Nuclear receptor LXRß controls fitness and functionality of activated T cells.

T cells increase cholesterol biosynthesis upon activation to generate substrates for cellular growth and proliferation. The ubiquitously expressed liver X receptor ß (LXRß) encoded by the Nr1h2 gene is a critical regulator of cholesterol homeostasis in mammalian cells; however, its cell-intrinsic role in T cell biology remains poorly understood. We report that ablation of LXRß in T cells leads to spontaneous T cell activation and T lymphocytopenia. Unexpectedly, analysis of mixed bone marrow chimeric mice revealed a cell-autonomous survival defect that reduced the fitness of LXRß-deficient effector T cells, suggesting that the heightened immune activation in mice harboring LXRß-deficient T cells was due to impaired regulatory T (T reg) cell functionality. Indeed, we found that single-copy deletion of Nr1h2 in T reg cells disrupted activated T reg cell metabolism and fitness and resulted in early-onset fatal autoimmune disease. Our study demonstrated an indispensable requirement for T reg cell-intrinsic LXRß function in immune homeostasis and provides a basis for immunological therapies through targeting of this receptor.

Complete Multilineage CD4 Expression Defect Associated With Warts Due to an Inherited Homozygous CD4 Gene Mutation.

Idiopathic T-CD4 lymphocytopenia (ICL) is a rare and heterogeneous syndrome characterized by opportunistic infections due to reduced CD4 T-lymphocytes (<300 cells/µl or <20% T-cells) in the absence of HIV infection and other primary causes of lymphopenia. Molecular testing of ICL has revealed defects in genes not specific to CD4 T-cells, with pleiotropic effects on other cell types. Here we report for the first time an absolute CD4 lymphocytopenia (<0.01 CD4+ T-cells/µl) due to an autosomal recessive CD4 gene mutation that completely abrogates CD4 protein expression on the surface membrane of T-cells, monocytes, and dendritic cells. A 45-year-old female born to consanguineous parents consulted because of exuberant, relapsing, and treatment-refractory warts on her hands and feet since the age of 10 years, in the absence of other recurrent infections or symptoms. Serological studies were negative for severe infections, including HIV 1/2, HTLV-1, and syphilis, but positive for CMV and EBV. Blood analysis showed the absence of CD4+ T-cells (<0.01%) with repeatedly increased counts of B-cells, naïve CD8+ T-lymphocytes, and particularly, CD4/CD8 double-negative (DN) TCRαß+ TCRγδ- T-cells (30% of T-cells; 400 cells/µl). Flow cytometric staining of CD4 using monoclonal antibodies directed against five different epitopes, located in two different domains of the protein, confirmed no cell surface membrane or intracytoplasmic expression of CD4 on T-cells, monocytes, and dendritic cells but normal soluble CD4 plasma levels. DN T-cells showed a phenotypic and functional profile similar to normal CD4+ T-cells as regards expression of maturation markers, T-helper and T-regulatory chemokine receptors, TCRvß repertoire, and in vitro cytokine production against polyclonal and antigen-specific stimuli. Sequencing of the CD4 gene revealed a homozygous (splicing) mutation affecting the last bp on intron 7-8, leading to deletion of the juxtamembrane and intracellular domains of the protein and complete abrogation of CD4 expression on the cell membrane. These findings support previous studies in CD4 KO mice suggesting that surrogate DN helper and regulatory T-cells capable of supporting antigen-specific immune responses are produced in the absence of CD4 signaling and point out the need for better understanding the role of CD4 on thymic selection and the immune response.

Rare Concurrence of Two Congenital Disorders: Miller-Dieker Syndrome and T-Cell Lymphopenia.

Miller-Dieker syndrome (MDS; OMIM 247200) is a rare contiguous gene deletion syndrome associated with lissencephaly and characteristic facial dysmorphism. T-cell lymphopenia is an immunodeficiency disorder which can be early detected by newborn blood screening, and all live vaccines should be avoided. We report a 2.32-Mb microdeletion at chromosome 17p13.3p13.2 and T-cell lymphopenia in a 6-month-old male infant with MDS. This is, to our knowledge, the first description of these 2 conditions co-occurring in the same patient.

Idiopathic lymphocytopenia.

PURPOSE OF REVIEW: Idiopathic CD4⁺ lymphocytopenia (ICL) is defined by the reduction of the main lymphocyte subtype in peripheral blood and CD4⁺ T cells below 300/µl in the absence of any secondary known causes of lymphopenia, including viral causes. The present review aims to state the latest available data on clinical, pathological and therapeutic aspects related to ICL, published from 1990 to 2014. The last observed clinical presentation and complications of ICL patients are described. The latest findings and possible mechanisms involved in the development of ICL features are included in the present review; however, pathogenesis of ICL has remained mainly obscured. Finally, recent therapeutic efforts considered in ICL patients are discussed. RECENT FINDINGS: In spite of the serious complications ICL has on the patients' quality of life, data on clinical, etiopathological and therapeutic behavior for ICL are very limited. On one side, an abnormal blood cell count may be the sole presentation; however, occurrence of disseminated malignant tumors is not uncommon in patients. Recent findings highlight the role of cytokines, especially interleukin-2, on features such as phenotype severity and responsiveness of the condition to therapy. In addition, some studies have suggested that a defect in hematopoietic stem cells may be involved in disease progression, an idea that is supported by the success of bone marrow transplantation in acquiring persistent remissions in ICL patients. SUMMARY: ICL is a hematologic condition of increasing importance due to its diverse clinical and pathological spectrum. Molecular studies have shown the presence of mutations involved in lymphocyte development as potential factors that may contribute to ICL occurrence. ICL patients could present either with common infections or really serious malignant conditions. The role of cytokines, especially interleukin-2, has emerged as one of the main possible mechanisms involved in clinical and pathological behavior of ICL. Today, the main therapeutic approaches are controlling life-threatening infections and underlying disorders along with efforts to cure ICL through rising CD4⁺ cell counts using cytokine interventions and transplantation.

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

BACKGROUND: Signals 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. OBJECTIVE: We 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. METHODS: Genetic, molecular, and functional analyses were performed to characterize the Lck deficiency, and the associated clinical and immunologic phenotypes are reported. RESULTS: The 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. CONCLUSION: We 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.

Newborn screening for SCID: three years of experience.

Over the past three years, newborn blood screening (NBS) for severe T cell lymphopenia/severe combined immunodeficiency (sTCL/SCID) using the T cell receptor excision circle (TREC) assay has revolutionized the early detection of infants with primary immunodeficiencies (PIDs) associated with T cell lymphopenia. Nonetheless, despite the comprehensive NBS protocols developed by each state, additional issues unique to screening for sTCL/SCID have surfaced, including variability in the performance of the TREC assay, diagnostic and treatment algorithms, definition of sTCL/SCID, and approach to the discovery of new genetic variants. Although NBS using the TREC assay has been highly successful, new and difficult challenges have emerged that need to be addressed to enhance our knowledge of the causes of sTCL/SCID and to optimize the detection and outcomes of affected infants.

Second messenger role for Mg2+ revealed by human T-cell immunodeficiency.

The magnesium ion, Mg(2+), is essential for all life as a cofactor for ATP, polyphosphates such as DNA and RNA, and metabolic enzymes, but whether it plays a part in intracellular signalling (as Ca(2+) does) is unknown. Here we identify mutations in the magnesium transporter gene, MAGT1, in a novel X-linked human immunodeficiency characterized by CD4 lymphopenia, severe chronic viral infections, and defective T-lymphocyte activation. We demonstrate that a rapid transient Mg(2+) influx is induced by antigen receptor stimulation in normal T cells and by growth factor stimulation in non-lymphoid cells. MAGT1 deficiency abrogates the Mg(2+) influx, leading to impaired responses to antigen receptor engagement, including defective activation of phospholipase Cγ1 and a markedly impaired Ca(2+) influx in T cells but not B cells. These observations reveal a role for Mg(2+) as an intracellular second messenger coupling cell-surface receptor activation to intracellular effectors and identify MAGT1 as a possible target for novel therapeutics.

Idiopathic CD4+ T lymphopenia without autoimmunity or granulomatous disease in the slipstream of RAG mutations.

A girl presented during childhood with a single course of extensive chickenpox and moderate albeit recurrent pneumonia in the presence of idiopathic CD4+ T lymphocytopenia (ICL). Her clinical condition remained stable over the past 10 years without infections, any granulomatous disease, or autoimmunity. Immunophenotyping demonstrated strongly reduced naive T and B cells with intact proliferative capacity. Antibody reactivity on in vivo immunizations was normal. T-cell receptor-Vß repertoire was polyclonal with a very low content of T-cell receptor excision circles (TRECs). Kappa-deleting recombination excision circles (KRECs) were also abnormal in the B cells. Both reflect extensive in vivo proliferation. Patient-derived CD34+ hematopoietic stem cells could not repopulate RAG2(-/-)IL2Rγc(-/-) mice, indicating the lymphoid origin of the defect. We identified 2 novel missense mutations in RAG1 (p.Arg474Cys and p.Leu506Phe) resulting in reduced RAG activity. This report gives the first genetic clue for ICL and extends the clinical spectrum of RAG mutations from severe immune defects to an almost normal condition.

Non-myeloablative hematopoietic stem cell transplantation in the treatment of severe idiopathic CD4+ lymphocytopenia.

A 40-year-old man with severe chronic idiopathic CD4+ lymphocytopenia complicated with opportunistic infections was successfully treated with non-myeloablative allogeneic hematopoietic stem cell transplantation. After conditioning with fludarabine plus low dose of total-body irradiation, CD34+ peripheral blood stem cells obtained by leukapheresis from his HLA-identical sister were infused. T cell and myeloid complete chimerism was achieved at day +28 and remained stable during the follow-up period. The patient did not develop infectious complications during the procedure. At 35 months of follow-up, his CD4+ T cell count was 1019 cells per microliter. Non-myeloablative allogeneic hematopoietic stem cell transplantation should be considered a treatment option for patients with severe forms of idiopathic CD4+ lymphocytopenia.

EBV(+) B-cell lymphoproliferative disorder associated with subsequent development of Burkitt lymphoma in a patient with idiopathic CD4(+) T-lymphocytopenia.

We report here a case of idiopathic CD4(+) T-lymphocytopenia (ICL) associated with Epstein-Barr virus (EBV)(+) lymphoproliferative disorder (LPD) terminating in Burkitt lymphoma (BL). A 33-year-old Japanese male was admitted to the hospital showing severe CD4(+) lymphocytopenia and neutropenia that was diagnosed as ICL in 1993. Twenty months after the onset of disease, right cervical lymphadenopathy was detected. Biopsy of the specimen showed reactive lymph node hyperplasia and interfollicular B-cell hyperplasia. Ninety-one months later, polypoid tumors were resected from the bilateral nasal cavities and were diagnosed as BL. Immunohistological studies suggested the reactive nature of the initial lymph node biopsy specimen. Polymerase chain reaction (PCR) analyses of immunoglobulin heavy-chain gene (IgH) demonstrated a polyclonal pattern in the initial lymph node lesion. However, the subsequent BL demonstrated a clonal band in the PCR assay for the IgH gene. As demonstrated in human immunodeficiency virus (HIV)-patients, clonal expansion of EBV infected B-cells in the initial lymph node lesion may progress to BL in this patient. The present case did not associate with severe opportunistic infections during the course of disease. EBV(+) BL may be the first manifestation of severe immunodeficiency of the ICL in this patient.

Induction of CTL responses by simultaneous administration of liposomal peptide vaccine with anti-CD40 and anti-CTLA-4 mAb.

Activation of APC via CD40-CD40 ligand pathway induces up-regulation of costimulatory molecules such as B7 and production of IL-12. Interaction between B7 on APC and CD28 on naive T cells is necessary for priming the T cells. On the other hand, interaction between B7 on APC and CTLA-4 on activated T cells transduces a negative regulatory signal to the activated T cells. In the present study, we attempted to generate tumor-specific CTL by s.c. administration of antigenic peptides encapsulated in multilamellar liposomes (liposomal peptide vaccine) with anti-CD40 mAb and/or anti-CTLA-4 mAb. Liposomal OVA257-264 and anti-CD40 mAb or anti-CTLA-4 mAb were administrated to C57BL/6 mice and the splenocytes were cocultured with OVA257-264 for 4 days. The splenic CD8+ T cells showed a significant cytotoxicity against EL4 cells transfected with cDNA of OVA. In addition, administration of both anti-CD40 and anti-CTLA-4 mAb enhanced the CTL responses. Considerable CTL responses were induced in MHC class II deficient mice by the same procedure. This finding indicated that CTL responses could be generated even in the absence of Th cells. When BALB/c mice were immunized with pRL1a peptide that are tumor-associated Ag of RLmale symbol1 leukemia cells using the same procedure, significant CTL responses were induced and prolonged survival of the BALB/c mice was observed following RLmale symbol1 inoculation. These results demonstrate that anti-CD40 mAb and anti-CTLA-4 mAb function as immunomodulators and may be applicable to specific cancer immunotherapy with antitumor peptide vaccine.

Hereditary CD4+ T lymphocytopenia.

Two siblings suffering from mental retardation, progressive bronchiectasis, extensive warts, and persistent hepatitis B are described. The propositus also had an unusual physiognomy and non-specific colitis. Both patients had a marked decrease in the population of CD4+ helper T cells.