Single-cell genomics details the maturation block in BCP-ALL and identifies therapeutic vulnerabilities in DUX4-r cases.

B cell progenitor acute lymphoblastic leukemia (BCP-ALL) is the most common childhood malignancy, driven by multiple genetic alterations that cause maturation arrest and accumulation of abnormal progenitor B cells. Current treatment protocols with chemotherapy have led to favorable outcomes but are associated with significant toxicity and risk of side effects, highlighting the necessity for highly effective, less toxic, targeted drugs, even in subtypes with a favorable outcome. Here, we used multimodal single-cell sequencing to delineate the transcriptional, epigenetic, and immunophenotypic characteristics of 23 childhood BCP-ALLs, belonging to the BCR::ABL1-positive, ETV6::RUNX1-positive, high hyperdiploid, and recently discovered DUX4-rearranged (DUX4-r) subtypes. Projection of the ALL cells along the normal hematopoietic differentiation axis revealed a diversity in the maturation pattern between the different BCP-ALL subtypes. Whereas the BCR::ABL1-, ETV6::RUNX1-positive, and high hyperdiploidy cells mainly showed similarities to normal pro-B cells, the DUX4-r ALL cells also displayed transcriptional signatures resembling mature B cells. Focusing on the DUX4-r subtype, we found that the blast population displayed multilineage priming toward non-hematopoietic cells, myeloid, and T cell lineages, but also an activation of PI3K/AKT signaling that sensitized the cells to PI3K inhibition in vivo. Given the multilineage priming of the DUX4-r blasts with aberrant expression of the myeloid marker CD371 (CLL-1), we generated chimeric antigen receptor T cells, which effectively eliminated DUX4-r ALL cells in vivo. These results provide a detailed characterization of BCP-ALL at the single-cell level and reveal therapeutic vulnerabilities in the DUX4-r subtype with implications for the understanding of ALL biology and new therapeutic strategies.

Thromboembolism in acute lymphoblastic leukemia: results of NOPHO ALL2008 protocol treatment in patients aged 1 to 45 years.

Thromboembolism frequently occurs during acute lymphoblastic leukemia (ALL) therapy. We prospectively registered thromboembolic events during the treatment of 1772 consecutive Nordic/Baltic patients with ALL aged 1 to 45 years who were treated according to the Nordic Society of Pediatric Hematology and Oncology ALL2008 protocol (July 2008-April 2017). The 2.5-year cumulative incidence of thromboembolism (N = 137) was 7.9% (95% confidence interval [CI], 6.6-9.1); it was higher in patients aged at least 10 years (P < .0001). Adjusted hazard ratios (HRas) were associated with greater age (range, 10.0-17.9 years: HRa, 4.9 [95% CI, 3.1-7.8; P < .0001]; 18.0-45.9 years: HRa, 6.06 [95% CI, 3.65-10.1; P < .0001]) and mediastinal mass at ALL diagnosis (HRa, 2.1; 95% CI, 1.0-4.3; P = .04). In a multiple absolute risk regression model addressing 3 thromboembolism risk factors, age at least 10 years had the largest absolute risk ratio (RRage, 4.7 [95% CI, 3.1-7.1]; RRenlarged lymph nodes, 2.0 [95% CI, 1.2-3.1]; RRmediastinal mass, 1.6 [95% CI, 1.0-2.6]). Patients aged 18.0 to 45.9 years had an increased hazard of pulmonary embolism (HRa, 11.6; 95% CI, 4.02-33.7; P < .0001), and patients aged 10.0 to 17.9 years had an increased hazard of cerebral sinus venous thrombosis (HRa, 3.3; 95% CI, 1.5-7.3; P = .003) compared with children younger than 10.0 years. Asparaginase was truncated in 38/128 patients with thromboembolism, whereas thromboembolism diagnosis was unassociated with increased hazard of relapse (P = .6). Five deaths were attributable to thromboembolism, and patients younger than 18.0 years with thromboembolism had increased hazard of dying compared with same-aged patients without thromboembolism (both P ≤ .01). In conclusion, patients aged at least 10 years could be candidates for preemptive antithrombotic prophylaxis. However, the predictive value of age 10 years or older, enlarged lymph nodes, and mediastinal mass remain to be validated in another cohort.

Individualized 6-mercaptopurine increments in consolidation treatment of childhood acute lymphoblastic leukemia: A NOPHO randomized controlled trial.

OBJECTIVES: This randomized controlled trial tested the hypothesis that children with non-high-risk acute lymphoblastic leukemia could benefit from individualized 6-mercaptopurine increments during consolidation therapy (NCT00816049). Primary and secondary end points were end of consolidation minimal residual disease (MRD) positivity and event-free survival. METHODS: 392 patients were randomized to experimental and 396 to standard therapy. Patients allocated to standard therapy received oral 6-mercaptopurine (25 mg/m2 /day) from days 30 to 85, while the experimental arm received stepwise increments of additional 25 mg/m2 /day beginning on days 50 and/or 71 unless dose-limiting myelosuppression had occurred. RESULTS: In the experimental arm, 166 patients (42%) received one dose increment, and 62 (16%) received two. Fifty-seven of 387 (15%) patients in the experimental arm were MRD positive at end of consolidation vs 77 of 389 (20%) in the control arm (P = .08). Five-year probability of event-free survival was 0.89 (95% CI: 0.85-0.93) in the experimental arm vs 0.93 (0.90-0.96) in the control arm (P = .13). The median accumulated length of 6-mercaptopurine treatment interruptions was 7 (IQR 2-12) in the experimental arm vs 4 (IQR 0-10) in the control arm (P = .002). CONCLUSION: This study found no benefit from individualized 6-mercaptopurine increments compared to standard therapy.