Nanovesicles released by OKT3 hybridoma express fully active antibodies

Recent findings have shown that nanovesicles preparations from either primary immune cells culture supernatants or plasma contain immunoglobulins, suggesting that a natural way of antibody production may be through exosome release. To verify this hypothesis, we used the OKT3 hybridoma clone, which produces a murine IgG2a monoclonal antibody used to reduce rejection in patients undergoing organ transplantation. We showed exosome-associated immunoglobulins in hybridoma supernatants, by Western blot, nanoscale flow cytometry and immunocapture-based ELISA. The OKT3-exo was also being able to trigger cytokines production in both CD4 and CD8 T cells. These results show that nanovesicles contain immunoglobulin and could be used for immunotherapy. These data could lead to a new approach to improve the effectiveness of therapeutic antibodies by exploiting their natural property to be expressed on nanovesicle membrane, that probably render them more stable and as a consequence more capable to interact with their specific ligand in the best way.

Isolation and preliminary characterization of a human 'phage display'-derived antibody against neural adhesion molecule-1 antigen interfering with fibroblast growth factor receptor-1 binding

BACKGROUND

The NCAM or CD56 antigen is a cell surface glycoprotein belonging to the immunoglobulin super-family involved in cell-cell and cell-matrix adhesion. NCAM is also over-expressed in many tumour types and is considered a tumour associated antigen, even if its role and biological mechanisms implicated in tumour progression and metastasis have not yet to be elucidated. In particular, it is quite well documented the role of the interaction between the NCAM protein and the fibroblast growth factor receptor-1 in metastasis and invasion, especially in the ovarian cancer progression.

OBJECTIVE

Here we describe the isolation and preliminary characterization of a novel human anti-NCAM single chain Fragment variable antibody able to specifically bind NCAM-expressing cells, including epithelial ovarian cancer cells.

METHODS

The antibody was isolate by phage display selection and was characterized by ELISA, FACS analysis and SPR experiments. Interference in EOC migration was analyzed by scratch test.

RESULTS

It binds a partially linear epitope lying in the membrane proximal region of two fibronectin-like domains with a dissociation constant of 3.43 × 10-8 M. Interestingly, it was shown to interfere with the NCAM-FGFR1 binding and to partially decrease migration of EOC cells.

CONCLUSIONS

According to our knowledge, this is the first completely human antibody able to interfere with this newly individuated cancer mechanism.

Inflammatory bowel disease in children and adolescents in Italy: data from the pediatric national IBD register (1996-2003)

BACKGROUND

The purpose was to assess in Italy the clinical features at diagnosis of inflammatory bowel disease (IBD) in children.

METHODS

In 1996 an IBD register of disease onset was established on a national scale.

RESULTS

Up to the end of 2003, 1576 cases of pediatric IBD were recorded: 810 (52%) ulcerative colitis (UC), 635 (40%) Crohn's disease (CD), and 131 (8%) indeterminate colitis (IC). In the period 1996-2003 an increase of IBD incidence from 0.89 to 1.39/10(5) inhabitants aged <18 years was observed. IBD was more frequent among children aged between 6 and 12 years (57%) but 20% of patients had onset of the disease under 6 years of age; 28 patients were <1 year of age. Overall, 11% had 1 or more family members with IBD. The mean interval between onset of symptoms and diagnosis was higher in CD (10.1 months) and IC (9 months) versus UC (5.8 months). Extended colitis was the most frequent form in UC and ileocolic involvement the most frequent in CD. Upper intestinal tract involvement was present in 11% of CD patients. IC locations were similar to those of UC. Bloody diarrhea and abdominal pain were the most frequent symptoms in UC and IC, and abdominal pain and diarrhea in CD. Extraintestinal symptoms were more frequent in CD than in UC.

CONCLUSIONS

The IBD incidence in children and adolescents in Italy shows an increasing trend for all 3 pathologies. UC diagnoses exceeded CD.

Genetic construction, expression, and characterization of a single chain anti-CEA antibody fused to cytosine deaminase from yeast

We report the genetic construction and expression of a fusion protein between a single chain fragment variable (scFv) human antibody (E8) specific for CEA cell surface antigen and yeast cytosine deaminase (yCD). Sequences encoding for the scFvE8 human monoclonal antibody recognizing an epitope shared by CEACAM1, CEACAM3 and CEACAM5 isoforms were assembled with a monomer of yCD. The construct was placed under the transcriptional regulation of the lac promoter, and in frame with 6xHis tag for protein purification. After transformation and induction of E. coli, the protein was recovered from cell lysates and processed for purification. The scFvE8:yCD fusion protein possessed the binding specificity for melanoma (Mel P5) and colon carcinoma (LoVo) cell lines similar to its cognate human scFv antibody. The scFv8:yCD system showed the ability to render tumor cells susceptible to the far less toxic substrate 5-fluorocytosine (5-FC) by its enzymatic conversion into 5-fluorouracil (5-FU). In vitro pre-treatment of Mel P5 and LoVo cell lines with scFvE8:yCD followed by cell washing and incubation with 5-FC, resulted in significant cell killing supporting the utility of this fusion protein as an agent for tumor-selective prodrug activation. This study shows the feasibility of constructing fusion proteins in a prokaryotic cell based system consisting of a human scFv antibody and yCD to convert the antifungal agent 5-FC to 5-FU, one of the widely used anticancer agent.

Genetic construction, expression, and characterization of a single chain anti-CEA antibody fused to cytosine deaminase from yeast

We report the genetic construction and expression of a fusion protein between a single chain fragment variable (scFv) human antibody (E8) specific for CEA cell surface antigen and yeast cytosine deaminase (yCD). Sequences encoding for the scFvE8 human monoclonal antibody recognizing an epitope shared by CEACAM1, CEACAM3 and CEACAM5 isoforms were assembled with a monomer of yCD. The construct was placed under the transcriptional regulation of the lac promoter, and in frame with 6xHis tag for protein purification. After transformation and induction of E. coli, the protein was recovered from cell lysates and processed for purification. The scFvE8:yCD fusion protein possessed the binding specificity for melanoma (Mel P5) and colon carcinoma (LoVo) cell lines similar to its cognate human scFv antibody. The scFv8:yCD system showed the ability to render tumor cells susceptible to the far less toxic substrate 5-fluorocytosine (5-FC) by its enzymatic conversion into 5-fluorouracil (5-FU). In vitro pre-treatment of Mel P5 and LoVo cell lines with scFvE8:yCD followed by cell washing and incubation with 5-FC, resulted in significant cell killing supporting the utility of this fusion protein as an agent for tumor-selective prodrug activation. This study shows the feasibility of constructing fusion proteins in a prokaryotic cell based system consisting of a human scFv antibody and yCD to convert the antifungal agent 5-FC to 5-FU, one of the widely used anticancer agent.

Selection, affinity maturation, and characterization of a human scFv antibody against CEA protein

BACKGROUND

CEA is a tumor-associated antigen abundantly expressed on several cancer types, including those naturally refractory to chemotherapy. The selection and characterization of human anti-CEA single-chain antibody fragments (scFv) is a first step toward the construction of new anticancer monoclonal antibodies designed for optimal blood clearance and tumor penetration.

METHODS

The human MA39 scFv, selected for its ability to recognize a CEA epitope expressed on human colon carcinomas, was first isolated from a large semi-synthetic ETH-2 antibody phage library, panned on human purified CEA protein. Subsequently, by in vitro mutagenesis of a gene encoding for the scFv MA39, a new library was established, and new scFv antibodies with improved affinity towards the CEA cognate epitope were selected and characterized.

RESULTS

The scFv MA39 antibody was affinity-maturated by in vitro mutagenesis and the new scFv clone, E8, was isolated, typed for CEA family member recognition and its CEACAM1, 3 and 5 shared epitope characterized for expression in a large panel of human normal and tumor tissues and cells.

CONCLUSION

The binding affinity of the scFv E8 is in a range for efficient, in vivo, antigen capture in tumor cells expressing a shared epitope of the CEACAM1, 3 and 5 proteins. This new immunoreagent meets all criteria for a potential anticancer compound: it is human, hence poorly or not at all immunogenic, and it binds selectively and with good affinity to the CEA epitope expressed by metastatic melanoma and colon and lung carcinomas. Furthermore, its small molecular size should provide for efficient tissue penetration, yet give rapid plasma clearance.

Immunodetection of partially glycosylated isoforms of alpha-dystroglycan by a new monoclonal antibody against its beta-dystroglycan-binding epitope

The alpha/beta dystroglycan (DG) complex links the extracellular matrix to the actin cytoskeleton. The extensive glycosylation of alpha-DG is believed to be crucial for the interaction with its extracellular matrix-binding partners. We characterized a monoclonal antibody, directed against the beta-DG-binding epitope ( approximately positions 550-565), which recognizes preferentially hypoglycosylated alpha-DG. In Western blot, the antibody was able to detect a number of partially glycosylated alpha-DG isoforms from rat brain and chicken skeletal muscle tissue samples. In addition, we demonstrated its inhibitory effect on the interaction between alpha- and beta-DG in vitro and preliminary immunostaining experiments suggest that such hypoglycosylated alpha-DG isoforms could play a role within cells.

Identification of a panel of tumor-associated antigens from breast carcinoma cell lines, solid tumors and testis cDNA libraries displayed on lambda phage

BACKGROUND

Tumor-associated antigens recognized by humoral effectors of the immune system are a very attractive target for human cancer diagnostics and therapy. Recent advances in molecular techniques have led to molecular definition of immunogenic tumor proteins based on their reactivity with autologous patient sera (SEREX).

METHODS

Several high complexity phage-displayed cDNA libraries from breast carcinomas, human testis and breast carcinoma cell lines MCF-7, MDA-MB-468 were constructed. The cDNAs were expressed in the libraries as fusion to bacteriophage lambda protein D. Lambda-displayed libraries were efficiently screened with sera from patients with breast cancer.

RESULTS

A panel of 21 clones representing 18 different antigens, including eight proteins of unknown function, was identified. Three of these antigens (T7-1, T11-3 and T11-9) were found to be overexpressed in tumors as compared to normal breast. A serological analysis of the 21 different antigens revealed a strong cancer-related profile for at least five clones (T6-2, T6-7, T7-1, T9-21 and T9-27).

CONCLUSIONS

Preliminary results indicate that patient serum reactivity against five of the antigens is associated with tumor disease. The novel T7-1 antigen, which is overexpressed in breast tumors and recognized specifically by breast cancer patient sera, is potentially useful in cancer diagnosis.

Analysis of the SAG5 locus reveals a distinct genomic organisation in virulent and avirulent strains of Toxoplasma gondii

We have recently characterised, in the virulent strain RH of Toxoplasma gondii, three glycosylphosphatidylinositol-anchored surface antigens related to SAG1 (p30) and encoded by highly homologous, tandemly arrayed genes named SAG5A, SAG5B and SAG5C. In the present study, we compared the genomic organisation of the SAG5 locus in strains belonging to the three major genotypes of T. gondii. Southern blot analysis using a SAG5-specific probe produced two related but distinct hybridisation patterns, one exclusive of genotype I virulent strains, the other shared by avirulent strains of either genotype II or genotype III. To understand the molecular bases of this intergenotypic heterogeneity, we cloned and sequenced the SAG5 locus in the genotype II strain Me49. We found that in this isolate the SAG5B gene is missing, with SAG5A and SAG5C laying contiguously. This genomic arrangement explains the hybridisation profiles observed for all the avirulent strains examined and indicates that the presence of SAG5B is a distinctive trait of genotype I. Furthermore, we identified two novel SAG1-related genes, SAG5D and SAG5E, mapping respectively 1.8 and 4.0 kb upstream of SAG5A. SAG5D is transcribed in tachyzoites and encodes a polypeptide of 362 amino acids sharing 50% identity with SAG5A-C, whereas SAG5E is a transcribed pseudogene. We also evaluated polymorphisms at the SAG5 locus by comparing the coding regions of SAG5A-E from strains representative of the three archetypal genotypes. In agreement with the strict allelic dimorphism of T. gondii, we identified two alleles for SAG5D, whereas SAG5A, SAG5C and SAG5E were found to be three distinct nucleotide variants. The higher intergenotypic polymorphism of SAG5A, SAG5C and SAG5E suggests that these genes underwent a more rapid genetic drift than the other members of the SAG1 family. Finally, we developed a new PCR-restriction fragment length polymorphism method based on the SAG5C gene that is able to discriminate between strains of genotype I, II and III by a single endonuclease digestion.

Identification of tumor-associated antigens by screening phage-displayed human cDNA libraries with sera from tumor patients

Screening cDNA libraries from solid human tumors with sera of autologous patients (SEREX) has proven to be a powerful approach to identifying tumor antigens recognized by the humoral arm of the immune system. In many cases, application of this methodology has led to the discovery of novel tumor antigens as unknown gene products. We tried to improve the potency of the SEREX approach by combining it with phage-display technology. We designed a new lambda vector to express protein fragments as N-terminal fusions to the D capsid protein and generated high-complexity cDNA libraries from human breast carcinoma cell lines and solid tumors. Screening these phage-displayed libraries required limited amounts of sera from patients and efficiently identified several tumor antigens specifically reacting with sera from breast cancer patients.

Identification by phage display of the linear continuous MRPr1 epitope in the multidrug resistance-associated protein (MRP1)

In order to study the structure of the multidrug resistance-associated protein (MRP1), which is one of the most important members of the ATP-binding cassette (ABC) protein family acting as drug-efflux systems, we have developed an epitope mapping-based strategy. By means of the mAb MRPr1, we have immunoselected clones from two distinct random peptide libraries displayed on phages and have identified several peptide sequences mimicking the internal conformation of this 190 kDa multidrug transporter protein. Phage clones able to block the immunolabeling of the MRPr1 antibody to MRP1-overexpressing multidrug resistance (MDR) H69/AR cells were isolated and, after sequencing the corresponding inserts, their amino acid sequence was compared to that of MRP1. This analysis led to the identification of the consensus sequence L.SLNWED, corresponding to the MRP1 segment LWSLNKED (residues 241-248). This MRP1 sequence is partially overlapping with the MRPr1 epitope GSDLWSLNKE (residues 238-247) previously mapped using peptide scanning techniques. These results demonstrate the high reliability of phage display technology to study not only the topography of complex integral membrane proteins such as MRP1, but also to help identify critical residues participating in the formation of the epitope structure.

Monoclonal antibodies as a tool for structure-function studies of the MDR1-P-glycoprotein

P-glycoprotein is considered one of the most important member of the rapidly growing superfamily of integral proteins known as the ATP-binding cassette (ABC) which in human also include several other multidrug resistance membrane proteins (i.e., MRP), the product of the cystic fibrosis gene, the TAP-1/TAP2 peptide transporters encoded by the major histocompatibility complex genes and the gene encoding for breast cancer resistance protein (BCRP) also known as MXR1 (mitoxantrone resistance protein). Many monoclonal antibodies (MAbs) reacting with distinct P-glycoprotein domains have been isolated and used to study the molecular organization and cellular functions of this ABC protein. MAbs have been used for multidrug resistance (mdr) gene cloning, delineation of the secondary and tertiary structure of P-glycoprotein and molecular analysis of the mechanisms involved in substrate recognition and transport. The immunodetection of the distinct products of the mdr gene family in normal and malignant cells and tissues has greatly contributed to the understanding of the physiological role of P-glycoprotein and its possible involvement in the refractory of tumors to chemotherapy. The present article deals with the immunological methods used for the structure-function studies of the P-glycoprotein. After introducing the basic structural features of this ABC transporter, the antibody based-approach is discussed with aiming to furnishing methodological perspectives for further investigations of the physiological role of P-glycoprotein and the multidrug resistance phenomenon.

Native and recombinant antigens in the immunodiagnosis of human cystic echinococcosis

To evaluate the diagnostic sensitivity and specificity of immunoelectrophoresis (IEP), indirect haemagglutination (IHA), enzyme-linked immunosorbent assay (ELISA) and immunoblotting (IB), we compared their ability in detecting IgG antibodies to a hydatid fluid fraction (HFF) and to native and recombinant antigen B of Echinococcus granulosus. We tested sera from patients who had cystic echinococcosis (CE) grouped according to their type of cysts (n = 204), from patients with other parasitic diseases (n = 21), lung or liver carcinomas (n = 6) or serous cysts (n = 26) and from healthy controls (n = 90). HFF-IB gave the highest sensitivity (80%) followed by ELISA (72%), IHA (54%) and IEP (31%), respectively. The diagnostic sensitivity significantly (P < 0.01) decreased as cysts matured from type I-II to type VII. Recombinant and native antigen B-IB yielded similar sensitivity (74%). A large number of clinically or surgically confirmed CE patients (20%) resulted negative. In these patients' sera, IB to assess the usefulness of the recombinant E. granulosus elongation factor-1 beta/delta in detecting IgE antibodies yielded 33% of positivity. Our findings underline the need to standardize techniques and antigenic preparations and to improve the performance of immunodiagnosis by characterizing new antigens and detecting distinct immunoglobulin classes.

Cloning and expression of a cDNA encoding an elongation factor 1beta/delta protein from Echinococcus granulosus with immunogenic activity

A cDNA clone (Eg EF-1beta/delta) of Echinococcus granulosus has been isolated by an expression library screened with immunoglobulin (Ig)E of sera from patients with cystic echinococcosis (CE). The Eg EF-1beta/delta was identified on the basis of sequence homology to the subunits beta or delta of the elongation factor-1. The amino acid sequence deduced from this open reading frame is 244 residues long with a predicted molecular mass of 31 kDa. In Southern blot under high stringent condition, Eg EF-1beta/delta hybridized to genomic DNA of E.granulosus at two bands of 4 and 2.5 Kb. In immunoblotting analysis, the Eg EF-1beta/delta protein shows immunological reactivity with sera from CE patients: 51.7% of sera contained IgE, 41.7% IgG and 18.3% IgG4 specific to the recombinant protein. We identify the Eg EF-1beta/delta by immunoblotting with specific monoclonal antibody both in protoscoleces and in sheep hydatid fluid. The higher percentage of humoral immune response against Eg EF-1beta/delta observed in CE patients with calcified cysts than in patients with active cysts indicates the possible release of the protein in the hydatid fluid after protoscoleces degeneration suggesting the possible use of this antigen in the immunosurveillance of CE. Overall, these findings seem to assign to Eg EF-1beta/delta a key role in the allergic disorders and in the complex host-parasite relationship in CE.

Cloning and expression of a cDNA encoding an elongation factor 1beta/delta protein from Echinococcus granulosus with immunogenic activity

A cDNA clone (Eg EF-1beta/delta) of Echinococcus granulosus has been isolated by an expression library screened with immunoglobulin (Ig)E of sera from patients with cystic echinococcosis (CE). The Eg EF-1beta/delta was identified on the basis of sequence homology to the subunits beta or delta of the elongation factor-1. The amino acid sequence deduced from this open reading frame is 244 residues long with a predicted molecular mass of 31 kDa. In Southern blot under high stringent condition, Eg EF-1beta/delta hybridized to genomic DNA of E.granulosus at two bands of 4 and 2.5 Kb. In immunoblotting analysis, the Eg EF-1beta/delta protein shows immunological reactivity with sera from CE patients: 51.7% of sera contained IgE, 41.7% IgG and 18.3% IgG4 specific to the recombinant protein. We identify the Eg EF-1beta/delta by immunoblotting with specific monoclonal antibody both in protoscoleces and in sheep hydatid fluid. The higher percentage of humoral immune response against Eg EF-1beta/delta observed in CE patients with calcified cysts than in patients with active cysts indicates the possible release of the protein in the hydatid fluid after protoscoleces degeneration suggesting the possible use of this antigen in the immunosurveillance of CE. Overall, these findings seem to assign to Eg EF-1beta/delta a key role in the allergic disorders and in the complex host-parasite relationship in CE.

Pneumocystis carinii infection in young non-immunosuppressed rabbits. Kinetics of infection and of the primary specific immune response

The aim of this study was to determine the kinetics, the dissemination of the infection and the immunological response to Pneumocystis carinii primary infection in a non-immunosuppressed rabbit model. For this purpose, we developed a nested PCR that amplified a portion of the mitochondrial large-subunit rRNA gene of rabbit-derived P. carinii. The PCR detected P. carinii DNA in lung and bronchoalveolar lavage fluids from 14- to 45-day-old rabbits but not in their serum. No P. carinii DNA was detected in extrapulmonary organs from 28-day-old rabbits with P. carinii pneumonia. ELISA and immunoblotting analysis showed that 5-day-old pups had elevated specific IgG. The IgG concentration sharply decreased, reaching a trough on day 21, and from then onwards progressively increased as the infection cleared. Conversely, the specific IgM concentration increased during the infection and peaked on day 28. IgG mainly recognized a 50-kDa subunit of P. carinii organisms; IgM recognized first a 45-kDa subunit on day 21, whereas from day 28 onwards it also recognized the 50-kDa subunit. A P. carinii-specific splenocyte proliferative response was observed on day 45. These findings suggest that P. carinii primary infection is a time-limited and a lung-limited event and contribute new information on the relationship between the kinetics of primary P. carinii infection and the immunological response in a model that mimics the primary infections in humans.

Association of the dystroglycan complex isolated from bovine brain synaptosomes with proteins involved in signal transduction

Dystroglycan is a transmembrane heterodimeric complex of alpha and beta subunits that links the extracellular matrix to the cell cytoskeleton. It was originally identified in skeletal muscle, where it anchors dystrophin to the sarcolemma. Dystroglycan is also highly expressed in nonmuscle tissues, including brain. To investigate the molecular interactions of dystroglycan in the CNS, we fractionated a digitonin-soluble extract from bovine brain synaptosomes by laminin-affinity chromatography and characterized the protein components. The 120-kDa alpha-dystroglycan was the major 125I-laminin-labeled protein detected by overlay assay. This complex, in addition to beta-dystroglycan, was also found to contain Grb2 and focal adhesion kinase p125FAK (FAK). Anti-FAK antibodies co-immunoprecipitated Grb2 with FAK. However, no direct interaction between beta-dystroglycan and FAK was detected by co-precipitation assay. Grb2, an adaptor protein involved in signal transduction and cytoskeleton organization, has been shown to bind beta-dystroglycan. We isolated both FAK and Grb2 from synaptosomal extracts by chromatography on immobilized recombinant beta-dystroglycan. In the CNS, FAK phosphorylation has been linked to membrane depolarization and neurotransmitter receptor activation. At the synapses, the adaptor protein Grb2 may mediate FAK-beta-dystroglycan interaction, and it may play a role in transferring information between the dystroglycan complex and other signaling pathways.

[Schönlein-Henoch syndrome: clinical-epidemiological analysis of 98 cases]

We analyzed the clinical and epidemiological data of 98 patients (50 males and 48 females) aged between 6 months and 16 years, hospitalized for Schönlein-Henoch syndrome in the last 20 years. The incidence was higher during spring time. Throat culture was positive for streptococcus pyogenes in 16% of patients. 14 of 60 (23%) had a positive allergometric response to various tests. The extrarenal manifestations were: purpura (100%), articular (68%) or gastrointestinal (32%) involvement and orchitis (10%). Renal symptoms were observed in 23% of the patients, but a clear nephropathy was documented just in 5% of the cases, with resolution within 2 years. Our data suggest, in agreement with the letterature, that renal involvement in Schönlein-Henoch syndrome has usually a benign course.

Long-term cultures of human fetal liver cells: a three-dimensional experimental model for monitoring liver tissue development

BACKGROUND/AIMS

The present study describes an embryonic-fetal liver culture system which allows morphogenetic interactions consistent with the development of the hepatocellular function.

METHODS

Intact livers from 8-12-week embryos were soaked in an extracellular matrix at 4 degrees C and gently dissociated without any enzymatic treatment. The resulting spherical hepatic units were cultured in a chemically defined serum-free medium and seeded into an extracellular matrix layer. Adherent three-dimensional tissue specimens were examined at various times by light and electron microscopy to evaluate the maintenance of hepatocyte morphology.

RESULTS

The liver cells were viable for over 4 months; erythropoietic burst colonies were detected for longer than 6 weeks. Parallel detection of bile salt production in the medium by high performance liquid chromatography proved liver tissue functionality. Bile salt composition revealed predominance of taurine-conjugates rather than glycine. Maximum bile salt concentration (approximately 3 months) coincided with structural and ultrastructural observations indicating a marked decline in hematopoiesis, well-defined biliary canaliculi and formation of an organ-like structure.

CONCLUSIONS

This three-dimensional culture system recapitulates fetal liver development with: (i) initial proliferation of both fetal erythropoietic and hepatic cells and (ii) subsequent shut-off of erythropoiesis and a shift to a more advanced stage of hepatocyte function, such as bile salt secretion.

Intracellular metabolism of 3'-azido-3'-deoxythymidine (AZT): a nuclear magnetic resonance study on T-lymphoblastoid cell lines with different resistance to AZT

This paper reports the results of 31P and 1H nuclear magnetic resonance (NMR) studies on the uptake and phosphorylation of 3'-azido-3'-deoxythymidine (AZT) in the human CD4+ T-lymphoblastoid cell line CCRF-CEM (CEM-1.3) and in its AZT-resistant cell variant MT-500, isolated by prolonged culturing of CEM cells in the presence of increasing AZT concentrations. After 3 hr of incubation in the presence of 0.5 mM AZT, both AZT and its monophosphorylated form (AZT-MP) could be detected in the sensitive cell line in concentrations above the NMR detection levels. In another cell line, MOLT-4, which is less sensitive to AZT effects, the intracellular level of AZT-MP was much lower and was only slightly raised by increasing the concentration of AZT in the extracellular and intracellular compartments. In the AZT-resistant clone MT-500, characterized by a very low thymidine kinase (TK, EC 2.7.1.21) activity with respect to the parental clone, the intracellular AZT-MP concentration was below detection (<0.02 nmol/10(6) cells). Since, however, not only AZT-MP but also AZT signals failed to be detected in MT-500 extracts following cell incubation with AZT, it was concluded that a TK deficiency cannot be the exclusive mechanism of AZT resistance in these cells. The possible effects of additional mechanisms of drug resistance, such as specific AZT cell extrusion and limited permeation, are discussed, together with the new prospects offered by NMR spectroscopy to further evaluate the limiting steps for the utilization of antiretroviral nucleoside analogues.

Molecular characterization and dynamics of hepatitis C virus replication in human fetal hepatocytes infected in vitro

The molecular features of hepatitis C virus (HCV) replication in human fetal hepatocytes (HFHs) were addressed in this study. Using a competitive reverse-transcription polymerase chain reaction (RT-PCR) assay for the quantitation of HCV-RNA molecules, the highest level of viral replication was detected 30 days' postinfection. At this time point, viral particles of 41 to 45 nm in diameter accumulated in the cell cytoplasm. Their density in cell extracts and culture medium was distributed between heavy (1.180-1.360 g/cm3) and light fractions (1.105-1.050 g/cm3) of a sucrose gradient, while, in the serum inoculum, they had a positive fraction at 1.180 g/cm3. In infected HFHs, minus-strand HCV RNA was observed in fractions displaying a sedimentation coefficient of 28 S to 18 S, while plus-strand HCV RNA showed a peak restricted to the 21 S fraction; the HCV RNA of serum inoculum had a sedimentation coefficient of 38 to 40 S, which revealed the presence of HCV RNA of unique positive polarity. The 21 S RNA fraction of cell extracts was resistant to 20 minutes of RNase I digestion, while the same incubation time totally inactivated a comparable amount of HCV RNA purified from the serum inoculum, revealing the presence of completely and/or partially double-stranded HCV-RNA molecules in the infected cells. Detection in HFHs of replicative forms and replicative intermediates suggests that the dynamic profile of HCV replication in these cells is similar to that described in other flaviviruses.

A chromatin-associated protein is encoded in a genomic region highly conserved in the Plasmodium genus

A single copy gene, pbB7, encoding a putative 26 kDa acidic protein has been isolated from Plasmodium berghei and appears to be part of a genomic region well conserved within the Plasmodium genus. The deduced amino acid sequence exhibits significant blocks of similarity with nucleosome assembly proteins from yeast and man. The nuclear localization of the natural protein and its close association with chromatin during the entire erythrocytic cycle of the parasite have been demonstrated using specific monoclonal antibodies against the pbB7 product expressed in Escherichia coli. These results suggest an involvement of this nuclear factor in the dynamics of chromatin packaging.

Pentose phosphate pathway alterations in multi-drug resistant leukemic T-cells: 31P NMR and enzymatic studies

31P NMR studies were carried out on the parental drug-sensitive human T-lymphoblastoid cell line CCRI-CEM (CEM) and its multi-drug-resistant (MDR) CEM-VBL100 variants, to assess the role of the pentose phosphate (PP) in MDR expression. CEM and CEM-VBL100 were incubated in the presence of 2-deoxyglucose, as recently proposed by our group (Clin. Chim. Acta 208: 39, 1992). Accumulation of 2-deoxyglucose 6-phosphate was much lower in the drug-resistant than in sensitive cells, indicating PP shunt activation in the MDR variants. This result was confirmed by enzymatic analyses, which demonstrated that, with respect to the parental line, the MDR variant was characterized by a) unaltered hexokinase activity; b) higher glucose 6-phosphate dehydrogenase activity; c) increased levels of reduced glutathione and marked increase of glutathione peroxidase activity after cell exposure to an oxidizing agent (tert-butylhydroperoxide). These results support the view that cell detoxification mechanisms mediated by the pentose phosphate pathway may contribute to the expression of MDR in tumours.

Inhibition of Friend leukemia cell visceral metastases by a new monoclonal antibody and role of the immune system of the host in its action

We developed a syngeneic mouse IgG2a monoclonal antibody (MAb) A9D41 directed against the Friend leukemia virus envelope gp70 antigen present on the cell surface membranes of virus producer 3C18 Friend leukemia cells (FLC). A9D41 showed a marked antitumor activity in DBA/2 mice given injections of gp70 positive 3C18 FLC, but it was ineffective in mice given injections of gp70 negative 745 FLC or unrelated tumor cells. A9D41 was particularly effective in inhibiting the development of 3C18 FLC liver and spleen metastases. MAb was also effective as adjuvant therapy in inhibiting visceral metastases after excision of an established s.c. FLC tumor, and combined therapy of A9D41 with mouse interferon alpha/beta was more effective than MAb or interferon alpha/beta alone. The immune system of the host played a decisive role in the antimetastatic action of A9D41. Thus, although MAb was cytotoxic for 3C18 FLC in vitro in the presence of rabbit complement, the F(ab')2 fragment was ineffective in vivo, and the antitumor effect of MAb was abolished in mice treated with an antibody to CD4 and diminished in natural killer cell-deficient beige and athymic nude mice. MAb-treated mice surviving injection of FLC developed an immune response to 3C18 FLC.

Expression of lymphocyte homing receptor gene is lost in multi-drug-resistant variants of human T-lymphoblastoid CCRF-CEM cells

The 2.2-kb human cDNA clone PBL32, encoding for the lymphocyte homing receptor (LHR) was used to study the expression of this determinant in multi-drug-resistant (MDR) variants of human T-lymphoblastoid CCRF-CEM (CEM) cells. LHR is significantly associated with the drug-sensitive phenotype, its expression being progressively and quantitatively reduced in MDR variants of CEM cells according to the extent of drug resistance.

Characterization by somatic cell genetics of a monoclonal antibody to the MDR1 gene product (P-glycoprotein): determination of P-glycoprotein expression in multi-drug-resistant KB and CEM cell variants

We isolated an IgG2a murine monoclonal antibody (MAb) termed MAb57, specifically reactive with multi-drug-resistant (MDR) human cells. Its specificity toward the MDRI gene product (P-glycoprotein) has been demonstrated by the concordant segregation of the MAb57 epitope with the MDRI gene in interspecific mouse x human cell hybrids, and the reactivity of several different MDRI gene-expressing cells with MAb57, particularly insect cells acutely infected with a baculovirus encoding the MDRI gene. MAb57 can be used to detect, by flow cytometry, variations in the relative drug-resistance levels of several MDR KB and CEM cell variants. This immunological probe has also proven useful in selectively destroying MDR target cells in an antibody-dependent cell-mediated (ADCC) assay system as well as in detecting P-glycoprotein expression in normal and malignant tissues and cells.

Murine monoclonal antibody recognizing a 90-kDa cell-surface determinant selectively lost by multi-drug-resistant variants of CEM cells

We describe a murine IgG1 monoclonal antibody (MAb56), specific for a cell-surface protein structure (MC56 determinant) expressed by the human CEM cell line. A large band of approximately 90 kDa was identified as the main specific component of the MC56 determinant. Such a 90-kDa protein is significantly associated with the drug-sensitive phenotype, its expression being progressively reduced quantitatively in multi-drug-resistant (MDR) variants of CEM cells, according to the extent of drug resistance. In addition, the MC56 determinant is expressed de novo in drug-sensitive revertant cell lines derived from MDR cells and unreactive with the MAb56. The MAb56 shows a high affinity towards the immunizing drug-sensitive CEM cell line (Ka = 1.86 x 10(9) L/mole) while not binding to MDR cell variants. The expression of the MC56 molecule on a variety of human cells and tissues makes such a cellular determinant a candidate as a marker for studying the MDR phenomenon both in vivo and in vitro.

High frequency production of hybridomas secreting antibodies to cell antigens

The efficiency of various immunization protocols for the production of hybridomas secreting immunoglobulins specific to cell antigens was evaluated in 15 different fusion experiments. Some of these experiments were performed with splenic B-lymphocytes from mice at different stages of immunization. This approach allowed a dynamic analysis of immunocompetent splenic B-lymphocyte production during the immunization cycle.