The expansion of human T-bethighCD21low B cells is T cell dependent.

Accumulation of human CD21low B cells in peripheral blood is a hallmark of chronic activation of the adaptive immune system in certain infections and autoimmune disorders. The molecular pathways underpinning the development, function, and fate of these CD21low B cells remain incompletely characterized. Here, combined transcriptomic and chromatin accessibility analyses supported a prominent role for the transcription factor T-bet in the transcriptional regulation of these T-bethighCD21low B cells. Investigating essential signals for generating these cells in vitro established that B cell receptor (BCR)/interferon-γ receptor (IFNγR) costimulation induced the highest levels of T-bet expression and enabled their differentiation during cell cultures with Toll-like receptor (TLR) ligand or CD40L/interleukin-21 (IL-21) stimulation. Low proportions of CD21low B cells in peripheral blood from patients with defined inborn errors of immunity (IEI), because of mutations affecting canonical NF-κB, CD40, and IL-21 receptor or IL-12/IFNγ/IFNγ receptor/signal transducer and activator of transcription 1 (STAT1) signaling, substantiated the essential roles of BCR- and certain T cell­derived signals in the in vivo expansion of T-bethighCD21low B cells. Disturbed TLR signaling due to MyD88 or IRAK4 deficiency was not associated with reduced CD21low B cell proportions. The expansion of human T-bethighCD21low B cells correlated with an expansion of circulating T follicular helper 1 (cTfh1) and T peripheral helper (Tph) cells, identifying potential sources of CD40L, IL-21, and IFNγ signals. Thus, we identified important pathways to target autoreactive T-bethighCD21low B cells in human autoimmune conditions, where these cells are linked to pathogenesis and disease progression.

Genetic, Immunological, and Clinical Features of 32 Patients with Autosomal Recessive STAT1 Deficiency.

Autosomal recessive (AR) STAT1 deficiency is a severe inborn error of immunity disrupting cellular responses to type I, II, and III IFNs, and IL-27, and conferring a predisposition to both viral and mycobacterial infections. We report the genetic, immunological, and clinical features of an international cohort of 32 patients from 20 kindreds: 24 patients with complete deficiency, and 8 patients with partial deficiency. Twenty-four patients suffered from mycobacterial disease (bacillus Calmette-Guérin = 13, environmental mycobacteria = 10, or both in 1 patient). Fifty-four severe viral episodes occurred in sixteen patients, mainly caused by Herpesviridae viruses. Attenuated live measles, mumps, and rubella and/or varicella zoster virus vaccines triggered severe reactions in the five patients with complete deficiency who were vaccinated. Seven patients developed features of hemophagocytic syndrome. Twenty-one patients died, and death was almost twice as likely in patients with complete STAT1 deficiency than in those with partial STAT1 deficiency. All but one of the eight survivors with AR complete deficiency underwent hematopoietic stem cell transplantation. Overall survival after hematopoietic stem cell transplantation was 64%. A diagnosis of AR STAT1 deficiency should be considered in children with mycobacterial and/or viral infectious diseases. It is important to distinguish between complete and partial forms of AR STAT1 deficiency, as their clinical outcome and management differ significantly.

Favorable outcomes of hematopoietic stem cell transplantation in children and adolescents with Diamond-Blackfan anemia.

Diamond-Blackfan anemia (DBA) is a congenital pure red cell aplasia associated with congenital abnormalities and cancer predisposition. Allogeneic hematopoietic stem cell transplantation (HSCT) can correct the hematological phenotype and is indicated in transfusion-dependent patients. In 70 children reported to the German DBA and French HSCT registries, HSCT was performed from 1985 to 2017. Median age at HSCT was 5.5 years (range, 0.9-17.3 years). Two-thirds of patients (64%) were transplanted from a matched sibling donor (MSD), and most procedures were performed after the year 1999 (73%). Primary engraftment was achieved in all patients. One patient developed secondary graft failure. Cumulative incidence of acute graft-versus-host disease (GVHD) was 24% for °II-IV (95% confidence interval [CI], 16% to 37%) and 7% for °III-IV (95% CI, 3% to 17%); cumulative incidence of chronic GVHD was 11% (95% CI, 5% to 22%). The probability of chronic GVHD-free survival (cGFS) was 87% (95% CI, 79% to 95%) and significantly improved over time (<2000: 68% [95% CI, 47% to 89%] vs ≥2000: 94% [95% CI, 87% to 100%], P < .01). cGFS was comparable following HSCT from a MSD and an unrelated donor (UD). Of note, no severe chronic GVHD or deaths were reported following MSD-HSCT after 1999. The difference of cGFS in children transplanted <10 years of age compared with older patients did not reach statistical significance (<10 years: 90% [95% CI, 81% to 99%] vs 10-18 years 78% [95% CI, 58% to 98%]). In summary, these data indicate that HSCT is efficient and safe in young DBA patients and should be considered if a MSD or matched UD is available. HSCT for transfusion dependency only must be critically discussed in older patients.

Recurring mutations in RPL15 are linked to hydrops fetalis and treatment independence in Diamond-Blackfan anemia.

Diamond-Blackfan anemia (DBA) is a rare inherited bone marrow failure disorder linked predominantly to ribosomal protein gene mutations. Here the European DBA consortium reports novel mutations identified in the RPL15 gene in 6 unrelated individuals diagnosed with DBA. Although point mutations have not been previously reported for RPL15, we identified 4 individuals with truncating mutations p.Tyr81* (in 3 of 4) and p.Gln29*, and 2 with missense variants p.Leu10Pro and p.Lys153Thr. Notably, 75% (3 of 4) of truncating mutation carriers manifested with severe hydrops fetalis and required intrauterine transfusions. Even more remarkable is the observation that the 3 carriers of p.Tyr81* mutation became treatment-independent between four and 16 months of life and maintained normal blood counts until their last follow up. Genetic reversion at the DNA level as a potential mechanism of remission was not observed in our patients. In vitro studies revealed that cells carrying RPL15 mutations have pre-rRNA processing defects, reduced 60S ribosomal subunit formation, and severe proliferation defects. Red cell culture assays of RPL15-mutated primary erythroblast cells also showed a severe reduction in cell proliferation, delayed erythroid differentiation, elevated TP53 activity, and increased apoptosis. This study identifies a novel subgroup of DBA with mutations in the RPL15 gene with an unexpected high rate of hydrops fetalis and spontaneous, long-lasting remission.

Deletion of human GP1BB and SEPT5 is associated with Bernard-Soulier syndrome, platelet secretion defect, polymicrogyria, and developmental delay.

The bleeding disorder Bernard-Soulier syndrome (BSS) is caused by mutations in the genes coding for the platelet glycoprotein GPIb/IX receptor. The septin SEPT5 is important for active membrane movement such as vesicle trafficking and exocytosis in non-dividing cells (i.e. platelets, neurons). We report on a four-year-old boy with a homozygous deletion comprising not only glycoprotein Ibß (GP1BB) but also the SEPT5 gene, located 5' to GP1BB. He presented with BSS, cortical dysplasia (polymicrogyria), developmental delay, and platelet secretion defect. The homozygous deletion of GP1BB and SEPT5, which had been identified by PCR analyses, was confirmed by Southern analyses and denaturing HPLC (DHPLC). The parents were heterozygous for this deletion. Absence of GPIbß and SEPT5 proteins in the patient's platelets was illustrated using transmission electron microscopy. Besides decreased GPIb/IX expression, flow cytometry analyses revealed impaired platelet granule secretion. Because the bleeding disorder was extremely severe, the boy received bone marrow transplantation (BMT) from a HLA-identical unrelated donor. After successful engraftment of BMT, he had no more bleeding episodes. Interestingly, also his mental development improved strikingly after BMT. This report describes for the first time a patient with SEPT5 deficiency presenting with cortical dysplasia (polymicrogyria), developmental delay, and platelet secretion defect.

Diagnosis and management of chronic ITP: comments from an ICIS expert group.

Immune thrombocytopenia (ITP) is a common disorder in children and adults. In a patient with newly diagnosed ITP, the treatment strategy is relatively well defined. Second-line treatments are more controversial, and the management of chronic ITP is even more so. During the 3rd ICIS Expert Meeting on Consensus and Development of Strategies in ITP, held in Basel on September 3-5, 2009, a group of experts were tasked with reaching a consensus on some frequently asked questions relating to diagnosis and management of children and adults with chronic ITP. The content of this article is designed to provide a practical support to trained haematologists in their care of patients with chronic ITP.

Identification of a novel factor X deletion in combination with a missense mutation in the F10 gene - Genotype-phenotype correlation in a girl with severe factor X deficiency.

The genotype-phenotype relationship of compound heterozygous factor X deficiency in a young girl with severe factor X deficiency and bleeding symptoms is characterized. We identified a novel deletion of exon 6 and a missense mutation (c.856G>A, Val286Met) in exon 7 of the F10 gene leading to a compound heterozygous state and causing severe factor X deficiency. Therapeutic options for patients with symptomatic factor X deficiency are demonstrated.

High incidence of t(7;12)(q36;p13) in infant AML but not in infant ALL, with a dismal outcome and ectopic expression of HLXB9.

The t(7;12)(q36;p13) is a recurrent translocation involving the ETV6/TEL gene (12p13) and a heterogeneous breakpoint at 7q36. A fusion transcript between HLXB9 and ETV6 in AML with t(7;12) is occasionally found. To study the incidence of t(7;12) in infant and childhood acute leukemia, we screened 320 cases <36 months using FISH. Additionally, 28 pediatric cases >36 months with cytogenetic breakpoints at 12p and 7q were investigated. We studied the presence of an HXLB9-ETV6 fusion transcript and quantified the expression of various genes located in the 7q36 breakpoint region. In total, six AML patients carried the t(7;12) of which five were infants and one child of 18 months. Only one out of 99 infant ALL patients harbored the t(7;12). No t(7;12) was found in older children with AML or ALL. AML patients carrying a t(7;12) had a poor outcome with a 3-year EFS of 0%. A fusion of HLXB9 to ETV6 was found in four AML cases with t(7;12). The 7q36 genes NOM1, LMBR1, RNF32, and SHH were equally expressed among t(7;12)-positive AML versus t(7;12)-negative AML, t(7;12)-negative ALL, or normal bone marrow. However, the HLXB9 expression was highly increased in t(7;12)-positive cases, including those with an HLXB9-ETV6 fusion. We conclude that the t(7;12) is almost exclusively present in infant AML and covers 30% of infant AML, while it is extremely rare in infant ALL and older children. The t(7;12) is associated with a poor outcome and an ectopic expression of HLXB9 is commonly involved in this genetic subtype of leukemia.

The novel human platelet septin SEPT8 is an interaction partner of SEPT4.

Septins are a family of GTP-binding proteins, which are essential for active membrane movement such as cytokinesis and vesicle trafficking. In non-dividing cells (such as platelets and neurons) septins are implicated in exocytosis. Platelets from a SEPT5 knockout mouse showed an altered serotonin secretion and platelet aggregation, suggesting that SEPT5 is involved in secretion in platelets. Septins form complexes consisting of multiple septin polypeptides. Using the yeast two-hybrid system we had demonstrated that SEPT5 partners with SEPT8. The aim of this study was to identify other interaction partners of the human platelet septin SEPT8. Using the yeast two-hybrid system with SEPT8 as bait protein we identified the human septin SEPT4 as an interaction partner of SEPT8. The interaction between SEPT4 and SEPT8 was confirmed by immunoprecipitation. Expression analysis revealed that SEPT4 is also expressed in human platelets. Thus, SEPT4 is the third described platelet septin besides SEPT5 and SEPT8. Transmission electron microscopy of platelets revealed that SEPT8 and SEPT4 are localized surrounding alpha-granules (as it had been shown for the septin SEPT5) suggesting that the three septins may be components of the septin complex in platelets and contribute in such a way to platelet biology. Activation of platelets by agonists resulted in the translocation of SEPT4 and SEPT8 to the platelet surface indicating a possible functional role of these proteins in platelet granular secretion.

Isolation of new splice isoforms, characterization and expression analysis of the human septin SEPT8 (KIAA0202).

SEPT8 (KIAA0202) is a member of the highly conserved septin family. Septins are membrane-associated GTPases which are involved in cytokinesis and cellular morphogenesis. Using the yeast two-hybrid system and the glutathione-S-transferase pull-down assay we previously had identified the SEPT8 (KIAA0202) as interaction partner of the human septin SEPT5 (cell division cycle related-1, CDCrel-1). Since the complete cDNA sequence of the human septin SEPT8 (KIAA0202) was not known at that time, we isolated new 5' and 3' cDNA sequence of SEPT8 (KIAA0202) by screening three different cDNA libraries. In addition, we performed the characterization of SEPT8 (KIAA0202) and identified new splice variants of SEPT8 (KIAA0202). The expression pattern of SEPT8 (KIAA0202) and its interaction partner SEPT5 (CDCrel-1) is illustrated.

Human septin-septin interaction: CDCrel-1 partners with KIAA0202.

Septins are evolutionary conserved cytoskeletal GTPases forming heteropolymer complexes involved in cytokinesis and other cellular processes. CDCrel-1 (cell division cycle related-1) is a recently cloned and characterized human septin which is highly expressed in non-dividing cells, such as neurons. Using a yeast two-hybrid system we demonstrate that CDCrel-1 partners with another uncharacterized human septin, KIAA0202. The interaction of CDCrel-1 and KIAA0202 was confirmed in the human leukemia cell line K-562 using pull-down assays with a KIAA0202-glutathione S-transferase fusion protein and by immunoprecipitation of the CDCrel-1-KIAA0202 complex with an anti-KIAA0202 antibody. Expression studies of the two human septins revealed a concomitant expression of both proteins in certain cells.