Lineage switch in childhood acute leukemia: an unusual event with poor outcome

CLL dedifferentiation to clonally related myeloid cells

Common progenitor cells exist in clonally related concomitant chronic lymphocytic leukemia and acute myeloid leukemias. CLL cells dedifferentiated to clonally related myeloid cells posttransplantation.

A Rare Case of Cutaneous T-Cell Lymphoma Accompanied by Acute Monoblastic Leukemia and Diffuse Large B-Cell Lymphoma

A 70-year-old female was referred for brown-to-gray colored papules and nodules on her lower legs. She had been diagnosed with diffuse large B-cell lymphoma (DLBCL) in her stomach, and myelodysplastic syndrome (MDS) by bone marrow biopsy. Three years after complete remission of DLBCL, she experienced DLBCL recurrence in her small bowel and was hospitalized. MDS had been stationary, but during the treatment of DLBCL, her laboratory findings suggested signs of leukemia. Bone marrow biopsy was done, and acute monoblastic leukemia (AMoL) was diagnosed. After 1 cycle of chemotherapy for AMoL, skin lesions developed, and her skin biopsy showed cutaneous T-cell lymphoma (CTCL). Terminal deoxynucleotidyl transferase staining and CD123 staining were negative, and bone marrow re-biopsy conducted after the skin lesion developed still showed monoblastic proliferation. Whether the CTCL represented with an AMoL lineage switch could not be completely proved due to the absence of molecular or clonal marker evaluations, but the possibility of coexistence of three different malignancies was higher. During treatment, a neutropenic fever developed, and the patient died due to sepsis. We herein report a rare case of CTCL accompanied by AmoL and DLBCL.

The Origin of B-cells: Human Fetal B Cell Development and Implications for the Pathogenesis of Childhood Acute Lymphoblastic Leukemia

Human B-lymphopoiesis is a dynamic life-long process that starts in utero by around six post-conception weeks. A detailed understanding of human fetal B-lymphopoiesis and how it changes in postnatal life is vital for building a complete picture of normal B-lymphoid development through ontogeny, and its relevance in disease. B-cell acute lymphoblastic leukemia (B-ALL) is one of the most common cancers in children, with many of the leukemia-initiating events originating in utero. It is likely that the biology of B-ALL, including leukemia initiation, maintenance and progression depends on the developmental stage and type of B-lymphoid cell in which it originates. This is particularly important for early life leukemias, where specific characteristics of fetal B-cells might be key to determining how the disease behaves, including response to treatment. These cellular, molecular and/or epigenetic features are likely to change with age in a cell intrinsic and/or microenvironment directed manner. Most of our understanding of fetal B-lymphopoiesis has been based on murine data, but many recent studies have focussed on characterizing human fetal B-cell development, including functional and molecular assays at a single cell level. In this mini-review we will give a short overview of the recent advances in the understanding of human fetal B-lymphopoiesis, including its relevance to infant/childhood leukemia, and highlight future questions in the field.

How I Diagnose Minimal/Measurable Residual Disease in B Lymphoblastic Leukemia/Lymphoma by Flow Cytometry

OBJECTIVES

Assessment for minimal/measurable residual disease (MRD) is a powerful prognostic factor in B lymphoblastic leukemia/lymphoma (B-LL/L) that is quickly becoming standard of care in assessing patients with B-LL/L posttherapy. MRD can be assessed using methodologies including flow cytometry and molecular genetics, with the former being rapid, relatively inexpensive, and widely applicable in many hematopathology/flow cytometry laboratories.

METHODS

This article presents an approach to MRD detection in B-LL/L by flow cytometry through case presentations with illustration of several potential pitfalls. We review normal maturation patterns, antigens used for assessment, flow panels that can be utilized, considerations to be made during therapy, and clinical impact. The benefits and drawbacks when using the "different from normal" and "leukemia associated phenotype" approaches are considered.

RESULTS

Evaluation for MRD in B-LL/L by flow cytometry relies on a knowledge of normal immunophenotypic patterns associated with B-cell maturation in states of rest and marrow regeneration so that one can identify patterns of antigen expression that differentiate abnormal, leukemic populations from regenerating hematogones or B-cell precursors. The nature of therapy can affect normal patterns, a phenomenon especially important to take into consideration given the increased use of targeted therapies in the treatment of B-LL/L.

CONCLUSIONS

Flow cytometry is widely available in many laboratories and is a cost-effective way to evaluate for B-LL/L MRD. However, panel validation and interpreter education are crucial for accurate assessment.

Bispecific antibodies in acute lymphoblastic leukemia therapy

INTRODUCTION

Blinatumomab, first in a class of bispecific T-cell engagers, revolutionized treatment paradigm of B-cell precursor relapsed/refractory or minimal residual disease positive acute lymphoblastic leukemia (ALL) in adults and children, inducing deep remissions in a proportion of patients. However, significant numbers of patients do not respond or eventually relapse. Strategies for improvement of treatment outcomes are required.

AREAS COVERED

This review discusses the main structural and functional features of blinatumomab, and its place in the treatment of ALL. Furthermore, prospects to increase the efficacy of blinatumomab are addressed. The developments in the field of bispecific antibodies and their possible implications for treatment of ALL are reviewed.

EXPERT OPINION

Better understanding the mechanisms of response and resistance to blinatumomab might help us to identify the group of patients benefiting most from treatment and to spare potentially toxic subsequent treatment strategies. Data emerging from ongoing clinical trials might change the treatment landscape of ALL and beyond. Early use of blinatumomab in frontline protocols with more advantageous treatment sequences and in combination with other targeted therapies might reduce the failure rates. Exponentially increasing number of novel treatment options and their possible combinations might complicate treatment decision-making without data from randomized trials.

No benefit of Interfant protocols compared to BFM-based protocols for infants with acute lymphoblastic leukemia. Results from an institution in Argentina

BACKGROUND

Infant acute lymphoblastic leukemia (ALL) is an infrequent disease characterized by clinical and biological features related to poor prognosis. Adapted therapies were designed without a clear consensus regarding the best treatment options. We aimed to compare the outcome between infant ALL cases receiving Interfant versus BFM-based protocols.

PROCEDURE

This is a retrospective observational study. From April 1990 to June 2018, infant ALL cases were enrolled in one of the five consecutive treatment protocols. Clinical, demographic, and biological features and outcome were evaluated. A comparative analysis was performed between Interfant protocols and BFM-based protocols.

RESULTS

During the studied period, 1913 ALL patients were admitted and 116 (6%) were infants. Treatment administered was: ALL-BFM'90 (n = 16), 1-ALL96-BFM/HPG (n = 7), Interfant-99 (n = 39), Interfant-06 (n = 35), and ALLIC-BFM'2009 (n = 19). The 5-year event-free survival probability (EFSp) was 31.9(standard error [SE] 4.6)% for the entire population, with a significant difference among risk groups according to Interfant-06 criteria (P = .0029). KMT2A-rearrangement status was the strongest prognostic factor (P = .048), independently of the protocol strategy. The median time for relapse was 24.1 months for patients with minimal residual disease (MRD)-negative versus 11.5 months for those with MRD-positive (P = .0386). EFSp and cumulative relapse risk probability (CRRp) were similar. Interfant protocols showed comparable induction (8.1% vs 7.1%, P = .852) and complete remission mortality (21.6% vs 28.6%, P = .438), failing to reduce the relapse rate (48.5% vs 30.7%, P = .149).

CONCLUSIONS

Interfant protocols and BFM-based protocols presented comparable results. The risk group stratification proposed by Interfant-06 was validated by our results, and MRD seems useful to identify patients with an increased risk of early relapse.

Escape From ALL-CARTaz: Leukemia Immunoediting in the Age of Chimeric Antigen Receptors

Chimeric antigen receptor (CAR) T-cell therapy has been transformative for the treatment of B-cell malignancies, with CD19- and CD22-directed CARs being prime examples. However, immunoediting and ensuing antigen loss remain the major obstacles to curative therapy in up to 25% of patients. For example, to achieve the CD19-negative phenotype, malignant cells can pick from a broad array of mechanisms, including focal loss-of-function mutations, dysregulated trafficking to the cell surface, alternative splicing, and lineage switching. In other cases, where resistance is mediated by insufficient antigen density, trogocytosis has been proposed as a possible underlying mechanism. To overcome these barriers, compensatory strategies will be needed, which could include using combinatorial CARs, harnessing epitope spreading, and targeting tumor neoantigens.

First case of near haploid philadelphia negative B-Cell acute lymphoblastic leukaemia relapsing as acute myeloid leukemia following allogeneic hematopoietic stem cell transplantation

Herein we present a female patient aged 61 with Philadelphia negative acute lymphoblastic leukaemia demonstrating near haploid karyotype and abnormal TP53 expression at diagnosis, who relapsed with lineage switch as Acute Monocytic Leukemia post allogeneic stem cell transplantation. Molecular analysis established that both neoplasms were derived from the same founder clone. The leukemic lineage switch phenomenon has recently re-attracted interest as mechanism of leukemic evasion post treatment with chimeric antigen receptor T-cells but there is paucity of data on its presence post allograft or following novel antibody treatments such as Inotuzumab Ozogamicin or Blinatumomab. Our proposition for cancer research is that near haploidy in ALL could be linked to leukemic stem cell plasticity evading stem cell transplantation and other immunotherapy approaches.

MLL-rearranged infant leukaemia: A 'thorn in the side' of a remarkable success story

Advances in treatment of childhood leukaemia has led to vastly improved survival rates, however some subtypes such as those characterised by MLL gene rearrangement (MLL-r), especially in infants, continue to have high relapse rates and poor survival. Natural history and molecular studies indicate that infant acute lymphoblastic leukaemia (ALL) originates in utero, is distinct from childhood ALL, and most cases are caused by MLL-r resulting in an oncogenic MLL fusion protein. Unlike childhood ALL, only a very small number of additional mutations are present in infant ALL, indicating that MLL-r alone may be sufficient to give rise to this rapid onset, aggressive leukaemia in an appropriate fetal cell context. Despite modifications in treatment approaches, the outcome of MLL-r infant ALL has remained dismal and a clear understanding of the underlying biology of the disease is required in order to develop appropriate disease models and more effective therapeutic strategies.

Coactivation of NF-κB and Notch signaling is sufficient to induce B-cell transformation and enables B-myeloid conversion

NF-κB and Notch signaling can be simultaneously activated in a variety of B-cell lymphomas. Patients with B-cell lymphoma occasionally develop clonally related myeloid tumors with poor prognosis. Whether concurrent activation of both pathways is sufficient to induce B-cell transformation and whether the signaling initiates B-myeloid conversion in a pathological context are largely unknown. Here, we provide genetic evidence that concurrent activation of NF-κB and Notch signaling in committed B cells is sufficient to induce B-cell lymphomatous transformation and primes common progenitor cells to convert to myeloid lineage through dedifferentiation, not transdifferentiation. Intriguingly, the converted myeloid cells can further transform, albeit at low frequency, into myeloid leukemia. Mechanistically, coactivation of NF-κB and Notch signaling endows committed B cells with the ability to self renew. Downregulation of BACH2, a lymphoma and myeloid gene suppressor, but not upregulation of CEBPα and/or downregulation of B-cell transcription factors, is an early event in both B-cell transformation and myeloid conversion. Interestingly, a DNA hypomethylating drug not only effectively eliminated the converted myeloid leukemia cells, but also restored the expression of green fluorescent protein, which had been lost in converted myeloid leukemia cells. Collectively, our results suggest that targeting NF-κB and Notch signaling will not only improve lymphoma treatment, but also prevent the lymphoma-to-myeloid tumor conversion. Importantly, DNA hypomethylating drugs might efficiently treat these converted myeloid neoplasms.

Immunophenotypic modulation in pediatric B lymphoblastic leukemia and its implications in MRD detection

Minimal/Measurable residual disease (MRD) is the most reliable and powerful indicator of prognosis in B cell precursor acute lymphoblastic leukemia (BCP-ALL). Modulation of antigenic expression in leukemic cells is known to occur postchemotherapy and thus carries a potential risk of false MRD quantification by flowcytometry. We studied the immunophenotypic modulation of nine antigens in residual leukemic cells at postinduction MRD assessment in 31 BCP - ALL children. We found significant downmodulation of CD10, CD38, CD58, CD81 and upmodulation of CD19, CD45 in leukemic cells. Downmodulation of CD34 was observed but was not statistically significant. Expression of CD20 and CD22 remained stable in most of the cases. MRD-positive cases showed loss of diagnostic LAIP and some showed gain of new LAIP compared to baseline. Various combination of antibodies including the novel markers should be incorporated into the panel to increase the sensitivity of MRD detection.

Chimeric antigen receptor T cell therapy comes to clinical practice

Adoptive cellular therapy with chimeric antigen receptor T cells (car-ts) has recently received approval from Health Canada and the U.S. Food and Drug Administration after remarkable and durable remissions were seen in children with recurrent or refractory leukemia and adults with non-Hodgkin lymphoma-responses that were so impressive that a shift in the paradigm of care has now occurred for children with acute lymphoblastic leukemia. The concept behind car-t immunotherapy is that modification of a patient's own T cells to facilitate their localization to the cancer cell, with subsequent activation of the T cell effector mechanism and proliferation, will result in targeted killing of cancer cells. The car-ts are a novel drug in that the starting material for the manufacture of the car-t product comes from the patient, whose viable T cells are then genetically modified. Thus, collaboration is needed between the pharmaceutical companies, which must meet good manufacturing standards for each patient's unique product, and the treating sites. For regulators and health authorities, this new class of drugs requires new paradigms for assessment and approval. Treatments with car-ts require that institutions address unique logistics requirements and management of novel toxicities. The Hospital for Sick Children has had early experience with both the licensing of clinical trials and the introduction of the first commercial product. Here, we provide an overview of basic concepts and treatment, with caveats drawn from what we have learned thus far in bringing this new therapy to the clinical front line.

Immunotherapy- (Blinatumomab-) Related Lineage Switch of KMT2A/AFF1 Rearranged B-Lymphoblastic Leukemia into Acute Myeloid Leukemia/Myeloid Sarcoma and Subsequently into B/Myeloid Mixed Phenotype Acute Leukemia

The presence of KMT2A/AFF1 rearrangement in B-lymphoblastic leukemia (B-ALL) is an independent poor prognostic factor and has been associated with higher rate of treatment failure and higher risk of linage switch under therapy. Blinatumomab has shown promising therapeutic results in refractory or relapsed B-ALL; however, it has potential risk of inducing lineage switch, especially in KMT2A/AFF1 rearranged B-ALL into acute myeloid leukemia and/or myeloid sarcoma. We report a 40-year-old female with KMT2A/AFF1-rearranged B-ALL that was refractory to conventional chemotherapy. Following administration of blinatumomab, she developed a breast mass proven to be myeloid sarcoma, in addition to bone marrow involvement by AML. Approximately six weeks after cessation of blinatumomab, a repeat bone marrow examination revealed B/myeloid MPAL.

KMT2A rearranged acute lymphoblastic leukaemia: Unravelling the genomic complexity and heterogeneity of this high-risk disease

KMT2A rearranged (KMT2Ar) acute lymphoblastic leukaemia (ALL) is a high-risk genomic subtype, with long-term survival rates of less than 60% across all age groups. These cases present a complex clinical challenge, with a high incidence in infants, high-risk clinical features and propensity for aggressive relapse. KMT2A rearrangements are highly pathogenic leukaemic drivers, reflected by the high incidence of KMT2Ar ALL in infants, who carry few leukaemia-associated cooperative mutations. However, transgenic murine models of KMT2Ar ALL typically exhibit long latency and mature or mixed phenotype, and fail to recapitulate the aggressive disease observed clinically. Next-generation sequencing has revealed that KMT2Ar ALL also occurs in adolescents and adults, and potentially cooperative genomic lesions such as PI3K-RAS pathway variants are present in KMT2Ar patients of all ages. This review addresses the aetiology of KMT2Ar ALL, with a focus on the cell of origin and mutational landscape, and how genomic profiling of KMT2Ar ALL patients in the era of next-generation sequencing demonstrates that KMT2Ar ALL is a complex heterogenous disease. Ultimately, understanding the underlying biology of KMT2Ar ALL will be important in improving long-term outcomes for these high-risk patients.

MLL-Rearranged Acute Leukemia with t(4;11)(q21;q23)-Current Treatment Options. Is There a Role for CAR-T Cell Therapy?

The MLL (mixed-lineage leukemia) gene, located on chromosome 11q23, is involved in chromosomal translocations in a subtype of acute leukemia, which represents approximately 10% of acute lymphoblastic leukemia and 2.8% of acute myeloid leukemia cases. These translocations form fusions with various genes, of which more than 80 partner genes for MLL have been identified. The most recurrent fusion partner in MLL rearrangements (MLL-r) is AF4, mapping at chromosome 4q21, accounting for approximately 36% of MLL-r leukemia and particularly prevalent in MLL-r acute lymphoblastic leukemia (ALL) cases (57%). MLL-r leukemia is associated with a sudden onset, aggressive progression, and notoriously poor prognosis in comparison to non-MLL-r leukemias. Despite modern chemotherapeutic interventions and the use of hematopoietic stem cell transplantations, infants, children, and adults with MLL-r leukemia generally have poor prognosis and response to these treatments. Based on the frequency of patients who relapse, do not achieve complete remission, or have brief event-free survival, there is a clear clinical need for a new effective therapy. In this review, we outline the current therapy options for MLL-r patients and the potential application of CAR-T therapy.

Resistance Mechanisms to CAR T-Cell Therapy and Overcoming Strategy in B-Cell Hematologic Malignancies

Chimeric antigen receptor (CAR) T-cell therapy has shown promising clinical impact against hematologic malignancies. CD19 is a marker on the surface of normal B cells as well as most B-cell malignancies, and thus has a role as an effective target for CAR T-cell therapy. In numerous clinical data, successes with cell therapy have provided anticancer therapy as a potential therapeutic option for patients who are resistant to standard chemotherapies. However, recent growing evidence showed the limitations of the treatment such as antigen-positive relapse due to poor CAR T-cell persistence and antigen-negative relapses associated with CAR-driven mutations, alternative splicing, epitope masking, low antigen density, and lineage switching. The understanding of the resistance mechanisms to the cell therapy has developed novel potential treatment strategies, including dual-targeting therapy (dual and tandem CAR), and armored and universal CAR T-cell therapies. In this review, we provide an overview of resistance mechanisms to CD19 CAR T-cell therapy in B-cell malignancies and also review therapeutic strategies to overcome these resistances.

Discovery of a CD10-negative B-progenitor in human fetal life identifies unique ontogeny-related developmental programs

Human lymphopoiesis is a dynamic lifelong process that starts in utero 6 weeks postconception. Although fetal B-lymphopoiesis remains poorly defined, it is key to understanding leukemia initiation in early life. Here, we provide a comprehensive analysis of the human fetal B-cell developmental hierarchy. We report the presence in fetal tissues of 2 distinct CD19+ B-progenitors, an adult-type CD10+ve ProB-progenitor and a new CD10-ve PreProB-progenitor, and describe their molecular and functional characteristics. PreProB-progenitors and ProB-progenitors appear early in the first trimester in embryonic liver, followed by a sustained second wave of B-progenitor development in fetal bone marrow (BM), where together they form >40% of the total hematopoietic stem cell/progenitor pool. Almost one-third of fetal B-progenitors are CD10-ve PreProB-progenitors, whereas, by contrast, PreProB-progenitors are almost undetectable (0.53% ± 0.24%) in adult BM. Single-cell transcriptomics and functional assays place fetal PreProB-progenitors upstream of ProB-progenitors, identifying them as the first B-lymphoid-restricted progenitor in human fetal life. Although fetal BM PreProB-progenitors and ProB-progenitors both give rise solely to B-lineage cells, they are transcriptionally distinct. As with their fetal counterparts, adult BM PreProB-progenitors give rise only to B-lineage cells in vitro and express the expected B-lineage gene expression program. However, fetal PreProB-progenitors display a distinct, ontogeny-related gene expression pattern that is not seen in adult PreProB-progenitors, and they share transcriptomic signatures with CD10-ve B-progenitor infant acute lymphoblastic leukemia blast cells. These data identify PreProB-progenitors as the earliest B-lymphoid-restricted progenitor in human fetal life and suggest that this fetal-restricted committed B-progenitor might provide a permissive cellular context for prenatal B-progenitor leukemia initiation.

Lineage switch from T-cell lymphoblastic leukemia/lymphoma to acute myeloid leukemia and back to T-cell lymphoblastic leukemia/lymphoma in a patient diagnosed during pregnancy

Although relapse of acute leukemia is common, a change of immunophenotype at relapse only occurs rarely. Some of these cases have been labeled "lineage switch". In most cases, B-cell lymphoblastic leukemia/lymphoma (B-ALL) relapses as acute myeloid leukemia (AML). We report a rare case of T-cell acute lymphoblastic leukemia/lymphoma (T-ALL) relapsing as AML and then returning as T-ALL again in a patient who began her therapy during the third trimester of pregnancy. The patient retained the same cytogenetic and next generation molecular findings in both leukemias. This case provides further evidence of the plasticity of the leukemic stem cell.

Spontaneous reversion of a lineage switch following an initial blinatumomab-induced ALL-to-AML switch in MLL-rearranged infant ALL

A case of MLL-rearranged leukemia that rapidly adapts to immunological stimuli illustrating the high plasticity of this phenotype.

The developmental stage of the hematopoietic niche regulates lineage in MLL-rearranged leukemia

Leukemia phenotypes vary with age of onset. Delineating mechanisms of age specificity in leukemia could improve disease models and uncover new therapeutic approaches. Here, we used heterochronic transplantation of leukemia driven by MLL/KMT2A translocations to investigate the contribution of the age of the hematopoietic microenvironment to age-specific leukemia phenotypes. When driven by MLL-AF9, leukemia cells in the adult microenvironment sustained a myeloid phenotype, whereas the neonatal microenvironment supported genesis of mixed early B cell/myeloid leukemia. In MLL-ENL leukemia, the neonatal microenvironment potentiated B-lymphoid differentiation compared with the adult. Ccl5 elaborated from adult marrow stroma inhibited B-lymphoid differentiation of leukemia cells, illuminating a mechanism of age-specific lineage commitment. Our study illustrates the contribution of the developmental stage of the hematopoietic microenvironment in defining the age specificity of leukemia.

Age-specific biological and molecular profiling distinguishes paediatric from adult acute myeloid leukaemias

Acute myeloid leukaemia (AML) affects children and adults of all ages. AML remains one of the major causes of death in children with cancer and for children with AML relapse is the most common cause of death. Here, by modelling AML in vivo we demonstrate that AML is discriminated by the age of the cell of origin. Young cells give rise to myeloid, lymphoid or mixed phenotype acute leukaemia, whereas adult cells give rise exclusively to AML, with a shorter latency. Unlike adult, young AML cells do not remodel the bone marrow stroma. Transcriptional analysis distinguishes young AML by the upregulation of immune pathways. Analysis of human paediatric AML samples recapitulates a paediatric immune cell interaction gene signature, highlighting two genes, RGS10 and FAM26F as prognostically significant. This work advances our understanding of paediatric AML biology, and provides murine models that offer the potential for developing paediatric specific therapeutic strategies.

Acute myeloid leukaemia (AML) affects people of all ages. Here, the authors model AML in vivo and demonstrate that the age of the cell of origin impacts leukaemia development and the genetic signature where adult cells of origin give rise exclusively to AML and young cells of origin give rise to myeloid, lymphoid or mixed phenotype acute leukaemia.

International cooperative study identifies treatment strategy in childhood ambiguous lineage leukemia

Despite attempts to improve the definitions of ambiguous lineage leukemia (ALAL) during the last 2 decades, general therapy recommendations are missing. Herein, we report a large cohort of children with ALAL and propose a treatment strategy. A retrospective multinational study (International Berlin-Frankfurt-Münster Study of Leukemias of Ambiguous Lineage [iBFM-AMBI2012]) of 233 cases of pediatric ALAL patients is presented. Survival statistics were used to compare the prognosis of subsets and types of treatment. Five-year event-free survival (EFS) of patients with acute lymphoblastic leukemia (ALL)-type primary therapy (80% ± 4%) was superior to that of children who received acute myeloid leukemia (AML)-type or combined-type treatment (36% ± 7.2% and 50% ± 12%, respectively). When ALL- or AML-specific gene fusions were excluded, 5-year EFS of CD19⁺ leukemia was 83% ± 5.3% on ALL-type primary treatment compared with 0% ± 0% and 28% ± 14% on AML-type and combined-type primary treatment, respectively. Superiority of ALL-type treatment was documented in single-population mixed phenotype ALAL (using World Health Organization and/or European Group for Immunophenotyping of Leukemia definitions) and bilineal ALAL. Treatment with ALL-type protocols is recommended for the majority of pediatric patients with ALAL, including cases with CD19⁺ ALAL. AML-type treatment is preferred in a minority of ALAL cases with CD19^- and no other lymphoid features. No overall benefit of transplantation was documented, and it could be introduced in some patients with a poor response to treatment. As no clear indicator was found for a change in treatment type, this is to be considered only in cases with ≥5% blasts after remission induction. The results provide a basis for a prospective trial.

Therapy-related myeloid neoplasm in an 18-year-old boy with B-lymphoblastic leukemia

BACKGROUND

Acute lymphoblastic leukemia (ALL) is the most common pediatric malignancy. Acute myeloid leukemia or myelodysplastic syndrome during the course of ALL is a rare entity. Some of these cases are therapy-related while the others occur due to lineage switch. The correct diagnosis relies on comparing the immunophenotypes and cytogenetic/molecular alterations of the myeloid neoplasm and the ALL. We present the clinical, pathologic and cytogenetic features of a case of an 18-year-old male with prior treatment for B-lymphoblastic leukemia (B-ALL) who developed therapy-related myeloid neoplasm (t-MN) 4-5years after his initial diagnosis of B-ALL.

CASE PRESENTATION

A 13-year-old boy with no significant past medical history presented to Harbor-UCLA Medical Center (HUMC) in November 2012 with night sweats, fevers and chills, nausea, vomiting, diarrhea, fatigue, weakness, and weight loss. Peripheral blood flow cytometric analysis disclosed B-ALL. The blasts expressed CD10, CD19, CD22 (dim), CD34, CD38, HLA-DR, and TdT, and were negative for CD20, CD13, CD33, CD117, and cytoplasmic MPO. Chromosomal analysis and a supplemental fluorescence in situ hybridization (FISH) study performed on the bone marrow aspirate showed an abnormal karyotype (47,XY,+X,del(9)(p21p21)[4]/46,XY[16]). He achieved remission after induction chemotherapy and remained in remission until March 2016 when bilateral testicular masses were noted. Biopsy of the left testicular mass showed relapsed B-ALL. Cerebrospinal fluid (CSF) contained rare TdT-positive blasts, suggestive of minimal/early involvement by B-ALL. However, there was no evidence of acute leukemia in his bone marrow at this time. He was then treated with COG protocol AALL1331 randomized to blinatumomab arm and achieved second remission. In June 2017, the patient's peripheral blood smear showed 11% circulating monoblasts. By flow cytometry, the blasts expressed CD4, CD11b, CD13, CD15, CD33, CD38, CD56, and CD64. In addition, a few TdT-positive blasts were seen in his CSF cytospin smear. Bone marrow biopsy was subsequently performed which was consistent with evolving acute myeloid leukemia. A diagnosis of myeloid neoplasm, consistent with t-MN was made. Chromosomal analysis and FISH studies performed on his bone marrow aspirate showed normal karyotype (46,XY[20]), negative FISH result for deletion 9p21 locus, and positive KMT2A (MLL) rearrangement, respectively. Despite of chemotherapy, the patient died within one month after diagnosis.

DISCUSSION AND CONCLUSION

Diagnosis of t-MN should be suspected in patients with a history of receiving cytotoxic agents and/or irradiation. In this case study, we diagnosed t-MN with KMT2A rearrangement in a patient with history of B-ALL with 9p deletion and gain of X chromosome. Unusual features associated with this case are discussed.

Transcriptional and Microenvironmental Regulation of Lineage Ambiguity in Leukemia

Leukemia is characterized by the uncontrolled production of leukemic cells and impaired normal hematopoiesis. Although the combination of chemotherapies and hematopoietic stem cell transplantation has significantly improved the outcome of leukemia patients, a proportion of patients still suffer from relapse after treatment. Upon relapse, a phenomenon termed “lineage switch” is observed in a subset of leukemia patients, in which conversion of lymphoblastic leukemia to myeloid leukemia or vice versa is observed. A rare entity of leukemia called mixed-phenotype acute leukemia exhibits co-expression of markers representing two or three lineages. These two phenotypes regarding the lineage ambiguity suggest that the fate of some leukemia retain or acquire a certain degree of plasticity. Studies using animal models provide insight into how lineage specifying transcription factors can enforce or convert a fate in hematopoietic cells. Modeling lineage conversion in normal hematopoietic progenitor cells may improve our current understanding of how lineage switch occurs in leukemia. In this review, we will summarize the role of transcription factors and microenvironmental signals that confer fate plasticity to normal hematopoietic progenitor cells, and their potential to regulate lineage switching in leukemias. Future efforts to uncover the mechanisms contributing to lineage conversion in both normal hematopoiesis and leukemia may pave the way to improve current therapeutic strategies.

Second Neoplasms in Children Following a Treatment for Acute Leukemia and/or Lymphoma: 29 Years of Experience in a Single Institution in Argentina

INTRODUCTION

Childhood acute leukemias (AL) and lymphomas achieve good survival rates. However, second neoplasms (SN) are a devastating event.

METHODS

From August 1987 to December 2016, 34 of 3321 (1%) patients with diagnosis of AL or lymphoma developed SN. SN were AL (n=16), CNS tumors (n=5), endocrinal tumors (n=3), lymphomas (n=2), schwannoma (n=2) assorted sarcomas (n=4), retinal melanoma (n=1), and Vanek tumor (n=1). Median latency was 51 (range, 10 to 110) months for hematological malignancies and 119 (range, 25 to 236) months for solid tumors (P=0.001).

RESULTS

A total of 33 patients with SN were treated taking into account cumulative doses of anthracyclines and radiotherapy. Twenty-three (67.6%) patients achieved complete remission (CR), 5 died early during therapy and 5 were refractory or partial responders. Six patients presented relapses of the SN and 1 died in CR. Seventeen patients remain alive in CR, with a median follow-up of 110 (range, 4 to 276) months.

CONCLUSIONS

(1) The latency period was significantly longer for patients developing solid tumors than for those developing AL. (2) AL was the most frequent SN. (3) Our results strongly encourage giving standard therapy to SN, considering cumulative doses of previous treatment, since similar probabilities of surviving as "de novo" counterparts can be achieved.

Lineage switch under blinatumomab treatment of relapsed common acute lymphoblastic leukemia without MLL rearrangement

Blinatumomab is a bispecific T-cell engaging αCD19 antibody used in refractory or relapsed B-cell precursor acute lymphoblastic leukemia (ALL). Recently, lineage switch to a myeloid phenotype has been described following CD19 targeting treatment in three pediatric patients with mixed lineage leukemia (MLL) rearranged ALL. We report the case of a female who received blinatumomab for a first relapse of ALL without MLL alterations. She suffered from a second relapse early after hematopoietic stem cell transplantation and was treated with blinatumomab again. During this treatment, the leukemia lost CD19 expression as well as nearly all other B-cell markers, while still harboring the initial minimal residual disease marker, and switched to a myeloid phenotype.

Mixed-Phenotype Acute Leukemia: Diagnostic Criteria and Pitfalls

Mixed-phenotype acute leukemia (MPAL) is a heterogeneous category in the World Health Organization classification that comprises acute leukemias with discrete admixed populations of myeloid and lymphoid blasts (“bilineal”) or with extensive coexpression of lymphoid and myeloid markers in a single blast population (“biphenotypic”). Flow cytometric findings suggestive of MPAL are often met with consternation by pathologists and oncologists alike, owing to unfamiliarity with the disease and uncertainty about how MPAL fits into established paradigms for treatment of acute leukemia. The purpose of this review is to explain the diagnostic criteria for MPAL, summarize its biological and clinical features, and address common diagnostic pitfalls of these unusual leukemias.

Lineage Switch Between B-Lymphoblastic Leukemia and Acute Myeloid Leukemia Intermediated by "Occult" Myelodysplastic Neoplasm: Two Cases of Adult Patients With Evidence of Genomic Instability and Clonal Selection by Chemotherapy

OBJECTIVES

Lineage switch occurs in rare leukemias, and the mechanism is unclear. We report two cases of B-lymphoblastic leukemia (B-ALL) relapsed as acute myeloid leukemia (AML).

METHODS

Retrospective review of clinical and laboratory data.

RESULTS

Complex cytogenetic abnormalities were detected in B-ALL for both cases with subclone heterogeneity. Postchemotherapy marrow biopsies showed trilineage hematopoiesis without detectable B-ALL. Cytogenetics in both showed stemline abnormalities. The cases were considered "occult" myelodysplastic syndrome (MDS) preceding B-ALL. The patients relapsed 6.5 and 9 months following induction, respectively. Case 1 relapsed as AML-M5 initially, was treated as such, and then relapsed again as B-ALL. Case 2 relapsed as AML-M6. Cytogenetics demonstrated persistent abnormalities. Both patients died soon after relapse.

CONCLUSIONS

Lineage switch between B-ALL and AML could be intermediated by occult MDS. A pluripotent progenitor likely undergoes neoplastic transformation, resulting in a genomically unstable clone. This leads to a repertoire of heterogeneous subclones that may be selected by chemotherapy. Lineage switch heralds a dismal clinical outcome.

The full transforming capacity of MLL-Af4 is interlinked with lymphoid lineage commitment

Chromosome rearrangements involving the mixed-lineage leukemia gene (MLL) create MLL-fusion proteins, which could drive both acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML). The lineage decision of MLL-fusion leukemia is influenced by the fusion partner and microenvironment. To investigate the interplay of fusion proteins and microenvironment in lineage choice, we transplanted human hematopoietic stem and progenitor cells (HSPCs) expressing MLL-AF9 or MLL-Af4 into immunodeficient NSGS mice, which strongly promote myeloid development. Cells expressing MLL-AF9 efficiently developed AML in NSGS mice. In contrast, MLL-Af4 cells, which were fully oncogenic under lymphoid conditions present in NSG mice, displayed compromised transformation capacity in a myeloid microenvironment. MLL-Af4 activated a self-renewal program in a lineage-dependent manner, showing the leukemogenic activity of MLL-Af4 was interlinked with lymphoid lineage commitment. The C-terminal homology domain (CHD) of Af4 was sufficient to confer this linkage. Although the MLL-CHD fusion protein failed to immortalize HSPCs in myeloid conditions in vitro, it could successfully induce ALL in NSG mice. Our data suggest that defective self-renewal ability and leukemogenesis of MLL-Af4 myeloid cells could contribute to the strong B-cell ALL association of MLL-AF4 leukemia observed in the clinic.

Recent advances in the management of pediatric acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is the most common malignancy in childhood. Despite enormous improvement of prognosis during the last half century, ALL remains a major cause of childhood cancer-related mortality. During the past decade, whole genomic methods have enhanced our knowledge of disease biology. Stratification of therapy according to early treatment response measured by minimal residual disease allows risk group assignment into different treatment arms, ranging from reduction to intensification of treatment. Progress has been achieved in academic clinical trials by optimization of combined chemotherapy, which continues to be the mainstay of contemporary treatment. The availability of suitable volunteer main histocompatibility antigen-matched unrelated donors has increased the rates of hematopoietic stem cell transplantation (HSCT) over the past two decades. Allogeneic HSCT has become an alternative treatment for selected, very-high-risk patients. However, intensive treatment burdens children with severe acute toxic effects that can cause permanent organ damage and even toxic death. Immunotherapeutic approaches have recently come to the forefront in ALL therapy. Monoclonal antibodies blinatumomab and inotuzumab ozogamicin as well as gene-modified T cells directed to specific target antigens have shown efficacy against resistant/relapsed leukemia in phase I/II studies. Integration of these newer modalities into combined regimens with chemotherapy may rescue a subset of children not curable by contemporary therapy. Another major challenge will be to incorporate less toxic regimens into the therapy of patients with low-risk disease who have a nearly 100% chance of being cured, and the ultimate goal is to improve their quality of life while maintaining a high cure rate.

Congenital B-lymphoblastic leukemia with a cryptic MLL rearrangement and post-treatment evolution to mixed phenotype acute leukemia

Congenital leukemia is a rare event with a poor prognosis. We report a case of congenital leukemia with a cryptic rearrangement of MLL demonstrable only with RT-PCR. Interestingly, with treatment, the patient showed lineage plasticity of the leukemia with the development of monocytic lineage blasts after presenting with B-cell lineage blasts. This was heralded by the development of a new clonal cytogenetic abnormality. This case highlights the primitive nature of the leukemic cells in congenital leukemia, and emphasizes that RT-PCR for MLL rearrangements may identify a subset of cases which are otherwise negative by karyotyping, FISH, and chromosomal microarrays.

CD19 CAR immune pressure induces B-precursor acute lymphoblastic leukaemia lineage switch exposing inherent leukaemic plasticity

Adoptive immunotherapy using chimeric antigen receptor (CAR) expressing T cells targeting the CD19 B lineage receptor has demonstrated marked success in relapsed pre-B-cell acute lymphoblastic leukaemia (ALL). Persisting CAR-T cells generate sustained pressure against CD19 that may drive unique mechanisms of resistance. Pre-B ALL originates from a committed pre-B cell or an earlier progenitor, with potential to reprogram into other hematopoietic lineages. Here we report changes in lineage markers including myeloid conversion in patients following CD19 CAR therapy. Using murine ALL models we study the long-term effects of CD19 CAR-T cells and demonstrate partial or complete lineage switch as a consistent mechanism of CAR resistance depending on the underlying genetic oncogenic driver. Deletion of Pax5 or Ebf1 recapitulates lineage reprogramming occurring during CD19 CAR pressure. Our findings establish lineage switch as a mechanism of CAR resistance exposing inherent plasticity in genetic subtypes of pre-B-cell ALL.

CAR-T targeting CD19 have been successfully used in a variety of B-cell malignancies but patients may eventually relapse. Here, the authors show that CD19 CAR-T resistance in pre-B cell ALL can be due to the induction of a myeloid lineage switch through an epigenetic alterations in master regulators of B cell development.

Lineage Switch in MLL-Rearranged Infant Leukemia Following CD19-Directed Therapy

Rearrangements of the mixed lineage leukemia (MLL) gene occur frequently in infants with both acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML). Conversions of leukemia cell lineage are rare, but occur most commonly in the setting of MLL-rearrangement. Blinatumomab is a bidirectional antibody targeting CD19 with significant activity in relapsed B-precursor ALL. We report an infant with ALL with t(4;11)(q21;q23) refractory to cytotoxic chemotherapy who was treated with blinatumomab. Following rapid initial clearance of peripheral lymphoblasts, bone marrow evaluation demonstrated a leukemic lineage switch to CD19-negative monoblastic AML. Complete remission was achieved with myeloid-directed chemotherapy.