MolecularDefects inHumanSevereCombinedImmunodeficiency andApproaches toImmuneReconstitution

Molecular analysis of T-B-NK+ severe combined immunodeficiency and Omenn syndrome cases in Saudi Arabia

Background

Children with Severe Combined Immunodeficiency (SCID) lack autologous T lymphocytes and present with multiple infections early in infancy. Omenn syndrome is characterized by the sole emergence of oligoclonal auto-reactive T lymphocytes, resulting in erythroderma and enteropathy. Omenn syndrome (OS) shares the genetic aetiology of T^-B^-NK⁺ SCID, with mutations in RAG1, RAG2, or DCLRE1C.

Methods

Patients diagnosed with T^-B^-NK⁺ SCID or phenotypes suggestive of Omenn syndrome were investigated by molecular genetic studies using gene tightly linked microsatellite markers followed by direct sequencing of the coding regions and splice sites of the respective candidate genes.

Results

We report the molecular genetic basis of T^-B^-NK⁺ SCID in 22 patients and of OS in seven patients all of Arab descent from Saudi Arabia. Among the SCID patients, six (from four families) displayed four homozygous missense mutations in RAG1 including V433M, R624H, R394W, and R559S. Another four patients (from three familes) showed 3 novel homozygous RAG2 mutations including K127X, S18X, and Q4X; all of which predict unique premature truncations of RAG2 protein. Among Omenn patients, four (from two families) have S401P and R396H mutations in RAG1, and a fifth patient has a novel I444M mutation in RAG2. Seven other patients (six SCID and one OS) showed a gross deletion in exons 1-3 in DCLRE1C. Altogether, mutations in RAG1/2 and DCLRE1C account for around 50% and 25%, respectively, in our study cohort, a proportion much higher than in previous reported series. Seven (24%) patients lack a known genetic aetiology, strongly suggesting that they carry mutations in novel genes associated with SCID and Omenn disorders that are yet to be discovered in the Saudi population.

Conclusion

Mutation-free patients who lack a known genetic aetiology are likely to carry mutations in the regulatory elements in the SCID-causing genes or in novel genes that are yet to be discovered. Our efforts are underway to investigate this possibility by applying the whole genome scans on these cases via the use of Affymetrix high density DNA SNP chips in addition to homozygosity mapping.

Regulation of memory T cells by γc cytokines

T cells rely on a duality of TCR and gammac cytokine signals for development, activation and peripheral T cell homeostasis. Previous data had suggested that the requirements for CD4 and CD8 memory T cell regulation were qualitatively distinct, but emerging data has shown that the requirements for true antigen specific memory T cells are very similar between these two cell types. This review will focus on contributions made by members of the gammac cytokine family (IL-2, IL-4, IL-7, IL-15 and IL-21) to homeostasis of naïve, memory phenotype and antigen experienced memory T cells.

Suppression of DNA-PKcs enhances FGF-2 dependent human endothelial cell proliferation via negative regulation of Akt

Angiogenesis initiation is crucially dependent on endothelial proliferation and can be stimulated by the fibroblast growth factor 2 (FGF-2). The DNA dependent protein kinase (DNA-PK), long known for its importance in repairing DNA double strand breaks, belongs to the phosphatidylinositol-3 kinase (PI3-K) super family and has recently been identified as one of the enzymes phosphorylating and activating Akt. Due to its similarity with PI3-K, we hypothesized that DNA-PK may have similar effects on endothelial angiogenic processes and signalling. We used primary endothelial cells (HUVEC and PAEC) and human microvascular endothelial cells (HMEC) to study the role of DNA-PK in endothelial proliferation and signalling. DNA-PKcs suppression with the compound NU7026 or with siRNA induced basal endothelial cell proliferation as well as enhanced FGF-2 dependent proliferation. This was associated with an increase in phosphorylated Akt. Tube formation was not affected by DNA-PKcs clearly showing that the role of DNA-PK in endothelial processes differs from that of PI3-K. Our findings indicate DNA-PK as an important enzyme maintaining the quiescent endothelial phenotype by actively inhibiting Akt thus restraining endothelial cell proliferation preventing excessive growth.

Partially corrected X-linked severe combined immunodeficiency: long-term problems and treatment options

Rapid progress has been made from the identification of the molecular defects causing X-linked severe combined immune deficiency (X-SCID) to the development of cutting-edge therapeutic approaches such as hematopoietic stem cell transplant and gene therapy for XSCID. Successful treatment of XSCID has created a new population of patients, many of whom are now adolescents and young adults and are facing a variety of chronic problems secondary to partial correction of their underlying disease. This review focuses on the clinical challenges facing these patients (and their caregivers) and provides an overview of some of the treatment options available, including gene therapy.

[Late onset of primary immune deficiencies]

Primary immune deficiencies (PID) are characterized by a failure of the immune system that is not explained by any infectious, neoplastic, or iatrogenic cause. The diagnosis of PID should be considered in cases of severe or recurrent infections but also in cases with granulomatosis, autoimmune diseases, hemophagocytic syndrome, lymphoproliferative disorders, or even some solid tumors. The onset of PID may be late, most often in adulthood. Nonetheless, late onset may also mean in the first years rather than months of life or in adolescence rather than early childhood. In adults, the diagnosis of PID cannot be considered before acquired immunodeficiencies--far more frequent--are ruled out. Factors affecting the late onset of PID are not known.

Potential large animal models for gene therapy of human genetic diseases of immune and blood cell systems

Genetic mutations involving the cellular components of the hematopoietic system--red blood cells, white blood cells, and platelets--manifest clinically as anemia, infection, and bleeding. Although gene targeting has recapitulated many of these diseases in mice, these murine homologues are limited as translational models by their small size and brief life span as well as the fact that mutations induced by gene targeting do not always faithfully reflect the clinical manifestations of such mutations in humans. Many of these limitations can be overcome by identifying large animals with genetic diseases of the hematopoietic system corresponding to their human disease counterparts. In this article, we describe human diseases of the cellular components of the hematopoietic system that have counterparts in large animal species, in most cases carrying mutations in the same gene (CD18 in leukocyte adhesion deficiency) or genes in interacting proteins (DNA cross-link repair 1C protein and protein kinase, DNA-activated catalytic polypeptide in radiation-sensitive severe combined immunodeficiency). Furthermore, we describe the potential of these animal models to serve as disease-specific preclinical models for testing the efficacy and safety of clinical interventions such as hematopoietic stem cell transplantation or gene therapy before their use in humans with the corresponding disease.

Development of a routine newborn screening protocol for severe combined immunodeficiency

BACKGROUND

Severe combined immunodeficiency (SCID) is characterized by the absence of functional T cells and B cells. Without early diagnosis and treatment, infants with SCID die from severe infections within the first year of life.

OBJECTIVE

To determined the feasibility of detecting SCID in newborns by quantitating T-cell receptor excision circles (TRECs) from dried blood spots (DBSs) on newborn screening (NBS) cards.

METHODS

DNA was extracted from DBSs on deidentified NBS cards, and real-time quantitative PCR (RT-qPCR) was used to determine the number of TRECs. Positive controls consisted of DBS from a 1-week-old T(-)B(-)NK(+) patient with SCID and whole blood specimens selectively depleted of naive T cells.

RESULTS

The mean and median numbers of TRECs from 5766 deidentified DBSs were 827 and 708, respectively, per 3.2-mm punch ( approximately 3 muL whole blood). Ten samples failed to amplify TRECs on initial analysis; all but 1 demonstrated normal TRECs and beta-actin amplification on retesting. No TRECs were detected in either the SCID or naive T-cell-depleted samples, despite the presence of normal levels of beta-actin.

CONCLUSIONS

The use of RT-qPCR to quantitate TRECs from DNA extracted from newborn DBSs is a highly sensitive and specific screening test for SCID. This assay is currently being used in Wisconsin for routine screening infants for SCID.

Regulatory lymphocytes and intestinal inflammation

The immune system is pivotal in mediating the interactions between host and microbiota that shape the intestinal environment. Intestinal homeostasis arises from a highly dynamic balance between host protective immunity and regulatory mechanisms. This regulation is achieved by a number of cell populations acting through a set of shared regulatory pathways. In this review, we summarize the main lymphocyte subsets controlling immune responsiveness in the gut and their mechanisms of control, which involve maintenance of intestinal barrier function and suppression of chronic inflammation. CD4(+)Foxp3(+) T cells play a nonredundant role in the maintenance of intestinal homeostasis through IL-10- and TGF-beta-dependent mechanisms. Their activity is complemented by other T and B lymphocytes. Because breakdown in immune regulatory networks in the intestine leads to chronic inflammatory diseases of the gut, such as inflammatory bowel disease and celiac disease, regulatory lymphocytes are an attractive target for therapies of intestinal inflammation.

Thymic output, T-cell diversity, and T-cell function in long-term human SCID chimeras

Severe combined immunodeficiency (SCID) is a syndrome of diverse genetic cause characterized by profound deficiencies of T, B, and sometimes NK-cell function. Nonablative human leukocyte antigen-identical or rigorously T cell-depleted haploidentical parental bone marrow transplantation (BMT) results in thymus-dependent genetically donor T-cell development in the recipients, leading to long-term survival. We reported previously that normal T-cell numbers, function, and repertoire developed by 3 to 4 months after transplantation in SCID patients, and the repertoire remained highly diverse for the first 10 years after BMT. The T-cell receptor diversity positively correlated with T-cell receptor excision circle levels, a reflection of thymic output. However, the fate of thymic function in SCID patients beyond 10 to 12 years after BMT remained to be determined. In this greater than 25-year follow-up study of 128 patients with 11 different molecular types of SCID after nonconditioned BMT, we provide evidence that T-cell function, thymic output, and T-cell clonal diversity are maintained long-term.

Polyclonal T-cell reconstitution of X-SCID recipients after in utero transplantation of lymphoid-primed multipotent progenitors

Although successful in utero hematopoietic cell transplantation (IUHCT) of X-linked severe combined immune deficiency (X-SCID) with enriched stem and progenitor cells was achieved more than a decade ago, it remains applied only in rare cases. Although this in part reflects that postnatal transplantations have overall given good results, there are no direct comparisons between IUHCT and postnatal transplantations of X-SCID. The proposed tolerance of the fetal immune system to foreign human leukocyte antigen early in gestation, a main rationale behind IUHCT, has recently been challenged by evidence for a considerable immune barrier against in utero transplanted allogeneic bone marrow cells. Consequently, there is need for further exploring the application of purified stem and progenitor cells to overcome this barrier also in IUHCT. Herein, we demonstrate in a congenic setting that recently identified lymphoid-primed multipotent progenitors are superior to hematopoietic stem cells in providing rapid lymphoid reconstitution after IUHCT of X-SCID recipients, and sustain in the long-term B cells, polyclonal T cells, as well as short-lived B-cell progenitors and thymic T-cell precursors. We further provide evidence for IUHCT of hematopoietic stem cells giving superior B- and T-cell reconstitution in fetal X-SCID recipients compared with neonatal and adolescent recipients.

Recent advances in primary immunodeficiencies: identification of novel genetic defects and unanticipated phenotypes

Primary immunodeficiencies (PIDs) have traditionally been defined according to their immunologic phenotype. Far from being concluded, the search for human genes that, when mutated, cause PID is actively being pursued. During the last year, four novel genetic defects that cause severe combined immunodeficiency and severe congenital neutropenia have been identified. At the same time, the immunologic definition of primary immunodeficiencies has been expanded by the recognition that genetic defects affecting innate immunity may result in selective predisposition to certain infections, such as mycobacterial disease, herpes simplex encephalitis, and invasive pneumococcal infections. Studies of genetically determined susceptibility to infections have recently shown that immunologic defects may also account for novel infectious phenotypes, such as malaria or leprosy. Finally, a growing body of evidence indicates that primary immunodeficiencies may present with a noninfectious clinical phenotype that may be restricted to single organs, as in the case of atypical hemolytic uremic syndrome or pulmonary alveolar proteinosis. Overall, these achievements highlight the importance of human models, which often differ from the corresponding animal models.

Enhanced transcription of complement and coagulation genes in the absence of adaptive immunity

A recessive nonsense mutation in the zebrafish recombination activating gene 1 (rag1) gene results in defective V(D)J recombination; however, animals homozygous for this mutation (rag1(-/-)) are reportedly viable and fertile in standard, nonsterile aquarium conditions but display increased mortality after intraperitoneal injection with mycobacteria. Based on their survival in nonsterile environments, we hypothesized that the rag1(-/-) zebrafish may possess an "enhanced" innate immune response to compensate for the lack of an adaptive immune system. To test this hypothesis, microarray analyses were used to compare the expression profiles of the intestines and hematopoietic kidneys of rag1 deficient zebrafish to the expression profiles of control (heterozygous) siblings. The expression levels of 12 genes were significantly altered in the rag1(-/-) kidney including the up regulation of a putative interferon stimulated gene, and the down regulation of genes encoding fatty acid binding protein 10, keratin 5 and multiple heat shock proteins. The expression levels of 87 genes were shown to be significantly altered in the rag1(-/-) intestine; the majority of these differences reflect increased expression of innate immune genes, including those of the coagulation and complement pathways. Subsequent analyses of orthologous coagulation and complement genes in Rag1(-/-) mice indicate increased transcription of the complement C4 gene in the Rag1(-/-) intestine.

Long-term outcome after hematopoietic stem cell transplantation of a single-center cohort of 90 patients with severe combined immunodeficiency

Allogeneic hematopoietic stem cell transplantation (HSCT) is a curative treatment for severe combined immunodeficiency (SCID). Detailed assessment of the long-term outcome of HSCT, ie, the occurrence of clinical events and the quality and stability of immune reconstitution, is now required. We performed a single-center retrospective analysis of the long-term outcome of HSCT in 90-patient cohort followed for between 2 and 34 years (median, 14 years). Clinical events and immune reconstitution data were collected. Almost half the patients have experienced one or more significant clinical events, including persistent chronic graft-versus-host disease (GVHD), autoimmune and inflammatory manifestations, opportunistic and nonopportunistic infections, chronic human papilloma virus (HPV) infections, and a requirement for nutritional support. With the notable exception of severe HPV infection, these complications tend to become less common 15 years later after HSCT. A multivariate analysis showed that the occurrence of these events correlated with non-genoidentical donors, diagnosis of Artemis SCID, and quality of immune reconstitution. In most cases, HSCT enables long-term survival with infrequent sequelae. However, the occurrence of relatively late-onset complications is a concern that requires specific means of prevention and justifies careful patient follow-up.

Long-term outcomes of nonconditioned patients with severe combined immunodeficiency transplanted with HLA-identical or haploidentical bone marrow depleted of T cells with anti-CD6 mAb

BACKGROUND

Between 1981 and 1995, 20 children with severe combined immunodeficiency (SCID; median age at transplant, 6.5 [range, 0.5-145] mo, 12 with serious infection) were treated with haploidentical T cell-depleted (anti-CD6 antibody) bone marrow (median number of 5.7 [0.8-18.8] x 10(8) nucleated cells/kg) from mismatched related donors (MMRDs), and 5 children with SCID (median age at transplant, 1.8 [0.5-5.0] mo, 1 with serious infection) were given unmanipulated bone marrow from matched related donors (MRDs). No conditioning or graft-versus-host disease (GvHD) prophylaxis was used.

OBJECTIVE

To assess the outcomes of patients with SCID who received bone marrow from MMRDs or MRDs.

METHODS

We reviewed the medical records of these 25 consecutive patients with SCID (4 with Omenn syndrome).

RESULTS

Of the 20 patients who received bone marrow from MMRDs, 12 engrafted, 10 survived at a median age of 15.2 [10.0-19.1] years, 4 had chronic GvHD (lung, intestine, skin), 5 required intravenous immunoglobulin, and 8 attended school or college. Two of 5 patients who died had chronic GvHD, and 2 developed lymphoproliferative disease. Of the 5 patients who received bone marrow from MRDs, 5 engrafted, 5 survived at a median age of 23.3 [18.5-26] years, 1 had chronic GvHD (lung, skin), 2 required intravenous immunoglobulin, and 4 attended school or college.

CONCLUSIONS

Treatment of critically ill patients with SCID with anti-CD6 antibody T cell-depleted MMRD marrow resulted in an overall 50% long-term survival of patients (83% survival of those engrafted). The principal barriers to long-term survival were delay in diagnosis, life-threatening infection, failure to engraft, and chronic GvHD. Educational goals were achieved in most of the survivors.

Mutations causing severe combined immunodeficiency: detection with a custom resequencing microarray

PURPOSE

Mutation diagnosis of severe combined immunodeficiency is challenging because of the multiplicity of disease genes and large number of disease-causing mutations, including unique ones that continue to be found. A resequencing microarray could facilitate mutation detection, increasing the chance of diagnosing infants early for optimal rescue by hematopoietic stem cell transplantation.

METHODS

After analyzing cumulative mutations, we developed a custom Affymetrix GeneChip microarray including probes representing exons and flanking regions of severe combined immunodeficiency disease genes. DNA samples were analyzed by array versus standard dideoxy genomic sequencing. We tested males and their mothers with X-linked IL2RG variants and patients and carriers with autosomal variants in IL7R, JAK3, and DCLRE1C.

RESULTS

New, unique severe combined immunodeficiency mutations are frequent. Resequencing array call rates of 95-98% exceeded GeneChip product specifications, and all of 47 point mutations in known samples were detected, as were the sites of 12 of 22 disease-causing insertions and deletions. Each gene had particular nucleotides that were often not called correctly and had to be excluded from analysis; exclusion rates ranged from 0.4% (hemizygous IL2RG) to 9.2% (heterozygous JAK3).

CONCLUSION

Microarray resequencing is a promising technology for severe combined immunodeficiency mutation diagnosis that can detect both known and new mutations. Future customization of probe sequences and analysis algorithms could increase the number of accurately called nucleotides.

IL-15 trans-presentation promotes human NK cell development and differentiation in vivo

The in vivo requirements for human natural killer (NK) cell development and differentiation into cytotoxic effectors expressing inhibitory receptors for self-major histocompatibility complex class I (MHC-I; killer Ig-like receptors [KIRs]) remain undefined. Here, we dissect the role of interleukin (IL)-15 in human NK cell development using Rag2(-/-)gamma c(-/-) mice transplanted with human hematopoietic stem cells. Human NK cell reconstitution was intrinsically low in this model because of the poor reactivity to mouse IL-15. Although exogenous human IL-15 (hIL-15) alone made little improvement, IL-15 coupled to IL-15 receptor alpha (IL-15R alpha) significantly augmented human NK cells. IL-15-IL-15R alpha complexes induced extensive NK cell proliferation and differentiation, resulting in accumulation of CD16(+)KIR(+) NK cells, which was not uniquely dependent on enhanced survival or preferential responsiveness of this subset to IL-15. Human NK cell differentiation in vivo required hIL-15 and progressed in a linear fashion from CD56(hi)CD16(-)KIR(-) to CD56(lo)CD16(+)KIR(-), and finally to CD56(lo)CD16(+)KIR(+). These data provide the first evidence that IL-15 trans-presentation regulates human NK cell homeostasis. Use of hIL-15 receptor agonists generates a robust humanized immune system model to study human NK cells in vivo. IL-15 receptor agonists may provide therapeutic tools to improve NK cell reconstitution after bone marrow transplants, enhance graft versus leukemia effects, and increase the pool of IL-15-responsive cells during immunotherapy strategies.

Severe combined immunodeficiency (SCID) and attention deficit hyperactivity disorder (ADHD) associated with a Coronin-1A mutation and a chromosome 16p11.2 deletion

Defects causing severe combined immunodeficiency (SCID) have been reported in pathways mediating antigen receptor rearrangement, antigen receptor and cytokine signaling, and purine metabolism. Recognizing that the actin regulator Coronin-1A is essential for development of a normal peripheral T cell compartment in mouse models, we identified absence of Coronin-1A in a girl with T-B+NK+ SCID who suffered recurrent infections including severe post-vaccination varicella at age 13 months. Murine Coronin-1A is essential for the release of T cells from the thymus, consistent with the paradoxically detectable thymus in our patient. Molecular analysis revealed a 2 bp deletion in the paternal CORO1A coding sequence paired with a 600 kb de novo deletion encompassing CORO1A on the maternal allele. This genomic region at 16p11.2 is subject to recurrent copy number variations associated with autism spectrum disorders, including attention deficit and hyperactivity, present in our patient. This case highlights the first link between actin cytoskeleton regulation and SCID.

Allogeneic hematopoietic cell transplantation for primary immune deficiency diseases: current status and critical needs

Allogeneic hematopoietic cell transplantation (HCT) has been used for 40 years to ameliorate or cure primary immune deficiency (PID) diseases, including severe combined immunodeficiency (SCID) and non-SCID PID. There is a critical need for evaluation of the North American experience of different HCT approaches for these diseases to identify best practices and plan future investigative clinical trials. Our survey of incidence and prevalence of PID in North American practice sites indicates that such studies are feasible. A conference of experts in HCT treatment of PID has recommended (1) a comprehensive cross-sectional and retrospective analysis of HCT survivors with SCID; (2) a prospective study of patients with SCID receiving HCT, with comparable baseline and follow-up testing across participating centers; (3) a pilot study of newborn screening for SCID to identify affected infants before compromise by infection; and (4) studies of the natural history of disease in patients who do or do not receive HCT for the non-SCID diseases of Wiskott-Aldrich syndrome and chronic granulomatous disease. To accomplish these goals, collaboration by a consortium of institutions in North America is proposed. Participation of immunologists and HCT physicians having interest in PID and experts in laboratory methods, clinical outcomes assessment, databases, and analysis will be required for the success of these studies.

FLT3 ligand and not TSLP is the key regulator of IL-7-independent B-1 and B-2 B lymphopoiesis

Phenotypically and functionally distinct progenitors and developmental pathways have been proposed to exist for fetally derived B-1 and conventional B-2 cells. Although IL-7 appears to be the primary cytokine regulator of fetal and adult B lymphopoiesis in mice, considerable fetal B lymphopoiesis and postnatal B cells are sustained in the absence of IL-7; in humans, B-cell generation is suggested to be largely IL-7-independent, as severe combined immune-deficient patients with IL-7 deficiency appear to have normal B-cell numbers. However, the role of other cytokines in IL-7-independent B lymphopoiesis remains to be established. Although thymic stromal lymphopoietin (TSLP) has been proposed to be the main factor driving IL-7-independent B lymphopoiesis and to distinguish fetal from adult B-cell progenitor development in mice, recent studies failed to support a primary role of TSLP in IL-7-independent fetal B-cell development. However, the role of TSLP in IL-7-independent adult B lymphopoiesis and in particular in regulation of B-1 cells remains to be established. Here we demonstrate that, rather than TSLP, IL-7 and FLT3 ligand are combined responsible for all B-cell generation in mice, including recently identified B-1-specified cell progenitors. Thus, the same IL-7- and FLT3 ligand-mediated signal-ing regulates alternative pathways of fetal and adult B-1 and B-2 lymphopoiesis.

IL-7 activates the phosphatidylinositol 3-kinase/AKT pathway in normal human thymocytes but not normal human B cell precursors

IL-7 signaling culminates in different biological outcomes in distinct lymphoid populations, but knowledge of the biochemical signaling pathways in normal lymphoid populations is incomplete. We analyzed CD127/IL-7Ralpha expression and function in normal (nontransformed) human thymocytes, and human CD19(+) B-lineage cells purified from xenogeneic cord blood stem cell/MS-5 murine stromal cell cultures, to further clarify the role of IL-7 in human B cell development. IL-7 stimulation of CD34(+) immature thymocytes led to phosphorylation (p-) of STAT5, ERK1/2, AKT, and glycogen synthase kinase-3 beta, and increased AKT enzymatic activity. In contrast, IL-7 stimulation of CD34(-) thymocytes (that included CD4(+)/CD8(+) double-positive, and CD4(+) and CD8(+) single-positive cells) only induced p-STAT5. IL-7 stimulation of CD19(+) cells led to robust induction of p-STAT5, but minimal induction of p-ERK1/2 and p-glycogen synthase kinase-3 beta. However, CD19(+) cells expressed endogenous p-ERK1/2, and when rested for several hours following removal from MS-5 underwent de-phosphorylation of ERK1/2. IL-7 stimulation of rested CD19(+) cells resulted in robust induction of p-ERK1/2, but no induction of AKT enzymatic activity. The use of a specific JAK3 antagonist demonstrated that all IL-7 signaling pathways in CD34(+) thymocytes and CD19(+) B-lineage cells were JAK3-dependent. We conclude that human CD34(+) thymocytes and CD19(+) B-lineage cells exhibit similarities in activation of STAT5 and ERK1/2, but differences in activation of the PI3K/AKT pathway. The different induction of PI3K/AKT may at least partially explain the different requirements for IL-7 during human T and B cell development.

B lymphocytes: how they develop and function

The discovery that lymphocyte subpopulations participate in distinct components of the immune response focused attention onto the origins and function of lymphocytes more than 40 years ago. Studies in the 1960s and 1970s demonstrated that B and T lymphocytes were responsible primarily for the basic functions of antibody production and cell-mediated immune responses, respectively. The decades that followed have witnessed a continuum of unfolding complexities in B-cell development, subsets, and function that could not have been predicted. Some of the landmark discoveries that led to our current understanding of B lymphocytes as the source of protective innate and adaptive antibodies are highlighted in this essay. The phenotypic and functional diversity of B lymphocytes, their regulatory roles independent of antibody production, and the molecular events that make this lineage unique are also considered. Finally, perturbations in B-cell development that give rise to certain types of congenital immunodeficiency, leukemia/lymphoma, and autoimmune disease are discussed in the context of normal B-cell development and selection. Despite the significant advances that have been made at the cellular and molecular levels, there is much more to learn, and cross-disciplinary studies in hematology and immunology will continue to pave the way for new discoveries.

Gene therapy for primary immunodeficiencies

Primary immunodeficiencies are a group of disorders that are highly amenable to gene therapy because of their defined pathophysiology and the accessibility of the hematopoietic system to molecular intervention. The development of this new therapeutic modality has been driven by the established morbidity and mortality associated with conventional allogeneic stem cell transplantation, particularly in the human leukocyte antigen-mismatched setting. Recently, several clinical studies have shown that gamma retroviral gene transfer technology can produce major beneficial therapeutic effects, but, as for all cellular and pharmacologic treatment approaches, with a finite potential for toxicity. Newer developments in vector design showing promise in overcoming these issues are likely to establish gene therapy as an efficacious strategy for many forms of primary immunodeficiencies.

Mutations in STAT3 and IL12RB1 impair the development of human IL-17-producing T cells

The cytokines controlling the development of human interleukin (IL) 17--producing T helper cells in vitro have been difficult to identify. We addressed the question of the development of human IL-17--producing T helper cells in vivo by quantifying the production and secretion of IL-17 by fresh T cells ex vivo, and by T cell blasts expanded in vitro from patients with particular genetic traits affecting transforming growth factor (TGF) beta, IL-1, IL-6, or IL-23 responses. Activating mutations in TGFB1, TGFBR1, and TGFBR2 (Camurati-Engelmann disease and Marfan-like syndromes) and loss-of-function mutations in IRAK4 and MYD88 (Mendelian predisposition to pyogenic bacterial infections) had no detectable impact. In contrast, dominant-negative mutations in STAT3 (autosomal-dominant hyperimmunoglobulin E syndrome) and, to a lesser extent, null mutations in IL12B and IL12RB1 (Mendelian susceptibility to mycobacterial diseases) impaired the development of IL-17--producing T cells. These data suggest that IL-12Rbeta1- and STAT-3--dependent signals play a key role in the differentiation and/or expansion of human IL-17-producing T cell populations in vivo.

Differential regulation of human IL-7 receptor alpha expression by IL-7 and TCR signaling

IL-7Ralpha is essential for the development and homeostatic maintenance of mature T cells. Studies in humans and mice have shown that IL-7Ralpha expression is reduced by its cognate cytokine, IL-7, and Ag, suggesting that active regulation of IL-7 responsiveness is necessary to balance T cell numbers. We show that IL-7- or TCR/CD28-mediated signaling induced a rapid down-regulation of IL-7Ralpha expression on naive T cells on the mRNA and protein level, with a mild (10-fold) or strong (50-fold) gene suppression, respectively. In both situations, the down-regulation of IL-7Ralpha was blocked by cyclohexamide and actinomycin D, indicating the involvement of an active mechanism dependent on new transcription and protein synthesis. Upon IL-7 withdrawal, IL-7Ralpha mRNA and surface protein reappeared in a transcription-dependent manner within 7 h. Yet, IL-7Ralpha was hardly re-expressed during the same period after TCR/CD28-activation. Likewise, T cells that were activated through CMV in vivo did not re-express IL-7Ralpha after in vitro culture. Functionally, IL-7-induced down-regulation of IL-7Ralpha did not hinder the responsiveness of naive T cells to IL-7. Conversely, down-regulation of IL-7Ralpha on TCR/CD28-activated cells limited IL-7 responsiveness. Strikingly, ectopic expression of IL-7Ralpha cells on TCR/CD28-activated cells conferred a selective advantage in the response to IL-7. In conclusion, our data show that IL-7- and TCR/CD28-mediated signaling differentially regulate IL-7Ralpha expression on human T cells with a transient and chronic effect, respectively. The stringent and active regulation of IL-7Ralpha may constitute a homeostatic mechanism to curtail unwarranted T cell expansion.

Glucose metabolism in lymphocytes is a regulated process with significant effects on immune cell function and survival

Lymphocytes require glucose uptake and metabolism for normal survival and function. The signals that regulate the expression and localization of glucose transporter 1 (Glut1) to allow glucose uptake in T cells are now beginning to be understood. Resting T cells require extracellular signals, such as cytokines, hormones, and growth factors, or low-level TCR stimulation to take up adequate glucose to maintain housekeeping functions. In the absence of extrinsic signals, resting T cells internalize and degrade Glut1 and cannot maintain viability. Activated T cells have dramatically increased metabolic requirements to support the energy and biosynthetic needs necessary for growth, proliferation, and effector function. In particular, glucose metabolism and aerobic glycolysis fuel this demand. Therefore, activation of T cells causes a large increase in Glut1 expression and surface localization. If glucose uptake is limited, glycolytic flux decreases to a level that no longer sustains viability, and proapoptotic Bcl-2 family members become activated, promoting cell death. However, excessive glucose uptake can promote hyperactive immune responses and possible immune pathology. Tight regulation of glucose uptake is required to maintain immune homeostasis, and understanding of these metabolic pathways may lead to therapeutic strategies to target some forms of cancer or autoimmunity.

An immunodeficiency disease with RAG mutations and granulomas

We describe three unrelated girls who had an immunodeficiency disease with granulomas in the skin, mucous membranes, and internal organs. All three girls had severe complications after viral infections, including B-cell lymphoma associated with Epstein-Barr virus (EBV). Other findings were hypogammaglobulinemia, a diminished number of T and B cells, and sparse thymic tissue on ultrasonography. Molecular analysis revealed that the patients were compound heterozygotes for mutations in recombination activating gene 1 or 2 (RAG1 or RAG2). In each case, both parents were heterozygous carriers of a RAG mutation. The mutations were associated with reduced function of RAG in vitro (3 to 30% of normal activity). The parents and one sibling in the three families were healthy.

Development of human lymph nodes and Peyer's patches

In contrast to our understanding of murine lymphoid organogenesis, detailed knowledge on the mechanisms of human lymph node development is virtually lacking. This is mainly due to the obvious difficulties that accompany research using human fetal organs. In this review we will highlight current knowledge on human lymph node and Peyer's patch development and will temporally align observations made in humans with data available from murine studies. In the final paragraphs we will put this knowledge in the context of human malignancies in which interactions between lymphocytes and stroma, resembling those seen in lymphoid organs, are recapitulated.

Regulation of human B lymphopoiesis by the transforming growth factor-beta superfamily in a newly established coculture system using human mesenchymal stem cells as a supportive microenvironment

OBJECTIVES

To characterize and evaluate the validity of a novel coculture system for studying human B-lymphocyte developmental biology.

MATERIALS AND METHODS

We developed a long-term culture system to produce B lymphocytes from human CD34(+) cells purified from umbilical cord blood using human mesenchymal stem cells (hMSC) as stroma. We evaluated the effects of several low molecular weight inhibitors, recombinant proteins, and neutralizing antibodies (Abs) as potential regulators of B-lymphocyte development.

RESULTS

Our cocultures of 2000 CD34(+) cells in the presence of stem cell factor and Flt3-ligand produced 1-5 x 10(5) CD10(+) cells after 4 weeks of culture. Surface IgM(+) immature B cells began to appear after 4 weeks. We evaluated the negative-regulatory effects of the transforming growth factor (TGF)-beta superfamily on human B lymphopoiesis, and found that adding an anti-activin A antibody enhanced generation of CD10(+) cells two- to three-fold. As well, the proportion of CD10(+) cells in the generated cells increased markedly, indicating that activin A downregulated B lymphopoiesis more efficiently than myelopoiesis. Addition of TGF-beta1 suppressed B-lymphocyte production by 20% to 30%, while addition of an anti-bone morphogenetic protein (BMP)-4 antibody or recombinant BMP-4 had no effect. Therefore, the strength of ability to suppress human B lymphopoiesis seemed to be activin A > TGF-beta1 > BMP-4. None of these three factors influenced the emergence of IgM(+) cells.

CONCLUSIONS

hMSC coculture supported human B lymphopoiesis. Activin A selectively suppressed B lymphocyte production.

Neonatal screening for severe combined immune deficiency

PURPOSE OF REVIEW

Severe combined immunodeficiency has been identified as a high-priority disease for inclusion in population-based newborn screening programs. In this review, the justification, advances to date and remaining challenges for universal severe combined immunodeficiency screening are outlined.

RECENT FINDINGS

Severe combined immunodeficiency is treatable by hematopoietic stem cell transplantation, with best outcome if recognized and treated early in life. Universal screening of newborns could make possible prompt diagnosis and lifesaving treatment for all affected infants. One screening test using the dried blood spots already collected from all newborns involves quantitation of T cell receptor excision circles, and other test methods have been proposed and are being evaluated. Development of screening programs will require integration of screening, contacting infants with abnormal screen results for definitive testing, prompt treatment of affected infants, and outcome tracking.

SUMMARY

Newborn screening for severe combined immunodeficiency is advancing toward pilot trials.

[Gene therapy of SCID-X1]

X-linked severe combined immunodeficiency (SCID-X1) is an inherited disease caused by inactivating mutations in the gene encoding the interleukin 2 receptor common gamma chain (IL2RG), which is located on the X-chromosome. Affected boys fail to develop two major effector cell types of the immune system (T cells and NK cells) and suffer from a functional B cell defect. Although drugs such as antibiotics can offer partial protection, the boys normally die in the first year of life in the absence of a curative therapy. For a third of the children, bone marrow transplantation from a fully matched donor is available and can cure the disease without major side effects. Mismatched bone marrow transplantation, however, is complicated by severe and potentially lethal side effects. Over the past decade, scientists worldwide have developed new treatments by introducing a correct copy of the IL2RG-cDNA. Gene therapy was highly effective when applied in young children. However, in a few patients the IL2RG-gene vector has unfortunately caused leukaemia. Activation of cellular proto-oncogenes by accidental integration of the gene vector has been identified as the underlying mechanism. In future clinical trials, improved vector technology in combination with other protocol modifications may reduce the risk of this side effect.

Altered intracellular and extracellular signaling leads to impaired T-cell functions in ADA-SCID patients

Mutations in the adenosine deaminase (ADA) gene are responsible for a form of severe combined immunodeficiency (SCID) caused by the lymphotoxic accumulation of ADA substrates, adenosine and 2'-deoxy-adenosine. The molecular mechanisms underlying T-cell dysfunction in humans remain to be elucidated. Here, we show that CD4(+) T cells from ADA-SCID patients have severely compromised TCR/CD28-driven proliferation and cytokine production, both at the transcriptional and protein levels. Such an impairment is associated with an intrinsically reduced ZAP-70 phosphorylation, Ca(2+) flux, and ERK1/2 signaling and to defective transcriptional events linked to CREB and NF-kappaB. Moreover, exposure to 2'-deoxy-adenosine results in a stronger inhibition of T-cell activation, mediated by the aberrant A(2A) adenosine receptor signaling engagement and PKA hyperactivation, or in a direct apoptotic effect at higher doses. Conversely, in T cells isolated from patients after gene therapy with retrovirally transduced hematopoietic stem/progenitor cells, the biochemical events after TCR triggering occur properly, leading to restored effector functions and normal sensitivity to apoptosis. Overall, our findings provide a better understanding of the pathogenesis of the immune defects associated with an altered purine metabolism and confirm that ADA gene transfer is an efficacious treatment for ADA-SCID. The trials in this study are enrolled at www.ClinicalTrials.gov as #NCT00598481 and #NCT0059978.

Self-inactivating gammaretroviral vectors for gene therapy of X-linked severe combined immunodeficiency

Gene therapy for X-linked severe combined immunodeficiency (SCID-X1) has proven highly effective for long-term restoration of immunity in human subjects. However, the development of lymphoproliferative complications due to dysregulated proto-oncogene expression has underlined the necessity for developing safer vector systems. To reduce the potential for insertional mutagenesis, we have evaluated the efficacy of self-inactivating (SIN) gammaretroviral vectors in cellular and in vivo models of SCID-X1. Vectors incorporating an internal human elongation factor-1alpha regulatory element were capable of fully restoring the lymphoid differentiation potential of gammac-deficient lineage negative cells. Multilineage lymphoid reconstitution of a murine model was achieved at a similar level to that achieved by a conventional long-terminal repeat (LTR)-regulated vector used in previous clinical trials. Functional proliferative responses to mitogenic stimuli were also restored, and serum immunoglobulin levels were normalized. The reduced mutagenic potential conferred by SIN vector configurations and alternative non-LTR-based regulatory elements, together with proven efficacy in correction of cellular defects provides an important platform for development of the next phase of clinical trials for SCID-X1.

Humanized immune system (HIS) mice as a tool to study human NK cell development

The study of human hematopoiesis is conditioned by access to nondiseased human tissue samples that harbor the cellular substrates for this developmental process. Technical and ethical concerns limit the availability to tissues derived from the fetal and newborn periods, while adult samples are generally restricted to peripheral blood. Access to a small animal model that faithfully recapitulates the process of human hematopoiesis would provide an important tool. Natural killer (NK) cells comprise between 10% and 15% of human peripheral blood lymphocytes and appear conserved in several species. NK cells are implicated in the recognition of pathogen-infected cells and in the clearance of certain tumor cells. In this chapter, we discuss NK cell developmental pathways and the use of humanized murine models for the study of human hematopoiesis and, in particular, human NK cell development.

Transduction of murine hematopoietic stem cells and in vivo selection of gene-modified cells

Hematopoietic stem cells (HSCs) were among the first targets of genetic manipulation for the purpose of treating human diseases. The translational aspects of the first human clinical trials were based on results obtained using the mouse as an experimental model. Murine studies have shown that the major limitations of HSC gene therapy are similar to those encountered when using non-hematopoietic cells as targets and include (1) an inability to genetically modify sufficient numbers of target cells, (2) the loss of transgene function over time, and (3) potential complications due to vector integration. With continued improvements in transduction protocols, murine HSC transduction and transplantation are now routine with transduction efficiencies >50% easily achievable and even >90% feasible. However, attaining high-level engraftment of gene-modified cells after transplantation is still problematic. Basic transduction conditions entail cytokine stimulation of HSC populations, such as stem cell antigen-1 positive (Sca-1(+)) cells isolated from bone marrow, in serum-free media followed by multiple additions of recombinant retrovirus. Analysis of peripheral blood 12 weeks post transplantation of transduced cells into lethally irradiated recipients shows genetic marking in all hematopoietic lineages. Transduction of HSCs is then confirmed by transplanting bone marrow cells harvested from primary transplant recipients into lethally irradiated secondary recipients. Analysis of these mice shows that recombinant retroviruses transduce murine HSCs efficiently and stably and that the genetically modified cells are capable of completely repopulating the hematopoietic system.

Primary Immunodeficiencies

Primary immunodeficiencies (PIDs), once considered to be very rare, are now increasingly recognized because of growing knowledge in the immunological field and the availability of more sophisticated diagnostic techniques and therapeutic modalities [161]. However in a database of >120,000 inpatients of a general hospital for conditions suggestive of ID 59 patients were tested, and an undiagnosed PID was found in 17 (29%) of the subjects tested [107]. The publication of the first case of agammaglobulinemia by Bruton in 1952 [60] demonstrated that the PID diagnosis is first done in the laboratory. However, PIDs require specialized immunological centers for diagnosis and management [33]. A large body of epidemiological evidence supports the hypothesis of the existence of a close etiopathogenetic relation between PID and atopy [73]. In particular, an elevated frequency of asthma, food allergy (FA), atopic dermatitis and enteric pathologies can be found in various PIDs. In addition we will discuss another subject that is certainly of interest: the pseudo-immunodepressed child with recurrent respiratory infections (RRIs), an event that often requires medical intervention and that very often leads to the suspicion that it involves antibody deficiencies [149].

Population-based newborn screening for severe combined immunodeficiency: steps toward implementation

Severe combined immune deficiency (SCID) has been identified as a disorder of high priority for population-based newborn screening. Most affected infants are not brought to medical attention until they develop serious infectious complications, and SCID is fatal if untreated. Effective treatment with allogeneic hematopoietic stem cell transplantation is widely established. The best outcome for SCID, as with many other conditions for which newborn screening is now done, is achieved if hematopoietic stem cell transplantation is performed in the first months of life, ideally before clinical presentation with infections and failure to thrive. A meeting in San Francisco in May 2007 brought together experts from newborn screening programs; the pediatric immunology community; pediatric transplant centers; and federal, state, and nongovernmental agencies to consider obstacles to and implications of developing newborn screening for SCID. Development of an appropriate low-cost, high-throughput screening algorithm has been a challenge, although absence of T-cell receptor gene excision circles is a sensitive marker of profound T lymphocytopenia and currently is the most developed screening method. A consensus was reached on several points: SCID newborn screening should be pursued with pilot studies in key locales, test methodologies need to be optimized, screening programs must be integrated with plans for definitive diagnosis and management, centralized specimen banks and registries are required to foster test validation and track outcomes that will guide future treatment, and SCID newborn screening will lead to important knowledge about human immune disorders as well as better care of patients.

Gene editing in human stem cells using zinc finger nucleases and integrase-defective lentiviral vector delivery

Achieving the full potential of zinc-finger nucleases (ZFNs) for genome engineering in human cells requires their efficient delivery to the relevant cell types. Here we exploited the infectivity of integrase-defective lentiviral vectors (IDLV) to express ZFNs and provide the template DNA for gene correction in different cell types. IDLV-mediated delivery supported high rates (13-39%) of editing at the IL-2 receptor common gamma-chain gene (IL2RG) across different cell types. IDLVs also mediated site-specific gene addition by a process that required ZFN cleavage and homologous template DNA, thus establishing a platform that can target the insertion of transgenes into a predetermined genomic site. Using IDLV delivery and ZFNs targeting distinct loci, we observed high levels of gene addition (up to 50%) in a panel of human cell lines, as well as human embryonic stem cells (5%), allowing rapid, selection-free isolation of clonogenic cells with the desired genetic modification.

Role of pulmonary adenosine during hypoxia: extracellular generation, signaling and metabolism by surface adenosine deaminase/CD26

Numerous parallels exist between limited oxygen availability (hypoxia) and acute inflammation. The lungs in particular are prone to acute inflammation during hypoxia, resulting in pulmonary edema, vascular leakage and neutrophil infiltration. The innate response elicited by hypoxia is associated with increased extracellular adenosine effects. Although studies on acute pulmonary hypoxia show a protective role of extracellular adenosine by attenuating pulmonary edema and excessive inflammation, chronic elevation of pulmonary adenosine may be detrimental. Adenosine deaminase (ADA)-deficient mice, for example, develop signs of chronic pulmonary injury in association with highly elevated levels of adenosine. Thus, the authors hypothesized the existence of hypoxia-elicited clearance mechanisms to offset deleterious influences of chronically elevated adenosine. Such studies indicated a second response to hypoxia characterized by pulmonary induction of ADA and CD26. In fact, hypoxia-inducible ADA is enzymatically active and tethered on the outside of the membrane via CD26 to form a complex capable of degrading extracellular adenosine to inosine. This paper reviews metabolic and transcriptional changes of extracellular adenosine generation, signaling and degradation during acute and prolonged pulmonary hypoxia.

Genetic causes of bronchiectasis: primary immune deficiencies and the lung

Primary immune deficiencies (PID) comprise a heterogeneous group of genetically determined disorders that affect development and/or function of innate or adaptive immunity. Consequently, patients with PID suffer from recurrent and/or severe infections that frequently involve the lung. While the nature of the immune defect often dictates the type of pathogens that may cause lung infection, there is substantial overlap of radiological findings, so that appropriate laboratory tests are mandatory to define the nature of the immune defect and to prompt appropriate treatment. At the same time, the recent identification of a large number of PID-causing genes now allows early, even presymptomatic diagnosis, thus representing an essential tool for prevention of lung damage. This review article describes the most common forms of PID, their cellular and molecular bases, and the associated lung abnormalities, and reports on available treatment.

Role of flow cytometry in the diagnosis and monitoring of primary immunodeficiency disease

This presentation is organized according to the recent classification of primary immunodeficiencies published by the International Union of Immunological Societies Primary Immunodeficiency meeting. The diseases have been classified into eight groups. After each list, individual diseases that are amenable to assessment by flow cytometry are reviewed with a brief clinical description and a discussion of the appropriate flow cytometry application.

IL-7 receptor deficient SCID with a unique intronic mutation and post-transplant autoimmunity due to chronic GVHD

Severe combined immunodeficiency (SCID) may result from a variety of genetic defects that impair the development of T cells. Signaling mediated by the cytokine interleukin-7 is essential for the differentiation of T cells from lymphoid progenitors, and mutations of either the interleukin-7 receptor alpha chain (IL-7Ralpha) or its associated cytokine receptor chain, the common gamma chain (gammac), result in SCID. Here we report a case of SCID due to heterozygous mutations of the IL7R gene encoding IL-7Ralpha. A previously unrecognized mutation found within intron 3 created a new exon between exons 3 and 4 in the mRNA transcribed from this allele, producing a truncated, unstable mRNA. This mutation illustrates the necessity of evaluating both coding and non-coding regions of genes when searching for pathogenic mutations. Following hematopoietic stem cell transplantation of our patient, immune reconstitution was accompanied by two unusual complications, immune-mediated myositis and myasthenia gravis.