Mutations in PIGS, Encoding a GPI Transamidase, Cause a Neurological Syndrome Ranging from Fetal Akinesia to Epileptic Encephalopathy

Inherited GPI deficiencies (IGDs) are a subset of congenital disorders of glycosylation that are increasingly recognized as a result of advances in whole-exome sequencing (WES) and whole-genome sequencing (WGS). IGDs cause a series of overlapping phenotypes consisting of seizures, dysmorphic features, multiple congenital malformations, and severe intellectual disability. We present a study of six individuals from three unrelated families in which WES or WGS identified bi-allelic phosphatidylinositol glycan class S (PIGS) biosynthesis mutations. Phenotypes included severe global developmental delay, seizures (partly responding to pyridoxine), hypotonia, weakness, ataxia, and dysmorphic facial features. Two of them had compound-heterozygous variants c.108G>A (p.Trp36^∗) and c.101T>C (p.Leu34Pro), and two siblings of another family were homozygous for a deletion and insertion leading to p.Thr439_Lys451delinsArgLeuLeu. The third family had two fetuses with multiple joint contractures consistent with fetal akinesia. They were compound heterozygous for c.923A>G (p.Glu308Gly) and c.468+1G>C, a splicing mutation. Flow-cytometry analyses demonstrated that the individuals with PIGS mutations show a GPI-AP deficiency profile. Expression of the p.Trp36^∗ variant in PIGS-deficient HEK293 cells revealed only partial restoration of cell-surface GPI-APs. In terms of both biochemistry and phenotype, loss of function of PIGS shares features with PIGT deficiency and other IGDs. This study contributes to the understanding of the GPI-AP biosynthesis pathway by describing the consequences of PIGS disruption in humans and extending the family of IGDs.

Human mesenchymal stromal cell-secreted lactate induces M2-macrophage differentiation by metabolic reprogramming

Human mesenchymal stromal cells (MSC) have been shown to dampen immune response and promote tissue repair, but the underlying mechanisms are still under investigation. Herein, we demonstrate that umbilical cord-derived MSC (UC-MSC) alter the phenotype and function of monocyte-derived dendritic cells (DC) through lactate-mediated metabolic reprogramming. UC-MSC can secrete large quantities of lactate and, when present during monocyte-to-DC differentiation, induce instead the acquisition of M2-macrophage features in terms of morphology, surface markers, migratory properties and antigen presentation capacity. Microarray expression profiling indicates that UC-MSC modify the expression of metabolic-related genes and induce a M2-macrophage expression signature. Importantly, monocyte-derived DC obtained in presence of UC-MSC, polarize naïve allogeneic CD4⁺ T-cells into Th2 cells. Treatment of UC-MSC with an inhibitor of lactate dehydrogenase strongly decreases lactate concentration in culture supernatant and abrogates the effect on monocyte-to-DC differentiation. Metabolic analysis further revealed that UC-MSC decrease oxidative phosphorylation in differentiating monocytes while strongly increasing the spare respiratory capacity proportional to the amount of secreted lactate. Because both MSC and monocytes are recruited in vivo at the site of tissue damage and inflammation, we propose the local increase of lactate concentration induced by UC-MSC and the consequent enrichment in M2-macrophage generation as a mechanism to achieve immunomodulation.

A Novel PGM3 Mutation Is Associated With a Severe Phenotype of Bone Marrow Failure, Severe Combined Immunodeficiency, Skeletal Dysplasia, and Congenital Malformations

Congenital disorders of glycosylation (CDGs) affect multiple systems and present a broad spectrum of clinical features, often including skeletal dysplasia. Exome sequencing has led to the identification of new CDG genes. Immune and skeletal phenotypes associated with mutations in PGM3, encoding a protein that converts N-acetyl-glucosamine-6-phosphate into N-acetyl-glucosamine-1-phosphate, were recently reported. Through exome sequencing, we identified a novel homozygous mutation (c.1135T>C; p.Phe379Leu) in PGM3 in two siblings with bone marrow failure, severe combined immunodeficiency, renal and intestinal malformations, and a skeletal dysplasia resembling Desbuquois dysplasia. Severe respiratory compromise secondary to lung hypoplasia and pulmonary hypertension, and intestinal obstruction led to their demise. We thus report the most severe phenotype described so far associated with PGM3 mutations. This CDG should be considered in the presence of skeletal dysplasia associated with severe immunodeficiency. © 2017 American Society for Bone and Mineral Research.

A case of C3 glomerulonephritis successfully treated with eculizumab

BACKGROUND

C3 glomerulonephritis (C3GN) is a rare form of glomerulopathy that is characterized by predominant C3 deposits. Eculizumab, a humanized monoclonal C5 antibody, has recently emerged as a treatment option for C3GN. We report a C3GN patient successfully treated with eculizumab.

CASE DIAGNOSIS/TREATMENT

A 5-year-old boy who presented with proteinuria, hematuria, high ASO titers, and low C3 levels was initially diagnosed with post-streptococcal GN. His first kidney biopsy confirmed this diagnosis, but complement investigations identified three alternative pathway dysregulation factors: C3 nephritic factor, complement factor I heterozygous mutation (I398L), and anti-factor H autoantibodies (4,500 AU/ml). A second biopsy performed 11 months after initial presentation (nephrotic range proteinuria) showed a C3GN suggestive of isolated C3 deposits. Despite the use of intensive immunosuppressive therapy (rituximab, corticosteroids, mycophenolate), nephrotic-range proteinuria persisted and a third kidney biopsy showed the same C3GN pattern with more endocapillary proliferation. The serum C5b-9 level was elevated. Eculizumab was initiated and resulted in a significant decline of proteinuria (5.3 to 1.3 g/day) and an improvement in pathologic features. A transient interruption of eculizumab resulted in a rapid rise in proteinuria to 9.3 g/day, which decreased to 0.8 g/day after resumption of treatment.

CONCLUSIONS

The administration of anti-C5 antibodies may represent a valuable therapeutic option in patients with C3GN.

Multiple intestinal atresia with combined immune deficiency related to TTC7A defect is a multiorgan pathology: study of a French-Canadian-based cohort

Hereditary multiple intestinal atresia (HMIA) is a rare cause of intestinal obstruction in humans associated with a profound combined immune deficiency. Deleterious mutations of the tetratricopeptide repeat domain-7A (TTC7A) gene lead to HMIA, although the mechanism(s) causing the disease in TTC7A deficiency has (have) not yet been clearly identified. To evaluate the consequences of TTC7A deficiency, we studied the morphology of several organs from HMIA patients at different developmental stages, as well as the expression of the TTC7A protein. We performed histological and immunohistochemical analyses on biopsies and autopsies of 6 patients and 1 fetus with HMIA. Moreover, we characterized for the first time the expression of the TTC7A protein by immunostaining it in several organs from control (including fetal samples), infants, and 1 fetus with HMIA. Besides the gastrointestinal tract, HMIA disease was associated with morphological alterations in multiple organs: thymus, lung, spleen, and liver. Moreover, we demonstrated that normal TTC7A protein was expressed in the cytoplasm of epithelial cells of the intestine, thymus, and pancreas. Surprisingly, altered TTC7A protein was highly expressed in tissues from patients, mainly in the epithelial cells. We have established that HMIA associated with a TTC7A defect is characterized by multiorgan impairments. Overall, this report suggests that TTC7A protein is critical for the proper development, preservation, and/or function of thymic and gastrointestinal epithelium.

Impaired interferon-alpha production by plasmacytoid dendritic cells after cord blood transplantation in children: implication for post-transplantation toll-like receptor ligand-based immunotherapy

Plasmacytoid dendritic cells (pDCs) initiate both innate and adaptive immune responses, making them attractive targets for post-transplantation immunotherapy, particularly after cord blood transplantation (CBT). Toll-like receptor (TLR) agonists are currently studied for pDC stimulation in various clinical settings. Their efficacy depends on pDC number and functionality, which are unknown after CBT. We performed a longitudinal study of pDC reconstitution in children who underwent bone marrow transplantation (BMT) and single-unit CBT. Both CBT and unrelated BMT patients received antithymocyte globulin as part of their graft-versus-host disease prophylaxis regimen. pDC blood counts were higher in CBT patients than in healthy volunteers from 2 to 9 months after transplantation, whereas they remained lower in BMT patients. We showed that cord blood progenitors gave rise in vitro to a 500-fold increase in functional pDCs over bone marrow counterparts. Upon stimulation with a TLR agonist, pDCs from both CBT and BMT recipients upregulated T cell costimulatory molecules, whereas interferon-alpha (IFN-α) production was impaired for 9 months after CBT. TLR agonist treatment is thus not expected to induce IFN-α production by pDCs after CBT, limiting its immunotherapeutic potential. Fortunately, in vitro production of large amounts of functional pDCs from cord blood progenitors paves the way for the post-transplantation adoptive transfer of pDCs.

Whole-exome sequencing reveals a rapid change in the frequency of rare functional variants in a founding population of humans

Whole-exome or gene targeted resequencing in hundreds to thousands of individuals has shown that the majority of genetic variants are at low frequency in human populations. Rare variants are enriched for functional mutations and are expected to explain an important fraction of the genetic etiology of human disease, therefore having a potential medical interest. In this work, we analyze the whole-exome sequences of French-Canadian individuals, a founder population with a unique demographic history that includes an original population bottleneck less than 20 generations ago, followed by a demographic explosion, and the whole exomes of French individuals sampled from France. We show that in less than 20 generations of genetic isolation from the French population, the genetic pool of French-Canadians shows reduced levels of diversity, higher homozygosity, and an excess of rare variants with low variant sharing with Europeans. Furthermore, the French-Canadian population contains a larger proportion of putatively damaging functional variants, which could partially explain the increased incidence of genetic disease in the province. Our results highlight the impact of population demography on genetic fitness and the contribution of rare variants to the human genetic variation landscape, emphasizing the need for deep cataloguing of genetic variants by resequencing worldwide human populations in order to truly assess disease risk.

Cord-blood-derived mesenchymal stromal cells downmodulate CD4+ T-cell activation by inducing IL-10-producing Th1 cells

The mechanisms by which mesenchymal stromal cells (MSCs) induce immunomodulation are still poorly understood. In the current work, we show by a combination of polymerase chain reaction (PCR) array, flow cytometry, and multiplex cytokine data analysis that during the inhibition of an alloantigen-driven CD4+ T-cell response, MSCs induce a fraction of CD4+ T-cells to coexpress interferon-γ (IFNγ) and interleukin-10 (IL-10). This CD4+ IFNγ+ IL-10+ cell population shares properties with recently described T-cells originating from switched Th1 cells that start producing IL-10 and acquire a regulatory function. Here we report that IL-10-producing Th1 cells accumulated with time during T-cell stimulation in the presence of MSCs. Moreover, MSCs caused stimulated T-cells to downregulate the IFNγ receptor (IFNγR) without affecting IL-10 receptor expression. Further, the inhibitory effect of MSCs could be reversed by an anti-IFNγR-blocking antibody, indicating that IFNγ is one of the major players in MSC-induced T-cell suppression. Stimulated (and, to a lesser extent, resting) CD4+ T-cells treated with MSCs were able to inhibit the proliferation of autologous CD4+ T-cells, demonstrating their acquired regulatory properties. Altogether, our results suggest that the generation of IL-10-producing Th1 cells is one of the mechanisms by which MSCs can downmodulate an immune response.

Reconstitution of protective immune responses against cytomegalovirus and varicella zoster virus does not require disease development in pediatric recipients of umbilical cord blood transplantation

CMV and varicella zoster virus (VZV) are significant causes of morbidity and mortality following umbilical cord blood transplantation (UCBT). However, the kinetics of reconstitution and protective potential of antiviral cell-mediated immune responses following UCBT remain poorly characterized. In this study, the reconstitution of CMV- and VZV-specific T cell responses was assessed using IFN-γ ELISPOT in 28 children who underwent UCBT to treat hematological or inherited disorders. Barely detectable in the first 3 mo posttransplantation, CMV- and VZV-specific T cell responses were observed in 30.4% and 40.3% of study subjects after 36 mo of follow-up. Four of five CMV-seropositive subjects developed detectable levels of circulating CMV DNA (DNAemia), and 5 of 17 VZV-seropositive patients experienced herpes zoster during the posttransplant period. Four CMV-seronegative subjects developed IFN-γ responses against CMV, and four subjects developed a VZV-specific IFN-γ response without clinical signs of infection. No CMV- or VZV-related events were observed in study subjects following the development of CMV- or VZV-specific responses > 150 spot-forming units/10(6) PBMCs, consistent with T cell-mediated protection. Finally, famciclovir prophylaxis did not strictly prevent the reconstitution of the VZV-specific T cell repertoire, because the frequency of T cells producing IFN-γ in response to VZV Ags reached levels consistent with protection in two nonzoster subjects. Monitoring of CMV- and VZV-specific cell-mediated immunity could inform immunocompetence and guide the initiation and cessation of antiherpetic prophylaxis in UCBT recipients.

Secondary pulmonary alveolar proteinosis after unrelated cord blood hematopoietic cell transplantation

PAP is a rare alveolointerstitial lung disorder characterized histologically by the intra-alveolar accumulation of eosinophilic and PAS-positive material. We observed two cases of PAP after unrelated CB hematopoietic progenitor cell transplantation in children with ALL. No antagonist activity toward GM-CSF was identified in the patient tested. The putative multifactorial PAP etiology is discussed. This potentially curable condition should be considered in a CB allograft recipient with alveolointerstial lung disorder.

Ataxia-telangiectasia presenting with a novel immunodeficiency

Ataxia-telangiectasia is a rare autosomal recessive disorder characterized by progressive cerebellar ataxia, oculocutaneous telangiectasias, and variable degrees of immunodeficiency. Immunologic evaluations of affected patients often reveal anomalies of humoral and cell-mediated immunity. We describe a case of ataxia-telangiectasia with an atypical immunodeficiency and a novel mutation in the ATM gene. The patient presented at age 3 years with a perineal cellulitis associated with profound neutropenia and T-cell lymphopenia. Serum immunoglobulin levels and antibody titers were normal. Neurologic evaluation revealed minimal hypotonia and wide-based gait, without other signs of cerebellar dysfunction. The alpha-fetoprotein level was elevated, and molecular genetic testing confirmed the diagnosis of ataxia-telangiectasia, uncovering a novel ATM gene mutation c.3931C>T (p.Gln1311X) in exon 28. This patient presents a unique immunologic pattern with normal immunoglobulin levels, significant lymphopenia, and profound neutropenia. The diagnosis of ataxia-telangiectasia should be considered in children presenting with gait disorder and immunologic defects, regardless of subtype and severity.

High prevalence of primary immune deficiencies in children with autoimmune disorders

OBJECTIVES

Autoimmunity is a well-recognised manifestation of primary immunodeficiency disorders. However, the prevalence of primary immunodeficiency among children with autoimmune diseases is not well characterised. The objective of this retrospective study was to describe the prevalence of primary immunodeficiency disorders in a paediatric population with autoimmune diseases.

METHODS

We retrospectively analysed a cohort of patients investigated for diverse autoimmune conditions from June 1st 2005 to December 31st 2006 in the Rheumatology and Immunology service of a tertiary care paediatric hospital in Canada. The clinical data of patients were reported. Independently of their baseline characteristics, patients underwent a systematic immunologic workup, which was performed before treatment initiation.

RESULTS

Thirty-three patients were included in this study. We identified 5 patients (15%) with a primary immunodeficiency disorder: common variable immunodeficiency (n=2), combined immunodeficiency (n=1) and complement component deficiency (n=2). Four other patients (12%) displayed decreased levels of immunoglobulins, B-cell lymphopenia and/or abnormal vaccinal response but did not fulfil the criteria of a defined primary immunodeficiency disorder at the time of the study. Importantly, none of these 9 patients had a particular familial history and none had a history of recurrent infections.

CONCLUSIONS

A significant proportion of patients presenting with an autoimmune condition have an underlying primary immunodeficiency disorder that may not be clinically obvious. Additional prospective investigations are needed to further define the role for routine immunologic testing in daily clinical rheumatologic practice.

Munc18-2 deficiency causes familial hemophagocytic lymphohistiocytosis type 5 and impairs cytotoxic granule exocytosis in patient NK cells

Familial hemophagocytic lymphohistiocytosis (FHL) is a genetically heterogeneous autosomal recessive immune disorder characterized by the occurrence of uncontrolled activation of lymphocytes and macrophages infiltrating multiple organs. Disease-causing mutations in the perforin (PRF1; also known as FHL2), Munc13-4 (UNC13D; also known as FHL3), and syntaxin-11 (STX11; also known as FHL4) genes have been identified in individuals with FHL. These genes all encode proteins involved in the cytotoxic activity of lymphocytes. Here, we show that the gene encoding syntaxin-binding protein 2 (Munc18-2; official gene symbol STXBP2) is mutated in another subset of patients with FHL (designated by us as "FHL5"). Lymphoblasts isolated from these patients had strongly decreased STXBP2 protein expression, and NK cells exhibited impaired cytotoxic granule exocytosis, a defect that could be overcome by ectopic expression of wild-type STXBP2. Furthermore, we provide evidence that syntaxin-11 is the main partner of STXBP2 in lymphocytes, as its expression required the presence of STXBP2. Our work shows that STXBP2 deficiency causes FHL5. These data indicate that STXBP2 is required at a late step of the secretory pathway for the release of cytotoxic granules by binding syntaxin 11, another component of the intracellular membrane fusion machinery.

Length of storage and in vitro immunomodulation induced by prestorage leukoreduced red blood cells

BACKGROUND

The relationship between length of storage of red blood cell (RBC) units and biochemical changes has been well studied, but little is known about the progression of cellular immunomodulative properties in blood recipients. This study aims to quantify in vitro T-cell activation and cytokine release by white blood cells, after incubation with supernatants from leukoreduced RBCs.

STUDY DESIGN AND METHODS

Whole blood cultures were incubated with supernatant from five leukoreduced RBC units stored for 1, 6, 10, 15, 24, and 42 days. Supernatant-induced T-cell activation was evaluated by quantifying CD25 expression. Supernatant-induced cytokine production was determined by measuring interleukin (IL)-6, IL-10, and tumor necrosis factor (TNF)-alpha levels.

RESULTS

No cytokines were detected in RBC supernatants even after 42 days of storage. However, IL-6 levels in whole blood culture increased significantly when incubated with supernatant from RBC units stored for 1, 6, and 15 days, by factors of 1.7 +/- 0.3, 1.7 +/- 0.3, and 1.4 +/- 0.3, respectively. TNF-alpha levels were significantly decreased on Days 24 and 42 of storage by factors of 0.50 +/- 0.42 and 0.33 +/- 0.21, respectively. IL-10 levels were significantly increased on Days 1 and 42 of storage by factors of 2.3 +/- 1.3 and 3.2 +/- 2.8, respectively. After an initial increase in IL-6 and TNF-alpha production, there was a significant linear decrease in their levels measured from units stored for longer times. No significant changes in CD25 expression were observed over time.

CONCLUSION

Although no cytokines were measured in the supernatants from leukoreduced RBCs, these supernatants exhibited variable immunomodulatory effects related to their length of storage.

Renal granuloma and immunoglobulin M-complex glomerulonephritis: a case of common variable immunodeficiency?

Common variable immunodeficiency (CVID) is characterized by reduced serum immunoglobulin levels and recurrent bacterial infections. Granulomatous infiltrations are occasionally found in the lymphoid or solid organs of affected patients, but renal involvement is rare. We present a case of possible CVID with interstitial noncaseating granuloma and immunoglobulin (IgM)-complex glomerulonephritis with a membranoproliferative pattern and with a favorable response to corticosteroids, intravenously administered immunoglobulins (IVIGs) and rituximab. CVID must be included in the differential diagnosis of renal granuloma and should be differentiated from sarcoidosis to ensure appropriate therapy.

Hematopoietic engraftment of XLA bone marrow CD34(+) cells in NOG/SCID mice

BACKGROUND AIMS

X-linked agammaglobulinemia (XLA) is a rare primary immunodeficiency associated with mutations of the BTK (Bruton agammaglobulinemia tyrosine kinase) gene. Non-functional BTK leads to a severe decline in peripheral B cells and profound pan-hypogammaglobulinemia. Substitutive immunoglobulin replacement therapy improves long-term survival but remains a symptomatic rather than curative treatment that does not provide an optimal quality of life. Hematopoietic stem cell gene therapy represents a potentially curative treatment. Thorough pre-clinical testing of innovative therapies requires that adequate disease models are available. Invalidation of the murine btk gene produces a phenotype that is less severe than the human disease; alternatively, xenotransplantation of human hematopoietic progenitors obtained from XLA patients may provide a model for testing new treatment procedures.

METHODS

The standard of care for XLA patients rarely offers an opportunity to collect peripheral blood or bone marrow (BM) hematopoietic progenitors; however, we had access to two BM samples obtained from such individuals. We analyzed hematopoietic engraftment of immunoselected CD34(+) cells from these samples in NOD/SCID/ gammac(null) (NOG) mice.

RESULTS

In both cases, human hematopoietic cells were readily detected in BM and thymus, and at low levels in spleen and peripheral blood. Unexpectedly, the early defect in B-lymphoid differentiation associated with XLA was not accurately reproduced in NOG mice, as large amounts of pre-B cells were found in BM.

CONCLUSIONS

These results support the existence of differences in environmental regulation of B-cell ontogeny between mice and humans. This questions the relevance of the NOG xenograft model for pre-clinical study of XLA gene therapy.

[Expression anomalies of the CD3-TCR complex expression and immunodeficiencies]

Molecular characterization of immunodeficiencies contributes to a better understanding of the physiological mechanisms of immune function. The T cell receptor is a heterodimer (alpha/beta or gamma/delta) associated with four transmembrane units of the CD3 complex (gamma, delta, epsilon and zeta). We herein summarize the immunodeficiency states resulting from defects in genes encoding the CD3 complex. Such analysis highlights the respective role of each of these chains in T lymphocyte development and underscores differences between T lymphocyte development in man and mouse. Currently, there is a growing body of knowledge on immunodeficiencies specifically involving the four chains of the CD3, namely gamma, delta, epsilon and zeta. Thus, we can compare the phenotypes observed in these patients with those seen in mice knockout for these genes. The main differences observed involve the respective roles of the CD3gamma chain as well as the CD3delta, whose functions seem to be reciprocal between the two species. Indeed, in the mouse, knockout of CD3delta allows some degree of T lymphocyte differentiation since mature CD4 and CD8 as well as TCRgammadelta T lymphocytes are observed in the periphery. In contrast, deleterious mutation of the CD3delta encoding gene in the human leads to a severe combined immunodeficiency characterised by the complete absence of mature T cell subpopulations including TCRalpha/beta and TCRgamma/delta. Reciprocally, in the human, mutation of the CD3gamma encoding gene leads to a moderate immunodeficiency which contrasts with the complete block of T cell differentiation observed in mice knockout for this gene. This article brings into focus the knowledge gained through studies of immunodeficiency mouse models with the pathophysiological state observed in human disease.

Long-term T-cell reconstitution after hematopoietic stem-cell transplantation in primary T-cell-immunodeficient patients is associated with myeloid chimerism and possibly the primary disease phenotype

We studied T-cell reconstitution in 31 primary T-cell-immunodeficient patients who had undergone hematopoietic stem-cell transplantation (HSCT) over 10 years previously. In 19 patients, there was no evidence of myeloid chimerism because little or no myeloablation had been performed. Given this context, we sought factors associated with good long-term T-cell reconstitution. We found that all patients having undergone full myeloablation had donor myeloid cells and persistent thymopoiesis, as evidenced by the presence of naive T cells carrying T-cell receptor excision circles (TRECs). In 9 patients with host myeloid chimerism, sustained thymic output was also observed and appeared to be associated with gammac deficiency. It is therefore possible that the complete absence of thymic progenitors characterizing this condition created a more favorable environment for thymic seeding by a population of early progenitor cells with the potential for self-renewal, thus enabling long-term (> 10 years) T-cell production.

Is Xenotransplantation of Embryonic Stem Cells a Realistic Option?

To test the purported immune privilege of embryonic stem cells (ESC) in the challenging setting of xenotransplantation, 14 immunocompetent baboons were subjected to a coronary artery occlusion-reperfusion sequence and, two weeks later, randomized to receive in-scar injections of culture medium or cardiac-committed mouse ESC engineered to express fluorescent reporter genes driven by cardiac-specific promoters. Two months after transplantation, left ventricular function, as assessed by echocardiography, deteriorated to a similar extent in control and treated baboons. This correlated with failure to identify the grafted cells by X-gal histology and immunofluorescence. Rejection did not seem to be mediated by xenoantibodies, but rather by T lymphocytes and natural killer cells as suggested by positive immunostaining for CD3 and CD56 early after transplantation. There was no increase in circulating levels of regulatory T cells. These data raise a cautionary note about the immune privilege of ESC and suggest that from a mere immunologic standpoint, ESC xenotransplantation is likely to be an unrealistic challenge.

Familial NK cell deficiency associated with impaired IL-2- and IL-15-dependent survival of lymphocytes

We previously reported the clinical phenotype of two siblings with a novel inherited developmental and immunodeficiency syndrome consisting of severe intrauterine growth retardation and the impaired development of specific lymphoid lineages, including transient CD8 alphabeta T lymphopenia and a persistent lack of blood NK cells. We describe here the elucidation of a plausible underlying pathogenic mechanism, with a cellular phenotype of impaired survival of both fresh and herpesvirus saimiri-transformed T cells, in the surviving child. Clearly, NK cells could not be studied. However, peripheral blood T lymphocytes displayed excessive apoptosis ex vivo. Moreover, the survival rates of CD4 and CD8 alphabeta T cell blasts generated in vitro, and herpesvirus saimiri-transformed T cells cultured in vitro, were low, but not nil, following treatment with IL-2 and IL-15. In contrast, Fas-mediated activation-induced cell death was not enhanced, indicating a selective excess of cytokine deprivation-mediated apoptosis. In keeping with the known roles of IL-2 and IL-15 in the development of NK and CD8 T cells in the mouse model, these data suggest that an impaired, but not abolished, survival response to IL-2 and IL-15 accounts for the persistent lack of NK cells and the transient CD8 alphabeta T lymphopenia documented in vivo. Impaired cytokine-mediated lymphocyte survival is likely to be the pathogenic mechanism underlying this novel form of inherited and selective NK deficiency in humans.

XIAP deficiency in humans causes an X-linked lymphoproliferative syndrome

The homeostasis of the immune response requires tight regulation of the proliferation and apoptosis of activated lymphocytes. In humans, defects in immune homeostasis result in lymphoproliferation disorders including autoimmunity, haemophagocytic lymphohystiocytosis and lymphomas. The X-linked lymphoproliferative syndrome (XLP) is a rare, inherited immunodeficiency that is characterized by lymphohystiocytosis, hypogammaglobulinaemia and lymphomas, and that usually develops in response to infection with Epstein-Barr virus (EBV). Mutations in the signalling lymphocyte activation molecule (SLAM)-associated protein SAP, a signalling adaptor molecule, underlie 60% of cases of familial XLP. Here, we identify mutations in the gene that encodes the X-linked inhibitor-of-apoptosis XIAP (also termed BIRC4) in patients with XLP from three families without mutations in SAP. These mutations lead to defective expression of XIAP. We show that apoptosis of lymphocytes from XIAP-deficient patients is enhanced in response to various stimuli including the T-cell antigen receptor (TCR)-CD3 complex, the death receptor CD95 (also termed Fas or Apo-1) and the TNF-associated apoptosis-inducing ligand receptor (TRAIL-R). We also found that XIAP-deficient patients, like SAP-deficient patients, have low numbers of natural killer T-lymphocytes (NKT cells), indicating that XIAP is required for the survival and/or differentiation of NKT cells. The observation that XIAP-deficiency and SAP-deficiency are both associated with a defect in NKT cells strengthens the hypothesis that NKT cells have a key role in the immune response to EBV. Furthermore, by identifying an XLP immunodeficiency that is caused by mutations in XIAP, we show that XIAP is a potent regulator of lymphocyte homeostasis in vivo.

Human leucocyte antigen-identical haematopoietic stem cell transplantation in major histocompatiblity complex class II immunodeficiency: reduced survival correlates with an increased incidence of acute graft-versus-host disease and pre-existing viral infections

Major histocompatibility complex class II deficiency, a rare autosomal recessive primary immunodeficiency, is caused by the defective expression of human leucocyte antigen (HLA) class II molecules due to mutated trans-acting elements of any one of four regulatory genes (CIITA, RFXANK, RFX5, RFXAP). The impaired CD4 T-cell differentiation and antigen presentation in the periphery results in a severe defect of cellular and humoral response consistent with severe recurrent infections, leading to a poor prognosis. Currently, allogeneic haematopoietic stem cell transplantation (HSCT) is the only curative approach, but the overall cure rate is lower than in other immunodeficiencies. We report a single centre experience of 17 HSCTs with 15 HLA-identical donors between 1981 and 2004. Eight patients survived, while the occurrence of acute graft-versus-host disease (GVHD) was 50%. This study aimed to identify potential risk factors for GVHD and outcome within pre-HSCT complications related to the immunodeficiency. Five of seven patients with pre-existing viral infections developed acute GVHD > or = grade II, of whom four died. Two of seven patients without detectable pre-existing viral infection developed GVHD > or = grade II, and one died. The difference was significant (P < 0.05). A plausible link with other factors potentially associated with the development of GVHD could not be found. We suggest that the reduced survival after HLA-identical HSCT may be caused by the high incidence of pre-existing viral infections and associated with the onset of severe acute GVHD.

T Cell-Dependent Activation of Dendritic Cells Requires IL-12 and IFN-γ Signaling in T Cells

Patients presenting with genetic deficiencies in IFNGR1, IFNGR2, IL-12B, and IL-12RB1 display increased susceptibility to mycobacterial infections. We analyzed in this group of patients the cross-talk between human CD4+ T lymphocytes and dendritic cells (DCs) that leads to maturation of DC into producers of bioactive IL-12 and to activation of T cells into IFN-gamma producers. We found that this cross-talk is defective in all patients from this group. Unraveling the mechanisms underlying this deficiency, we showed that IL-12 signaling in T cells is required to induce expression of costimulatory molecules and secretion of IL-12 by DCs and that IFNGR expression is required on both DCs and CD4+ T cells to induce IL-12 secretion by DCs. These data suggest that CD4+ T cell-mediated activation of DCs plays a critical role in the defense against mycobacterial infections in humans.

Défaut d’exocytose des granules lytiques

An in vivo disturbance of lymphocyte homeostasis occurs during the course of the hemophagocytic syndrome (HS). HS is a severe and often fatal syndrome resulting from potent and uncontrolled activation and proliferation of T-lymphocytes, mainly polyclonal CD8 lymphocytes, leading to excessive macrophage activation, high level of proinflammatory cytokine production and multiple deleterious effects. The onset of HS characterizes several inherited disorders in humans. In most of these conditions, the molecular defect impairs the granule-dependent cytotoxic activity of lymphocytes, thus highlighting the determinant role of this function in driving back the immune system to a state of equilibrium following infection. Several lines of evidence suggest that an increase in the expansion phase rather than a decrease in the contraction phase of the CD8+ T cells population characterizes the HS. Failure to kill antigen presenting cells through a transaction mechanism of cytotoxic cells should favor a sustained response, although the mechanism may be more complex than simple decrease of antigen load. Defect in the granule dependent cytotoxic function of lymphocytes result from perforin mutation in familial hemophagocytic lymphohistiocytosis type 2, from Munc13-4 (UNC13D) mutation in familial hemophagocytic lymphohistiocytosis type 3, from Rab27a mutation in Griscelli syndrome type 2, and from CHS/LYST mutation in Chediak-Higashi syndrome. The characterization of the molecular causes leading to these conditions identified Rab27a and Munc13-4 as two critical effectors of the exocytic machinery, required for the terminal transport/docking or priming of the cytotoxic granules, respectively. Different members of the Rab and Munc13 family of proteins are also used in neurotransmitter release at the neurological synapse, highlighting the similarity of the mechanisms regulating both secretory pathways. Future investigations regarding HS will continue to elucidate this exocytic pathway machinery and improve our understanding of how it finely regulates the immune response, an area that is likely to be useful for therapeutic intervention.

Kaposi's sarcoma in a child with Wiskott-Aldrich syndrome

INTRODUCTION

Kaposi's sarcoma (KS) is rare in childhood. It may be favored by acquired immune deficiencies, but the predisposing factors to KS in other children are unclear.

DISCUSSION

KS has been reported in only two children and one adult with primary immunodeficiency. We report here a Tunisian child with a Wiskott-Aldrich syndrome who developed KS at the age of 14 months.

CONCLUSION

This observation expands the spectrum of primary immunodeficiencies associated with KS in childhood.

Successful allogeneic hemopoietic stem cell transplantation in a child who had anhidrotic ectodermal dysplasia with immunodeficiency

Anhidrotic ectodermal dysplasia with immunodeficiency is associated with multiple infections and a poor clinical outcome. Hypomorphic mutations in nuclear factor kappaB essential modulator (NEMO)/IkappaB kinase complex and a hypermorphic mutation in inhibitor alpha of nuclear factor kappaB (IkappaBalpha) both result in impaired nuclear factor kappaB activation and are associated with X-recessive and autosomal-dominant forms of anhidrotic ectodermal dysplasia with immunodeficiency, respectively. Autosomal-dominant anhidrotic ectodermal dysplasia with immunodeficiency is also associated with a severe T-cell phenotype. It is not known whether hematopoietic stem cell transplantation can cure immune deficiency in children with anhidrotic ectodermal dysplasia with immunodeficiency. A boy with autosomal-dominant anhidrotic ectodermal dysplasia with immunodeficiency and a severe T-cell immunodeficiency underwent transplantation at 1 year of age with haploidentical T-cell-depleted bone marrow after myeloablative conditioning. Engraftment occurred, with full hematopoietic chimerism. Seven years after transplantation, clinical outcome is favorable, with normal T-cell development. As expected, the developmental features of the anhidrotic ectodermal dysplasia syndrome have appeared and persisted. This is the first report of successful hematopoietic stem cell transplantation in a child with anhidrotic ectodermal dysplasia with immunodeficiency. Hematopoietic stem cell transplantation is well tolerated and efficiently cures the profound immunodeficiency associated with autosomal-dominant anhidrotic ectodermal dysplasia with immunodeficiency.

Inherited and somatic CD3zeta mutations in a patient with T-cell deficiency

A four-month-old boy with primary immunodeficiency was found to have a homozygous germ-line mutation of the gene encoding the CD3zeta subunit of the T-cell receptor-CD3 complex. CD3zeta is necessary for the development and function of T cells. Some of the patient's T cells had low levels of the T-cell receptor-CD3 complex and carried the Q70X mutation in both alleles of CD3zeta, whereas other T cells had normal levels of the complex and bore the Q70X mutation on only one allele of CD3zeta, plus one of three heterozygous somatic mutations of CD3zeta on the other allele, allowing expression of poorly functional T-cell receptor-CD3 complexes.

Hematopoietic stem cell transplantation in hemophagocytic lymphohistiocytosis: a single-center report of 48 patients

OBJECTIVES

Familial hemophagocytic lymphohistiocytosis (FHLH) is a genetically determined disorder characterized by the early onset of fever, hepatosplenomegaly, central nervous system disease, thrombocytopenia, coagulation disorders, and hemophagocytosis. It is caused by genetic defects that impair T cell-mediated and natural cytotoxicity. Chemotherapy- or immunotherapy-based treatments can achieve remission. Hematopoietic stem cell transplantation (HSCT), however, is the only curative option, but optimal modalities and long-term outcome are not yet well known.

METHODS

We retrospectively analyzed the outcome of HSCT that was performed in 48 consecutive patients who had FHLH and were treated in a single center between 1982 and 2004.

RESULTS

The overall survival was 58.5% with a median follow-up of 5.8 years and extending to 20 years. A combination of active disease and haploidentical HSCT had a poor prognosis because in this situation, HLH disease is more frequently associated with graft failure. Twelve patients received 2 transplants because of graft failure (n = 7) or secondary graft loss that led to HLH relapse (n = 5). Transplant-related toxicity essentially consisted in veno-occlusive disease, which occurred in 28% of transplants and was associated with young age, haploidentical transplantation, and the use of antithymocyte globulin (ATG) in the conditioning regimen. A sustained remission was achieved in all patients with a donor chimerism > or = 20% of leukocytes. Long-term sequelae were limited, because only 2 (7%) of 28 patients experienced a mild neurologic disorder.

CONCLUSIONS

This survey demonstrates the long-term efficacy of HSCT as a cure of FHLH. HSCT preserves quality of life. It shows that HSCT should be performed as early as a complete remission has been achieved. Additional studies are required to improve the procedure and reduce its toxic effects.

A novel immunodeficiency associated with hypomorphic RAG1 mutations and CMV infection

Amorphic mutations in the recombination activating genes RAG1 and RAG2 have been reported to cause T- B- SCID, whereas hypomorphic mutations led to the expansion of a few autoimmune T cell clones responsible for the Omenn syndrome phenotype. We report here a novel clinical and immunological phenotype associated with recessive RAG1 hypomorphic mutations in 4 patients from 4 different families. The immunological phenotype consists of the oligoclonal expansion of TCR gammadelta T cells combined with TCR alphabeta T cell lymphopenia. The clinical phenotype consists of severe, disseminated CMV infection and autoimmune blood cell manifestations. Repertoire studies suggest that CMV infection, in the setting of this particular T cell immunodeficiency, may have driven the TCR gammadelta T cell clonal expansion. This observation extends the range of clinical and immunological phenotypes associated with RAG mutations, emphasizing the role of the genetic background and microbial environment in determining disease phenotype.

CD3 deficiencies

PURPOSE OF REVIEW

The molecular characterization of inherited T-cell immunodeficiencies has contributed to delineating key factors in human T-cell development. This review reports on the recent description of deleterious mutations in the genes encoding CD3 subunits expressed at the T-lymphocyte membrane in association with the T-cell receptor.

RECENT FINDINGS

Homozygous mutations in CD3D and CD3E genes lead to a complete block in T-cell development and thus to an early-onset severe combined immunodeficiency phenotype. Thymic studies have shown that the defect in T-cell development occurs at the transition between 'double-negative' and 'double-positive' thymocytes. These results contrast with the partial T-cell immunodeficiency caused by a deficiency in CD3G.

SUMMARY

Two new severe combined immunodeficiency conditions have been reported as a consequence of either CD3D or CD3E deficiency. The distinct phenotype of CD3G deficiency sheds light on the differential roles of CD3 subunits in T-lymphocyte development.

Severe combined immunodeficiency. A model disease for molecular immunology and therapy

Severe combined immunodeficiencies (SCIDs) consist of genetically determined arrest of T-cell differentiation. Ten different molecular defects have now been identified, which all lead to early death in the absence of therapy. Transplantation of allogeneic hematopoietic stem cells (HSCT) can restore T-cell development, thus saving the lives of SCID patients. In this review, the different characteristics of HSCT are discussed along with the available data regarding the long-term outcome. Transient thymopoiesis caused by an exhaustion of donor progenitor cells and possibly a progressive loss of thymus function can lead to a progressive decline in T-cell functions. The preliminary results of gene therapy show the correction of two SCID conditions. Based on the assumption that long-lasting pluripotent progenitor cells are transduced, these data suggest that gene therapy could overcome the long-term recurrence of the T-cell immunodeficiency. SCID is thus a disease model for experimental therapy in the hematopoietic system.

Ca2+ ionophores trigger membrane remodeling without a need for store-operated Ca2+ entry

Calcium (Ca2+) ionophores are the most effective agents able to elicit rapid membrane remodeling in vitro. This process exposes aminophospholipids at the surface of platelets and blood cells, thus providing a catalytic surface for coagulation. To explore the underlying mechanism, we examined if cytosolic Ca2+ ([Ca2+]i) increase through store-operated Ca2+ entry (SOCE) was necessary for the potent effect of ionophores. Recent studies have demonstrated that the Ca2+-ATPase inhibitor thapsigargin, although able to elevate [Ca2+]i through SOCE, does not trigger the rapid membrane remodeling. However, it was not known if the additional effect of ionophores to promote the process required SOCE or could it occur independently. We took advantage of two mutant B lymphoblast cell lines, characterized either by defective SOCE or altered membrane remodeling, to simultaneously assess [Ca2+]i increase and membrane remodeling in the presence of ionophores or thapsigargin. Results imply that ionophores trigger membrane remodeling without the requirement for a functional SOCE.

Severe combined immunodeficiency caused by deficiency in either the delta or the epsilon subunit of CD3

We investigated the molecular mechanism underlying a severe combined immunodeficiency characterized by the selective and complete absence of T cells. The condition was found in 5 patients and 2 fetuses from 3 consanguineous families. Linkage analysis performed on the 3 families revealed that the patients were carrying homozygous haplotypes within the 11q23 region, in which the genes encoding the gamma, delta, and epsilon subunits of CD3 are located. Patients and affected fetuses from 2 families were homozygous for a mutation in the CD3D gene, and patients from the third family were homozygous for a mutation in the CD3E gene. The thymus from a CD3delta-deficient fetus was analyzed and revealed that T cell differentiation was blocked at entry into the double positive (CD4+CD8+) stage with the accumulation of intermediate CD4-single positive cells. This indicates that CD3delta plays an essential role in promoting progression of early thymocytes toward double-positive stage. Altogether, these findings extend the known molecular mechanisms underlying severe combined immunodeficiency to a new deficiency, i.e., CD3epsilon deficiency, and emphasize the essential roles played by the CD3epsilon and CD3delta subunits in human thymocyte development, since these subunits associate with both the pre-TCR and the TCR.

Severe and progressive encephalitis as a presenting manifestation of a novel missense perforin mutation and impaired cytolytic activity

Mutations in the perforin gene cause familial hemophagocytic lymphohistiocytosis (FHL). The first symptoms of FHL are usually intractable fever, hepatosplenomegaly, and pancytopenia. Most FHL patients subsequently develop central nervous system (CNS) manifestations due to infiltration of tissues by activated lymphocytes and macrophages. We report 2 FHL patients with an atypical phenotype characterized by isolated severe neurologic symptoms mimicking chronic encephalitis and leading to an early death. Functional and molecular analyses revealed the same novel missense mutation in the perforin gene in both patients; this mutation affected the calcium-binding domain of the protein. This missense mutation did not affect perforin maturation or expression in cytotoxic cells but impaired in vitro cytotoxic activity. Diagnosis was delayed in both patients because of the initial neurologic expression and the normal expression of perforin in circulating lymphocytes. This emphasizes the importance of early diagnosis of this atypical form of FHL, as CNS involvement causes severe, irreversible encephalopathy. This observation also raises the question of the role of some mutations in the neurologic expression of FHL.

The VP6 protein of rotavirus interacts with a large fraction of human naive B cells via surface immunoglobulins

Immunity to human group A rotavirus (RV), a major cause of viral gastroenteritis in infants, involves B lymphocytes that provide RV-specific antibodies. Additionally, some arguments suggest that naive B cells could be implicated in the first steps of the immune response against RV. The aim of our study was to analyze the interaction of VP6 and VP7 RV capsid proteins with human B cells depending on the immune status of the individual, i.e., naive or RV experienced. For this purpose, a two-color virus-like particle flow cytometry assay was devised to evaluate the blood B-lymphocyte reactivity to VP6 and VP7 proteins from healthy RV-exposed adults, recently infected infants, and neonates at birth. Both VP6 and VP7 interactions with B cells were mediated by surface immunoglobulins and probably by their Fab portions. VP7-reactive B lymphocytes were mainly detected from RV-experienced patients and almost exclusively in the CD27-positive memory cell fraction. Conversely, VP6-reactive B lymphocytes were detected at similar and high frequencies in adult, infant, and neonate samples. In adult samples, VP6 reacted with about 2% of the CD27-negative (CD27(neg)) naive B cells. These results demonstrated that the VP6 RV protein interacted with a large fraction of naive B lymphocytes from both adults and neonates. We propose that naive B cell-VP6 interaction might influence the strength and quality of the acquired immune response and should be considered for elaborating RV vaccine strategies.