Pediatric pre-B Acute Lymphoblastic Leukemia Research Articles

Drivers of Differential Time to Diagnosis in Pediatric ALL Tied to Race and Ethnicity.

Acute lymphoblastic leukemia (ALL) is the most common childhood malignancy, with diagnosis preceded by symptoms that may include fever, weight loss, fatigue, bleeding, and bruising. Timely diagnosis and treatment of ALL may lead to improved outcomes and reduced morbidity from associated complications, including tumor lysis syndrome, hyperviscosity, and stroke. We performed a retrospective cohort analysis of 274 pediatric pre-B cell ALL and acute lymphoblastic lymphoma patients within Montefiore Health System to determine whether there were factors associated with time from symptom onset to diagnosis. The median time to diagnosis for all patients was 11.5 days (interquartile range: 7.8, 14.3). Those with Medicaid insurance (n=189) were diagnosed sooner than those with private/self-pay insurance (n=85) (median of 10 vs. 16 days; P =0.05). English and other language speakers experienced fewer median days from symptom onset to diagnosis date compared with Spanish speakers (11 vs. 7 vs. 14; P =0.05). Insurance status may impact the time to diagnosis to a greater degree in non-Hispanic patients, while the English language and female sex may represent a greater advantage to Hispanic patients. Insurance status and language preference may impact the time to diagnosis of pediatric ALL. There is a further need to confirm our findings and to study possible causes driving these disparities.

MiR-128-3p as blood based liquid biopsy biomarker in childhood acute lymphoblastic leukemia

BackgroundMinimal residual disease (MRD) is one of the most valuable independent prognostic factors in acute lymphoblastic leukemia (ALL). Bone marrow (BM) aspiration, however, is an invasive process. Previous studies have shown that microRNAs (miR) and extracellular vesicle (EV)-related miRs show different expression profiles at the presence of malignant cells compared to healthy controls. In our previous project, we have reported that two miRs previously described to be overexpressed in blasts were significantly decreased over the first week of the therapy of patients with ALL in the platelet free plasma fraction (PFP) of peripheral blood samples (PB). The aim of the current study was to assess the relation between day 15 flow cytometry (FC) MRD and expression of miR-128-3p and miR-222-3p miRs in exosome-enriched fraction (EEF) of PFP to evaluate whether their expression in EEF correlates with day 15 FC MRD more precisely. MethodsPB was collected from 13 patients diagnosed with pediatric pre-B ALL at 4 time points. Expression of miR-128-3p and miR-222-3p was measured by qPCR in PFP and EEF. ResultsPositive correlation was found between changes of miR-128-3p expression in EEF or PFP by day 8 of chemotherapy and day 15 FC MRD (rEEF = 0.99, pEEF = 1.13E-9 and rPFP = 0.99, pPFP = 4.75E-9, respectively). Furthermore, the decrease of miR-128-3p in EEF by day 15 of treatment also showed a positive correlation with day 15 FC MRD (rEEF = 0.96; pEEF = 4.89E-5). ConclusionOur results show that circulating miRs are potential biomarkers of ALL MRD, asmiR-128-3p level both in PFP and EEF predicts day 15 FC MRD. In addition, the assessment of the EEF gave a more promising result.

Complete Peripheral Blast Clearance is Superior to the Conventional Cut-Off of 1000/µL in Predicting Relapse in Pediatric Pre-B Acute Lymphoblastic Leukemia.

Risk-stratification has contributed to a dramatic improvement in survival in pediatric acute lymphoblastic leukemia (ALL). This study evaluated the utility of prephase response and day 15 bone marrow when a minimal residual disease (MRD) assessment was available. A file review of children aged ≤ 15years diagnosed with precursor-B ALL from 2014 to 2019 was performed. The protocol used for risk stratification and treatment was based on a UKALL-2003 backbone. All patients received one week of prephase therapy comprised of intravenous dexamethasone in the first 48h followed by oral prednisolone. The median age of the 255 patients in the study was 5years. Following the prephase, the peripheral blood absolute blast count was 0 and ≥ 1000/µL blasts in 141 (56%) and 29 (11%), respectively. Ten of 199 (5%) patients with an evaluable day 15 bone marrow had M3 status. At the end of induction, 30 (12%), 127 (50%) and 98 (38%) patients belonged to the standard-risk, intermediate-risk and high-risk (HR) groups, respectively. An M3 day15 bone marrow was the sole reason for escalation in three (3%) of the patients in the HR group. A lack of complete clearance of peripheral blood blasts post-prephase [HR: 2.45 (1.04-5.75), p = 0.040] and a positive MRD [HR: 3.00 (1.28-7.02), p = 0.011] independently predicted risk of relapse. Complete blast clearance is superior to the traditional cut-off of 1000/µL in predicting relapse. The role of a day 15 bone marrow morphology is diminished when an end of induction MRD is available.

Transcriptomic Profile of Bone Marrow-Derived Mesenchymal Stromal Cells of Pediatric Pre-B Acute Lymphoblastic Leukemia Patients and Healthy Donors after Interaction with Leukemic Cells

Background: Acute lymphoblastic leukemia (ALL) is a hematological malignancy characterized by the abnormal expansion of clonal lymphoblasts in the bone marrow (BM). The behavior of malignant lymphoblasts is not only dependent on their genomic abnormalities but also, on their complex and reciprocal relationships with their local niche. BM microenvironment is a dynamic network of growth factors, cytokines, and stromal cells, providing a permissive environment for leukemogenesis and progression. Despite some evidence about the implication of the bidirectional interaction between mesenchymal stromal cells (MSCs) and leukemic cell on growth and survival, it is still largely unknown. Although an increasing number of studies are reporting on the expression of specific genes in leukemic cells-interacting MSCs, gene expression profiling in cocultured MSCs (with respect to mono culture conditions) has not been done on a transcriptome-wide basis. Taking all this into consideration, we have established cocultures between BM-derived MSCs and the leukemic mononuclear cells and performed gene expression profile (GEP) studies on the MSC population to determine those deregulated genes due to the coculture condition with respect to MSCs in mono culture. Methods: Primary MSCs from BM samples of healthy donors (n=4) and pediatric pre-B ALL patients (n=4) were isolated and expanded and mononuclear cells were, also, isolated from patients peripheral blood. At passage 2, healthy/patient (h/p) MSCs were cocultured with the leukemic cells for 72 hours and subsequently subjected to GEP analyses. RNA isolated from h/pMSCs and biotinylated amplified RNA was synthesized. For the hybridization HG-U133 Plus, 2.0 GeneChip oligonucleotide arrays (Affymetrix) was used. Raw microarray data were processed into expression values through the Affy package in R. RMA (robust multi-array average) algorithm was used for preprocessing. The linear regression model package LIMMA (Linear Models for Microarray Data) was used to identify significant differential expression of genes (DEGs) compared to h/pMSCs after coculture with MSCs from the same origin in mono culture. Minimum 1.5 fold change and p-value < 0.001 were defined as the threshold. Functional enrichment, gene network and pathway analysis, were performed on selected sets of genes after differential expression analyses using two bioinformatics tools: DAVID Bioinformatics Resources 6.8 and WebGestalt 2019. Results: We identified 293 DEGs when analyzing pMSC samples vs. hMSC in coculture condition and 853 DEGs of pMSC vs. hMSC analyze in mono culture condition and only 15 DEGs common in both group. According to the result of functional enrichment analysis of pMSC vs. hMSC in coculture condition, 29 gene ontology (GO) term biological process including (top five) apoptotic process, axon guidance, regulation of JNK cascade, cell-cell adhesion and protein phosphorylation and 4 KEGG pathways of DEGs including axon guidance, FoxO signalling pathway, Wnt signalling pathway and signalling pathways regulating pluripotency of stem cells were determined. Comparing pMSC vs. hMSC in mono culture condition, 292 GO term biological process including extracellular matrix organization, skeletal system development, angiogenesis and signal transduction and 43 KEGG pathways of DEGs including pathways in cancer, TGFß signalling pathway, ECM-receptor interaction, p53 signalling pathway and PI3-Akt signalling pathway were determined.Five genes with upregulated expression after coculture (COL18A1, EFNA5, MAP3K8, CASP1, IGF1R) and after mono culture (MMP1, CXCL1, IL1B, PCDH10, CXCL6) were identified. Conclusions: Deregulated genes especially after coculture condition in axon guidance and ephrin receptor-mediated signalling pathway of which the importance is not yet understood in cancer microenvironment including EPHB1, ephrinA5, ephrinB3, p21 activated kinase 2 (PAK2), and ROBO3 showed highly differential expression pattern between pMSCs and hMSCs. This is the first report indicating the importance of axon guidance genes as a result of interaction between MSCs and leukemic cells. The elucidation of deregulated mechanisms and pathways provides new molecular insights to the contribution of these cells to ALL pathophysiology and understanding cross talk between these cells may lead to found new therapeutic targets. Disclosures No relevant conflicts of interest to declare.

Blinatumomab As a Successful Bridge to Hematopoietic Stem Cell Transplant in a Down Syndrome Patient with Relapsed B-Precursor Acute Lymphoblastic Leukemia

Introduction Children with Down syndrome (DS) carry a 20-fold higher risk of developing acute lymphoblastic leukemia (ALL) than other children and have increased rates of treatment-related mortality (TRM) and relapse. The prognosis for relapsed DS-ALL patients is grim with long-term survival rates of 20%. Blinatumomab, a CD19/CD3 bispecific antibody, is FDA approved for relapsed pediatric pre-B ALL, and recently approved for patients with minimal residual disease (MRD). However there are few reports of the use of blinatumomab in DS-ALL patients, and no reports of blinatumomab as a bridge to stem cell transplant (SCT) in this population. Case Description A 19 year old male with DS presented with thrombocytopenia and was diagnosed with pre-B ALL. Upfront therapy included fractionated cyclophosphamide, vincristine, doxorubicin, dexamethasone, pegaspargase, and rituximab for 8 cycles, and he achieved complete remission (CR). Maintenance therapy included 26 months of 6-mercaptopurine, vincristine, methotrexate, and prednisone. He relapsed 5 months after completion of therapy and was found to have a P2RY8-CRLF2 fusion. IgH gene rearrangement analysis by next generation sequencing (LymphoTrack assay) demonstrated clonal rearrangement. Re-induction therapy included vincristine, pegaspargase, and prednisone. He completed 2 additional courses of chemotherapy but continued to have MRD both by flow cytometry and LymphoTrack. Given persistent MRD with CD19+ lymphoblasts, he was treated with blinatumomab at the FDA recommended dosing; he had no signs of toxicity. He achieved negative MRD by flow cytometry and LymphoTrack after 1 cycle. He then proceeded to a T-cell depleted peripheral blood SCT from a 10/10 matched sibling after conditioning with total body irradiation, thiotepa, and cyclophosphamide. Post-SCT course was uncomplicated and he is now 1 year post-SCT with no evidence of leukemia and 100% donor chimerism. Conclusion Blinatumomab is clinically effective and safe for patients with relapsed/refractory pre-B ALL, yet there is limited information on its use in DS-ALL patients. These patients have been largely excluded from blinatumomab trials given their altered immune system and unknown level of innate T cell dysfunction, potentially altering the efficacy of blinatumomab. We present here the case of a 22 year old male with relapsed DS-ALL who remained MRD positive after several cycles of re-induction chemotherapy, but achieved a CR following 1 cycle of blinatumomab with no toxicities, and safely proceeded to SCT. Although this is a single case, it demonstrates clinical efficacy of blinatumomab in relapsed DS-ALL, suggesting that these patients' T cells can be engaged to recognized CD19-positive leukemic blasts. Furthermore, blinatumomab represents a particularly attractive bridging therapy to SCT for DS-ALL patients who experience high rates of TRM with traditional agents.

Exposure to Inflammatory Immune Responses As Driver of Clonal Evolution in Childhood Acute Lymphoblastic Leukemia

Background: Pediatric pre-B acute lymphoblastic leukemia (ALL) may develop from prenatal chromosomal translocations acquired in utero. For instance, the ETV6-RUNX1 gene rearrangement (~25% of childhood ALL) is found in the umbilical cord blood and Guthrie blood spots of 1 in 100 healthy newborns, however, only 1 in 14,000 carriers develop overt leukemia. The molecular mechanisms driving clonal evolution towards overt leukemia were not clear.Rationale: Activation Induced Cytidine Deaminase (AID) and Recombination Activation Genes 1 and 2 (RAG1-RAG2) are genetic modifiers of the immunoglobulin (Ig) genes that are expressed during normal B cell development. Although AID and RAG1/RAG2 are thought to be segregated to early (RAG1/RAG2) and late (AID) stages of B cell development, respectively, we found that the two enzymes can be concurrently expressed during early B-lymphopoiesis in the context of repeated inflammatory stimuli.Results: Our experiments identified transitional pre-B cells as the subset that is particularly vulnerable to concomitant expression of AID and RAG1-RAG2 with earlier B cells being protected by IL7 signaling.Human B cells from children lacking a functional IL-7 receptor (IL-7R) displayed both increased expression and activity of AID concurrently with RAG1-RAG2. These results demonstrated that AID activation in both mouse and human early B cell compartments increases genetic instability. Although concurrent activation of AID and RAG1-RAG2 in patient samples implicated a correlation between the two enzymes in the pathogenesis of leukemia, this as such did not prove that the enzymes causally induce overt leukemogenesis. Therefore, we next evaluated the requirement of AID and RAG1-RAG2 in leukemogenic transformation, and identified a condition that leads to massive activation of these enzymes in a pre-leukemic B cell. Importantly, AID and RAG1-RAG2 expression increased dramatically during inflammatory immune responses (e.g. infection), where both these enzymes diversify the antibody repertoire and improve its affinity to antigens from infectious pathogens. We therefore tested whether the pre-B cell subset that concurrently expresses AID and RAG1-RAG2 can respond to an inflammatory stimulus, such as LPS. We observed that pre-B cells require protection from IL7, which prevents aberrant activation of AID. In the absence of protective IL-7, these pre-B cells acquired responsiveness to LPS and strongly activated AID concurrently with RAG1-RAG2 enzymes. We developed IL7-dependent pre-B cell cultures as a disease model for ETV6-RUNX1 pre-leukemia and tested the role of AID and RAG1 in the progression of pre-leukemic clones. To this end, we expanded ETV6-RUNX1 pre-B cells from wildtype (AID and RAG1 expressing) mice, or from mice lacking AID (Aid-/-Rag1+/+) or RAG1 (Aid+/+Rag1-/-). We then challenged pre-B cell cultures by withdrawal of IL7 (loss of protection) and inflammatory stimuli (LPS) and transplanted pre-B cells that had undergone five cycles of -IL7/LPS challenge. Upon transplanting -IL7/LPS-treated Aid+/+Rag1+/+ or Aid-/-Rag1+/+ or Aid+/+Rag1-/- pre-B cells containing ETV6-RUNX1 into NOD-SCID recipient mice, we observed that loss of either Aid or Rag1 dramatically prolonged the latency and reduced the penetrance of leukemia in transplant recipients. This proved that AID and RAG1-RAG2 causally accelerate clonal evolution of a pre-leukemic B cell towards leukemia. Our findings provide a mechanism by which pre-leukemic clones carrying a prenatal genetic lesion such as ETV6-RUNX1 can evolve through infectious and inflammatory stimuli ultimately leading to full blown leukemia.Conclusion: The impact of inflammatory stimuli on leukemogenesis has been previously implicated in multiple epidemiological studies. For instance, day-care attendance primed the immune system during early childhood and is thought to protect against exacerbation of B cell responses and to prevent collateral damage driving clonal evolution towards leukemia. Although inflammation (LPS stimulation) seems to play a role in accelerating pre-B leukemogenesis in our model, further experiments testing actual infectious pathogens are needed to corroborate this concept. Moreover, it is crucial to test whether leukemogenesis is accelerated in individuals infected with restricted classes of pathogens, not all of which may activate AID in pre-B cells. DisclosuresNo relevant conflicts of interest to declare.

Bafilomycin A1 Targets Both Autophagy and Apoptosis Pathways in Pediatric t(1;19) Pre-B Acute Lymphoblastic Leukemia Cells

The t (1; 19) subtype leukemia accounts for a quarter of pre-B acute lymphoblastic leukemia (ALL) and up to 5% of all ALL patients. Despite plausible remission rate, current treatment regimen on the pediatric pre-B ALL is associated with side effects and CNS relapse, which poses the need for more effective and safer drugs. Bafilomycin A1 (Baf-A1) is known as an inhibitor of late phase of autophagy by inhibiting fusion between autophagosomes and lysosomes as well as by inhibiting lysosomal degradation.Here we show that Baf-A1 of low concentration (1 nM) effectively and specifically inhibits and kills the pre-B ALL cells. E2A/Pbx1 fusion gene positivepre-B ALL 697 cells were used for In vitro experiments. The results of flow cytometry analysis and western blotting showed that Baf-A1 induced cell cycle arrest and proliferation inhibition of ALL cells by upregualting cell cycle negative regulators and downregulating cell cycle positive regulators. In contrast, AML and CML cell lines were insensitive to Baf-A1 treatment. Western blotting and confocal observation on protein LC3 also showed that Baf-A1 at 1 nM blocked basal autophagic flux. Baf-A1 treatment activated mTOR signaling and induced the formation of Becn1–Bcl-2 complex to inhibit the induction of autophagy. Furthermore, apoptosis was induced in ALL cells treated with Baf-A1 for 72 h. However, procaspase-3 and poly-(ADP-ribose) polymerase (PARP) were not cleaved in these cells. We observed that AIF relocalized to the nucleus after 72h Baf-A1 treatment by confocal and immunoblotting. Knockdown of AIF significantly attenuated apoptosis induced by Baf-A1. These data suggest that Baf-A1 targets mitochondria membrane to trigger apoptosis via AIF pathway. In the in vivo experiment, Baf-A1 treatment extended survival and improved pathology of 697 xenograft mice, and significantly reduced the E2A/PBX1 positive leukemia cells in the bone marrow of mice. In vivomouse toxicity assay confirms Baf-A1 as a safe compound. The bone marrow cells of pre-B ALL leukemia patients were sorted against CD133+CD19+ markers, and treatment with Baf-A1 induced a clear inhibition on the CD133+CD19+ primary cells with a significant increased cell death in the sorted B-ALL patient samples. Conversely, Baf-A1 had no inhibitory effect on the bone marrow cells isolated from acute myeloid leukemia patients and healthy people.In summary, Baf-A1 treatment at low concentration effectively and specifically inhibited autophagy by activating mTOR and inducing beclin1-Bcl-2 interaction and induced AIF-dependent apoptosis in t (1; 19) pre-B ALL 697 cells. In the pre-B ALL xenograft mouse model, Baf-A1 specifically targets the leukemia cells while sparing normal cells. More importantly, Baf-A1 potently inhibits and kills the primary cells from pediatric pre-B ALL patients both at initial diagnosis and relapse without compromising normal human hematopoietic cells, all proposing Baf-A1 as a promising drug candidate for this pre-B ALL. DisclosuresNo relevant conflicts of interest to declare.

CITED2 Facilitates Apoptosis Induced By Histone Deacetylase Inhibitor SAHA In Human Pediatric Pre-B Acute Lymphoblastic Leukemia Cells

Acute lymphoblastic leukemia (ALL) is the most common malignancy in childhood, representing 31% of all tumors, and about 85% of children with ALL have B-cell ALL. Although the survival rate is approaching 90%, ALL remains the main cause of death from disease in children and young adults. The activity of histone deacetylases (HDAC) in childhood ALL is increased compared with that in normal peripheral blood mononuclear cells or bone marrow cells. Treatment of mice engrafted with T or B-ALL cells with HDAC inhibitor (HDACi) increases the acetylation of Histone 3 and Histone 4 and prolongs survival of these mice. <>Vorinostat (Suberoylamilide Hydroxamic Acid, SAHA) was the first HDACi approved by the FDA for the treatment of refractory cutaneous T-cell lymphoma. Currently, several clinical trials are being conducted to evaluate its effects on other cancers, including ALL. However, some patients are resistant to HDACi therapy, and concerns regarding toxic side effects of HDACi exist due to the roles of HDACs in multiple pathways. Therefore, identification of new therapeutic targets is required which could improve the efficacy of HDACi by reducing the dose of HDACi administered without compromising the treatment benefits but alleviating the side effects of HDACi. <>CBP/p300-interacting transactivator with glutamic acid (E) and aspartic acid (D)–rich tail 2 (CITED2) is a cytokine-inducible gene that plays various roles during mouse development and, in particular, is essential for normal hematopoiesis. While the role of CITED2 in the pathogenesis of leukemia is currently unclear, dysregulation of CITED2 has been implicated in various types of leukemia, including ALL, in which downregulation of CITED2 is frequently observed. In this study, we tested the hypothesis that CITED2 may enhance the sensitivity of human pediatric pre-B ALL cells to HDACi SAHA. <>SAHA treatment of NALM-6 and 697 cells (human pediatric pre-B ALL cell lines) significantly induced apoptosis and cell cycle arrest in a dose dependent manner. The protein level of CITED2 was not affected by SAHA treatment. Although overexpression of CITED2 alone only slightly increased apoptosis, it significantly enhanced apoptosis resulted from SAHA treatment in both NALM-6 (15.1% versus 39.2%) and 697 cells (9.4% versus 14.6%) as assessed by annexin V/Propidium Iodide double staining and flow cytometry analysis (Figure 1). Accordingly, compared with control (i.e. NALM-6 cells transduced with GFP), overexpression of CITED2 also greatly reduced mitochondrial membrane potential of NALM-6 cells caused by SAHA treatment. [Display omitted] To explore the potential mechanisms underlying enhanced apoptosis by overexpression of CITED2 in NALM-6 cells treated with SAHA, we determined the levels of pro- and anti- apoptotic proteins by Western blot and real-time quantitative PCR. We found that SAHA treatment increased the levels of pro-apoptotic molecules Bak, Puma, and Noxa, and decreased the levels of anti-apoptotic molecule Bcl-xL and apoptosis inhibitors XIAP and survivin. Importantly, overexpression of CITED2 markedly increased the protein levels of pro-apoptotic molecules Bak and Bim. Furthermore, knockdown of Bim by shRNA significantly attenuated apoptosis in Cited2 overexpressing NALM-6 cells treated with SAHA.Taken together, these results suggest that modulation of the CITED2 activity may confer its cooperative effect with SAHA in pre-B ALL cells and warrant future evaluation of such a combination in inducing apoptosis of primary ALL cells. Disclosures:No relevant conflicts of interest to declare.

Sulforaphane induces cell cycle arrest and apoptosis in acute lymphoblastic leukemia cells.

Acute lymphoblastic leukemia (ALL) is the most common hematological cancer in children. Although risk-adaptive therapy, CNS-directed chemotherapy, and supportive care have improved the survival of ALL patients, disease relapse is still the leading cause of cancer-related death in children. Therefore, new drugs are needed as frontline treatments in high-risk disease and as salvage agents in relapsed ALL. In this study, we report that purified sulforaphane, a natural isothiocyanate found in cruciferous vegetables, has anti-leukemic properties in a broad range of ALL cell lines and primary lymphoblasts from pediatric T-ALL and pre-B ALL patients. The treatment of ALL leukemic cells with sulforaphane resulted in dose-dependent apoptosis and G2/M cell cycle arrest, which was associated with the activation of caspases (3, 8, and 9), inactivation of PARP, p53-independent upregulation of p21CIP1/WAF1, and inhibition of the Cdc2/Cyclin B1 complex. Interestingly, sulforaphane also inhibited the AKT and mTOR survival pathways in most of the tested cell lines by lowering the levels of both total and phosphorylated proteins. Finally, the administration of sulforaphane to the ALL xenograft models resulted in a reduction of tumor burden, particularly following oral administration, suggesting a potential role as an adjunctive agent to improve the therapeutic response in high-risk ALL patients with activated AKT signaling.

YB-1 Is Activated by IL-7 and Is Overexpressed in Pediatric Pre-B Acute Lymphoblastic Leukemia

Abstract 1468 Background:Increased YB-1 expression correlates with poor prognosis, drug resistance and metastasis in several different cancers including B cell lymphoma. Phosphorylation and nuclear localization of YB-1 in response to growth factors leads to increased survival through expression of proteins such as survivin and multidrug resistance protein 1. Until now, its role in leukemia has not been investigated. We hypothesized that YB-1 expression is aberrantly regulated in pediatric pre-B acute lymphoblastic leukemia (pre-B ALL), and that YB-1 may be activated downstream of IL-7. This cytokine facilitates the differentiation and survival of pre-B cells and has been implicated in the drug resistance of pre-B ALL. Methods:YB-1 and IL-7Ra protein expression was investigated by flow cytometry in normal pre-B cells (CD19+CD10+CD20−), and mature B cells (CD19+CD10−CD20+) as well as diagnostic and relapsed pre-B ALL (CD19+CD10+/−). Cell surface and cytoplasmic expression was quantified by mean fluorescent intensity (MFI). Bone marrow from healthy donors was used as a source of normal pre-B cells, while mature B cells were derived from PBMCs; leukemic cells at presentation and relapse were obtained following local IRB approval and informed consent. Activation of YB-1 downstream of IL-7 stimulation (25 ng/ml) was examined in pre-B ALL cell lines or NSG (NOD scid gamma) mice-expanded pre-B ALL by Western blotting using anti-phosphoYB-1(S012). Pre-B ALL cell lines used in these experiments were 697, 380, RCH and RS-4;11. Signaling pathways were investigated by pre-treatment of cells with pharmacological inhibitors followed by Western analyses. For the transient overexpression of YB-1, pEGFP or a pEGFP/YB-1 fusion protein was electroporated into freshly isolated mature B cells (which have a low basal expression of YB-1) and YB-1 and IL-7Ra expression was assessed by flow cytometry after 24 h. Results:While intracellular YB-1 expression was significantly higher in leukemia samples at presentation compared to normal pre-B cells, the highest YB-1 levels were found in relapsed pre-B ALL (see figure, part A). All examined pre-B ALL cell lines had levels comparable to those of the relapse samples. Similarly, surface IL-7Ra (CD127) levels (MFI medians; upper-lower range) were increased in onset (221; 150–286), and relapsed (1840; 651–2030) ALL compared to normal pre-B cells (528; 333–2673). (normal pre-B vs. leukemia at presentation, p<0.001, Mann-Whitney). Overexpression of YB-1-GFP in normal mature B cells resulted in increased expression of IL-7Ra (see figure, part B), suggesting an link between the YB-1 and IL-7 signaling pathways.Activated YB-1 is phosphorylated on S102 and relocated to the nucleus. Addition of IL-7 to pre-B ALL cell lines led to phosphorylation of YB-1 within 30 min. Similar results were shown for patient-derived, NSG mice-expanded pre-B ALL samples. Intracellular immunostaining using Imagestream technology (Amnis) showed that IL-7 treatment of pre-B ALL cell lines increased nuclear YB-1 levels 4-fold.As PI3K and MEK1 are involved in signaling downstream of IL-7, we investigated their role in YB-1 signaling in both pre-B ALL cell lines and NSG-mouse expanded pre-B ALL using pharmacological inhibitors. Western analyses showed that inhibition of PI3K using LY294002 did not prevent IL-7-mediated phosphorylation of YB-1 but the MEK1 inhibitor U0126 did, indicating the involvement of MAPK (see figure, part C). Conclusion:We show that YB-1, which is highly expressed in pediatric pre-B ALL compared to normal pre-B cells, is expressed at even higher levels after relapse. We demonstrate a link between the YB-1 and IL-7 signaling pathways which could offer a novel target for the treatment of refractory leukemia. [Display omitted] Disclosures:No relevant conflicts of interest to declare.

A Key Role for Tumor Suppressor BTG1 In the Regulation of Metabolic Stress Responses: Implications for Asparaginase Resistance In Pediatric Acute Lymphoblastic Leukemia.

AbstractAbstract 1028 Background:L-Asparaginase (ASNase) is a key component of multi-agent chemotherapy regimens used in the treatment of pediatric Acute Lymphoblastic Leukemia (ALL). This bacterially-derived enzyme lowers blood asparagine levels by catalyzing the hydrolysis of L-asparagine, leading to specific killing of leukemic blasts. However, relapses and associated therapy resistance occur in about 20% of the patients. Although the molecular mechanisms that contribute to ASNase resistance are not well understood, increased expression of asparagine synthethase (ASNS), the enzyme responsible for asparagine synthesis, has been linked to ASNase resistance both in ALL cell lines and in primary leukemias. We recently reported that micro-deletions affecting the B-cell translocation gene 1 (BTG1) occur in about 10% of pediatric pre-B ALL cases. Here we show that BTG1 loss contributes to ASNase resistance by up-regulation of ASNS. Results:Using RNA interference, we show that loss of BTG1 expression promotes cell growth and renders pre-B ALL cells completely refractory to ASNase induced cell death. Resistance to ASNase in the BTG1 knockdown cells is accompanied by increased expression of ASNS, while knockdown of this metabolic enzyme is sufficient to reverse therapy resistance, indicating that upregulation of ASNS is required for the observed resistance phenotype. We further show that BTG1 associates with and regulates the activity of the transcription factor ATF4, a key regulator of metabolic stress responses and a central component in the regulatory network that controls ASNS expression. Conclusion:Together, our experiments identify BTG1 as an important regulator of ASNS expression which acts by modulating ATF4 function. We expect that a detailed molecular understanding of how BTG1 loss contributes to ASNase resistance, will lead to the identification of pharmacological targets that can be used to improve treatment responses in therapy-resistant ALL. [Display omitted] Disclosures:No relevant conflicts of interest to declare.

Stimulation of Precursor-B Acute Lymphoblastic Leukemia Cells with Toll-Like Receptor Ligands Alters Their Immunogenicity.

Pediatric pre-B acute lymphoblastic leukemia is the most common childhood cancer. Although current therapies achieve a high rate of remission, relapse of pre-B ALL remains a significant clinical challenge and new forms of therapy are needed. The graft-vs-leukemia (GVL) effect after bone marrow transplantation has shown that the immune system is capable of producing an effective anti-tumor response, which suggests that immune-mediated therapies may provide a complementary treatment strategy. Toll-like receptors (TLR), found on many immune cells, including B cells, have been shown to be important molecules in both innate and adaptive immune responses. Ligation of TLRs with their respective ligands results in an increase in the immunogenicity of antigen presenting cells (APC), through upregulation of MHC antigens and costimulatory molecules and production of cytokines and chemokines. We have previously reported that stimulation of pre-B ALL cells with the TLR9 ligand, CpG DNA, enhances the induction of Th1 immune responses by allogeneic T cells. In this study we examined the expression profile of TLRs 1-8 in precursor-B ALL cells and the effects of TLR ligation on the immune stimulatory capacity of precursor-B ALL cell lines. Eight precursor-B ALL cell lines were used in this study (Nalm6, REH, Sup-B15, KOPN-57bi, 380, 697, OP-1 and RS4:11). Standard RT-PCR analysis was used to examine the expression of TLRs 1-8 by the cell lines. The cell lines were stimulated with ligands for TLR2 (peptidoglycan), TLR3 (poly I:C) and TLR4 (LPS) and evaluated for changes in costimulatory molecule expression and allogeneic T cell stimulation. Non-quantatative PCR detected each TLR, with the exception of TLR8, in the majority of the cell lines. TLR8 was only detected, at low level, in RS4:11 cells. Despite the broad expression profile of the TLRs, significant differences in the effect of TLR ligation were observed between cell lines. In general, only modest increases in CD40 and CD86 expression were observed on responsive cell lines, with the majority of the lines showing no significant changes in response to TLR2, 3 or 4 ligation, despite receptor detection by PCR. Changes in allogeneic T cell proliferation in response to TLR stimulated ALL cell lines were observed, with the largest increases occurring with peptidoglycan and LPS. As was the case with costimulatory molecule expression, no T cell proliferative response change was common to all cell lines. However, analysis of cytokine production by T cells revealed a consistent increase in IFN-gamma and reduction in IL-5 levels in response to peptidoglycan stimulated ALL cells. The results reported in this study indicate that precursor-B ALL cell lines express several TLR molecules and that TLR ligation alters the immunogenicity of the majority of these lines. Interestingly, ligation of TLR2 with peptidoglycan induced a profound shift towards Th1 cytokine production. These observatios suggest that TLR ligation, most notably TLR2 ligation, may provide a strategy to influence anti-ALL immune responses and enhance immune mediated control of this disease.

In Vitro Growth Regulation and the Identification of Potential Signaling Pathways in T (4; 11), Pediatric Pre-B Acute Lymphoblastic Leukemia (ALL).

Among the various chromosomal translocations found in pediatric pre-B cell acute leukemias, the t (4; 11) group contains patients of all ages as well as a clustering of children at birth or in the first year of life. As with all 11q23 abnormalities, t (4; 11) fusion confers an extremely poor prognosis. Using cell lines, many recent studies have described important molecular and cellular growth properties of these cells. We have investigated in vitro growth regulation of freshly isolated infant pre-B ALL cells with t (4; 11).Leukemic blasts were affinity purified with anti CD19 antibodies and cultured in the presence of various cytokines including IL-3, IL-1, FLT-3 ligand (FL), SCF, IL-6, IL-7, GM-CSF, PDGF, SDF-1, VEGF, EPO and GCSF. Cell proliferation after four days in culture was quantified by Alamar blue assay. At pg/ ml concentrations, significant growth stimulation was seen in the presence of FL and IL-7. The FLT-3 effect was much less prominent against leukemic cells without t (4; 11). Then we aimed to identify the possible signaling pathways utilized by the FLT-3 mediated stimulation of these cells. Purified blasts were cultured in serum free medium for 24 hours and stimulated for 0, 5 and 10 minutes with 10 pg/ml of FL. These cells were subsequently lysed and total cellular extracts were analyzed by an antibody array technique. The arrays used consisted of antibodies against a selection of fifty proteins involved in all known signaling pathways. Changes in the amount of phosphorylated proteins following FL treatment were identified by enzyme conjugated anti phospho specific antibodies. A number of reproducible FL specific changes were observed. These include increased Ets-1/2, JNK1, 2,3, p38MAPK and Src. We describe the detail analysis of the signaling pathways potentially utilized by these cells and illustrate the use of this experimental approach to identify possible targeted therapeutic agents against this particular form of leukemia.

Identification of immune evasion strategies of pediatric pre-B acute lymphoblastic leukemia after bone marrow transplantation

8555 Background: Bone marrow transplantation (BMT) is the only curative option for refractory/relapsed pediatric acute lymphoblastic leukemia (ALL). However, post-BMT relapse remains an important cause of transplantation failure. Immune mechanisms play a critical role in the anti-leukemic efficacy of BMT, suggesting that mechanisms allowing leukemic blasts to evade immune responses are important in leukemia relapse. An improved understanding of the processes underlying post-BMT ALL relapse is required. Methods: In this study several methods were utilised to assess and compare the allogeneic and autologous T cell responses induced by pediatric pre-B ALL cells which had been obtained at various time points from a pediatric patient with pre-B ALL who relapsed following allogeneic BMT. All patient samples were also extensively phenotyped in order to determine the degree of co-stimulatory molecule expression on the leukemic blasts. Results: We observed a dramatic loss of T cell stimulatory capacity by later relapse samples. Also, the autologous anti-leukemic T cell response demonstrated a Th2 shift compared to the Th1 allogeneic response. These immune stimulatory changes induced by ALL cells at relapse were associated with changes in expression of MHC and costimulatory molecules. HLA-ABC expression was increased on all relapse samples. HLA-DR expression was substantially reduced in those relapse samples obtained following immunosuppression cessation. Expression of the costimulatory molecule CD137L was decreased on post-BMT relapse samples whereas B7-H1 expression was increased. Conclusions: These results reveal mechanisms involved in pre-B ALL relapse, and suggest strategies to prevent evasion of the graft-versus-leukemia effect by ALL cells. No significant financial relationships to disclose.

Identification of immune evasion strategies of pediatric pre-B acute lymphoblastic leukemia after bone marrow transplantation

8555 Background: Bone marrow transplantation (BMT) is the only curative option for refractory/relapsed pediatric acute lymphoblastic leukemia (ALL). However, post-BMT relapse remains an important cause of transplantation failure. Immune mechanisms play a critical role in the anti-leukemic efficacy of BMT, suggesting that mechanisms allowing leukemic blasts to evade immune responses are important in leukemia relapse. An improved understanding of the processes underlying post-BMT ALL relapse is required. Methods: In this study several methods were utilised to assess and compare the allogeneic and autologous T cell responses induced by pediatric pre-B ALL cells which had been obtained at various time points from a pediatric patient with pre-B ALL who relapsed following allogeneic BMT. All patient samples were also extensively phenotyped in order to determine the degree of co-stimulatory molecule expression on the leukemic blasts. Results: We observed a dramatic loss of T cell stimulatory capacity by later relapse samples. Also, the autologous anti-leukemic T cell response demonstrated a Th2 shift compared to the Th1 allogeneic response. These immune stimulatory changes induced by ALL cells at relapse were associated with changes in expression of MHC and costimulatory molecules. HLA-ABC expression was increased on all relapse samples. HLA-DR expression was substantially reduced in those relapse samples obtained following immunosuppression cessation. Expression of the costimulatory molecule CD137L was decreased on post-BMT relapse samples whereas B7-H1 expression was increased. Conclusions: These results reveal mechanisms involved in pre-B ALL relapse, and suggest strategies to prevent evasion of the graft-versus-leukemia effect by ALL cells. No significant financial relationships to disclose.

TEL-AML1 fusion precedes differentiation to pre-B cells in childhood acute lymphoblastic leukemia

The TEL-AML1 gene fusion results from a karyotypically cryptic t(12;21) translocation, the most common genetic abnormality in pediatric acute lymphoblastic leukemia (ALL). The presence of the TEL-AML1 fusion in utero, its protracted latency to overt leukemia, and secondary loss of the untranslocated TEL suggest it is an initiating event. Sequences of the TEL-AML1 genomic breakpoint and the immunoglobulin heavy chain (IgH) and/or T-cell receptor (TCR) gene rearrangements were characterized in four pediatric pre-B ALL patients. Analysis of these markers in relapsed patients revealed that immunophenotypically and cytogenetically distinct, and clonally unrelated antigen receptor leukemic cell populations harbored the same initiating TEL-AML1 molecular abnormality. Furthermore, TEL-AML1-positive cells persisted during remission even in the absence of detectable clone-specific IgH and TCR markers. We demonstrate that the TEL-AML1 translocation can occur in vivo during B-cell development before rearrangement of the IgH and TCR genes. We propose, in some cases, that the TEL-AML1 translocation occurs in a stem or B progenitor cell, and that recurrent TEL-AML1-positive pre-B ALL represents a de novo-transformed population that retains the same diagnostic initiating event.

Origin of a Central Nervous System Lymphoid Neoplasm in an Immunocompromised Host with Acute Lymphoblastic Leukemia

We describe a case of relapsed pediatric pre-B acute lymphoblastic leukemia (ALL) with asimultaneous presentation of an intracerebral lymphoid mass. Cytogenetic, immunophenotypic andmolecular analysis (immunoglobulin heavy chain and T-cell receptor gene rearrangements) revealedthat the brain neoplasm was distinct from the relapsed leukemia. We discuss the etiology of thisextremely rare event, and raise issues about the clonality of lymphoid neoplasms and the behavior ofhematopoietic cells within the central nervous system (CNS).

CAMP-Dependent Transactivation Involving the Homeodomain Protein Pbx1

Pbx1 is a DNA-binding homeodomain protein originally discovered in the t(1;19) chromosomal translocation associated with pediatric pre-B acute lymphoblastic leukemia. Previously we reported a cAMP-regulatory sequence (CRS1) in the promoter region of the bovine CYP17 gene encoding steroid 17α-hydroxylase cytochrome P450 (P450c17) to be the first endogenous Pbx1 binding site and that overexpression of Pbx1 in mouse adrenal Y1 tumor cells enhances cAMP-dependent transcription mediated by this element. Here we report further characterization of Pbx1 binding site in CRS1 and role of Pbx1 in cAMP-dependent, CRS1-mediated transcription. By gel shift analysis utilizing nuclear extracts from Y1 cells, a high-affinity Pbx-binding sequence has been determined to be TTGAT(T/G)GA(T/C)A which represents the 5′ portion of CRS1. An artificial Pbx-binding sequence (PRS), previously determined by random PCR analysis, is similar to the Pbx1-binding sequence in CRS1 and by both gel shift analysis and transfection studies shows characteristics very similar to CRS1. Upon overexpression, Pbx1 is found capable of enhancing CRS1-mediated transcription in both steroidogenic (Y1, JEG3) and nonsteroidogenic (HepG2 and S194) cells when coexpressed with the catalytic subunit of cAMP-dependent protein kinase A. Thus even though Pbx1 has been found to be involved only in cAMP-dependent transcription of a gene involved in steroidogenesis (CYP17), Pbx1 is capable of participating in cAMP-dependent transcription of target genes without complex formation with steroidogenic tissue-specific nuclear factors.