Current hemophagocytic lymphohistiocytosis 2004 (HLH-2004)-based diagnostic criteria for familial hemophagocytic lymphohistiocytosis (FHL) are based on expert opinion. Here, we performed a case-control study to test and possibly improve these criteria. We also developed 2 complementary expert opinion-based diagnostic strategies for FHL in patients with signs/symptoms suggestive of HLH, based on genetic and cellular cytotoxicity assays. The cases (N = 366) were children aged <16 years with verified familial and/or genetic FHL (n = 341) or Griscelli syndrome type 2 (n = 25); 276 from the HLH-94/HLH-2004 databases and 90 from the Italian HLH Registry. All fulfilled the HLH-94/HLH-2004 patient inclusion criteria. Controls were 374 children with systemic-onset juvenile idiopathic arthritis (sJIA) and 329 + 361 children in 2 cohorts with febrile infections that could be confused with HLH and sepsis, respectively. To provide complete data sets, multiple imputations were performed. The optimal model, based on 17 variables studied, revealed almost similar diagnostic thresholds as the existing criteria, with accuracy 99.1% (sensitivity 97.1%; specificity 99.5%); the original HLH-2004 criteria had accuracy 97.4% (sensitivity 99.0%; specificity 97.1%). Because cellular cytotoxicity assays here constitute a separate diagnostic strategy, HLH-2004 criteria without natural killer (NK)-cell function was also studied, which showed accuracy 99.0% (sensitivity, 96.2%; specificity, 99.5%). Thus, we conclude that the HLH-2004 criteria (without NK-cell function) have significant validity in their current form when tested against severe infections or sJIA. It is important to exclude underlying malignancies and atypical infections. In addition, complementary cellular and genetic diagnostic guidelines can facilitate necessary confirmation of clinical diagnosis.

The histone H3 at lysine 27 (H3K27) demethylase lysine demethylase 6A (KDM6A) is a tumor suppressor in multiple cancers, including multiple myeloma (MM). We created isogenic MM cells disrupted for KDM6A and tagged the endogenous protein to facilitate genome-wide studies. KDM6A binds genes associated with immune recognition and cytokine signaling. Most importantly, KDM6A binds and activates NLRC5 and CIITA, which encode regulators of major histocompatibility complex genes. Patient data indicate that NLRC5 and CIITA are downregulated in MM with low KDM6A expression. Chromatin analysis shows that KDM6A binds poised and active enhancers and KDM6A loss led to decreased H3K27ac at enhancers, increased H3K27me3 levels in body of genes bound by KDM6A, and decreased gene expression. Reestablishing histone acetylation with an HDAC3 inhibitor leads to upregulation of major histocompatibility complex expression, offering a strategy to restore immunogenicity of KDM6A-deficient tumors. Loss of Kdm6a in Kirsten rat sarcoma virus (K-RAS)-transformed murine fibroblasts led to increased growth in vivo associated with decreased T-cell infiltration.

In REACH4, a phase 1/2, open-label, single-arm, multicenter study, the pharmacokinetics (PK), efficacy, and safety of ruxolitinib were evaluated in treatment-naïve and steroid-refractory pediatric patients with grade 2 to 4 acute graft-versus-host disease (aGVHD; n = 45). Ruxolitinib dosing was based on age and targeted the exposure in adults receiving 10 mg twice daily; group 1 (aged ≥12 to <18 years) received 10 mg twice daily and preliminary starting doses for groups 2 (aged ≥6 to <12 years) and 3 (aged ≥2 to <6 years) were 5 mg twice daily and 4 mg/m2 twice daily, respectively. The phase 1 primary objective was to assess ruxolitinib PK parameters and define an age-appropriate recommended phase 2 dose (RP2D) for patients aged <12 years. The phase 2 primary objective was to measure the activity of ruxolitinib as assessed by overall response rate (ORR) at day 28; the key secondary objective was to assess the durable ORR at day 56. Ruxolitinib exposure was comparable across age groups; starting doses were confirmed as the RP2D. The median duration of ruxolitinib exposure was 3.8 months (range, 0.3-11.2). ORR in all patients was 84.4% (90% confidence interval [CI], 72.8-92.5) at day 28, with a durable ORR at day 56 of 66.7% (90% CI, 53.4-78.2); high response rates were observed across age groups and in both treatment-naïve and steroid-refractory subgroups. Adverse events were consistent with those expected in patients with aGVHD (anemia, decreased neutrophil and leukocyte count) treated with ruxolitinib. In pediatric patients with aGVHD, ruxolitinib showed clinically meaningful efficacy with no new safety signals. This trial was registered at www.clinicaltrials.gov as #NCT03491215.

Atypical acute promyelocytic leukemia (aAPL) presents a complex landscape of retinoic acid receptor (RAR) fusion genes beyond the well-known PML::RARA fusion. Among these, 31 individually rare RARA and RARG fusion genes have been documented, often reported in the canonical X::RAR bipartite fusion form. Intriguingly, some artificially mimicked bipartite X::RAR fusions respond well to all-trans retinoic acid (ATRA) in vitro, contrasting with the ATRA resistance observed in patients. To unravel the underlying mechanisms, we conducted a comprehensive molecular investigation into the fusion transcripts in 27 RARA fusion gene-positive aAPL (RARA-aAPL) and 21 RARG-aAPL cases. Our analysis revealed an unexpected novel form of X::RAR::X- or X::RAR::Y-type tripartite fusions in certain RARA-aAPL and all RARG-aAPL cases, with shared features and notable differences between these 2 disease subgroups. In RARA-aAPL cases, the occurrence of RARA 3' splices was associated with their 5' fusion partner genes, mapping across the coding region of helix 11_12 (H11_12) within the ligand-binding domain (LBD), resulting in LBD-H12 or H11_12 truncation. In RARG-aAPL cases, RARG 3' splices were consistently localized to the terminus of exon 9, leading to LBD-H11_12 truncation. Significant differences were also observed between RARA and RARG 5' splice patterns. Our analysis also revealed extensive involvement of transposable elements in constructing RARA and RARG 3' fusions, suggesting transposition mechanisms for fusion gene ontogeny. Both protein structural analysis and experimental results highlighted the pivotal role of LBD-H11_12/H12 truncation in driving ATRA unresponsiveness and leukemogenesis in tripartite fusion-positive aAPL, through a protein allosteric dysfunction mechanism.

Abatacept plus calcineurin inhibitors/methotrexate (CNI/MTX) is the first US Food and Drug Administration (FDA)-approved regimen for acute graft-versus-host disease (aGVHD) prophylaxis during unrelated-donor hematopoietic cell transplantation (URD-HCT). Using Center for International Blood and Marrow Transplant Research data, we investigated its impact in patients receiving 7/8 HLA-mismatched unrelated donor (MMUD) or 8/8 HLA-matched unrelated donor (MUD) URD-HCT between 2011 and 2018. Primary outcomes included day-180, 1-year, and 2-year overall survival (OS) and relapse-free survival (RFS) for abatacept + CNI/MTX vs CNI/MTX, CNI/MTX + antithymocyte globulin (ATG), and posttransplant cyclophosphamide-based prophylaxis (PT-Cy). For 7/8 MMUDs, day-180 OS (primary end point supporting FDA approval) was significantly higher for abatacept + CNI/MTX vs CNI/MTX (98% vs 75%; P = .0028). Two-year RFS was significantly higher for abatacept + CNI/MTX vs CNI/MTX (74% vs 49%; P = .0098) and CNI/MTX + ATG (77% vs 35%; P = .0002), and similar vs PT-Cy (72% vs 56%; P = .1058). For 8/8 MUDs, 2-year RFS for abatacept + CNI/MTX was numerically higher vs CNI/MTX (63% vs 52%; P = .1497), with an improved hazard ratio (HR) of 0.46 (0.25-0.86), and vs CNI/MTX + ATG (66% vs 55%; P = .1193; HR, 0.39 [0.21-0.73]), and was similar vs PT-Cy (68% vs 57%; P = .2356; HR, 0.54 [0.26-1.11]). For 7/8 MMUD and 8/8 MUD recipients, abatacept + CNI/MTX prophylaxis improved survival outcomes vs CNI/MTX and CNI/MTX + ATG; outcomes were similar to PT-Cy-based regimens. Abatacept + CNI/MTX may facilitate unrelated donor pool expansion for HCT.

T-cell lymphoblastic lymphoma (T-LBL) and T-cell acute lymphoblastic leukemia (T-ALL) have common and distinguishing clinical and molecular features. Molecular prognostic factors are needed for T-LBL. We assessed the prevalence and prognostic impact of the T-cell receptor β (TRB)::NOTCH1 fusion in 192 pediatric patients with T-LBL and 167 pediatric patients with T-ALL, using novel multiplex polymerase chain reaction and genomic capture high-throughput sequencing techniques. The fusion was detected in 12 patients with T-LBL (6.3%) but in none of the patients with T-ALL (P = .0006, Fisher exact test). In T-LBL, the TRB::NOTCH1 fusion was associated with a significantly higher incidence of relapse (67% vs 17% in gene fusion-negative patients, P < .001, Fisher exact test). The breakpoint in TRB was most frequently located in J2-7 (n = 6). In NOTCH1, the breakpoints varied between exon 24 and 27. Consequently, a truncated NOTCH1 with its dimerization, regulation, and signal transduction domains gets controlled by strong TRB enhancer elements. This study reveals a novel recurrent genetic variant with significant prognostic relevance in T-LBL, which was absent in T-ALL. The TRB::NOTCH1 fusion in T-LBL suggests a possible unique pathogenic mechanism divergent from T-ALL. Further studies will validate the role of the TRB::NOTCH1 fusion as prognostic marker in T-LBL and elucidate its pathogenic mechanisms.

Chronic graft-versus-host disease (cGVHD) is associated with morbidity, mortality, impaired quality of life, prolonged immunosuppressive therapy, and infection risk after allogeneic hematopoietic cell transplantation (HCT). Major strides have occurred in the understanding of cGVHD biology; National Institutes of Health Consensus meetings have refined rigorous approaches to diagnosis, staging, and response criteria; major interventional trials have established standard benchmarks for treatment outcome; and 3 agents to date have been US Food and Drug Administration approved for treating corticosteroid-refractory cGVHD. Promising results from several recent trials have led some, but not others, to conclude that the risk of developing cGVHD is sufficiently low to be considered a major post-HCT complication of the past. We propose that it is time to critically examine the results of contemporary graft-versus-host disease (GVHD) prophylaxis regimens and discuss the state of the science and associated controversies in the spectrum of conclusions reached as to the risk of cGVHD. With these data, the current cGVHD incidence can be most precisely determined, and the present and future burden of cGVHD-affected patients can be accurately modeled. Through review of existing evidence, we highlight unresolved needs and opportunities to refine best GVHD prophylaxis or preemptive therapy approaches and optimize established cGVHD therapy, and make the argument that support of preclinical and clinical research is critical in improving patient outcomes.