hepatic sinusoidal obstruction syndrome/veno-occlusive disease (SOS/VOD) is a major complication following hematopoietic stem cell transplantation, resulting from immune and chemical toxicity in the sinusoidal endothelium and hepatocellular damage. In the most severe cases, multiorgan dysfunction occurs, so it is essential to promptly identify patients at greater risk of SOS/VOD and to adopt prophylactic strategies. Objectives: This study aims to systematize the impact of different approaches as primary prophylaxes against SOS/VOD in patients undergoing hematopoietic stem cell transplantation (HSCT). Methods: A systematic review and meta-analysis of randomized clinical trials evaluating different strategies for primary prophylaxis of SOS/VOD was carried out in pairwise fashion and with a consistent network structure. The odds ratio (OR) and corresponding confidence intervals were calculated using the random-effects model. Heterogeneity was assessed by the I2 method and the efficacy of each approach was estimated by SUCRA (surface under the cumulative ranking curve). Results: Considering all patients undergoing HSCT, ursodeoxycholic acid (UDCA) [OR = 0.38, 95%CI 0.14-1.06, SUCRA = 0.720] was associated with a lower incidence of VOD while defibrotide reached a modest reduction in its incidence [OR = 0.64, 95%CI 0.23-1.67; SUCRA = 0.486]. Considering the subgroup of patients undergoing hematopoietic progenitors allotransplantation, defibrotide scored higher [OR = 0.51, 95%CI 0.09-2.85, SUCRA = 0.650] by comparison with UDCA [OR = 0.53, 95%CI 0.14-1.96, SUCRA = 0.639]. Conclusions: This is the first meta-analysis comparing primary prophylaxes against SOS/VOD. UDCA yielded more promising results when considering all patients undergoing hematopoietic stem cell transplantation, yet, in a subgroup analysis of the ones exposed to allogeneic grafts, it becomes not significantly overrun by defibrotide.

The benefits of prophylactic defibrotide: Are the tides turning?

BACKGROUND

Veno-occlusive disease (VOD) is a life-threatening endotheliopathy that can occur after stem cell transplant (SCT). Numerous risk factors contribute to the development of VOD during SCT, and the role of prophylactic defibrotide (DF) in mitigating these risks remains unclear.

OBJECTIVE

We compare not only the incidence of VOD development, but also the severity of VOD and survival outcomes between patients who did and did not develop VOD and did or did not receive prophylactic DF.

STUDY DESIGN

In this single-center retrospective study of 58 pediatric SCT patients from 2008 to 2022, we compare the demographics, risk profiles, and outcomes within three cohorts: Group 1: prophylactic DF and no VOD (n = 5), Group 2: prophylactic DF and development of VOD (n = 6), and Group 3: treatment DF for patients who developed VOD (n = 47).

RESULTS

Patients with VOD who did not receive prophylactic DF had higher severity classification of disease at onset (very severe 80.9% vs. 66.7%, p = .592) and at maximum severity (very severe 89.4% vs. 83.3%, p = .532), as opposed to mild, moderate, or severe categorization compared to those who did not receive prophylactic DF. Patients who developed VOD and did not receive prophylactic DF had a lower 1-year survival probability compared to those who received prophylactic DF and still developed VOD (51.1% vs. 75% alive at 1 year, excluding the two subjects without adequate follow-up time, p = .266).

CONCLUSION

Although, not statistically significant in our small retrospective study, there is potential overall survival and decreased VOD severity benefits of prophylactic DF.

Verification of the Prediction Accuracy of a Biomarker-Based Prognostic for Veno-Occlusive Disease/Sinusoidal Obstruction Syndrome (VOD/SOS) After Hematopoietic Cell Transplantation (HCT)

Veno-occlusive disease/sinusoidal obstruction syndrome (VOD/SOS) is a potentially life-threatening complication of hematopoietic cell transplantation (HCT), especially in severe cases. Patient outcomes are improved with prompt treatment; however, diagnosing this disease is challenging as many clinical symptoms of VOD/SOS overlap with other post-HCT complications. A biomarker-based prognostic test for the assessment of VOD/SOS risk, termed "VODCheck" was developed in a previous study but has not yet been validated. This study aimed to validate the accuracy of VODCheck as a prognostic test for VOD/SOS in an independent cohort of patients. VODCheck incorporates hyaluronan (HA), angiopoietin-2 (ANG-2), and thrombomodulin (TM) based on their association with VOD/SOS, their analytical characteristics, and their ability to complement each other in a multivariate prognostic model. To validate VODCheck we measured plasma biomarker levels from a subset of patients enrolled in the control arm of a phase 3 study that tested VOD/SOS prophylaxis. We used a hierarchical design with prespecified primary (day 7), secondary A (day 15), and secondary B (day 1) hypotheses to verify the prognostic accuracy of VODCheck post-HCT. The cases of VOD/SOS (n = 22) were age-matched ∼1:3 with controls (n = 65). VODCheck was prognostic of VOD/SOS risk at all 3 time points with an area under the curve (AUC) of .815 (P < .001) for day 7, .836 (P < .001) for day 15, and .706 (P = .002) for day 1 post-HCT. A multivariate analysis confirmed the prognostic accuracy of VODCheck after adjustment for confounders such as age, VOD/SOS risk status, primary disease, and ozogamicin treatment. VODCheck was validated as an independent predictor of risk for VOD/SOS within 15 days post-HCT and appears to provide clinicians with actionable information to improve patient care.

ANZTCT practice statement: sinusoidal obstruction syndrome/veno-occlusive disease diagnosis and management

Sinusoidal obstruction syndrome/veno-occlusive disease (SOS/VOD) is a life-threatening complication which can develop after haemopoietic stem cell transplantation (HSCT) and some antibody-drug conjugates. Several SOS/VOD diagnostic and management guidelines exist, with the most recent and refined being the European Society for Blood and Marrow Transplantation adult and paediatric guidelines. Timely diagnosis and effective management (including the availability of therapeutic options) significantly contribute to improved patient outcomes. In Australia and New Zealand, there is variability in clinical practice and access to SOS/VOD therapies. This review aims to summarise the current evidence for SOS/VOD diagnosis, prevention and treatment and to provide recommendations for SOS/VOD in the context of contemporary Australasian HSCT clinical practice.

Diagnosing and Grading of Sinusoidal Obstructive Syndrome after Hematopoietic Stem Cell Transplant of Children, Adolescent and Young Adults treated in a Pediatric Institution with Pediatric Protocols

Sinusoidal obstructive syndrome (SOS), or veno-occlusive disease, of the liver has been recognized as a complex, life-threatening complication in the posthematopoietic stem cell transplant (HSCT) setting. The diagnostic criteria for SOS have evolved over the last several decades with a greater understanding of the underlying pathophysiology, with 2 recent diagnostic criteria introduced in 2018 (European Society of Bone Marrow Transplant [EBMT] criteria) and 2020 (Cairo criteria). We sought out to evaluate the performance characteristics in diagnosing and grading SOS in pediatric patients of the 4 different diagnostic criteria (Baltimore, Modified Seattle, EBMT, and Cairo) and severity grading systems (defined by the EBMT and Cairo criteria). Retrospective chart review of children, adolescent, and young adults who underwent conditioned autologous and allogeneic HSCT between 2017 and 2021 at a single pediatric institution. A total of 250 consecutive patients underwent at least 1 HSCT at UCSF Benioff Children's Hospital San Francisco for a total of 307 HSCT. The day 100 cumulative incidence of SOS was 12.1%, 21.1%, 28.4%, and 28.4% per the Baltimore, Modified Seattle, EBMT, and Cairo criteria, respectively (P < .001). We found that patients diagnosed with grade ≥4 SOS per the Cairo criteria were more likely to be admitted to the Pediatric Intensive Care Unit (92% versus 58%, P = .035) and intubated (85% versus 32%, P = .002) than those diagnosed with grade ≥4 per EBMT criteria. Age <3 years-old (HR 1.76, 95% [1.04 to 2.98], P = .036), an abnormal body mass index (HR 1.69, 95% [1.06 to 2.68], P = .027), and high-risk patients per our institutional guidelines (HR 1.68, 95% [1.02 to 2.76], P = .041) were significantly associated with SOS per the Cairo criteria. We demonstrate that age <3 years, abnormal body mass index, and other high-risk criteria associate strongly with subsequent SOS development. Patients with moderate to severe SOS based on Cairo severity grading system may correlate better with clinical course based on ICU admissions and intubations when compared to the EBMT severity grading system.

Retrospective analysis of veno-occlusive disease/sinusoidal obstruction syndrome in paediatric patients undergoing hematopoietic cell transplantation -a multicentre study

Background

Sinusoidal obstruction syndrome is a potentially fatal complication following hematopoietic cell transplantation, high-intensity chemotherapies and increasingly seen with calicheamicin based leukemia therapies. Paediatric specific European Society for Blood and Marrow Transplantation (pEBMT) diagnostic criteria have demonstrated benefit in single center studies compared to historic criteria. Yet, the extent to which they have been universally implemented remains unclear.

Methods

We conducted a retrospective multi-centre study to examine the potential impact of the Baltimore, modified Seattle and pEBMT criteria on the incidence, severity, and outcomes of sinusoidal obstruction syndrome among paediatric hematopoietic cell transplantation patients.

Findings

The incidence of sinusoidal obstruction syndrome in this cohort (n = 488) was higher by pEBMT (21.5%) vs historic modified Seattle (15.6%) and Baltimore (7.0%) criteria (p < 0.001). Application of pEBMT criteria identified 44 patients who were not previously diagnosed with sinusoidal obstruction syndrome. Overall, 70.5% of all patients diagnosed with sinusoidal obstruction syndrome ultimately developed very severe disease and almost half of diagnosed patients required critical care support. Overall survival was significantly lower in patients who were diagnosed with sinusoidal obstruction syndrome vs those who were not.

Interpretation

Taken together, pEBMT criteria may be a sensitive method for prompter diagnosis of patients who subsequently develop severe/very severe sinusoidal obstruction syndrome. To our knowledge, this is the first multi-centre study in the United States (US) to demonstrate that pEBMT guidelines are associated with earlier detection of sinusoidal obstruction syndrome. Since early initiation of definitive treatment for sinusoidal obstruction syndrome has been associated with improved survival in paediatric patients and implementation of pEBMT criteria appears feasible in the US, universal adoption should facilitate prompter diagnosis and lead to improved outcomes of children with sinusoidal obstruction syndrome.

Funding

None.

Prevention and management of acute toxicities from conditioning regimens during hematopoietic stem cell transplantation

Hematopoietic stem cell transplantation (HSCT) remains the only curative option for several hematological malignancies. Its use has continued to grow, with an estimated 23,500 transplants performed annually in the United States alone. The acute toxicities that occur from conditioning chemotherapy can impact the peri-transplant period and have substantial implications on patients' tolerability and outcomes, irrespective of the treatment of their disease. Chemotherapy-induced nausea vomiting (CINV), mucositis, transplant-associated thrombotic microangiopathy (TA-TMA), and sinusoidal obstruction syndrome, also known as a veno-occlusive disease (SOS/VOD) can all have significant implications for patients. These acute complications begin with the start of conditioning chemotherapy and add to potential toxicity for patients throughout the early post-transplant period, from Day +30 for CINV, mucositis, and SOS, and which can continue through at least Day +100 with the onset of TA-TMA. These toxicities must be prevented and managed appropriately. This review will summarize the literature surrounding them and guide their management.

Utility of the refined EBMT diagnostic and severity criteria 2023 for sinusoidal obstruction syndrome/veno-occlusive disease

Sinusoidal obstruction syndrome/veno-occlusive disease (SOS/VOD) is a life-threatening complication of hematopoietic stem cell transplantation (HSCT). Early diagnosis of SOS/VOD is associated with improved clinical outcomes. In 2023, the refined European Society for Blood and Marrow Transplantation diagnostic and severity criteria (refined EBMT criteria 2023) have been advocated. The revision has introduced new diagnostic categories, namely; probable, clinical, and proven SOS/VOD. In addition, the Sequential Organ Failure Assessment (SOFA) score has been newly incorporated into the SOS/VOD severity grading. We performed a retrospective analysis to evaluate the utility of these criteria. We analyzed 161 cases who underwent allogeneic HSCT. We identified 53 probable, 23 clinical, and 4 proven SOS/VOD cases. Probable SOS/VOD was diagnosed a median of 5.0 days earlier (interquartile range: 2-13 days, P < 0.001) than that of clinical SOS/VOD. The development of probable SOS/VOD alone was associated with a significantly inferior survival proportion compared to non-SOS/VOD (100-day survival, 86.2% vs. 94.3%, P = 0.012). The SOFA score contributed to the prediction of prognosis. Consequently, the refined EBMT criteria 2023 demonstrated the utility of SOS/VOD diagnosis and severity grading. Further investigations and improvements in these criteria are warranted.

Mobilization-based engraftment of haematopoietic stem cells: a new perspective for chemotherapy-free gene therapy and transplantation

INTRODUCTION

In haematopoietic stem cell transplantation (HSCT), haematopoietic stem cells (HSCs) from a healthy donor replace the patient's ones. Ex vivo HSC gene therapy (HSC-GT) is a form of HSCT in which HSCs, usually from an autologous source, are genetically modified before infusion, to generate a progeny of gene-modified cells. In HSCT and HSC-GT, chemotherapy is administered before infusion to free space in the bone marrow (BM) niche, which is required for the engraftment of infused cells. Here, we review alternative chemotherapy-free approaches to niche voidance that could replace conventional regimens and alleviate the morbidity of the procedure.

SOURCES OF DATA

Literature was reviewed from PubMed-listed peer-reviewed articles. No new data are presented in this article.

AREAS OF AGREEMENT

Chemotherapy exerts short and long-term toxicity to haematopoietic and non-haematopoietic organs. Whenever chemotherapy is solely used to allow engraftment of donor HSCs, rather than eliminating malignant cells, as in the case of HSC-GT for inborn genetic diseases, non-genotoxic approaches sparing off-target tissues are highly desirable.

AREAS OF CONTROVERSY

In principle, HSCs can be temporarily moved from the BM niches using mobilizing drugs or selectively cleared with targeted antibodies or immunotoxins to make space for the infused cells. However, translation of these principles into clinically relevant settings is only at the beginning, and whether therapeutically meaningful levels of chimerism can be safely established with these approaches remains to be determined.

GROWING POINTS

In pre-clinical models, mobilization of HSCs from the niche can be tailored to accommodate the exchange and engraftment of infused cells. Infused cells can be further endowed with a transient engraftment advantage.

AREAS TIMELY FOR DEVELOPING RESEARCH

Inter-individual efficiency and kinetics of HSC mobilization need to be carefully assessed. Investigations in large animal models of emerging non-genotoxic approaches will further strengthen the rationale and encourage application to the treatment of selected diseases.

Inotuzumab ozogamicin in B-cell precursor acute lymphoblastic leukemia: efficacy, toxicity, and practical considerations

Inotuzumab ozogamicin (InO) is an antibody drug conjugate composed of a humanized monoclonal antibody targeting the cell surface receptor CD22 coupled to a cytotoxic calicheamicin payload via an acid labile linker. InO has shown significant activity in relapsed and refractory B-cell precursor acute lymphoblastic leukemia (BCP-ALL) in both single agent and combination chemotherapy regimens in adult and pediatric trials. Its use in newly diagnosed elderly patients has also been established while clinical trials investigating its use in newly diagnosed pediatric patients and fit adults are ongoing. Notable toxicities include sinusoidal obstruction syndrome (SOS), particularly in patients who undergo hematopoietic stem cell transplantation (HSCT) after InO as well as myelosuppression and B-cell aplasia which confer increased infection risk, particularly in combination with cytotoxic chemotherapy. In the relapsed/refractory (R/R) setting, the planned subsequent curative therapy modality must be considered when using InO to mitigate SOS risk if proceeding to HSCT and account for potential B-cell aplasia if proceeding to chimeric antigen receptor CAR-T therapy. Studies exploring mechanisms of resistance or failure of InO are ongoing but modulation or loss CD22 expression, alternative CD22 splicing, and high Bcl-2 expression have been implicated. In this review, we will summarize the currently available data on InO, with an emphasis on pediatric trials, and explore future directions including combinatorial therapy.