Anti-TTR Nanobodies Allow the Identification of TTR Neuritogenic Epitope Associated with TTR-Megalin Neurotrophic Activities

Transthyretin (TTR) has intrinsic neurotrophic physiological activities independent from its thyroxine ligands, which involve activation of signaling pathways through interaction with megalin. Still, the megalin binding motif on TTR is unknown. Nanobodies (Nb) have the ability to bind "hard to reach" epitopes being useful tools for protein/structure function. In this work, we characterize two anti-TTR Nanobodies, with similar mouse TTR binding affinities, although only one is able to block its neuritogenic activity (169F7_Nb). Through epitope mapping, we identified amino acids 14-18, at the entrance of the TTR central channel, to be important for interaction with megalin, and a stable TTR K15N mutant in that region was constructed. The TTR K15N mutant lacks neuritogenic activity, indicating that K15 is critical for TTR neuritogenic activity. Thus, we identify the putative binding site for megalin and describe two Nanobodies that will allow research and clarification of TTR physiological properties, regarding its neurotrophic effects.

Delivery of an anti-transthyretin Nanobody to the brain through intranasal administration reveals transthyretin expression and secretion by motor neurons

Transthyretin (TTR) is a transport protein of retinol and thyroxine in serum and CSF, which is mainly secreted by liver and choroid plexus, and in smaller amounts in other cells throughout the body. The exact role of TTR and its specific expression in Central Nervous System (CNS) remains understudied. We investigated TTR expression and metabolism in CNS, through the intranasal and intracerebroventricular delivery of a specific anti-TTR Nanobody to the brain, unveiling Nanobody pharmacokinetics to the CNS. In TTR deficient mice, we observed that anti-TTR Nanobody was successfully distributed throughout all brain areas, and also reaching the spinal cord. In wild-type mice, a similar distribution pattern was observed. However, in areas known to be rich in TTR, reduced levels of Nanobody were found, suggesting potential target-mediated effects. Indeed, in wild-type mice, the anti-TTR Nanobody was specifically internalized in a receptor-mediated process, by neuronal-like cells, which were identified as motor neurons. Whereas in KO TTR mice Nanobody was internalized by all cells, for late lysosomal degradation. Moreover, we demonstrate that in vivo motor neurons also actively synthesize TTR. Finally, in vitro cultured primary motor neurons were also found to synthesize and secrete TTR into culture media. Thus, through a novel intranasal CNS distribution study with an anti-TTR Nanobody, we disclose a new cell type capable of synthesizing TTR, which might be important for the understanding of the physiological role of TTR, as well as in pathological conditions where TTR levels are altered in CSF, such as amyotrophic lateral sclerosis.

Novel half-life extended anti-MIF nanobodies protect against endotoxic shock

Sepsis-leading to septic shock-is the leading cause of death in intensive care units. The systemic inflammatory response to infection, which is initiated by activated myeloid cells, plays a key role in the lethal outcome. Macrophage migration inhibitory factor (MIF) is an upstream immunoregulatory mediator, released by myeloid cells, that underlies a common genetic susceptibility to different infections and septic shock. Accordingly, strategies that are aimed at inhibiting the action of MIF have therapeutic potential. Here, we report the isolation and characterization of tailorable, small, affinity-matured nanobodies (Nbs; single-domain antigen-binding fragments derived from camelid heavy-chain Abs) directed against MIF. Of importance, these bioengineered Nbs bind both human and mouse MIFs with nanomolar affinity. NbE5 and NbE10 inhibit key MIF functions that can exacerbate septic shock, such as the tautomerase activity of MIF (by blocking catalytic pocket residues that are critical for MIF's conformation and receptor binding), the TNF-inducing potential, and the ability of MIF to antagonize glucocorticoid action. A lead NbE10, tailored to be a multivalent, half-life extended construct (NbE10-NbAlb8-NbE10), attenuated lethality in murine endotoxemia when administered via single injection, either prophylactically or therapeutically. Hence, Nbs, with their structural and pharmacologic advantages over currently available inhibitors, may be an effective, novel approach to interfere with the action of MIF in septic shock and other conditions of inflammatory end-organ damage.-Sparkes, A., De Baetselier, P., Brys, L., Cabrito, I., Sterckx, Y. G.-J., Schoonooghe, S., Muyldermans, S., Raes, G., Bucala, R., Vanlandschoot, P., Van Ginderachter, J. A., Stijlemans, B. Novel half-life extended anti-MIF nanobodies protect against endotoxic shock.

Protective effect of different anti-rabies virus VHH constructs against rabies disease in mice

Rabies virus causes lethal brain infection in about 61000 people per year. Each year, tens of thousands of people receive anti-rabies prophylaxis with plasma-derived immunoglobulins and vaccine soon after exposure. Anti-rabies immunoglobulins are however expensive and have limited availability. VHH are the smallest antigen-binding functional fragments of camelid heavy chain antibodies, also called Nanobodies. The therapeutic potential of anti-rabies VHH was examined in a mouse model using intranasal challenge with a lethal dose of rabies virus. Anti-rabies VHH were administered directly into the brain or systemically, by intraperitoneal injection, 24 hours after virus challenge. Anti-rabies VHH were able to significantly prolong survival or even completely rescue mice from disease. The therapeutic effect depended on the dose, affinity and brain and plasma half-life of the VHH construct. Increasing the affinity by combining two VHH with a glycine-serine linker into bivalent or biparatopic constructs, increased the neutralizing potency to the picomolar range. Upon direct intracerebral administration, a dose as low as 33 µg of the biparatopic Rab-E8/H7 was still able to establish an anti-rabies effect. The effect of systemic treatment was significantly improved by increasing the half-life of Rab-E8/H7 through linkage with a third VHH targeted against albumin. Intraperitoneal treatment with 1.5 mg (2505 IU, 1 ml) of anti-albumin Rab-E8/H7 prolonged the median survival time from 9 to 15 days and completely rescued 43% of mice. For comparison, intraperitoneal treatment with the highest available dose of human anti-rabies immunoglobulins (65 mg, 111 IU, 1 ml) only prolonged survival by 2 days, without rescue. Overall, the therapeutic benefit seemed well correlated with the time of brain exposure and the plasma half-life of the used VHH construct. These results, together with the ease-of-production and superior thermal stability, render anti-rabies VHH into valuable candidates for development of alternative post exposure treatment drugs against rabies.

Llama-derived single variable domains (nanobodies) directed against chemokine receptor CXCR7 reduce head and neck cancer cell growth in vivo

The chemokine receptor CXCR7, belonging to the membrane-bound G protein-coupled receptor superfamily, is expressed in several tumor types. Inhibition of CXCR7 with either small molecules or small interference (si)RNA has shown promising therapeutic benefits in several tumor models. With the increased interest and effectiveness of biologicals inhibiting membrane-bound receptors we made use of the "Nanobody platform" to target CXCR7. Previously we showed that Nanobodies, i.e. immunoglobulin single variable domains derived from naturally occurring heavy chain-only camelids antibodies, represent new biological tools to efficiently tackle difficult drug targets such as G protein-coupled receptors. In this study we developed and characterized highly selective and potent Nanobodies against CXCR7. Interestingly, the CXCR7-targeting Nanobodies displayed antagonistic properties in contrast with previously reported CXCR7-targeting agents. Several high affinity CXCR7-specific Nanobodies potently inhibited CXCL12-induced β-arrestin2 recruitment in vitro. A wide variety of tumor biopsies was profiled, showing for the first time high expression of CXCR7 in head and neck cancer. Using a patient-derived CXCR7-expressing head and neck cancer xenograft model in nude mice, tumor growth was inhibited by CXCR7-targeting Nanobody therapy. Mechanistically, CXCR7-targeting Nanobodies did not inhibit cell cycle progression but instead reduced secretion of the angiogenic chemokine CXCL1 from head and neck cancer cells in vitro, thus acting here as inverse agonists, and subsequent angiogenesis in vivo. Hence, with this novel class of CXCR7 inhibitors, we further substantiate the therapeutic relevance of targeting CXCR7 in head and neck cancer.

Selection of nanobodies that target human neonatal Fc receptor

FcRn is a key player in several immunological and non-immunological processes, as it mediates maternal-fetal transfer of IgG, regulates the serum persistence of IgG and albumin, and transports both ligands between different cellular compartments. In addition, FcRn enhances antigen presentation. Thus, there is an intense interest in studies of how FcRn binds and transports its cargo within and across several types of cells, and FcRn detection reagents are in high demand. Here we report on phage display-selected Nanobodies that target human FcRn. The Nanobodies were obtained from a variable-domain repertoire library isolated from a llama immunized with recombinant human FcRn. One candidate, Nb218-H4, was shown to bind FcRn with high affinity at both acidic and neutral pH, without competing ligand binding and interfering with FcRn functions, such as transcytosis of IgG. Thus, Nb218-H4 can be used as a detection probe and as a tracker for visualization of FcRn-mediated cellular transport.

Enhancement of polymeric immunoglobulin receptor transcytosis by biparatopic VHH

The polymeric immunoglobulin receptor (pIgR) ensures the transport of dimeric immunoglobulin A (dIgA) and pentameric immunoglobulin M (pIgM) across epithelia to the mucosal layer of for example the intestines and the lungs via transcytosis. Per day the human pIgR mediates the excretion of 2 to 5 grams of dIgA into the mucosa of luminal organs. This system could prove useful for therapies aiming at excretion of compounds into the mucosa. Here we investigated the use of the variable domain of camelid derived heavy chain only antibodies, also known as VHHs or Nanobodies®, targeting the human pIgR, as a transport system across epithelial cells. We show that VHHs directed against the human pIgR are able to bind the receptor with high affinity (∼1 nM) and that they compete with the natural ligand, dIgA. In a transcytosis assay both native and phage-bound VHH were only able to get across polarized MDCK cells that express the human pIgR gene in a basolateral to apical fashion. Indicating that the VHHs are able to translocate across epithelia and to take along large particles of cargo. Furthermore, by making multivalent VHHs we were able to enhance the transport of the compounds both in a MDCK-hpIgR and Caco-2 cell system, probably by inducing receptor clustering. These results show that VHHs can be used as a carrier system to exploit the human pIgR transcytotic system and that multivalent compounds are able to significantly enhance the transport across epithelial monolayers.

Nanobodies® specific for respiratory syncytial virus fusion protein protect against infection by inhibition of fusion

Despite the medical importance of respiratory syncytial virus (RSV) infections, there is no vaccine or therapeutic agent available. Prophylactic administration of palivizumab, a humanized monoclonal RSV fusion (F) protein-specific antibody, can protect high-risk children. Previously, we have demonstrated that RSV can be neutralized by picomolar concentrations of a camelid immunoglobulin single-variable domain that binds the RSV protein F (F-VHHb nanobodies). Here, we investigated the mechanism by which these nanobodies neutralize RSV and tested their antiviral activity in vivo. We demonstrate that bivalent RSV F-specific nanobodies neutralize RSV infection by inhibiting fusion without affecting viral attachment. The ability of RSV F-specific nanobodies to protect against RSV infection was investigated in vivo. Intranasal administration of bivalent RSV F-specific nanobodies protected BALB/c mice from RSV infection, and associated pulmonary inflammation. Moreover, therapeutic treatment with these nanobodies after RSV infection could reduce viral replication and reduced pulmonary inflammation. Thus, nanobodies are promising therapeutic molecules for treatment of RSV.

Llama-derived single domain antibodies to build multivalent, superpotent and broadened neutralizing anti-viral molecules

For efficient prevention of viral infections and cross protection, simultaneous targeting of multiple viral epitopes is a powerful strategy. Llama heavy chain antibody fragments (VHH) against the trimeric envelope proteins of Respiratory Syncytial Virus (Fusion protein), Rabies virus (Glycoprotein) and H5N1 Influenza (Hemagglutinin 5) were selected from llama derived immune libraries by phage display. Neutralizing VHH recognizing different epitopes in the receptor binding sites on the spikes with affinities in the low nanomolar range were identified for all the three viruses by viral neutralization assays. By fusion of VHH with variable linker lengths, multimeric constructs were made that improved neutralization potencies up to 4,000-fold for RSV, 1,500-fold for Rabies virus and 75-fold for Influenza H5N1. The potencies of the VHH constructs were similar or better than best performing monoclonal antibodies. The cross protection capacity against different viral strains was also improved for all three viruses, both by multivalent (two or three identical VHH) and biparatopic (two different VHH) constructs. By combining a VHH neutralizing RSV subtype A, but not subtype B with a poorly neutralizing VHH with high affinity for subtype B, a biparatopic construct was made with low nanomolar neutralizing potency against both subtypes. Trivalent anti-H5N1 VHH neutralized both Influenza H5N1 clade1 and 2 in a pseudotype assay and was very potent in neutralizing the NIBRG-14 Influenza H5N1 strain with IC₅₀ of 9 picomolar. Bivalent and biparatopic constructs against Rabies virus cross neutralized both 10 different Genotype 1 strains and Genotype 5.

The results show that multimerization of VHH fragments targeting multiple epitopes on a viral trimeric spike protein is a powerful tool for anti-viral therapy to achieve “best-in-class” and broader neutralization capacity.

Production, characterization and in vitro testing of HBcAg-specific VHH intrabodies

Hepatitis B virus (HBV) infections represent a global health problem, since these account for 350 million chronic infections worldwide that result in 500,000-700,000 deaths each year. Control of viral replication and HBV-related disease and mortality are of utmost importance. Because the currently available antiviral therapies all have major limitations, new strategies to treat chronic HBV infection are eagerly awaited. Six single-domain antibodies (VHHs) targeting the core antigen of HBV (HBcAg) have been generated and three of these bound strongly to HBcAg of both subtype ayw and adw. These three VHHs were studied as intrabodies directed towards the nucleus or the cytoplasm of a hepatoma cell line that was co-transfected with HBV. A speckled staining of HBcAg was observed in the cytoplasm of cells transfected with nucleotropic VHH intrabodies. Moreover, an increased intracellular accumulation of hepatitis B e antigen (HBeAg) and a complete disappearance of intracellular HBcAg signal were observed with nuclear targeted HBcAg-specific VHHs. These results suggest that HBcAg-specific VHHs targeted to the nucleus affect HBcAg and HBeAg expression and trafficking in HBV-transfected hepatocytes.

Llama-derived single-domain intrabodies inhibit secretion of hepatitis B virions in mice

Hepatitis B virus (HBV) infections cause 500,000 to 700,000 deaths per year as a consequence of chronic hepatitis, cirrhosis, and hepatocellular carcinoma. Efficient and safe antivirals to treat chronically infected patients and consequently to prevent development of hepatocellular carcinoma are still awaited. We isolated five single-domain antibodies (VHHs) that recognize the most abundant envelope protein (S) of HBV. VHHs, when expressed and retained in the endoplasmic reticulum as intrabodies, reduced levels of secreted hepatitis B surface antigen (HBsAg) particles in a cellular HBV model. In a hydrodynamics-based HBV mouse model, these intrabodies caused a marked reduction in HBsAg concentrations and a 10- to >100-fold reduction in the concentration of HBV virions in plasma.

CONCLUSION

VHHs potently inhibited secretion of HBV virions in vivo, showing that this approach might be useful in the treatment of HBV. To our knowledge, this is the first report of intrabody-mediated inhibition of viral secretion in mammals.

Inhibition of replication of primary HIV-1 isolates in huPBL-NOD/Scid mice by antibodies from HIV-1 infected patients

Although a limited number of HIV-infected patients have broadly neutralizing antibodies, it has not been examined whether these antibodies can protect against infection with primary virus in vivo. Here we screened the plasma of 23 HIV-1-infected patients for broadly neutralizing antibodies. Purified antibodies from subjects with broad and more narrow responses were administered to huPBL-NOD/Scid mice that were subsequently challenged with primary viruses of clade A, B and CRF01_AE. Although we observed a lack of correlation between the data from the in vitro neutralization assay and the results from the passive immunization experiments, we report for the first time that antibodies from HIV-infected persons can inhibit replication of primary virus isolates in an animal model.

Expression, purification and characterization of full-length RNA-free hepatitis B core particles

The nucleocapsid or core particle of the hepatitis B virus has become one of the favourite recombinant vaccine carriers for foreign peptides, proteins and stimulatory oligonucleotides. The core protein consists of three regions: an N-terminal, a central and a C-terminal region that can accommodate the addition or insertion of the foreign sequences. The protamine-like C-terminal region that binds host RNA randomly during recombinant particle formation is often truncated. It is commonly thought that these truncations do not affect particle assembly. Recent studies have demonstrated that the C-terminal domains mediate a glycosaminoglycan-dependent attachment of nucleocapsids to the plasma membranes of host cells. This interaction might well contribute to the immunogenicity of nucleocapsids. Testing the hypothesis that full-length particles might be safer and superior for the induction of an immune response against the nucleocapsids and inserted sequences, requires the availability of purified particles. In this report, we detail a novel method for the synthesis and purification of full-length core particles essentially free of RNA from Escherichia coli.

The intraspleen huPBL NOD/SCID model to study the human HIV-specific antibody response selected in the course of natural infection

The intrasplenic injection of human peripheral blood mononuclear cells (PBMCs) into severely immune deficient NOD/SCID mice, causes a massive and transient dominant expansion of human B cells in the spleen. This permits the easy isolation of human monoclonal antibodies specific for different antigens by a Kohler and Milstein-based method. Here we studied the human HIV-specific antibody response in the circulation of mice after intrasplenic transfer of PBMC from untreated HIV-infected patients with detectable to high viral load as well as from HAART-treated and from untreated patients, who kept an undetectable viral load (the latter referred to as “natural suppressors”). Excellent B cell expansion was obtained for all PBMC. High level replication of virus was observed after transfer of PBMC of untreated viremic patients only. A strong and multispecific HIV-specific antibody response was observed after transfer of PBMC of untreated viremic patients and natural suppressors. In contrast, only a weak and pauci-specific antibody response was detected in mice reconstituted with PBMC from successfully treated patients. Based on these observations we conclude that the use of the intraspleen mouse model confirmed a) the presence of HIV-specific circulating memory B cells in untreated patients and natural suppressors; b) the nearly complete absence of circulating memory B cells in patients receiving highly active antiretroviral therapy. Using the intraspleen model we generated large numbers of immortalized B cells and isolated two anti-p24 human monoclonal antibodies. We further conclude that the intraspleen huPBL NOD/SCID model is a small animal model useful for the analysis of the antibody response against HIV found in patients.

Human hepatocytes secrete soluble CD14, a process not directly influenced by HBV and HCV infection

BACKGROUND

Chronic hepatitis B (HBV) and hepatitis C (HCV) patients have elevated plasma levels of soluble CD14 (sCD14). We examined whether human hepatocytes produce sCD14 in vivo, and whether HBV or HCV infections influence this chimeric production.

METHODS

uPA-SCID mice were transplanted with primary human hepatocytes and some animals were subsequently infected with HBV or HCV. Plasma from these mice was analyzed for the presence of human sCD14. The liver was examined via immunohistochemistry.

RESULTS

A soluble form of human CD14 could be detected in the plasma from successfully transplanted mice, while it was completely absent in non-transplanted control animals. The isoform of this human sCD14 corresponded with the most abundant isoform found in human plasma. CD14 levels in circulation were not significantly different between non-infected, HBV infected and HCV infected animals.

CONCLUSIONS

Our data indicate that human hepatocytes produce sCD14 in vivo, and that liver cells might be the major source of sCD14 in normal human plasma. In addition we demonstrate that HBV and HCV infections have no direct influence on the production of sCD14 by human hepatocytes in this chimeric model.

Immunostimulatory potential of hepatitis B nucleocapsid preparations: lipopolysaccharide contamination should not be overlooked

The nucleocapsid of hepatitis B virus (HBV) allows insertions of heterologous peptides and even complete proteins. Because of its outstanding capacity to induce B-cell, T-helper and cytotoxic T-cell responses, this structure is considered to be an important instrument for future vaccine development. Most of the evidence for the unique immunogenic qualities of nucleocapsids has been generated in mice, which are not natural hosts of HBV. Moreover, most nucleocapsid preparations used in these studies were produced in a recombinant manner in Escherichia coli. Such preparations have been shown to contain lipopolysaccharide (LPS). Not unexpectedly, it is shown here that contaminating LPS, rather than the nucleocapsid structure itself, is responsible for the activation of human antigen-presenting cells. Careful examination of the literature dealing with the immunogenicity of HBV nucleocapsids suggests that the possible presence of LPS has been largely ignored or underestimated in several studies. This raises doubts on some of the underlying mechanisms that have been proposed to explain the unique immunogenicity of the HBV nucleocapsid.

The arginine-rich carboxy-terminal domain of the hepatitis B virus core protein mediates attachment of nucleocapsids to cell-surface-expressed heparan sulfate

Binding of hepatitis B virus nucleocapsids to mouse B cells leads to production of nucleocapsid-specific antibodies, class II presentation of peptides and the generation of T helper-1 immunity. This T-cell-independent activation of B cells is thought to result from cross-linking of cell-surface immunoglobulin molecules, if these contain a specific motif in the framework region 1-complementarity determining region 1 junction. In the present study, it was observed that nucleocapsids bound to different B-cell lines, an interaction that was not dependent on cell-surface-expressed immunoglobulins. Furthermore, binding to several non-B-cell lines was observed. Capsids that lacked the carboxy-terminal protamine-like domains did not bind to cells. Treatment of nucleocapsids with ribonucleases enhanced the attachment of nucleocapsids to cells. Various soluble glycosaminoglycans inhibited attachment of nucleocapsids, while treatment of cells with heparinase I also reduced binding. These observations demonstrated that the arginine-rich protamine-like regions of the core proteins are responsible for the attachment of nucleocapsids to glycosaminoglycans expressed on the plasma membranes of cells.

A temperature-dependent inhibitory activity of serum on the capacity of Saccharomyces cerevisiae-derived hepatitis B surface antigen to bind to monocytes

Hepatitis B surface antigen, when produced in yeast (rHBsAg), is capable of binding to cells that express the lipopolysaccharide coreceptor CD14. This interaction is enhanced by a serum protein, the lipopolysaccharide binding protein (LBP). Here we report that most of the rHBsAg particles that attached to monocytes at 0 degrees C, were not endocytosed but were released back into the serum-containing binding buffer at 37 degrees C. Additionally, serum-dependent binding at 37 degrees C was weak when compared to the serum-dependent attachment at 0 degrees C. Pre-incubation at 37 degrees C of cells together with serum did not abolish binding of freshly added rHBsAg at 0 degrees C. However, pre-incubation of rHBsAg with serum at 37 degrees C reduced attachment to cells following incubation at 0 degrees C. Soluble CD14 and LBP, two serum proteins which can act as phospholipid transfer molecules, were shown not to be responsible for the inhibitory effect. Pre-incubation at 37 degrees C of rHBsAg in serum-free hepatoma cell line-conditioned media resulted in a pronounced reduction in subsequent binding to cells at 0 degrees C. These observations suggest that the temperature-dependent inhibitory effect is caused by serum factors that are probably secreted by hepatocytes.

The nucleocapsid of the hepatitis B virus: a remarkable immunogenic structure

The hepatitis B virus nucleocapsid or core antigen is extremely immunogenic during infection and after immunization. This review summarizes several features of the nucleocapsid which explain this exceptionally high immunogenicity: a unique three-dimensional folding, the presence of a region that interacts with immunoglobulins outside the classical antibody-binding site, the presence of many CD4+ T cell epitopes, and the presence of encapsidated nucleic acids. Because of these features, nucleocapsids efficiently interact and activate antigen presenting cells, especially nai;ve B cells. This leads to the generation of a dominant Th1 immunity phenotype and the secretion of high levels of IgM and IgG anti-nucleocapsid antibodies.

Soluble CD14 levels are increased and inversely correlated with the levels of hepatitis B surface antigen in chronic hepatitis B patients

Because it was observed recently that yeast-derived recombinant HBsAg interacts in a lipopolysaccharide binding protein-dependent manner with CD14 expressed on human monocytes, we investigated whether HBsAg influences the serum levels of sCD14, lipopolysaccharide binding protein and C-reactive protein in hepatitis B patients. Samples from acute and chronic hepatitis B and chronic hepatitis C patients were tested. All analytes were measured using commercial assays. HBsAg was quantified using an NIBSC titrated standard. sCD14 levels were higher in chronic hepatitis B and C patients than in healthy controls (P = 0.0006 and P < 0.0001, respectively). In chronic hepatitis B patients an inverse correlation was found between sCD14 and HBsAg (P = 0.0309). Lipopolysaccharide binding protein and C-reactive protein levels were higher in acute hepatitis B patients than in control subjects (P = 0.0217 and P = 0.0034, respectively). In chronic hepatitis B and C, sCD14 and C-reactive protein levels were higher in cirrhotic than in non-cirrhotic patients (P = 0.0072 and P = 0.0223, respectively).

A simple and rapid method to determine the zygosity of uPA-transgenic SCID mice

Successful transplantation of xenogeneic hepatocytes into uPA-transgenic SCID mice depends on the zygosity of the recipient mice. Normally, the difference between homozygous and heterozygous animals is determined via a quantitative Southern blot. We sequenced a part of the mouse genome that is eliminated upon integration of the transgene in the genome. Based on that sequence we developed a multiplex PCR that allows the unambiguous discrimination of negative, heterozygous, and homozygous uPA-transgenic SCID mice in a single day procedure. The speed of the procedure is an essential quality because transplantation of xenogeneic hepatocytes into uPA-SCID mice should be done as soon as possible after birth.

Saccharomyces cerevisiae-derived HBsAg preparations differ in their attachment to monocytes, immune-suppressive potential, and T-cell immunogenicity

Expression of the hepatitis B virus S protein results in the formation of a lipoprotein particle, the hepatitis B surface antigen (HBsAg). Such particles, produced in Saccharomyces cerevisiae, bind to the cell surface of monocytes through interaction with the lipopolysaccharide binding protein and the lipopolysaccharide receptor, CD14. This attachment is suggested to depend on the presence of charged phospholipids in the particles. In addition, such particles interfere with the lipopolysaccharide and interleukin-2-induced activation of monocytes. In the present study, it is reported that of three Saccharomyces cerevisiae-derived HBsAg preparations, two have a reduced capacity to bind to monocytes. A correlation with a reduced potential to inhibit the lipopolysaccharide-induced activation of monocytes and an increased potential to stimulate HBsAg-specific T-cell proliferation is observed. Surprisingly, differences in phospholipid content that might explain these observations, were not detected.

Viral apoptotic mimicry: an immune evasion strategy developed by the hepatitis B virus?

The co-existence of viruses and organisms for millions of years has influenced the evolution of both. Various viral strategies to enter a host and take over the control of cells to produce virus progeny have developed. Several antiviral (immune) responses have also been developed. The apoptotic death program is a conserved feature of eukaryotic cells. In multicellular organisms the binding and engulfment of apoptotic material is considered to be the end stage of the apoptotic process. Because of its importance, it seems probable that viruses have targeted this ancient removal system to suppress immune responses and to establish or maintain infection. The possibility that the hepatitis B virus has evolved such a mechanism, termed "viral apoptotic-like mimicry", is presented here.

Characterization of HLA DR13-restricted CD4(+) T cell epitopes of hepatitis B core antigen associated with self-limited, acute hepatitis B

The HLA DR13 allele has been associated with a self-limited course of hepatitis B virus infection, possibly through the induction of a more vigorous hepatitis B core antigen (HBcAg) and/or hepatitis B e antigen-specific CD4(+) T cell response. HBcAg-specific CD4(+) T cell responses were investigated in three HLA DR13-positive subjects with self-limited, acute hepatitis B. HBcAg-specific, short-term T cell lines derived from these three subjects showed a dominant recognition of HBcAg peptides spanning aa 1-20 (P1), 11-30 (P2), 41-60 (P5), 111-131 (P12) and 141-160 (P15). In order to characterize these epitopes in more detail, CD4(+) T cell clones and cell lines were generated using HBcAg. Surprisingly, 11 of 12 T cell clones examined recognized P15; one recognized P10 (aa 91-111). Of four T cell lines, two recognized P15 and two recognized P5. By peptide mapping, the minimal epitope of P15 was located to residues (147)TVVRRRGRSP(156).

Recombinant HBsAg, an apoptotic-like lipoprotein, interferes with the LPS-induced activation of ERK-1/2 and JNK-1/2 in monocytes

Yeast expressed Hepatitis B surface antigen (rHBsAg) binds to monocytes through interaction with the LPS binding protein (LBP) and the LPS receptor CD14. Charged phospholipids of rHBsAg determine the interaction with these proteins. Although attachment of rHBsAg resembles the pro-inflammatory binding of LPS to CD14, rHBsAg does not activate monocytes and even reduces the expression of pro-inflammatory cytokines by LPS-stimulated monocytes. It is reported here that addition of rHBsAg to LPS-stimulated PBMC often results in increased secretion of IL-10, suggesting a similarity between the interaction of monocytes with apoptotic cells and rHBsAg. Using THP-1 cells, it is shown that IL-10 is not necessary to reduce TNFalpha protein levels. Addition of rHBsAg to LPS-stimulated cells reduces TNFalpha mRNA levels, but does not affect phosphorylation of p65 NF-kappaB and p38 MAP kinase. Instead, a reduced phosphorylation of ERK-1/2 and JNK-1/2 MAP kinases is observed.

LPS-binding protein and CD14-dependent attachment of hepatitis B surface antigen to monocytes is determined by the phospholipid moiety of the particles

It was observed recently that recombinant yeast-derived hepatitis B surface antigen (rHBsAg) particles, which contain the S protein only, bind almost exclusively to monocytes. It is shown here that binding requires the presence of the LPS receptor CD14. Furthermore, evidence is presented that a domain on CD14 that is identical to or largely overlaps with the LPS-binding pocket is instrumental for the attachment of rHBsAg. Additionally, it is shown that the heat-labile LPS-binding protein (LBP) catalyses the binding of rHBsAg to the cells. Remarkably, natural plasma-derived HBsAg (pHBsAg) does not have this property. pHBsAg devoid of its lipids and reconstituted with phosphatidylserine or phosphatidylglycerol acquires the characteristic of yeast-derived HBsAg. Clearly, the interaction of rHBsAg with the cell membrane is determined by the presence of charged phospholipids that are absent in pHBsAg. Although a lipid-receptor interaction is suggested, antibody-inhibition experiments suggest a possible involvement of the C-terminal region of the S protein in the interaction with monocytes. The possible implications of these observations for hepatitis B virus (HBV) infection and HBV vaccine efficiency are discussed.

Hepatitis B virus surface antigen suppresses the activation of monocytes through interaction with a serum protein and a monocyte-specific receptor

During hepatitis B virus (HBV) infection, high numbers of non-infectious HBV surface antigen (HBsAg) particles are present in circulation. It is shown here that recombinant HBsAg (rHBsAg) particles, which contain the S protein only, bind almost exclusively to monocytes. Attachment of rHBsAg to the THP-1 pre-monocytic cell line occurs upon 1,25-dihydroxyvitamin D3-induced differentiation. Binding to monocytes is enhanced by a heat-labile serum protein and is inhibited by Ca(2+)/Mg(2+), low pH and an HBsAg-specific monoclonal antibody. Furthermore, it is shown that rHBsAg suppresses lipopolysaccharide- and IL-2-induced production of cytokines. These results suggest the existence of a monocyte-specific receptor, the engagement of which by HBsAg suppresses the activity of these cells.

Prevention of hepatitis B infections: vaccination and its limitations

Infection with hepatitis B virus has become a vaccine-preventable disease. The recombinant hepatitis B vaccines available today are safe and immunogenic. In order for these vaccines to eradicate HBV a universal vaccination of neonates and/or children needs to be implemented. Major obstacles on the road to global hepatitis B vaccination are poverty and scarcity of human resources in those parts of the world who are most badly in need of these vaccines. Despite their proven immunogenicity hepatitis B vaccines are unable to induce an adequate immune response in 5-10% of healthy adults. The non-responsiveness of these subjects is a selective phenomenon and not the expression of a general immune deficiency. Studies that correlated the HLA haplotype of vaccine recipients with their anti-HBs response patterns has led to the identification of markers of good and non/poor response. Universal vaccination of neonates and children has elicited questions about the durability of antibody persistence and the need for booster doses later in life. The European Consensus Group on Hepatitis B Immunity has proposed a series of recommendations that are summarized in this review.

Hepatitis B virus core antigen binds and activates naive human B cells in vivo: studies with a human PBL-NOD/SCID mouse model

The hepatitis B virus (HBV) core (HBc) antigen (HBcAg) is a highly immunogenic subviral particle. Studies with mice have shown that HBcAg can bind and activate B cells in a T-cell-independent fashion. By using a human peripheral blood leukocyte (hu-PBL)-Nod/LtSz-Prkdc(scid)/Prkdc(scid) (NOD/SCID) mouse model, we show here that HBcAg also activates human B cells in vivo in a T-cell-independent way. HBcAg was capable of inducing the secretion of HBcAg-binding human immunoglobulin M (IgM) in naive human B cells derived from adult human and neonatal (cord blood) donors when these hu-PBL were transferred directly into the spleens of optimally conditioned NOD/SCID mice. No such responses were found in chimeric mice that were given hu-PBL plus HBV e antigen or hu-PBL plus phosphate-buffered saline. In addition, HBcAg activated purified human B cells to produce anti-HBc IgM in the chimeric mice, thus providing evidence that HBcAg behaves as a T-cell-independent antigen in humans. However, HBcAg-activated hu-PBL from naive donors were unable to switch from IgM to IgG production, even after a booster dose of HBcAg. Production of HBcAg-specific IgG could only be induced when hu-PBL from subjects who had recovered from or had an ongoing chronic HBV infection were transferred into NOD/SCID mice. Our data suggest that humans also have a population of naive B cells that can bind HBcAg and is subsequently activated to produce HBcAg-binding IgM.

A universal influenza A vaccine based on the extracellular domain of the M2 protein

The antigenic variation of influenza virus represents a major health problem. However, the extracellular domain of the minor, virus-coded M2 protein is nearly invariant in all influenza A strains. We genetically fused this M2 domain to the hepatitis B virus core (HBc) protein to create fusion gene coding for M2HBc; this gene was efficiently expressed in Escherichia coli. Intraperitoneal or intranasal administration of purified M2HBc particles to mice provided 90-100% protection against a lethal virus challenge. The protection was mediated by antibodies, as it was transferable by serum. The enhanced immunogenicity of the M2 extracellular domain exposed on HBc particles allows broad-spectrum, long-lasting protection against influenza A infections.

Protection of mice against a lethal influenza virus challenge after immunization with yeast-derived secreted influenza virus hemagglutinin

The A/Victoria/3/75 (H3N2-subtype) hemagglutinin (HA) gene was engineered for expression in Pichia pastoris as a soluble secreted molecule. The HA cDNA lacking the C-terminal transmembrane anchor-coding sequence was fused to the Saccharomyces cerevisiae alpha-mating factor secretion signal and placed under control of the methanol-inducible P. pastoris alcohol oxidase 1 (AOX1) promoter. Growth of transformants on methanol-containing medium resulted in the secretion of recombinant non-cleaved soluble hemagglutinin (HA0s). Remarkably, the pH of the induction medium had an important effect on the expression level, the highest level being obtained at pH 8.0. The gel filtration profile and the reactivity against a panel of different HA-conformation specific monoclonal antibodies indicated that HA0s was monomeric. Analysis of the N-linked glycans revealed a typical P. pastoris type of glycosylation, consisting of glycans with 10-12 glycosyl residues. Mice immunized with purified soluble hemagglutinin (HA0s) showed complete protection against a challenge with 10 LD50 of mouse-adapted homologous virus (X47), whereas all control mice succumbed. Heterologous challenge with X31 virus [A/Aichi/2/68 (H3N2-subtype)], resulted in significantly higher survival rates in the immunized group compared with the control group. These results, together with the safety, reliability and economic potential of P. pastoris, as well as the flexibility and fast adaptation of the expression system may allow development of an effective recombinant influenza vaccine.

Evaluation of recombinant A/Victoria/3/75 (H3N2) influenza neuraminidase mutants as potential broad-spectrum subunit vaccines against influenza A

Current influenza vaccines require repeated administration for long-term protection. Failure to develop broad-spectrum vaccines may be attributed to the chronic presentation of hypervariable, immunodominant epitopes displayed on the viral surface that keep the immune response somewhat fixed and limited by suppression of broadly neutralizing, low-titered antibodies. To test this hypothesis, we have attempted to dampen the immunogenicity of variable epitopes and potential immunodominant domains of the A/Victoria/3/75 (H3N2) neuraminidase by site-directed mutagenesis. The results suggest that the neuraminidase structure is extremely flexible, since many substitution combinations were tolerated, and constitute proof-of-principle that the antigenicity of this protein can be modulated to a large extent. However, mice immunized with neuraminidase mutants containing multiple amino acid substitutions showed a reduced protection rate against heterologous virus in comparison with the reference groups.

An antibody which binds to the membrane-proximal end of influenza virus haemagglutinin (H3 subtype) inhibits the low-pH-induced conformational change and cell-cell fusion but does not neutralize virus

A monoclonal antibody, LMBH6, was derived from mice which had been sequentially immunized with bromelain-cleaved haemagglutinin (BHA) from influenza virus A/Aichi/2/68, A/Victoria/3/75 and A/Philippines/2/82 (all H3N2). LMBH6 recognizes the haemagglutinin (HA) of all H3N2 influenza A strains tested, which were isolated between 1968 and 1989. HA in the low-pH-induced conformation is not recognized, and cleavage of the HA0 precursor to HA1 and HA2 is needed to obtain efficient binding. Compared to other monoclonal antibodies, binding of LMBH6 to virus and to virus-infected cells is weak, while binding to BHA is comparable. Electron microscopy demonstrates binding to the membrane proximal end of the stem structure. The antibody shows no haemagglutination-inhibition activity, but inhibits polykaryon formation and the low-pH-induced conformational change of BHA. However, LMBH6 cannot prevent infection of MDCK cells but slows the growth of virus when included in a plaque assay overlay.

pH-dependent aggregation and secretion of soluble monomeric influenza hemagglutinin

We previously reported the expression of soluble A/Victoria/3/75 (H3N2) hemagglutinin in insect cells and the molecular and immunological structure of an aggregated fraction, only observed in cell supernatant when expression was performed at low pH [23]. Here we report that besides this aggregated a monomeric and possibly a trimeric structure is detected in cell supernatant, irrespective of the pH of the medium. Evidence is presented that the aggregated fraction is generated out of monomeric HAOs molecules due to a low intracellular pH encountered during secretion.

Molecular and immunological characterization of soluble aggregated A/Victoria/3/75 (H3N2) influenza haemagglutinin expressed in insect cells

A/Victoria/3/75 (H3N2)-derived cDNA coding for a secreted haemagglutinin (HA0s) was cloned into the polyhedrin promoter-based pVL1392 transfer vector, and a recombinant baculovirus was isolated. 5 to 10 micrograms/ml of secreted HA were obtained following infection of Spodoptera frugiperda-9 cells. Gel filtration revealed the presence in the cell supernatant of immunoreactive HA molecules with varying M(r). The high M(r) fraction (aHA0s) could be purified by Matrex Cellufine Sulphate and Lentil-lectin affinity chromatography, followed by Sephacryl S300 HR gel filtration. aHA0s consisted of aggregated, non-covalently linked subunits which were not cleaved into HA1 and HA2 polypeptides; aHA0s was highly susceptible to trypsin treatment and reacted with two low pH-specific monoclonal antibodies, suggesting that a HA0s consists of monomeric subunits. When the expression medium was adjusted to pH 8.5, no aHA0s was observed, suggesting that aggregation occurred in the cells due to a low intracellular pH. Balb/c mice immunized with purified aHA0s developed high, aHA0s-specific antibody titres. Despite these high titres, almost no binding to trimeric viral HA was observed, and immunized mice were not protected against a challenge with homologous mouse-adapted X47 virus. However, when virus was subjected to low pH, resulting in a profound conformational rearrangement, strong binding was observed. Moreover, binding to the low pH-treated HA of different drift variants, isolated between 1968 and 1989, occurred.

A fairly conserved epitope on the hemagglutinin of influenza A (H3N2) virus with variable accessibility to neutralizing antibody

A monoclonal antibody LMBH5 was derived from mice which had been immunized with A/Victoria/3/75 (H3N2)-type recombinant, secreted hemagglutinin (HA), and were subsequently challenged with a potentially lethal dose of X31 [A/Aichi/2/68 (H3N2) x A/PR/8/34 (H1N1)] virus. LMBH5 reacted strongly with the native and low-pH-induced conformations of the HA of A/Aichi (X31 strain) and A/Victoria (X47 strain), but very weakly with the native structure of the HA of A/Philippines/2/82 (X79 strain) and not at all with the HA of A/Guizhou/54/89 H3 (NIB25 strain). However, the acid-induced conformations of the latter two viruses were recognized by LMBH5. The antibody prevented infection of MDCK cells with X31 and X47, whereas X79 virus was partially neutralized by LMBH5. X31 monoclonal escape variants had single amino acid substitutions (Ser 227-->Pro) near the interface. The data obtained suggest that the neutralizing LMBH5 reacts with a fairly conserved epitope of influenza A (H3N2) virus, which as a result of antigenic drift becomes inaccessible in the native state of the HA.

Recombinant secreted haemagglutinin protects mice against a lethal challenge of influenza virus

Balb/c mice were immunized with 2 x 2 micrograms of purified recombinant secreted haemagglutinin, derived from the A/Victoria/3/75 (H3N2) virus. In the first immunization, Ribi adjuvant was used, while for the booster injection a monophosphoryl lipid A/muramyl dipeptide combination was chosen. Mice immunized in this way were 90-100% protected against a challenge with 20 LD50 of mouse-adapted, homologous virus (strain X47). Bromelain-solubilized haemagglutinin gave only 70% protection under comparable conditions.