HLA-haploidentical T-cell receptor αßT/B-cell-depleted stem cell transplantation for Fanconi anemia.

HLA-haploidentical stem cell transplantation (haplo-SCT) using post-transplant high-dose cyclophosphamide (PT-CY) is an alternative choice when a suitable donors is unavailable. However, PT-CY is difficult in patients with Fanconi anemia (FA) due to their high vulnerability to alkylating agents. For FA, we prefer haplo-SCT by T-cell receptor αßT-cell and B-cell depletion (αßT/B-depleted haplo-SCT), which can reduce the risks of PT-CY-related complications and graft-versus-host disease (GVHD). An 11-year-old boy with diagnosed FA (FANCG mutation) and bone marrow failure was to receive αßT/B-depleted haplo-SCT from his father (HLA 4/8 allele matched) due to absence of an HLA-matched donors. αßT/B-depleted peripheral blood stem cells (CD34 + cell count, 1.17 × 107/kg; αß + T-cell count, 1.3 × 105/kg) were infused following conditioning consisting of fludarabine (150 mg/m2), cyclophosphamide (40 mg/kg), anti-thymocyte globulin (5 mg/kg), rituximab (375 mg/m2), and thoraco-abdominal irradiation (3 Gy). Tacrolimus was used for GVHD prophylaxis until day + 30. Neutrophil engraftment was achieved on day + 9, and complete chimerism was confirmed on days + 28 and + 96. At 12-month post-SCT, the patient was well without GVHD or any other complications. αßT/B-depleted haplo-SCT is a good choice not only for patients unsuitable for PT-CY, but also for all pediatric recipients to reduce SCT-related complications.

Prognostic and Pharmacotypic Heterogeneity of Hyperdiploidy in Childhood ALL.

PURPOSE: High hyperdiploidy, the largest and favorable subtype of childhood ALL, exhibits significant biological and prognostic heterogeneity. However, factors contributing to the varied treatment response and the optimal definition of hyperdiploidy remain uncertain. METHODS: We analyzed outcomes of patients treated on two consecutive frontline ALL protocols, using six different definitions of hyperdiploidy: chromosome number 51-67 (Chr51-67); DNA index (DI; DI1.16-1.6); United Kingdom ALL study group low-risk hyperdiploid, either trisomy of chromosomes 17 and 18 or +17 or +18 in the absence of +5 and +20; single trisomy of chromosome 18; double trisomy of chromosomes 4 and 10; and triple trisomy (TT) of chromosomes 4, 10, and 17. Additionally, we characterized ALL ex vivo pharmacotypes across eight main cytotoxic drugs. RESULTS: Among 1,096 patients analyzed, 915 had B-ALL and 634 had pharmacotyping performed. In univariate analysis, TT emerged as the most favorable criterion for event-free survival (EFS; 10-year EFS, 97.3% v 86.8%; P = .0003) and cumulative incidence of relapse (CIR; 10-year CIR, 1.4% v 8.8%; P = .002) compared with the remaining B-ALL. In multivariable analysis, accounting for patient numbers using the akaike information criterion (AIC), DI1.16-1.6 was the most favorable criterion, exhibiting the best AIC for both EFS (hazard ratio [HR], 0.45; 95% CI, 0.23 to 0.88) and CIR (HR, 0.45; 95% CI, 0.21 to 0.99). Hyperdiploidy and subgroups with favorable prognoses exhibited notable sensitivities to asparaginase and mercaptopurine. Specifically, asparaginase sensitivity was associated with trisomy of chromosomes 16 and 17, whereas mercaptopurine sensitivity was linked to gains of chromosomes 14 and 17. CONCLUSION: Among different definitions of hyperdiploid ALL, DI is optimal based on independent prognostic impact and also the large proportion of low-risk patients identified. Hyperdiploid ALL exhibited particular sensitivities to asparaginase and mercaptopurine, with chromosome-specific associations.

Ex vivo Drug Sensitivity Imaging-based Platform for Primary Acute Lymphoblastic Leukemia Cells.

Resistance of acute lymphoblastic leukemia (ALL) cells to chemotherapy, whether present at diagnosis or acquired during treatment, is a major cause of treatment failure. Primary ALL cells are accessible for drug sensitivity testing at the time of new diagnosis or at relapse, but there are major limitations with current methods for determining drug sensitivity ex vivo. Here, we describe a functional precision medicine method using a fluorescence imaging platform to test drug sensitivity profiles of primary ALL cells. Leukemia cells are co-cultured with mesenchymal stromal cells and tested with a panel of 40 anti-leukemia drugs to determine individual patterns of drug resistance and sensitivity ("pharmacotype"). This imaging-based pharmacotyping assay addresses the limitations of prior ex vivo drug sensitivity methods by automating data analysis to produce high-throughput data while requiring fewer cells and significantly decreasing the labor-intensive time required to conduct the assay. The integration of drug sensitivity data with genomic profiling provides a basis for rational genomics-guided precision medicine. Key features Analysis of primary acute lymphoblastic leukemia (ALL) blasts obtained at diagnosis from bone marrow aspirate or peripheral blood. Experiments are performed ex vivo with mesenchymal stromal cell co-culture and require four days to complete. This fluorescence imaging-based protocol enhances previous ex vivo drug sensitivity assays and improves efficiency by requiring fewer primary cells while increasing the number of drugs tested to 40. It takes approximately 2-3 h for sample preparation and processing and a 1.5-hour imaging time. Graphical overview.

Preclinical pharmacokinetic and pharmacodynamic evaluation of dasatinib and ponatinib for the treatment of T-cell acute lymphoblastic leukemia.

LCK is a novel therapeutic target in ~40% of T-cell acute lymphoblastic leukemia (T-ALL), and dasatinib and ponatinib can act as LCK inhibitors with therapeutic effects. We herein report a comprehensive preclinical pharmacokinetic and pharmacodynamic evaluation of dasatinib and ponatinib in LCK-activated T-ALL. In 51 human T-ALL cases, these two drugs showed similar patterns of cytotoxic activity, with ponatinib being slightly more potent. Given orally in mice, ponatinib was associated with slower clearance with a longer Tmax and higher AUC0-24 h, although maximum pLCK inhibition was comparable between the two drugs. After establishing the exposure-to-response models, we simulated the steady-state pLCK inhibitory effects of each drug at currently approved dosages in humans: dasatinib at 140 mg and ponatinib at 45 mg once daily are both sufficient to achieve >50% pLCK inhibition for 13.0 and 13.9 h/day, respectively, comparable to pharmacodynamic profiles of these agents in BCR::ABL1 leukemias. Moreover, we developed a dasatinib-resistant T-ALL cell line model with LCK T316I mutation, in which ponatinib retained partial activity against LCK. In conclusion, we described the pharmacokinetic and pharmacodynamic profiles of dasatinib and ponatinib as LCK inhibitors in T-ALL, providing critical data for the development of human trials of these agents.

Cord Blood Transplantation in 2 Infants Presenting Monosomy 7 Clonal Hematopoiesis: SAMD9 / SAMD9L Germline Mutation.

Recently, germline mutations in SAMD9 and SAMD9L were increasingly found in children with monosomy 7. We report the outcomes in 2 infants with the SAMD9/SAMD9L variant, who presented with anemia and thrombocytopenia (patient 1), and neutropenia and nonsymptomatic white-matter-encephalopathy (patient 2). Both patients received cord blood transplantation and experienced critical post-cord blood transplantation adverse events; patients 1 and 2 developed fulminant engraftment syndrome and life-threatening graft-versus-host disease, respectively. Of note, selective loss of chromosome 7 in bone marrow-derived CD34 + cells was inferred.

A novel Menin-MLL1 inhibitor, DS-1594a, prevents the progression of acute leukemia with rearranged MLL1 or mutated NPM1.

BACKGROUND: Mixed lineage leukemia 1-rearranged (MLL1-r) acute leukemia patients respond poorly to currently available treatments and there is a need to develop more effective therapies directly disrupting the Menin‒MLL1 complex. Small-molecule-mediated inhibition of the protein‒protein interaction between Menin and MLL1 fusion proteins is a potential therapeutic strategy for patients with MLL1-r or mutated-nucleophosmin 1 (NPM1c) acute leukemia. In this study, we preclinically evaluated the new compound DS-1594a and its salts. METHODS: We evaluated the preclinical efficacy of DS-1594a as well as DS-1594a·HCl (the HCl salt of DS-1594a) and DS-1594a·succinate (the succinic acid salt of DS-1594a, DS-1594b) in vitro and in vivo using acute myeloid leukemia (AML)/acute lymphoblastic leukemia (ALL) models. RESULTS: Our results showed that MLL1-r or NPM1c human leukemic cell lines were selectively and highly sensitive to DS-1594a·HCl, with 50% growth inhibition values < 30 nM. Compared with cytrabine, the standard chemotherapy drug as AML therapy, both DS-1594a·HCl and DS-1594a·succinate mediated the eradication of potential leukemia-initiating cells by enhancing differentiation and reducing serial colony-forming potential in MLL1-r AML cells in vitro. The results were confirmed by flow cytometry, RNA sequencing, RT‒qPCR and chromatin immunoprecipitation sequencing analyses. DS-1594a·HCl and DS-1594a·succinate exhibited significant antitumor efficacy and survival benefit in MOLM-13 cell and patient-derived xenograft models of MLL1-r or NPM1c acute leukemia in vivo. CONCLUSION: We have generated a novel, potent, orally available small-molecule inhibitor of the Menin-MLL1 interaction, DS-1594a. Our results suggest that DS-1594a has medicinal properties distinct from those of cytarabine and that DS-1594a has the potential to be a new anticancer therapy and support oral dosing regimen for clinical studies (NCT04752163).

Pharmacotypes across the genomic landscape of pediatric acute lymphoblastic leukemia and impact on treatment response.

Contemporary chemotherapy for childhood acute lymphoblastic leukemia (ALL) is risk-adapted based on clinical features, leukemia genomics and minimal residual disease (MRD); however, the pharmacological basis of these prognostic variables remains unclear. Analyzing samples from 805 children with newly diagnosed ALL from three consecutive clinical trials, we determined the ex vivo sensitivity of primary leukemia cells to 18 therapeutic agents across 23 molecular subtypes defined by leukemia genomics. There was wide variability in drug response, with favorable ALL subtypes exhibiting the greatest sensitivity to L-asparaginase and glucocorticoids. Leukemia sensitivity to these two agents was highly associated with MRD although with distinct patterns and only in B cell ALL. We identified six patient clusters based on ALL pharmacotypes, which were associated with event-free survival, even after adjusting for MRD. Pharmacotyping identified a T cell ALL subset with a poor prognosis that was sensitive to targeted agents, pointing to alternative therapeutic strategies. Our study comprehensively described the pharmacological heterogeneity of ALL, highlighting opportunities for further individualizing therapy for this most common childhood cancer.

Monogenic inflammatory bowel disease with STXBP2 mutations is not resolved by hematopoietic stem cell transplantation but can be alleviated via immunosuppressive drug therapy.

STXBP2, encoding syntaxin-binding protein 2, is involved in intracellular organelle trafficking and is associated with familial hemophagocytic lymphohistiocytosis type 5. Although STXBP2 mutations reportedly cause monogenic inflammatory bowel disease, the clinical course and underlying pathogenic mechanisms remain unclear. We identified a novel mutation in STXBP2 [c.1197delC, p.Ala400fs] in a boy with congenital intractable diarrhea and hemophagocytic lymphohistiocytosis (HLH). HLH was treated with intravenous prednisolone, cyclosporine, and dexamethasone palmitate. Hematopoietic stem cell transplantation (HSCT) along with prophylaxis for graft-versus-host-disease was performed at 5 months of age. Additionally, colonoscopies done before and after HSCT showed mild colitis with cryptitis. The patient showed elevated fecal calprotectin levels and persistent diarrhea even after HSCT and required partial parenteral nutrition. While anti-inflammatory treatment reduced diarrhea, it was not completely normalized even after HSCT, suggesting that the pathogenesis of inflammatory bowel disease associated with STXBP2 mutations involves both hyperinflammation and functional epithelial barrier defects.

Fatal X-linked lymphoproliferative disease type 1-associated limbic encephalitis with positive anti-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor antibody.

BACKGROUND: X-linked lymphoproliferative disease type 1 (XLP1) is a rare monogenic immune dysregulation disorder caused by a deficiency of a signaling lymphocyte activation molecule-associated protein (SAP). While many patients with XLP1 present with fatal hemophagocytic lymphohistiocytosis upon Epstein Barr virus (EBV) infection, a small fraction present with limbic encephalitis in the absence of EBV infection. It is poorly understood why SAP deficiency may cause limbic encephalitis in XLP1. CASE: A 12-year-old boy presented with seizures, changes in personality, memory loss, and cognitive deficits during treatment for interstitial pneumonia. A diagnosis of limbic encephalitis was made. Despite treatment against CD8+ T cell-mediated autoimmunity with intravenous methylprednisolone, dexamethasone, intravenous immunoglobulin, plasma exchange, cyclosporine, weekly etoposide, mycophenolate mofetil, and adalimumab, encephalitis progressed until the patient died after one month of treatment intitiation. Post-mortem genetic testing revealed a de novo SH2D1A truncating mutation. Tests for EBV infection were negative. Initial spinal fluid revealed markedly elevated protein levels, mild pleocytosis, and elevation of two chemokines (C-X-C motif chemokine ligand [CXCL] 10 and CXCL 13). Moreover, initial spinal fluid was tested positive for anti-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) autoantibody. DISCUSSION: In XLP1-associated limbic encephalitis, anti-AMPAR autoantibody production by the dysregulated immune system due to SAP deficiency might be a pathogenic mechanism of central nervous system manifestations. In addition to the standard treatment for XLP1, targeted treatment against B-cell-mediated immunity might be indicated for patients with XLP1-associated limbic encephalitis.

Amino acid stress response genes promote L-asparaginase resistance in pediatric acute lymphoblastic leukemia.

Understanding the genomic and epigenetic mechanisms of drug resistance in pediatric acute lymphoblastic leukemia (ALL) is critical for further improvements in treatment outcomes. The role of transcriptomic response in conferring resistance to l-asparaginase (LASP) is poorly understood beyond asparagine synthetase (ASNS). We defined reproducible LASP response genes in LASP-resistant and LASP-sensitive ALL cell lines as well as primary leukemia samples from newly diagnosed patients. Defining target genes of the amino acid stress response-related transcription factor activating transcription factor 4 (ATF4) in ALL cell lines using chromatin immunoprecipitation sequencing (ChIP-seq) revealed 45% of genes that changed expression after LASP treatment were direct targets of the ATF4 transcription factor, and 34% of these genes harbored LASP-responsive ATF4 promoter binding events. SLC7A11 was found to be a response gene in cell lines and patient samples as well as a direct target of ATF4. SLC7A11 was also one of only 2.4% of LASP response genes with basal level gene expression that also correlated with LASP ex vivo resistance in primary leukemia cells. Experiments using chemical inhibition of SLC7A11 with sulfasalazine, gene overexpression, and partial gene knockout recapitulated LASP resistance or sensitivity in ALL cell lines. These findings show the importance of assessing changes in gene expression following treatment with an antileukemic agent for its association with drug resistance and highlight that many response genes may not differ in their basal expression in drug-resistant leukemia cells.

Genome-wide CRISPR/Cas9 screening identifies determinant of panobinostat sensitivity in acute lymphoblastic leukemia.

Epigenetic alterations, including histone acetylation, contribute to the malignant transformation of hematopoietic cells and disease progression, as well as the emergence of chemotherapy resistance. Targeting histone acetylation provides new strategies for the treatment of cancers. As a pan-histone deacetylase inhibitor, panobinostat has been approved by the US Food and Drug Administration for the treatment of multiple myeloma and has shown promising antileukemia effects in acute lymphoblastic leukemia (ALL). However, the underlying drug resistance mechanism in ALL remains largely unknown. Using genome-wide Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRISPR-associated (Cas)9 (CRISPR/Cas9) screening, we identified mitochondrial activity as the driver of panobinostat resistance in ALL. Mechanistically, ectopic SIRT1 expression activated mitochondrial activity and sensitized ALL to panobinostat through activating mitochondria-related apoptosis pathway. Meanwhile, the transcription level of SIRT1 was significantly associated with panobinostat sensitivity across diverse tumor types and thus could be a potential biomarker of panobinostat response in cancers. Our data suggest that patients with higher SIRT1 expression in cancer cells might benefit from panobinostat treatment, supporting the implementation of combinatorial therapy with SIRT1 or mitochondrial activators to overcome panobinostat resistance.

A Prospective Viral Monitoring Study After Pediatric Allogeneic Hematopoietic Stem Cell Transplantation for Malignant and Nonmalignant Diseases.

Allogeneic hematopoietic stem cell transplantation (HSCT) is the treatment of choice for many high-risk pediatric hematological malignant diseases (MD) and several nonmalignant diseases (NMD), including primary immune deficiencies. Infections must be managed to obtain better outcomes after HSCT. In this prospective observational study, viral monitoring was performed on 74 pediatric patients with MD and NMD who underwent HSCT. The incidence, risk factors, and impact of common opportunistic viral infections occurring within the first 100 days following HSCT were assessed. The viral pathogens included human herpesviruses, BK polyomavirus (BKV), adenovirus, parvovirus B19, and hepatitis B virus. In total, 52 (70%) patients had viral DNAemia, and 53% and 41% of patients developed human herpesvirus 6 (HHV-6) and cytomegalovirus (CMV) DNAemia, respectively. The risk factors were as follows: negative CMV serology for any viral infections; age ≥ 2 years and negative CMV serology for HHV-6; age ≥5 years and female sex for BKV. The risk of viral infection did not significantly differ between MD and NMD, and no risk factor was identified for viral disease, likely because of the small sample numbers. However, despite the absence of symptoms, CMV DNAemia was found to increase the risk of mortality. The findings of the current study could improve the risk stratification and the management of pediatric HSCT recipients.

Network-based systems pharmacology reveals heterogeneity in LCK and BCL2 signaling and therapeutic sensitivity of T-cell acute lymphoblastic leukemia.

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy, and novel therapeutics are much needed. Profiling patient leukemia' drug sensitivities ex vivo, we discovered that 44.4% of childhood and 16.7% of adult T-ALL cases exquisitely respond to dasatinib. Applying network-based systems pharmacology analyses to examine signal circuitry, we identified preTCR-LCK activation as the driver of dasatinib sensitivity, and T-ALL-specific LCK dependency was confirmed in genome-wide CRISPR-Cas9 screens. Dasatinib-sensitive T-ALLs exhibited high BCL-XL and low BCL2 activity and venetoclax resistance. Discordant sensitivity of T-ALL to dasatinib and venetoclax is strongly correlated with T-cell differentiation, particularly with the dynamic shift in LCK vs. BCL2 activation. Finally, single-cell analysis identified leukemia heterogeneity in LCK and BCL2 signaling and T-cell maturation stage, consistent with dasatinib response. In conclusion, our results indicate that developmental arrest in T-ALL drives differential activation of preTCR-LCK and BCL2 signaling in this leukemia, providing unique opportunities for targeted therapy.

Integrative genomic analyses reveal mechanisms of glucocorticoid resistance in acute lymphoblastic leukemia.

Identification of genomic and epigenomic determinants of drug resistance provides important insights for improving cancer treatment. Using agnostic genome-wide interrogation of mRNA and miRNA expression, DNA methylation, SNPs, CNAs and SNVs/Indels in primary human acute lymphoblastic leukemia cells, we identified 463 genomic features associated with glucocorticoid resistance. Gene-level aggregation identified 118 overlapping genes, 15 of which were confirmed by genome-wide CRISPR screen. Collectively, this identified 30 of 38 (79%) known glucocorticoid-resistance genes/miRNAs and all 38 known resistance pathways, while revealing 14 genes not previously associated with glucocorticoid-resistance. Single cell RNAseq and network-based transcriptomic modelling corroborated the top previously undiscovered gene, CELSR2. Manipulation of CELSR2 recapitulated glucocorticoid resistance in human leukemia cell lines and revealed a synergistic drug combination (prednisolone and venetoclax) that mitigated resistance in mouse xenograft models. These findings illustrate the power of an integrative genomic strategy for elucidating genes and pathways conferring drug resistance in cancer cells.

Genetic defects in hematopoietic transcription factors and predisposition to acute lymphoblastic leukemia.

Recent genome-wide studies have revealed a plethora of germline variants that significantly influence the susceptibility to acute lymphoblastic leukemia (ALL), thus providing compelling evidence for genetic inheritance of this blood cancer. In particular, hematopoietic transcription factors (eg, ETV6, PAX5, IKZF1) are most frequently implicated in familial ALL, and germline variants in these genes confer strong predisposition (albeit with incomplete penetrance). Studies of germline risk factors for ALL provide unique insights into the molecular etiology of this leukemia.

Therapy-related Secondary Malignancy After Treatment of Childhood Malignancy: Cases from a Single Center.

BACKGROUND: Therapeutic outcomes for childhood malignancy have dramatically improved. However, secondary malignancies are a major concern, as they greatly affect the quality of life of survivors. This retrospective study evaluated the cumulative incidence, clinical features, and outcomes of secondary malignancies at Nippon Medical School Hospital. METHODS: We examined data from 275 cases of primary childhood malignancy diagnosed between 1980 and 2014. Information regarding treatment of the primary malignancy, including irradiation dose, site, and cumulative dose of anticancer drugs, was assessed. We also collected data on secondary malignancy, including patient sex, age at diagnosis, malignancy site, time from primary to secondary malignancy, and outcomes. RESULTS: Secondary malignancies developed in 11 patients and included acute myeloid leukemia (AML) (4), meningioma (4), Ewing sarcoma (1), germ cell tumor (1), and malignant parotid gland tumor (1). The primary malignancies included acute lymphoblastic leukemia (ALL) (9), non-Hodgkin lymphoma (1) and brain tumor (1). In 7 of the 9 ALL patients, chemoradiotherapy was the primary treatment. The meningiomas and 1 solid tumor developed within the radiation field. All AMLs and meningiomas developed within 5 years and after 20 years, respectively, of the primary diagnosis. The 10- and 20-year cumulative incidence rates for secondary malignancy in our hospital were 1.9% and 5.8%, respectively. CONCLUSIONS: Our results revealed that the type of secondary malignancy depends on the interval after the end of treatment for primary malignancy. Meningioma, notably, develops many years after completion of primary malignancy treatment. Early detection during long-term follow-up is therefore essential.

Genome-Wide Association Study of Susceptibility Loci for T-Cell Acute Lymphoblastic Leukemia in Children.

BACKGROUND: Acute lymphoblastic leukemia (ALL) is the most common cancer in children and can arise in B or T lymphoid lineages. Although risk loci have been identified for B-ALL, the inherited basis of T-ALL is mostly unknown, with a particular paucity of genome-wide investigation of susceptibility variants in large patient cohorts. METHODS: We performed a genome-wide association study (GWAS) in 1191 children with T-ALL and 12 178 controls, with independent replication using 117 cases and 5518 controls. The associations were tested using an additive logistic regression model. Top risk variants were tested for effects on enhancer activity using luciferase assay. All statistical tests were two sided. RESULTS: A novel risk locus in the USP7 gene (rs74010351, odds ratio [OR] = 1.44, 95% confidence interval [CI] = 1.27 to 1.65, P = 4.51 × 10-8) reached genome-wide significance in the discovery cohort, with independent validation (OR = 1.51, 95% CI = 1.03 to 2.22, P = .04). The USP7 risk allele was overrepresented in individuals of African descent, thus contributing to the higher incidence of T-ALL in this race/ethnic group. Genetic changes in USP7 (germline variants or somatic mutations) were observed in 56.4% of T-ALL with TAL1 overexpression, statistically significantly higher than in any other subtypes. Functional analyses suggested this T-ALL risk allele is located in a putative cis-regulatory DNA element with negative effects on USP7 transcription. Finally, comprehensive comparison of 14 susceptibility loci in T- vs B-ALL pointed to distinctive etiology of these leukemias. CONCLUSIONS: These findings indicate strong associations between inherited genetic variation and T-ALL susceptibility in children and shed new light on the molecular etiology of ALL, particularly commonalities and differences in the biology of the two major subtypes (B- vs T-ALL).

PDGFRB mutation and tyrosine kinase inhibitor resistance in Ph-like acute lymphoblastic leukemia.

Philadelphia chromosome (Ph)-like acute lymphoblastic leukemia (ALL) comprises ∼10% to 15% of childhood ALL cases, many of which respond exquisitely to tyrosine kinase inhibitors (TKIs), for example, imatinib in PDGFRB-rearranged ALL. However, some cases developed drug resistance to TKIs and the mechanisms are poorly understood. In this study, we identified a novel PDGFRB fusion gene, namely AGGF1-PDGFRB, and functionally characterized its oncogenic potential in vitro. Further genomic profiling of longitudinally collected samples during treatment revealed the emergence of a mutation, PDGFRBC843G , which directly conferred resistance to all generations of ABL TKIs, including imatinib, dasatinib, nilotinib, and ponatinib. PDGFRB-mutant leukemia cells are highly sensitive to multitarget kinase inhibitor CHZ868, suggesting potential therapeutic options for some patients resistant to ABL TKIs. In summary, we describe a complex clonal evolution pattern in Ph-like ALL and identified a novel PDGFRB point mutation that drives leukemia relapse after ABL TKI treatment.