Biosynthesis and immunobiochemical characterization of gp17/GCDFP-15. A glycoprotein from seminal vesicles and from breast tumors, in HeLa cells and in Pichia pastoris yeast

The gp17 factor is a secretory product of human seminal vesicle cells which binds to CD4 and acts as a potent inhibitor of T lymphocyte apoptosis induced by CD4 crosslinking and subsequent T-cell receptor (TCR) activation. The protein is identical to gross cystic disease fluid protein-15 (GCDFP-15), a breast tumor secretory marker PIP (prolactin inducible protein), a prolactin-controlled and androgen-controlled protein; secretory actin binding protein (SABP), a seminal plasma actin binding protein and extra-parotid glycoprotein (EP-GP), a secretory protein from the salivary gland. The structure of this protein has not yet been elucidated and no biological function has been clearly attributed to date. Expression of recombinant gp17/GCDFP-15 cDNA in bacteria and insect cells leads to the production of a misfolded insoluble protein. In this study, we describe the production of gp17/GCDFP-15 in two different eukaryotic systems, namely HeLa cells and the Pichia pastoris yeast. Using constructs in which gp17/GCDFP-15 was tagged with enhanced green fluorescent protein (EGFP) in various combinations, we observed expression only when the fusion protein was directed to the secretory compartment by the correct signal peptide. The resulting fluorescent protein was inefficiently secreted, thus suggesting that gp17/GCDFP-15 is not appropriately post-translationally processed and/or transported in HeLa cells. The use of the P. pastoris secretory pathway allowed instead the accumulation in the culture medium of a GCDFP-15/gp17 species which retained the ability to bind to CD4 and also most of the biochemical and immunological properties of the native protein. The production of an active recombinant molecule opens the way to correlate the structural properties of this peculiar factor to its ability to bind several proteins, including CD4, and to block CD4-mediated T cell programmed death.

In vitro immunization with a recombinant antigen carrying the HIV-1 RT248-262 determinant inserted at different locations results in altered TCRVB region usage

Immunodominance or cripticity of a peptide-borne determinant may be influenced by the protein context in which the epitope is embedded. In this frame, we previously showed that certain human T cell clones, derived from different donors, may differentially recognize the RT248-262 helper determinant depending on whether it is provided to the presenting cells as a synthetic peptide or as a recombinant carrier protein to which the sequence of interest is fused. We now report that, upon in vitro immunization of human PBL with autologous APC, the epitope-specific TCRVB repertoire obtained when selection is applied by pulsing the APC with the cognate synthetic peptide is different from that found when a recombinant protein is used in which the antigenic sequence is placed at either a N-terminal or C-terminal location of the GST carrier. As the TCRVB distribution is not a function of the APC used, we propose that processing of different recombinant molecules containing the same epitope may generate MHC/peptide complexes which, being antigenically diverse, may recruit distinct TCR specificities. These findings may be relevant for evaluating and predicting the immunogenic potential of subunit vaccines based on synthetic peptides or on recombinant proteins as compared to the native antigen.

[Liver retransplantation in adults: clinical course and results of 13 years' experience]

INTRODUCTION

Liver retransplantation is the only alternative to irreversible graft failure. However, it remains a controversial treatment. The aim of this study was to analyze the clinical course and the results of liver retransplantation in our center.

PATIENTS AND METHODS

The actuarial survival in a series of 54 retransplantations in 49 patients between February 1984 and December 1997 was analyzed. The retransplantations were grouped according to period: group A (n = 16) 1984-1992, group B (n = 22) 1993-1995 and group C (n = 16) 1996-1997.

RESULTS

The actuarial survival per group according to year was: 31.25%, 54.55% and 62.50% for groups A, B, and C, respectively, which shows a clear improvement with time, although differences were not statistically significant.

CONCLUSIONS

The results of liver transplantation in our series show a lower actuarial survival rate than those of primary transplantation but these results have improved in recent years.

Abnormal restriction pattern of PIP gene associated with human primary prostate cancers

The PIP gene, localized in the 7q34 region that contains a number of fragile sites such as FRA 7H and FRA TI, codes for gp17/PIP, a protein secreted by breast apocrine tumors. We analyzed the integrity of this gene in 20 tumors of the urogenital tract. We found rearranged EcoRI fragments in 5 of 15 primary prostate carcinomas. No rearrangement was found in normal prostates derived from five patients undergoing prostatocystectomy during treatment of bladder cancers. By Southern blot hybridization with PIP gene exon-specific probes, the rearrangements were mapped at or near the 3' end of the gene. These abnormalities were found, not only in the neoplastic cells invading the prostatic tissues, but also in seminal vesicles without histologic tumoral features. These data suggest a critical role of the PIP gene or neighboring genes in prostate cancer.

Antagonistic activity of HIV-1 T helper peptides flanked by an unrelated carrier protein

Antagonism is the ability of a modified antigenic peptide (altered peptide ligand, APL) to prevent CD4 T cell activation by the original peptide. Here we show that antagonistic activity can be conferred to peptides of HIV envelope glycoprotein gp120 and reverse transcriptase p66 by adding flanking polypeptide sequences at the C or at the N terminus by genetic engineering, rather than by introducing substitutions by synthesis. The glutathione S-transferase (GST)-peptide system has been used to produce molecules that display the peptide at the appropriate end of the GST carrier. When the gp120 peptide 191-205 (pep24) was expressed at the C terminus of GST (GST-24), antigenicity of specific human CD4 T cells was maintained. In contrast, when the peptide was expressed at the N terminus of GST (24-GST), antigenicity was abolished and antagonistic activity was introduced. Similar results were obtained with a p66-derived peptide at the C terminus of the GST carrier. Antagonism was (1) specific; proliferation of a CD4 T cell line from the same donor responding to the envelope glycoprotein of another retrovirus, HTLV-1, was not affected; (2) reversible; proliferative response was rescued in T cells exposed to antigen-presenting cells (APC) pulsed with the antagonist; (3) dominant; T cells cultured with APC pulsed with the agonist and with APC pulsed with the antagonist did not proliferate. The carrier could be cleaved by proteolysis while the antagonistic activity was preserved. Thus a minimal sequence that confers antagonistic activity can be engineered or synthesized with peptides to antagonize undesired CD4 responses as an alternative to the use of APL.

Definition of the alpha 2 region of HLA-DR molecules involved in CD4 binding

HLA class II molecules present antigenic peptides to the T cell receptor of CD4+ T lymphocytes and interact with CD4 during the antigen recognition process. A major CD4 binding site encompassing amino acids (aa) 134-148 in the beta 2 domain of HLA-DR has been previously identified and residues located within the alpha 2 subunit of murine MHC class II I-Ad molecules have been shown to contribute to CD4-class II interaction. To characterize the alpha 2 region of HLA-DR molecules involved in the binding of CD4, we have synthesized overlapping linear and cyclic peptides derived from a region encompassing aa 121-143. We demonstrate that two linear peptides (aa 124-138 and 130-143) and a cyclic one (aa 121-138) specifically bind to CD4-sepharose affinity columns. Although cyclic analogues exhibit more ordered populations as detected by circular dichroism measurements, cyclization did not improve the activity of some peptides. Peptide sequence positioning in HLA-DR1 dimer model indicates that alpha 2 residues 124 to 136 form a solvent-exposed loop which faces the beta 2 loop delimited by residues 134-148. These data suggest that one CD4 molecule contacts both alpha 2 and beta 2 loops of the HLA-DR homodimer.

Recognition of HIV-derived B and T cell epitopes displayed on filamentous phages

The amino acid sequence of HIV reverse transcriptase (RT) from residue 248 to residue 262 was expressed on the surface of filamentous phage fd, fused to the major coat protein gVIIIp. The chimeric phage was used to assess the ability of anti-RT (248-262) human T cell lines and clones to become activated by the phage-displayed peptide. The RT peptide displayed on phage was recognized by the T-cells and induced production of Abs. However, not all T cells raised against the synthetic RT (248-262) peptide could respond. Lack of recognition did not depend on differences in the ability of different APCs to present the phage, but was apparently determined by the TCR specificity. The results presented here may be relevant to the design of recombinant protein-based subunit vaccines.

Potent inhibition of CD4/TCR-mediated T cell apoptosis by a CD4-binding glycoprotein secreted from breast tumor and seminal vesicle cells

We previously isolated a CD4 ligand glycoprotein, gp17, from human seminal plasma; this glycoprotein is identical with gross cystic disease fluid protein-15 (GCDFP-15), a factor specifically secreted from primary and secondary breast tumors. The function of gp17/GCDFP-15 in physiological as well as in pathological conditions has remained elusive thus far. As a follow up to our previous findings that gp17 binds to CD4 with high affinity and interferes with both HIV-1 gp120 binding to CD4 and syncytium formation, we investigated whether gp17 could affect the T lymphocyte apoptosis induced by a separate ligation of CD4 and TCR. We show here that gp17/GCDFP-15 is in fact a strong and specific inhibitor of the T lymphocyte programmed cell death induced by CD4 cross-linking and subsequent TCR activation. The antiapoptotic effect observed in the presence of gp17 correlates with a moderate up-regulation of Bcl-2 expression in treated cells. The presence of gp17 also prevents the down-modulation of Bcl-2 expression in Bcl-2bright CD4+ T cells that is caused by the triggering of apoptosis. Our results suggest that gp17 may represent a new immunomodulatory CD4 binding factor playing a role in host defense against infections and tumors.

Differential antibody reactivity and CD4 binding of the mammary tumor marker protein GCDFP-15 from breast cyst and its counterparts from exocrine epithelia

Analysis of biopsies from breast cancer patients demonstrated that GCDFP-15 (gross cystic disease fluid protein-15) is a specific immunocytochemical marker of primary and secondary apocrine breast tumors. The protein has an amino acid sequence identical to SABP (secretory actin-binding protein), to PIP (prolactin-inducible protein) and to gp17, a protein isolated from human seminal plasma. The latter was found to bind to CD4, a T-cell co-receptor involved in antigen recognition, thereby inhibiting the ability of the receptor to interact with the HIV-1 envelope protein gp120. We compare here the ability of independently purified GCDFP-15, SABP and gp17 and of recombinant PIP both to cross-react with a panel of monoclonal antibodies (MAbs) raised against GCDFP-15 or gp17, respectively, and to bind to CD4. We show that, although the various factors share the ability to bind to the panel of antibodies used, differences in the pattern of MAb recognition can be demonstrated. By comparing the kinetic constants for binding of GCDFP-5 and gp17 to CD4 by biosensor technology, significant differences in binding affinities were observed between the 2 factors, thus reflecting structural differences. Surface plasmon resonance analysis also showed that anti-GCDFP-15 and anti-gp17 antibodies inhibit the binding of CD4 to GCDFP-15 and gp17, respectively, to different extents. Our data thus indicate that, while the various forms of the protein are encoded by the same cDNA, tissue specificities due to post-translational modifications exist. This information may be relevant for developing more sensitive and accurate tests for the use of GCDFP-15 as a diagnostic mammary tumor marker and, most importantly, raises the possibility that GCDFP-15 may constitute a breast tumor-specific antigen.

Hepatic hydrothorax

Hepatic hydrothorax is the accumulation of ascitic fluid in the pleural space and requires the same treatment as ascites: salt restriction, diuretics, and paracentesis. Refractory hydrothorax appears when there is no response to those measures and its management is not well established. Videothoracoscopy is a promising therapy that permits the detection and closure of diaphragmatic defects, and when used with pleurodesis resulted in long-lasting control of hydrothorax in six of eight patients without appreciable morbidity. The transjugular intrahepatic portosystemic shunt is an effective therapy in more than 75% of refractory hydrothorax cases. Hepatic encephalopathy and worsening of liver function in some patients are the main adverse effects. Spontaneous bacterial empyema, the infection of a hydrothorax, was reported in 13% of 120 cirrhotic patients with hydrothorax. Forty percent of the episodes of spontaneous bacterial empyema were not associated with spontaneous bacterial peritonitis. The sensibility of pleural fluid culture improves inoculating pleural fluid into a blood culture bottle at the bedside. Patients with refractory hydrothorax or those having an episode of spontaneous bacterial empyema should be considered candidates for liver transplantation.

Majority of gliadin-specific T-cell clones from celiac small intestinal mucosa produce interferon-gamma and interleukin-4

An abnormal mucosal cell-mediated immune response plays a fundamental role in the pathogenesis of celiac disease. To characterize locally infiltrating T cells, gliadin-specific T-cell clones were isolated from two treated celiac patients. Mucosal biopsies were cultured in vitro for 24 hr with a peptic-tryptic digest (PT) of gliadin. T-cell clones (TCC) were then isolated by limiting dilution. The production of interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) was evaluated by ELISA in culture supernatants obtained after a short incubation with anti-CD3 and PMA, or with antigen. Twenty-two TCC were specific for gliadin and/or PT. All were CD3+, CD4+, CD8-, TCR alphabeta+. In one such clone the PT-specific response was inhibited by an anti-DQ, but not by an anti-DR antibody. Of the five gliadin-specific TCC examined, four produced IL-4 and high levels of IFN-gamma; the remaining one initially produced only IL-4, but subsequently also IFN-gamma. All clones obtained from the celiac mucosa, including the gliadin-specific ones, produced high levels of IFN-gamma, in most cases with IL-4. This cytokine profile could explain most of the immunological features of the celiac mucosa.

CD4-mediated anchoring of the seminal antigen gp17 onto the spermatozoon surface

A soluble 1, kDa glycoprotein, namely gp17, was previously isolated from human semen and used to obtain mouse monoclonal or chicken polyclonal antibodies. This protein was shown to bind CD4+ T-cells and to soluble recombinant CD4 in vitro. Here, we report that the anti-gp17 monoclonal antibodies are captured by ejaculated spermatozoa and that gp17-like antigens are released by cell acid extraction. Immunoblotting experiments with monoclonal antibodies indicated that SDS-lysates from spermatozoa contain proteins with the same electrophoretic and antigenic properties of CD4 and gp17. Anti-CD4 mouse monoclonal antibodies were used to coprecipitate from NP40-lysate proteins reacting with chicken anti-gp17 antibodies. Analytical chromatography demonstrated that a number of gp17-like forms are present in the seminal plasma, put that only the 1 kDa species can be detected in the spermatozoa lysate. This protein was localised by immunofluorescence on the post-acrosomal region of the spermatozoon. The same surface domain was also reactive with anti-CD4 antibodies. After treatment to induce in vitro capacitation, gp17 was detected all over the spermatozoon head. Conversely, only a minor part of the treated spermatozoa exhibited CD4 immunostaining, which remained localised on the post-acrosomal region. The possible function of CD4 and gp17 on male germ cells is discussed.

Differential expression of insulin-dependent diabetes mellitus-associated HLA-DQA1 alleles in vivo

The strong association of HLA-DQ genes with insulin-dependent diabetes mellitus (IDDM) susceptibility is persuasive evidence of their central role in the etiology of this autoimmune disease. Among other possibilities, it has been proposed that an unbalanced expression of IDDM-associated DQA, and/or DQB alleles may lead to alterations in the composition of alpha beta heterodimers and preferential expression of a particular heterodimer on the antigen-presenting cell surface, leading to self-recognition. In this report, we demonstrate the differential expression of DQA1 alleles in vivo, in particular of the two diabetogenic alleles DQA1*0301 and DQA1*0501. Family studies suggest that unequal HLA-DQA1 allele expression in heterozygous individuals is not associated in cis with the HLA-DQA1 gene, but may be affected by trans-acting determinant(s). We also discuss the segregation of this phenotype in IDDM-affected members. Furthermore, we examined historical samples of PBL from an IDDM-affected individual and an HLA-identical unaffected sibling acting in a kidney transplant program as donor and recipient, respectively. This analysis allowed us to establish that unbalanced expression of DQA1*0301 and DQA1*0501 can be induced by microenvironmental conditions. Inducible differential expression of HLA-DQA1 alleles may account for the discordance in the outcome of autoimmune disease in monozygotic twins and HLA-identical siblings.

Identical T-cell receptor beta chain rearrangements are present in T cells infiltrating the jejunal mucosa of untreated celiac patients

The intestinal mucosal lesion in celiac disease is characterized by a predominant T-cell infiltration of both epithelium and lamina propria. However, a restricted use of T-cell receptors (TCR) in T lymphocytes infiltrating the jejunal mucosa of celiac patients has not been reported. Based on an immunohistochemical survey of jejunal biopsies from a cohort of untreated celiac patients, we demonstrated a small but significant increase of V beta 8.1/2+ T cells in the lamina propria, but not in the epithelium nor in the peripheral blood. Sequence analysis indicated the existence of a variable degree of clonality of V beta 8+ T cells in the celiac mucosa. More importantly, the recurrence of identical CDR3 regions in some patients was also observed. The altered distribution of V beta 8+ T cells and the presence of identical CDR3 regions in celiac patients, but not in controls was independently confirmed by CDR3 size analysis in a further cohort of patients. These findings suggest that disease-specific variations of the TCRBV8 repertoire are present in the small intestinal mucosa of untreated celiac patients.

Epitope context and reshaping of activated T helper cell repertoire

In recent years, a growing interest in the study of peptide antigenicity in relation to the role of flanking sequences and protein topology in processing, presentation, and recognition has been observed. However, the information available on the antigenicity of recombinant fusion proteins and their effect on the selection of antigen receptor repertoires is limited. To analyze the role of molecular topology of T epitopes in a system relevant to human pathology, we have used the bacterially expressed Schistosoma japonicum glutathione S transferase (GST) to construct recombinant antigens containing HIV-1 derived T cell determinants, and human T cell clones specific for these determinants. We found that antigenicity of a given GST-peptide combination was not the same when T cells and antigen presenting cells from different individuals were tested. Our results show that differences in processing and presentation of chimeric proteins are not dictated by the use of diverse restriction elements. We also found that the context in which an antigenic peptide is delivered affects the recruited repertoire as defined according to T cell receptor V beta usage and fine specificities of selected T cells.

Polymorphism in the 5' terminal region of the mRNA of HLA-DQA1 gene: identification of four groups of transcripts and their association with polymorphism in the alpha 1 domain

Relative to other loci in the MHC, the HLA-DQ locus exhibits an exceptional degree of polymorphism of both A1 and B1 genes, particularly in the region coding for alpha and beta chains. Diversification of the association between different alpha and beta molecules either in cis or in trans contributes to the structural diversity of the repertoire of cell-surface class II protein's in the population. In addition, structural allelic polymorphisms in the 5' regulatory region of both DQB1 and DQA1 shows several linkage groups with respect to the allelic coding sequence of the respective genes. We describe here the allelic polymorphism in the DQA1 mRNA structure located at the 5' untranslated terminal region. This portion of the mRNA molecule represents, in many genes, a cis-acting regulatory sequence playing a role in the posttranscriptional mechanisms by which gene expression can be modulated. Based on detailed transcriptional analysis, we have been able to define at least four groups of transcripts in DQA1. The mRNA variability was associated with the polymorphism of the second exon of the DQA1 gene, coding for the alpha 1 domain and not with the DNA polymorphism in the 5' regulatory region.

Surface plasmon resonance analysis of gp17, a natural CD4 ligand from human seminal plasma inhibiting human immunodeficiency virus type-1 gp120-mediated syncytium formation

We have previously isolated from human seminal plasma a CD4 ligand, the gp17 glycoprotein, which shares sequence identity with three previously identified proteins: secretory actin-binding protein (SABP) from seminal plasma, gross-cystic-disease fluid protein-15 (GCDFP-15) and prolactin-inducible protein (PIP) from breast tumor cells. Functions of these glycoproteins are unknown. To further characterize the physical interaction between gp17 and CD4 we used surface plasmon resonance and demonstrated that gp17-CD4 binding affinity is high. Competition experiments indicated that gp17 interferes with human immunodeficiency virus (HIV) envelope protein/CD4 binding, although it binds to a site distinct from but close to the gp120-binding site. We observed moreover that gp17 inhibits syncytium formation between transfected cells expressing the wild-type HIV-1 envelope glycoprotein and CD4, respectively. Our results suggest that gp17, which may function as an immunomodulatory CD4-binding factor playing a role at insemination, may also play a role in controlling HIV spread in the sexual tract.

Structural heterogeneity, post-translational modifications, and biological activities of SV-IV, a major protein secreted from the rat seminal vesicle epithelium

The primary structure of purified SV-IV, a major secretory protein synthesized by the rat seminal vesicle (SV) epithelium, was analysed by electrospray mass spectrometry (ES-MS). The protein was found to be highly heterogeneous. The various components were separated and identified by reversed phase high-performance liquid chromatography (HPLC) on line with ES-MS. Structural characterization of the SV-IV cyanogen bromide digests revealed the occurrence of a Val/Met substitution in about 50% of the purified protein molecules. We suggest that this mutation is the expression of a genetic polymorphism. Other minor components, corresponding to structural changes (fragmentation, deletion, and phosphorylation) of SV-IV and probably due to post-translational modifications of the native protein, were also detected. In particular, by using protein tyrosine phosphatase hydrolysis combined with ES-MS, we demonstrated that, in the phosphorylated species of SV-IV, a single phosphate group was covalently bound to the Tyr-36 residue. The significance of these findings in relation to the regulation of important biological processes, such as immune response, blood coagulation, inflammatory reaction, and mammalian reproduction, are discussed.

Functional significance of polymorphism among MHC class II gene promoters

The functional significance of polymorphism among MHC class II promoters in man and mouse is here reviewed, mainly in terms of the hypothesis of differential expression. The hypothesis proposes that differences between antigen-presenting cells in MHC class II expression exert a co-dominant effect on the Th1-Th2 cytokine balance, such that class II molecules of one type come to control to a greater extent the production of one group of cytokines, and those of another type the production of the alternative group. The survey deals with the influence of signal strength and antigen-presenting cell type on T-cell subset differentiation; functional differences between MHC class II molecules not obviously related to determinant selection; disease protection mediated by HLA alleles; mechanisms possibly responsible for allotypic and isotypic bias; overdominance (heterozygous advantage) in selection for expression of class II alleles; MHC class II promoter structure and function; inter-locus and inter-allele variability within human MHC class II gene upstream regulatory regions; a comparison of these polymorphisms in mouse and man; read-out of class II promoter function; and a comparison with expression of MHC class I. We conclude that the evidence that this variation is functionally active (i.e. controls expression) is increasing, but is not yet compelling. The crucial test still to come, we suggest, is whether or not the biological effects attributable to this polymorphism will line up with molecular studies on expression.