Cell Precursor ALL Research Articles

The genomic basis of childhood T-lineage acute lymphoblastic leukaemia.

T-lineage acute lymphoblastic leukaemia (T-ALL) is a high-risk tumour1 that has eluded comprehensive genomic characterization, which is partly due to the high frequency of noncoding genomic alterations that result in oncogene deregulation2,3. Here we report an integrated analysis of genome and transcriptome sequencing of tumour and remission samples from more than 1,300 uniformly treated children with T-ALL, coupled with epigenomic and single-cell analyses of malignant and normal T cell precursors. This approach identified 15 subtypes with distinct genomic drivers, gene expression patterns, developmental states and outcomes. Analyses of chromatin topology revealed multiple mechanisms of enhancer deregulation that involve enhancers and genes in a subtype-specific manner, thereby demonstrating widespread involvement of the noncoding genome. We show that the immunophenotypically described, high-risk entity of early T cell precursor ALL is superseded by a broader category of 'early T cell precursor-like' leukaemia. This category has a variable immunophenotype and diverse genomic alterations of a core set of genes that encode regulators of hematopoietic stem cell development. Using multivariable outcome models, we show that genetic subtypes, driver and concomitant genetic alterations independently predict treatment failure and survival. These findings provide a roadmap for the classification, risk stratification and mechanistic understanding of this disease.

Abstract 624: Ptpn1 deficiency collaborates with a NUP98::HOXD13 fusion gene to generate B cell precursor acute lymphoblastic leukemia

Abstract Background: Acute lymphoid leukemia is characterized by inherited or acquired mutations that effect critical differentiation and proliferation pathways. We have shown that Mcm2 deficient mice developed T cell acute lymphoblastic leukemia, due to copy number variations, most commonly interstitial deletions throughout the genome. When crossed with mice that expressed a NUP98::HOXD13 (NHD13) fusion gene, Mcm2−/−NHD13 mice developed B cell precursor ALL (BCP-ALL). A majority of these BCP-ALL had acquired homozygous deletions of Ptpn1, a protein tyrosine phosphatase, leading to the hypothesis that Ptpn1 deficiency combined with NHD13 expression leads to BCP ALL. Objective: To investigate the role of Ptpn1 deletion in BCP-ALL development using mouse models. Methods: Mice expressing an NHD13 fusion gene were crossed with Ptpn1 knockout mice, generating 6 possible genotypes. Mice were followed for 18 months. Mice with signs of leukemia were characterized by clinical evaluation, CBC, flow cytometry, and IHC. Primary BCP-ALL and derived BCP-ALL cell lines were also evaluated with RNA-seq and molecular pathway analysis. Results: NHD13+Ptpn1-/- mice developed BCP-ALL with 65% penetrance, characterized by hyperleukocytosis, anemia, thrombocytopenia, and invasion of non-hematopoietic tissues. Similar to human BCP-ALL, NHD13+Ptpn1-/- BCP-ALL had clonal IGH as well as clonal Tcrd gene rearrangements. Flow cytometry revealed CD19 and/or B220 expression. NHD13+Ptpn1+/- mice with BCP-ALL frequently lost the wild-type (WT) Ptpn1 allele in leukemic cells, reinforcing the hypothesis that Ptpn1 can function as a classic tumor suppressor gene in this context. Whole exome sequencing revealed acquired mutations in B-cell differentiation genes (Pax5 or Bcor) and activating mutations in tyrosine kinase genes (Jak1/3 and Flt3). Transcription signature analysis showed significant upregulation of Hoxa/b gene clusters, RNase12 and LncRNAs subsets. Conclusion: This study demonstrates that Ptpn1 loss combined with expression of NHD13 fusion gene leads to highly penetrant BCP-ALL in mice, suggesting a role for Ptpn1 in preventing malignant transformation. These findings present a collaborative model for BCP-ALL in which the NHD13 transgene leads to increased stem cell self-renewal, somatic Bcor or Pax5 mutations block normal B cell differentiation, and somatic signaling mutations (Jak1/3,Flt3) lead to hyperproliferation, which is potentiated by Ptpn1 deficiency. Citation Format: Nupur Nigam, Toshihiro Matsukawa, Ryan Bertoli, Michel L. Tremblay, Mianmian Yin, Peter D. Aplan. Ptpn1 deficiency collaborates with a NUP98::HOXD13 fusion gene to generate B cell precursor acute lymphoblastic leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 624.

ALL-389 Venetoclax in the Treatment of Relapsed Refractory Early T Cell Precursor ALL (ETP-ALL). Case Report and Review of The Literature

ALL-389 Venetoclax in the Treatment of Relapsed Refractory Early T Cell Precursor ALL (ETP-ALL). Case Report and Review of The Literature

POSTER: ALL-389 Venetoclax in the Treatment of Relapsed Refractory Early T Cell Precursor ALL (ETP-ALL). Case Report and Review of The Literature

POSTER: ALL-389 Venetoclax in the Treatment of Relapsed Refractory Early T Cell Precursor ALL (ETP-ALL). Case Report and Review of The Literature

Treating relapsed B cell-precursor ALL in children with a setting-adapted mitoxantrone-based intensive chemotherapy protocol (TMH rALL-18 PROTOCOL) - experience from Tata Memorial Hospital, India.

The outlook of relapsed ALL in low- and middle-income countries (LMICs) is dismal due to high treatment-related toxicities and inadequate resources. We report our experience of using a locally adapted mitoxantrone-based protocol for non-high risk (HR) relapsed B-ALL (rALL). A retrospective cum prospective study of standard and intermediate risk (SR and IR) rALL patients treated on TMH rALL-18 protocol (adapted from COG/UKALLR3/Int-Re-ALL protocols) between November 2018 and January 2021 was analyzed. The protocol comprising of 7 blocks of multi-agent chemotherapy including mitoxantrone in induction followed by local irradiation and maintenance, underwent serial modifications based on our experience with initial patients. Eighty-two patients (SR rALL, 3; IR rALL, 79) were treated on TMH rALL-18 protocol. Of 321 grade 3/4 reported toxicities, around 43% (138 toxicities) were noted during induction. Induction chemotherapy was outpatient-based; however, 68 patients (82.9%) required supportive care admissions. Twelve out of 19 patients with gram negative bacilli sepsis (included 7 MDRO) died during reinduction. Five remission deaths were seen during block 3 after which cytarabine was dose reduced (3g to 2g/m2). Post-reinduction minimal residual disease was negative in 54 (80.6%) out of 67 evaluable patients. At a median follow-up of 24months (95% CI 22-27), the estimated 2-year event-free and overall survival of the entire cohort was 58% (95% CI 48.1-69.9) and 60.3% (95% CI 50.5-72). Until the time, targeted therapies are freely accessiblein LMICs, strengthening supportive careas well as local adaptation of protocols that strike a fine balance between efficacy and tolerability are mandated.

Association of ethnicity with overall survival in patients with T-cell acute lymphoblastic leukemia/lymphoblastic lymphoma

e18557 Background: T-cell acute lymphoblastic leukemia/lymphoblastic lymphoma (T-ALL/T-LBL) is a rare and aggressive form of malignancy of immature T-Cells. Despite advancements in treatment, disparities in survival rates among different racial/ethnic groups have been reported. While there is some data available comparing survival outcomes in children with ALL based on ethnicity, there is limited data on comparison of survival outcomes in patients specifically with T-ALL. Here we compared the survival outcomes of T-ALL patients from a minority rich cohort including both children and adults. Methods: This is a single center observational retrospective study analyzing T-ALL patients from 2004-2022 who were followed up at our center. We collected and analyzed data on demographics, race, immunophenotype, treatment regimens, and survival outcomes. Race (used here interchangeably with ethnicity) was categorized as Hispanic, Black, White and other races. Immunophenotype was classified as Pro-TALL, Pre-TALL, Cortical TALL, Medullary TALL and Early T cell precursor-ALL. Univariate and multivariate Cox regression models were used for analysis. Overall survival (OS) was compared using the Kaplan-Meier curve and log-rank test. P-values < / = 0.05 were considered as statistically significant. All analyses were done using R statistical software. Results: We included 59 patients with T-ALL (78% males and 22% females) for analysis. The median age at diagnosis was 20 years (range 1-48 years). Thirty two percent were Black, 29% Hispanic, 17% White and 14% were of other races (8%-not reported). Median follow up duration was 30 months. We compared OS based on sex, race, and immunophenotype. Univariate analysis showed significant difference in OS only for race (p value 0.006). Hispanic patients had the worse outcomes with lower OS compared to White (p = 0.02), and other ethnicities (p = 0.04). The difference was still significant (p = 0.016 and 0.01 respectively) after correction for age using multivariate analysis (age groups: < 15 and = / > 15 years; 15 years being the median age for Hispanic population). There was no difference in OS between remaining races. Median overall survival was not reached in any group. Conclusions: Although sample size is small, our study showed that the OS in Hispanics was lower than in White and other races in a minority rich population including adults and children with T-ALL. Whether this difference is due to systemic barriers in accessing care and/or due to inherent characteristics affecting disease severity/response to treatment remains to be explored. Interestingly, we didn’t find any difference in survival outcomes for black race and for different immunophenotypes. This study adds to the literature demonstrating disparities in survival among different racial groups with T-ALL and the need to address these disparities through targeted interventions.

Diagnostic Utility of Whole Genome Sequencing in Adults with B-Other Acute Lymphoblastic Leukaemia

Background B-other ALL represents a working definition for patients with B cell precursor (BCP) ALL without a known primary chromosomal abnormality at diagnosis. In this study we use whole genome sequencing (WGS) to characterize the molecular pathogenesis of adult B-other cases (age ≥ 25yrs) from the UKALL14 trial (NCT01085617). Methods Of 652 patients aged 25-65yrs enrolled onto UKALL14, 333 (51%) had B-other ALL. Sufficient material was available to screen 156/333 B-other cases for recurrent Ph-like fusion events (CRLF2, JAK2, ABL1, ABL2 & PDGFRB) using FISH and MLPA (kit P335). This identified 28 (18%) "Ph-like" fusion events (21 CRLF2, 5 ABL-class and 2 JAK2). Of the remaining 128 B-other cases 57 had available samples for tumor normal paired WGS (read depth 60x and 30x respectively). Diagnostic RNA was available for 33 of the 57 cases Bioinformatic analysis was performed to determine small somatic mutations; single nucleotide variants (SNVs) and insertion/deletions (INDELs) as well as copy number aberrations (CNA) and structural variants (SV). We developed WGS approaches to identify IGH enhancer hijack and DUX4 rearrangements, utilizing gGnome and GRIDSS respectively. For 33 cases RNA-seq data was analyzed to validate fusion genes and genetic classification into one of 18 ALL subtypes using the ALLSorts v2 classifier. Results 52/57 cases passed QC. In 5 (10%) cases an established WHO2016 genetic subtype was identified that was missed by standard of care including three high-risk (2 low hypodiploid and a near haploid) and 2 standard risk (high hyperdiploid and TCF3::PBX1) cases. Cytogenetic analysis for these 5 cases either failed (n=2) or produced a normal karyotype (n=3). The WGS inferred tumor purity for these 5 cases was variable with a median of 46% and a range of 33% to 96% compared to 89% (range 13%-99%) for the remaining cases (n=47) in the dataset. Among the remaining 47 B-other cases, WGS analysis identified abnormalities enabling 41 (87%) cases to be classified into a genetic ALL subtype: DUX4 rearrangements (DUX4r, n=8), PAX5alt (n=7), PAX5 P80R (n=4), ZNF384 rearrangements (ZNF384r, n=5), ZEB2/CEBP (n=4), MEF2D rearrangements (MEF2Dr, n=3), UBTF::ATXN7L3 fusions (n=2), IDH1/2 mutations (n=2), JAK-STAT abnormalities (n=2), along with single cases of IGK::BCL2, IGH::CEBPA, IGH::ID4 and IGH::MIR125B1. WGS resolves 8 cases with complex karyotype into one of 6 different genomic subtypes: 2xDUX4r, 2xMEF2Dr, ZEB2/CEBP, UBTF::ATXN7L3, IGK::BCL2 & IGH::ID4. The MEF2Dr subtype (n=3), is enriched in chromothripsis (2/3), and complex SVs targeting the MEF2D gene. Lastly, in all cases with PAX5 mutations (PAX5 P80R (n=4) and PAX5alt (n=4)) we observe bi-allelic targeting of locus by mutations, deletions or LOH. The remaining 6 (13%) B-other cases could not be classified into a recognized B-other subtype. A MYO18A::FGFR1 fusion (t(8;17)(p11;q23)), which most likely maps to the WHO2016 "Lymphoid neoplasms with FGFR1 rearrangement" classification. Two cases had clonal frameshifts in genes associated with T-ALL (PTPN2 p.A108fs*5 and WT1 p.V371fs*14 respectively). A case with a somatic ETV6 p.R399C previously reported in germline risk with a ZNF292::KDM6A fusion. Lastly a case with a clonal mutation typically associated with myeloid disease ASXL1 p.R417*. Among the 52 cases studied, WGS only failed to identify a driver or putative driver in one case, which had the lowest burden of SNVs (861) and an estimated tumor purity, 28%. For the 31 cases with both DNA and RNA, WGS and RNA analysis were concordant for 100% of cases, with RNA identifying an additional KDM6A::CGA fusion. In 3 cases WGS provides evidence that would have challenged diagnosis and/or treatment; IGK::BCL2 with BCL2 and MYC overexpression, IGH::DUX4 with hypermutation (MSH6 loss) and IGH::ID4 with homozygous loss of CD58 and concurrent LOH of HLA-B. Conclusions WGS assigned 88% (46/52) of cases called B-other to an established genetic subtype of ALL. This includes 5 cases with WHO2016 defined subtypes, 3 were high-risk ploidy subtypes that would have changed their UKALL14 risk group and post-induction treatment in the absence of other risk factors. Among the true B-other cases, 87% (41/47) were assigned to one of the newly described genetic subtypes of ALL. Taken together our findings demonstrate the clinical utility of WGS as a diagnostic assay to inform and improve the management of adult B-Other ALL patients in the future.

UBTF::ATXN7L3 gene fusion defines novel B cell precursor ALL subtype with CDX2 expression and need for intensified treatment

UBTF::ATXN7L3 gene fusion defines novel B cell precursor ALL subtype with CDX2 expression and need for intensified treatment

Transcriptome-wide subtyping of pediatric and adult T cell acute lymphoblastic leukemia in an international study of 707 cases

T cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy of T cell progenitors, known to be a heterogeneous disease in pediatric and adult patients. Here we attempted to better understand the disease at the molecular level based on the transcriptomic landscape of 707 T-ALL patients (510 pediatric, 190 adult patients, and 7 with unknown age; 599 from published cohorts and 108 newly investigated). Leveraging the information of gene expression enabled us to identify 10 subtypes (G1–G10), including the previously undescribed one characterized by GATA3 mutations, with GATA3R276Q capable of affecting lymphocyte development in zebrafish. Through associating with T cell differentiation stages, we found that high expression of LYL1/LMO2/SPI1/HOXA (G1–G6) might represent the early T cell progenitor, pro/precortical/cortical stage with a relatively high age of disease onset, and lymphoblasts with TLX3/TLX1 high expression (G7–G8) could be blocked at the cortical/postcortical stage, while those with high expression of NKX2-1/TAL1/LMO1 (G9–G10) might correspond to cortical/postcortical/mature stages of T cell development. Notably, adult patients harbored more cooperative mutations among epigenetic regulators, and genes involved in JAK-STAT and RAS signaling pathways, with 44% of patients aged 40 y or above in G1 bearing DNMT3A/IDH2 mutations usually seen in acute myeloid leukemia, suggesting the nature of mixed phenotype acute leukemia.

The treatment development for T cell acute lymphoblastic leukemia in children, adolescents, and young adults

T-cell acute lymphoblastic leukemia (T-ALL) accounts for 10%-15% of pediatric ALL, and its frequency increases during the adolescent and young adult (AYA) periods. The improvements in pediatric T-ALL outcomes have been achieved through the treatment intensification strategies addressing the cranial radiotherapy omission issue. Furthermore, pediatric-inspired regimens have been adopted for AYA patients with T-ALL, improving outcomes. In Japan, the Japanese Pediatric Leukemia/Lymphoma Study Group (JPLSG) ALL-T11/JALSG T-ALL-211-U trial has been conducted for newly diagnosed patients with T-ALL aged <25 years and has been shown to have excellent outcomes. While early T cell precursor ALL is not an obvious poor prognostic factor in recent treatment strategies for pediatric T-ALL, the minimal residual disease (MRD) has been recognized as the most reliable prognostic indicator. Therefore, MRD is now widely used in T-ALL clinical trials for risk stratification and stem cell transplantation indications. Further progress in the novel therapeutic approaches can potentially improve the outcomes of pediatric and AYA patients with T-ALL.

Leukemic Cells Expressing ETV6-Frk Identified in a Refractory B-ALL Patient Are Sensitive to Dasatinib in Vitro

[Background]ETV6-FRK is a rare kinase-related fusion gene which was identified only in acute myeloid leukemia (Hosoya N, et al. Genes Chromosomes Cancer. 2005). Herein, we firstly identified ETV6-FRK fusion gene in a patient with high-risk pediatric B cell precursor ALL (B-ALL). Because FRK is Src family tyrosine kinase, we performed functional analysis of ETV6-FRK to establish molecular targeting therapy.[Patient]A 11-year-old boy with B-ALL was refractory to conventional chemotherapy and received allogeneic bone marrow transplantation (allo-BMT) following two courses of blinatumomab. This patient maintains complete remission for three months after allo-BMT. Cytogenetic analysis demonstrated t(6;12)(q21;p13) as a part of complex karyotype. Targeted capture mRNA sequencing identified ETV6-FRK fusion transcript in this patient.[Materials and methods]ETV6-FRK fusion was validated by RT-PCR of the diagnostic leukemic sample from this patient. Full length of ETV6-FRK cDNA was cloned into retroviral vector with Tet-On system. Then, Ba/F3 cells, which are IL-3 dependent murine pro B-ALL cells, were transduced with retroviral vector to establish Ba/F3 cells expressing ETV6-FRK (Ba/F3-ETV6-FRK) under doxycycline (DOX) dependent manner. Ba/F3-ETV6-FRK was analyzed whether IL-3 independent growth was achieved. To determine whether aberrant activation of FRK-STAT pathway as the downstream effects of ETV6-FRK, activation of FRK-STAT pathway was evaluated by western blot. Finally, in cytotoxic assay, proliferation of Ba/F3-ETV6-FRK was assessed under the media with various concentrations of dasatinib, a tyrosine kinase inhibitor.[Results and discussions]Sequencing of RT-PCR product revealed that ETV6 exon 4 was fused in-frame to FRK exon 3, creating an ETV6-FRK fusion gene. The ETV6-FRK fusion gene produced a chimeric protein consisting of the entire pointed (PNT) oligomerization domain of ETV6 and the kinase domain of FRK (Fig 1). The expression of ETV6-FRK in Ba/F3 cells under DOX dependent manner was confirmed by western blot. Ba/F3-ETV6-FRK proliferated without IL-3 in contrast to Ba/F3 cells not expressing ETV6-FRK (p<0.01), suggesting ETV6-FRK had proliferation activity. Western blot analysis revealed constitutive phosphorylation of tyrosine residues of ETV6-FRK and STAT5/STAT3/STAT1, suggesting constitutive activation of FRK-STATs pathway was associated with IL-3 independent proliferation activity of ETV6-FRK. Considering that dasatinib, which is Src-kinase inhibitor, could block constitutive phosphorylation of ETV6-FRK, we hypothesized that dasatinib might block the IL-3 independent proliferation of Ba/F3-ETV6-FRK. In vitro killing assay showed that dasatinib suppressed efficiently the proliferation of Ba/F3-ETV6-FRK with 50% inhibitory concentration (IC50) 1.64 ± 0.02 nM, although dasatinib didn't show any effect on Ba/F3 cells not expressing ETV6-FRK (Fig. 2). Annexin V assay determined that 35.8 ± 6.9 % of Ba/F3-ETV6-FRK with dasatinib (10nM, 48hrs) were apoptotic than Ba/F3 cells not expressing ETV6-FRK (Fig. 3, p<0.01). These findings suggested that dasatinib abolished the proliferation activity of ETV6-FRK selectively.[Conclusion]We identified the first patient of pediatric high-risk B-ALL harboring ETV6-FRK fusion by targeted capture mRNA sequencing, who was refractory to the conventional chemotherapy. We also provide the first evidence that dasatinib could abrogate proliferation activity of ETV6-FRK in vitro, suggesting that dasatinib might be effective for the patient with B-ALL carrying a ETV6-FRK fusion. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Aberrant FLT3 Transcription Arised from Polycomb Repressive Complex 2 Inactivation Indiactes a Potential Therapy Target for Pediatric T Cell Acute Lymphoblastic Leukemia

Pediatric T cell acute lymphoblastic leukemia (T-ALL) is an aggressive subtype of pediatric ALL, and is characterized by recurring genetic and epigenetic alterations. Loss-of-function mutations and deletions of Polycomb repressive complex 2 (PRC2) core components, including EED, EZH2 and SUZ12 ,have been identified in around 25% of T-ALL and are associated with diseases progression and poor prognosis. One presented study has demonstrated the specific loss of the repressive mark Lys27 trimethylation of histone 3 (H3K27me3) by abrogating the activity of PRC2 leads to Notch pathway activation; In a mouse model of early T cell precursor ALL (ETP-ALL), inactivation of PRC2 has been revealed to be associated with increasing transcription of early hematopoietic programs and contribute to hyperactive JAK/STAT signaling pathway. However, the detailed mechanism of pediatric T-ALL tumorigenesis driven by PRC2 remains to be further clarified.Through targeted sequencing of PRC2 components of 62 diagnostic pediatric T-ALL samples, we discovered mutations in EZH2 (8/62), SUZ12 (4/62), and EED (2/62) in 12 patients. RNA sequence profiling of the sorted primary samples from these 12 patients revealed a surprisingly upregulated expression of FLT3 and this upregulation was confirmed to be specifically presented in PRC2 mutated patients by qRT-PCR analysis in all the 62 T-ALL primary samples.To explore the interplay between the inactivation of PRC2 and upregulation of FLT3, we constructed EZH2 disrupted Jurkat cell lines by CRISPR-Cas9. QRT-PCR reflected eight-to-twenty-fold increasing of FLT3 mRNA expressions in homozygousknockout clones; ChIP-qPCR showed that EZH2 deletions led to remarkably attenuated H3K27me3 histone mark and prominent enrichment of POLII binding in FLT3 promoter region, which were highly consistent with gene expression levels; Besides, elevation in phosphorylation of STAT5, AKT and ERK also showed high correlation with increased FLT3 expressions, which was reversed by the treatment of FLT3 inhibitors, Sorafeinib and Quizartinib, respectively. This, in turn, suggested that the loss of H3K27me3 caused by PRC2 disruption closely coupled to the activation of FLT3 downstream signaling pathway in human T-ALL.To examine the regulation of FLT3 transcription by PRC2 in hematologic malignances, we exposed cell lines of T-lineage (Jurkat, Molt4, CEM), B-Lineage (Ramos, Raji), and other myeloid malignancies (K562, HL-60, THP-1) to EZH2 inhibitors and observed only T-lineage cell lines specifically presented response to EZH2 inhibitors with increased expression of FLT3, and therefore the activation of downstream pathway. Rather, inhibitions of PRC2 seemed not to uprgulate FLT3 transcriptions in other cell lines.In a model of T-lineage differentiation from immature hematopoietic cells on OP9-DL1 cells exposed to EZH2 inhibitors, lineage-negative, Sca1-positive, and C-kit-positive (LSK) cells, and ETP cells derived from C57BL/6 mice displayed markedly differentiation arrest via flow cytometric analysis, accompanied by upregulation of Flt3 expression and accentuation of down stream signaling pathway.To further test whether the hyperactive signaling pathway mediated by EZH2 -inactivation was a potential therapy target, pediatric T-ALL cells from EZH2 -mutated primary samples were transplanted into NSG mouse and treated with FLT3 inhibitors. Surprisingly, FLT3 inhibitors treated group conferred hypersensitivity to the drugs, and the median survival span from treatment to death in FLT3 inhibitors group was significantly longer than control group treated with PBS (P < 0.0001).In conclusion, our study provides strong evidence that loss of H3K27me3 arised from PRC2 inactivation leads to high level of FLT3 transcription and downstream signaling pathway upregulation in human T-ALL, indicating both a possible mechanism and a potential therapy target for pediatric T-ALL with PRC2 mutations in future clinical practice. DisclosuresNo relevant conflicts of interest to declare.

Investigating the Efficacy of Anti-CD200 Immunotherapy in MRD Low and Risk B Cell Precursor ALL

Despite remission rates of >90% in childhood B cell precursor acute lymphoblastic leukaemia (BCP ALL) using frontline treatment, the incidence of relapse remains high. Immunotherapeutic approaches, including chimeric antigen receptor (CAR)-T cells targeting CD19 have resulted in improved outcomes for refractory cases. However, such therapies do not target CD19- ALL cells, a population known to have leukaemia initiating ability, and there are several reports of patients relapsing with CD19- leukaemia after CAR-T cell therapy. CD200 (OX-2) is an immunosuppressive molecule overexpressed in BCP ALL. In low risk minimal residual disease (MRD) ALL samples, only CD200+ cells have leukaemia initiating capacity in NOD.Cg- Prkdcscid Il2r gtm1Wjl/Sz (NSG) mice, suggesting that CD200 may be a suitable target for therapy in these cases. When CD200 binds to its receptor (CD200R) the immune response is suppressed. Consequently, malignant cells that overexpress CD200 may capitalise on this immune suppression and avoid destruction. Anti-CD200 antibodies (Ab) may be used to prevent such cancer cell evasion by binding to CD200 antigen and blocking its interaction with CD200R. The aim of this study was to investigate the expression of CD200 in MRD low and risk BCP ALL cases and assess the effects of using monoclonal (Mo) TTI-CD200 Ab in vitro and in vivo. Samples from MRD low and risk BCP ALL cases were stained with anti-CD200 Ab to quantify (i) the proportion of cells expressing CD200, (ii) the median fluorescence intensity (MFI) of CD200 and (iii) the number of CD200 antigen binding sites. Results were compared to those obtained using normal bone marrow (NBM) controls. The proportion of CD200+ cells was higher in ALL cases (median 40.0%, range 5.4-74.4%) compared to NBM cells (median 0.001%, range 0-0.003%, P =0.0004). There was no significant difference between the MRD low (median 33.8%, range 18.1-74.1%) and risk (median 44.93%, range 36.35-74.4%) ALL cases. However, CD200 MFI levels were significantly higher in the low risk cases (median 593, range 469-1313) compared to those observed in MRD risk cases (median 191, range 138-572, P =0.04). CD200 MFI levels in the low risk group were also significantly higher than in NBM cells (median 0.9, range 0-27, P =0.001). Additionally, the number of CD200 antigen sites on ALL cells was 5-fold higher in MRD low risk cases (median 1372, range 324-2179) than in risk cases (median 264, range 87-1500), while the number of CD200 sites on BM cells was only 17 (range 13-112, P =0.006 vs low risk cases). Monocyte-derived macrophages and CD4+ T cells from healthy donors were cultured with low risk BCP ALL cells ± TTI-CD200 in a mixed lymphocyte reaction assay. The production of interleukin (IL)-2 was measured as an indicator of immune system activation using an enzyme-linked immunosorbent assay. Median CD200 expression in these cases was 46.9% (range 0.7-94.2%) and MFI was 249 (34.8-1659). The median IL-2 increase observed on addition of TTI-CD200 was 16-fold (range 1.7-120) and it did not correlate with the proportion of CD200+ cells or MFI. In these cases, samples with very low proportions of CD200+ cells (0.9±0.4%) demonstrated a 2.5-fold increase in IL-2, whereas samples with higher proportions of CD200+ cells (91.1±4.4%) produced a 17.2-fold rise. To assess the effects of TTI-CD200 on ALL cells in vivo, NSG were inoculated with BCP ALL cells from MRD low and risk cases. Once leukaemia levels exceeded 0.5% in peripheral blood, animals received 4 doses of TTI-CD200 (20mg/kg i.v.) over 10 days. Consistent with previous findings, TTI-CD200 treatment of mice engrafted with MRD risk cases had no effect on disease burden. This may be due to the lower proportion of CD200+ cells in these cases (34.1±11.7% CD200+) and also that CD200- cells contribute to engraftment in risk cases. In contrast, in low risk ALL cases a 47.5±29% reduction in leukaemia burden was observed after treatment with TTI-CD200. The proportion of inoculated CD200+ cells was higher in these low risk cases (74.9±30.3% CD200+) and had significantly reduced by 99.4±0.6% (P =0.04) in ALL cells recovered from the murine BM on termination. The dose and schedule of TTI-CD200 used was much less intensive than standard chemotherapy. It may be possible to improve the in vivo efficacy using another round of therapy. These findings demonstrate the potential of using anti-CD200 MoAb therapy for low risk BCP ALL. DisclosuresPetrova:Trillium Therapeutics: Employment, Equity Ownership. Uger:Trillium Therapeutics: Employment, Equity Ownership, Patents & Royalties.

Prognostic significance of CD45 antigen expression in pediatric acute lymphoblastic leukemia

ObjectivesThe treatment of pediatric acute lymphoblastic leukemias (ALL) has seen remarkable advances recently. However, relapse occurs in approximately 20% of cases which necessitates identifying additional high risk parameters for treatment intensification. The aim of this study is to assess the prognostic significance of CD45 antigen expression in pediatric ALL. MethodsWe studied 363 pediatric patients with B cell precursor-ALL (BCP-ALL) (n = 313) and T-ALL (n = 50). The ratio of median fluorescence intensity of CD45 expressed in leukemic blasts and normal lymphocytes was calculated. The 75th percentile was taken as cut-off to categorise patients into CD45 high and CD45 low groups. ResultsThe 75th percentile was 0.141 in BCP-ALL and 0.548 in T-ALL. In BCP-ALL, there was a statistically significant association of age (≥10 years) (p = 0.027) and National Cancer Institute high risk group (p = 0.001) with high CD45 expression but not in T-ALL. Worse event-free survival (EFS) was seen with high CD45 expression in BCP-ALL (42.17% versus 60.83%, p = 0.0053). In T-ALL, there was no association between CD45 expression and EFS (CD45 high 40.40% versus low 67.35%, p = 0.414). The overall survival (OS) was 70% versus 60% (p = 0.38) in BCP-ALL and the OS was 82% versus 68% (p = 0.16) in T-ALL for CD45 low versus CD45 high groups, respectively. ConclusionWe conclude that high CD45 surface expression is associated with worse EFS in pediatric BCP-ALL.

Molecular Subtypes with Distinct Clinical Phenotypes and Actionable Targets in Adult B Cell Precursor ALL Treatment According to GMALL Protocols

Targeted interventions and new risk stratification approaches for the improvement of outcomes in B cell precursor acute lymphoblastic leukemia (BCP-ALL) require an understanding of high-risk driver subtypes, their clinical phenotypes and actionable targets. Currently, over 20 BCP-ALL subtypes have been identified based on genomic driver alterations and corresponding gene expression signatures, in particular in pediatric ALL. This complex molecular landscape is so far only partially defined in adult BCP-ALL patients. To characterize driver subtypes and their clinical phenotypes we performed transcriptome sequencing (Illumina) on Ph-negative adult BCP-ALL patients (n=376) treated on subsequent pediatric inspired protocols of the German Acute Lymphoblastic Leukemia Study Group (GMALL). Using random forest analyses of a well-defined patient subset with available WES/gene panel and DNA-methylation data, we established a 300-gene classifier which together with fusion calling and hotspot mutation calling reliably allocated samples to driver subtypes. Subgroup allocation was feasible for n=267 / 308 Ph-negative patients (86.7%) with Ph-like ALL (27.7%) being the most frequently observed subtype followed by DUX4 (14.6%), KMT2A (10.1%), PAX5-plus (9.7%), ZNF384 (9.0%), Near haploid - High hyperdiploid (NH-HeH, 6.0%), Low haploid - Near triploid (LH-NT, 6.0%) and TCF3-PBX1 (5.6%). With frequencies below 5% were observed: PAX5-alt, MEF2D, BCL2/MYC, ETV6-RUNX1, CEBP family member fusions and TCF3-HLF. The age distribution of these driver subtypes varied across our cohort (median age: 37 years, range: 16 - 81; left panel). Adult patients harboring ETV6-RUNX1 fusions (n=4) were 25 years or younger. NH-HeH, PAX5-plus and DUX4 ALL were also observed predominantly in younger patients (median ages: 24, 24, 30 years respectively; p&amp;lt;0.03) Conversely, LH-NT and KMT2A rearranged ALL frequencies increased in older patients (median ages: 47, 46 years respectively; p&amp;lt;0.04). As expected, male patients were slightly more represented in the cohort (55% male). However, significant differences were observed in the sex-distribution of molecular subgroups with a predominance of male patients in Ph-like (65.4%; p=0.045) and NH-HeH (82.4% p=0.024) ALL, while female patients were more frequent in DUX4 (60%, p=0.046) or KMT2A (75.5%; p=0.031) ALL. These data implicate that sex-specific host factors favor the selection of ALL driver alterations in adult ALL patients. We measured MRD by qRT-PCR quantification of patient specific immune gene rearrangement markers in our GMALL central reference lab. Data on MRD status after consolidation I which is the most relevant time-point for identification of high-risk patients in the GMALL protocol, were available in 132 patients (aged 18-55 years; right panel). Ph-like and KMT2A patients showed an unfavorable response to intensive induction with Molecular CR achieved in 60.6% and 61.1% respectively. In ZNF384 ALL patients, only n=5/13 achieved Molecular CR, while n=4 each were MRD-positive or had MRD below the quantitative detection range, suggesting that ZNF384 ALL might be a novel high-risk subgroup in adult BCP-ALL. Gene set enrichment analyses showed comparable patterns of JAK/STAT activation in ZNF384 and Ph-like cases as possible functional underpinning of a shared poor-response phenotype. Actionable genomic alterations were identified in n=13/74 Ph-like patients (17.6%). Out of these, ABL-class fusions as targets of ABL-TKI were identified in n=14 patients (PDGFRB: n=5; ABL1: n=4; CSF1R n=2) and one patient harbored an ETV6-NTRK3 fusion amenable to specific inhibitors. Our data extent the in-depth characterization of BCP-ALL molecular landscape in adult patients. We observe that sex-specific host factors favor the selection of leukemogenic drivers (male predominance: Ph-like, NH-HeH, female predominance: DUX4, KMT2A). ZNF384 ALL seems to be associated with unfavorable therapy response in adults and shares JAK/STAT activation patterns with Ph-like ALL. Figure Disclosures Fiedler: Jazz Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel accomodations; Novartis: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: support in medical writing; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel accomodations, support in medical writing, Research Funding; Daiichi Sankyo Oncology: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel accomodations; BerGenBio ASA: Research Funding; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: support in medical writing; BMS: Honoraria; Gilead: Honoraria; Ariad/Incyte: Membership on an entity's Board of Directors or advisory committees; Servier: Honoraria, Other; Morphosys: Membership on an entity's Board of Directors or advisory committees. Viardot:Novartis: Honoraria, Other: advisory board; Kite/Gilead: Honoraria, Other: advisory board; Roche: Honoraria, Other: advisory board; Amgen: Honoraria, Other: advisory board. Topp:Amgen, Boehringer Ingelheim, KITE, Regeneron, Roche: Research Funding; Amgen, KITE, Novartis, Regeneron, Roche: Consultancy. Goekbuget:Servier: Consultancy, Research Funding; Jazz: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; Erytech: Consultancy; Kite: Consultancy; Gilead: Consultancy. Brüggemann:Affimed: Research Funding; Incyte: Consultancy; Celgene: Consultancy; Amgen: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria; Roche: Consultancy; Regeneron: Research Funding.

Is It Time to Take MRD More Seriously? Relationship between MRD, Functional Cure and Life Expectancy Among Patients with Ph- B Cell Precursor ALL (BCP-ALL)

Background: Although BCP-ALL patients can achieve complete remission (CR) after induction chemotherapy, about 40% of them have residual leukemia cells in the bone marrow which is called minimal residual disease (MRD). Complete MRD response is defined as lack of MRD with an assay sensitivity of &amp;gt;= 10-4, which, if sustained for more than five years, may be regarded as a functional cure for ALL. On the contrary, presence of MRD is a signal of high risk of relapse leading to poor health outcomes. Blinatumomab is the only drug approved for BCP-ALL patients with MRD based on the results from BLAST, a single-arm phase 2 study conducted to assess the efficacy and safety of blinatumomab in adult BCP-ALL patients in CR with MRD. Currently, there is limited evidence on the relationship between MRD response and functional cure in ALL and life years gained. Objectives: The objective of this study was to assess the relationship between complete MRD response after blinatumomab treatment and 1) functional cure; 2) life years and quality adjusted life years (QALYs) gained among BCP-ALL patients with MRD. Methods: The relationship between MRD response, and clinical outcomes was analyzed using an existing cost-effectiveness analysis (CEA) based on combined decision tree and Markov cohort model over a lifetime horizon (50 years). The model includes survival conditional on treatment and MRD status for time to stem transplant, relapse and death. In the CEA, blinatumomab was compared to standard of care (SOC, defined as conventional maintenance chemotherapy). Clinical probabilities were derived primarily from blinatumomab clinical trial data and a non-interventional cohort study (used as a historical control). Life years gained were adjusted for quality based on utility values from trial EQ-5D scores. An annual discount rate of 3.5% was applied to estimate future outcomes. Results: In the base case, the complete MRD response rate was 83.6%, and blinatumomab yielded more life years gained (8.26 vs. 5.68) and more QALYs (6.56 vs. 4.44) compared with SOC. The proportion of patients achieving a functional cure was 43.59% in blinatumomab group vs. 26.78% in the SOC group. Clinical response varied with variations in MRD response rate at 75%, 78%, 80%, 85%. Specifically, when the complete MRD response rate increased from 75% to 85%, the total life years gained in the blinatumomab group increased by 0.51, QALYS increased by 0.42, and the proportion of patients cured increased by 3.05%. Conclusion: Achieving complete MRD response is associated with longer life expectancy, higher probability of being cured, and more QALYs among patients with BCP-ALL and MRD. Disclosures Shao: Amgen: Employment. Tiwana:Amgen: Employment, Equity Ownership. Despiegel:Amgen: Employment, Equity Ownership. Dirnberger:Amgen: Employment, Equity Ownership.

Whole Genome Profiling of Adult B-Other Acute Lymphoblastic Leukaemia on the UKALL14 Trial

B-other ALL represents a working definition for patients with B cell precursor (BCP) ALL without a known primary chromosomal abnormality. In this study we use whole genome sequencing (WGS) to characterize adult B-other cases (age ≥ 25yrs) from the UKALL14 trial (NCT01085617). Of 652 patients aged 25-65yrs enrolled onto UKALL14, 333 (51%) had B-other ALL. Sufficient material was available to screen 156/333 B-other cases for recurrent Ph-like fusion events (CLRF2, JAK2, ABL1, ABL2PDGFRB) using FISH and MLPA (kit P335). This identified 28 (18%) Ph-like fusion events (21 CRLF2, 5 ABL-class fusions and 2 JAK). Of the remaining 128 B-other cases 57 had available samples for tumor normal paired WGS (read depth 60x and 30x respectively). Bioinformatic analysis was performed to determine small somatic mutations (SSMs); single nucleotide variants (SNVs) and insertion/deletions (INDELs) as well as copy number aberrations (CNA) and structural variants (SV). We also undertook de novo motif analysis to identify RAG mediated deletions. We present data for 30/57 cases (median age of diagnosis 44, range 25-65), the remainder are undergoing sequencing. Within this cohort we identified 784 SVs, 49,244 SNVs and 2,881 INDELs, with each case having a median representation of 23 SVs, 1,674 SNVs and 86 INDELs. The Median SSM burden was 0.55 per megabase (range 0.31-0.81), which is in the upper third of previous ALL estimates (median 0.26 range 0.03-2.9) but low compared to most other cancer types (Alexandrov et al. 2013 Nature). Fusion gene analysis identified 11/30 (37%) cases with recurrent rearrangements (2 ZNF384r, 2 PAX5r, 5 DUX4r and FGFR1r); this identified a novel 5' partner for ZNF384r (AKAP8) and MYO18A-FGFR1 a fusion previously seen in a single case of 8p11 myeloproliferative syndrome. A further 7 clonal coding drivers were identified, 3 PAX5alt, 3 Ph-like candidates and a single ETV6-RUNX1-like candidate (ETV6 R399C, a dominant negative mutation). We classified our cohort into 6 driver subgroups as shown in table 1 using Gu et al. as a framework (Gu et al. 2019 Nat Gen). We found no evidence of driver subgroups clustering with age, although the Ph-like candidates were all identified in patients 39yrs or older. There was evidence that known driver subgroups have differing mutation burdens but these were not significant in this preliminary cohort; the single MEF2Dr case had a high SV burden compared to all other known subgroups (137 vs. cohort median 22); Favorable outcome subgroups (ZNF384r and DUX4r n=7) had a lower SNV coding mutation burden (median 14 vs. 20; U = 60, p = 0.057; Mann-Whitney U test); PAX5alt (n=5) cases had a higher INDEL burden (median 174 vs. 82; U = 16.5, p =0.057). As expected we found recurrent CNA in CDKN2A/B (63%; 19/30), PAX5 (33%; 10/30), IKZF1 (27%; 8/30), ETV6 (11%; 3/30) and BTG1 (7%; 2/30) across the cohort. IKZF1 deletions were enriched in the Ph-like candidate (n=4) subgroup compared to all other known groups (75% vs. 12%; p = 0.028; Fisher's Exact). RAG mediated deletions have been established as an oncogenic driver mechanism in childhood ALL, so we sought to ascertain its role in adults. We identified 54% (128/236) of the breakpoint resolved deletions had a RAG heptamer site. There was a significant difference (U = 167.5, p = 0.021) in RAG deletion burden between patients over 40yrs and under 40yrs at diagnosis (median 1.5 vs 3). Within the unknown driver subgroup; three cases carried ZEB2 H1038R mutations, two with concurrent IGH-CEBPA/B fusions, identifying them as likely belonging to the G12 cluster identified by Li et al. (Li et al. 2018 PNAS); one case had a high translocation burden (37 cohort median 2) and a single case had a high RAG deletion burden (45, cohort median 2); of the remaining 7 cases, four had either a NRAS or FLT3 subclonal hotspot mutation. Here we present the WGS analyses of 30 cases classified as B-other on the basis of no cytogenetic findings by standard clinical assays. The landscape of adult B-other ALL is highly heterogeneous but with WGS we were able to find at least one disease defining event in 60% of our cohort. These events often encompass novel fusion partners of established genomic subtypes or a cytogenetically cryptic lesion such as IGH-DUX4. Taken together our findings demonstrate the clinical utility of WGS as a diagnostic assay to inform and improve the management of adult B-other ALL patients in the future. Disclosures Fielding: Pfizer: Consultancy; Incyte: Consultancy; Amgen: Consultancy; Novartis: Consultancy. Papaemmanuil:Celgene: Research Funding.

CDKN2B downregulation and other genetic characteristics in T-acute lymphoblastic leukemia

We identified principal genetic alterations in 97.1% (99/102) of patients with T-acute lymphoblastic leukemia (T-ALL) using integrative genetic analyses, including massive parallel sequencing and multiplex ligation-dependent probe amplification (MLPA). A total of 133 mutations were identified in the following genes in descending order: NOTCH1 (66.7%), FBXW7 (19.6%), PHF6 (15.7%), RUNX1 (12.7%), NRAS (10.8%), and DNMT3A (9.8%). Copy number alterations were most frequently detected in CDKN2B, CDKN2A, and genes on 9p21.3 in T-ALL (45.1%). Gene expression data demonstrated the downregulation of CDKN2B in most cases of T-ALL, whereas CDKN2A downregulation was mainly restricted to deletions. Additional quantitative methylation analysis demonstrated that CDKN2B downregulation stemmed from deletion and hypermethylation. Analysis of 64 patients with CDKN2B hypermethylation indicated an association with an older age of onset and early T cell precursor ALL, which involved very early arrest of T cell differentiation. Genes associated with methylation and myeloid neoplasms, including DNMT3A and NRAS, were more commonly mutated in T-ALL with CDKN2B hypermethylation. In particular, a CDKN2B biallelic deletion or high methylation level (≥45%), the age of onset, and the GATA3 and SH2B3 mutations were factors associated with a poor prognosis. This study clarifies that one of the most important genetic events in T-ALL, namely, CDKN2B downregulation, occurs mechanistically via deletion and hypermethylation. Different susceptible genetic backgrounds exist based on the CDKN2B downregulation mechanism.

Clinical Profile of Childhood Early T cell Precursor ALL

Clinical Profile of Childhood Early T cell Precursor ALL

Characteristics and Outcome of Early T Cell Precursor ALL (ETP-ALL) Patients Treated with High-Risk Spanish Pethema Protocols

▪Background:ETP-ALL was included as a provisional identity in the 2016 WHO classification of ALL. This subtype was first identified by Coustan-Smith et al. in 2009. However, this immunophenotype-based classification does not fully enclose all ETP-ALL cases identified by gene expression profile (GEP). Although early studies in small series of ETP-ALL suggested a very poor outcome for ETP ALL more recent and larger series have showed improvement in outcome treating children with a contemporary protocol based on chemotherapy schedules, or after allogeneic stem cell transplantation (allo-SCT) in adults.Aim:To investigate the clinical and biological features of ETP-ALL cases in the Spanish cohort of adult T-cell ALL (T-ALL) patients and to assess the potential impact of high-risk therapy on their outcome.Method:One hundred eighty-five adults with T-ALL treated according to two consecutive MRD-oriented high-risk adult PETHEMA protocols -ALL-HR-2003 (NCT00853008) and ALL-HR-11 (NCT01540812; still ongoing)- were included in this study. The EGIL criteria were used to define the immunologic subtype of T-ALL after central review of immunophenotype reports, and the criteria proposed by Zuurbier et al. (Zuurbier L. et al. Haematologica 2014; 99:94-102) were used to define ETP-ALL. These later criteria consist of a combination of immunophenotypic markers (absence of CD1a-/CD4-/CD8-, cut-off <10%, and expression of the stem cell marker CD34+and/or at least one myeloid marker such as CD13+or CD33+, cut-off >25%), that resemble those published by Coustan-Smith, with the advantage that include most ETP-ALL cases, as identified by GEP, avoiding the use of partial expression of CD5 marker to immuno-classify these patients.Results:Thirty-four out of 167 evaluable patients (20%) with T-ALL showed an ETP-ALL immunophenotype. Patients with ETP-ALL were older (mean 39 [SD 12] vs. 33 [12] yr; p=0.011), showed more frequently lymph node involvement (79% vs. 56%; p=0.021) and lower WBC counts at diagnosis (mean, 72 [155] vs. 97 [112] x109/L; p=0.004). At genetic level, ETP-ALL patients were associated with the absence of deletions in CDKN2A/B gene cluster (91% vs. 26%; p<0.001) (10/11 cases) and with the absence of bi-allelic deletions in TCRG gene (67% vs. 5%; p=0.001) (6/9 cases). In turn, ETP-ALL patients showed poorer response to induction therapy: 82% of ETP-ALL had poorer early cytologic response (>10% BM blasts on day+14) vs. 37% of non-ETP (p<0.001), and 23% of ETP-ALL patients did not reach CR vs. 6% non-ETP T-ALL cases (p=0.005). Flow-MRD data at CR (available in 141/167 patients) showed MRD levels ≥0.1% in 65% of ETP-ALL vs. 18% of non-ETP ALL (p<0.001), and MRD level ≥0.01% in 85% vs. 37%, respectively (p<0.001). Forty-six percent of ETP-ALL patients required a second induction treatment compared to 8% of non-ETP-ALL (p<0.001). Consequently, more ETP-ALL patients underwent allo-SCT (70% vs. 21%, p<0.001). The OS of ETP-ALL patients was poorer after censoring or not the follow-up at the time of transplant (Figures 1A and B).Conclusions:ETP-ALL accounts for 20% of adult T-ALL in the PETHEMA cohort and it is associated with a poorer initial response to treatment (lower CR rate, poorer MRD clearance) than the remaining T-ALL patients. Such poorer outcome is not overcome by allo-SCT in our series.Supported by grants from: Asociación Española Contra el Cáncer, AECC (GC16173697BIGA), Instituto Carlos III (PI14/01971 FI), 2017-SGR288 (GRC), CERCA Program from Generalitat de Catalunya, and “La Caixa” Foundation. [Display omitted] DisclosuresMontesinos:Daiichi Sankyo: Consultancy, Speakers Bureau; Novartis: Research Funding, Speakers Bureau.