Novel T-lymphocyte population in combined immunodeficiency with features of graft-versus-host disease

Omenn syndrome associated with a functional reversion due to a somatic second-site mutation in CARD11 deficiency

Omenn syndrome (OS) is a severe immunodeficiency associated with erythroderma, lymphoproliferation, elevated IgE, and hyperactive oligoclonal T cells. A restricted T-cell repertoire caused by defective thymic T-cell development and selection, lymphopenia with homeostatic proliferation, and lack of regulatory T cells are considered key factors in OS pathogenesis. We report 2 siblings presenting with cytomegalovirus (CMV) and Pneumocystis jirovecii infections and recurrent sepsis; one developed all clinical features of OS. Both carried homozygous germline mutations in CARD11 (p.Cys150*), impairing NF-κB signaling and IL-2 production. A somatic second-site mutation reverting the stop codon to a missense mutation (p.Cys150Leu) was detected in tissue-infiltrating T cells of the OS patient. Expression of p.Cys150Leu in CARD11-deficient T cells largely reconstituted NF-κB signaling. The reversion likely occurred in a prethymic T-cell precursor, leading to a chimeric T-cell repertoire. We speculate that in our patient the functional advantage of the revertant T cells in the context of persistent CMV infection, combined with lack of regulatory T cells, may have been sufficient to favor OS. This first observation of OS in a patient with a T-cell activation defect suggests that severely defective T-cell development or homeostatic proliferation in a lymphopenic environment are not required for this severe immunopathology.

Histological spectrum of mycophenolate mofetil-related colitis: association with apoptosis

AIMS

The main purpose of this study was to define diagnostic histological characteristics of mycophenolate mofetil (MMF)-related colitis in association with crypt epithelial cell turnover.

METHODS AND RESULTS

The examined material included 43 colonic biopsies from renal transplant recipients with MMF administration and persistent diarrhoea. Thirty-three cases showed MMF-related colitis, while 10 showed no significant changes. The histological findings were scored and correlated with the apoptotic index (AI) and with the proliferation rate (PR) of the crypt epithelium examined by TUNEL assay and Ki-67 immunoexpression. Ten cases of Crohn disease and 10 of ulcerative colitis were used as comparative groups. Crypt distortion and loss as well as increased apoptosis constituted the main features, their degree and combination leading either to an inflammatory bowel disease (IBD)-like (82%) or to a graft-versus-host disease-like pattern (18%). A high AI was associated more frequently with moderate and severe crypt distortion, while the values were significantly higher compared with the control groups (P < 0.01). High PR was noted in 18 of 29 (62.1%) of the cases.

CONCLUSIONS

The diagnostic hallmark of MMF-related colitis is an IBD-like histological pattern in association with increased epithelial apoptosis, while apoptotic cell death seems to be a potential pathogenetic factor of mucosa injury.

Clinical implications of maternal-fetal cellular trafficking

Maternal-fetal cellular trafficking (MFCT) is the bidirectional passage of cells that results in the presence of fetal cells in the mother and maternal cells in the fetus. This naturally occurring biological phenomenon has been implicated in the pathogenesis of autoimmune diseases in both mothers and children. However, MFCT may also have beneficial consequences in establishing and maintaining maternal-fetal tolerance and may have long-term consequences for transplantation tolerance. There is also evidence that trafficking is altered during pregnancy complications and fetal intervention. An improved understanding of cellular trafficking during pregnancy will lead to progress in multiple fields including autoimmunity, transplantation, and fetal surgery.

Rapid full engraftment and successful immune reconstitution after allogeneic hematopoietic stem cell transplantation with reduced intensity conditioning in Omenn syndrome

OS is a variant of SCID characterized by generalized erythroderma, alopecia, eosinophilia, and elevated IgE levels. It is fatal unless treated with allogeneic HSCT, which is the only curative approach. However, treatment related complications and graft rejection are major obstacles to the success of treatment. In this report, we describe a patient with OS, complicated by prolonged cytomegalovirus infection, successfully treated by reduced intensity conditioning allogeneic HSCT from sibling donor.

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.

Immunodeficiencies with Autoimmune Consequences

Far from being mutually exclusive, immunodeficiency and autoimmunity may occur simultaneously. During the last years, analysis of Autoimmune Polyendocrinopathy--Candidiasis--Ectodermal Dystrophy (APECED) and Immunodysregulation--Polyendocrinopathy--Enteropathy--X-linked (IPEX), two rare monogenic forms of immunodeficiency associated with autoimmunity, has led to the identification of Auto Immune Regulator (AIRE) and Forkhead Box P3 (FOXP3), essential transcriptional regulators, involved in central tolerance and peripheral immune homeostasis, respectively. Characterization of the molecular and cellular mechanisms involved in APECED, and recognition that AIRE expression is sustained by effective thymopoiesis, has recently allowed to define that the autoimmunity of Omenn syndrome, a combined immunodeficiency due to defects of V(D)J recombination, also results from defective expression of AIRE. The implications of identification of the basis of autoimmunity in these rare forms of immunodeficiency have important implications for a better understanding of more common autoimmune disorders, and for development of novel therapeutic approaches.

A variant of SCID with specific immune responses and predominance of gamma delta T cells

We describe here a patient with a clinical and molecular diagnosis of recombinase activating gene 1-deficient (RAG1-deficient) SCID, who produced specific antibodies despite minimal B cell numbers. Memory B cells were detected and antibodies were produced not only against some vaccines and infections, but also against autoantigens. The patient had severely reduced levels of oligoclonal T cells expressing the alphabeta TCR but surprisingly normal numbers of T cells expressing the gammadelta TCR. Analysis at a clonal level and TCR complementarity-determining region-3 spectratyping for gammadelta T cells revealed a diversified oligoclonal repertoire with predominance of cells expressing a gamma4-delta3 TCR. Several gammadelta T cell clones displayed reactivity against CMV-infected cells. These observations are compatible with 2 non-mutually exclusive explanations for the gammadelta T cell predominance: a developmental advantage and infection-triggered, antigen-driven peripheral expansion. The patient carried the homozygous hypomorphic R561H RAG1 mutation leading to reduced V(D)J recombination but lacked all clinical features characteristic of Omenn syndrome. This report describes a new phenotype of RAG deficiency and shows that the ability to form specific antibodies does not exclude the diagnosis of SCID.

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.

Isolation and characterization of human antigen-specific TCR alpha beta+ CD4(-)CD8- double-negative regulatory T cells

Down-regulation of immune responses by regulatory T (Treg) cells is an important mechanism involved in the induction of tolerance to allo-antigens (Ags). Recently, a novel subset of Ag-specific T-cell receptor (TCR)alpha beta+ CD4(-)CD8- (double-negative [DN]) Treg cells has been found to be able to prevent the rejection of skin and heart allografts by specifically inhibiting the function of antigraft-specific CD8+ T cells. Here we demonstrate that peripheral DN Treg cells are present in humans, where they constitute about 1% of total CD3+ T cells, and consist of both naive and Ag-experienced cells. Similar to murine DN Treg cells, human DN Treg cells are able to acquire peptide-HLA-A2 complexes from antigen-presenting cells by cell contact-dependent mechanisms. Furthermore, such acquired peptide-HLA complexes appear to be functionally active, in that CD8+ T cells specific for the HLA-A2-restricted self-peptide, Melan-A, became sensitive to apoptosis by neighboring DN T cells after acquisition of Melan-A-HLA-A2 complexes and revealed a reduced proliferative response. These results demonstrate for the first time that a sizable population of peripheral DN Treg cells, which are able to suppress Ag-specific T cells, exists in humans. DN Treg cells may serve to limit clonal expansion of allo-Ag-specific T cells after transplantation.

Histologic features of mycophenolate mofetil-related colitis: a graft-versus-host disease-like pattern

Mycophenolate mofetil (MMF) is widely used for maintenance immunosuppression in solid organ transplantation. Gastrointestinal toxicity, usually manifested as diarrhea, is the most common side effect of MMF. We evaluated colonic biopsies from 20 renal transplant patients with MMF-related diarrhea. The latter was defined by the absence of any other demonstrable etiology and improvement or resolution of symptoms by the discontinuation or reduction of the dose of MMF alone. These biopsies were compared with colon biopsies from patients with the following: acute graft-versus-host disease (GVHD, n=10), inflammatory bowel disease (IBD) or infectious colitis (n=10), and colon biopsies from renal transplant patients not receiving MMF (n=8). Normal colonic segments from surgical specimens served as normal controls (n=5). Colonic biopsies from patients with MMF-related diarrhea showed prominent crypt cell apoptosis and reactive/reparative changes including enterocyte cytologic atypia, increased neuroendocrine cells, and glandular architectural distortion. The changes were similar, although of milder degree to the ones seen in patients with acute intestinal GVHD. This pattern of injury was not seen in controls or in biopsies from transplant patients not receiving MMF, and it was markedly different from the one seen in idiopathic inflammatory or infectious colitis. The severity of histologic changes correlated significantly with the endoscopic degree of "colitis." There was no statistically significant correlation between histologic damage and the dose of MMF (corrected for body weight and renal function). MMF-related colitis is a distinct entity that displays histologic features remarkably similar to the ones associated with intestinal GVHD. This form of injury could be related to either direct toxicity or an "innocent by-stander" phenomenon secondary to the alteration of the immunologic microenvironment of the colon caused by the MMF.

Identification of anti-herpes simplex virus antibody-producing B cells in a patient with an atypical RAG1 immunodeficiency

Mutations of the RAG1 or RAG2 protein that eliminate their recombination activity result in T-B-severe combined immunodeficiency (SCID), whereas mutations retaining partial recombination activity lead to Omenn syndrome, a peculiar SCID characterized by increased host T cells and absence of circulating B cells. The prognosis of this disease is fatal, unless hematopoietic stem cell transplantation is performed. This study reports a case of atypical SCID, carrying RAG1 mutations. The patient survived for 6 years without hematopoietic stem cell transplantation. The missense mutation, tested by in vivo recombination assay, revealed residual recombination activity. By the age of 5 years, the patient developed host B cells, but not T cells, possibly due to engrafted maternal T cells. In addition, the host B cells were able to produce antibodies, including anti-herpes simplex virus-antibodies. The fact that host B cells could produce antibodies in this patient could explain not only the mild phenotype observed but also, at least in part, how patients with Omenn syndrome produce immunoglobulin E and sometimes immunoglobulin M, as the same missense mutation of RAG1 gene has been reported in a patient with Omenn syndrome.

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.

Autoimmune lymphoproliferative syndrome. A human disorder of abnormal lymphocyte survival

The importance of Fas in the homeostatic balance between lymphocyte survival and death is underscored by the three main consequences of defective Fas-mediated apoptosis, as experienced by patients with ALPS: (1) abnormal accumulation of lymphocytes results in lymphadenopathy, hepatosplenomegaly, and hypersplenism; (2) failure of removal of potentially autoreactive lymphocytes, a process normally used to eliminate lymphocytes that have escaped negative selection in the thymus and bone marrow (see article by Fleisher and Blessing, p. 1197), is associated with the appearance of autoimmune manifestations; and (3) inappropriate survival of lymphocytes may lead to the development of malignancies. As with other "experiments of nature," the many aspects of ALPS have provided valuable new insights into the immune system and the importance of a proper balance between life and death of lymphocytes. ALPS is an example of how a mouse disease model was applied directly to the identification of the molecular basis and the understanding of a remarkable disease in humans. It is also an example of clinical observations being linked to basic scientific data to unlock the underlying defect(s) causing a disease. Despite the difficulty in fully understanding the complex nature of the clinical course, the immunologic abnormalities, and the genetic aspects of ALPS, the accumulated experience in diagnosis, treatment, and follow-up of patients and relatives has generated a "road map" that can be used as a guide for their care. As examples, the appreciation that manifestations of lymphoproliferation usually subside over time has allowed a "wait-and-see" approach in many patients who might previously have been treated aggressively. The appreciation that these patients are at increased risk for malignancies has mandated the adoption of careful and lifelong follow-up. Future efforts directed at careful clinical follow-up and scientific investigation are required to learn more about the incidence and natural history of ALPS, therapeutic interventions directed at altering the consequences of TNFRSF6 mutations, and the identification of other genetic and environmental factors that may have a role in the pathogenesis of ALPS.

An unusual concurrence of graft versus host disease caused by engraftment of maternal lymphocytes with DiGeorge anomaly

We describe a girl with DiGeorge anomaly and normal cytogenetic and molecular studies, whose clinical course was complicated by graft versus host disease caused by intrauterine materno-fetal transfusion, and several immunohematological alterations including a monoclonal gammapathy of undetermined significance (first IgG, which subsequently changed to IgM). The main clinical features and pathological findings are discussed.

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.

Microchimerism of maternal origin persists into adult life

Recent studies indicate that fetal cells persist in maternal blood for decades after pregnancy. Maternal cells are known to engraft and persist in infants with immunodeficiency, but whether maternal cells persist long-term in immunocompetent offspring has not specifically been investigated. We developed sensitive human leukocyte antigen-specific (HLA-specific) PCR assays and targeted nonshared maternal HLA genes to test for persistent maternal microchimerism in subjects with scleroderma and in healthy normal subjects. Nonshared maternal-specific DNA was found in 6 of 9 scleroderma patients. In situ hybridization with double labeling for X and Y chromosome-specific sequences revealed female cells in peripheral blood samples from 2 male scleroderma patients. HLA-specific PCR also frequently revealed persistent maternal microchimerism in healthy control subjects. The mean age of all subjects with maternal microchimerism was 28 years (range: 9-49 years). With few exceptions, mothers of subjects with persistent maternal microchimerism were HLA incompatible with subjects for class I and class II alleles. These results clearly indicate that HLA-disparate maternal cells can persist in immunocompetent offspring well into adult life. The biological significance of maternal microchimerism and whether it might contribute to autoimmune disease requires further investigation.

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.

Omenn syndrome: a disorder of Rag1 and Rag2 genes

In vertebrates, generation of the T- and B-cell repertoire relies on genomic rearrangement of T-cell receptor and immunoglobulin gene coding segments. This process, known as V(D)J recombination, is initiated by the lymphoid specific proteins Rag1 and Rag2. Both in humans and in animal models, mutations that abrogate expression of either the Rag1 or Rag2 proteins result in severe combined immune deficiency with a complete lack of circulating T and B cells due to an early block in lymphoid development. We have recently shown that mutations that impair, but do not completely abolish the function of Rag1 and Rag2 in humans result in Omenn syndrome, an enigmatic form of combined immune deficiency characterized by oligoclonal, activated T lymphocytes with a skewed Th2 profile.

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.

Pathological findings in human autoimmune lymphoproliferative syndrome

The defects in lymphocyte apoptosis that underlie the autoimmune lymphoproliferative syndrome (ALPS) are usually attributable to inherited mutations of the CD95 (Fas) gene. In this report, we present the histopathological and immunophenotypic features seen in the lymph nodes (n = 16), peripheral blood (n = 10), bone marrow (n = 2), spleen (n = 3), and liver (n = 2) from 10 patients with ALPS. Lymph nodes showed marked paracortical hyperplasia. Interfollicular areas were expanded and populated by T cell receptor-alphabeta CD3+ CD4-CD8- (double-negative, DN) T cells that were negative for CD45RO. CD45RA+ T cells were increased in all cases studied. The paracortical infiltrate was a result of both reduced apoptosis and increased proliferation, as measured by in situ detection of DNA fragmentation and staining with MIB-1, respectively. The paracortical proliferation may be extensive enough to suggest a diagnosis of malignant lymphoma. Many of the paracortical lymphocytes expressed markers associated with cytotoxicity, such as perforin, TIA-1, and CD57. CD25 was negative. In addition, most lymph nodes exhibited florid follicular hyperplasia, often with focal progressive transformation of germinal centers; in some cases, follicular involution was seen. A polyclonal plasmacytosis also was present. The spleens were markedly enlarged, more than 10 times normal size. There was expansion of both white pulp and red pulp, with increased DN T cells. DN T cells also were observed in liver biopsies exhibiting portal triaditis. In the peripheral blood, the T cells showed increased expression of HLA-DR and CD57 but not CD25. CD45RA+ T cells were increased in the four cases studied. Polyclonal B cell lymphocytosis with expansion of CD5+ B cells was a characteristic finding. Taken together, the histopathological and immunophenotypic findings, particularly in lymph nodes and peripheral blood, are sufficiently distinctive to suggest a diagnosis of ALPS. Of note, two affected family members of one proband developed lymphoma (T-cell-rich B-cell lymphoma and nodular lymphocyte predominance Hodgkin's disease, respectively).

Age-related persistent clonal expansions of CD28(-) cells: phenotypic and molecular TCR analysis reveals both CD4(+) and CD4(+)CD8(+) cells with identical CDR3 sequences

In a small group of subjects we had identified persistent expansions (range 6-72%) of CD4(+)CD8(+) double-positive (DP) peripheral blood (PB) cells which express the CD8 alpha/alpha homodimer. Here, DP cells present in a larger cohort were further investigated and found by FACS analysis to express a single or a dominant TCRBV family. In these subjects, with a mean age of about 64 years, expansions of CD4(+) cells with the same TCRBV family specificity as in the respective DP cells also were consistently detected. TCR heterogeneity of the dominant TCRBV family was specifically evaluated: The amplified CDR3 region was cloned and found to consist of one single or two largely dominant sequence patterns. Furthermore, cloning of the CDR3 region from FACS-sorted DP, CD4(+), or CD8(+) cells indicates that both DP and CD4(+), but not CD8(+) cells, isolated from the same individual possess a striking identity of the CDR3 regions. As indicated by FACS analysis, the clonally expanded cells occur in the CD4(+)CD28(-) cells. Taken together, these results suggest that expanded CD4(+)CD28(-) cells might also acquire CD8 alpha/alpha expression and become DP and imply that CD4 clonality is a more frequent phenomenon than previously suspected. In conclusion, the persistent expansions described in this report represent a novel group of age-related benign clonal expansions of still undefined significance of a rare CD28(-) T cell subset.

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.

Changes in peripheral blood double-negative T-lymphocyte (CD3+ CD4- CD8-) populations associated with acute cellular rejection after liver transplantation

Circulating CD3+ T lymphocytes that express neither the CD4 nor CD8 surface molecules (double-negative T lymphocytes) are phenotypically and functionally distinct from single-positive CD3+CD4+ and CD3+CD8+ lymphocytes and are thought to represent a distinct T-cell lineage. The presence of low numbers of double-negative T cells in healthy individuals and the increase observed in association with lymphoproliferative disorders, graft-versus-host disease, and autoimmune diseases suggest a pathogenic or immunoregulatory role for this population of T lymphocytes. In this study, peripheral blood double-negative T cells were assessed quantitatively using three-color flow cytometry in 10 patients after liver transplantation during a 6-week period. During this time, 12 episodes of histologically proven acute cellular rejection occurred in 8 patients. The median postoperative baseline double-negative T-cell count expressed as a proportion of the CD3+ T cells was 2.4 +/- 1.2 (median +/- SD; n = 10), which was identical to a control group of healthy adults (2.5 +/- 2.4; n = 9). Circulating numbers of double-negative T cells were increased significantly during acute cellular rejection (6.8 +/- 6.7; P < .001; n = 12). After pulse corticosteroid therapy for rejection, there was a significant decrease in the double-negative T-cell population (3.5 +/- 5.0 v 6.8 +/- 6.7; P = .01). No significant changes occurred in the double-negative T-cell count in the absence of clinical events (2.4 +/- 3.5; n = 73). These findings are consistent with a role for double-negative T cells in the initiation of acute cellular rejection or a possible regulatory role in the immunologic changes associated with rejection.

Development of Autologous, Oligoclonal, Poorly Functioning T Lymphocytes in a Patient With Autosomal Recessive Severe Combined Immunodeficiency Caused by Defects of the Jak3 Tyrosine Kinase

Defects of the common gamma chain subunit of the cytokine receptors (γc) or of Jak3, a tyrosine kinase required for γc signal transduction, result in T−B+ severe combined immunodeficiency (SCID). However, atypical cases, characterized by progressive development of T lymphocytes, have been also reported. We describe a child with SCID caused by Jak3 gene defects, which strongly but not completely affect Jak3 protein expression and function, who developed a substantial number (>3,000/μL) of autologous CD3+CD4+ T cells. These cells showed a primed/activated phenotype (CD45R0+ Fas+HLA-DR+ CD62Llo), defective secretion of T-helper 1 and T-helper 2 cytokines, reduced proliferation to mitogens, and a high in vitro susceptibility to spontaneous (caused by downregulation of bcl-2 expression) as well as activation-induced cell death. A restricted T-cell receptor repertoire was observed, with oligoclonal expansion within each of the dominant segments. These features resemble those observed in γc-/y and in Jak3−/−mice, in which a population of activated, anergic T cells (predominantly CD4+) also develops with age. These results suggest that residual Jak3 expression and function or other Jak3-independent signals may also permit the generation of CD4+ T cells that undergo in vivo clonal expansion in humans; however, these mechanisms do not allow development of CD8+ T cells, nor do they fully restore the functional properties of CD4+ T lymphocytes.

γ-Interferon Production in Peripheral Blood Mononuclear Cells and Tumor Infiltrating Lymphocytes From Kaposi's Sarcoma Patients: Correlation With the Presence of Human Herpesvirus-8 in Peripheral Blood Mononuclear Cells and Lesional Macrophages

Evidence indicates that, at least in the early stage, Kaposi's sarcoma (KS) is a cytokine-mediated disease and that it is consistently associated with a novel herpesvirus termed human herpesvirus-8 (HHV-8). To gain insights into the mechanisms by which cytokines and HHV-8 may cooperate in disease pathogenesis, we examined the phenotype, the Th1 (γ-interferon [γIFN]) and Th2 (interleukin-4 [IL-4]) cytokine profile and the presence of HHV-8 in peripheral blood mononuclear cells (PBMC), tumor-infiltrating lymphocytes (TIL), and spindle cell cultures derived from skin lesions of patients affected by classical KS (C-KS) and acquired immunodeficiency syndrome (AIDS)-associated KS (AIDS-KS). TIL and spindle cell cultures were examined at day 0 or after culture in conditioned media from activated T cells (TCM) that contain the same cytokines increased in KS tissues. No differences were found in the immunophenotype of PBMC from C-KS patients versus controls, except for AIDS-KS patients who showed a T-CD8+ expansion. However, a preferential infiltration of T-CD8+ cells was found in all KS lesions examined, which was maintained after culture of TIL in TCM. γIFN production was found in both PBMC and cultures derived from all KS examined; some IL-4 positive supernatants were found only in three AIDS-KS cases. Uninvolved skin did not show appreciable lymphocyte infiltration or cytokine production. The culture conditions of the lesional skin allowed also the appearance of adherent, spindle-like cells bearing markers of tissue macrophages. Finally, most or all of the PBMC, lesions, and macrophagic cell cultures from the skin lesions were found to be positive for HHV-8 infection by nested polymerase chain reaction (PCR). These findings indicate that patients with KS express a Th1 phenotype with a prevalent γIFN production, likely accounted for by the local T-CD8+ infiltration. By analogy with other viral infections (ie, Epstein-Barr virus), this suggests that in loco recruitment of lymphoid cells and the subsequent γIFN production may be in response to or elicited by HHV-8 that was found in both PBMC and macrophagic cell cultures from the lesions of the same patients.

γ-Interferon Production in Peripheral Blood Mononuclear Cells and Tumor Infiltrating Lymphocytes From Kaposi's Sarcoma Patients: Correlation With the Presence of Human Herpesvirus-8 in Peripheral Blood Mononuclear Cells and Lesional Macrophages

Evidence indicates that, at least in the early stage, Kaposi's sarcoma (KS) is a cytokine-mediated disease and that it is consistently associated with a novel herpesvirus termed human herpesvirus-8 (HHV-8). To gain insights into the mechanisms by which cytokines and HHV-8 may cooperate in disease pathogenesis, we examined the phenotype, the Th1 (γ-interferon [γIFN]) and Th2 (interleukin-4 [IL-4]) cytokine profile and the presence of HHV-8 in peripheral blood mononuclear cells (PBMC), tumor-infiltrating lymphocytes (TIL), and spindle cell cultures derived from skin lesions of patients affected by classical KS (C-KS) and acquired immunodeficiency syndrome (AIDS)-associated KS (AIDS-KS). TIL and spindle cell cultures were examined at day 0 or after culture in conditioned media from activated T cells (TCM) that contain the same cytokines increased in KS tissues. No differences were found in the immunophenotype of PBMC from C-KS patients versus controls, except for AIDS-KS patients who showed a T-CD8+ expansion. However, a preferential infiltration of T-CD8+ cells was found in all KS lesions examined, which was maintained after culture of TIL in TCM. γIFN production was found in both PBMC and cultures derived from all KS examined; some IL-4 positive supernatants were found only in three AIDS-KS cases. Uninvolved skin did not show appreciable lymphocyte infiltration or cytokine production. The culture conditions of the lesional skin allowed also the appearance of adherent, spindle-like cells bearing markers of tissue macrophages. Finally, most or all of the PBMC, lesions, and macrophagic cell cultures from the skin lesions were found to be positive for HHV-8 infection by nested polymerase chain reaction (PCR). These findings indicate that patients with KS express a Th1 phenotype with a prevalent γIFN production, likely accounted for by the local T-CD8+ infiltration. By analogy with other viral infections (ie, Epstein-Barr virus), this suggests that in loco recruitment of lymphoid cells and the subsequent γIFN production may be in response to or elicited by HHV-8 that was found in both PBMC and macrophagic cell cultures from the lesions of the same patients.

Development of Autologous, Oligoclonal, Poorly Functioning T Lymphocytes in a Patient With Autosomal Recessive Severe Combined Immunodeficiency Caused by Defects of the Jak3 Tyrosine Kinase

Defects of the common gamma chain subunit of the cytokine receptors (γc) or of Jak3, a tyrosine kinase required for γc signal transduction, result in T−B+ severe combined immunodeficiency (SCID). However, atypical cases, characterized by progressive development of T lymphocytes, have been also reported. We describe a child with SCID caused by Jak3 gene defects, which strongly but not completely affect Jak3 protein expression and function, who developed a substantial number (>3,000/μL) of autologous CD3+CD4+ T cells. These cells showed a primed/activated phenotype (CD45R0+ Fas+HLA-DR+ CD62Llo), defective secretion of T-helper 1 and T-helper 2 cytokines, reduced proliferation to mitogens, and a high in vitro susceptibility to spontaneous (caused by downregulation of bcl-2 expression) as well as activation-induced cell death. A restricted T-cell receptor repertoire was observed, with oligoclonal expansion within each of the dominant segments. These features resemble those observed in γc-/y and in Jak3−/−mice, in which a population of activated, anergic T cells (predominantly CD4+) also develops with age. These results suggest that residual Jak3 expression and function or other Jak3-independent signals may also permit the generation of CD4+ T cells that undergo in vivo clonal expansion in humans; however, these mechanisms do not allow development of CD8+ T cells, nor do they fully restore the functional properties of CD4+ T lymphocytes.

In vitro cell death of activated lymphocytes in Omenn's syndrome

Omenn's syndrome (OS) is characterized by erythrodermia, hepatosplenomegaly, lymphadenopathy, hypereosinophilia and elevated IgE levels associated with increased susceptibility to severe infections. Peripheral blood T cells, though usually present in normal number, show an activated phenotype (including an increased expression of CD95/Fas), a Th2 pattern of cytokine secretion and defective proliferative response to mitogens. In this report, we demonstrate that T cells from patients with OS undergo an excessive cell death in vitro resulting from two mechanisms. First, a substantial number of peripheral blood lymphocytes from OS patients die in unstimulated cultures (p = 0.009 vs. healthy controls). This spontaneous apoptosis is associated with reduced expression of bcl-2 gene product (p < 0.05) and can be prevented by addition of interleukin (IL)-2 (which also prevents down-modulation of bcl-2), while is independent from CD95 signaling. Second, lymphocytes from OS patients are highly susceptible to activation-induced cell death (AICD) induced with mitogens. This mechanism is largely independent from IL-2, while it can be significantly inhibited blocking CD95 with an IgG2b monoclonal antibody (mAb). The dependence of AICD from signals transduced via CD95 was confirmed showing that cross-linking CD95 with an IgM mAb induces a higher cell death in purified CD4+ CD45R0+ cells from OS patients than in controls (comparable for CD95 expression). Both mechanisms of cell death observed in this study result from lymphocyte hyperactivation occurring in vivo in these patients and may contribute to functional T cell defects of OS.

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.

Naturally occurring primary deficiencies of the immune system

Naturally occurring genetic disorders of the immune system provide many models for the study of its development and function. In a way, their analysis complements the information provided by the generation of genetic defects in mice created using homologous recombination techniques. In this review, the recent findings made in three areas are focused upon deficiencies in T cell differentiation and in T lymphocyte activation, and on the control process of peripheral immune response.

Cellular radiosensitivity in human severe-combined-immunodeficiency (SCID) syndromes

PURPOSE

The aim of the work was to establish to what extent a variety of human severe-combined-immunodeficiency (SCID) disorders are associated with in vitro cellular hypersensitivity to ionizing radiation.

MATERIALS AND METHODS

A study was made of fibroblast strains established from individuals with adenosine deaminase deficiency, T(-)B(-) SCID, Omenn's syndrome and a SCID heterozygote. For comparison, an assessment was also made of the radiosensitivity of a series of fibroblast strains derived from: normal donors, a patients with ataxia-telangiectasia (A-T) and an A-T heterozygote. Radiosensitivity was determined using a clonogenic assay following both high (HDR) and low (LDR) dose-rate irradiation.

RESULTS

Following HDR irradiation, the fibroblast strains derived from the different human SCID disorders displayed a wide range of radiosensitivity: the adenosine deaminase deficiency cells were similar in radiosensitivity to normal fibroblasts, T(-)B(-) cells were as hypersensitive to radiation as A-T cells and the Omenn's syndrome cells showed intermediate radiosensitivity. However, whereas all four normal cell strains studied showed significant LDR sparing, none of the SCID fibroblasts did.

CONCLUSIONS

These data indicate that human SCID is variable in terms of radiosensitivity depending on the particular defect. In addition, the lack of LDR sparing of radiation-induced damage suggests the involvement of some form(s) of DNA repair defect in all the human SCID syndromes.

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.

Acquired immune deficiency syndrome caused by hyperimmunity

Normal immunocytes including T and B cells are equilibrated by a reciprocal attacking mechanism called a network. Continuous disequilibrium of this network results in general immunodeficiency with oligo- and polyclonal hyperimmunity, for example, T-cell activation due to spontaneous reticuloendotheliosis, paraneoplastic autoimmune syndromes, and human immunodeficiency virus infection. In these disorders, reciprocal self-reactivity, including autologous graft-versus-host reaction, plays a role in the immunodeficiency. A priori self-targeting immunity is a key mechanism to explain autoimmunity in the acquired immunodeficiency syndrome. In the treatment of the immunodeficiency due to hyperimmunity, I propose immunological suppression by agents and reconstitution of the network by bone-marrow transplantation.

CD30 cell expression and abnormal soluble CD30 serum accumulation in Omenn's syndrome: evidence for a T helper 2-mediated condition

Omenn's syndrome (OS) is a severe immunodeficiency, characterized by clinical and laboratory features reminiscent of a T helper type-2 (Th2) response. CD30, a member of the tumor necrosis factor receptor superfamily, has been found to be preferentially expressed by human T cell clones exhibiting a Th2-line profile and function. We investigated whether there are derangement in CD30 expression in tissues, and/or abnormalities in soluble CD30 (sCD30) levels in the serum, or both, of three children with OS and one child with maternal engraftment and Omenn's-like syndrome (OLS). Large proportions of tissue-infiltrating T lymphocytes from all four patients expressed CD30, whereas in control tissues, including peripheral blood, CD30+ T lymphocytes were extremely few or absent. In addition, levels of sCD30 were abnormally increased in all patients' sera. T cell clones were generated from sorted CD30+ and CD30-peripheral blood T cells of the patient with OLS who showed unusually high numbers of circulating CD30+ T lymphocytes. Most CD4+ T cell clones derived from CD30+ cells showed a Th2-like cytokine profile, whereas the majority of clones generated from CD30-T cells were Th1. These findings support the hypothesis that Th2 cells are involved in the pathogenesis of OS. Moreover, they provide evidence that detection of CD30+ T cells in tissues, increased levels of sCD30 in biological fluids, or both, reflect the presence of immune responses characterized by prevalent activation of T cells producing Th2 cytokines.

A pathway of costimulation that prevents anergy in CD28- T cells: B7-independent costimulation of CD1-restricted T cells

A class of molecules that is expressed on antigen presenting cells, exemplified by CD80 (B7), has been found to provide a necessary costimulatory signal for T cell activation and proliferation. CD28 and CTLA4 are the B7 counterreceptors and are expressed on the majority of human CD4+ T cells and many CD8+ T cells. The signal these molecules mediate is distinguished from other costimulatory signals by the finding that T cell recognition of antigen results in a prolonged state of T cell unresponsiveness or anergy, unless these costimulatory molecules are engaged. However, nearly half of the CD8+ and CD4-CD8- T cells lack CD28, and the costimulatory signals required for the activation of such cells are unknown. To understand the pathways of activation used by CD28- T cells, we have examined the costimulatory requirements of antigen-specific CD4-CD8- TCR(+)-alpha/beta circulating T cells that lack the expression of CD28. We have characterized two T cell lines, DN1 and DN6, that recognize a mycobacterial antigen, and are restricted not by major histocompatibility complex class I or II, but by CD1b or CD1c, two members of a family of major histocompatibility complex-related molecules that have been recently implicated in a distinct pathway for antigen presentation. Comparison of antigen-specific cytolytic responses of the DN1 and DN6 T cell lines against antigen-pulsed CD1+ monocytes or CD1+ B lymphoblastoid cell lines (B-LCL) demonstrated that these T cells recognized antigen presented by both types of cells. However, T cell proliferation occurred only when antigen was presented by CD1+ monocytes, indicating that the CD1+ monocytes expressed a costimulatory molecule that the B-LCL transfectants lacked. This hypothesis was confirmed by demonstrating that the T cells became anergic when incubated with the CD1(+)-transfected B-LCL in the presence of antigen, but not in the absence of antigen. The required costimulatory signal occurred by a CD28-independent mechanism since both the CD1+ monocytes and CD1+ B-LCL transfectants expressed B7-1 and B7-2, and DN1 and DN6 lacked surface expression of CD28. We propose that these data define a previously unrecognized pathway of costimulation for T cells distinct from that involving CD28 and its counterreceptors. We suggest that this B7-independent pathway plays a crucial role in the activation and maintenance of tolerance of at least a subset of CD28- T cells.

Treatment of Omenn syndrome by bone marrow transplantation

We report the outcome of allogeneic bone marrow transplantation (BMT) in nine consecutive patients with Omenn syndrome treated between 1980 and 1989. Five patients received unmanipulated marrow from a related matched donor, and four received T cell-depleted marrow from a haploidentical donor. The patients were conditioned with cyclophosphamide (200 mg/kg) and, except in one case, busulfan (16 mg/kg). Antithymocyte globulin and etoposide were given to three patients each; three recipients of T cell-depleted haploidentical marrow also received intravenous injections of an anti-leukocyte function-associated antigen type 1 antibody as graft rejection prophylaxis. All the patients were fed parenterally for 1 to 5 months before BMT to improve nutritional status and received topical corticosteroids (n = 8), systemic steroids (n = 2), etoposide (n = 1), or cyclosporine (n = 1) to control T-cell activation. Engraftment occurred in four of five recipients of human leukocyte antigen (HLA)-identical marrow and three of four recipients of HLA-haploidentical marrow. One patient died with cytomegalovirus infection. The other six patients are alive 4 to 11 years after BMT, with full chimerism in all but one case. Chronic graft-versus-host disease persists in one patient; the other five survivors have fully restored immune function and have no manifestations of Omenn syndrome, including failure to thrive. We conclude that both HLA-identical and haploidentical BMT can cure Omenn syndrome, provided that parenteral nutrition and immunosuppressive therapy are given before transplantation.

Lambert-Eaton myasthenic syndrome (LEMS) in association with lymphoproliferative disorders

LEMS is a presynaptic neuromuscular junction disorder typically associated with small cell lung carcinoma. The characteristic electrophysiological abnormality is a low amplitude compound muscle action potential that shows a marked increment after short maximal contraction or brief tetanic nerve stimulation. Here we describe 3 patients who had LEMS in association with lymphoproliferative disorder. The first patient had Castleman's syndrome with typical clinical and electrophysiological features of LEMS, which responded partially to treatment with 3-4-diaminopyridine. The second patient was a 7-year-old boy who had an unusual acute onset of LEMS associated with relapse of his Burkitt's leukemia. The third patient was a 60-year-old woman with non-Hodgkin's lymphoma. These 3 patients (together with 6 additional patients identified in the literature) lead us to suggest that lymphoproliferative diseases are another, hitherto unrecognized, type of malignancy associated with LEMS. Thus, any patient with these malignancies and unexplained muscle weakness should have electrophysiological evaluation for LEMS.

Association of increased numbers of peripheral blood double-negative T-lymphocytes with elevated serum IgG levels in severely handicapped children

CD3+4-8- double negative cells in peripheral blood lymphocytes were examined in 21 severely handicapped children divided into two groups according to serum IgG level. All children were bedridden and were taking multiple anticonvulsants and there were no apparent clinical differences between these two groups. Serum levels of IgG correlated well with percentages of CD3+4-8- double negative lymphocytes in patients of both groups. In comparisons between the two groups, the high IgG group had higher counts of CD3+4-8- double negative lymphocytes in peripheral blood than the normal IgG group. Two distinct types of double negative cells were identified in the patients with high IgG: one had T-cell antigen receptors of gamma delta heterodimers, the other had receptors of alpha beta chains on their surface. As double negative T-cells are reported to have an important role in defence against bacterial infections, the increased numbers of CD3+4-8- T-cells of both phenotypes in the high IgG patients may reflect exposure to repetitive bacterial stimuli or persistent subclinical infection which in many cases, may be undetectable clinically. Moreover, the hyperimmune states shown by the high serum IgG of these patients may result from the appearance of these unique lymphocytes because they are reported to have a helper function for IgG synthesis in vitro. Taken together, the increased numbers of double negative cells in patients with high IgG may reflect activated defence mechanisms and the development of hyperimmune status.

Perforin expression by thyroid-infiltrating T cells in autoimmune thyroid disease

Infiltration of the thyroid gland by lymphocytes is a hall-mark of autoimmune thyroid disease; it is particularly evident in Hashimoto's thyroiditis but is also seen in most patients with Graves' disease. Infiltrating cells are comprised primarily of T lymphocytes, of which only a minority appears to be activated. Their precise pathogenic role is largely unknown. Since perforin has been a marker for functionally activated cytotoxic T cells in situ we elected to assess the presence of perforin-containing cells in thyroid-infiltrating lymphocytes and establish their phenotype. Cells were isolated from seven subtotal thyroidectomy specimens, five from patients with Graves' disease and two with Hashimoto's thyroiditis. The novel findings were as follows: CD4+ perforin-containing T cells occurred only in Hashimoto's glands, suggesting a class II-restricted component of cytotoxicity; in Graves' disease, and to a lesser extent in Hashimoto's, perforin-expressing cells were primarily T cell receptor alpha beta- CD4-CD8- (double negative); double negative perforin-containing cells in peripheral blood of normal individuals were largely gamma delta + T cells. In Hashimoto's samples, the predominant population of T cells expressing perforin was CD8+. By comparison, in studies of the synovial fluid of knee joints from patients with rheumatoid arthritis only a minor population of the perforin-containing cells was double-negative. The data suggest significant differences in cytotoxic autoimmune mechanisms between the two autoimmune thyroid diseases. Functional characterization of double-negative T cells is necessary to define their role in autoimmunity.

A unique syndrome of immunodeficiency and autoimmunity associated with absent T cell CD2 expression

CD2 is a glycoprotein expressed on the surface of human T cells that mediates adhesion between T cells and antigen presenting cells. CD2 also functions in concert with the T cell receptor to transduce signals that lead to T cell activation. The CD8 and CD4 molecules are transmembrane glycoproteins that are expressed on mutually exclusive populations of mature T cells and bind to determinants on major histocompatibility complex class I and class II molecules respectively. Like CD2, CD4 and CD8 function to promote adhesion between T cells and antigen presenting cells and potentiate signaling via the T cell receptor. We studied a patient with idiopathic lymphopenia and disseminated infection with Mycobacterium avium. The patient also suffered from recurrent deep venous thrombosis in association with anticardiolipin and anti-DNA antibodies. Peripheral blood T cells from this patient were polyclonal and expressed no detectable CD2 RNA or protein as determined by northern blotting, immunofluorescent staining with anti-CD2 antibodies, and failure to form rosettes with sheep red blood cells. In addition, the majority (85%) of this patient's T cells did not express either CD4 or CD8 but did express the alpha/beta T cell receptor. T cells from this patient failed to respond to stimulation with alloantigen or specific antigen. In contrast, there was a normal response to stimulation with immobilized anti-CD3 antibody. The clinical and immunologic findings in this patient provide in vivo evidence that the accessory molecules CD2, CD4, and CD8 play important roles in the regulation of normal human T cell activation.

Monoclonal proliferation of double-negative (CD4-CD8-) T-cells bearing T-cell receptor-alpha beta followed by subsequent development of Hodgkin's disease

Expression of CD4 or CD8 on the cell surface is an important guide for discriminating the immunologic functions of T-cells. However, a minor T-cell subset lacking both CD4 and CD8 molecules but bearing the usual form of T-cell receptor (TCR)-alpha beta (CD4-CD8-TCR-alpha beta+ T-cells) has recently been found not only in mice but also in humans, and the clinical relevance of this newly defined subpopulation to human diseases is now of considerable interest. The authors present a patient in whom CD4-CD8-TCR-alpha beta+ T-cells showed monoclonal proliferation in the peripheral blood for more than 3 years, then disappeared spontaneously, followed by subsequent development of Hodgkin's disease. The pathologic roles of double-negative T-cell proliferation in this case are discussed from the viewpoint of premalignancy in lymphoproliferative diseases.