Fabien Touzot

Clinical similarities and differences of patients with X-linked lymphoproliferative syndrome type 1 (XLP-1/SAP-deficiency) versus type 2 (XLP-2/XIAP-deficiency)

X-linked lymphoproliferative syndromes (XLP) are primary immunodeficiencies characterized by a particular vulnerability toward Epstein-Barr virus infection, frequently resulting in hemophagocytic lymphohistiocytosis (HLH). XLP type 1 (XLP-1) is caused by mutations in the gene SH2D1A (also named SAP), whereas mutations in the gene XIAP underlie XLP type 2 (XLP-2). Here, a comparison of the clinical phenotypes associated with XLP-1 and XLP-2 was performed in cohorts of 33 and 30 patients, respectively. HLH (XLP-1, 55%; XLP-2, 76%) and hypogammaglobulinemia (XLP-1, 67%; XLP-2, 33%) occurred in both groups. Epstein-Barr virus infection in XLP-1 and XLP-2 was the common trigger of HLH (XLP-1, 92%; XLP-2, 83%). Survival rates and mean ages at the first HLH episode did not differ for both groups, but HLH was more severe with lethal outcome in XLP-1 (XLP-1, 61%; XLP-2, 23%). Although only XLP-1 patients developed lymphomas (30%), XLP-2 patients (17%) had chronic hemorrhagic colitis as documented by histopathology. Recurrent splenomegaly often associated with cytopenia and fever was preferentially observed in XLP-2 (XLP-1, 7%; XLP-2, 87%) and probably represents minimal forms of HLH as documented by histopathology. This first phenotypic comparison of XLP subtypes should help to improve the diagnosis and the care of patients with XLP conditions.

Outcomes Following Gene Therapy in Patients With Severe Wiskott-Aldrich Syndrome

IMPORTANCEnWiskott-Aldrich syndrome is a rare primary immunodeficiency associated with severe microthrombocytopenia. Partially HLA antigen-matched allogeneic hematopoietic stem cell (HSC) transplantation is often curative but is associated with significant comorbidity.nnnOBJECTIVEnTo assess the outcomes and safety of autologous HSC gene therapy in Wiskott-Aldrich syndrome.nnnDESIGN, SETTING, AND PARTICIPANTSnGene-corrected autologous HSCs were infused in 7 consecutive patients with severe Wiskott-Aldrich syndrome lacking HLA antigen-matched related or unrelated HSC donors (age range, 0.8-15.5 years; mean, 7 years) following myeloablative conditioning. Patients were enrolled in France and England and treated between December 2010 and January 2014. Follow-up of patients in this intermediate analysis ranged from 9 to 42 months.nnnINTERVENTIONnA single infusion of gene-modified CD34+ cells with an advanced lentiviral vector.nnnMAIN OUTCOMES AND MEASURESnPrimary outcomes were improvement at 24 months in eczema, frequency and severity of infections, bleeding tendency, and autoimmunity and reduction in disease-related days of hospitalization. Secondary outcomes were improvement in immunological and hematological characteristics and evidence of safety through vector integration analysis.nnnRESULTSnSix of the 7 patients were alive at the time of last follow-up (mean and median follow-up, 28 months and 27 months, respectively) and showed sustained clinical benefit. One patient died 7 months after treatment of preexisting drug-resistant herpes virus infection. Eczema and susceptibility to infections resolved in all 6 patients. Autoimmunity improved in 5 of 5 patients. No severe bleeding episodes were recorded after treatment, and at last follow-up, all 6 surviving patients were free of blood product support and thrombopoietic agonists. Hospitalization days were reduced from a median of 25 days during the 2 years before treatment to a median of 0 days during the 2 years after treatment. All 6 surviving patients exhibited high-level, stable engraftment of functionally corrected lymphoid cells. The degree of myeloid cell engraftment and of platelet reconstitution correlated with the dose of gene-corrected cells administered. No evidence of vector-related toxicity was observed clinically or by molecular analysis.nnnCONCLUSIONS AND RELEVANCEnThis study demonstrated the feasibility of the use of gene therapy in patients with Wiskott-Aldrich syndrome. Controlled trials with larger numbers of patients are necessary to assess long-term outcomes and safety.

Evidence of innate lymphoid cell redundancy in humans

Innate lymphoid cells (ILCs) have potent immunological functions in experimental conditions in mice, but their contributions to immunity in natural conditions in humans have remained unclear. We investigated the presence of ILCs in a cohort of patients with severe combined immunodeficiency (SCID). All ILC subsets were absent in patients with SCID who had mutation of the gene encoding the common γ-chain cytokine receptor subunit IL-2Rγ or the gene encoding the tyrosine kinase JAK3. T cell reconstitution was observed in patients with SCID after hematopoietic stem cell transplantation (HSCT), but the patients still had considerably fewer ILCs in the absence of myeloablation than did healthy control subjects, with the exception of rare cases of reconstitution of the ILC1 subset of ILCs. Notably, the ILC deficiencies observed were not associated with any particular susceptibility to disease, with follow-up extending from 7 years to 39 years after HSCT. We thus report here selective ILC deficiency in humans and show that ILCs might be dispensable in natural conditions, if T cells are present and B cell function is preserved.

Function of Apollo (SNM1B) at telomere highlighted by a splice variant identified in a patient with Hoyeraal-Hreidarsson syndrome.

Telomeres, the protein–DNA complexes at the ends of linear chromosomes, are protected and regulated by the shelterin molecules, the telomerase complex, and other accessory factors, among which is Apollo, a DNA repair factor of the β-lactamase/β-CASP family. Impaired telomere protection in humans causes dyskeratosis congenita and Hoyeraal–Hreidarsson (HH) syndrome, characterized by premature aging, bone marrow failure, and immunodeficiency. We identified a unique Apollo splice variant (designated Apollo-Δ) in fibroblasts from a patient with HH syndrome. Apollo-Δ generates a dominant negative form of Apollo lacking the telomeric repeat-binding factor homology (TRFH)-binding motif (TBM) required for interaction with the shelterin TRF2 at telomeres. Apollo-Δ hampers the proper replication of telomeres, leading to major telomeric dysfunction and cellular senescence, but maintains its DNA interstrand cross-link repair function in the whole genome. These results identify Apollo as a crucial actor in telomere maintenance in vivo, independent of its function as a general DNA repair factor.

Primary T-cell immunodeficiency with immunodysregulation caused by autosomal recessive LCK deficiency.

BACKGROUNDnSignals emanating from the antigen T-cell receptor (TCR) are required for T-cell development and function. The T lymphocyte-specific protein tyrosine kinase (Lck) is a key component of the TCR signaling machinery. On the basis of its function, we considered LCK a candidate gene in patients with combined immunodeficiency.nnnOBJECTIVEnWe identify and describe a child with a T-cell immunodeficiency caused by a homozygous missense mutation of the LCK gene (c.1022T>C) resulting from uniparental disomy.nnnMETHODSnGenetic, molecular, and functional analyses were performed to characterize the Lck deficiency, and the associated clinical and immunologic phenotypes are reported.nnnRESULTSnThe mutant LCK protein (p.L341P) was weakly expressed with no kinase activity and failed to reconstitute TCR signaling in LCK-deficient T cells. The patient presented with recurrent respiratory tract infections together with predominant early-onset inflammatory and autoimmune manifestations. The patient displayed CD4(+) T-cell lymphopenia and low levels of CD4 and CD8 expression on the T-cell surface. The residual T lymphocytes had an oligoclonal T-cell repertoire and exhibited a profound TCR signaling defect, with only weak tyrosine phosphorylation signals and no Ca(2+) mobilization in response to TCR stimulation.nnnCONCLUSIONnWe report a new form of T-cell immunodeficiency caused by a LCK gene defect, highlighting the essential role of Lck in human T-cell development and responses. Our results also point out that defects in the TCR signaling cascade often result in abnormal T-cell differentiation and functions, leading to an important risk factor for inflammation and autoimmunity.

Major histocompatibility complex class II expression deficiency caused by a RFXANK founder mutation: a survey of 35 patients

Inherited deficiency of major histocompatibility complex (MHC) class II molecules impairs antigen presentation to CD4(+) T cells and results in combined immunodeficiency (CID). Autosomal-recessive mutations in the RFXANK gene account for two-thirds of all cases of MHC class II deficiency. We describe here the genetic, clinical, and immunologic features of 35 patients from 30 unrelated kindreds from North Africa sharing the same RFXANK founder mutation, a 26-bp deletion called I5E6-25_I5E6 + 1), and date the founder event responsible for this mutation in this population to approximately 2250 years ago (95% confidence interval [CI]: 1750-3025 years). Ten of the 23 patients who underwent hematopoietic stem cell transplantation (HSCT) were cured, with the recovery of almost normal immune functions. Five of the patients from this cohort who did not undergo HSCT had a poor prognosis and eventually died (at ages of 1-17 years). However, 7 patients who did not undergo HSCT (at ages of 6-32 years) are still alive on Ig treatment and antibiotic prophylaxis. RFXANK deficiency is a severe, often fatal CID for which HSCT is the only curative treatment. However, some patients may survive for relatively long periods if multiple prophylactic measures are implemented.

Gene therapy for inherited immunodeficiency

Introduction: During the last decade, gene therapy has emerged as a convincing therapy for primary immunodeficiencies (PIDs). Ex vivo gene transfer into autologous hematopoietic stem cells (HSCs) via viral vectors permits sustained correction of T cell immunodeficiency in two forms of severe combined immunodeficiency: X–linked SCID (SCID-X1) (γ chain [γc] deficiency) and adenosine deaminase deficiency. However, this success has been balanced by the occurrence of genotoxicity generated by the integration of first-generation retroviral vectors. Recently, the development of safer self-inactivating vectors has led to the initiation of new studies with the hope of equivalent efficacy and a better safety profile. Areas covered: This review article focuses on the updated results of gene therapy trials for PIDs – from early studies to ongoing clinical trials. We detail the major advances made in gene transfer and repair technologies, and discuss the many ways to extend our present experience. Expert opinion: With optimization in terms of safety and efficacy, gene therapy by lentiviral transduction could become a compelling alternative to allogeneic HSC transplantation, and thus may take center stage in the management of PIDs in coming years.

Faster T-cell development following gene therapy compared with haploidentical HSCT in the treatment of SCID-X1

During the last decade, gene therapy via ex vivo gene transfer into autologous hematopoietic stem cells has emerged as a convincing therapy for severe combined immunodeficiency caused by ILR2G mutation (SCID-X1) despite the occurrence of genotoxicity caused by the integration of first-generation retroviral vectors. However, the place of gene therapy among the therapeutic armamentarium remains to be defined. We retrospectively analyze and compare clinical outcomes and immune reconstitution in 13 consecutive SCID-X1 patients having undergone haploidentical hematopoietic stem cell transplantation (HSCT) and 14 SCID-X1 patients treated with gene therapy over the same period at a single center level: the Necker Childrens Hospital (Paris, France). Our results show a clear advantage in terms of T-cell development of gene therapy over HSCT with a mismatched donor. Patients treated with gene therapy display a faster T-cell reconstitution and a better long-term thymic output. Interestingly, this advantage of gene therapy vs haploidentical HSCT seems to be independent of the existence of clinical graft-versus-host disease in the latter condition. If data of safety are confirmed over the long term, gene therapy for SCID-X1 appears to be an equal, if not superior, alternative to haploidentical HSCT.

Unraveling the pathogenesis of Hoyeraal–Hreidarsson syndrome, a complex telomere biology disorder

Hoyeraal–Hreidarsson (HH) syndrome is a multisystem genetic disorder characterized by very short telomeres and considered a clinically severe variant of dyskeratosis congenita. The main cause of mortality, usually in early childhood, is bone marrow failure. Mutations in several telomere biology genes have been reported to cause HH in about 60% of the HH patients, but the genetic defects in the rest of the patients are still unknown. Understanding the aetiology of HH and its diverse manifestations is challenging because of the complexity of telomere biology and the multiple telomeric and non‐telomeric functions played by telomere‐associated proteins in processes such as telomere replication, telomere protection, DNA damage response and ribosome and spliceosome assembly. Here we review the known clinical complications, molecular defects and germline mutations associated with HH, and elucidate possible mechanistic explanations and remaining questions in our understanding of the disease.

Inherited CD70 deficiency in humans reveals a critical role for the CD70–CD27 pathway in immunity to Epstein-Barr virus infection

Epstein-Barr virus (EBV) infection in humans is a major trigger of malignant and nonmalignant B cell proliferations. CD27 is a co-stimulatory molecule of T cells, and inherited CD27 deficiency is characterized by high susceptibility to EBV infection, though the underlying pathological mechanisms have not yet been identified. In this study, we report a patient suffering from recurrent EBV-induced B cell proliferations including Hodgkin’s lymphoma because of a deficiency in CD70, the ligand of CD27. We show that EBV-specific T lymphocytes did not expand properly when stimulated with CD70-deficient EBV-infected B cells, whereas expression of CD70 in B cells restored expansion, indicating that CD70 on B cells but not on T cells is required for efficient proliferation of T cells. CD70 was found to be up-regulated on B cells when activated and during EBV infection. The proliferation of T cells triggered by CD70-expressing B cells was dependent on CD27 and CD3 on T cells. Importantly, CD27-deficient T cells failed to proliferate when stimulated with CD70-expressing B cells. Thus, the CD70–CD27 pathway appears to be a crucial component of EBV-specific T cell immunity and more generally for the immune surveillance of B cells and may be a target for immunotherapy of B cell malignancies.