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Biomedical subjects

Alain Fischer

Publications and source records attributed to Alain Fischer.

At least 19 recordsLinked to original sources
PubMed2007

p56lck, LFA-1 and PI3K but not SHP-2 interact with GM1- or GM3-enriched microdomains in a CD4-p56lck association-dependent manner.

We previously showed that the association of CD4 and G(M3) ganglioside induced by CD4 ligand binding was required for the down-regulation of adhesion and that aggregation of ganglioside-enriched domains was accompanied by transient co-localization of LFA-1 (lymphocyte function-associated antigen-1), PI3K (phosphoinositide 3-kinase) and CD4. We also showed that these proteins co-localized with the G(M1) ganglioside that partially co-localized with G(M3) in these domains. In the present study, we show that CD4-p56(lck) association in CD4 signalling is required for the redistribution of p56(lck), PI3K and LFA-1 in ganglioside-enriched domains, since ganglioside aggregation and recruitment of these proteins were not observed in a T-cell line (A201) expressing the mutant form of CD4 that does not bind p56(lck). In addition, we show that although these proteins associated in different ways with G(M1) and G(M3), all of the associations were dependent on CD4-p56(lck) association. Gangliosides could associate with these proteins that differ in affinity binding and could be modified following CD4 signalling. Our results suggest that through these associations, gangliosides transiently sequestrate these proteins and consequently inhibit LFA-1-dependent adhesion. Furthermore, while structural diversity of gangliosides may allow association with distinct proteins, we show that the tyrosine phosphatase SHP-2 (Src homology 2 domain-containing protein tyrosine phosphatase 2), also required for the down-regulation of LFA-1-dependent adhesion, transiently and partially co-localized with PI3K and p56(lck) in detergent-insoluble membranes without association with G(M1) or G(M3). We propose that CD4 ligation and binding with p56(lck) and their interaction with G(M3) and/or G(M1) gangliosides induce recruitment of distinct proteins important for CD4 signalling to form a multimolecular signalling complex.

Antibodies↗
PubMed2006

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.

Adult↗
PubMed2006

CD34 stem cell top-ups without conditioning after initial haematopoietic stem cell transplantation for correction of incomplete haematopoietic and immunological recovery in severe congenital immunodeficiencies.

Haematopoietic stem cell transplantation can be limited by ineffective haematopoiesis and poor immune recovery. A CD34(+) cell infusion without conditioning has the potential to improve stem cell function with limited toxicity. Eighteen patients with congenital immunodeficiencies received CD34(+) boosts for various defects. When given <1 year after the original graft, six of seven cytopenic patients achieved transfusion independence. A second cohort (n = 11) received boosts >1 year after the original graft; only minimal changes in immune function or chimaerism were noted. Unconditioned stem cell boosts have limited toxicity but should be given early after the original graft to be effective.

Adolescent↗
PubMed2006

Gene therapy: X-SCID transgene leukaemogenicity.

Gene therapy has been remarkably effective for the immunological reconstitution of patients with severe combined immune deficiency, but the occurrence of leukaemia in a few patients has stimulated debate about the safety of the procedure and the mechanisms of leukaemogenesis. Woods et al. forced high expression of the corrective therapeutic gene IL2RG, which encodes the gamma-chain of the interleukin-2 receptor, in a mouse model of the disease and found that tumours appeared in a proportion of cases. Here we show that transgenic IL2RG does not necessarily have potent intrinsic oncogenic properties, and argue that the interpretation of this observation with respect to human trials is overstated.

Animals↗
PubMed2006

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.

Chimerism↗
PubMed2006

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.

Base Sequence↗
PubMed2006

Competition within the early B-cell compartment conditions B-cell reconstitution after hematopoietic stem cell transplantation in nonirradiated recipients.

Severe combined immunodeficiency (SCID) is characterized by a complete block in T-lymphocyte differentiation. Most SCID also affects B-cell development or function, although a normal pool of pro-B cells is detectable. Treatment of SCID consists of allogeneic hematopoietic stem cell transplantation (HSCT), but in the absence of a myeloablative conditioning regimen, only T cells, and in some cases, natural killer (NK) cells, are of donor origin, while all other leukocytes subsets are of host origin. We hypothesized that donor B-cell development success could be conditioned by the competitive ability of recipient B-cell precursors in the bone marrow. We therefore compared the outcome of unconditioned HSCT in mice that differed with respect to their pro-B-cell compartments. B-cell reconstitution was limited in recipient mice containing a normal pro-B-cell pool, whereas immature and mature B-cell numbers reached wild-type levels in mice with compromised early B-cell precursors. Interestingly, host NK cells did not modify the outcome of unconditioned HSCT as long as the early B-cell compartment was compromised. These observations suggest that recipient B-cell precursors condition the reconstitution of the donor B-cell pool and, if extrapolative to humans, suggest that conditioning regimens targeting host pro-B cells may help improve B-cell reconstitution after allogeneic HSCT.

Animals↗
PubMed2006

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.

Combined Modality Therapy↗
PubMed2006

Cernunnos interacts with the XRCC4 x DNA-ligase IV complex and is homologous to the yeast nonhomologous end-joining factor Nej1.

DNA double strand breaks are considered as the most harmful DNA lesions and are repaired by either homologous recombination or nonhomologous end joining (NHEJ). A new NHEJ factor, Cernunnos, has been identified, the defect of which leads to a severe immunodeficiency condition associated with microcephaly and other developmental defects in humans. This presentation is reminiscent to that of DNA-ligase IV deficiency and suggests a possible interplay between Cernunnos and the XRCC4 x DNA-ligase IV complex. We show here that Cernunnos physically interacts with the XRCC4 x DNA-ligase IV complex. Moreover, a combination of sensitive methods of sequence analysis revealed that Cernunnos can be associated with the XRCC4 family of proteins and that it corresponds to the genuine homolog of the yeast Nej1 protein. Altogether these results shed new lights on the last step, the DNA religation, of the NHEJ pathway.

Amino Acid Sequence↗
PubMed2006

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.

Adolescent↗
PubMed2006

Cernunnos, a novel nonhomologous end-joining factor, is mutated in human immunodeficiency with microcephaly.

DNA double-strand breaks (DSBs) occur at random upon genotoxic stresses and represent obligatory intermediates during physiological DNA rearrangement events such as the V(D)J recombination in the immune system. DSBs, which are among the most toxic DNA lesions, are preferentially repaired by the nonhomologous end-joining (NHEJ) pathway in higher eukaryotes. Failure to properly repair DSBs results in genetic instability, developmental delay, and various forms of immunodeficiency. Here we describe five patients with growth retardation, microcephaly, and immunodeficiency characterized by a profound T+B lymphocytopenia. An increased cellular sensitivity to ionizing radiation, a defective V(D)J recombination, and an impaired DNA-end ligation process both in vivo and in vitro are indicative of a general DNA repair defect in these patients. All five patients carry mutations in the Cernunnos gene, which was identified through cDNA functional complementation cloning. Cernunnos/XLF represents a novel DNA repair factor essential for the NHEJ pathway.

Adolescent↗
PubMed2006

Severe combined immunodeficiency and microcephaly in siblings with hypomorphic mutations in DNA ligase IV.

DNA double-strand breaks (dsb) during V(D)J recombination of T and B lymphocyte receptor genes are resolved by the non-homologous DNA end joining pathway (NHEJ) including at least six factors: Ku70, Ku80, DNA-PK(cs), Artemis, Xrcc4, and DNA ligase IV (Lig4). Artemis and Lig4 are the only known V(D)J/NHEJ factors found deficient in human genetic disorders. Null mutations of the Artemis gene result in a complete absence of T and B lymphocytes and increased cellular sensitivity to ionizing radiations, causing radiosensitive-SCID. Mutations of Lig4 are exclusively hypomorphic and have only been described in six patients, four exhibiting mild immunodeficiency associated with microcephaly and developmental delay, while two patient had leukemia. Here we report a SCID associated with microcephaly caused by compound heterozygous hypomorphic mutations in Lig4. Residual activity of Lig4 in these patients is underscored by a normal pattern of TCR-alpha and -beta junctions in the T cells of the patients and a moderate impairment of V(D)J recombination as tested in vitro. These observations contrast with the severity of the clinical immunodeficiency, suggesting that Lig4 may have additional critical roles in lymphocyte survival beyond V(D)J recombination.

Base Sequence↗
PubMed2006

Activation-induced cytidine deaminase: structure-function relationship as based on the study of mutants.

Activation-induced cytidine deaminase (AID; gene symbol AICDA) is the key molecule required to induce immunoglobulin (Ig) class switch recombination (CSR) and somatic hypermutation (SHM) of the variable regions of Ig genes. Its deficiency causes a form of hyper-IgM (HIGM) syndrome. The study of natural AID mutants associated with HIGM as well as engineered mutants led to the characterization of the active domains of the protein. AID, through its cytidine deaminase activity, induces a targeted DNA lesion as an early step required for both CSR and SHM. Besides its cytidine deaminase activity, AID plays a further essential role in CSR, likely by recruiting CSR-specific cofactors by its C-terminus. A similar binding of SHM-specific cofactors to the N-terminal part is suggested by the functional characteristics of N(ter) AID artificial mutants. These data require confirmation in vivo. Finally, AID acts as a homo-, di-, or multimeric complex. Together, these data strongly suggest that AID, a master molecule for antibody diversification, exerts its activity on CSR not only as a cytidine deaminase enzyme but also as a docking protein, recruiting specific cofactors to a multimeric complex.

Base Sequence↗
PubMed2006

Primary immunodeficiency diseases: an update from the International Union of Immunological Societies Primary Immunodeficiency Diseases Classification Committee Meeting in Budapest, 2005.

Although relatively rare, primary immunodeficiency diseases (PIDs) provide an excellent window into the functioning of the immune system. In the late 1960s, observations on these diseases, with their associated infections and genetics, bisected the immune system into humoral immunity and cell-mediated immunity. These diseases also represent a challenge in their diagnosis and treatment. Beginning in 1970, a unified nomenclature for the then-known PIDs was created by a committee convoked by the World Health Organization. Since then, and later under the aegis of the International Union of Immunological Societies, an international committee of experts has met every 2 to 3 years to update the classification of PIDs. During the past 15 years, the molecular basis of more than 120 PIDs has been elucidated. This update results from the latest meeting of this committee in Budapest, Hungary, in June 2005, which followed 2 1/2 days of scientific discussions. As a result of this work, new entities have been included, and the nomenclature of some PIDs (specifically of the various forms of class-switch recombination defects, previously known as hyper-IgM syndromes) has been changed.

B-Lymphocytes↗
PubMed2006

Omenn syndrome in an infant with IL7RA gene mutation.

Omenn syndrome (OS) is a rare combined immunodeficiency characterized by erythroderma, lymphadenopathy, and autoimmune manifestations. Most cases are due to mutations in the RAG genes. We report a case of OS due to mutations of IL7RA, thus defining Omenn syndrome as a genetically heterogeneous condition.

Amino Acid Substitution↗
PubMed2006

Hyper-IgM syndromes.

PURPOSE OF REVIEW: The recent elucidation of the molecular defects leading to hyper-IgM syndromes has provided considerable insight into the complex mechanisms that govern the antibody maturation in humans. RECENT FINDINGS: The study of a large cohort of patients revealed unexpected clinical, immunological and genetic findings, which have significant implications on the molecular basis of immunoglobulin class switch recombination and somatic hypermutation, as shown for hypomorphic mutations in the nuclear factor-kappaB essential modulator (NEMO) gene and peculiar activation-induced cytidine deaminase defects that differently affect class switch recombination and somatic hypermutation. The description of the hyper-IgM condition due to mutations in the gene encoding uracil-N glycosylase has been essential for defining the DNA-editing activity of activation-induced cytidine deaminase. Novel findings are awaited from the study of the yet genetically undefined hyper-IgM syndromes, leading to the identification of activation-induced cytidine deaminase cofactors and proteins involved in class switch recombination-induced DNA repair. In the genetically characterized hyper-IgM syndromes, the precise identification of the molecular defect allows the evaluation of hyper-IgM complications, and thus aids assessment of prognosis and proper survey and treatment. SUMMARY: The important contribution made by investigation of this condition improves our understanding of the physiology of the antibody response in humans.

Chromosomes, Human, X↗