Expansion of CD3+CD4-CD8- T cell population expressing high levels of IL-5 in Omenn's syndrome

RAG Deficiency: Two Genes, Many Diseases

PURPOSE

To review the clinical and laboratory spectrum of RAG gene defects in humans, and discuss the mechanisms underlying phenotypic heterogeneity, the basis of immune dysregulation, and the current and perspective treatment modalities.

METHODS

Literature review and analysis of medical records RESULTS: RAG gene defects in humans are associated with a surprisingly broad spectrum of clinical and immunological phenotypes. Correlation between in vitro recombination activity of the mutant RAG proteins and the clinical phenotype has been observed. Altered T and B cell development in this disease is associated with defects of immune tolerance. Hematopoietic cell transplantation is the treatment of choice for the most severe forms of the disease, but a high rate of graft failure has been observed.

CONCLUSIONS

Phenotypic heterogeneity of RAG gene defects in humans may represent a diagnostic challenge. There is a need to improve treatment for severe, early-onset forms of the disease. Optimal treatment modalities for patients with delayed-onset disease presenting with autoimmunity and/or inflammation remain to be defined.

Omenn syndrome: inflammation in leaky severe combined immunodeficiency

Omenn syndrome (OS) was reported until recently as a distinct form (phenotype and genotype) of severe combined immunodeficiency (SCID). Similar to other patients with SCID, patients with OS present early in infancy with viral or fungal pneumonitis, chronic diarrhea, and failure to thrive. Unlike typical SCID, patients with OS have enlarged lymphoid tissue, severe erythroderma, increased IgE levels, and eosinophilia. The inflammation observed in these patients is believed to be triggered by clonally expanded T cells, which are predominantly of the T(H)2 type. These abnormal T cells, in the absence of proper regulation by other components of the immune system, secrete a host of cytokines that promote autoimmune as well as allergic inflammation. The emergence of these T-cell clones occurs in patients with hypomorphic mutations in recombination activating gene 1 or 2, but not in patients with deleterious mutations in these enzymes which render them inactive. Recently, OS was also identified in a growing list of other leaky SCIDs with mutations in RNA component of mitochondrial RNA processing endoribonuclease, adenosine deaminase, IL-2 receptor gamma, IL-7 receptor alpha, ARTEMIS, and DNA ligase 4. This new information revealed OS is a distinct inflammatory process that can be associated with genetically diverse leaky SCIDS.

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].

Homeostatically proliferating CD4 T cells are involved in the pathogenesis of an Omenn syndrome murine model

Patients with Omenn syndrome (OS) have hypomorphic RAG mutations and develop varying manifestations of severe combined immunodeficiency. It is not known which symptoms are caused directly by the RAG mutations and which depend on other polymorphic genes. Our current understanding of OS is limited by the lack of an animal model. In the present study, we identified a C57BL/10 mouse with a spontaneous mutation in, and reduced activity of, RAG1. Mice bred from this animal contained high numbers of memory-phenotype T cells and experienced hepatosplenomegaly and eosinophilia, had oligoclonal T cells, and demonstrated elevated levels of IgE, major symptoms of OS. Depletion of CD4+ T cells in the mice caused a reduction in their IgE levels. Hence these "memory mutant" mice are a model for human OS; many symptoms of their disease were direct results of the Rag hypomorphism and some were caused by malfunctions of their CD4+ T cells.

Human T cell immunodeficiency: when signal transduction goes wrong

Severe combined immunodeficiency (SCID) is a heterogeneous group of diseases that are invariably fatal in infancy unless treated by hematopoietic stem cell replacement. For many years we have worked to better manage patients affected by SCID through rapid and accurate diagnosis followed by treatment aimed at achieving long-lasting immune reconstitution. By extensive immunological, biochemical, and genetic studies of patient samples, and with the realization of differences between human and murine T cell development, we have successfully been able to identify some of the molecular defects causing SCID. Among these discoveries, we described the first mutated signal transduction protein in T cells (ZAP-70); the first genetic defect leading to SCID and autoimmune phenomena (IL2R alpha); and, recently, the critical importance of CD3delta in the development of T cells. Our efforts have significantly advanced the understanding of the role of some of the signal-transducing proteins in T cell maturation and function. This review summarizes several of these discoveries and some of their impact on our understanding of T cells development, function, and homeostasis in humans.

Novel RAG1 mutation in a case of severe combined immunodeficiency

OBJECTIVE

The recombination activating enzymes RAG1 and RAG2 are essential to the process of V(D)J rearrangement in B and T cells and thus to the development of normal immune function. Mutations in RAG1 or RAG2 can lead to a spectrum of disorders, ranging from typical (B-)(T-) severe combined immunodeficiency to Omenn's syndrome. We present a unique presentation of RAG1 deficiency.

PATIENT

We report on a 6-month-old girl who presented with severe respiratory distress, which continued to progress despite antibiotic therapy but seemed to respond to treatment with corticosteroids. The patient exhibited no erythroderma or eosinophilia, and her lymphoid organs were not enlarged.

RESULTS

Investigation of the immune system showed normal numbers of CD3+ T cells, which expressed either CD4 or CD8. Subsequent analysis of the T-cell receptor demonstrated that nearly all CD3+ T cells were clonal; one clone expressed CD4, whereas the other expressed CD8. The extremely restricted T-cell repertoire and the lack of circulating B cells prompted analysis of the RAG1 gene, which revealed a novel homozygous thymine to cytosine substitution at nucleotide position 2686.

CONCLUSIONS

This case underscores the importance of more extensive evaluation of the immune system even when widely available, standard, flow cytometric analysis shows normal numbers of T cells that express CD4 or CD8, especially in the absence of circulating B cells.

Studies of patients' thymi aid in the discovery and characterization of immunodeficiency in humans

Studying the molecular and genetic bases of primary immunodeficiency is valuable at several levels. First, such information directly benefits patients in both short- and long-term management. Sophisticated diagnostic tools based on these studies can be used early and lead to appropriate treatment before potentially fatal infections and complications arise. Genotyping is also critical for future development and implementation of gene therapy. Secondly, investigating primary immunodeficiency helps understand the normal immune system in humans. As described in this report, the roles of zeta-associated protein of 70 kDa (Zap-70), CD25, and CD3delta are substantially different in humans when compared with the roles of homologous molecules in other species. Last, information obtained from these studies can be applied to other fields of investigation. Prominent examples for such applications include the intensive effort to design and produce specific inhibitors of Zap-70 and Janus kinase 3 as specific immunosuppressive agents. Most types of primary immunodeficiency in general and severe combined immunodeficiency in particular are rare and therefore cannot be easily studied by using traditional genetic methodology. Instead, biochemical methods were used to explore for candidate genes as was the case in the discovery of Zap-70 deficiency. Critical to the success of these discoveries was the careful analysis of patients' thymus glands. Detection of abnormalities in the thymus in these patients, which preceded identification of the genetic defect, aided in the assessment of the severity and nature of the immune disorder (primary versus secondary). Such assessment is critical before high-risk bone marrow transplantation. Equally important was the contribution of studies of the thymus to the description of novel phenotype of immunodeficiency as clearly demonstrated in defining CD8 lymphocytopenia, Zap-70 deficiency, and CD25 deficiency. Indeed, analysis of the thymus directly pointed to CD25 as candidate gene. Recently, the study of thymocyte-derived transcripts using DNA microarrays was key to discovering CD3delta deficiency. Finally, immunohistochemical analysis of the thymus was critical in pinpointing the roles of Zap-70, CD25, and CD3delta in the development of human T cells.

Detection of RAG mutations and prenatal diagnosis in families presenting with either T-B- severe combined immunodeficiency or Omenn's syndrome

It has been recently shown that mutations in both of the recombination activating genes RAG1 and RAG2 are involved in each of the two different types of severe combined immunodeficiency (SCID) syndromes: T-B- SCID and Omenn's syndrome (OS). The objective of the study was to search for novel mutations in the RAG genes and to offer prenatal diagnosis for families that have been identified as at risk of T-B- SCID or OS. Mutation analyses of polymerase chain reaction products of RAG1/RAG2 genes were performed in 14 cases (T-B- SCID = 6 and OS = 8). Consanguinity was reported in seven (50%) families. Four missense mutations in the RAG2 gene in six of eight OS patients and in four of six T-B- SCID patients were detected. The C1845T transition leading to a Tre215Ile substitution is a novel mutation. All but one of the patients were homozygous for the detected mutations, possibly reflecting the consanguinity in these families and the relative rarity of the disease-causing mutations. In addition, three putative polymorphic sites were found. Prenatal diagnosis was offered to seven families, but three of them declined genetic counseling for religious reasons. In the remaining families, four pregnancies were successfully completed, and in one case, the family chose to have an abortion because of a homozygous mutation. Mutations in RAG1/RAG2 genes were detected in only some of the T-B- SCID or OS patients, and the molecular basis for the remaining cases has yet to be elucidated. Important factors such as religious beliefs need to be considered when offering prenatal diagnosis to certain families.

Identical mutations in RAG1 or RAG2 genes leading to defective V(D)J recombinase activity can cause either T-B-severe combined immune deficiency or Omenn syndrome

Omenn syndrome (OS) is an inherited disorder characterized by an absence of circulating B cells and an infiltration of the skin and the intestine by activated oligoclonal T lymphocytes, indicating that a profound defect in the lymphoid developmental program could be accountable for this condition. Inherited mutations in either the recombination activating genes RAG1 or RAG2, resulting in partial V(D)J recombinase activity, were shown to be responsible for OS. This study reports on the characterization of new RAG1/2 gene mutations in a series of 9 patients with OS. Given the occurrence of the same mutations in patients with T-B-severe combined immune deficiency or OS on 3 separate occasions, the proposal is made that an additional factor may be required in certain circumstances for the development of the Omenn phenotype. The nature of this factor is discussed.

Human IL-2 receptor alpha chain deficiency

Profound cellular immunodeficiency occurs as the result of mutations in proteins involved in both the differentiation and function of mature lymphoid cells. We describe here a novel human immune aberration arising from a truncation mutation of the IL-2 receptor alpha chain (CD25), a subunit of the tripartite high-affinity receptor for IL-2. Decreased numbers of peripheral T cells displaying abnormal proliferation but normal B-cell development characterize this immunodeficiency. Extensive lymphocytic infiltration of tissues, including lung, liver, gut, and bone, is observed, accompanied by tissue atrophy and inflammation. Although mature T cells are present, the absence of CD25 does affect the differentiation of thymocytes. Although displaying normal development of CD2, CD3, CD4, and CD8 expression, CD25-deficient cortical thymocytes do not express CD1. Furthermore, they fail to down-regulate levels of bcl-2 and, subsequently, apoptosis in the thymus is markedly reduced, resulting in expansion of autoreactive clones in multiple tissues.

Matched unrelated bone marrow transplantation for combined immunodeficiency

Bone marrow transplantation (BMT) from siblings is the treatment of choice for severe combined immunodeficiency (SCID). The objective of this study was to evaluate the efficiency of BMT from matched unrelated donors (MUD) in congenital immunodeficiencies when a sibling donor is unavailable. Sixteen consecutive patients with SCID (n = 9) and CID (n= 7), were referred for an unrelated donor search. Acceptable donors were found for all patients. Fifteen patients received busulfan and cyclophosphamide pretransplant conditioning. One patient had an early loss of graft and was reconditioned using cyclophosphamide and total body irradiation. The graft-versus-host disease (GVHD) prophylaxis used was methylprednisolone, cyclosporin A with or without methotrexate. Neutrophil engraftment was rapid and was achieved in all patients within a mean of 15.4 days. Only 13 episodes of fever were recorded shortly after BMT. GVHD of grade II or more was apparent in 2/9 (22%) of SCID patients and in 4/7 (57%) of CID patients. Overall survival was 75% with a mean follow-up of 47.4 months (range 18-101). Six out of nine SCID patients (67%) and 6/7 (86%) of CID patients are alive and well. Eleven patients had normal humoral immunity, and cell-mediated immunity as measured by flow cytometry and mitogenic responses, was intact in all patients. Intradermal candida skin test was positive in 9/10 patients tested. We conclude that BMT from MUD results in rapid engraftment and is therefore associated with a low rate of infection contributing to the improved survival rate. The protocol used is especially favorable for patients with combined immunodeficiency.

Characterization of immune function and analysis of RAG gene mutations in Omenn syndrome and related disorders

Omenn syndrome was recently found to be caused by missense mutations in RAG1 or RAG2 gene that result in partial V(D)J recombination activity. Although the clinical hallmarks of the disease are well defined, there have been several cases with clinical findings similar to, but distinct from Omenn syndrome. The data on immune functions and RAG gene mutations of such cases are limited. We described five Japanese infants from four unrelated families, including two cases of Omenn syndrome and three cases of related disorders. Sibling cases with typical Omenn phenotype were found to be compound heterozygotes of R396C and L885R mutations in RAG1. The former has been reported in European cases and may constitute a hot spot. The latter is a novel missense mutation. Infants with related disorders exhibited erythroderma, eosinophilia, hypogammaglobulinaemia, decreased number of B cells and skewing to Th2, and their lymph node specimens showed architectural effacement, lymphocyte depletion and histiocytic hyperplasia, each of which is seen characteristically in Omenn syndrome. However, in these cases serum IgE levels were low or undetectable. We found no mutation in RAG genes except for a K820R substitution in RAG1, which was regarded to be a functional polymorphism, in two of these cases. Our study suggests that RAG missense mutation may be a genetic abnormality unique to Omenn syndrome with characteristic clinical and laboratory findings. Variations of Omenn syndrome, or related disorders, may represent a different type of immunodeficiency, distinct from abnormalities in lymphoid-specific recombinase activity.

Intrathymic Restriction and Peripheral Expansion of the T-Cell Repertoire in Omenn Syndrome

Mutations in the human RAG genes that impair, but do not abolish, recombination activity lead to Omenn syndrome, a severe primary immune deficiency that is associated with clinical and pathological features of graft-versus-host disease and oligoclonal expansion of activated, autologous T cells. We have analyzed the mechanisms accounting for peripheral oligoclonality of the T-cell repertoire. Predominance of few T-cell receptor clonotypes (both within TCRAB- and within TCRGD-expressing lymphocytes) is already detectable in the thymus and is further selected for in the periphery, with a different distribution of clonotypes in different tissues. These data indicate that oligoclonality of the T-cell repertoire in Omenn syndrome is due both to intrathymic restriction and to peripheral expansion. Moreover, the RAG genes defect that causes Omenn syndrome directly affects early stages of V(D)J recombination, but does not alter the process of double-strand-break DNA repair, including N and P nucleotide insertion.

Clonal dissemination of T-lymphocytes in scid mice from familial hemophagocytic lymphohistiocytosis

BACKGROUND

Although familial hemophagocytic lymphohistiocytosis (FHL) has been considered a disorder of T-cell dysfunction, there is no evidence of the clonal origin of T-cells in this disease.

PROCEDURE

We engrafted mononuclear cells (MNCs) from five FHL patients into scid mice and examined the infiltration of human cells in mouse organs. The characterization of human cells that infiltrated in the mouse organs was then performed.

RESULTS

A diffuse infiltration of human lymphoid cells was detected in scid mice treated with 1 x 10(6) MNCs from one of the five patients. These cells were positive for HLA-DR and CD3, but negative for CD4, CD8, CD20, and CD68, suggesting the infiltration of double negative (DN) T-cells. The MNCs from the other four patients induced murine lymphoma-like disease; T-cell lymphoma in one and lymphoma of unknown origin in three. The characterization of these human DN T-cells was performed. The analysis of the Vbeta repertoire showed no preferential usage of the Vbeta family in MNCs, while the dominant expression of Vbeta13 was detected in T-cells infiltrating in the spleen and lung. A Jbeta analysis showed the restricted usage of Jbeta1.2 for Vbeta13 in these cells, and the clonality of Vbeta13-Jbeta1.2 fragment was confirmed by a single-strand confirmation polymorphism analysis. The analysis of the Valpha repertoire showed that Valpha24 was exclusively used in these DN T-cells, but no usage of JalphaQ for Valpha24 was observed.

CONCLUSIONS

A clonal expansion of T-cells was induced in scid mice by the engraftment of MNCs from an FHL patient. The infiltration of DN alphabeta T-cells bearing invariant Valpha24 T-cell receptor in mouse organs may provide a useful clue to the pathogenesis of FHL. In the patients whose MNCs induced murine lymphoma-like disease, some cytokines or unknown factors that stimulate the growth and the tumorigenicity of murine lymphocytes might be produced by the MNCs engrafted in scid mice. Further study is needed to confirm the validity of our experimental approach and the findings observed in scid mice by using more FHL samples.

T-Cell Receptor Analysis in Omenn’s Syndrome: Evidence for Defects in Gene Rearrangement and Assembly

Patients with Omenn’s syndrome have a form of severe immune deficiency that is associated with pathological features of graft-versus-host disease, except for the lack of foreign engraftment. It has been hypothesized that the disease’s unique clinical features are mediated by an expanded population of autologous self-reactive T cells of limited clonality. In the current study, an investigation of the T-cell receptor (TCR) repertoire was undertaken to identify defects in T-cell rearrangement and development. The TCR repertoire in this group of patients was exquisitely restricted in the number of different TCR clonotypes, and some of these clonotypes seemed to have similar recognition motifs in the antigen-binding region, indicating antigen-driven proliferation of T lymphocytes. The TCRs from some patients lacked N- or P-nucleotide insertions and used proximal variable and joining gene segments, suggesting abnormal intrathymic T-cell development. Finally, abnormal assembly of gene segments and truncated rearrangements within nonproductive alleles suggested abnormalities in TCR rearrangement mechanisms. Overall, the findings suggest that inefficient and/or abnormal generation of TCRs may be a consistent feature of this disease.

T-Cell Receptor Analysis in Omenn’s Syndrome: Evidence for Defects in Gene Rearrangement and Assembly

Patients with Omenn’s syndrome have a form of severe immune deficiency that is associated with pathological features of graft-versus-host disease, except for the lack of foreign engraftment. It has been hypothesized that the disease’s unique clinical features are mediated by an expanded population of autologous self-reactive T cells of limited clonality. In the current study, an investigation of the T-cell receptor (TCR) repertoire was undertaken to identify defects in T-cell rearrangement and development. The TCR repertoire in this group of patients was exquisitely restricted in the number of different TCR clonotypes, and some of these clonotypes seemed to have similar recognition motifs in the antigen-binding region, indicating antigen-driven proliferation of T lymphocytes. The TCRs from some patients lacked N- or P-nucleotide insertions and used proximal variable and joining gene segments, suggesting abnormal intrathymic T-cell development. Finally, abnormal assembly of gene segments and truncated rearrangements within nonproductive alleles suggested abnormalities in TCR rearrangement mechanisms. Overall, the findings suggest that inefficient and/or abnormal generation of TCRs may be a consistent feature of this disease.

Highly restricted human T cell repertoire in peripheral blood and tissue-infiltrating lymphocytes in Omenn's syndrome

Omenn's syndrome is an inherited human combined immunodeficiency condition characterized by the presence of a large population of activated and tissue-infiltrating T cells. Analysis of the TCRB repertoire revealed a highly restricted TCRBV usage in three patients. More strikingly, T cell clones from the three patients expressed TCRB chains with VDJ junction similarities, suggesting a common antigenic specificity. Analysis of the TCRA repertoire in one patient also revealed a restricted TCRAV usage. Finally, analysis of the TCRBV repertoire of tissue-infiltrating T cells in one patient suggested nonrandom tissue migration. These results suggest that the oligoclonal expansion of T cells observed in Omenn's syndrome could be the consequence of autoimmune proliferation generated by a profound defect in lymphocyte development.

An interleukin-2 receptor gamma chain mutation with normal thymus morphology

One of the most common human immunodeficiencies is an X-linked condition arising from mutations of the gamma subunit of the interleukin-2 receptor (IL-2Rgamma). The IL-2Rgamma protein is one chain of the heterotrimeric (alpha, beta, gamma) IL-2 receptor, but also participates in the formation of the IL-4, 7, 9, and 15 receptor complexes. The diagnosis of X-linked SCID is usually relatively simple due to the distinctive immunological presentation; IL-2Rgamma-deficient patients typically lacking mature T lymphocytes (T-B+). However, it is becoming clear that this merely represents one extreme of a potential range of clinical presentations. We describe here a novel mutation of the human IL-2Rgamma chain (R222C) resulting in an unusual immunological phenotype. Although clinically immunodeficient, this patient has normal numbers of peripheral T and B cells, responds normally to mitogenic stimuli, and unusually, has a normal thymus gland. This IL-2Rgamma mutation is distinctive in that the protein is sufficiently stable to be expressed at the cell surface. While the T cell receptor repertoire appears complete, suggesting normal T cell differentiation occurs, patient T cells demonstrate a reduced ability to bind IL-2 and this appears sufficient to cause a deficiency in their ability to participate in antigenic responses. Early clinical recognition of this phenotype is critical as a delay in diagnosis may result in a fatal infection.

Oligoclonal expansion of CD45RO+ T lymphocytes in Omenn syndrome

Omenn syndrome comprises a rare form of combined immunodeficiency with TH2-type features of eosinophilia and elevated IgE. Previous studies have led to reports of restricted heterogeneity in the T lymphocyte repertoire, and in vitro cloned T lymphocytes have been shown to produce IL-4 and IL-5. We hypothesized that (1) T cell receptor beta V(D)J DNA sequence analysis would confirm and further define the putative restricted heterogeneity, and (2) increased production of IL-4 and IL-5 should be found in nonstimulated T lymphocytes, if the molecular pathogenesis of Omenn syndrome is an uncontrolled TH2 state. We report the results of molecular analyses of T lymphocytes from an untreated 3-month-old patient. Oligoclonal T cell receptor beta variable gene usage was found. Sequence analysis revealed sets of identical V(D)J sequences, each in-frame, with apparently normal N-diversification and no obvious antigen combining site motif. From fresh, nonstimulated lymphocytes, proinflammatory TH1 cytokines could be detected, but TH2 cytokines could not, so that a simple TH1/TH2 paradigm cannot explain the eosinophilia and elevated IgE in Omenn syndrome. Our studies fully document for the first time at the molecular level that clonally expanded populations of T lymphocytes are present in Omenn syndrome.

Selective gamma-chain T-cell receptor gene rearrangements in a patient with Omenn's syndrome: absence of V-II subgroup (V gamma 9) transcripts

Only gamma-chain T-cell receptor transcripts utilizing V-1 subgroup gene segments were found in peripheral blood lymphocytes from a patient with Omenn's syndrome. gamma-Chain T-cell receptor transcripts utilizing the V gamma 9 (V-II subgroup) gene segment were absent in peripheral blood lymphocytes from this patient. V gamma 9 J gamma 1.2 C gamma 1 rearrangements are those primarily found in peripheral blood lymphocytes (70 to 85%) from normal donors.

Functional platelet-derived growth factor-beta (PDGF-beta) receptor expressed on early B-lineage precursor cells

Growth and maturation of B lymphocytes from stem cells require a series of complex processes that are dependent at least in part on growth factors. Uncontrolled expression of receptors from these early growth factors may contribute to a leukaemogenesis of such early B cell progenitors. We show here that early pre-pre-B cells, but not mature B cells, express the PDGF receptor-beta (PDGFR-beta). These receptors contain a protein tyrosine kinase domain which is activated upon ligation with PDGF in pre-pre-B cells. Further, pre-pre-B leukaemia cells seem to express more PDGFR-beta compared with their normal counterparts, suggesting a role for these receptors in growth promotion of leukaemia cells.