Risk-directed treatment of infant acute lymphoblastic leukaemia based on early assessment of MLL gene status: results of the Japan Infant Leukaemia Study (MLL96)

Infant Acute Lymphoblastic Leukemia-New Therapeutic Opportunities

Infant acute lymphoblastic leukemia (Infant ALL) is a kind of pediatric ALL, diagnosed in children under 1 year of age and accounts for less than 5% of pediatric ALL. In the infant ALL group, two subtypes can be distinguished: KMT2A-rearranged ALL, known as a more difficult to cure form and KMT2A- non-rearranged ALL with better survival outcomes. As infants with ALL have lesser treatment outcomes compared to older children, it is pivotal to provide novel treatment approaches. Progress in the development of molecularly targeted therapies and immunotherapy presents exciting opportunities for potential improvement. This comprehensive review synthesizes the current literature on the epidemiology, clinical presentation, molecular genetics, and therapeutic approaches specific to ALL in the infant population.

The RORɣ/SREBP2 pathway is a master regulator of cholesterol metabolism and serves as potential therapeutic target in t(4;11) leukemia

Dysregulated cholesterol homeostasis promotes tumorigenesis and progression. Therefore, metabolic reprogramming constitutes a new hallmark of cancer. However, until today, only few therapeutic approaches exist to target this pathway due to the often-observed negative feedback induced by agents like statins leading to controversially increased cholesterol synthesis upon inhibition. Sterol regulatory element-binding proteins (SREBPs) are key transcription factors regulating the synthesis of cholesterol and fatty acids. Since SREBP2 is difficult to target, we performed pharmacological inhibition of retinoic acid receptor (RAR)-related orphan receptor gamma (RORγ), which acts upstream of SREBP2 and serves as master regulator of the cholesterol metabolism. This resulted in an inactivated cholesterol-related gene program with significant downregulation of cholesterol biosynthesis. Strikingly, these effects were more pronounced than the effects of fatostatin, a direct SREBP2 inhibitor. Upon RORγ inhibition, RNA sequencing showed strongly increased cholesterol efflux genes leading to leukemic cell death and cell cycle changes in a dose- and time-dependent manner. Combinatorial treatment of t(4;11) cells with the RORγ inhibitor showed additive effects with cytarabine and even strong anti-leukemia synergism with atorvastatin by circumventing the statin-induced feedback. Our results suggest a novel therapeutic strategy to inhibit tumor-specific cholesterol metabolism for the treatment of t(4;11) leukemia.

Evolution and optimization of therapies for acute lymphoblastic leukemia in infants

Acute lymphoblastic leukemia (ALL) in infants accounts for less than 5% of pediatric ALL and is biologically and clinically unique. Approximately 70% to 80% of cases present as an aggressive leukemia with KMT2A gene rearrangement (KMT2A-r), which is one of the most difficult-to-cure forms of pediatric leukemia. Owing to continuing global efforts through multicenter clinical trials since the mid-1990s, a standard of care for infant KMT2A-r ALL, including minimal residual disease-based risk stratifications, "hybrid chemotherapy" incorporating myeloid leukemia-like drugs (e.g., cytarabine) into the ALL chemotherapy backbone, and selective use of allogeneic hematopoietic stem cell transplantation, has now been established. However, there are still many concerns regarding treatment of infants with KMT2A-r ALL, including insufficient efficacy of the current standard therapies, limited pharmacokinetic/pharmacodynamic data on drugs in infants, and management of both acute and late toxicities. Refinements in risk stratification based on leukemia biology, as well as the introduction of emerging novel immunotherapies and molecular-targeted drugs to contemporary therapy, through international collaboration would provide key solutions for further improvement in outcomes.

Acute lymphoblastic leukemia in infants: A quarter century of nationwide efforts in Japan

Acute lymphoblastic leukemia (ALL) with KMT2A gene rearrangement (KMT2A-r) in infants is a biologically and clinically unique disease and one of the most difficult to cure forms of pediatric leukemia. Multicenter clinical trials have been carried out in Japan since the mid-1990s by introducing allogeneic hematopoietic stem cell transplantation (HSCT) in first remission, which led to a modest improvement in outcome of infants with KMT2A-r ALL. Because of the emerging evidence that HSCT does not benefit every infant with KMT2A-r ALL, the Japanese Pediatric Leukemia/Lymphoma Study Group trial MLL-10 introduced risk stratification using age and presence of central nervous system leukemia, and introduced intensive chemotherapy, including high-dose cytarabine in early consolidation; indication of HSCT was restricted to the patients with high-risk features. The trial resulted in excellent 3-year event-free survival of 66.2% (standard error, 5.6%) and overall survival of 83.9% (standard error, 4.3%) for 75 patients with KMT2A-r ALL recruited between 2011 and 2015. This Japanese experience and the results of the infant ALL trials worldwide suggest the importance of introducing effective therapy in the early phase of therapy, thus clearing minimal residual disease as rapidly as possible. However, further improvement in outcome is unlikely with conventional treatment approaches. Introduction of biology-driven novel agents and/or immunotherapies through international collaboration would be key solutions to overcome the disease.

Hematopoietic stem cell transplantation for infants with high-risk KMT2A gene-rearranged acute lymphoblastic leukemia

The role of allogeneic hematopoietic stem cell transplantation (HSCT) for infants with acute lymphoblastic leukemia (ALL) and KMT2A gene rearrangement (KMT2A-r) is controversial in terms of both its efficacy and potential for acute and late toxicities. In Japanese Pediatric Leukemia/Lymphoma Study Group trial MLL-10, by introducing intensive chemotherapy, indication of HSCT was restricted to patients with high-risk (HR) features only (KMT2A-r and either age <180 days or presence of central nervous system leukemia). Of the 56 HR patients, 49 achieved complete remission. Forty-three patients received HSCT in first remission including 38 patients receiving protocol-specified HSCT with conditioning consisting of individualized targeted doses of busulfan, etoposide, and cyclophosphamide. Three-year event-free survival (EFS) of 56.8% (95% confidence interval [CI], 42.4% to 68.8%) and overall survival of 80.2% (95% CI, 67.1% to 88.5%) were accomplished. Univariable analysis showed that Interfant-HR criteria and flow cytometric minimal residual disease (MRD; ≥0.01%), both at the end of induction and at the end of consolidation (EOC), were significantly associated with poorer EFS. In the multivariable analysis, positive MRD at EOC was solely associated with poor EFS (P < .001). Rapid pretransplant MRD clearance and tailored HSCT strategy in the MLL-10 trial resulted in a favorable outcome for infants with HR KMT2A-r ALL. However, considering the high rate of potentially life-threatening toxicities and the risk of late effects, its indication should be further restricted or even eliminated in the future by introducing more effective therapeutic modalities with minimal toxicities. This trial was registered at the University Hospital Medical Information Network Clinical Trials Registry (UMIN-CTR) as #UMIN000004801.

A risk-stratified therapy for infants with acute lymphoblastic leukemia: a report from the JPLSG MLL-10 trial

The prognosis for infants with acute lymphoblastic leukemia (ALL), particularly those with KMT2A gene rearrangement (KMT2A-r), is dismal. Continuous efforts have been made in Japan to investigate the role of hematopoietic stem cell transplantation (HSCT) for infants with KMT2A-r ALL, but improvement in outcome was modest. In the Japanese Pediatric Leukemia/Lymphoma Study Group MLL-10 trial, infants with ALL were stratified into 3 risk groups (low risk [LR], intermediate risk [IR], and high risk [HR]) according to KMT2A status, age, and presence of central nervous system leukemia. Children's Oncology Group AALL0631 modified chemotherapy with the addition of high-dose cytarabine in early intensification was introduced to KMT2A-r patients, and the option of HSCT was restricted to HR patients only. The role of minimal residual disease (MRD) was also evaluated. Ninety eligible infants were stratified into LR (n = 15), IR (n = 19), or HR (n = 56) risk groups. The 3-year event-free survival (EFS) rate for patients with KMT2A-r ALL (IR + HR) was 66.2% (standard error [SE], 5.6%), and for those with germline KMT2A (KMT2A-g) ALL (LR), the 3-year EFS rate was 93.3% (SE, 6.4%). The 3-year EFS rate was 94.4% (SE, 5.4%) for IR patients and 56.6% (SE, 6.8%) for HR patients. In multivariable analysis, female sex and MRD ≥0.01% at the end of early consolidation were significant factors for poor prognosis. Risk stratification and introduction of intensive chemotherapy in this study were effective and were able to eliminate HSCT for a subset of infants with KMT2A-r ALL. Early clearance of MRD seems to have translated into favorable outcomes and should be incorporated into risk stratifications in future trials. This trial was registered at the University Hospital Medical Information Network Clinical Trials Registry (UMIN-CTR) as #UMIN000004801.

Analysis of outcomes and prognostic factors of acute lymphoblastic leukemia patients treated by MCP841 protocol: A regional cancer center experience

Background:

A dramatic improvement in the survival of acute lymphoblastic leukemia (ALL) patients in the last three decades has been observed. MCP 841 protocol is an old but effective tool with tolerable toxicities. The objective of this study was to estimate the relapse-free survival of ALL patients treated uniformly with MCP 841 protocol on the basis of various prognostic factors.

Materials and Methods:

The study design was retrospective and it was conducted in a regional cancer center of Northwest India. Three hundred and ten ALL patients who underwent treatment with MCP 841 protocol and regular follow-up for up to 5 years were selected for this study. Relapse-free survival was calculated by Kaplan–Meier analysis and Cox regression analysis was used to calculate the hazards ratio (HR) using Statistical Package for the Social Sciences (SPSS) software for windows version 20.0.

Results:

Fifty-four percent patients were <15 years of age and 69% were males. 53.2% patients were in remission at the end of 5 years of starting the treatment. Relapse-free survival at 5 years by Kaplan–Meir analysis for B-cell ALL was 62% [HR 0.67 {95% confidence interval (CI) 0.47-0.95}] with patients with unknown lineage taken as reference] while for T cell it was 28% [HR 1.41 (95% CI 1.19-1.63), P 0.001]. Patients with total leukocyte count (TLC) <1 lakh/cmm at presentation, relapse-free survival was 68% and those with TLC >1 lakh/cmm had 41% survival [HR 2.14 (1.76-2.48) with, P < 0.001].

Conclusion:

MCP 841 protocol is a useful tool for the treatment of ALL in children when more aggressive protocols can not be used.

[Infant acute leukemia]

If acute leukemia is the most frequent cancer in childhood (33%), it remains a very rare diagnosis in infants less than one year old, e.g. less than 5% of cases. At this age, the frequency of acute lymphoblastic leukemia (ALL) (almost all of B-lineage) is quite similar to the one of myeloblastic forms (AML). Infant leukemia frequently presents with high hyperleucocytosis, major tumoral burden and numerous extra-hematological features, especially in central nervous system and skin. Whatever the lineage, the leukemic cell is often very immature cytologically and immunologically. Rearrangements of the Mixed Lineage Leukemia (MLL) gene, located on band 11q23, are the hallmark of these immature leukemias and confer a particular resistance to conventional approaches, corticosteroids and chemotherapy. The immaturity of infants less than 1-year-old is associated to a decrease of the tolerable dose-intensity of some drugs (anthracyclines, alkylating agents) or asks questions about some procedures like radiotherapy or high dose conditioning regimen, responsible of inacceptable acute and late toxicities. The high level of severe infectious diseases and other high-grade side effects limits also the capacity to cure these infants. The survival of infants less than 1-year-old with AML is only 50% but similar to older children. On the other hand, survival of those with ALL is the same, then quite limited comparing the 80% survival in children over one year. Allogeneic stem cell transplantations are indicated in high-risk subgroups of infant ALL (age below 6 months, high hyperleucocytosis >300.10(9)/L, MLL-rearrangement, initial poor prednisone response). However, morbidity and mortality remain very important and these approaches cannot be extended to all cases. During the neonatal period, the dismal prognosis linked to the high number of primary failures or very early relapses and uncertainties about the late toxicities question physicians about ethics. It is an emergency to propose different strategies (targeted therapies) to these infants with acute leukemia as conventional trials failed to improve outcome.

Recent progress in the treatment of infant acute lymphoblastic leukemia

Treatment of infants with acute lymphoblastic leukemia (ALL), especially those with mixed lineage leukemia (MLL) rearrangement (MLL-r), which account for approximately 80% of cases, is still a major challenge for pediatric hematologists and oncologists worldwide. Continuing efforts by collaborative clinical study groups in Europe, North America, and Japan have rescued approximately half of the MLL-r ALL patients with intensive chemotherapy with or without allogeneic hematopoietic stem cell transplantation. Recent progress has clarified the unique mechanism of MLL-r ALL: the aberrant methylation and histone modifications via DOT1L and other related molecules by MLL fusion proteins lead to leukemogenetic gene expression, thus to overt leukemia. In order to overcome this dismal subtype of ALL, novel targeted therapy based on leukemia biology is urgently needed. Due to the extreme rarity of the disease, collaboration between the study groups in Europe (Interfant), North America (Children's Oncology Group), and Japan (Japanese Pediatric Leukemia/Lymphoma Study Group) is under way.

Intensified chemotherapy without SCT in infant ALL: results from COG P9407 (Cohort 3)

BACKGROUND

Infants with acute lymphoblastic leukemia (ALL) present with aggressive disease and a poor prognosis. Early relapse within 6-9 months of diagnosis is common. Approximately 75% of infants have MLL-rearranged (MLL-R) ALL with event free survival (EFS) ranging from 20% to 30%. Children's Oncology Group (COG) P9407 used shortened (46 weeks), intensified therapy to address early relapse and poor EFS.

PROCEDURE

P9407 therapy was modified three times for induction toxicity resulting in three cohorts of therapy. One hundred forty-seven infants were enrolled in the third cohort.

RESULTS

We report an overall 5-year EFS and OS of 42.3 ± 6% and 52.9 ± 6.5% respectively. Poor prognostic factors included age ≤90 days at diagnosis, MLL-R ALL and white cell count ≥50,000/μl. For infants ≤90 days of age, the 5-year EFS was 15.5 ± 10.1% and 48.5 ± 6.7% for those >90 days (P < 0.0001). Among infants >90 days of age, 5-year EFS rates were 43.8 ± 8% for MLL-R versus 69.1 ± 13.6% for MLL-germline ALL (P < 0.0001).

CONCLUSIONS

Age ≤90 days at diagnosis was the most important prognostic factor. Despite shortened therapy with early intensification, EFS remained less than 50% overall in MLL-R ALL.

Beyond CD19: Opportunities for Future Development of Targeted Immunotherapy in Pediatric Relapsed-Refractory Acute Leukemia

Chimeric antigen receptor (CAR) T cell therapy has been used as a targeted approach in cancer therapy. Relapsed and refractory acute leukemia in pediatrics has been difficult to treat with conventional therapy due to dose-limiting toxicities. With the recent success of CD 19 CAR in pediatric patients with B cell acute lymphoblastic leukemia (ALL), this mode of therapy has become a very attractive option for these patients with high-risk disease. In this review, we will discuss current treatment paradigms of pediatric acute leukemia and potential therapeutic targets for additional high-risk populations, including T cell ALL, AML, and infant ALL.

MuLV-related endogenous retroviral elements and Flt3 participate in aberrant end-joining events that promote B-cell leukemogenesis

During V(D)J recombination of immunoglobulin genes, p53 and nonhomologous end-joining (NHEJ) suppress aberrant rejoining of DNA double-strand breaks induced by recombinase-activating genes (Rags)-1/2. However, Rag deficiency does not prevent B-cell leukemogenesis in p53/NHEJ mutant mice. Johnson et al. identified a novel class of activating mutations in Flt3 in Rag/p53/NHEJ triple-mutant B-cell leukemias. These mutant Flt3 alleles were created by complex genomic rearrangements with Moloney leukemia virus (MuLV)-related endogenous retroviral (ERV) elements. Mutant Flt3 induced ligand-independent STAT5 phosphorylation and promoted development of clinically aggressive B-cell leukemia.

During V(D)J recombination of immunoglobulin genes, p53 and nonhomologous end-joining (NHEJ) suppress aberrant rejoining of DNA double-strand breaks induced by recombinase-activating genes (Rags)-1/2, thus maintaining genomic stability and limiting malignant transformation during B-cell development. However, Rag deficiency does not prevent B-cell leukemogenesis in p53/NHEJ mutant mice, revealing that p53 and NHEJ also suppress Rag-independent mechanisms of B-cell leukemogenesis. Using several cytogenomic approaches, we identified a novel class of activating mutations in Fms-like tyrosine kinase 3 (Flt3), a receptor tyrosine kinase important for normal hematopoiesis in Rag/p53/NHEJ triple-mutant (TM) B-cell leukemias. These mutant Flt3 alleles were created by complex genomic rearrangements with Moloney leukemia virus (MuLV)-related endogenous retroviral (ERV) elements, generating ERV-Flt3 fusion genes encoding an N-terminally truncated mutant form of Flt3 (trFlt3) that was transcribed from ERV long terminal repeats. trFlt3 protein lacked most of the Flt3 extracellular domain and induced ligand-independent STAT5 phosphorylation and proliferation of hematopoietic progenitor cells. Furthermore, expression of trFlt3 in p53/NHEJ mutant hematopoietic progenitor cells promoted development of clinically aggressive B-cell leukemia. Thus, repetitive MuLV-related ERV sequences can participate in aberrant end-joining events that promote development of aggressive B-cell leukemia.

The evolution of clinical trials for infant acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) in infants has a significantly inferior outcome in comparison with older children. Despite initial improvements in survival of infants with ALL since establishment of the first pediatric cooperative group ALL trials, the poor outcome has plateaued in recent years. Historically, infants were treated on risk-adapted childhood ALL protocols. These studies were pivotal in identifying the need for infant-specific protocols, delineating prognostic categories and the requirement for a more unified approach between study groups to overcome limitations in accrual because of low incidence. This subsequently led to the development of collaborative infant-specific studies. Landmark outcomes have included the elimination of cranial radiotherapy following the discovery of intrathecal and high-dose systemic therapy as a superior and effective treatment strategy for central nervous system disease prophylaxis, with improved neurodevelopmental outcome. Universal prospective identification of independent adverse prognostic factors, including presence of a mixed lineage leukemia rearrangement and young age, has established the basis for risk stratification within current trials. The infant-specific trials have defined limits to which conventional chemotherapeutic agents can be intensified to optimize the balance between treatment efficacy and toxicity. Despite variations in therapeutic intensity, there has been no recent improvement in survival due to the equilibrium between relapse and toxicity. Ultimately, to improve the outcome for infants with ALL, key areas still to be addressed include identification and adaptation of novel prognostic markers and innovative therapies, establishing the role of hematopoietic stem cell transplantation in first complete remission, treatment strategies for relapsed/refractory disease and monitoring and timely intervention of late effects in survivors. This would be best achieved through a single unified international trial.

Improved outcome with hematopoietic stem cell transplantation in a poor prognostic subgroup of patients with mixed-lineage-leukemia-rearranged acute leukemia: Results from a prospective, multi-center study

The purpose of this study is to define the role for allogeneic hematopoietic stem cell transplantation (allo-HSCT) in mixed-lineage-leukemia (MLL)-rearranged acute leukemia, which is now poorly understood. A prospective, multi-center cohort study to determine whether allo-HSCT could decrease relapse rates and improve long-term survival of MLL+ leukemia patients was performed. Fifty-six consecutive patients diagnosed with MLL-rearranged acute leukemia undergoing allo-HSCT from two transplant centers in China were enrolled between October 2007 and October 2012. The trial was registered at www.chictr.org as # ChiCTR-ONC-12002739. The incidences of grades II to IV acute graft versus host disease (aGVHD) and of grades III and IV aGVHD were 28.8% (CI, 16.87-40.8%), and 14.2% (CI, 5.4-23.0%), respectively. The cumulative incidences for chronic GVHD (cGVHD) at 2 years after HSCT were 35.2% (CI, 21.2-49.2%). Up to April 30, 2013, 12 patients had relapsed and 11 died from relapse, and 37 patients were still alive without disease recurrence. The relapse and NRM rates at 3 years were 25.3% (CI, 12.7-37.9%) and 18.0% (CI, 2.6-33.4%), respectively. The probalities of overall survival and leukemia free survival were 61.8% (CI, 46.0-77.6%) and 56.3% (CI, 38.1-74.5%) at 3 years, respectively. Patients transplanted during their hematological first complete remission (CR1) had a lower relapse rate (17.9% vs. 48.1%, P = 0.03) compared with patients transplanted beyond CR1. The median overall survival for the 29 patients not receiving allo-HSCT during the study period was 145 days from diagnosis. This study showed that allo-HSCT could be a valuable treatment choice for MLL+ acute leukemia.

Does hematopoietic stem cell transplantation benefit infants with acute leukemia?

A 6-month-old girl was diagnosed with acute lymphoblastic leukemia (ALL). She has completed induction therapy and is currently in first complete remission (CR1). You are asked by your resident if hematopoietic stem cell transplantation (HSCT) would benefit infants with acute leukemia.

Outcome of recurrent or refractory acute lymphoblastic leukemia in infants with MLL gene rearrangements: A report from the Japan Infant Leukemia Study Group

BACKGROUND

Despite the poor outcome of recurrent or refractory acute lymphoblastic leukemia (ALL) in infants with MLL gene rearrangement, few studies have focused on this specific group. We conducted a retrospective analysis of infants with recurrent or refractory ALL from two previous consecutive Japanese studies to clarify the characteristics and prognostic factors among these patients

PROCEDURE

All recurrent or refractory ALL infants with MLL gene rearrangement (MLL-R) who were registered in two consecutive Japanese nation-wide multicentric trials (MLL96 and MLL98; between 1995 and 2001) were eligible for the study.

RESULTS

Among 80 MLL-R ALL infants, 34 cases of recurrence and 5 induction failures occurred. The median duration of first remission was 5 months (range, 0-28 months). All patients underwent various salvage chemotherapies; remission was achieved in 40.5% (15/37). A total of 23 patients received subsequent hematopoietic stem cell transplantations (HSCT): 9 in remission, 12 without remission, and 2 with unknown status. With median follow-up period of 5.5 years, the 5-year overall survival (OS) rate after the second-line treatment was 25.6% +/- 6.9%. Young age (<3 months) and central nervous system involvement at initial diagnosis were associated with poor outcome; however, failure to achieve remission after salvage therapy was the sole independent poor prognostic factor in multivariate analysis (P = 0.01).

CONCLUSIONS

The prognosis of infants with recurrent or refractory MLL-R ALL is extremely poor despite alternative treatments including HSCT; therefore, it is necessary to develop novel treatment strategies.

Fms-like tyrosine kinase 3 ligand stimulation induces MLL-rearranged leukemia cells into quiescence resistant to antileukemic agents

Fms-like tyrosine kinase 3 (FLT3) is highly expressed in acute lymphoblastic leukemia with the mixed-lineage leukemia (MLL) gene rearrangement refractory to chemotherapy. We examined the biological effect of FLT3-ligand (FL) on 18 B-precursor leukemic cell lines with variable karyotypic abnormalities, and found that nine of nine MLL-rearranged cell lines with wild-type FLT3, in contrast to other leukemic cell lines, are significantly inhibited in their proliferation in a dose-dependent manner by FL. This inhibition was due to induction of the G0-G1 arrest. A marked up-regulation of p27 by suppression of its protein degradation and an abrogation of constitutive signal transducers and activators of transcription 5 phosphorylation were revealed in arrested leukemia cells after FL stimulation. Importantly, FL treatment rendered not only cell lines but also primary leukemia cells with MLL rearrangement resistant to chemotherapeutic agents. MLL-rearranged leukemia cells adhering to the bone marrow stromal cell line, which expresses FL as the membrane-bound form, were induced to quiescent state resistant to chemotherapeutic agents, but their chemosensitivity was significantly restored in the presence of neutralizing anti-FL antibody. The FL/FLT3 interaction between leukemia cells and bone marrow stromal cells expressing FL at high levels should contribute, at least in part, to persistent minimal-residual disease of MLL-rearranged leukemia in bone marrow.

Acute lymphoblastic leukemia in infancy

Infant ALL is uncommon, biologically distinctive from the disease in older children, and associated with a relatively poor prognosis. Adverse prognostic factors include the presence of an MLL gene rearrangement (observed in up to 80% of infants with ALL), younger age at diagnosis, high presenting leukocyte counts, and slow early response to therapy. The role of stem cell transplant in first remission remains controversial. Current research efforts to improve the outcome of MLL-rearranged ALL in infants include clinical trials testing cytarabine-intensive regimens and translational investigations of novel, targeted therapies, such as FLT3-inhibitors.

Insights from clinical studies into the role of the MLL gene in infant and childhood leukemia

Translocations involving the Mixed Lineage Leukemia (MLL) gene at 11q23 are found in both acute lymphoblastic leukemia (ALL) and acute myeloblastic leukemia (AML), but have different prognostic implications depending on the phenotype of the leukemia in de novo pediatric cases. The majority of MLL gene rearrangements are associated with infant ALL, and their presence predicts a poor prognosis which worsens with earlier age of presentation. Rearrangements of the MLL gene are found in most cases of infant AML and regardless of age confer an intermediate risk. The treatment of MLL-rearranged ALL in children involves increased intensification of chemotherapy, and infants with ALL are treated with an intensive regimen of ALL- and AML-like chemotherapy, with the proportion of MLL-rearranged cases being responsible for the poor outcome in this age group. The use of DNA microarray analysis to distinguish a particular gene signature for MLL-rearranged leukemias is shedding light on the molecular mechanisms and potential therapeutic targets of these leukemias. It may also prove to have a useful role in both diagnosis and prognosis. This review considers recent advances in our understanding of the role of MLL gene rearrangements in pediatric clinical practice.

Expression of matrix metalloproteinase (MMP) and tissue inhibitor of MMP (TIMP) genes in blasts of infant acute lymphoblastic leukemia with organ involvement

The mRNA contents of matrix metalloproteinase (MMP)-2, MMP-9, tissue inhibitor of MMP (TIMP)-1 and TIMP-2 in leukemia cells from 33 infants with acute lymphoblastic leukemia (ALL) were quantified at initial presentation, and the correlation between their expression and patient clinical characteristics was examined. The mRNA contents of MMP-2 and MMP-9 were not associated with any patient characteristics. Positive correlation was found between hepatosplenomegaly and the MMP-2/TIMP-1 and MMP-2/TIMP-2 ratios (p=0.005 and 0.009) and between CNS involvement and the MMP-2/TIMP-2 ratio (p=0.012). The results suggest that MMP/TIMP balance is closely related to the infiltration of leukemia cells into extramedullary organs.

Outcome of risk-based therapy for infant acute lymphoblastic leukemia with or without an MLL gene rearrangement, with emphasis on late effects: a final report of two consecutive studies, MLL96 and MLL98, of the Japan Infant Leukemia Study Group

We evaluated the efficacy of a treatment strategy in which infants with acute lymphoblastic leukemia (ALL) were stratified by their MLL gene status and then assigned to different risk-based therapies. A total of 102 patients were registered on two consecutive multicenter trials, designated MLL96 and MLL98, between 1995 and 2001. Those with a rearranged MLL gene (MLL-R, n=80) were assigned to receive intensive chemotherapy followed by hematopoietic stem cell transplantation (HSCT), while those with germline MLL (MLL-G, n=22) were treated with chemotherapy alone. The 5-year event-free survival (EFS) rate for all 102 infants was 50.9% (95% confidence interval, 41.0-60.8%). The most prominent late effect was growth impairment, observed in 58.9% of all evaluable patients in the MLL-R group. This plan of risk-based therapy appears to have improved the overall prognosis for infants with ALL, compared with previously reported results. However, over half the events in patients with MLL rearrangement occurred before the instigation of HSCT, and that HSCT-related toxic events comprised 36.3% (8/22) of post-transplantation events, suggesting that further stratification within the MLL-R group and the development of more effective early-phase intensification chemotherapy will be needed before the full potential of this strategy is realized.

Features and outcome of neonatal leukemia in Japan: experience of the Japan infant leukemia study group

BACKGROUND

Neonatal leukemia characterized by early stem cell origin and extramedullary infiltration in the first 4 weeks of life is rare. We analyzed the features and outcome of neonatal leukemia in Japan to establish an appropriate treatment strategy for this rare disorder.

PROCEDURE

Patients with infant leukemia registered and treated in the Japan Infant Leukemia Study between 1996 and 2001 were analyzed.

RESULTS

Among 162 infant leukemia patients, 11 exhibited neonatal leukemia; frequencies for all infant leukemias were 6.9% (8/116) for acute lymphoblastic leukemia (ALL) and 7.3% (3/41) for acute myeloid leukemia (AML). Positive MLL gene rearrangement was observed in all eight patients with ALL; a single patient with AML displayed germline configuration. Acute monoblastic leukemia was apparent in all three patients with AML (M5a in the FAB classification). Most of the patients demonstrated hepatoplenomegaly and hyperleukocytosis at diagnosis. Cutaneous and central nervous system involvement were detected in half of the patients. Four patients (one with AML, and three with ALL) have survived following stem cell transplantation (SCT); however, growth impairment related to SCT was observed in these patients.

CONCLUSIONS

These results suggest an improvement attributable to treatment of neonatal leukemia. International-based collaborative studies are necessary to investigate the biology of this condition and to establish appropriate therapeutic strategies.

Favorable outcome for infant acute lymphoblastic leukemia after hematopoietic stem cell transplantation

Infants with acute lymphoblastic leukemia (ALL) have a poor prognosis when treated with standard chemotherapy. A subset of these infants, particularly those with mixed-lineage leukemia (MLL) rearrangements, has a high likelihood of relapse. Hematopoietic stem cell transplantation (HSCT) performed early in first remission may improve outcome. We present the results of 16 patients with infant ALL who were treated with HSCT in first remission. Six patients were < or =6 months of age at diagnosis, 11 had an initial white blood cell count of >50000/microL, and all patients with determinable cytogenetics had a high-risk karyotype [t(4:11) abnormality or other MLL rearrangement]. All patients received 150 cGy of total body irradiation for 8 doses (1200 cGy). Fifteen of 16 patients received etoposide at 1000 mg/m(2) as a continuous infusion over 24 hours and cyclophosphamide at 60 mg/kg/d for 3 days. Eight patients received HSCT from an HLA-identical sibling, and 8, from unrelated cord blood. Twelve (75%) patients remain long-term survivors (median follow-up, 4.7 years). Two patients, 1 of whom had minimal residual disease at HSCT, died after relapse following HSCT. Two patients died of transplant-related causes. The HSCT was well tolerated; 15 patients achieved neutrophil engraftment at a median of 16 days. Acute and chronic graft-versus-host disease were minimal in these patients. These results support the use of HSCT in the treatment of infant ALL, especially when used as consolidation in first remission. The risk of relapse seems to be decreased with this approach. Further work is being performed to determine the long-term effects from this therapy.

Towards targeted therapy for infant acute lymphoblastic leukaemia

Despite the greatly improved treatment regimes for childhood acute lymphoblastic leukaemia (ALL) in general, resulting in long-term survival in approximately 80% of cases, current therapies still fail in >50% of ALL cases diagnosed within the first year of life (i.e. in infants). Therefore, more adequate treatment strategies are urgently needed to also improve the prognosis for these very young patients with ALL. Here we review the current acquaintance with the biology of infant ALL and describe how this knowledge may lead to innovative therapeutic approaches.

Successful outcome of mismatched hematopoietic stem cell transplantation from a related donor in an infant with acute lymphoblastic leukemia and 9;11 translocation: case report and review of the literature

Although infants with acute lymphoblastic leukemia (ALL) and MLL gene rearrangements have a poor prognosis, those with acute myeloid leukemia (AML) have been shown to have a superior outcome with intensive chemotherapy alone despite the presence of MLL gene rearrangements. We report the case of an ALL infant with t(9;11), a common cytogenetic abnormality in infant AML, who after relapse underwent successful hematopoietic stem cell transplantation (HSCT) from her HLA 2-loci-mismatched mother. Analysis of the outcome among ALL infants with MLL gene rearrangements registered in the Japan Infant Leukemia Study between 1996 and 1999 showed the event-free survival of patients with t(9;11) was not different from that of those with other 11q23 translocations. Most of the patients with t(9;11) described in the reviewed literature also experienced either induction failure or early relapse after achievement of complete remission, but some of them were rescued with subsequent HSCT. These findings suggest that infant ALL with t(9;11) has features distinct from those of infant AML with the same karyotype and that the prognosis among these patients can be improved only with the combination of intensive chemotherapy and HSCT An appropriate strategy for the treatment of ALL infants with different 11q23 translocations must be clarified.

Infantile Case of Occlusive Microvascular Retinopathy After Bone Marrow Transplantation

BACKGROUND

A variety of anterior and posterior segment ocular complications following bone marrow transplantation (BMT) have been well documented in adults and children, but retinal complications after BMT in infants have rarely been reported.

CASE

A 6-month-old male infant developed occlusive microvascular retinopathy after BMT to treat acute lymphocytic leukemia.

OBSERVATIONS

Four months after the transplantation, retinal edema, hemorrhage, soft exudates, and neovascularization were found in the posterior pole fundus of the right eye and in the peripheral fundus of the left eye. After oral prednisolone was administered, the retinal lesions regressed and cicatrices with chorioretinal atrophy and fibrous tissue formed.

CONCLUSIONS

Neovascularization following occlusive microvascular retinopathy after BMT in infant eyes responds well to oral prednisolone. The visual prognosis depends on the foveal involvement of the retinopathy.

Clinical Aspects of Infant Leukemia-Experiences of a Single Institution of Japan: High Level of Serum Immunoglobulin M in Infant Leukemia

The prognosis and clinical and biological characteristics of infant leukemia differ from those of leukemia in children 1 year or older. We reviewed the charts of patients younger than 1 year in whom leukemia was diagnosed from January 1981 through December 2003 at our institution. Fourteen infants had leukemia, 6 had acute lymphoblastic leukemia (ALL), and 8 had acute myeloid leukemia (AML). The age of patients at diagnosis ranged from 2 to 11 months. Five of 8 AML patients presented with cutaneous manifestations, such as erythema and nodules, at diagnosis. Central nervous system (CNS) involvement was seen in 1 AML patient at diagnosis. Hyperleukocytosis of more than 50 x 10(9)/L was seen in 4 of 6 ALL patients and in 4 of 8 AML patients at diagnosis. All ALL patients showed a morphological diagnosis of L1 using the French-America-British classification system. For patients with AML, the morphological diagnoses were M0 for 1 patient, M2 for 1 patient, M4 for 2 patients (1 with eosinophilia), M5b for 2 patients, and M7 for 2 patients. One patient showing M7 morphology had Down syndrome. Surface markers were examined in 5 of 6 ALL patients and all AML patients. Five ALL patients showed a B-cell precursor immunophenotype. Two of 5 patients with ALL had CD10-positive leukemic cells and 3 of 5 patients with ALL had CD10-negative leukemic cells. All AML patients were positive for CD13 or CD33 or both. Three of 5 patients with ALL showed abnormal chromosomes related to 11q. Six of 7 patients with AML showed abnormal karyotypes. MLL gene rearrangements were seen in 3 (2 ALL, 1 AML) of 5 (2 ALL, 3 AML) patients. Serum immunoglobulin M levels were increased in 9 of 14 patients. Complete remission (CR) was achieved in all infants with ALL. Three patients relapsed and then died of the original disease. One of these 3 patients died after cord blood transplantation. Three ALL patients are alive without leukemia. CR was achieved in 6 of 8 AML patients. Four of 6 patients are alive without leukemia. Infant leukemia patients in our institution had some special features. CNS involvement at diagnosis was seen in only 1 patient and serum IgM levels were higher than those in children whose leukemia was diagnosed at 1 to 10 years of age.

The biological and clinical significance of MLL abnormalities in haematological malignancies

The MLL (Mixed Lineage Leukaemia or Myeloid/Lymphoid Leukaemia) gene on chromosome 11q23 is frequently involved in chromosomal translocations associated with human acute leukaemias. These translocations lead to fusion genes generally resulting in novel chimeric proteins containing the amino terminus of MLL fused in-frame to one of about 30 distinct partner proteins. Abnormalities involving the MLL gene are observed in leukaemias of either lymphoid or myeloid lineage derivation, as well as in poorly differentiated or biphenotypic leukaemias. They are frequently seen in infant patients, and patients with therapy-related secondary AML following treatment with inhibitors of topoisomerase II (epipodophyllotoxins). In the majority of cases, abnormalities involving the MLL gene are associated with a very poor prognostic outcome. In this review, we will discuss some of the recent advances in MLL research resulting from biological as well as clinical studies.

The role of the MLL gene in infant leukemia

The MLL gene is a major player in leukemia, particularly in infant leukemia and in secondary, therapy-related acute leukemia. The normal MLL gene plays a key role in developmental regulation of gene expression (including HOX genes), and in leukemia this function is subverted by breakage, recombination, and chimeric fusion with one of 40 or more alternative partner genes. In infant leukemias, the chromosome translocations involving MLL arise during fetal hematopoiesis, possibly in a primitive lymphomyeloid stem cell. In general, these leukemias have a very poor prognosis. The malignancy of these leukemias is all the more dramatic considering their very short preclinical natural history or latency. These data raise fundamental issues of how such divergent MLL chimeric genes transform cells, why they so rapidly evolve to a malignant status, and what alternative or novel therapeutic strategies might be considered. We review here progress in tackling these questions.

Newly diagnosed childhood acute lymphoblastic leukemia: update on prognostic factors and treatment

The development of effective therapy for children with acute lymphoblastic leukemia is one of the great successes of clinical hematology andoncology. Fifty years ago, childhood acute lymphoblastic leukemia was universally fatal, but current long-term event-free survival rates are nearly 80%. Despite this improved outcome, there are still many challenges facing investigators today. In some recent clinical trials, the outcome of "high-risk" patients has approached that of "lower risk" patients, suggesting that currently applied clinical factors, such as age and presenting leukocyte count, no longer identify the 20% of newly diagnosed patients who ultimately will relapse. Additionally, therapy remains nonspecific, toxic, and sometimes lethal. As more children with acute lymphoblastic leukemia survive into adolescence and adulthood, there is a need to address the late sequelae of current therapy and to develop more leukemia-specific treatments. Promising avenues of research, which may identify biologically distinctive subsets of acute lymphoblastic leukemia and potential targets for novel therapies, include studies of minimal residual disease, lymphoblast genetics (including genetic profiling studies), and host-related pharmacogenomics.

Recent advances in the treatment of infant acute myeloid leukemia

Infant acute myeloid leukemia (AML) of less than 12 months old is generally characterized by a high incidence of acute monoblastic or myelomonoblastic leukemia with hyperleukocytosis and extramedullary involvement. Most of the leukemic cells have 11q23 translocations, which lead to the MLL gene rearrangements. The MLL gene rearrangements occur at a high frequency in monoblastic subtype, hyperleukocytosis or young age in infant AML. Compared with acute lymphoblastic leukemia, however, it remains unknown whether prenatal origin exists in the pathogenesis of infant AML. Recently, the treatment outcome of infant AML has been clarified by two study groups, which confirmed the effect of intensive chemotherapy including repeated cycles of cytarabine and anthracyclines for infant AML. Presence of the MLL gene rearrangements, gender, age and white blood cell count showed no influence on the outcome of infant AML. The allogeneic hematopoietic stem cell transplantation (HSCT) remains the treatment of choice for infant AML when a matched related donor is available. Monitoring of minimal residual disease by real-time PCR is a useful technique to predict the outcome or efficacy of the treatment in infant AML. Although intensive chemotherapy and/or allogeneic HSCT have cured most AML infants, some still relapse and ultimately die. A need remains for future development by exploiting the unusual biologic properties of leukemic progenitor cells expressing the abnormal MLL gene product.