A New Set of in Silico Tools to Support the Interpretation of ATM Missense Variants Using Graphical Analysis

Establishing the pathogenic nature of variants in ATM, a gene associated with breast cancer and other hereditary cancers, is crucial for providing patients with adequate care. Unfortunately, achieving good variant classification is still difficult. To address this challenge, we extended the range of in silico tools with a series of graphical tools devised for the analysis of computational evidence by health care professionals. We propose a family of fast and easy-to-use graphical representations in which the impact of a variant is considered relative to other pathogenic and benign variants. To illustrate their value, the representations are applied to three problems in variant interpretation. The assessment of computational pathogenicity predictions showed that the graphics provide an intuitive view of prediction reliability, complementing and extending conventional numerical reliability indexes. When applied to variant of unknown significance populations, the representations shed light on the nature of these variants and can be used to prioritize variants of unknown significance for further studies. In a third application, the graphics were used to compare the two versions of the ATM-adapted American College of Medical Genetics and Genomics and Association for Molecular Pathology guidelines, obtaining valuable information on their relative virtues and weaknesses. Finally, a server [ATMision (ATM missense in silico interpretation online)] was generated for users to apply these representations in their variant interpretation problems, to check the ATM-adapted guidelines' criteria for computational evidence on their variant(s) and access different sources of information.

Identification of compounds with activity against Trypanosoma cruzi within a collection of synthetic nucleoside analogs

Introduction

Chagas disease is caused by the protozoan parasite Trypanosoma cruzi, and it is the most important neglected tropical disease in the Americas. Two drugs are available to treat the infection, but their efficacy in the chronic stage of the disease, when most cases are diagnosed, is reduced. Their tolerability is also hindered by common adverse effects, making the development of safer and efficacious alternatives a pressing need. T. cruzi is unable to synthesize purines de novo, relying on a purine salvage pathway to acquire these from its host, making it an attractive target for the development of new drugs.

Methods

We evaluated the anti-parasitic activity of 23 purine analogs with different substitutions in the complementary chains of their purine rings. We sequentially screened the compounds' capacity to inhibit parasite growth, their toxicity in Vero and HepG2 cells, and their specific capacity to inhibit the development of amastigotes. We then used in-silico docking to identify their likely targets.

Results

Eight compounds showed specific anti-parasitic activity, with IC₅₀ values ranging from 2.42 to 8.16 μM. Adenine phosphoribosyl transferase, and hypoxanthine-guanine phosphoribosyl transferase, are their most likely targets.

Discussion

Our results illustrate the potential role of the purine salvage pathway as a target route for the development of alternative treatments against T. cruzi infection, highlithing the apparent importance of specific substitutions, like the presence of benzene groups in the C8 position of the purine ring, consistently associated with a high and specific anti-parasitic activity.

(−)-Oleocanthal induces death preferentially in tumor hematopoietic cells through caspase dependent and independent mechanisms

Olive oil is a key component of the highly cardiovascular protective Mediterranean diet.

Novel Purine Chemotypes with Activity against Plasmodium falciparum and Trypanosoma cruzi

Malaria and Chagas disease, caused by Plasmodium spp. and Trypanosoma cruzi parasites, remain important global health problems. Available treatments for those diseases present several limitations, such as lack of efficacy, toxic side effects, and drug resistance. Thus, new drugs are urgently needed. The discovery of new drugs may be benefited by considering the significant biological differences between hosts and parasites. One of the most striking differences is found in the purine metabolism, because most of the parasites are incapable of de novo purine biosynthesis. Herein, we have analyzed the in vitro anti-P. falciparum and anti-T. cruzi activity of a collection of 81 purine derivatives and pyrimidine analogs. We firstly used a primary screening at three fixed concentrations (100, 10, and 1 µM) and progressed those compounds that kept the growth of the parasites < 30% at 100 µM to dose–response assays. Then, we performed two different cytotoxicity assays on Vero cells and human HepG2 cells. Finally, compounds specifically active against T. cruzi were tested against intracellular amastigote forms. Purines 33 (IC₅₀ = 19.19 µM) and 76 (IC₅₀ = 18.27 µM) were the most potent against P. falciparum. On the other hand, 6D (IC₅₀ = 3.78 µM) and 34 (IC₅₀ = 4.24 µM) were identified as hit purines against T. cruzi amastigotes. Moreover, an in silico docking study revealed that P. falciparum and T. cruzi hypoxanthine guanine phosphoribosyltransferase enzymes could be the potential targets of those compounds. Our study identified two novel, purine-based chemotypes that could be further optimized to generate potent and diversified anti-parasitic drugs against both parasites.

Synthesis and screening of 6-alkoxy purine analogs as cell type-selective apoptotic inducers in Jurkat cells

Purines are ubiquitous structures in cell biology involved in a multitude of cellular processes, because of which substituted purines and analogs are considered excellent scaffolds in drug design. In this study, we explored the key structural features of a purine-based proapoptotic hit, 8-tert-butyl-9-phenyl-6-benzyloxy-9H-purine (1), by setting up a library of 6-alkoxy purines with the aim of elucidating the structural requirements that govern its biological activity and to study the cell selectivity of this chemotype. This was done by a phenotypic screening approach based on cell cycle analysis of a panel of six human cancer cell lines, including T cell leukemia Jurkat cells. From this study, two derivatives (12 and 13) were identified as Jurkat-selective proapoptotic compounds, displaying superior potency and cell selectivity than hit 1.

A Collaborative Effort to Define Classification Criteria for ATM Variants in Hereditary Cancer Patients

BACKGROUND

Gene panel testing by massive parallel sequencing has increased the diagnostic yield but also the number of variants of uncertain significance. Clinical interpretation of genomic data requires expertise for each gene and disease. Heterozygous ATM pathogenic variants increase the risk of cancer, particularly breast cancer. For this reason, ATM is included in most hereditary cancer panels. It is a large gene, showing a high number of variants, most of them of uncertain significance. Hence, we initiated a collaborative effort to improve and standardize variant classification for the ATM gene.

METHODS

Six independent laboratories collected information from 766 ATM variant carriers harboring 283 different variants. Data were submitted in a consensus template form, variant nomenclature and clinical information were curated, and monthly team conferences were established to review and adapt American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) criteria to ATM, which were used to classify 50 representative variants.

RESULTS

Amid 283 different variants, 99 appeared more than once, 35 had differences in classification among laboratories. Refinement of ACMG/AMP criteria to ATM involved specification for twenty-one criteria and adjustment of strength for fourteen others. Afterwards, 50 variants carried by 254 index cases were classified with the established framework resulting in a consensus classification for all of them and a reduction in the number of variants of uncertain significance from 58% to 42%.

CONCLUSIONS

Our results highlight the relevance of data sharing and data curation by multidisciplinary experts to achieve improved variant classification that will eventually improve clinical management.

Reconstitution of the Ataxia-Telangiectasia Cellular Phenotype With Lentiviral Vectors

Ataxia-telangiectasia (A-T) is a complex disease arising from mutations in the ATM gene (Ataxia-Telangiectasia Mutated), which plays crucial roles in repairing double-strand DNA breaks (DSBs). Heterogeneous immunodeficiency, extreme radiosensitivity, frequent appearance of tumors and neurological degeneration are hallmarks of the disease, which carries high morbidity and mortality because only palliative treatments are currently available. Gene therapy was effective in animal models of the disease, but the large size of the ATM cDNA required the use of HSV-1 or HSV/AAV hybrid amplicon vectors, whose characteristics make them unlikely tools for treating A-T patients. Due to recent advances in vector packaging, production and biosafety, we developed a lentiviral vector containing the ATM cDNA and tested whether or not it could rescue cellular defects of A-T human mutant fibroblasts. Although the cargo capacity of lentiviral vectors is an inherent limitation in their use, and despite the large size of the transgene, we successfully transduced around 20% of ATM-mutant cells. ATM expression and phosphorylation assays indicated that the neoprotein was functional in transduced cells, further reinforced by their restored capacity to phosphorylate direct ATM substrates such as p53 and their capability to repair radiation-induced DSBs. In addition, transduced cells also restored cellular radiosensitivity and cell cycle abnormalities. Our results demonstrate that lentiviral vectors can be used to rescue the intrinsic cellular defects of ATM-mutant cells, which represent, in spite of their limitations, a proof-of-concept for A-T gene therapy.

Regulated expression of murine CD40L by a lentiviral vector transcriptionally targeted through its endogenous promoter

BACKGROUND

Targeted lentiviral vectors may contribute to circumventing genotoxicity associated with uncontrolled transcription of therapeutic genes. Some vectors replacing strong viral sequences for gene promoters such as β-globin, CD4, CD19 or Igκ were able to drive tissue-specific expression of the transgene. Gene therapy, however, faces even greater hurdles when the therapeutic transgene is subject to strict regulatory mechanisms. This is the case of the CD40LG gene, which encodes for the CD154 (also known as CD40L) molecule, transiently expressed upon activation on CD4(+) T cells. Mutations in this gene cause the X-linked hyper IgM syndrome (HIGM1) in humans because the interaction of CD40L with its ligand CD40 triggers signals that are critical for the immunobiology of B lymphocytes.

METHODS

We developed a lentiviral vector containing the murine Cd40lg cDNA under the control of its endogenous promoter.

RESULTS

The CD4(+) BW5147 T cells transduced with the pCd40lg-Cd40lg lentiviral vector express CD40L only upon stimulation. The intensity of the expression correlates with the number of vector integrations per cell and detected molecules rapidly decay after removing the stimulating agent. The tissue-specific, activation-dependent and reversible expression of CD40L fully mimics the physiological induction and disappearance of the molecule from the surface of murine T lymphocytes. The functional activity of the regulated lentiviral vector is demonstrated by the ability of transduced BW5147 cells to promote the proliferation of purified B cell splenocytes.

CONCLUSIONS

We have developed a fine-regulated lentiviral vector that can be a model for expressing molecules subject to stringent regulatory mechanisms.

Synthesis of 6,8,9 poly-substituted purine analogue libraries as pro-apoptotic inducers of human leukemic lymphocytes and DAPK-1 inhibitors

A 18-member library of 6,8,9-poly-substituted purines was prepared from pyrimidines, primary alcohols, and N,N-dimethylamides under basic conditions via a novel one-pot synthetic pathway controlled by amide sizes and the novel analogues were tested against two leukemia cell lines: Jurkat (acute T cell leukemia) and K562 (chronic erythroleukemia) cells. Compounds having a benzoxy group at C6 position of the aromatic ring exhibited antiproliferative activity in Jurkat cells whereas all compounds induced a lower effect on K562 cells. Analysis of cell cycle, Annexin-V staining, and cleavage of initiator caspases assays showed that the active purine analogues induce cell death by apoptosis. Based on these results, a new purine derivative was synthesized, 6-benzyloxy-9-tert-butyl-8-phenyl-9H-purine (6d), which displayed the highest activity of the series against Jurkat cell lines. Finally, (33)P-radiolabeled kinase assays using 96 recombinant human kinases known to be involved in apoptotic events were performed. Just one of the kinases tested, DAPK-1, was inhibited 50% or more by the phenotypic hits at 10 μM, suggesting that the inhibition of this target could be responsible for the induction of cell death by apoptosis. In agreement with the phenotypic results, the most active antiproliferative agent, 6d, displayed also the lowest IC50 value against recombinant DAPK1 (2.5 μM), further supporting the potential role of this protein on the observed functional response. DAPK-1 inhibition led by 6d together with its pro-apoptotic properties against the Jurkat line makes it an interesting candidate to further investigate the role of DAPK1 kinase in triggering apoptosis in cancer cells, a role which is attracting recent interest.

IL-17 producing T cells in celiac disease: angels or devils?

Celiac disease (CD) is a very common chronic condition in human beings, affecting approximately one in 100 individuals. It is an autoimmune disease with a defined environmental trigger, the gluten contained in dietary cereals, occurring in genetically susceptible individuals. The disease has a very strong HLA association. More than 90% of CD patients have HLA-DQ2, and almost all of the remaining celiac population possesses HLA-DQ8 molecules. Th17 cells seem to participate in the disease pathogenesis producing and secreting either proinflammatory or anti-inflammatory cytokines.

Characterization of gliadin-specific Th17 cells from the mucosa of celiac disease patients

OBJECTIVES

Celiac disease (CD) is a disorder characterized by a deregulated immune response to ingested wheat gluten and related cereal proteins in susceptible individuals. It has been considered that the onset of CD is mediated by a skewed Th1 response. However, the participation of Th17 cells in the pathogenesis of the disease, a key cell population in other autoimmune disorders, has not been studied in detail. We have investigated the presence of Th17 cells in the mucosa of active CD patients and their functional implications in the pathogenesis of the disease.

METHODS

T cells obtained from duodenum biopsies from 15 untreated patients and 11 control individuals were characterized by flow cytometry, immunoassays, and real-time PCR.

RESULTS

We found gliadin-specific CD4(+) interleukin (IL)-17A-producing T cells in the mucosa of CD patients with a phenotype consisting of TCR (T-cell receptor)αβ(+) CD45RO(+) CD161(+) CCR6(+) (C-C chemokine receptor type 6) and IL-23R(+). Functional analysis showed that Th17 cells from CD patients are different from those of control individuals in terms of cytokines production. Th17 cells from CD patients, but not from controls, simultaneously express transforming growth factor-β (TGFβ). Th17 CD cells also produce interferon-γ (IFNγ), IL-21, and IL-22. The analysis of the transcription factors revealed a high expression of interferon regulatory factor-4 as a feature of gliadin-specific cells from CD patients with respect to controls.

CONCLUSIONS

Gliadin-specific Th17 cells are present in the mucosa of CD patients having a dual role in the pathogenesis of the disease as they produce proinflammatory cytokines (such as IL-17, IFNγ, IL-21), mucosa-protective IL-22, and regulatory TGFβ, which actively modulates IL-17A production by T cells in the celiac mucosa.

An exopolysaccharide produced by the novel halophilic bacterium Halomonas stenophila strain B100 selectively induces apoptosis in human T leukaemia cells

Microbial exopolysaccharides (EPSs) are highly heterogeneous polymers produced by fungi and bacteria and have recently been attracting considerable attention from biotechnologists because of their potential applications in many fields, including biomedicine. We have screened the antitumoural activity of a panel of sulphated EPSs produced by a newly discovered species of halophilic bacteria. We found that the novel halophilic bacterium Halomonas stenophila strain B100 produced a heteropolysaccharide that, when oversulphated, exerted antitumoural activity on T cell lines deriving from acute lymphoblastic leukaemia (ALL). Only tumour cells were susceptible to apoptosis induced by the sulphated EPS (B100S), whilst primary T cells were resistant. Moreover, freshly isolated primary cells from the blood of patients with ALL were also susceptible to B100S-induced apoptosis. The newly discovered B100S is therefore the first bacterial EPS that has been demonstrated to exert a potent and selective pro-apoptotic effect on T leukaemia cells, and thus, we propose that the search for new antineoplastic drugs should include the screening of other bacterial EPSs, particularly those isolated from halophiles.

IL-17-producing CD8+ T lymphocytes from psoriasis skin plaques are cytotoxic effector cells that secrete Th17-related cytokines

IL-17-producing CD4+ T lymphocytes (Th17) are currently considered relevant participants in the pathogenesis of psoriasis skin lesions. However, little is known about the potential role of IL-17-producing CD8+ T cells, which are also present at the psoriatic plaque. We have addressed the functional characterization of this CD8+ subtype of T lymphocytes from psoriasis patients. Our results show that CD8+IL-17+ cells from psoriasis-inflamed skin tissue produce TNF-alpha and IFN-gamma (Th1-related cytokines) as well as IL-17, IL-21, and IL-22 (Th17-related cytokines) efficiently. A significant up-regulation of the RORC transcription factor is also observed. These cells are refractory to Tregs but show a proliferative response to anti-CD3/CD28 stimulation that is enhanced by IL-12 and IL-15. Blocking of TNF-alpha activity inhibits TCR-mediated activation and IL-17 production. CD8+IL-17+ T cells are cytotoxic cells that display TCR/CD3-mediated cytotoxic abilities to kill target cells. Thus, CD8+IL-17+ T cells share some key features with Th17 cells and exhibit remarkable differential abilities attributable to the CD8+ lineage of T lymphocytes, adding new insights into the functional resources of IL-17-producing cells from human epidermis that could be of potential interest to our understanding of the pathogenesis of psoriasis.

Hematopoietic-specific lentiviral vectors circumvent cellular toxicity due to ectopic expression of Wiskott-Aldrich syndrome protein

Efficient and safe gene modification of hematopoietic stem cells is a requirement for gene therapy of primary immunodeficiencies such as Wiskott-Aldrich syndrome. However, deregulated expression or ectopic expression in the progeny of transduced nonhematopoietic progenitor cells may lead to unwanted toxicity. We therefore analyzed the effect of ectopic expression of Wiskott-Aldrich syndrome protein (WASp) and the potential benefits of hematopoietic-specific lentiviral vectors (driven by the WAS proximal promoter). Overexpression of WASp by constitutive lentiviral vectors is highly toxic in nonhematopoietic cells because it causes dramatic changes in actin localization and polymerization that result in decreased cell viability, as evidenced by a significant growth disadvantage of WASp-overexpressing nonhematopoietic cells and increased cell death. These toxic effects do not affect cells of hematopoietic origin because, remarkably, we found that WASp cannot be readily overexpressed in T cells, even after multiple vector integrations per cell. The adverse cellular effects found after transduction of nonhematopoietic cells with constitutive lentiviral vectors are overcome by the use of transcriptionally targeted lentiviral vectors expressing WASp, which, at the same time, are efficient tools for gene therapy of WAS as demonstrated by their ability to reconstitute cellular defects from WASp-deficient mouse and human cells. We therefore postulate that transcriptionally regulated lentiviral vectors represent a safer and efficient alternative for the development of clinical protocols of WAS gene therapy.

A novel Wiskott-Aldrich syndrome protein (WASP) complex mutation identified in a WAS patient results in an aberrant product at the C-terminus from two transcripts with unusual polyA signals

Wiskott-Aldrich syndrome (WAS) is an X-linked recessive disorder characterized by immunodeficiency, thrombocytopenia and eczema. A broad spectrum of mutations in the WASP gene has been identified as causing the disease. In the present paper, we report on a patient affected by WAS with a novel complex mutation, characterized by a small 9 bp deletion followed by an inversion of 151 bp and a gross deletion of 4.3 kb within the Xp11.23 region. The small deletion and the inverted fragment are found in intron 11. The large deletion initiates downstream of exon 11 of the WASP gene, including exon 12, and a genomic region upstream of the promoter of the contiguous SUV39H1 gene. Expression studies of the mRNA of the patient's sample showed the presence of two aberrant transcripts that code for a protein of 519 amino acids. We demonstrate that these two transcripts differ in the 3' UTR region, and result from the use of two alternative polyadenylation signals. The severe phenotype of the patient correlates with the presence of an aberrant protein.

Role for NKG2-A and NKG2-C surface receptors in chronic CD4+ T-cell responses

The participation of CD94 and NKG2 gene family members in the function of NK cells and CD8+ cytolytic cells has recently been addressed in detail. However, the role that these molecules play in the key CD4+ regulatory cells remains largely unexplored. This study has examined the expression and regulation of CD94 and NKG2 genes in purified human peripheral CD4+ cells stimulated with several agents. We found a constitutive expression of NKG2-E in CD94-depleted resting peripheral CD4+ cells, whereas inductions of NKG2-A and NKG2-C required chronic cell activation and occurred after expression of CD94. We found that CD3-mediated stimulation induces the expression of CD94 first by day 5 of culture, followed by NKG2-A by day 15 and finally NKG2-C, which is not detected until 20 days after repeated stimulation. This pattern of gene expression differs sharply from that observed in purified CD8+ T cells, where mRNA from all NKG2 gene family members are detected after 5 days of stimulation. Selective activation of TCR V beta 2-bearing cells with toxic shock syndrome toxin-1 superantigen reveals that mRNA induction of NKG2-A and NKG2-C genes is significantly influenced by the presence of cytokines (IL-10 and TGF-beta) and by the restimulation of the cells. In addition, the occupancy of the CD94/NKG2-A receptor expressed on these superantigen-stimulated CD4+ T lymphocytes abrogates TNF-alpha and IFN-gamma production, whereas NKG2-C enhances production of these cytokines. Taken together our results reveal strict gene regulatory mechanisms for CD94 and NKG2 gene expression on CD4+ cells that are different from those governing the expression of these same genes in CD8+ cells. The results suggest that these genes also participate in chronic CD4+ T-cell responses.

Lentiviral vectors transcriptionally targeted to hematopoietic cells by WASP gene proximal promoter sequences

The development of vectors that express a therapeutic transgene efficiently and specifically in hematopoietic cells (HCs) is an important goal for gene therapy of hematological disorders. In order to achieve this, we used a 500 bp fragment from the proximal WASP gene promoter to drive the expression of the WASP cDNA in the context of a self-inactivating lentiviral vector. Single-round transduction of WASp-deficient herpesvirus saimiri (HVS)-immortalized cells as well as primary allospecific T cells from Wiskott-Aldrich syndrome (WAS) patients with this vector (WW) resulted in expression levels similar to those of control cells. Non-HCs were transduced with similar efficiency, but the levels of WASp were 135-350 times lower than those achieved in HCs. Additionally, transduction of WASp-deficient cells with WW conferred a selective growth advantage in vitro. Therefore, lentiviral vectors incorporating proximal promoter sequences from the WASP gene confer hematopoietic-specific, and physiological protein expression.

Efficient lentiviral transduction of Herpesvirus saimiri immortalized T cells as a model for gene therapy in primary immunodeficiencies

Infection of human T lymphocytes with the Herpesvirus saimiri (HVS) yields immortalized T-cell lines (HVS-T) which retain all the phenotypical and functional characteristics of their parental cells. This represents a new experimental model for studying genetic disorders of T lymphocytes. In spite of the efforts of many laboratories, no satisfactory way has been found so far to modify HVS-T cells genetically. We have analyzed the capacity of oncoretroviral (MLV)- and lentiviral (HIV-1)-based vectors pseudotyped with vesicular stomatitis virus glycoprotein (VSVg) to transduce HVS-T cells. HIV-1-derived vectors efficiently transduced HVS-T cell lines, reaching up to 85% of cells expressing the transgene in a single round of infection. MLV-based vectors, on the other hand, were unable to transduce more than 1% of any of the HVS-T cell lines analyzed. Lentiviral-driven gene expression was maintained constant and stable in HVS-T cells for a minimum of 48 days. We also observed that although the lentiviral transduction efficiency achieved on HVS-T cells is lower than that obtained with tumor or primary endothelial cells, it is nevertheless similar to that found with activated primary T cells.

Expression of CD94 and NKG2 molecules on human CD4(+) T cells in response to CD3-mediated stimulation

We investigated the ability of human peripheral CD4(+) cells to express CD94 and NKG2 molecules as a consequence of CD3-mediated activation. Using highly purified peripheral CD4(+) T cells, we found expression of both CD94 and NKG2A 15 days after CD3-mediated stimulation of cells. We also determined by reverse transcriptase-PCR that all gene members of NKG2 family-namely, NKG2A, -C, -D, and -E-are sequentially expressed on CD4(+) cells. We found that this expression is tightly regulated by cytokines, and we identified transforming growth factor-beta1 and interleukin-10 as the main factors that, on CD3-dependent stimulation, positively contribute to the expression of CD94 and NKG2A on CD4(+) cells. We also investigated the functional role of NKG2A and found that coligation of CD3 and NKG2A by specific monoclonal antibodies results in significant inhibition of interferon gamma and tumor necrosis factor alpha production by stimulated CD4(+) cells. The presence and function of these receptors on CD4(+) lymphocytes support a more general role for NKG2 molecules, whose functions were originally thought to be confined to cytotoxic cells, in the immune system.

Altered expression of CD43-hexasaccharide isoform on peripheral T lymphocytes from HIV-infected individuals

OBJECTIVE

To examine if peripheral T lymphocytes from HIV-infected individuals show abnormalities in the surface expression of CD43, the major sialoglycoprotein of leukocytes.

DESIGN

A series of 86 HIV-positive individuals was studied. The subjects, grouped by their peripheral CD4 cell count, were in different stages of the disease as defined by the Centers for Disease Control and Prevention (CDC).

METHODS

Peripheral leukocytes and isolated lymphocytes were examined by double and triple immunofluorescence flow cytometric and Western blot analyses with monoclonal antibodies, which discriminate between CD43 isoforms.

RESULTS

We found elevated percentages of the surface expression of CD43-hexasaccharide isoform on T lymphocytes from 82 out of 86 individuals tested. Increasing percentages are progressively found in CDC groups 1, 2 and 3 patients. The expression of the molecule is remarkably biased towards the CD8 cell subpopulation. The percentage of cells bearing human leukocyte antigen-DR locus molecules (HLA-DR) is also augmented. Two subsets expressing T305 have been identified: a minor subset that co-expresses HLA-DR and T305; and a second population formed by the majority of T305-positive cells, which lack surface HLA-DR. Finally, we found CD43 bands with altered electrophoretic mobility in lysates from peripheral lymphocytes from all HIV-positive individuals tested.

CONCLUSION

The augmented expression of CD43-hexasaccharides and the observed cellular distribution suggest an important regulatory role for this molecule in HIV-specific responses.

Functional expression of CD43 on human natural killer cells

CD43 is the major leukocyte sialoglyco-protein that plays important functional roles in neutrophils and lymphocytes. However, the expression of CD43 on human natural killer (NK) cells and its participation in the regulation of NK activity has not been studied. We have therefore investigated the expression of CD43 isoforms on human NK cell subpopulations as well as the role of this molecule in NK cell activation and cytotoxicity. We found that CD56bright and CD56dim NK cells express different sialylated forms of CD43, observing that activation of the CD56bright NK cells induces the change of tetrasaccharide O-glycans to hexasaccharide O-glycans on CD43. Cross-linking of the molecule with mAbs results in a metalloprotease-dependent loss of CD43 from the NK cell surface, whereas soluble anti-CD43 mAbs induce a vigorous NK cell proliferation. This property is distinct from T cells, which proliferate after CD43 cross-linking only in the presence of monocytes. Occupancy of the CD43 receptor on NK cells transduces specific signals, leading to enhanced killing activity and tyrosine phosphorylation and de-phosphorylation of several substrates. We therefore propose that CD43 significantly contributes to the regulation of the NK cell function by participating in the control of effector/target interactions and, if pertinent, by transducing activation signals.

Defective actin reorganization and polymerization of Wiskott-Aldrich T cells in response to CD3-mediated stimulation

The Wiskott-Aldrich syndrome (WAS) is a severe immunodeficiency and platelet deficiency disease arising from mutation(s) in the WASP gene, which in normal cells encodes an intracellular protein able to interact with other proteins relevant to the control of cytoskeleton organization. Immunodeficiency is mainly due to T-cell progressive malfunction. Salient defects of WAS T cells are a CD3-restricted impairment in proliferative responses and cytoskeletal abnormalities, including the frequent appearance of T cells with atypical morphology. We have investigated the possibility that the CD3-restricted defect and some of the cytoskeletal defects of WAS T cells are linked. For this purpose, we immortalized by means of infection with Herpesvirus Saimiri a number of previously described allospecific WAS T-cell lines. The resulting cells preserve the surface, molecular, and functional phenotypes of their parental lines, including a negligible WASP mRNA expression as well as the CD3-restricted defect and cytoskeleton abnormalities. Results show that, in CD3-stimulated WAS T cells, the pattern of temporal changes in cell shape and F-actin distribution is substantially different from that of control cells. Furthermore, polymerization of actin, a critical step in the CD3-mediated cytoskeleton reorganization, does not occur in WAS T-cell lines in response to OKT3 stimulation. In conclusion, our data link both CD3 and cytoskeletal defects in WAS T cells, strongly suggesting that cytoskeleton abnormalities are an underlying cause for WAS immunodeficiency.

Specific monoclonal antibodies against leukocyte-restricted cell surface molecule CD43 react with nonhematopoietic tumor cells

CD43 is the major sialoglycoprotein found on the surface of cells of hemopoietic origin. Because CD43 is a typical member of the surface mucins, molecules that play a relevant role in tumor progression, we have addressed the expression of CD43 in nonhematopoietic tumor cells. For this purpose, we have tested a broad panel of anti-CD43 antibodies on tumors of different embryonic origins. Of the 17 anti-CD43 mAbs used, 9 reacted with leukocytes in paraffin-fixed formalin-embedded lymph node tissues. Two mAbs, BS1 and L10, stained 24 out of 31 (78%) nonhematopoietic tumors analyzed; ie., some tumors were positive for both antibodies, and others were positive for either L10 or BSL We have also found reactivity of these two anti-CD43 mAbs in 13 out of 20 metastases studied.

Defective B7 expression on antigen-presenting cells underlying T cell activation abnormalities in systemic lupus erythematosus (SLE) patients

Defective T cell functions, including IL-2 production and proliferation, have been shown in SLE patients. After T cell stimulation (first signal), a costimulatory signal (second signal) is required to achieve complete T cell activation. Main costimulatory signals are provided to T cells by B7 antigens (CD80 and CD86, expressed on antigen-presenting cells (APC)) upon interaction with its receptor, the CD28 molecule expressed on T cells. The aim of this study was to investigate the role of CD28/B7 interactions in the impaired T cell responses of SLE patients. We show that stimulation of T cells with phytohaemagglutinin (PHA) in the presence, but not in the absence, of anti-CD28 MoAb or B7+ cells results in tyrosine phosphorylation of specific substrates, transcription of mRNA and production of IL-2 that is indistinguishable in SLE patients and healthy controls. Moreover, proliferation of costimulated T cells from SLE and controls was specifically abrogated by blocking the CD28/B7 interactions by means of addition to the culture of the CTLA4-Ig fusion protein. However, in most patients activated APC failed to up-regulate B7 molecules, giving rise to ineffective costimulatory signalling to T cells. These results indicate that the CD28/B7 costimulatory pathway is defective in SLE patients.

T cells of patients with the Wiskott-Aldrich syndrome have a restricted defect in proliferative responses

The Wiskott-Aldrich syndrome (WAS) is a disease of profound thrombocytopenia and severe immune defects caused by an unidentified defective X chromosome gene. In this study, T lymphocyte function is examined using a panel of allospecific WAS patient T cell lines, previously found to express the abnormal disease gene and the cytoarchitectural defect characteristic of the disease. Although T cell lines from normal individuals proliferate vigorously in response to immobilized anti-CD3 mAb OKT3 and SPV-T3b, five of seven WAS patient T cell lines failed to proliferate and two lines showed significantly decreased proliferation when challenged with the immobilized anti-CD3 mAb. The deficient responsiveness of the WAS T cell lines to immobilized anti-CD3 mAb is a restricted defect, because the cells proliferate normally when challenged with allospecific Ag, PHA, or PMA plus ionomycin. Addition of anti-CD28 mAb did not correct the deficient proliferation of the WAS cells challenged with immobilized anti-CD3. Deficient response of the WAS T cell lines to immobilized anti-CD3 was detected also when earlier events of the proliferation process, IL-2 production and up-regulation of activation Ag CD69 and CD28, were measured. On the other hand, WAS cell lines did not differ from normal cell lines in binding of anti-CD3 mAb, mobilization of Ca2+ in response to soluble OKT3, and tyrosine phosphorylation and GTP binding of the CD3 zeta-chain in response to OKT3. Cumulatively, these findings demonstrate a striking restricted defect in the proliferative response of WAS T cells, which because it is found in cell lines free of secondary changes that occur in the patient circulation must be a reflection of the inherited defective disease gene product.

T cells of patients with the Wiskott-Aldrich syndrome have a restricted defect in proliferative responses

The Wiskott-Aldrich syndrome (WAS) is a disease of profound thrombocytopenia and severe immune defects caused by an unidentified defective X chromosome gene. In this study, T lymphocyte function is examined using a panel of allospecific WAS patient T cell lines, previously found to express the abnormal disease gene and the cytoarchitectural defect characteristic of the disease. Although T cell lines from normal individuals proliferate vigorously in response to immobilized anti-CD3 mAb OKT3 and SPV-T3b, five of seven WAS patient T cell lines failed to proliferate and two lines showed significantly decreased proliferation when challenged with the immobilized anti-CD3 mAb. The deficient responsiveness of the WAS T cell lines to immobilized anti-CD3 mAb is a restricted defect, because the cells proliferate normally when challenged with allospecific Ag, PHA, or PMA plus ionomycin. Addition of anti-CD28 mAb did not correct the deficient proliferation of the WAS cells challenged with immobilized anti-CD3. Deficient response of the WAS T cell lines to immobilized anti-CD3 was detected also when earlier events of the proliferation process, IL-2 production and up-regulation of activation Ag CD69 and CD28, were measured. On the other hand, WAS cell lines did not differ from normal cell lines in binding of anti-CD3 mAb, mobilization of Ca2+ in response to soluble OKT3, and tyrosine phosphorylation and GTP binding of the CD3 zeta-chain in response to OKT3. Cumulatively, these findings demonstrate a striking restricted defect in the proliferative response of WAS T cells, which because it is found in cell lines free of secondary changes that occur in the patient circulation must be a reflection of the inherited defective disease gene product.

T cell lines characterize events in the pathogenesis of the Wiskott-Aldrich syndrome

The Wiskott-Aldrich syndrome (WAS) is a severe immunodeficiency and platelet deficiency disease arising from an X-linked defect. The disease is correctable by transplantation of hematopoietic stem cells, but the product of the defective gene is unidentified and the number of defects in patient blood cells is large. The current hurdle is the need to identify the early pathogenic event(s) that are the cause of other defects. As a step toward this goal, we have generated and examined a panel of interleukin 2-dependent allospecific T cell lines from peripheral lymphocytes of seven WAS patients and five normal individuals. WAS cell lines, like normal lines, undergo vigorous proliferation when challenged with specific allostimulant or with phorbol myristate acetate and ionomycin. Both normal and WAS T cell lines express cell surface molecules CD2, CD3, T cell receptor-alpha/beta, human histocompatibility leukocyte antigen class I, CD45 and CD11a, and varying ratios of CD4 and CD8, and are negative for natural killer cell and monocyte surface molecules. WAS T cell lines express CD43 (sialophorin/leukosialin) with molecular weight and in an amount comparable with normal T cell lines. WAS T cell lines thus do not express defects in CD43 (decreased amount, abnormal molecular weight), previously documented in WAS circulating lymphocytes. On the other hand, as detected by scanning electron microscopy, WAS cell lines exhibit severe morphological abnormalities, including decreased size and density of the microvillus surface projections. The morphological abnormalities of WAS T cell lines are similar to, or more extensive than, those previously reported for WAS peripheral lymphocytes, indicating that the generation of morphological (cytoarchitectural) defects is an early pathogenic event in this disease. The findings suggest that the gene that is defective in the WAS encodes a protein that normally functions to maintain or regulate the cytoskeletal structure of blood cells.

Regulation of macrophage activation markers by IL-4 and IFN-gamma is subpopulation-specific

We have addressed the differential regulatory properties that IFN-gamma and IL-4 exert on macrophage (M phi) subpopulations. For this purpose, Thyoglicolate-, Peptone-, and Con A-elicited M phi, as well as bone marrow-derived M phi and P388D1 cells, were cultured in the presence of either IFN-gamma or IL-4. The expression of LFA-1, Mac-1, and Mac-2 after this treatment was studied by FACS analysis. We have found that these surface molecules are differentially modulated by the two lymphokines, depending on the M phi subpopulation studied. Mac-1 is upregulated only in Thyoglicolate-elicited cells after treatment with IFN-gamma, while no change in the expression of Mac-2 was observed in any of the groups. LFA-1 is upregulated by IFN-gamma in Thyoglicolate- and bone marrow-derived M phi and P388D1 cells, while IL-4 does not induce LFA-1 on these cells. Interestingly, however, we have observed the reverse situation on Con A-elicited M phi, where a strong induction of LFA-1 is achieved by treatment of the cells with IL-4, while IFN-gamma does not modify the expression of this antigen. Our results obtained with the lymphokine-stimulated M phi are interpreted in the context of functionally induced M phi subpopulations, which might be regulated by either Th1 or Th2 CD4+ T cells. Thyoglicolate-elicited M phi may represent the in vitro equivalent of a M phi subpopulation regulated in vivo by Th1 cells while Con A-elicited M phi could be the equivalent of a subpopulation regulated by Th2 cells.

The expression of a tissue-specific self-peptide is required for allo-recognition

We have compared the functional properties of I-Ad expressed on different cell types. Specifically, we have transfected I-A alpha d and I-A beta d cDNA into a panel of T cell thymomas of various phenotypes. Excellent class II surface expression was achieved in all T cell tumors, equivalent in level to that found on the B cell lymphoma A20. Interestingly, however, two allo-I-Ad-specific Thy differed in their recognition of the transfected tumor cells: whereas the 42H11 T cell hybridoma (THy) was stimulated very efficiently by all transfectants, the RK38.2.2 Thy did not react to any of them. Both THy responded equally well to I-Ad on A20 B lymphoma cells. Purified macrophages isolated from various sources were also differentially recognized by the two THy, although there was only a quantitative difference in stimulation. Taken together, these results are best interpreted to show that the TCR of the RK38.2.2 THy is specific for I-Ad in the context of a B cell-specific determinant, possibly a self-peptide that is naturally associated with Ia. A cross-reactive molecule could be expressed by macrophages and COS-1 cells, but not by T cells.

The expression of a tissue-specific self-peptide is required for allo-recognition

We have compared the functional properties of I-Ad expressed on different cell types. Specifically, we have transfected I-A alpha d and I-A beta d cDNA into a panel of T cell thymomas of various phenotypes. Excellent class II surface expression was achieved in all T cell tumors, equivalent in level to that found on the B cell lymphoma A20. Interestingly, however, two allo-I-Ad-specific Thy differed in their recognition of the transfected tumor cells: whereas the 42H11 T cell hybridoma (THy) was stimulated very efficiently by all transfectants, the RK38.2.2 Thy did not react to any of them. Both THy responded equally well to I-Ad on A20 B lymphoma cells. Purified macrophages isolated from various sources were also differentially recognized by the two THy, although there was only a quantitative difference in stimulation. Taken together, these results are best interpreted to show that the TCR of the RK38.2.2 THy is specific for I-Ad in the context of a B cell-specific determinant, possibly a self-peptide that is naturally associated with Ia. A cross-reactive molecule could be expressed by macrophages and COS-1 cells, but not by T cells.

Macrophages and T cells do not express Mlsa determinants

In order to test the tissue distribution of Mlsa determinants, we have generated highly purified stimulator cell populations. First, Mlsa expression in bone marrow derived macrophages (M phi) of Mlsa genotype was tested in primary MLR and on Mlsa-specific T cell hybridomas (THy). Second, a similar experimental approach was used to analyze thioglycolate, peptone or Con A elicited peritoneal M phi. In all cases, these M phi cell populations were able to generate an excellent alloresponse, whereas no functional Mlsa determinants could be detected. Third, to further investigate whether the expression of Mlsa is lymphocyte specific, but dependent on expression of class II molecules, we have transfected I-Ek alpha and beta cDNA into a panel of thymomas of Mlsa genotype. Although we achieved a high level of surface I-Ek expression in all of these T cell tumors, none of them was able to trigger the Mlsa-specific THy. These results strongly suggest that Mlsa expression is limited to B cells. It is likely that Mlsa is a tissue-specific self-peptide that associates with class II molecules.

Macrophages and T cells do not express Mlsa determinants

In order to test the tissue distribution of Mlsa determinants, we have generated highly purified stimulator cell populations. First, Mlsa expression in bone marrow derived macrophages (M phi) of Mlsa genotype was tested in primary MLR and on Mlsa-specific T cell hybridomas (THy). Second, a similar experimental approach was used to analyze thioglycolate, peptone or Con A elicited peritoneal M phi. In all cases, these M phi cell populations were able to generate an excellent alloresponse, whereas no functional Mlsa determinants could be detected. Third, to further investigate whether the expression of Mlsa is lymphocyte specific, but dependent on expression of class II molecules, we have transfected I-Ek alpha and beta cDNA into a panel of thymomas of Mlsa genotype. Although we achieved a high level of surface I-Ek expression in all of these T cell tumors, none of them was able to trigger the Mlsa-specific THy. These results strongly suggest that Mlsa expression is limited to B cells. It is likely that Mlsa is a tissue-specific self-peptide that associates with class II molecules.

Mlsa determinants: relationship to Fc gamma receptor and tissue distribution

We have analysed the genetic relationship between Mlsa and Fc gamma R in mice. Using the Fc gamma R-specific DNA probes, we were unable to detect a restriction fragment length polymorphism (RFLP) which is consistent in DNA derived from Mlsa strains and which differed from that of Mlsb strains, while we could see a polymorphism that distinguishes Ly17.1 from Ly17.2, alleles of the Fc gamma R. These results strongly suggest that Mlsa is neither a product of the alpha Fc gamma R nor of the beta Fc gamma R gene. Furthermore, we have re-examined the tissue distribution of Mlsa determinants using a major histocompatibility complex (MHC) class II antigen-positive T-cell tumour as well as a pure population of bone marrow derived macrophages of Mlsa genotype. Both these cell types were recognized to varying degrees by alloreactive cells; however, none of them expressed functionally detectable Mlsa determinants. We conclude from our studies that Mlsa is a highly stimulatory self peptide that is exclusively expressed in B cells.