In this issue of Blood, Simeoni et al describe exciting results using a high-throughput sequencing (HTS) platform with 63 targeted genes in patients with heritable bleeding and thrombotic disorders, and Stritt et al advance a diaphanous-related formin 1 (DIAPH1) variant as a cause of inherited macrothrombocytopenia (MTP) and hearing loss.,

Idiopathic aplastic anemia (AA) is an immune-mediated and serious form of bone marrow failure. Akin to other autoimmune diseases, we have previously shown that in AA regulatory T cells (Tregs) are reduced in number and function. The aim of this study was to further characterize Treg subpopulations in AA and investigate the potential correlation between specific Treg subsets and response to immunosuppressive therapy (IST) as well as their in vitro expandability for potential clinical use. Using mass cytometry and an unbiased multidimensional analytical approach, we identified 2 specific human Treg subpopulations (Treg A and Treg B) with distinct phenotypes, gene expression, expandability, and function. Treg B predominates in IST responder patients, has a memory/activated phenotype (with higher expression of CD95, CCR4, and CD45RO within FOXP3(hi), CD127(lo) Tregs), expresses the interleukin-2 (IL-2)/STAT5 pathway and cell-cycle commitment genes. Furthermore, in vitro-expanded Tregs become functional and take on the characteristics of Treg B. Collectively, this study identifies human Treg subpopulations that can be used as predictive biomarkers for response to IST in AA and potentially other autoimmune diseases. We also show that Tregs from AA patients are IL-2-sensitive and expandable in vitro, suggesting novel therapeutic approaches such as low-dose IL-2 therapy and/or expanded autologous Tregs and meriting further exploration.

Repair of DNA double-strand breaks (DSBs) by the nonhomologous end-joining pathway (NHEJ) is important not only for repair of spontaneous breaks but also for breaks induced in developing lymphocytes during V(D)J (variable [V], diversity [D], and joining [J] genes) recombination of their antigen receptor loci to create a diverse repertoire. Mutations in the NHEJ factor XLF result in extreme sensitivity for ionizing radiation, microcephaly, and growth retardation comparable to mutations in LIG4 and XRCC4, which together form the NHEJ ligation complex. However, the effect on the immune system is variable (mild to severe immunodeficiency) and less prominent than that seen in deficiencies of NHEJ factors ARTEMIS and DNA-dependent protein kinase catalytic subunit, with defects in the hairpin opening step, which is crucial and unique for V(D)J recombination. Therefore, we aimed to study the role of XLF during V(D)J recombination. We obtained clinical data from 9 XLF-deficient patients and performed immune phenotyping and antigen receptor repertoire analysis of immunoglobulin (Ig) and T-cell receptor (TR) rearrangements, using next-generation sequencing in 6 patients. The results were compared with XRCC4 and LIG4 deficiency. Both Ig and TR rearrangements showed a significant decrease in the number of nontemplated (N) nucleotides inserted by terminal deoxynucleotidyl transferase, which resulted in a decrease of 2 to 3 amino acids in the CDR3. Such a reduction in the number of N-nucleotides has a great effect on the junctional diversity, and thereby on the total diversity of the Ig and TR repertoire. This shows that XLF has an important role during V(D)J recombination in creating diversity of the repertoire by stimulating N-nucleotide insertion.

Elevated expression of the activating Fcγ receptor (FcγR) I and FcγRIIa together with decreased expression of the inhibitory FcγRIIb are involved in the pathogenesis of primary immune thrombocytopenia (ITP). Thrombopoietin receptor agonists (TPO-RAs) have been used clinically for the management of ITP; however, little is known about the effect of TPO-RAs on FcγR modulation in ITP. In this prospective study, we measured the alteration in monocyte FcγR expression from 21 corticosteroid-resistant/relapsed patients with chronic ITP receiving eltrombopag therapy. Results showed that the mRNA and protein levels of FcγRIIb were significantly elevated after 6-week eltrombopag treatment. Concurrently, FcγRI and IIa levels decreased remarkably, whereas FcγRIII expression did not change. In vitro phagocytosis assays indicated that a shift in the balance of FcγR toward inhibitory FcγRIIb on monocytes was accompanied with a considerable decrease in monocyte/macrophage phagocytic capacity. The response to eltrombopag therapy in patients with ITP was associated with FcγR phenotype and functional changes of monocytes/macrophages. Moreover, the plasma transforming growth factor-β1 (TGF-β1) concentrations increased significantly in eltrombopag responders. Modulation of monocyte FcγR balance by TPO-RAs was also found in a murine model of ITP established by transferring splenocytes from immunized CD61 knockout mice into CD61(+) severe combined immunodeficient mice. Romiplostim administration in ITP mice significantly upregulated inhibitory FcγRII expression and downregulated activating FcγRI expression. These findings showed that recovery of platelet counts after TPO-RA treatment in ITP is associated with the restoration of FcγR balance toward the inhibitory FcγRIIb on monocytes, and suggested that thrombopoietic agents have a profound effect on immune modulation in ITP. This study is registered at ClinicalTrials.gov as #NCT01864512.

Autophagy is a cellular adaptive mechanism to stress, including that induced by chemotherapeutic agents. Reverse phase protein array suggested that high expression of the essential autophagy-related protein, Atg7, was associated with shorter remission in newly diagnosed acute myeloid leukemia (AML) patient samples, indicating a role in chemoresistance. Knockdown of Atg7 in AML cells using short hairpin RNA markedly increased apoptosis and DNA damage following treatment with cytarabine and idarubicin. Interestingly, coculture of AML cells with stromal cells increased autophagy and chemoresistance in the AML cells exposed to chemotherapeutic agents, and this was reversed following Atg7 knockdown. This effect was further enhanced by concomitant knockdown of Atg7 in both AML and stromal cells. These findings strongly suggest that Atg7, and likely microenvironment autophagy in general, plays an important role in AML chemoresistance. Mechanistic studies revealed that Atg7 knockdown induced a proapoptotic phenotype in AML cells, which was manifested by an increased NOXA expression at the transcriptional level. Finally, in a mouse model of human leukemia, Atg7 knockdown extended overall survival after chemotherapy. Thus, the inhibition of Atg7 appears to be a valid strategy to enhance chemosensitivity, and it could indeed improve outcomes in AML therapy.

Programmed death ligands (PDLs) are immune-regulatory molecules that are frequently affected by chromosomal alterations in B-cell lymphomas. Although PDL copy-number variations are well characterized, a detailed and comprehensive analysis of structural rearrangements (SRs) and associated phenotypic consequences is largely lacking. Here, we used oligonucleotide capture sequencing of 67 formalin-fixed paraffin-embedded tissues derived from primary B-cell lymphomas and 1 cell line to detect and characterize, at base-pair resolution, SRs of the PDL locus (9p24.1; harboring PDL1/CD274 and PDL2/PDCD1LG2). We describe 36 novel PDL SRs, including 17 intrachromosomal events (inversions, duplications, deletions) and 19 translocations involving BZRAP-AS1, CD44, GET4, IL4R, KIAA0226L, MID1, RCC1, PTPN1 and segments of the immunoglobulin loci. Moreover, analysis of the precise chromosomal breakpoints reveals 2 distinct cluster breakpoint regions (CBRs) within either CD274 (CBR1) or PDCD1LG2 (CBR2). To determine the phenotypic consequences of these SRs, we performed immunohistochemistry for CD274 and PDCD1LG2 on primary pretreatment biopsies and found that PDL SRs are significantly associated with PDL protein expression. Finally, stable ectopic expression of wild-type PDCD1LG2 and the PDCD1LG2-IGHV7-81 fusion showed, in coculture, significantly reduced T-cell activation. Taken together, our data demonstrate the complementary utility of fluorescence in situ hybridization and capture sequencing approaches and provide a classification scheme for PDL SRs with implications for future studies using PDL immune-checkpoint inhibitors in B-cell lymphomas.

The importance of glutamine (Gln) metabolism in multiple myeloma (MM) cells and its potential role as a therapeutic target are still unknown, although it has been reported that human myeloma cell lines (HMCLs) are highly sensitive to Gln depletion. In this study, we found that both HMCLs and primary bone marrow (BM) CD138(+) cells produced large amounts of ammonium in the presence of Gln. MM patients have lower BM plasma Gln with higher ammonium and glutamate than patients with indolent monoclonal gammopathies. Interestingly, HMCLs expressed glutaminase (GLS1) and were sensitive to its inhibition, whereas they exhibited negligible expression of glutamine synthetase (GS). High GLS1 and low GS expression were also observed in primary CD138(+) cells. Gln-free incubation or treatment with the glutaminolytic enzyme l-asparaginase depleted the cell contents of Gln, glutamate, and the anaplerotic substrate 2-oxoglutarate, inhibiting MM cell growth. Consistent with the dependence of MM cells on extracellular Gln, a gene expression profile analysis, on both proprietary and published datasets, showed an increased expression of the Gln transporters SNAT1, ASCT2, and LAT1 by CD138(+) cells across the progression of monoclonal gammopathies. Among these transporters, only ASCT2 inhibition in HMCLs caused a marked decrease in Gln uptake and a significant fall in cell growth. Consistently, stable ASCT2 downregulation by a lentiviral approach inhibited HMCL growth in vitro and in a murine model. In conclusion, MM cells strictly depend on extracellular Gln and show features of Gln addiction. Therefore, the inhibition of Gln uptake is a new attractive therapeutic strategy for MM.

Bipotent megakaryocyte/erythroid progenitors (MEPs) give rise to progeny limited to the megakaryocyte (Mk) and erythroid (E) lineages. We developed a novel dual-detection functional in vitro colony-forming unit (CFU) assay for single cells that differentiates down both the Mk and E lineages (CFU-Mk/E), which allowed development and validation of a novel purification strategy for the identification and quantitation of primary functional human MEPs from granulocyte colony-stimulating factor-mobilized peripheral blood and bone marrow. Applying this assay to fluorescence-activated cell sorter-sorted cell populations, we found that the Lin(-)CD34(+)CD38(mid)CD45RA(-)FLT3(-)MPL(+)CD36(-)CD41(-) population is much more highly enriched for bipotent MEPs than any previously reported subpopulations. We also developed purification strategies for primary human lineage-committed Mk and E progenitors identified as CFU-Mk and burst forming unit-E. Comparative expression analyses in MEP, MkP, and ErP populations revealed differential expression of MYB We tested whether alterations in MYB concentration affect the Mk-E fate decision at the single cell level in MEPs and found that short hairpin RNA-mediated MYB knockdown promoted commitment of MEPs to the Mk lineage, further defining its role in MEP lineage fate. There are numerous applications for these novel enrichment strategies, including facilitating mechanistic studies of MEP lineage commitment, improving approaches for in vitro expansion of Mk and E cells, and developing improved therapies for benign and malignant hematologic disease.

Increased understanding of pediatric acute lymphoblastic leukemia (ALL) pathobiology has led to dramatic improvements in patient survival. However, there is still a need to develop targeted therapies to enable reduced chemotherapy intensity and to treat relapsed patients. The interleukin-7 receptor α (IL-7Rα) signaling pathways are prime therapeutic targets because these pathways harbor genetic aberrations in both T-cell ALL and B-cell precursor ALL. Therapeutic targeting of the IL-7Rα signaling pathways may lead to improved outcomes in a subset of patients.

Clonal evolution is believed to be a main driver for progression of various types of cancer and implicated in facilitating resistance to drugs. However, the hierarchical organization of malignant clones in the hematopoiesis of myelodysplastic syndromes (MDS) and its impact on response to drug therapy remain poorly understood. Using high-throughput sequencing of patient and xenografted cells, we evaluated the intratumoral heterogeneity (n= 54) and reconstructed mutational trajectories (n = 39) in patients suffering from MDS (n = 52) and chronic myelomonocytic leukemia-1 (n = 2). We identified linear and also branching evolution paths and confirmed on a patient-specific level that somatic mutations in epigenetic regulators and RNA splicing genes frequently constitute isolated disease-initiating events. Using high-throughput exome- and/or deep-sequencing, we analyzed 103 chronologically acquired samples from 22 patients covering a cumulative observation time of 75 years MDS disease progression. Our data revealed highly dynamic shaping of complex oligoclonal architectures, specifically upon treatment with lenalidomide and other drugs. Despite initial clinical response to treatment, patients' marrow persistently remained clonal with rapid outgrowth of founder-, sub-, or even fully independent clones, indicating an increased dynamic rate of clonal turnover. The emergence and disappearance of specific clones frequently correlated with changes of clinical parameters, highlighting their distinct and far-reaching functional properties. Intriguingly, increasingly complex mutational trajectories are frequently accompanied by clinical progression during the course of disease. These data substantiate a need for regular broad molecular monitoring to guide clinical treatment decisions in MDS.

Neutrophils are the key effectors for generating innate immunity in response to pathogenic infection and tissue injury in vertebrates. Dysregulation of neutrophil development and function is known to associate with various human disorders. Yet, the genetic network that orchestrates lineage commitment, differentiation, and maturation of neutrophils remains incompletely defined. Here, we present an in vivo study to delineate the genetic program underlying neutrophil development during zebrafish embryonic myelopoiesis. We show that loss of c-Myb function has no effect on macrophages but severely impairs neutrophil terminal differentiation, resulting in the accumulation of neutrophils with unsegmented nuclei and scant granule. This neutrophilic defect, which resembles the neutrophil-specific granule deficiency (SGD) caused by the mutations in CCAAT/enhancer-binding protein ε (C/EBPε) in humans, is attributed, at least in part, to the downregulation of the granule protein transcription. Likewise, genetic inactivation of Cebp1, the zebrafish functional homolog of mammalian C/EBPε, also leads to a similar SGD-like phenotype in zebrafish. Genetic epistasis and biochemical analysis further reveals that c-Myb and Cebp1 act in parallel and cooperatively to control neutrophil differentiation by directly regulating granule protein gene transcription. Our study indicates that c-MYB is an intrinsic master regulator for neutrophil terminal differentiation and a potential target in SGD patients.

Despite intensive efforts in recent years, a curative therapy for cutaneous T-cell lymphoma (CTCL) has not yet been developed. Therefore, the establishment of new therapeutic approaches with higher efficacy rates and milder side effects is strongly desired. A characteristic feature of the malignant T-cell population in CTCL is resistance toward cell death resulting from constitutive NF-κB activation. Therefore, NF-κB-dependent cell death resistance represents an interesting therapeutic target in CTCL because an NF-κB-directed therapy would leave bystander T cells widely unaffected. We investigated the effects of dimethyl fumarate (DMF) on CTCL cells in vitro and in vivo. DMF induced cell death in primary patient-derived CD4(+) cells and CTCL cell lines, but hardly in T cells from healthy donors. DMF-induced cell death was linked specifically to NF-κB inhibition. To study the impact of DMF in vivo, we developed 2 CTCL xenograft mouse models with different cutaneous localizations of the T-cell infiltrate. DMF treatment delayed the growth of CTCL tumors and prevented formation of distant metastases. In addition, DMF induced increased cell death in primary CTCL tumors and in liver metastases. In summary, DMF treatment represents a remarkable therapeutic option in CTCL because it restores CTCL apoptosis in vitro and in preclinical models in vivo and prevents spreading of the disease to distant sites. DMF treatment is of particular promise in CTCL because DMF is already in successful clinical use in the treatment of psoriasis and multiple sclerosis allowing fast translation into clinical studies in CTCL.

Myeloma immunosurveillance remains incompletely understood. We have demonstrated proteolytic processing of the matrix proteoglycan, versican (VCAN), in myeloma tumors. Whereas intact VCAN exerts tolerogenic activities through Toll-like receptor 2 (TLR2) binding, the immunoregulatory consequences of VCAN proteolysis remain unknown. Here we show that human myeloma tumors displaying CD8(+) infiltration/aggregates underwent VCAN proteolysis at a site predicted to generate a glycosaminoglycan-bereft N-terminal fragment, versikine Myeloma-associated macrophages (MAMs), rather than tumor cells, chiefly produced V1-VCAN, the precursor to versikine, whereas stromal cell-derived ADAMTS1 was the most robustly expressed VCAN-degrading protease. Purified versikine induced early expression of inflammatory cytokines interleukin 1β (IL-1β) and IL-6 by human myeloma marrow-derived MAMs. We show that versikine signals through pathways both dependent and independent of Tpl2 kinase, a key regulator of nuclear factor κB1-mediated MAPK activation in macrophages. Unlike intact VCAN, versikine-induced Il-6 production was partially independent of Tlr2. In a model of macrophage-myeloma cell crosstalk, versikine induced components of "T-cell inflammation," including IRF8-dependent type I interferon transcriptional signatures and T-cell chemoattractant CCL2. Thus the interplay between stromal cells and myeloid cells in the myeloma microenvironment generates versikine, a novel bioactive damage-associated molecular pattern that may facilitate immune sensing of myeloma tumors and modulate the tolerogenic consequences of intact VCAN accumulation. Therapeutic versikine administration may potentiate T-cell-activating immunotherapies.