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BCR/ABL1 causes dysregulated cell proliferation and is responsible for chronic myelogenous leukemia (CML) and Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph1-ALL). In addition to the deregulatory effects of its kinase activity on cell proliferation, BCR/ABL1 induces genomic instability by downregulating BRCA1. PARP inhibitors (PARPi) effectively induce cell death in BRCA-defective cells. Therefore, PARPi are expected to inhibit growth of CML and Ph1-ALL cells showing downregulated expression of BRCA1. Here, we show that PARPi effectively induced cell death in BCR/ABL1 positive cells and suppressed colony forming activity. Prevention of BCR/ABL1-mediated leukemogenesis by PARP inhibition was tested in two in vivo models: wild-type mice that had undergone hematopoietic cell transplantation with BCR/ABL1-transduced cells, and a genetic model constructed by crossing Parp1 knockout mice with BCR/ABL1 transgenic mice. The results showed that a PARPi, olaparib, attenuates BCR/ABL1-mediated leukemogenesis. One possible mechanism underlying PARPi-dependent inhibition of leukemogenesis is increased interferon signaling via activation of the cGAS/STING pathway. This is compatible with the use of interferon as a first-line therapy for CML. Because tyrosine kinase inhibitor (TKI) monotherapy does not completely eradicate leukemic cells in all patients, combined use of PARPi and a TKI is an attractive option that may eradicate CML stem cells. [ABSTRACT FROM AUTHOR]

Poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi) function by inhibiting base excision repair and inducing synthetic lethality in homologous recombination repair-deficient cells, such as BRCA1/2-mutated cancer cells. The BCR/ABL1 fusion protein causes dysregulated cell proliferation and is responsible for chronic myelogenous leukemia and Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ALL). BCR/ABL1 also induces genomic instability by downregulating BRCA1. We investigated the effect of the PARPi, olaparib, against Ph+ALL cell lines and found that they show variable sensitivity, presumably due to cancer-associated genetic alterations other than BCR/ABL1. To investigate the reasons for the variable responses of Ph+ALL cells to PARPi treatment, we analyzed the transcriptomes of olaparib-sensitive and -resistant Ph+ALL cell lines, which revealed that activation of the phosphatidylinositol 3-kinase (PI3K) pathway was a hallmark of PARPi resistance. Based on these findings, we examined the effects of adding a PI3K inhibitor (PI3Ki) to PARPi treatment to overcome PARPi insensitivity in Ph+ALL cell lines. Combination with PI3Ki increased PARPi cytotoxicity in PARPi-resistant Ph+ALL cell lines. Tyrosine kinase inhibitor (TKI) therapy is the gold standard for Ph+ALL, and, based on our findings, we propose that PARPi combined with TKI and PI3K inhibition could be a novel therapeutic strategy for Ph+ALL. [ABSTRACT FROM AUTHOR]

I Biomolecules i was able to uphold its high standards for published papers due to the outstanding efforts of our reviewers. [Extracted from the article]

NK/T-cell lymphoma (NKTCL) and γδ T-cell non-Hodgkin lymphomas (γδ T-NHL) are highly aggressive lymphomas that lack rationally designed therapies and rely on repurposed chemotherapeutics from other hematological cancers. Histone deacetylases (HDACs) have been targeted in a range of malignancies, including T-cell lymphomas. This study represents exploratory findings of HDAC6 inhibition in NKTCL and γδ T-NHL through a second-generation inhibitor NN-429. With nanomolar in vitro HDAC6 potency and high in vitro and in cellulo selectivity for HDAC6, NN-429 also exhibited long residence time and improved pharmacokinetic properties in contrast to older generation inhibitors. Following unique selective cytotoxicity towards γδ T-NHL and NKTCL, NN-429 demonstrated a synergistic relationship with the clinical agent etoposide and potential synergies with doxorubicin, cytarabine, and SNS-032 in these disease models, opening an avenue for combination treatment strategies. [ABSTRACT FROM AUTHOR]

Summary: Inherited genetic variation is associated with 6‐mercaptopurine (6‐MP) dose reduction and frequent toxicities induced by 6‐MP. However, the tolerable dose for 6‐MP is not fully predicted by the known variation in NUDT15 and TPMT among Asian children with acute lymphoblastic leukaemia (ALL). We performed a genome‐wide association study (GWAS) related to 6‐MP dose among Japanese children with ALL. This GWAS comprised 224 patients previously enrolled in Tokyo Children's Cancer Study Group clinical studies with replication attempted in 55 patients. Genome‐wide single nucleotide polymorphism (SNP) genotypes were evaluated for association with average 6‐MP dose during the initial 168 days of maintenance therapy. Possible associations were observed across five gene‐coding regions, among which only variants at 13q14.2 were significant and replicated genome‐wide (rs116855232, NUDT15, β = −10.99, p = 3.7 × 10−13). Notable findings were observed for variants in AFF3 (rs75364948, p = 2.05 × 10−6) and CHST11 (rs1148407, p = 2.09 × 10−6), but were not replicated possibly due to small numbers. A previously reported candidate SNP in MTHFR was associated with higher average 6‐MP dose (rs1801133, p = 0.045), and FOLH1 (rs12574928) was associated in an evaluation of candidate regions (padjust = 0.013). This study provides strong evidence that rs116855232 in NUDT15 is the genetic factor predominantly associated with 6‐MP tolerable dose in children in Japan. [ABSTRACT FROM AUTHOR]

Imatinib and second-generation tyrosine kinase inhibitors (TKIs) have dramatically improved the prognosis of Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL). However, overcoming TKI resistance due to the T315I gatekeeper mutation of BCR/ABL1 is crucial for further improving the prognosis. The clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 system is appropriate for establishing a human model of Ph+ ALL with the T315I mutation, because it can induce specific mutations via homologous recombination (HR) repair in cells with intact endogenous HR pathway. Here we used CRISPR/Cas9 to introduce the T315I mutation into the Ph+ lymphoid leukemia cell line KOPN55bi, which appeared to have an active HR pathway based on its resistance to a poly (ADP-Ribose) polymerase-1 inhibitor. Single-guide RNA targeting at codon 315 and single-strand oligodeoxynucleotide containing ACT to ATT nucleotide transition at codon 315 were electroporated with recombinant Cas9 protein. Dasatinib-resistant sublines were obtained after one-month selection with the therapeutic concentration of dasatinib, leading to T315I mutation acquisition through HR. T315I-acquired sublines were highly resistant to imatinib and second-generation TKIs but moderately sensitive to the therapeutic concentration of ponatinib. This authentic human model is helpful for developing new therapeutic strategies overcoming TKI resistance in Ph+ ALL due to T315I mutation. [ABSTRACT FROM AUTHOR]

In chemotherapy for childhood acute lymphoblastic leukaemia (ALL), maintenance therapy consisting of oral daily mercaptopurine and weekly methotrexate is important. NUDT15 variant genotype is reportedly highly associated with severe myelosuppression during maintenance therapy, particularly in Asian and Hispanic populations. It has also been demonstrated that acquired somatic mutations of the NT5C2 and PRPS1 genes, which are involved in thiopurine metabolism, are detectable in a portion of relapsed childhood ALL. To directly confirm the significance of the NUDT15 variant genotype and NT5C2 and PRPS1 mutations in thiopurine sensitivity of leukaemia cells in the intrinsic genes, we investigated 84 B‐cell precursor‐ALL (BCP‐ALL) cell lines. Three and 14 cell lines had homozygous and heterozygous variant diplotypes of the NUDT15 gene, respectively, while 4 and 2 cell lines that were exclusively established from the samples at relapse had the NT5C2 and PRPS1 mutations, respectively. Both NUDT15 variant genotype and NT5C2 and PRPS1 mutations were significantly associated with DNA‐incorporated thioguanine levels after exposure to thioguanine at therapeutic concentration. Considering the continuous exposure during the maintenance therapy, we evaluated in vitro mercaptopurine sensitivity after 7‐day exposure. Mercaptopurine concentrations lethal to 50% of the leukaemia cells were comparable to therapeutic serum concentration of mercaptopurine. Both NUDT15 variant genotype and NT5C2 and PRPS1 mutations were significantly associated with mercaptopurine sensitivity in 83 BCP‐ALL and 23 T‐ALL cell lines. The present study provides direct evidence to support the general principle showing that both inherited genotype and somatically acquired mutation are crucially implicated in the drug sensitivity of leukaemia cells. [ABSTRACT FROM AUTHOR]

Identification of genetic variants associated with glucocorticoids (GC) sensitivity of leukaemia cells may provide insight into potential drug targets and tailored therapy. In the present study, within 72 leukaemic cell lines derived from Japanese patients with B‐cell precursor acute lymphoblastic leukaemia (ALL), we conducted genome‐wide genotyping of single nucleotide polymorphisms (SNP) and attempted to identify genetic variants associated with GC sensitivity and NR3C1 (GC receptor) gene expression. IC50 measures for prednisolone (Pred) and dexamethasone (Dex) were available using an alamarBlue cell viability assay. IC50 values of Pred showed the strongest association with rs904419 (P = 4.34 × 10−8), located between the FRMD4B and MITF genes. The median IC50 values of prednisolone for cell lines with rs904419 AA (n = 13), AG (n = 31) and GG (n = 28) genotypes were 0.089, 0.139 and 297 µmol/L, respectively. For dexamethasone sensitivity, suggestive association was observed for SNP rs2306888 (P = 1.43 × 10−6), a synonymous SNP of the TGFBR3 gene. For NR3C1 gene expression, suggestive association was observed for SNP rs11982167 (P = 6.44 × 10−8), located in the PLEKHA8 gene. These genetic variants may affect GC sensitivity of ALL cells and may give rise to opportunities in personalized medicine for effective and safe chemotherapy in ALL patients. [ABSTRACT FROM AUTHOR]

High ENT1 and DCK gene expression levels are a potential biomarker to predict favorable response to nelarabine therapy in T-cell acute lymphoblastic leukemia In contrast, I DCK i gene expression levels were relatively high in I BCL11B-TLX3 i -positive cell lines compared with I STIL-TAL1 i -positive cell lines and other cell lines (Figure C). As a result, the sum of I ENT1 i and I DCK i gene expression levels was relatively high in I BCL11B-TLX3 i -positive cell lines compared with I STIL-TAL1 i -positive cell lines and other cell lines (Figure D). [Extracted from the article]

t(17;19)(q21‐q22;p13), responsible for TCF3‐HLF fusion, is a rare translocation in childhood B‐cell precursor acute lymphoblastic leukemia(BCP‐ALL). t(1;19)(q23;p13), producing TCF3‐PBX1 fusion, is a common translocation in childhood BCP‐ALL. Prognosis of t(17;19)‐ALL is extremely poor, while that of t(1;19)‐ALL has recently improved dramatically in intensified chemotherapy. In this study, TCF3‐HLF mRNA was detectable at a high level during induction therapy in a newly diagnosed t(17;19)‐ALL case, while TCF3‐PBX1 mRNA was undetectable at the end of induction therapy in most newly diagnosed t(1;19)‐ALL cases. Using 4 t(17;19)‐ALL and 16 t(1;19)‐ALL cell lines, drug response profiling was analyzed. t(17;19)‐ALL cell lines were found to be significantly more resistant to vincristine (VCR), daunorubicin (DNR), and prednisolone (Pred) than t(1;19)‐ALL cell lines. Sensitivities to three (Pred, VCR, and l‐asparaginase [l‐Asp]), four (Pred, VCR, l‐Asp, and DNR) and five (Pred, VCR, l‐Asp, DNR, and cyclophosphamide) agents, widely used in induction therapy, were significantly poorer for t(17;19)‐ALL cell lines than for t(1;19)‐ALL cell lines. Consistent with poor responses to VCR and DNR, gene and protein expression levels of P‐glycoprotein (P‐gp) were higher in t(17;19)‐ALL cell lines than in t(1;19)‐ALL cell lines. Inhibitors for P‐gp sensitized P‐gp‐positive t(17;19)‐ALL cell lines to VCR and DNR. Knockout of P‐gp by CRISPRCas9 overcame resistance to VCR and DNR in the P‐gp‐positive t(17;19)‐ALL cell line. A combination of cyclosporine A with DNR prolonged survival of NSG mice inoculated with P‐gp‐positive t(17;19)‐ALL cell line. These findings indicate involvement of P‐gp in resistance to VCR and DNR in Pgp positive t(17;19)‐ALL cell lines. In all four t(17;19)‐ALL cell lines, RAS pathway mutation was detected. Furthermore, among 16 t(1;19)‐ALL cell lines, multiagent resistance was usually observed in the cell lines with RAS pathway mutation in comparison to those without it, suggesting at least a partial involvement of RAS pathway mutation in multiagent resistance of t(17;19)‐ALL. [ABSTRACT FROM AUTHOR]

Abstract: Cytosine arabinoside (Ara‐C) is one of the key drugs for the treatment of acute myeloid leukemia. It is also used for consolidation therapy of acute lymphoblastic leukemia (ALL). Ara‐C is a deoxyadenosine analog and is phosphorylated to form cytosine arabinoside triphosphate (Ara‐CTP) as an active form. In the first step of the metabolic pathway, Ara‐C is phosphorylated to Ara‐CMP by deoxycytidine kinase (DCK). However, the current cumulative evidence in the association of the Ara‐C sensitivity in ALL appears inconclusive. We analyzed various cell lines for the possible involvement of DCK in the sensitivities of B‐cell precursor ALL (BCP‐ALL) to Ara‐C. Higher DCK expression was associated with higher Ara‐C sensitivity. DCK knockout by genome editing with a CRISPR‐Cas9 system in an Ara‐C‐sensitive‐ALL cell line induced marked resistance to Ara‐C, but not to vincristine and daunorubicin, indicating the involvement of DCK expression in the Ara‐C sensitivity of BCP‐ALL. DCK gene silencing due to the hypermethylation of a CpG island and reduced DCK activity due to a nonsynonymous variant allele were not associated with Ara‐C sensitivity. Clofarabine is a second‐generation deoxyadenosine analog rationally synthesized to improve stability and reduce toxicity. The IC50 of clofarabine in 79 BCP‐ALL cell lines was approximately 20 times lower than that of Ara‐C. In contrast to Ara‐C, although the knockout of DCK induced marked resistance to clofarabine, sensitivity to clofarabine was only marginally associated with DCK gene expression level, suggesting a possible efficacy of clofarabine for BCP‐ALL that shows relative Ara‐C resistance due to low DCK expression. [ABSTRACT FROM AUTHOR]

Prognosis of childhood acute lymphoblastic leukemia (ALL) has been dramatically improved. However, prognosis of the cases refractory to primary therapy is still poor. Recent phase 2 study on the efficacy of combination chemotherapy with bortezomib (BTZ), a proteasome inhibitor, for refractory childhood ALL demonstrated favorable clinical outcomes. However, septic death was observed in over 10% of patients, indicating the necessity of biomarkers that could predict BTZ sensitivity. We investigated in vitro BTZ sensitivity in a large panel of ALL cell lines that acted as a model system for refractory ALL, and found that Philadelphia chromosome-positive (Ph+) ALL, IKZF1 deletion, and biallelic loss of CDKN2A were associated with favorable response. Even in Ph-negative ALL cell lines, IKZF1 deletion and bilallelic loss of CDKN2A were independently associated with higher BTZ sensitivity. BTZ showed only marginal cross-resistance to four representative chemotherapeutic agents (vincristine, dexamethasone, l-asparaginase, and daunorubicin) in B-cell precursor-ALL cell lines. To improve the efficacy and safety of proteasome inhibitor combination chemotherapy, we also analyzed the anti-leukemic activity of carfilzomib (CFZ), a second-generation proteasome inhibitor, as a substitute for BTZ. CFZ showed significantly higher activity than BTZ in the majority of ALL cell lines except for the P-glycoprotein-positive t(17;19) ALL cell lines, and IKZF1 deletion was also associated with a favorable response to CFZ treatment. P-glycoprotein inhibitors effectively restored the sensitivity to CFZ, but not BTZ, in P-glycoprotein-positive t(17;19) ALL cell lines. P-glycoprotein overexpressing ALL cell line showed a CFZ-specific resistance, while knockout of P-glycoprotein by genome editing with a CRISPR/Cas9 system sensitized P-glycoprotein-positive t(17;19) ALL cell line to CFZ. These observations suggested that IKZF1 deletion could be a useful biomarker to predict good sensitivity to CFZ and BTZ, and that CFZ combination chemotherapy may be a new therapeutic option with higher anti-leukemic activity for refractory ALL that contain P-glycoprotein-negative leukemia cells. [ABSTRACT FROM AUTHOR]

Activation of tyrosine kinase 2 (TYK2) contributes to the aberrant survival of T-cell acute lymphoblastic leukaemia (T-ALL) cells. Here we demonstrate the anti-leukaemic activity of a novel TYK2 inhibitor, NDI-031301. NDI-031301 is a potent and selective inhibitor of TYK2 that induced robust growth inhibition of human T-ALL cell lines. NDI-031301 treatment of human T-ALL cell lines resulted in induction of apoptosis that was not observed with the JAK inhibitors tofacitinib and baricitinib. Further investigation revealed that NDI-031301 treatment uniquely leads to activation of three mitogen-activated protein kinases (MAPKs), resulting in phosphorylation of ERK, SAPK/JNK and p38 MAPK coincident with PARP cleavage. Activation of p38 MAPK occurred within 1 h of NDI-031301 treatment and was responsible for NDI-031301-induced T-ALL cell death, as pharmacological inhibition of p38 MAPK partially rescued apoptosis induced by TYK2 inhibitor. Finally, daily oral administration of NDI-031301 at 100 mg/kg bid to immunodeficient mice engrafted with KOPT-K1 T-ALL cells was well tolerated, and led to decreased tumour burden and a significant survival benefit. These results support selective inhibition of TYK2 as a promising potential therapeutic strategy for T-ALL. [ABSTRACT FROM AUTHOR]

Senescent erythrocytes undergo a loss of phospholipid asymmetry in the plasma membrane and are removed from the circulation by phagocytosis. To examine the loss of phospholipid asymmetry in mature erythrocytes after chemotherapy, we monitored phosphatidylserine (PS)-exposing erythrocytes by using flow cytometry to detect annexin V-bound erythrocytes in the circulation of acute lymphoblastic leukemia patients after consolidation chemotherapy. Both the percentage and the absolute number of annexin V-positive erythrocytes gradually increased immediately after chemotherapy. This result paralleled the change in the serum levels of bilirubin, suggesting a direct induction of PS-externalization in mature erythrocytes and a subsequent increase in erythrocyte clearance by splenic macrophages. The PS-exposing erythrocyte counts showed negative correlations to platelet and reticulocyte counts, which reflect the hematopoietic potential in the bone marrow. This result suggests that bone marrow suppression could be responsible for the enlarged senescent population in the circulation. Moreover, PS-exposing erythrocytes in the circulation remained at relatively high levels even after the serum level of bilirubin normalized, indicating that the decreased clearance of senescent erythrocytes as a result of impaired phagocytosis following bone marrow suppression might also be involved in the increase in PS-exposing erythrocytes in the circulation late after chemotherapy. [ABSTRACT FROM AUTHOR]

A 9-year-old boy with paroxysmal nocturnal hemoglobinuria/aplastic anemia syndrome ( PNH/ AA) developed hemolytic crisis after receiving immunosuppressive therapy. Eculizumab dramatically relieved the signs and symptoms and then he safely underwent unrelated bone marrow transplantation, suggesting the feasibility and effectiveness of eculizumab before stem cell transplantation in children with PNH/ AA in hemolytic crisis. [ABSTRACT FROM AUTHOR]

Immunotherapies specific for B-cell precursor acute lymphoblastic leukemia (BCP-ALL), such as anti-CD19 chimeric antigen receptor (CAR) T-cells and blinatumomab, have dramatically improved the therapeutic outcome in refractory cases. In the anti-leukemic activity of those immunotherapies, TNF-related apoptosis-inducing ligand (TRAIL) on cytotoxic T-cells plays an essential role by inducing apoptosis of the target leukemia cells through its death receptors (DR4 and DR5). Since there are CpG islands in the promoter regions, hypermethylation of the DR4 and DR5 genes may be involved in resistance of leukemia cells to immunotherapies due to TRAIL-resistance. We analyzed the DR4 and DR5 methylation status in 32 BCP-ALL cell lines by sequencing their bisulfite PCR products with a next-generation sequencer. The DR4 and DR5 methylation status was significantly associated with the gene and cell-surface expression levels and the TRAIL-sensitivities. In the clinical samples at diagnosis (459 cases in the NOPHO study), both DR4 and DR5 genes were unmethylated in the majority of cases, whereas methylated in several cases with dic(9;20), MLL-rearrangement, and hypodiploidy, suggesting that evaluation of methylation status of the DR4 and DR5 genes might be clinically informative to predict efficacy of immunotherapy in certain cases with such unfavorable karyotypes. These observations provide an epigenetic rational for clinical efficacy of immunotherapy in the vast majority of BCP-ALL cases. [ABSTRACT FROM AUTHOR]

Background: The genetic variants of the ARID5B gene have recently been reported to be associated with disease susceptibility and treatment outcome in childhood acute lymphoblastic leukemia (ALL). However, few studies have explored the association of ARID5B with sensitivities to chemotherapeutic agents. Methods: We genotyped susceptibility-linked rs7923074 and rs10821936 as well as relapse-linked rs4948488, rs2893881, and rs6479778 of ARDI5B by direct sequencing of polymerase chain reaction (PCR) products in 72 B-cell precursor-ALL (BCP-ALL) cell lines established from Japanese patients. We also quantified their ARID5B expression levels by real-time reverse transcription PCR, and determined their 50% inhibitory concentration (IC50) values by alamarBlue assays in nine representative chemotherapeutic agents used for ALL treatment. Results: No significant associations were observed in genotypes of the susceptibility-linked single nucleotide polymorphisms (SNPs) and the relapsed-linked SNPs with ARID5B gene expression levels. Of note, IC50 values of vincristine (VCR) (median IC50: 39.6 ng/ml) in 12 cell lines with homozygous genotype of risk allele (C) in the relapse-linked rs4948488 were significantly higher (p = 0.031 in Mann–Whitney U test) than those (1.04 ng/ml) in 60 cell lines with heterozygous or homozygous genotypes of the non-risk allele (T). Furthermore, the IC50 values of mafosfamide [Maf; active metabolite of cyclophosphamide (CY)] and cytarabine (AraC) tended to be associated with the genotype of rs4948488. Similar associations were observed in genotypes of the relapse-linked rs2893881 and rs6479778, but not in those of the susceptibility-linked rs7923074 and rs10821936. In addition, the IC50 values of methotrexate (MTX) were significantly higher (p = 0.023) in 36 cell lines with lower ARID5B gene expression (median IC50: 37.1 ng/ml) than those in the other 36 cell lines with higher expression (16.9 ng/ml). Conclusion: These observations in 72 BCP-ALL cell lines suggested that the risk allele of the relapse-linked SNPs of ARID5B may be involved in a higher relapse rate because of resistance to chemotherapeutic agents such as VCR, CY, and AraC. In addition, lower ARID5B gene expression may be associated with MTX resistance. [ABSTRACT FROM AUTHOR]

A heritable polymorphism within regulatory sequences of the LMO1 gene is associated with its elevated expression and increased susceptibility to develop neuroblastoma, but the oncogenic pathways downstream of the LMO1 transcriptional co-regulatory protein are unknown. Our ChIP-seq and RNA-seq analyses reveal that a key gene directly regulated by LMO1 and MYCN is ASCL1, which encodes a basic helix-loop-helix transcription factor. Regulatory elements controlling ASCL1 expression are bound by LMO1, MYCN and the transcription factors GATA3, HAND2, PHOX2B, TBX2 and ISL1—all members of the adrenergic (ADRN) neuroblastoma core regulatory circuitry (CRC). ASCL1 is required for neuroblastoma cell growth and arrest of differentiation. ASCL1 and LMO1 directly regulate the expression of CRC genes, indicating that ASCL1 is a member and LMO1 is a coregulator of the ADRN neuroblastoma CRC. Polymorphisms in LMO1 are associated with increased susceptibility to develop neuroblastoma. Here, the authors show that LMO1 directly induces the transcription factor ASCL1, which regulates the differentiation of neurons, demonstrating that ASCL1 is part of the adrenergic neuroblastoma core regulatory circuit. [ABSTRACT FROM AUTHOR]

JMML is an aggressive hematopoietic malignancy of early childhood, and allogeneic HSCT is the only curative treatment for this disease. Umbilical cord blood is one of donor sources for HSCT in JMML patients who do not have an HLA‐compatible relative, but engraftment failure remains a major problem. Here, we report two cases of JMML who were successfully rescued by HSCT from an HLA‐mismatched parent after development of primary engraftment failure following unrelated CBT. Both patients had severe splenomegaly and underwent unrelated CBT from an HLA‐mismatched donor. Immediately after diagnosis of engraftment failure, both patients underwent HSCT from their parent. For the second HSCT, we used RIC regimens consisting of FLU, CY, and a low dose of rabbit ATG with or without TBI and additionally administered ETP considering their persistent severe splenomegaly. Both patients achieved engraftment without severe treatment‐related adverse effects. After engraftment of second HSCT, their splenomegaly was rapidly regressed, and both patients showed no sign of relapse for over 4 years. These observations demonstrate that HSCT from an HLA‐mismatched parent could be a feasible salvage treatment for primary engraftment failure in JMML patients. [ABSTRACT FROM AUTHOR]

T cell acute lymphoblastic leukemia (T-ALL) is an aggressive immature T cell cancer. Mutations in IL7R have been analyzed genetically, but downstream effector functions such as STAT5A and STAT5B hyperactivation are poorly understood. Here, we studied the most frequent and clinically challenging [STAT5B.sup.N642H] driver in T cell development and immature T cell cancer onset and compared it with STAT5A hyperactive variants in transgenic mice. Enhanced STAT5 activity caused disrupted T cell development and promoted an early T cell progenitor-ALL phenotype, with upregulation of genes involved in T cell receptor (TCR) signaling, even in absence of surface TCR. Importantly, TCR pathway genes were overexpressed in human T-ALL and mature T cell cancers and activation of TCR pathway kinases was STAT5 dependent. We confirmed STAT5 binding to these genes using ChIP-Seq analysis in human T-ALL cells, which were sensitive to pharmacologic inhibition by dual STAT3/5 degraders or ZAP70 tyrosine kinase blockers in vitro and in vivo. We provide genetic and biochemical proof that STAT5A and STAT5B hyperactivation can initiate T-ALL through TCR pathway hijacking and suggest similar mechanisms for other T cell cancers. Thus, STAT5 or TCR component blockade are targeted therapy options, particularly in patients with chemoresistant clones carrying [STAT5B.sup.N642H]., Introduction Acute lymphoblastic leukemia (ALL) is subdivided into B and T cell acute lymphoblastic leukemia (T-ALL), of which T-ALL represents up to 15% of pediatric and 25% of adult ALL [...]