Search

To investigate the role of Aire in thymic selection, we examined the cellular requirements for generation of ovalbumin (OVA)–specific CD4 and CD8 T cells in mice expressing OVA under the control of the rat insulin promoter. Aire deficiency reduced the number of mature single-positive OVA-specific CD4+ or CD8+ T cells in the thymus, independent of OVA expression. Importantly, it also contributed in 2 ways to OVA-dependent negative selection depending on the T-cell type. Aire-dependent negative selection of OVA-specific CD8 T cells correlated with Aire-regulated expression of OVA. By contrast, for OVA-specific CD4 T cells, Aire affected tolerance induction by a mechanism that operated independent of the level of OVA expression, controlling access of antigen presenting cells to medullary thymic epithelial cell (mTEC)–expressed OVA. This study supports the view that one mechanism by which Aire controls thymic negative selection is by regulating the indirect presentation of mTEC-derived antigens by thymic dendritic cells. It also indicates that mTECs can mediate tolerance by direct presentation of Aire-regulated antigens to both CD4 and CD8 T cells.

Omenn syndrome (OS) is a severe immunodeficiency associated with erythroderma, lymphoproliferation, elevated IgE, and hyperactive oligoclonal T cells. A restricted T-cell repertoire caused by defective thymic T-cell development and selection, lymphopenia with homeostatic proliferation, and lack of regulatory T cells are considered key factors in OS pathogenesis. We report 2 siblings presenting with cytomegalovirus (CMV) and Pneumocystis jirovecii infections and recurrent sepsis; one developed all clinical features of OS. Both carried homozygous germline mutations in CARD11 (p.Cys150*), impairing NF-κB signaling and IL-2 production. A somatic second-site mutation reverting the stop codon to a missense mutation (p.Cys150Leu) was detected in tissue-infiltrating T cells of the OS patient. Expression of p.Cys150Leu in CARD11-deficient T cells largely reconstituted NF-κB signaling. The reversion likely occurred in a prethymic T-cell precursor, leading to a chimeric T-cell repertoire. We speculate that in our patient the functional advantage of the revertant T cells in the context of persistent CMV infection, combined with lack of regulatory T cells, may have been sufficient to favor OS. This first observation of OS in a patient with a T-cell activation defect suggests that severely defective T-cell development or homeostatic proliferation in a lymphopenic environment are not required for this severe immunopathology.

Despite the importance of thymic stromal cells to T-cell development, relatively little is known about their biology. Here, we use single-cell analysis of stromal cells to analyze extensive changes in the number and composition of thymic stroma throughout life, revealing a surprisingly dynamic population. Phenotypic progression of thymic epithelial subsets was assessed at high resolution in young mice to provide a developmental framework. The cellular and molecular requirements of adult epithelium were studied, using various mutant mice to demonstrate new cross talk checkpoints dependent on RelB in the cortex and CD40 in the medulla. With the use of Ki67 and BrdU labeling, the turnover of thymic epithelium was found to be rapid, but then diminished on thymic involution. The various defects in stromal turnover and composition that accompanied involution were rapidly reversed following sex steroid ablation. Unexpectedly, mature cortical and medullary epithelium showed a potent capacity to stimulate naive T cells, comparable to that of thymic dendritic cells. Overall, these studies show that the thymic stroma is a surprisingly dynamic population and may have a more direct role in negative selection than previously thought. ispartof: Blood vol:108 issue:12 pages:3777-3785 ispartof: location:United States status: published

Patients with the dedicator of cytokinesis 8 (DOCK8) immunodeficiency syndrome suffer from recurrent viral and bacterial infections, hyper-immunoglobulin E levels, eczema, and greater susceptibility to cancer. Because natural killer T (NKT) cells have been implicated in these diseases, we asked if these cells were affected by DOCK8 deficiency. Using a mouse model, we found that DOCK8 deficiency resulted in impaired NKT cell development, principally affecting the formation and survival of long-lived, differentiated NKT cells. In the thymus, DOCK8-deficient mice lack a terminally differentiated subset of NK1.1(+) NKT cells expressing the integrin CD103, whereas in the liver, DOCK8-deficient NKT cells express reduced levels of the prosurvival factor B-cell lymphoma 2 and the integrin lymphocyte function-associated antigen 1. Although the initial NKT cell response to antigen is intact in the absence of DOCK8, their ongoing proliferative and cytokine responses are impaired. Importantly, a similar defect in NKT cell numbers was detected in DOCK8-deficient humans, highlighting the relevance of the mouse model. In conclusion, our data demonstrate that DOCK8 is required for the development and survival of mature NKT cells, consistent with the idea that DOCK8 mediates survival signals within a specialized niche. Accordingly, impaired NKT cell numbers and function are likely to contribute to the susceptibility of DOCK8-deficient patients to recurrent infections and malignant disease.

Introduction: Diffuse large B-cell lymphoma (DLBCL) is an aggressive lymphoma with ~30% of cases failing treatment or relapsing after R-CHOP chemotherapy. Treatment options for refractory/ relapsed DLBCL are limited and often have a poor outcome. Tumour evolution and selection of a chemo resistant clone are likely explanations making it important to understand clonal heterogeneity at diagnosis and relapse. Green et al have noted a hierarchical acquisition of mutations with disease progression in follicular lymphoma (FL), with BCL2 and CREBBP mutations seen in earlier precursors and MLL2 and TNFRSF14 mutations proposed to be later events. Notably, 1 case analysed at diagnosis and at relapse had variable IgVH indicating origin in a more immature precursors. [Green, M.R., Blood, 2013]. More recent studies indicate that the dominant clone of FL and transformed FL arise by either convergent or divergent evolution from a common mutated precursor through the acquisition of additional genetic events [Pasqualucci, L., Cell Rep, 2014]. Defining the deregulated pathways and oncogenic mutations at diagnosis and later at relapse could help identify novel therapeutic targets for treatment at relapse. We aimed to map clonal evolution at relapse using immunophenotyping, sequencing for the Immunoglobulin variable heavy chain gene (IGHV) and genotyping for known somatic mutations in key lymphoma genes, within matched diagnostic and relapsed DLBCL pairs. Methods: Six matched diagnostic and relapsed DLBCL cryopreserved samples were subjected to comprehensive immunophenotyping using 10-colour B-cell flow cytometry panels based on normal ontogeny. PCR on initial and relapsed samples was performed to amplify clonally rearranged IgHV genes from fresh/paraffin embedded primary diagnostic samples. Sanger sequencing was done for IgHV mutation status by targeting the conserved framework regions (FR) FR1 [IGHA: VHFR1-JH] or FR3 [IGHC: VHFR3-JH] using the Invivoscribe kit based on the Biomed-2 protocols. A custom Haloplex library preparation kit designed and ordered from Agilent was used to capture the exons of ~40 genes commonly mutated in DLBCL. Targeted fragments were PCR amplified and target enriched samples sequenced on an Illumina MiSeq sequencer Results: Table 1. Immunophenotypic diversity was noted among cases but the phenotype did not change at relapse. IGHV sequencing showed that 3 cases with two distinct lymphoma clones at diagnosis evolved to a single detectable IGHV clonal population at relapse. Lymphoma-associated somatic mutations detected at diagnosis were preserved at relapse and in 4 cases, acquisition of additional mutations was observed. Table 1: Immunophenotype, IgHV sequence and somatic lymphoma mutations in paired DLBCL samples at diagnosis and relapse Patient number Disease course Immunophenotype IgHV sequence Lymphoma mutations DL157 Diagnosis IgM+, IgD+++, IgG-, CD27-, CD21+++, CD38++, CD10- N/A (not available) EP300 I->V EZH2 D->H NOTCH2 L->H TRAF2 A->T DL157 Relapse Same as diagnosis IgHV3-64 IgHV3-30 EZH2 D->H FOXO1G->D NOTCH2L->HTRAF2 A->T DL214 Diagnosis IgM+++,IgD++, IgG-, CD27-, CD21-, CD38+++, CD10+ IgHV4-30 IgHV4-39 N/A DL214 Relapse Same as diagnosis IgHV4-39 EP300 I->V MYD88 L->P NOTCH1 R->W PRDM1 C->Y SPEN D->E TP53 Y->N DL215 Diagnosis IgM-,IgD- IgG++, CD27++,CD21++, CD38-, CD10- IGHV3-23 IGHV3-23D KMT2D R->C MYD88 L->P NOTCH1 E->K DL215 Relapse Same as diagnosis IGHV3-23 BTG1 H->Y BTG1 Q->Stop BTG2 S->N FOXO1 V->E GNA13 R->H KMT2D R->C MYD88 L->P NOTCH1 E->K PIM1 L->F PIM1 K->N PIM1 V->L DL245 Diagnosis N/A IGHV3-11 IGHV3-33 EP300,I->V,997 NOTCH2,L->V,1559 DL245 Relapse N/A IGHV3-11 EP300,I->V,997 NOTCH2,L->V,1559 DL213 Diagnosis IgM+,IgD-, IgG-, CD27-,CD21+++, CD38+++, CD10++ IGHV3-15 ETS1 A->T EZH2 D->H PRDM1 L->F TNFRSF14 C->S DL213 Relapse Same as diagnosis IGHV3-15 ETS1 A->T EZH2 D->H KMT2D R->Stop PRDM1 L->FSTAT3 R->W DL252 Diagnosis IgM-,IgD++, IgG-, CD27-,CD21-, CD38+, CD10- IGHV1-2 NOTCH2,P->A,2359 TNFRSF14,V->I,241 DL252 Relapse Same as diagnosis IGHV1-2 N/A Conclusions: While multiple IGHV sub-clones are present at diagnosis of DLBCL, evolution of a single clone is noted at relapse (convergent model) with acquisition of additional somatic mutations. Immunophenotyping using B-cell maturation flow cytometry panels demonstrates heterogeneity of differentiation between cases but no change in immunophenotype at relapse. Disclosures No relevant conflicts of interest to declare.

The human β globin locus consists of an upstream locus control region (LCR) and five functional genes arranged sequentially in the order of their expression during development: 5′-ε-Gγ-Aγ- δ- β-3′. Haemoglobin switching entails the successive recruitment of these genes into an active chromatin hub (ACH). Although much is known about the cis elements and transcription factors involved in globin gene regulation, less is known about ACH formation. Here we show that the transcription factor Ikaros plays an essential role in both the formation of the β-globin ACH, and in haemoglobin switching. In Plastic mice, where the DNA-binding region of Ikaros is disrupted by a point mutation (H191R), there is concomitant marked (10 fold) down-regulation of human β-globin, and up-regulation of γ-globin gene expression. We show Ikaros binds to a critical cis elements in the LCR near the HS3 core and upstream of the δ-globin gene in the β-globin locus by electormobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) and that this DNA binding activity is lost in Plast mice. This latter site is implicated in deletional hereditary persistence of fetal haemoglobin (HPFH). Furthermore, chromatin conformation capture (3C) data suggest Ikaros facilitates long range looping between the LCR and a region upstream of the δ-globin gene. This study provides new insights into the mechanism of adult stage-specific assembly of the β-globin ACH. In addition the findings could lead to the development of novel drugs to reactivate HbF in adults with β-thalassemia and sickle cell disease.

The zinc finger transcription factor Ikaros is recognized as a key regulator of lymphocyte differentiation. Recently generated dominant negative mutants have hinted at a broader role in haematopoietic stem cell generation. Most recently, a mouse strain, IkarosPlastic, with a point mutation in Ikaros that disrupts DNA binding but preserves efficient assembly of Ikaros protein complexes, is embryonically lethal due to severe defects in erythrocyte differentiation (Papathanasiou P, et al,. Immunity, 2003). (1). These mice display normal murine globin gene expression in the fetal liver. However in humans the globin locus is under alternative regulatory control, particularly with respect to the fetal-to-adult globin switch. Thus, to determine if Ikaros plays a role in human globin switching we crossed the IkarosPlastic mice with mice transgenic for a YAC containing the entire human b-globin locus, which show human fetal to adult globin gene switching from E12 to E17. Embryos were harvested from E12.5 to E15.5 and globin expression was determined in the fetal liver by real-time PCR (relative to actin). At all time points human gamma-globin gene expression was not significantly altered by the presence of the IkarosPlastic mutatation (relative expression Ikaroswt/wt 1±0.11, IkarosPlastic/Plastic 0.82±0.12). In contrast, human beta-globin gene expression was significantly down-regulated in IkarosPlastic fetal livers (relative expression Ikaroswt/wt 1±0.14, IkarosPlastic/Plastic 0.18±0.07). Interestingly, neither murine a- or b-globin gene expression was significantly different to wild type mice, which suggests that the transcription factor Ikaros plays a specific role in the transcriptional activation of the human b-globin gene during development. The mechanism by which this occurs remains to be elucidated, however it is intriguing to consider that Ikaros may act as a potentiator of transcription for erythroid specific transcription factors such as EKLF. Experiments to address this will be presented.