Camelid immunoglobulins and nanobody technology

It is well established that all camelids have unique antibodies circulating in their blood. Unlike antibodies from other species, these special antibodies are devoid of light chains and are composed of a heavy-chain homodimer. These so-called heavy-chain antibodies (HCAbs) are expressed after a V-D-J rearrangement and require dedicated constant gamma-genes. An immune response is raised in these so-called heavy-chain antibodies following classical immunization protocols. These HCAbs are easily purified from serum, and the antigen-binding fragment interacts with parts of the target that are less antigenic to conventional antibodies. Since the antigen-binding site of the dromedary HCAb is comprised in one single domain, referred to as variable domain of heavy chain of HCAb (VHH) or nanobody (Nb), we designed a strategy to clone the Nb repertoire of an immunized dromedary and to select the Nbs with specificity for our target antigens. The monoclonal Nbs are well produced in bacteria, are very stable and highly soluble, and bind their cognate antigen with high affinity and specificity. We have successfully developed recombinant Nbs for research purposes, as probe in biosensors, to diagnose infections, and to treat diseases like cancer or trypanosomosis.

ABINs inhibit EGF receptor-mediated NF-kappaB activation and growth of EGF receptor-overexpressing tumour cells

The epidermal growth factor receptor (EGFR) is frequently overexpressed in various tumours of epidermal origin and is held responsible for tumourigenicity and tumour persistence. Increased nuclear factor (NF)-kappaB activity has been suggested to be involved in the malignant behaviour of EGFR-overexpressing cells. However, the mechanisms that regulate EGF-induced NF-kappaB activation are still largely unknown. Here we show that EGF can induce NF-kappaB-dependent gene expression independently from IkappaBalpha degradation or p100 processing in EGFR-overexpressing HEK293T cells. Moreover, EGF-induced NF-kappaB activation could be inhibited by overexpression of ABINs, which were previously identified as intracellular inhibitors of tumour necrosis factor, interleukin-1 and lipopolysaccharide-induced NF-kappaB activation. Knockdown of ABIN-1 by RNA interference boosted the NF-kappaB response upon EGF stimulation. The C-terminal ubiquitin-binding domain containing region of ABINs was crucial and sufficient for NF-kappaB inhibition. Adenoviral gene transfer of ABINs reduced constitutive NF-kappaB activity as well as the proliferation of EGFR-overexpressing A431 and DU145 human carcinoma cells. Altogether, these results demonstrate an important role for an ABIN-sensitive non-classical NF-kappaB signalling pathway in the proliferation of EGFR-overexpressing tumour cells, and indicate a potential use for ABIN gene therapy in the treatment of cancer.

Radioimmunoimaging. Advances and prospects

The advent of biotechnology has made it possible to overcome the undesired host antiglobulin response evidenced following the injection of rodent antibodies for radioimmunoimaging; initially through the construction of chimeric and CDR-grafted antibodies and more recently through the derivation of completely human antibodies. Available platforms for derivation of completely human antibodies include phage- and ribosome-display techniques and transgenic mice that are deleted in their own antibody genes and reconstituted with large parts of the genes encoding for human antibodies. Additionally, biotechnology has made it possible to tailor affinity, respectively through CDR-walking or chain schuffling, and avidity, respectively through manifold engineering, of antibodies and derivatives. More recent developments include the development of highly stable single domain binders based on the use of a conserved framework region and a highly variable antigen-binding site, using other proteins or molecules that are smaller in size and easier to manufacture than antibodies. Finally, novel technologies have been and are being developed optimizing the concept of pretargeting.

Screening for enterocins and detection of hemolysin and vancomycin resistance in enterococci of different origins

The inhibitory activity of 122 out of 426 Enterococcus strains of geographically widespread origin and from different sources (food and feed, animal isolates, clinical and nonclinical human isolates) was tested against a wide range of indicator bacteria. Seventy-two strains, mainly belonging to the species Enterococcus faecium and Enterococcus faecalis were bacteriocinogenic. A remarkable variation of inhibitory spectra occurred among the strains tested, including inhibition of, for instance, only closely related enterococci, other lactic acid bacteria (LAB), food spoilage and pathogenic bacteria. No correlation could be found between the origin of the strains and the type of inhibitory spectrum, although a clustering of human isolates from both fecal and clinical origin was observed in the group of strains inhibiting lactic acid bacteria, Listeria, and either Staphylococcus or Clostridium. No relationship could be established between the presence of enterocin structural genes and the origin of the strain either, and hence no correlation seemed to exist between the presence of known enterocin genes and the activity spectra of these enterococci. The structural gene of enterocin A was widely distributed among E. faecium strains, whereas that of enterocin B only occurred in the presence of enterocin A. The vancomycin resistance phenotype as well as the presence of vancomycin resistance genes was also investigated. The vanA gene only occurred among E. faecium strains. The incidence of beta-hemolysis was not restricted to E. faecalis strains, but among the E. faecium strains the structural genes of cytolysin were not detected. beta-Hemolysis occurred in strains both from food and nonfood origin. It has been concluded that bacteriocin-producing E. faecium strains lacking hemolytic activity and not carrying cytolysin nor vancomycin resistance genes may be useful as starter cultures, cocultures, or probiotics.

Differentiation of EL4 lymphoma cells by tumoral environment is associated with inappropriate expression of the large chondroitin sulfate proteoglycan PG-M and the tumor-associated antigen HTgp-175

Progression to malignancy of transformed cells involves complex genetic alterations and aberrant gene expression patterns. While aberrant gene expression is often caused by alterations in individual genes, the contribution of the tumoral environment to the triggering of this gene expression is less well established. The stable but heterogeneous expression in cultured EL4/13 cells of a novel tumor-associated antigen, designated as HTgp-175, was chosen for the investigation of gene expression during tumor formation. Homogeneously HTgp-175-negative EL4/13 cells, isolated by cell sorting or obtained by subcloning, acquired HTgp-175 expression as a result of tumor formation. The tumorigenicity of HTgp-175-negative vs. HTgp-175-positive EL4 variants was identical, indicating that induction but not selection accounted for the phenotypic switch from HTgp-175-negative to HTgp-175-positive. Although mutagenesis experiments showed that the protein was not essential for tumor establishment, tumor-derived cells showed increased malignancy, linking HTgp-175 expression with genetic changes accompanying tumor progression. This novel gene expression was not an isolated event, since it was accompanied by ectopic expression of the large chondroitin sulfate proteoglycan PG-M and of normal differentiation antigens. We conclude that signals derived from the tumoral microenvironment contribute significantly to the aberrant gene expression pattern of malignant cells, apparently by fortuitous activation of differentiation processes and cause expression of novel differentiation antigens as well as of inappropriate tumor-associated and ectopic antigens.

A new membrane-bound OprI lipoprotein expression vector. High production of heterologous fusion proteins in gram (-) bacteria and the implications for oral vaccination

We have previously described the development of cloning vectors for the production of OprI-based outer membrane fusion proteins in E. coli (Cornelis et al., 1996) and now describe the construction of a new vector, containing a lacI(q) gene, resulting in tight repression of the promotor and allowing its use in other Gram (-) bacteria. The new pVUB3 expression vector encodes a truncated but active LacI(q)(341) repressor which binds to the single operator in the vector. A high repression of the trc promotor was observed, resulting in a very low basal leakage of expression and very high production levels of OprI or derivatives after IPTG induction in E. coli. Bacterial viability was not affected under uninduced conditions, but the number of viable cell counts decreased after production of large amounts of the outer membrane-bound OprI lipoprotein and its derivatives, both in E. coli and Salmonella typhimurium. This highly repressible system allows us to extend the use of OprI vectors in other Gram (-) bacteria, resulting in the production of outer membrane-bound lipid-modified molecules, opening the possibility for its application in the design of potential live Salmonella-based subunit vaccines.

Identification and cloning of a glucan- and lipopolysaccharide-binding protein from Eisenia foetida earthworm involved in the activation of prophenoloxidase cascade

Coelomic fluid of Eisenia foetida earthworms contains a 42-kDa protein named coelomic cytolytic factor 1 (CCF-1) that was described previously to be involved in cytolytic, opsonizing, and hemolytic properties of the coelomic fluid. Cloning and sequencing of CCF-1 reveal significant homology with the putative catalytic region of beta-1,3- and beta-1,3-1,4-glucanases. CCF-1 also displays homology with coagulation factor G from Limulus polyphemus and with Gram-negative bacteria-binding protein of Bombyx mori silkworm, two proteins involved in invertebrate defense mechanisms. We show that CCF-1 efficiently binds both beta-1,3-glucan and lipopolysaccharide. Moreover, CCF-1 participates in the activation of prophenoloxidase cascade via recognition of yeast and Gram-negative bacteria cell wall components. These results suggest that the 42-kDa CCF-1 protein of E. foetida coelomic fluid likely plays a role in the protection of earthworms against microbes.

Occurrence of multiple genomovars of Burkholderia cepacia in cystic fibrosis patients and proposal of Burkholderia multivorans sp. nov

We performed an integrated genotypic and phenotypic analysis of 128 strains of the genera Burkholderia, Ralstonia, and Pseudomonas in order to study the taxonomic structure of Burkholderia cepacia and its relationships with other Burkholderia species. Our data show that presumed B. cepacia strains isolated from cystic fibrosis patients belong to at least five distinct genomic species, one of which was identified as Burkholderia vietnamiensis. This group of five phenotypically similar species is referred to as the B. cepacia complex. The name Burkholderia multivorans is proposed for one of these genomic species, which was formerly referred to as B. cepacia genomovar II; the remaining B. cepacia groups are referred to as genomovars I, III, and IV, pending additional differential phenotypic tests. The role and pathogenic potential of each of these taxa, particularly in view of the potentially fatal infections in cystic fibrosis patients, need further evaluation. The data presented also demonstrate that Pseudomonas glathei and Pseudomonas pyrrocinia should be reclassified as Burkholderia species.

Analysis of epidemic Pseudomonas aeruginosa isolates by isoelectric focusing of pyoverdine and RAPD-PCR: modern tools for an integrated anti-nosocomial infection strategy in burn wound centres

The Gram-negative bacterium Pseudomonas aeruginosa is an important life-threatening nosocomial pathogen in burn units. In this study we analysed epidemic P. aeruginosa isolates from patients and their hospital environment using two new molecular techniques in order to establish strain relatedness for epidemiological purposes. One technique was pyoverdine typing by isoelectric focusing (PVD-IEF) and the other was a genomic PCR-based fingerprinting technique called random amplification of polymorphic DNA actually referred to as RAPD-PCR. The described short epidemic (6 weeks) included 37 consecutive isolates from 9 different patients as well as two environmental isolates recovered, at the same time, from one of the hydrotherapy facilities. Only two of the three known pyoverdine types of P. aeruginosa could be found. Type I was absent while type II represented 49 per cent and type III, 51 per cent of the isolates. The two consecutive isolates from the environment were both of type III. The RAPD-PCR fingerprinting discriminated four patterns. Profile 1 represented 60 per cent; profile 2, 34 per cent; and profiles 3 and 4 only 3 per cent of the isolates respectively. The environmental isolates also had a RAPD-PCR 1 profile, arguing for the hydrotherapy facility as a possible contamination source. Prompt measures could prevent an outbreak. The study demonstrates the applicability of the techniques in a routine microbiology lab as well as their usefulness, in combination with other techniques, in the fight against nosocomial infections, which are so critical in burn units. Both techniques showed undoubtable evidence of the occurrence of polymicrobial infection of individual patients by P. aeruginosa species. Meanwhile pyoverdine typing by IEF seems suited to studying more profoundly the role of pyoverdines in burns.

Isolation of Campylobacter concisus from feces of children with and without diarrhea

A prospective study compared fecal isolation rates of Campylobacter concisus for children with diarrhea and without diarrhea by a filter technique in which media were incubated for 4 days in a microaerobic atmosphere. No statistically significant difference in isolation rates was found (13.2% in patients with diarrhea and 9% in controls). Moreover, 35 of 37 children attending the same day care center harbored different C. concisus strains, as was demonstrated by arbitrary primer PCR DNA fingerprinting. These data suggest a lack of a pathogenic role for C. concisus in enteritis.

Comparative evaluation of NASBA HIV-1 RNA QT, AMPLICOR-HIV monitor, and QUANTIPLEX HIV RNA assay, three methods for quantification of human immunodeficiency virus type 1 RNA in plasma

Three commercial assays for quantifying plasma human immunodeficiency virus type 1 (HIV-1) RNA were evaluated. The assays differed in their sample volumes, the means of preparing samples, and methods of amplification and detection. Plasma samples were obtained from 36 HIV-1-infected patients representing all stages of HIV-1 infection and were analyzed as coded specimens. Measurement of HIV-1 RNA baseline levels revealed no significant difference in sensitivity between the three assays. The assays were also applied to the quantitation of HIV-1 RNA levels in the plasma of patients who were changing their antiretroviral therapy. The changes measured in HIV-1 RNA levels in plasma in response to therapy were comparable by the three assays. No close correlation was found between the amount of HIV-1 RNA and the CD4 T-cell count; HIV-1 RNA assays were more sensitive than p24 antigen assays as an indicator of plasma viremia. Overall, the study demonstrates that all three quantitative assays for HIV-1 RNA can be used to measure the HIV-1 RNA copy number representing the HIV-1 viremia status in patients with HIV-1 infection. Since this copy number is likely to be useful in monitoring the effectiveness of antiviral therapy, these quantitative assays for HIV-1 RNA are ready to be built into clinical trials.

Burkholderia (Pseudomonas) cepacia and cystic fibrosis: the epidemiology in Belgium

Burkholderia cepacia has become an increasingly recognized pathogen among cystic fibrosis (CF) patients and its potential role in declining pulmonary function or unexpected fatal outcome has caused widespread concern. Direct person-to-person transmission has been documented and a segregation policy of CF patients colonized with B.cepacia from non-colonized CF patients is widely adopted. Since this policy has a dramatic impact on social behaviour of CF patients it is imperative that clinical laboratories accurately isolate and identify B.cepacia in the respiratory secretions. In order to comprehend the epidemiology of B.cepacia in the Belgian CF population a multicentre study was conducted during a period of 1 year (March'93-February'94). B.cepacia was isolated in only 12 of 465 CF patients (2.6%). Routine biochemical tests identified these strains as authentic B.cepacia. However, the combined data from protein and DNA-DNA hybridization analyses revealed that the Belgian CF "B.cepacia" isolates showed patterns different from reference B.cepacia isolates and belong to 3 different, newly identified Burkholderia genomovars, but not to B.cepacia. Comparative analysis of the selective media used for recovery of these "B.cepacia" strains from respiratory secretions indicated that the commercial medium (Mast) containing polymyxin B and ticarcillin as the selective agents was the best and most user-friendly. Molecular typing of these Burkholderia isolates by arbitrarily-primed PCR (AP-PCR) and pulsed-field gel electrophoresis (PFGE) showed that spread of a single strain within a same centre occurred but the mode of transmission remains unknown; inter-centre spread of strains was not observed. Interestingly, neither colonization with a distinct or an epidemic strain (belonging to either of the three newly identified Burkholderia genomovars) nor colonization for a prolonged period of time, led to a rapid deterioration of lung function in these CF patients. It appears essential to determine the prevalence of these "new" Burkholderia genomovars in larger populations of CF patients and to evaluate their virulence and other features as this may have important clinical and practical implications.

Eimeria species which infect the chicken contain virus-like RNA molecules

There is increasing support for the presence of viruses and virus-like particles inside protozoan cells. This study describes viral-like RNA molecules that have been detected in two species of Eimeria that infect the chicken. The RNA molecule identified in E. maxima has been characterized: subcellular fractionation studies have shown that the RNA is present in the cytoplasm, probably as an abundant ribonucleoprotein that is insensitive to RNAse A treatment. Electron microscopy has demonstrated that this RNA molecule is double stranded. In addition, all E. maxima strains examined so far contain this RNA molecule.

Identification of virus-like particles in Eimeria stiedae

When nucleic acid samples purified from sporozoites of Eimeria stiedae were analyzed by agarose gel electrophoresis, an ethidium-stainable band with an apparent electrophoretic mobility of 6.5 kb was consistently observed. The band was readily degradable upon RNAse treatment, and its susceptibility towards ribonuclease A on a decreasing ionic strength was suggestive of double-stranded RNA (dsRNA). Electron microscopy revealed spherical, probably icosahedral, virus-like particles (VLP) with a diameter of 35 nm in sporozoite lysates. The VLP were purified by CsCl buoyant density gradient centrifugation. Upon extraction, these particles yielded dsRNA molecules of a uniform length of 1.63 microns. The presence of the VLP was investigated in different Eimeria strains. All E. stiedae isolates contained the RNA virus, whereas the Eimeria intestinalis and Eimeria magna isolates tested did not. RNA/RNA hybridization experiments where the E. stiedae VLP dsRNA was probed to the genomes of the dsRNA viruses of Trichomonas vaginalis and Giardia intestinalis revealed a strong relatedness of the E. stiedae virus to the G. intestinalis virus, in contrast with the T. vaginalis virus, where no homology could be detected.