Impact of high-sensitivity flow cytometry on peri-transplant minimal residual disease kinetics in acute leukemia

Minimal residual disease (MRD) detected before hematopoietic cell transplantation (HCT) is associated with adverse outcomes in patients with high-risk acute leukemia. However, the ideal time points for post-transplant MRD assessment and the clinical significance of low levels of residual disease in this context are unclear. We conducted a prospective real-world analysis of high-sensitivity flow cytometry MRD performed before and after transplant (at days 30, 60 and 100) in 77 acute leukemia patients. The aim was to evaluate the kinetics of disease elimination and correlate it with transplant outcomes. Pre-transplant MRD was negative in 42 (MRD-) and positive in 35 patients (MRD+). Post-transplant MRD assessment was feasible at day 30 (n = 30, 38.9%), day 60 (n = 27, 35.0%) and day 100 (n = 60, 77.9%). Relapses occurred in 8 patients in the MRD + group (22.9%) and three in the MRD-negative group (7.1%), p = 0.02. Pre-transplant MRD correlated with a decrease in overall survival (OS; 87.9% MRD- vs. 54.0% MRD+) and event-free survival (EFS; 85.3% MRD- vs. 51.1% MRD+), p = 0.001. Cumulative incidence of relapse (CIR) was 17.5% in MRD + vs. 2.6% in MRD- (p = 0.049). Non-relapse mortality (NRM) was 31.4% in MRD + vs. 12.1% in MRD- (p = 0.019). One-year OS was higher in patients with negative MRD at d100 (92.4%, 95% CI: 0.81-0.971) than positive d100 MRD (53.3%, 95% CI: 0.177-0.796), p < 0.0001. Disease status and d100 MRD were associated with OS, EFS and CIR. Differences in NRM between leukemia types (ALL: 18.9% MRD- vs. 50% MRD+, and AML 0% MRD- vs. 21.7% MRD+, p = 0.0158) were also observed. In conclusion, pre-transplant MRD assessed by highly sensitive flow cytometry accurately identified patients with adverse prognoses. Persistent MRD after HCT could predict relapse with high specificity and clinical sensitivity. These results highlight the importance of incorporating peri-transplant MRD kinetics into the routine treatment of acute leukemia, particularly in low/middle-income countries.

Allogeneic Hemopoietic Cell Transplantation as a Paradigm for Cellular Immunotherapy

BACKGROUND

Allogeneic hematopoietic cell transplantation (alloHCT) is an established curative treatment for hematological malignancies and other severe blood disorders. However, alloHCT is also known for its significant side effects.

SUMMARY

Here we review recent advances in targeted molecular therapy, immunotherapy, infectiology, and diagnostics that have enhanced the tolerability and efficacy of alloHCT, expanding its use to less fit and elderly patients. We analyze developments in conditioning regimens, donor selection, and the management of graft versus host disease (GVHD) and infections and discuss posttransplantation strategies to prevent relapse.

KEY MESSAGE

In a fresh perspective, alloHCT can serve as a platform to enhance the potential of emerging targeted and immune therapies.

[Current situation and prospect of minimal residual disease in pediatric T cell acute lymphoblastic leukemia]

Pediatric T-cell acute lymphoblastic leukemia (T-ALL) has been attracted much attention due to its high aggressiveness and complexity of treatment. Recently, with the development of technology and clinical research, the curative effect of T-ALL in children has been significantly improved. However, the presence of minimal residual disease (MRD) is still a key factor affecting the outcomes of children with T-ALL. With the continuous development of detection methods, the clinical applications of real-time quantitative PCR, multi-parameter flow cytometry, and high-throughput sequencing technology, MRD can be detected accurately to achieve personalized and precise treatment for each patient. The purpose of this article is to review the current detection methods of MRD in T-ALL, the clinical significance of MRD monitoring and evaluation in multi-agent combined chemotherapy and hematopoietic stem cell transplantation, and applying MRD to measure the responsiveness and effectiveness of new therapies in recent T-ALLs. Research directions and potential treatment strategies in the near future were also proposed.

Measurable residual disease (MRD)-testing in haematological cancers: A giant leap forward or sideways?

Measurable residual disease (MRD)-testing is used in many haematological cancers to estimate relapse risk and to direct therapy. Sometimes MRD-test results are used for regulatory approval. However, some people including regulators wrongfully believe results of MRD-testing are highly accurate and of proven efficacy in directing therapy. We review MRD-testing technologies and evaluate the accuracy of MRD-testing for predicting relapse and the strength of evidence supporting efficacy of MRD-guided therapy. We show that at the individual level MRD-test results are often an inaccurate relapse predictor. Also, no convincing data indicate that increasing therapy-intensity based on a positive MRD-test reduces relapse risk or improves survival. We caution against adjusting therapy-intensity based solely on results of MRD-testing.

How I use next-generation sequencing-MRD to plan approach and prevent relapse after HCT for children and adults with ALL

ABSTRACT

Measurable residual disease (MRD) evaluation by multiparameter flow cytometry (MFC) or quantitative polymerase chain reaction methods is an established standard of care for assessing risk of relapse before or after hematopoietic cell transplantation (HCT) for acute lymphoblastic leukemia (ALL). Next-generation sequencing (NGS)-MRD has emerged as a highly effective approach that allows for the detection of lymphoblasts at a level of <1 in 106 nucleated cells, increasing sensitivity of ALL detection by 2 to 3 logs. Early studies have shown superior results compared with MFC and suggest that NGS-MRD may allow for the determination of patients in whom reduced toxicity transplant preparative approaches could be deployed without sacrificing outcomes. Many centers/study groups have implemented immune modulation approaches based on MRD measurements that have resulted in improved outcomes. Challenges remain with NGS-MRD, because it is not commercially available in many countries, and interpretation of results can be complex. Through patient case review, discussion of relevant studies, and detailed expert opinion, we share our approach to NGS-MRD testing before and after HCT in pediatric and adult ALL. Improved pre-HCT risk classification and post-HCT monitoring for relapse in bone marrow and less invasive peripheral blood monitoring by NGS-MRD may lead to alternative approaches to prevent relapse in patients undergoing this challenging procedure.

Molecular relapse monitoring reveals the domination of impaired NK cell education over impaired inhibition in missing KIR-ligand recognition in patients after unrelated hematopoietic stem cell transplantation for malignant diseases

Transplantation of HLA and/or KIR mismatched allogeneic hematopoietic stem cells can lead NK cells to different states of activation/inhibition or education/resetting and change anti-tumor immunosurveillance. In this study, we used molecular relapse monitoring to investigate a correlation between either missing ligand recognition or variation of the cognate iKIR-HLA pairs with clinical outcomes in patients with hematological malignancies requiring allogeneic hematopoietic stem cell transplantation (allo-HSCT). Patients (N = 418) with acute myeloid leukemia (AML), chronic myeloid leukemia (CML), acute lymphoblastic leukemia (ALL), myelodysplastic syndrome (MDS), or lymphoma receiving T-cell repleted graft from HLA-matched or partly mismatched unrelated donors between 2012 and 2020 in our center were included in this study. Missing-ligand recognition was assessed through the presence or absence of recipients' HLA ligand for a particular inhibitory KIR (iKIR) exhibited by the donor. Inhibitory KIR-HLA pair number variation was defined by loss or gain of a new cognate pair of HLA-KIR within the new HLA environment of the recipient, compared with the donor's one. Considering the results of our research, we drew the following conclusions: (i) loss of iKIR-HLA cognate pair for C1, C2, and/or Bw4 groups led to significant deterioration of disease-free survival (DFS), molecular relapse, overall survival (OS) and non-relapse mortality (NRM) for patients undergoing allo-HSCT in the standard phase of the disease. This phenomenon was not observed in patients who underwent transplantation in advanced hematological cancer. (ii) The missing ligand recognition had no impact if the proportion of HLA mismatches was not considered; however, adjustments of HLA mismatch level in the compared groups highlighted the adverse effect of the missing ligand constellation. (iii) The adverse effect of adjusted missing ligand suggests a predominance of lost NK cell education over lost NK cell inhibition in posttransplant recipients' new HLA environment. Our results suggested that donors with the loss of an iKIR-HLA cognate pair after transplantation should be avoided, and donors who provided an additional iKIR-HLA cognate pair should be preferred in the allo-HSCT donor selection process.

Low rate of nonrelapse mortality in under-4-year-olds with ALL given chemotherapeutic conditioning for HSCT: a phase 3 FORUM study

ABSTRACT

Allogeneic hematopoietic stem cell transplantation (HSCT) is highly effective for treating pediatric high-risk or relapsed acute lymphoblastic leukemia (ALL). For young children, total body irradiation (TBI) is associated with severe late sequelae. In the FORUM study (NCT01949129), we assessed safety, event-free survival (EFS), and overall survival (OS) of 2 TBI-free conditioning regimens in children aged <4 years with ALL. Patients received fludarabine (Flu), thiotepa (Thio), and either busulfan (Bu) or treosulfan (Treo) before HSCT. From 2013 to 2021, 191 children received transplantation and were observed for ≥6 months (median follow-up: 3 years). The 3-year OS was 0.63 (95% confidence interval [95% CI], 0.52-0.72) and 0.76 (95% CI, 0.64-0.84) for Flu/Thio/Bu and Flu/Thio/Treo (P = .075), respectively. Three-year EFS was 0.52 (95% CI, 0.41-0.61) and 0.51 (95% CI, 0.39-0.62), respectively (P = .794). Cumulative incidence of nonrelapse mortality (NRM) and relapse at 3 years were 0.06 (95% CI, 0.02-0.12) vs 0.03 (95% CI: <0.01-0.09) (P = .406) and 0.42 (95% CI, 0.31-0.52) vs 0.45 (95% CI, 0.34-0.56) (P = .920), respectively. Grade >1 acute graft-versus-host disease (GVHD) occurred in 29% of patients receiving Flu/Thio/Bu and 17% of those receiving Flu/Thio/Treo (P = .049), whereas grade 3/4 occurred in 10% and 9%, respectively (P = .813). The 3-year incidence of chronic GVHD was 0.07 (95% CI, 0.03-0.13) vs 0.05 (95% CI, 0.02-0.11), respectively (P = .518). In conclusion, both chemotherapeutic conditioning regimens were well tolerated and NRM was low. However, relapse was the major cause of treatment failure. This trial was registered at www.clinicaltrials.gov as #NCT01949129.

Clinical application of next-generation sequencing-based monitoring of minimal residual disease in childhood acute lymphoblastic leukemia

BACKGROUND

Next-generation sequencing (NGS) is an emerging technology that can comprehensively assess the diversity of the immune system. We explored the feasibility of NGS in detecting minimal residual disease (MRD) in childhood acute lymphoblastic leukemia (ALL) based on immunoglobulin and T cell receptor.

METHODS

Bone marrow samples were collected pre- and post-treatment with pediatric ALL admitted to Shenzhen Children's Hospital from February 1st, 2020 to January 31st, 2021. We analyzed the MRD detected by NGS, multiparametric flow cytometry (MFC) and real-time quantitative PCR (RQ-PCR), and analyzed risk factors of positive NGS-MRD at the end of B-ALL induction chemotherapy.

RESULTS

A total of paired 236 bone marrow samples were collected from 64 children with ALL (58 B-ALL and 6 T-ALL). The decrease in the clonal rearrangement frequency of IGH, IGK, and IGL was generally consistent after treatment. Positive MRD was detected in 57.5% (77/134) of B-ALL and 80% (12/15) of T-ALL by NGS after chemotherapy, which was higher than those detected by MFC and RQ-PCR. In B-ALL patients, MRD results detected by NGS were consistent with MFC (r = 0.708, p < 0.001) and RQ-PCR (r = 0.618, p < 0.001). At the end of induction, NGS-MRD of 40.4% B-ALL was > 0.01% and multivariate analysis indicated that ≧2 clonal rearrangement sequences before treatment were an independent factor of negative NGS-MRD.

CONCLUSIONS

NGS is more sensitive than MFC and RQ-PCR for MRD measurement. B-ALL children with ≧2 clonal rearrangements detected by NGS before treatment are difficult to switch to negative MRD after chemotherapy.

Post-Hematopoietic Cell Transplantation Relapsed Acute Lymphoblastic Leukemia: Current Challenges and Future Directions

Allogeneic hematopoietic cell transplantation (allo-HCT) represents an important and potentially curative treatment option for adult patients with acute lymphoblastic leukemia. Relapse continues to remain the most important factor influencing overall survival post allo-HCT. We discuss early identification, clinical manifestations, and management of relapsed disease. Routine evaluation of measurable residual disease (MRD) and change in donor chimerism play a crucial role in early detection. Pivotal clinical trials have led to FDA approval of multiple novel agents like blinatumomab and inotuzumab. Combining targeted therapy with cellular immunotherapy serves as the backbone for prolonging overall survival in these patients. Donor lymphocyte infusions have traditionally been used in relapsed disease with suboptimal outcomes. This review provides insight into use of cellular therapy in MRD positivity and decreasing donor chimerism. It also discusses various modalities of combining cellular therapy with novel agents and discussing the impact of chimeric antigen receptor T-cell therapy in the setting of post allo-HCT relapse both as consolidative therapy and as a bridge to second transplant.

Immunophenotypic measurable residual disease monitoring in adult acute lymphoblastic leukemia patients undergoing allogeneic hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) offers a survival benefit to adult patients affected by acute lymphoblastic leukemia (ALL). However, to avoid an overt disease relapse, patients with pre or post transplant persistence or occurrence of measurable residual disease (MRD) may require cellular or pharmacological interventions with eventual side effects. While the significance of multiparametric flow cytometry (MFC) in the guidance of ALL treatment in both adult and pediatric patients is undebated, fewer data are available regarding the impact of MRD monitoring, as assessed by MFC analysis, in the allo-HSCT settings. Aim of this article is to summarize and discuss currently available information on the role of MFC detection of MRD in adult ALL patients undergoing allo-HSCT. The significance of MFC-based MRD according to sensitivity level, timing, and in relation to molecular techniques of MRD and chimerism assessment will be also discussed.

[Updated AWMF Guideline on the Diagnosis and Treatment of Acute Lymphoblastic Leukaemia in Children]

Depending on the initial risk factors survival rates of childhood acute lymphoblastic leukemia (ALL) nowadays reach an average of 85%. The successful treatment of this severe disease is based on the development of multi-modal treatment concepts, on the basis of a continuously improving molecular genetic characteri-zation of the disease with the identification of new risk factors. The diagnosis of the response to therapy and the resulting stratification of patients into different therapy strata plays an essential role in this progress. These risk-adapted treatment approaches have minimized therapy-associated complications as well as late effects. In the upcoming years, the goal will be to improve the cure rate of patients with unfavorable prognosis. The development of im-munotherapeutic approaches, which are currently being tested in clinical trials in the con-text of ALL therapy, can play an important role in this context.

Droplet Digital PCR: A New View on Minimal Residual Disease Quantification in Acute Lymphoblastic Leukemia

Real-time quantitative PCR (qPCR) using immunoglobulin/T-cell receptor gene rearrangements has been used as the gold standard for minimal residual disease (MRD) monitoring in acute lymphoblastic leukemia (ALL) for >20 years. Recently, new PCR-based technologies have emerged, such as droplet digital PCR (ddPCR), which could offer several methodologic advances for MRD monitoring. In the current work, qPCR and ddPCR were compared in an unbiased blinded prospective study (n = 88 measurements) and in a retrospective study with selected critical low positive samples (n = 65 measurements). The former included flow cytometry (Flow; n = 31 measurements) as a third MRD detection method. Published guidelines (qPCR) and the latest, revised evaluation criteria (ie, ddPCR, Flow) have been applied for data analysis. The prospective study shows that ddPCR outperforms qPCR with a significantly better quantitative limit of detection and sensitivity. The number of critical MRD estimates below quantitative limit was reduced by sixfold and by threefold in the retrospective and prospective cohorts, respectively. Furthermore, the concordance of quantitative values between ddPCR and Flow was higher than between ddPCR and qPCR, probably because ddPCR and Flow are absolute quantification methods independent of the diagnostic sample, unlike qPCR. In summary, our data highlight the advantages of ddPCR as a more precise and sensitive technology that could be used to refine response monitoring in ALL.

What Is the Role of HSCT in Philadelphia-Chromosome-Positive and Philadelphia-Chromosome-Like ALL in the Tyrosine Kinase Inhibitor Era?

Previously, the outcome of paediatric Philadelphia-chromosome-positive (Ph+) ALL treated with conventional chemotherapy alone was poor, necessitating the use of haematopoietic stem cell transplantation (HSCT) for the best outcomes. The recent addition of tyrosine kinase inhibitors (TKIs) alongside the chemotherapy regimens for Ph+ ALL has markedly improved outcomes, replacing the need for HSCT for lower risk patients. An additional poor prognosis group of Philadelphia-chromosome-like (Ph-like) ALL has also been identified. This group also can be targeted by TKIs in combination with chemotherapy, but the role of HSCT in this population is not clear. The impact of novel targeted immunotherapies (chimeric antigen receptor T cells and bispecific or drug-conjugated antibodies) has improved the outcome of patients, in combination with chemotherapy, and made the role of HSCT as the optimal curative therapy for Ph+ ALL and Ph-like ALL less clear. The prognosis of patients with Ph+ ALL and persistent minimal residual disease (MRD) at the end of consolidation despite TKI therapy or with additional genetic risk factors remains inferior when HSCT is not used. For such high-risk patients, HSCT using total-body-irradiation-containing conditioning is currently recommended. This review aims to provide an update on the current and future role of HSCT for Ph+ ALL and addresses key questions related to the management of these patients, including the role of HSCT in first complete remission, MRD evaluation and related actions post HSCT, TKI usage post HSCT, and the putative role of HSCT in Ph-like ALL.

Bispecific Antibodies and Other Non-CAR Targeted Therapies and HSCT: Decreased Toxicity for Better Transplant Outcome in Paediatric ALL?

This review will address the place of innovative, non-chemotherapy, non-CAR-T targeted therapies in the treatment of Acute Lymphoblastic Leukaemia (ALL), focusing on their use in the hematopoietic stem cell transplant (HSCT) context. The focus will be on the agent with the most experience to date, namely the bispecific T-cell engater (BiTE) blinatumomab, but references to antibody-drug conjugates (ADCs) such as inotuzumab ozogamicin and monoclonal antibodies such as daratumamab will be made as well. Specific issues to be addressed include: (1) The use of these agents to reduce measurable residual disease (MRD) prior to HSCT and their potential for improved transplant outcomes due to reduced toxicity compared to traditional chemotherapy salvage, as well as potentially increased toxicity with HSCT with particular agents; (2) the appropriate sequencing of innovative therapies, i.e., when to use BiTEs or antibodies versus CARs pre- and/or post-HSCT; this will include also the potential for impact on response of one group of agents on response to the other; (3) the role of these agents particularly in the post-HSCT relapse setting, or as maintenance to prevent relapse in this setting; (4) special populations in which these agents may substitute for traditional chemotherapy during induction or consolidation in patients with predisposing factors for toxicity with traditional therapy (e.g., Trisomy 21, infants), or those who develop infectious complications precluding delivery of full standard-of-care (SOC) chemotherapy during induction/consolidation (e.g., fungal infections); (5) the evidence we have to date regarding the potential for substitution of blinatumomab for some of the standard chemotherapy agents used pre-HSCT in patients without the above risk factors for toxicity, but with high risk disease going into transplant, in an attempt to decrease current rates of transplant-related mortality as well as morbidity; (6) the unique toxicity profile of these agents and concerns regarding particular side effects in the HSCT context. The manuscript will include both the data we have to date regarding the above issues, ongoing studies that are trying to explore them, and suggestions for future studies to further refine our knowledge base.

Chimeric Antigen Receptor T-Cell Therapy in Paediatric B-Cell Precursor Acute Lymphoblastic Leukaemia: Curative Treatment Option or Bridge to Transplant?

Chimeric antigen receptor T-cell therapy (CAR-T) targeting CD19 has been associated with remarkable responses in paediatric patients and adolescents and young adults (AYA) with relapsed/refractory (R/R) B-cell precursor acute lymphoblastic leukaemia (BCP-ALL). Tisagenlecleucel, the first approved CD19 CAR-T, has become a viable treatment option for paediatric patients and AYAs with BCP-ALL relapsing repeatedly or after haematopoietic stem cell transplantation (HSCT). Based on the chimeric antigen receptor molecular design and the presence of a 4-1BB costimulatory domain, tisagenlecleucel can persist for a long time and thereby provide sustained leukaemia control. "Real-world" experience with tisagenlecleucel confirms the safety and efficacy profile observed in the pivotal registration trial. Recent guidelines for the recognition, management and prevention of the two most common adverse events related to CAR-T - cytokine release syndrome and immune-cell-associated neurotoxicity syndrome - have helped to further decrease treatment toxicity. Consequently, the questions of how and for whom CD19 CAR-T could substitute HSCT in BCP-ALL are inevitable. Currently, 40-50% of R/R BCP-ALL patients relapse post CD19 CAR-T with either CD19- or CD19+ disease, and consolidative HSCT has been proposed to avoid disease recurrence. Contrarily, CD19 CAR-T is currently being investigated in the upfront treatment of high-risk BCP-ALL with an aim to avoid allogeneic HSCT and associated treatment-related morbidity, mortality and late effects. To improve survival and decrease long-term side effects in children with BCP-ALL, it is important to define parameters predicting the success or failure of CAR-T, allowing the careful selection of candidates in need of HSCT consolidation. In this review, we describe the current clinical evidence on CAR-T in BCP-ALL and discuss factors associated with response to or failure of this therapy: product specifications, patient- and disease-related factors and the impact of additional therapies given before (e.g., blinatumomab and inotuzumab ozogamicin) or after infusion (e.g., CAR-T re-infusion and/or checkpoint inhibition). We discuss where to position CAR-T in the treatment of BCP-ALL and present considerations for the design of supportive trials for the different phases of disease. Finally, we elaborate on clinical settings in which CAR-T might indeed replace HSCT.

Next-Generation Sequencing of Minimal Residual Disease for Predicting Relapse after Tisagenlecleucel in Children and Young Adults with Acute Lymphoblastic Leukemia

We assessed minimal residual disease (MRD) detection and B-cell aplasia after tisagenlecleucel therapy for acute lymphoblastic leukemia (ALL) to define biomarkers predictive of relapse (N = 143). Next-generation sequencing (NGS) MRD detection >0 in bone marrow (BM) was highly associated with relapse. B-cell recovery [signifying loss of functional chimeric antigen receptor (CAR) T cells] within the first year of treatment was associated with a hazard ratio (HR) for relapse of 4.5 [95% confidence interval (CI), 2.03-9.97; P < 0.001]. Multivariate analysis at day 28 showed independent associations of BMNGS-MRD >0 (HR = 4.87; 95% CI, 2.18-10.8; P < 0.001) and B-cell recovery (HR = 3.33; 95% CI, 1.44-7.69; P = 0.005) with relapse. By 3 months, the BMNGS-MRD HR increased to 12 (95% CI, 2.87-50; P < 0.001), whereas B-cell recovery was not independently predictive (HR = 1.27; 95% CI, 0.33-4.79; P = 0.7). Relapses occurring with persistence of B-cell aplasia were largely CD19^- (23/25: 88%). Detectable BMNGS-MRD reliably predicts risk with sufficient time to consider approaches to relapse prevention such as hematopoietic cell transplantation (HCT) or second CAR-T cell infusion. SIGNIFICANCE: Detectable disease by BMNGS-MRD with or without B-cell aplasia is highly predictive of relapse after tisagenlecleucel therapy for ALL. Clonotypic rearrangements used to follow NGS-MRD did not change after loss of CD19 or lineage switch. High-risk patients identified by these biomarkers may benefit from HCT or investigational cell therapies.See related commentary by Ghorashian and Bartram, p. 2.This article is highlighted in the In This Issue feature, p. 1.

How I Use Measurable Residual Disease in the Clinical Management of Adult Acute Lymphoblastic Leukemia

Over the last decade the use of measurable residual disease (MRD) diagnostics in adult acute lymphoblastic leukemia (ALL) has expanded from a limited number of study groups in Europe and the United States to a world-wide application. In this review, we summarize the advantages and drawbacks of the current available techniques used for MRD monitoring. Through the use of three representative case studies, we highlight the advances in the use of MRD in clinical decision-making in the management of ALL in adults. We acknowledge discrepancies in MRD monitoring and treatment between different countries, reflecting differing availability, accessibility and affordability.

Intensive monitoring of minimal residual disease and chimerism after allogeneic hematopoietic stem cell transplantation for acute leukemia in children

Posttransplant leukemia detection before overt relapse is key to the success of immunotherapeutic interventions, as they are more efficient when leukemia burden is low. However, optimal schedule and monitoring methods are not well defined. We report the intensive bone marrow monitoring of minimal residual disease (MRD) using flow cytometry (FC) and nested reverse transcription polymerase chain reaction (RT-PCR) whenever a fusion transcript allowed it and chimerism by PCR at 11 timepoints in the first 2 years after transplant. Seventy-one transplants were performed in 59 consecutive children, for acute myeloid (n = 38), lymphoid (n = 31), or mixed-phenotype (n = 2) leukemia. MRD was monitored in 62 cases using FC (n = 58) and/or RT-PCR (n = 35). Sixty-seven percent of leukemia recurrences were detected before overt relapse, with a detection rate of 89% by RT-PCR and 40% by FC alone. Increased mixed chimerism was never the first evidence of recurrence. Two patients monitored by RT-PCR relapsed without previous MRD detection, one after missed scheduled evaluation and the other 4.7 years post transplant. Among the 22 cases with MRD detection without overt relapse, 19 received therapeutic interventions. Eight (42%) never relapsed. In conclusion, intensive marrow monitoring by RT-PCR effectively allows for early detection of posttransplant leukemia recurrence.

Cardiac Relapse of Acute Lymphoblastic Leukemia Following Hematopoietic Stem Cell Transplantation: A Case Report and Review of Literature

Isolated extramedullary relapse of acute lymphoblastic leukemia (ALL) occurs in soft tissues and various organs outside the testis and central nervous system. Treatments such as hematopoietic stem cell transplantation and more novel modalities such as immunotherapy have eradicated ALL at extramedullary sites. In some instances, survival times for relapsed ALL at these sites are longer than those for relapsed disease involving only the bone marrow. Isolated relapse of ALL in the myocardium is rare, especially in children, making diagnosis and treatment of it difficult. More recent treatment options such as chimeric antigen receptor T-cell therapy carry a high risk of cytokine release syndrome and associated risk of worsening cardiac function. Herein we present the case of an 11-year-old boy who presented with relapsed symptomatic B-cell ALL in the myocardium following allogeneic hematopoietic stem cell transplantation. This is an unusual presentation of relapsed ALL and this case demonstrates the associated challenges in its diagnosis and treatment. The case report is followed by a literature review of the advances in treatment of pediatric leukemia and their application to extramedullary relapse of this disease in particular.

Multivariate Analysis of Immune Reconstitution and Relapse Risk Scoring in Children Receiving Allogeneic Stem Cell Transplantation for Acute Leukemias

A timely and effective immune reconstitution after hematopoietic stem cell transplantation (HSCT) is of crucial importance to enhance graft-versus-leukemia reaction in hematological malignancies. Several factors can influence the yield of this process, and new mathematical models are needed to describe this complex phenomenon.

Targeted Therapy in the Treatment of Pediatric Acute Lymphoblastic Leukemia-Therapy and Toxicity Mechanisms

Targeted therapy has revolutionized the treatment of poor-prognosis pediatric acute lymphoblastic leukemia (ALL) with specific genetic abnormalities. It is still being described as a new landmark therapeutic approach. The main purpose of the use of molecularly targeted drugs and immunotherapy in the treatment of ALL is to improve the treatment outcomes and reduce the doses of conventional chemotherapy, while maintaining the effectiveness of the therapy. Despite promising treatment results, there is limited clinical research on the effect of target cell therapy on the potential toxic events in children and adolescents. The recent development of highly specific molecular methods has led to an improvement in the identification of numerous unique expression profiles of acute lymphoblastic leukemia. The detection of specific genetic mutations determines patients’ risk groups, which allows for patient stratification and for an adjustment of the directed and personalized target therapies that are focused on particular molecular alteration. This review summarizes the knowledge concerning the toxicity of molecular-targeted drugs and immunotherapies applied in childhood ALL.

Utilizing the prognostic impact of minimal residual disease in treatment decisions for pediatric acute lymphoblastic leukemia

INTRODUCTION

Acute lymphoblastic leukemia (ALL) is the first pediatric cancer where the assessment of early response to therapy by minimal residual disease (MRD) monitoring has demonstrated its importance to improve risk-based treatment approaches. The most standardized tools to study MRD in ALL are multiparametric flow cytometry and realtime-quantitative polymerase chain reaction amplification-based methods. In recent years, MRD measurement has reached greater levels of sensitivity and standardization through international laboratory networks collaboration.

AREAS COVERED

We herewith describe how to assess and apply the prognostic impact of MRD in treatment decisions, with specific focus on pediatric ALL. We also highlight the role of MRD monitoring in the context of genetically homogeneous subgroups of pediatric ALL. However, some queries remain to be addressed and emerging technologies hold the promise of improving MRD detection in ALL patients.

EXPERT OPINION

Emerging technologies, like next generation flow cytometry, droplet digital PCR, and next generation sequencing appear to be important methods for assessing MRD in pediatric ALL. These more specific and/or sensitive MRD monitoring methods may help to predict relapse with greater accuracy, and are currently being used in clinical trials to improve pediatric ALL outcome by optimizing patient stratification and earlier MRD-based interventional therapy.

Whole-genome sequencing facilitates patient-specific quantitative PCR-based minimal residual disease monitoring in acute lymphoblastic leukaemia, neuroblastoma and Ewing sarcoma

Background

Minimal residual disease (MRD) measurement is a cornerstone of contemporary acute lymphoblastic leukaemia (ALL) treatment. The presence of immunoglobulin (Ig) and T cell receptor (TCR) gene recombinations in leukaemic clones allows widespread use of patient-specific, DNA-based MRD assays. In contrast, paediatric solid tumour MRD remains experimental and has focussed on generic assays targeting tumour-specific messenger RNA, methylated DNA or microRNA.

Methods

We examined the feasibility of using whole-genome sequencing (WGS) data to design tumour-specific polymerase chain reaction (PCR)-based MRD tests (WGS-MRD) in 18 children with high-risk relapsed cancer, including ALL, high-risk neuroblastoma (HR-NB) and Ewing sarcoma (EWS) (n = 6 each).

Results

Sensitive WGS-MRD assays were generated for each patient and allowed quantitation of 1 tumour cell per 10⁻⁴ (0.01%)–10^–5 (0.001%) mononuclear cells. In ALL, WGS-MRD and Ig/TCR-MRD were highly concordant. WGS-MRD assays also showed good concordance between quantitative PCR and droplet digital PCR formats. In serial clinical samples, WGS-MRD correlated with disease course. In solid tumours, WGS-MRD assays were more sensitive than RNA-MRD assays.

Conclusions

WGS facilitated the development of patient-specific MRD tests in ALL, HR-NB and EWS with potential clinical utility in monitoring treatment response. WGS data could be used to design patient-specific MRD assays in a broad range of tumours.

The Role of Allogeneic Hematopoietic Stem Cell Transplantation in Pediatric Leukemia

Allogeneic hematopoietic stem cell transplantation (HSCT) offers potentially curative treatment for many children with high-risk or relapsed acute leukemia (AL), thanks to the combination of intense preparative radio/chemotherapy and the graft-versus-leukemia (GvL) effect. Over the years, progress in high-resolution donor typing, choice of conditioning regimen, graft-versus-host disease (GvHD) prophylaxis and supportive care measures have continuously improved overall transplant outcome, and recent successes using alternative donors have extended the potential application of allotransplantation to most patients. In addition, the importance of minimal residual disease (MRD) before and after transplantation is being increasingly clarified and MRD-directed interventions may be employed to further ameliorate leukemia-free survival after allogeneic HSCT. These advances have occurred in parallel with continuous refinements in chemotherapy protocols and the development of targeted therapies, which may redefine the indications for HSCT in the coming years. This review discusses the role of HSCT in childhood AL by analysing transplant indications in both acute lymphoblastic and acute myeloid leukemia, together with current and most promising strategies to further improve transplant outcome, including optimization of conditioning regimen and MRD-directed interventions.

Predictive Value of Dynamic Peri-Transplantation MRD Assessed By MFC Either Alone or in Combination with Other Variables for Outcomes of Patients with T-Cell Acute Lymphoblastic Leukemia

We performed a retrospective analysis to investigate dynamic peri-hematopoietic stem cell transplantation (HSCT) minimal/measurable residual disease (MRD) on outcomes in patients with T-cell acute lymphoblastic leukemia (T-ALL). A total of 271 patients were enrolled and classified into three groups: unchanged negative MRD pre- and post-HSCT group (group A), post-MRD non-increase group (group B), and post-MRD increase group (group C). The patients in group B and group C experienced a higher cumulative incidence of relapse (CIR) (42% vs. 71% vs. 16%, P<0.001) and lower leukemia-free survival (LFS) (46% vs. 21% vs. 70%, P<0.001) and overall survival (OS) (50% vs. 28% vs. 72%, P<0.001) than in group A, but there was no significant difference in non-relapse mortality (NRM) among three groups (14% vs. 12% vs. 8%, P=0.752). Multivariate analysis showed that dynamic peri-HSCT MRD was associated with CIR (HR=2.392, 95% CI, 1.816-3.151, P<0.001), LFS (HR=1.964, 95% CI, 1.546-2.496, P<0.001) and OS (HR=1.731, 95% CI, 1.348-2.222, P<0.001). We also established a risk scoring system based on dynamic peri-HSCT MRD combined with remission status pre-HSCT and onset of chronic graft-versus-host disease (GVHD). This risk scoring system could better distinguish CIR (c=0.730) than that for pre-HSCT MRD (c=0.562), post-HSCT MRD (c=0.616) and pre- and post-MRD dynamics (c=0.648). Our results confirm the outcome predictive value of dynamic peri-HSCT MRD either alone or in combination with other variables for patients with T-ALL.

One-Step Multiplexed Droplet Digital Polymerase Chain Reaction for Quantification of p190 BCR-ABL1 Fusion Transcript in B-Lymphoblastic Leukemia

CONTEXT.—

Quantification and detection of the t(9;22) (BCR-ABL1) translocation in chronic myelogenous leukemia and B-lymphoblastic leukemia are important for directing treatment protocols and monitoring disease relapse. However, quantification using traditional reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) is dependent on a calibration curve and is prone to laboratory-to-laboratory variation. Droplet digital polymerase chain reaction (ddPCR) is a novel method that allows for highly sensitive absolute quantification of transcript copy number. As such, ddPCR is a good candidate for disease monitoring, an assay requiring reproducible measurements with high specificity and sensitivity.

OBJECTIVE.—

To compare results of ddPCR and RT-qPCR BCR-ABL1 fusion transcript measurements of patient samples and determine if either method is superior.

DESIGN.—

We optimized and standardized a 1-step multiplexed ddPCR assay to detect BCR-ABL1 p190 and ABL1 e10 transcripts. The ddPCR optimization included varying cycle number and primer concentration with standardization of droplet generation and droplet number and analyses to improve data sensitivity. Following optimization, ddPCR measurements were performed on clinical samples and compared with traditional RT-qPCR results.

RESULTS.—

Droplet digital polymerase chain reaction was able to detect the BCR-ABL1 p190 transcript to 0.001% (1:10-5) with a calculated limit of detection and limit of quantitation of 4.1 and 5.3 transcripts, respectively. When tested on patient samples, ddPCR was able to identify 20% more positives than a laboratory-developed 2-step RT-qPCR assay.

CONCLUSIONS.—

Droplet digital polymerase chain reaction demonstrated increased detection of BCR-ABL1 compared with RT-qPCR. Improved detection of BCR-ABL1 p190 and the potential for improved standardization across multiple laboratories makes ddPCR a suitable method for the disease monitoring in patients with acute B-lymphoblastic leukemia.

A risk score system for stratifying the risk of relapse in B cell acute lymphocytic leukemia patients after allogenic stem cell transplantation

BACKGROUND

For patients with B cell acute lymphocytic leukemia (B-ALL) who underwent allogeneic stem cell transplantation (allo-SCT), many variables have been demonstrated to be associated with leukemia relapse. In this study, we attempted to establish a risk score system to predict transplant outcomes more precisely in patients with B-ALL after allo-SCT.

METHODS

A total of 477 patients with B-ALL who underwent allo-SCT at Peking University People's Hospital from December 2010 to December 2015 were enrolled in this retrospective study. We aimed to evaluate the factors associated with transplant outcomes after allo-SCT, and establish a risk score to identify patients with different probabilities of relapse. The univariate and multivariate analyses were performed with the Cox proportional hazards model with time-dependent variables.

RESULTS

All patients achieved neutrophil engraftment, and 95.4% of patients achieved platelet engraftment. The 5-year cumulative incidence of relapse (CIR), overall survival (OS), leukemia-free survival (LFS), and non-relapse mortality were 20.7%, 70.4%, 65.6%, and 13.9%, respectively. Multivariate analysis showed that patients with positive post-transplantation minimal residual disease (MRD), transplanted beyond the first complete remission (≥CR2), and without chronic graft-versus-host disease (cGVHD) had higher CIR (P  < 0.001, P = 0.004, and P  < 0.001, respectively) and worse LFS (P  < 0.001, P = 0.017, and P  < 0.001, respectively), and OS (P  < 0.001, P = 0.009, and P  < 0.001, respectively) than patients without MRD after transplantation, transplanted in CR1, and with cGVHD. A risk score for predicting relapse was formulated with the three above variables. The 5-year relapse rates were 6.3%, 16.6%, 55.9%, and 81.8% for patients with scores of 0, 1, 2, and 3 (P  < 0.001), respectively, while the 5-year LFS and OS values decreased with increasing risk score.

CONCLUSION

This new risk score system might stratify patients with different risks of relapse, which could guide treatment.

A validated pediatric disease risk index for allogeneic hematopoietic cell transplantation

A disease risk index (DRI) that was developed for adults with hematologic malignancy who were undergoing hematopoietic cell transplantation is also being used to stratify children and adolescents by disease risk. Therefore, to develop and validate a DRI that can be used to stratify those with AML and ALL by their disease risk, we analyzed 2569 patients aged <18 years with acute myeloid (AML; n = 1224) or lymphoblastic (ALL; n = 1345) leukemia who underwent hematopoietic cell transplantation. Training and validation subsets for each disease were generated randomly with 1:1 assignment to the subsets, and separate prognostic models were derived for each disease. For AML, 4 risk groups were identified based on age, cytogenetic risk, and disease status, including minimal residual disease status at transplantation. The 5-year leukemia-free survival for low (0 points), intermediate (2, 3, 5), high (7, 8), and very high (>8) risk groups was 78%, 53%, 40%, and 25%, respectively (P < .0001). For ALL, 3 risk groups were identified based on age and disease status, including minimal residual disease status at transplantation. The 5-year leukemia-free survival for low (0 points), intermediate (2-4), and high (≥5) risk groups was 68%, 51%, and 33%, respectively (P < .0001). We confirmed that the risk groups could be applied to overall survival, with 5-year survival ranging from 80% to 33% and 73% to 42% for AML and ALL, respectively (P < .0001). This validated pediatric DRI, which includes age and residual disease status, can be used to facilitate prognostication and stratification of children with AML and ALL for allogeneic transplantation.

Minimal Residual Disease Prior to and After Haematopoietic Stem Cell Transplantation in Children and Adolescents With Acute Lymphoblastic Leukaemia: What Level of Negativity Is Relevant?

Minimal residual disease (MRD) assessment plays a central role in risk stratification and treatment guidance in paediatric patients with acute lymphoblastic leukaemia (ALL). As such, MRD prior to haematopoietic stem cell transplantation (HSCT) is a major factor that is independently correlated with outcome. High burden of MRD is negatively correlated with post-transplant survival, as both the risk of leukaemia recurrence and non-relapse mortality increase with greater levels of MRD. Despite growing evidence supporting these findings, controversies still exist. In particular, it is still not clear whether multiparameter flow cytometry and real-time quantitative polymerase chain reaction, which is used to recognise immunoglobulin and T-cell receptor gene rearrangements, can be employed interchangeably. Moreover, the higher sensitivity in MRD quantification offered by next-generation sequencing techniques may further refine the ability to stratify transplant-associated risks. While MRD quantification from bone marrow prior to HSCT remains the state of the art, heavily pre-treated patients may benefit from additional staging, such as using ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography to detect focal residues of disease. Additionally, the timing of MRD detection (i.e., immediately before administration of the conditioning regimen or weeks before) is a matter of debate. Pre-transplant MRD negativity has previously been associated with superior outcomes; however, in the recent For Omitting Radiation Under Majority age (FORUM) study, pre-HSCT MRD positivity was associated with neither relapse risk nor survival. In this review, we discuss the level of MRD that may require pre-transplant therapy intensification, risking time delay and complications (as well as losing the window for HSCT if disease progression occurs), as opposed to an adapted post-transplant strategy to achieve long-term remission. Indeed, MRD monitoring may be a valuable tool to guide individualised treatment decisions, including tapering of immunosuppression, cellular therapies (such as donor lymphocyte infusions) or additional immunotherapy (such as bispecific T-cell engagers or chimeric antigen receptor T-cell therapy).

B-Cell Precursor-Acute Lymphoblastic Leukemia With EBF1-PDGFRB Fusion Treated With Hematopoietic Stem Cell Transplantation and Imatinib: A Case Report and Literature Review

A 9-year-old girl was diagnosed with B-cell precursor-acute lymphoblastic leukemia (BCP-ALL). Although she entered remission after induction therapy, she relapsed 15 months after maintenance therapy cessation. Since further investigation revealed EBF1-PDGFRB fusion, her condition was treated as BCR-ABL1-like acute lymphoblastic leukemia. She was started on a tyrosine kinase inhibitor, imatinib, and chemotherapy and underwent umbilical cord blood transplantation following reduced intensity conditioning. She has remained in complete remission for 36 months after cord blood transplantation. This case demonstrates the successful use of a tyrosine kinase inhibitor to treat BCP-ALL with a fusion transcript and highlights the need for a standardized treatment protocol.

How I treat measurable (minimal) residual disease in acute leukemia after allogeneic hematopoietic cell transplantation

Although allogeneic hematopoietic cell transplantation (allo-HCT) is currently the standard curative treatment of acute leukemia, relapse remains unacceptably high. Measurable (minimal) residual disease (MRD) after allo-HCT may be used as a predictor of impending relapse and should be part of routine follow-up for transplanted patients. Patients with MRD may respond to therapies aiming to unleash or enhance the graft-versus-leukemia effect. However, evidence-based recommendations on how to best implement MRD testing and MRD-directed therapy after allo-HCT are lacking. Here, I describe our institutional approach to MRD monitoring for preemptive MRD-triggered intervention, using patient scenarios to illustrate the discussion.

CAR T cells vs allogeneic HSCT for poor-risk ALL

For subgroups of children with B-cell acute lymphoblastic leukemia (B-ALL) at very high risk of relapse, intensive multiagent chemotherapy has failed. Traditionally, the field has turned to allogeneic hematopoietic stem cell transplantation (HSCT) for patients with poor outcomes. While HSCT confers a survival benefit for several B-ALL populations, often HSCT becomes standard-of-care in subsets of de novo ALL with poor risk features despite limited or no data showing a survival benefit in these populations, yet the additive morbidity and mortality can be substantial. With the advent of targeted immunotherapies and the transformative impact of CD19-directed chimeric antigen receptor (CAR)-modified T cells on relapsed or refractory B-ALL, this approach is currently under investigation in frontline therapy for a subset of patients with poor-risk B-ALL: high-risk B-ALL with persistent minimal residual disease at the end of consolidation, which has been designated very high risk. Comparisons of these 2 approaches are fraught with issues, including single-arm trials, differing eligibility criteria, comparisons to historical control populations, and vastly different toxicity profiles. Nevertheless, much can be learned from available data and ongoing trials. We will review data for HSCT for pediatric B-ALL in first remission and the efficacy of CD19 CAR T-cell therapy in relapsed or refractory B-ALL, and we will discuss an ongoing international phase 2 clinical trial of CD19 CAR T cells for very-high-risk B-ALL in first remission.

Preemptive low-dose interleukin-2 or DLI for late-onset minimal residual disease in acute leukemia or myelodysplastic syndrome after allogeneic hematopoietic stem cell transplantation

Minimal residual disease (MRD) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) heralds high risk of relapse. Whether preemptive recombinant interleukin-2 (pre-IL2) is effective for patients with late-onset MRD (LMRD) remains unknown. We retrospectively compared the efficacy and safety of pre-IL2 (n = 30) and pre-DLI (n = 25) for LMRD in patients receiving allo-HSCT for acute leukemia or myelodysplastic syndrome. The 1-year overall survival (OS) and disease-free survival (DFS) rates were 86.7% and 78.4% (P = 0.267), 83.3% and 75.6% (P = 0.329), the cumulative incidence of grades III-IV acute graft-versus-host disease (aGVHD) at 100 days post-preemptive intervention was 3.3% and 12.0% (P = 0.226) in the pre-IL2 group and pre-DLI group, respectively. The 1-year cumulative incidence of moderate/severe chronic GVHD (cGVHD), relapse (CIR), and non-relapse mortality (NRM) were 7.7% and 27.9% (P = 0.018), 13.6% and 20.0% (P = 0.561) and 3.3% and 5.5% (P = 0.321) in the two groups, respectively. No remarkable differences in CIR, OS, and DFS between the two intervention groups were found in multivariate analysis. The GVHD-free and relapse-free survival (GRFS) were better in the pre-IL2 group than in the pre-DLI group (HR = 0.31, 95% confidence interval (CI), 0.12-0.76; P = 0.011). In conclusion, preemptive low-dose IL2 and preemptive DLI yield comparable outcomes for patients with LMRD receiving allo-HSCT, in terms of aGVHD, NRM, relapse, OS, and DFS. However, preemptive low-dose IL2 has a lower incidence of moderate/severe cGVHD and a higher CRFS. Preemptive low-dose IL2 may be an alternative method for patients who develop LMRD after allo-HSCT, particularly for patients who cannot receive preemptive DLI.

ADCC can improve graft vs leukemia effect after T- and B-cell depleted haploidentical stem cell transplantation in pediatric B-lineage ALL

Posttransplant relapsed B-cell precursor ALL can be cured by 2nd hematopoietic stem cell transplantation (HSCT) in 20% of patients. The major cause of death after second HSCT is leukemic relapse. One reliable predictor for survival after 2nd-HSCT are posttransplant MRD levels. Patients with detectable or increase of MRD are likely to relapse. Patients in complete molecular remission show the best leukemia-free survival and lowest cumulative incidence (CI) of relapse. As patients who undergo second or subsequent HSCT are high-risk patients, we evaluated the prophylactic use of the chimeric Fc-optimized CD19-4G7SDIE-mAb. Posttransplant relapsed CD19⁺ BCP-ALL patients, who underwent a second or subsequent haplo-HSCT from a T- and B-cell depleted graft received posttransplant prophylactic CD19-4G7SDIE-mAb treatment on compassionate use in complete molecular remission, to increase the antileukemic activity of the new reconstituting immune system by recruiting Fc-expressing effector cells. NK cells recovered early and robust. The 3 year overall survival in 15 evaluable patients was 56%, the 3 year event-free survival was 55% and the CI of relapse 38%. Compared to a historical control group, the CI of relapse was markedly lower and consecutively the EFS higher. Posttransplant-targeted therapy may overcome the need for unspecific GvL effect of undesired GvHD, that can cause severe morbidity and mortality. Due to a low adverse event profile the CD19-4G7SDIE-mAb may be suitable for broad administration to consolidate posttransplant MRD negativity.

Novel Biomarkers for Outcome After Allogeneic Hematopoietic Stem Cell Transplantation

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a well-established curative treatment for various malignant hematological diseases. However, its clinical success is substantially limited by major complications including graft-vs.-host disease (GVHD) and relapse of the underlying disease. Although these complications are known to lead to significant morbidity and mortality, standardized pathways for risk stratification of patients undergoing allo-HSCT are lacking. Recent advances in the development of diagnostic and prognostic tools have allowed the identification of biomarkers in order to predict outcome after allo-HSCT. This review will provide a summary of clinically relevant biomarkers that have been studied to predict the development of acute GVHD, the responsiveness of affected patients to immunosuppressive treatment and the risk of non-relapse mortality. Furthermore, biomarkers associated with increased risk of relapse and subsequent mortality will be discussed.

The impact of donor type on the outcome of pediatric patients with very high risk acute lymphoblastic leukemia. A study of the ALL SCT 2003 BFM-SG and 2007-BFM-International SG

Allogeneic HSCT represents the only potentially curative treatment for very high risk (VHR) ALL. Two consecutive international prospective studies, ALL-SCT-(I)BFM 2003 and 2007 were conducted in 1150 pediatric patients. 569 presented with VHR disease leading to any kind of HSCT. All patients >2 year old were transplanted after TBI-based MAC. The median follow-up was 5 years. 463 patients were transplanted from matched donor (MD) and 106 from mismatched donor (MMD). 214 were in CR1. Stem cell source was unmanipulated BM for 330 patients, unmanipulated PBSC for 135, ex vivo T-cell depleted PBSC for 62 and cord-blood for 26. There were more advanced disease, more ex vivo T-cell depletion, and more chemotherapy based conditioning regimen for patients transplanted from MMD as compared to those transplanted from MSD or MD. Median follow up (reversed Kaplan Meier estimator) was 4.99 years, median follow up of survivals was 4.88, range (0.01–11.72) years. The 4-year CI of extensive cGvHD was 13 ± 2% and 17 ± 4% (p = NS) for the patients transplanted from MD and MMD, respectively. 4-year EFS was statistically better for patients transplanted from MD (60 ± 2% vs. 42 ± 5%, p < 0.001) for the whole cohort. This difference does not exist if considering separately patients treated in the most recent study. There was no difference in 4-year CI of relapse. The 4-year NRM was lower for patients transplanted from MD (9 ± 1% vs. 23 ± 4%, p < 0.001). In multivariate analysis, donor-type appears as a negative risk-factor for OS, EFS, and NRM. This paper demonstrates the impact of donor type on overall results of allogeneic stem cell transplantation for very-high risk pediatric acute lymphoblastic leukemia with worse results when using MMD stem cell source.

Addition of Thiotepa to Total Body Irradiation and Cyclophosphamide Conditioning for Allogeneic Hematopoietic Stem Cell Transplantation in Pediatric Acute Lymphoblastic Leukemia

Total body irradiation (TBI)/cyclophosphamide (CY) is a standard-of-care conditioning regimen in allogeneic hematopoietic stem cell transplant (HSCT) for pediatric acute lymphoblastic leukemia (ALL). This study sought to identify whether the addition of thiotepa (TT) to TBI/CY improves HSCT outcomes for pediatric patients with ALL. A retrospective analysis was performed on 347 pediatric ALL patients who underwent HSCT between 1995 and 2015, with 242 receiving TBI/CY/TT and 105 patients receiving TBI/CY. There were no statistical differences in age, donor source, or complete remission status between the 2 groups. Comparison of the TBI/CY/TT versus TBI/CY groups demonstrated no difference in transplant-related mortality at 1 (11% versus 11%), 5 (13% versus 16%), or 10 years (16% versus 16%). There was lower relapse in the TBI/CY/TT group at 1 (14% versus 26%), 5 (24% versus 36%), 10 (26% versus 37%), and 15 years (26% versus 37%) (P= .02) but was not statistically significant on multivariate analysis. The TBI/CY/TT group showed a trend toward improved disease-free survival (DFS) at 5 (59% versus 47%), 10 (56% versus 46%), and 15 years (49% versus 40%) (P = .05) but was not statistically significant on multivariate analysis. Comparing overall survival at 5 (62% versus 53%), 10 (57% versus 50%), and 15 years (50% versus 44%) demonstrated no statistical difference between the 2 groups. The addition of thiotepa to TBI/CY demonstrated no increase in transplant-related mortality for pediatric ALL HSCT but was unable to demonstrate significant benefit in disease control. Minimal residual disease status remained the key risk factor impacting both relapse and DFS. More studies are warranted to better clarify the benefits of using thiotepa in conditioning for ALL HSCT.

Measurable residual disease (MRD) testing for acute leukemia in EBMT transplant centers: a survey on behalf of the ALWP of the EBMT

Detectable measurable residual disease (MRD) is a key prognostic factor in both acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML) patients. Thus, we conducted a survey in EBMT transplant centers focusing on pre- and post-allo-HCT MRD. One hundred and six centers from 29 countries responded. One hundred had a formal strategy for routine MRD assessment, 91 for both ALL and AML. For ALL (n = 95), assessing MRD has been routine practice starting from 2010 (range, 1990-2019). Techniques used for MRD assessment consisted of PCR techniques alone (n = 27), multiparameter flow cytometry (MFC, n = 16), both techniques (n = 43), next-generation sequencing (NGS) + PCR (n = 2), or PCR + MFC + NGS (n = 7). The majority of centers assessed MRD every 2-3 months for 2 (range, 1-until relapse) years. For AML, assessing MRD was routine in 92 centers starting in 2010 (range 1990-2019). Assessment of MRD was by PCR (n = 23), MFC (n = 13), both PCR and MFC (n = 39), both PCR and NGS (n = 3), and by all three techniques (n = 14). The majority assesses MRD for AML every 2-3 months for 2 (range, 1-until relapse) years. This survey is the first step in the aim to include MRD status as a routine registry capture parameter in acute leukemia.

Measurable residual disease of acute lymphoblastic leukemia in allograft settings: how to evaluate and intervene

INTRODUCTION

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) remains a curable strategy for acute lymphoblastic leukemia (ALL), especially for adult cases. However, leukemia relapse after allograft restricts the improvement of transplant outcomes. Measurable residual disease (MRD) has been the strongest predictor for relapse after allo-HSCT, allowing MRD-directed preemptive therapy.

AREAS COVERED

This manuscript summarizes the detection of MRD in patients with ALL who undergo allo-HSCT, focusing the effects of positive pre-HSCT MRD and post-HSCT MRD on outcomes as well as MRD-directed interventions.

EXPERT OPINION

Except for MFC and RQ-PCR, other strategies, such as next-generation sequencing and RNAseq, have been developed for MRD determination. Negative effects of positive MRD peri-transplantation on outcomes of ALL patients were observed both in human leukocyte antigen (HLA)-matched sibling donor transplantation and in alternative donor transplantation. Advances have been made in determining the need for transplant according to MRD evaluation after induction or consolidation therapy. A number of approaches, including CAR-T-cell therapy, antibodies (blinatumomab, etc), targeted therapy (imatinib, etc), transplant donor selection, as well as donor lymphocyte infusion and interferon-α, have been successfully used or are promising for peri-transplantation MRD interventions. This progress could lead to the significant improvement of transplant outcomes for ALL patients.

Cutting to the Front of the Line: Immunotherapy for Childhood Acute Lymphoblastic Leukemia

Although many children and young adults with B-cell acute lymphoblastic leukemia (B-ALL) are cured with modern, risk-adapted chemotherapy regimens, 10% to 15% of patients will experience relapse or have refractory disease. Recent efforts to further intensify cytotoxic chemotherapy regimens in the frontline setting have failed as a result of excessive toxicity or lack of improvement in efficacy. As a result, novel approaches will be required to achieve cures in more newly diagnosed patients. Multiple immune-based therapies have demonstrated considerable efficacy in the setting of relapsed or refractory (R/R) disease, including CD19 targeting with blinatumomab and tisagenlecleucel and CD22 targeting with inotuzumab ozogamicin. These agents are now under investigation by the Children's Oncology Group (COG) in clinical trials for newly diagnosed B-ALL, with integration into standard chemotherapy regimens based on clinically and biology-based risk stratification as well as disease response.

Minimal Residual Disease Detection in Acute Lymphoblastic Leukemia

Minimal residual disease (MRD) refers to a chemotherapy/radiotherapy-surviving leukemia cell population that gives rise to relapse of the disease. The detection of MRD is critical for predicting the outcome and for selecting the intensity of further treatment strategies. The development of various new diagnostic platforms, including next-generation sequencing (NGS), has introduced significant advances in the sensitivity of MRD diagnostics. Here, we review current methods to diagnose MRD through phenotypic marker patterns or differential gene patterns through analysis by flow cytometry (FCM), polymerase chain reaction (PCR), real-time quantitative polymerase chain reaction (RQ-PCR), reverse transcription polymerase chain reaction (RT-PCR) or NGS. Future advances in clinical procedures will be molded by practical feasibility and patient needs regarding greater diagnostic sensitivity.

Disease risk and GVHD biomarkers can stratify patients for risk of relapse and nonrelapse mortality post hematopoietic cell transplant

The graft-versus-leukemia (GVL) effect after allogeneic hematopoietic cell transplant (HCT) can prevent relapse but the risk of severe graft-vs-host disease (GVHD) leads to prolonged intensive immunosuppression and possible blunting of the GVL effect. Strategies to reduce immunosuppression in order to prevent relapse have been offset by increases in severe GVHD and non-relapse mortality (NRM). We recently validated the MAGIC algorithm probability (MAP) that predicts the risk for severe GVHD and NRM in asymptomatic patients using serum biomarkers. In this study we tested whether the MAP could identify patients whose risk for relapse is higher than their risk for severe GVHD and NRM. The multicenter study population (n=1604) was divided into two cohorts: historical (2006–2015, n=702) and current (2015–2017, n=902) with similar non-relapse mortality, relapse, and survival. On day 28 post-HCT, patients who had not developed GVHD (75% of the population) and who possessed a low MAP were at much higher risk for relapse (24%) than severe GVHD and NRM (16% and 9%); this difference was even more pronounced in patients with a high disease risk index (relapse 33%, NRM 9%). Such patients are good candidates to test relapse prevention strategies that might enhance GVL.

The impact of total body irradiation-based regimens on outcomes in children and young adults with acute lymphoblastic leukemia undergoing allogeneic hematopoietic stem cell transplantation

INTRODUCTION

Total body irradiation (TBI)-based conditioning is the standard of care in the treatment of acute lymphoblastic leukemia (ALL) that requires allogeneic hematopoietic stem cell transplantation (HSCT). However, TBI is known to be associated with an increased risk of late effects, and therefore, non-TBI regimens have also been utilized successfully. A recent study showed that patients that were next-generation sequencing-minimal residual disease (NGS-MRD) negative prior to allogeneic HSCT had a very low risk of relapse, and perhaps could avoid exposure to TBI without compromising disease control. We examined outcomes at our institution in patients that received a TBI or non-TBI regimen, as well as explored the impact of NGS-MRD status in predicting risk of relapse post transplant.

PROCEDURES

This retrospective analysis included 57 children and young adults with ALL that received their first myeloablative allogeneic HSCT from 2012 to 2017 at the University of California San Francisco. Our primary endpoint was the cumulative incidence of relapse at 3 years post transplant.

RESULTS

We demonstrated similar cumulative incidence of relapse for patients treated with either a TBI or non-TBI conditioning regimen, while NGS-MRD positivity prior to transplant was highly predictive of relapse. The presence of acute graft-versus-host disease was associated with decreased relapse rates, particularly among patients that received a TBI conditioning regimen and patients that were NGS-MRD positive prior to HSCT.

CONCLUSIONS

Our data suggest that the decision to use either a TBI or non-TBI regimens in ALL should depend on NGS-MRD status, with conditioning regimens based on TBI reserved for patients that cannot achieve NGS-MRD negativity prior to allogeneic HSCT.

Monitoring minimal residual/relapsing disease after allogeneic haematopoietic stem cell transplantation in adult patients with acute lymphoblastic leukaemia

Relapse after allogeneic haematopoietic stem cell transplantation (SCT) is a major cause of death in patients with acute lymphoblastic leukaemia (ALL). Here, we retrospectively analysed the contributions of lineage-sorted donor cell chimerism (sDCC) and quantitative PCR (qPCR) targeting disease-specific genetic rearrangements to detect minimal residual/relapsing disease (MRD) and predict impending relapse in 94 adult ALL patients after SCT. With a median follow-up of surviving patients (n = 61) of 3.3 years, qPCR and/or sDCC measurements turned positive in 38 patients (40%). Of these, 22 patients relapsed and 16 remained in complete remission. At 3 years, qPCR and/or sDCC positive patients showed an increased incidence of relapse (50% vs. 4%, p < 0.0001), decreased relapse-free survival (RFS, 40% vs. 85%, p < 0.0001), and decreased overall survival (OS, 47% vs. 87%, p 0.004). Both, qPCR and sDCC pre-detected 11 of 21 relapses occurring within the first two years after SCT and, overall, complemented for each other method in four of the relapsing and four of the non-relapsing cases. Patients receiving pre-emptive MRD-driven interventions (n = 11) or not (n = 10) showed comparable median times until relapse, RFS, and OS. In our single centre cohort, qPCR and sDCC were similarly effective and complementary helpful to indicate haematological relapse of ALL after SCT.

Drug Resistance Biomarkers and Their Clinical Applications in Childhood Acute Lymphoblastic Leukemia

Biomarkers are biological molecules found in body fluids or tissues, which can be considered as indications of a normal or abnormal process, or of a condition or disease. There are various types of biomarkers based on their application and molecular alterations. Treatment-sensitivity or drug resistance biomarkers include prognostic and predictive molecules with utmost importance in selecting appropriate treatment protocols and improving survival rates. Acute lymphoblastic leukemia (ALL) is the most prevalent hematological malignancy diagnosed in children with nearly 80% cure rate. Despite the favorable survival rates of childhood ALL (chALL), resistance to chemotherapeutic agents and, as a consequence, a dismal prognosis develops in a significant number of patients. Therefore, there are urgent needs to have robust, sensitive, and disease-specific molecular prognostic and predictive biomarkers, which could allow better risk classification and then better clinical results. In this article, we review the currently known drug resistance biomarkers, including somatic or germ line nucleic acids, epigenetic alterations, protein expressions and metabolic variations. Moreover, biomarkers with potential clinical applications are discussed.

More precisely defining risk peri-HCT in pediatric ALL: pre- vs post-MRD measures, serial positivity, and risk modeling

Detection of minimal residual disease (MRD) pre- and post-hematopoietic cell transplantation (HCT) for pediatric acute lymphoblastic leukemia (ALL) has been associated with relapse and poor survival. Published studies have had insufficient numbers to: (1) compare the prognostic value of pre-HCT and post-HCT MRD; (2) determine clinical factors post-HCT associated with better outcomes in MRD+ patients; and (3) use MRD and other clinical factors to develop and validate a prognostic model for relapse in pediatric patients with ALL who undergo allogeneic HCT. To address these issues, we assembled an international database including sibling (n = 191), unrelated (n = 259), mismatched (n = 56), and cord blood (n = 110) grafts given after myeloablative conditioning. Although high and very high MRD pre-HCT were significant predictors in univariate analysis, with bivariate analysis using MRD pre-HCT and post-HCT, MRD pre-HCT at any level was less predictive than even low-level MRD post-HCT. Patients with MRD pre-HCT must become MRD low/negative at 1 to 2 months and negative within 3 to 6 months after HCT for successful therapy. Factors associated with improved outcome of patients with detectable MRD post-HCT included acute graft-versus-host disease. We derived a risk score with an MRD cohort from Europe, North America, and Australia using negative predictive characteristics (late disease status, non-total body irradiation regimen, and MRD [high, very high]) defining good, intermediate, and poor risk groups with 2-year cumulative incidences of relapse of 21%, 38%, and 47%, respectively. We validated the score in a second, more contemporaneous cohort and noted 2-year cumulative incidences of relapse of 13%, 26%, and 47% (P < .001) for the defined risk groups.