Development of a cocktail of recombinant-expressed human rabies virus-neutralizing monoclonal antibodies for postexposure prophylaxis of rabies

Expert consensus on the clinical application of ormutivimab injection for use against the rabies virus

BACKGROUND

There are no local or international guidelines or consensus on the use of mAbs against the rabies virus.

RESEARCH DESIGN AND METHODS

An expert group in the field of rabies prevention and control formulated the consensus presented in this paper.

RESULTS

Class III exposed persons to rabies for the first time; Identify type II exposed persons with immune deficiency; those who are first exposed to Class II and re-exposed to Class III within 7 days. They can use ormutivimab injection after completing the PEP wound treatment. In the case of injection restrictions or a wound that is difficult to detect, it is recommended that the entire Ormutivimab dose be infiltrated close to the wound. For severe multi-wound bites, the recommended dosage of ormutivimab is 20 IU/kg. If the recommended dose cannot meet all of the wound infiltration requirements, appropriate dilution can be conducted at a dilution ratio of 3 ~ 5 times. If the requirements for infiltration cannot be met after dilution, it is recommended that the dosage be increased with caution (maximum dosage, 40 IU/kg). The use of Ormutivimab is safe and effective without any contraindications by all age groups.

CONCLUSIONS

This consensus standardizes clinical use of Ormutivimab, improves post-exposure prophylaxis of rabies in China, reduces infection rate.

mAb therapy controls CNS-resident lyssavirus infection via a CD4 T cell-dependent mechanism

Infections with rabies virus (RABV) and related lyssaviruses are uniformly fatal once virus accesses the central nervous system (CNS) and causes disease signs. Current immunotherapies are thus focused on the early, pre-symptomatic stage of disease, with the goal of peripheral neutralization of virus to prevent CNS infection. Here, we evaluated the therapeutic efficacy of F11, an anti-lyssavirus human monoclonal antibody (mAb), on established lyssavirus infections. We show that a single dose of F11 limits viral load in the brain and reverses disease signs following infection with a lethal dose of lyssavirus, even when administered after initiation of robust virus replication in the CNS. Importantly, we found that F11-dependent neutralization is not sufficient to protect animals from mortality, and a CD4 T cell-dependent adaptive immune response is required for successful control of infection. F11 significantly changes the spectrum of leukocyte populations in the brain, and the FcRγ-binding function of F11 contributes to therapeutic efficacy. Thus, mAb therapy can drive potent neutralization-independent T cell-mediated effects, even against an established CNS infection by a lethal neurotropic virus.

Co-administration of an effector antibody enhances the half-life and therapeutic potential of RNA-encoded nanobodies

The incidence of Clostridioides difficile infection (CDI) and associated mortality have increased rapidly worldwide in recent years. Therefore, it is critical to develop new therapies for CDI. Here we report on the development of mRNA-LNPs encoding camelid-derived VHH-based neutralizing agents (VNAs) targeting toxins A and/or B of C. difficile. In preclinical models, intravenous administration of the mRNA-LNPs provided serum VNA levels sufficient to confer protection of mice against severe disease progression following toxin challenge. Furthermore, we employed an mRNA-LNP encoded effector antibody, a molecular tool designed to specifically bind an epitopic tag linked to the VNAs, to prolong VNA serum half-life. Co-administration of VNA-encoding mRNA-LNPs and an effector antibody, either provided as recombinant protein or encoded by mRNA-LNP, increased serum VNA half-life in mice and in gnotobiotic piglets. Prolonged serum half-life was associated with higher concentrations of serum VNA and enhanced prophylactic protection of mice in challenge models.

Isolation and Characterization of Cross-Reactive Human Monoclonal Antibodies That Potently Neutralize Australian Bat Lyssavirus Variants and Other Phylogroup 1 Lyssaviruses

Australian bat lyssavirus (ABLV) is a rhabdovirus that circulates in four species of pteropid bats (ABLVp) and the yellow-bellied sheath-tailed bat (ABLVs) in mainland Australia. In the three confirmed human cases of ABLV, rabies illness preceded fatality. As with rabies virus (RABV), post-exposure prophylaxis (PEP) for potential ABLV infections consists of wound cleansing, administration of the rabies vaccine and injection of rabies immunoglobulin (RIG) proximal to the wound. Despite the efficacy of PEP, the inaccessibility of human RIG (HRIG) in the developing world and the high immunogenicity of equine RIG (ERIG) has led to consideration of human monoclonal antibodies (hmAbs) as a passive immunization option that offers enhanced safety and specificity. Using a recombinant vesicular stomatitis virus (rVSV) expressing the glycoprotein (G) protein of ABLVs and phage display, we identified two hmAbs, A6 and F11, which completely neutralize ABLVs/ABLVp, and RABV at concentrations ranging from 0.39 and 6.25 µg/mL and 0.19 and 0.39 µg/mL respectively. A6 and F11 recognize overlapping epitopes in the lyssavirus G protein, effectively neutralizing phylogroup 1 lyssaviruses, while having little effect on phylogroup 2 and non-grouped diverse lyssaviruses. These results suggest that A6 and F11 could be effective therapeutic and diagnostic tools for phylogroup 1 lyssavirus infections.

mRNA mediates passive vaccination against infectious agents, toxins, and tumors

The delivery of genetic information has emerged as a valid therapeutic approach. Various reports have demonstrated that mRNA, besides its remarkable potential as vaccine, can also promote expression without inducing an adverse immune response against the encoded protein. In the current study, we set out to explore whether our technology based on chemically unmodified mRNA is suitable for passive immunization. To this end, various antibodies using different designs were expressed and characterized in vitro and in vivo in the fields of viral infections, toxin exposure, and cancer immunotherapies. Single injections of mRNA-lipid nanoparticle (LNP) were sufficient to establish rapid, strong, and long-lasting serum antibody titers in vivo, thereby enabling both prophylactic and therapeutic protection against lethal rabies infection or botulinum intoxication. Moreover, therapeutic mRNA-mediated antibody expression allowed mice to survive an otherwise lethal tumor challenge. In conclusion, the present study demonstrates the utility of formulated mRNA as a potent novel technology for passive immunization.

Comparison of rabies virus protection by single chain and leucine zipper Fv fragments cocktail derived from a monoclonal antibody cocktail

Monoclonal antibodies (MAbs) are a unique and attractive class of biologics and are potential substitutes for post-exposure rabies prophylaxis. The safety, tolerance, and broad neutralization efficiency of a MAb cocktail called CL184, composed of the antibodies CR4098 and CR57, was confirmed in a phase I clinical trial. We have prepared a series of single-chain Fv fragments (scFvs) and leucine zipper Fv fragments (zipFvs) from CR57 and CR4098. In this study, we selected and formed scFv and zipFv cocktails and compared their protective effects against the rabies virus. Mice and hamster challenge models demonstrated the improved protection of the zipFv cocktail compared with scFv cocktail, because of its stronger affinity. The results indicate that zipFv production is a promising novel method for the genetic engineering of antibody fragments and improving affinity through systematic screening may be important when designing small molecule antibodies against RV.

Transient Expression of Biologically Active Anti-rabies Virus Monoclonal Antibody in Tobacco Leaves

Background

Rabies virus is a neurotropic virus that causes fatal, but, a preventable disease in mammals. Administration of rabies immunoglobulin (RIG) is essential for the post-exposure of the prophylaxis to prevent the disease. However, replacement of polyclonal RIGs with alternative monoclonal antibodies (MAbs) that are capable of neutralizing rabies virus has been recommended.

Objectives

Here, we have investigated the transient expression of the full-size human MAb against rabies virus glycoprotein; the MAb SO57 in the tobacco plants using vacuum agro-infiltration. Previously, stably transformed plants expressing the MAb have been reported.

Materials and Methods

In this study three vectors carrying the codon-optimized genes for the heavy or light chain and p19 silencing-suppressor were constructed. These vectors were co-infiltrated into Nicotiana tabacum leaves and the transgenes were expressed.

Results

Dot blot, Western blotting, ELISA, and in vitro neutralization assays of the plant extracts showed that the human MAb could assemble in tobacco leaves and was able to neutralize rabies virus.

Conclusions

This study is the first report of transient expression of human MAb SO57 gene in tobacco plant within a few days after vacuum agro-infiltration.

Development and characterization of novel chimeric monoclonal antibodies for broad spectrum neutralization of rabies virus

Current post-exposure prophylaxis for rabies virus infection has several limitations in terms of supply, cost, safety, and efficacy. Attempts to replace human or equine rabies immune globulins (HRIG or ERIG) have been made by several companies and institutes. We developed potent monoclonal antibodies to neutralize a broad spectrum of rabies viruses by screening hybridomas received from the U.S. Centers for Disease Control and Prevention (CDC). Two kinds of chimeric human antibodies (chimeric #7 and #17) were constructed by cloning the variable regions from selected hybridomas and the constant region of a human antibody. Two antibodies were bound to antigenic site III and I/IV, respectively, and were able to neutralize 51 field isolates of rabies virus that were isolated at different times and places such as Asia, Africa, North America, South America, and Australia. These two antibodies neutralize rabies viruses with high efficacy in an in vivo test using Syrian hamster and mouse models and show low risk for adverse immunogenicity.

In Vivo Efficacy of a Cocktail of Human Monoclonal Antibodies (CL184) Against Diverse North American Bat Rabies Virus Variants

Following rabies virus (RABV) exposure, a combination of thorough wound washing, multiple-dose vaccine administration and the local infiltration of rabies immune globulin (RIG) are essential components of modern post-exposure prophylaxis (PEP). Although modern cell-culture-based rabies vaccines are increasingly used in many countries, RIG is much less available. The prohibitive cost of polyclonal serum RIG products has prompted a search for alternatives and design of anti-RABV monoclonal antibodies (MAbs) that can be manufactured on a large scale with a consistent potency and lower production costs. Robust in vitro neutralization activity has been demonstrated for the CL184 MAb cocktail, a 1:1 protein mixture of two human anti-RABV MAbs (CR57/CR4098), against a large panel of RABV isolates. In this study, we used a hamster model to evaluate the efficacy of experimental PEP against a lethal challenge. Various doses of CL184 and commercial rabies vaccine were assessed for the ability to protect against lethal infection with representatives of four distinct bat RABV lineages of public health relevance: silver-haired bat (Ln RABV); western canyon bat (Ph RABV); big brown bat (Ef-w1 RABV) and Mexican free-tailed bat RABV (Tb RABV). 42⁻100% of animals survived bat RABV infection when CL184 (in combination with the vaccine) was administered. A dose-response relationship was observed with decreasing doses of CL184 resulting in increasing mortality. Importantly, CL184 was highly effective in neutralizing and clearing Ph RABV in vivo, even though CR4098 does not neutralize this virus in vitro. By comparison, 19⁻95% survivorship was observed if human RIG (20 IU/kg) and vaccine were used following challenge with different bat viruses. Based on our results, CL184 represents an efficacious alternative for RIG. Both large-scale and lower cost production could ensure better availability and affordability of this critical life-saving biologic in rabies enzootic countries and as such, significantly contribute to the reduction of human rabies deaths globally.

Post-exposure Treatment with Anti-rabies VHH and Vaccine Significantly Improves Protection of Mice from Lethal Rabies Infection

Post-exposure prophylaxis (PEP) against rabies infection consists of a combination of passive immunisation with plasma-derived human or equine immune globulins and active immunisation with vaccine delivered shortly after exposure. Since anti-rabies immune globulins are expensive and scarce, there is a need for cheaper alternatives that can be produced more consistently. Previously, we generated potent virus-neutralising VHH, also called Nanobodies, against the rabies glycoprotein that are effectively preventing lethal disease in an in vivo mouse model. The VHH domain is the smallest antigen-binding functional fragment of camelid heavy chain-only antibodies that can be manufactured in microbial expression systems. In the current study we evaluated the efficacy of half-life extended anti-rabies VHH in combination with vaccine for PEP in an intranasal rabies infection model in mice. The PEP combination therapy of systemic anti-rabies VHH and intramuscular vaccine significantly delayed the onset of disease compared to treatment with anti-rabies VHH alone, prolonged median survival time (35 versus 14 days) and decreased mortality (60% versus 19% survival rate), when treated 24 hours after rabies virus challenge. Vaccine alone was unable to rescue mice from lethal disease. As reported also for immune globulins, some interference of anti-rabies VHH with the antigenicity of the vaccine was observed, but this did not impede the synergistic effect. Post exposure treatment with vaccine and human anti-rabies immune globulins was unable to protect mice from lethal challenge. Anti-rabies VHH and vaccine act synergistically to protect mice after rabies virus exposure, which further validates the possible use of anti-rabies VHH for rabies PEP.

Rabies is an infectious disease causing 59,000 deaths and millions are exposed each year worldwide. Post-exposure prophylaxis (PEP) against rabies consists of a combination of passive (immune globulins) and active immunisation (vaccine) directly after viral exposure. Currently used plasma-derived anti-rabies immune globulins are expensive and scarce, urging the development of alternatives. Nanobodies or VHH are the smallest antigen-binding fragments of camelid heavy chain antibodies and are easy to produce with intrinsic good thermal stability and solubility. Combined treatment with anti-rabies VHH and vaccine gave significantly better protection than either compound alone in an intranasal rabies challenge model in mice, which validates the potential use of anti-rabies VHH as replacement of immune globulins in PEP.

Plant-Derived Monoclonal Antibodies for Prevention and Treatment of Infectious Disease

Numerous monoclonal antibodies (MAbs) that recognize and neutralize infectious pathogens have been isolated and developed over the years. The fact that infectious diseases can involve large populations of infected individuals is an important factor that has motivated the search for both cost-effective and scalable methods of antibody production. The current technologies for production of antibodies in plants allow for very rapid expression and evaluation that can also be readily scaled for multikilogram production runs. In addition, recent progress in manipulating glycosylation in plant production systems has allowed for the evaluation of antibodies containing glycans that are nearly homogeneous, are mammalian in structure, and have enhanced neutralizing capabilities. Among the anti-infectious disease antibodies that have been produced in plants are included those intended for prevention or treatment of anthrax, Clostridium perfringens, Ebola virus, human immunodeficiency virus, herpes simplex virus, rabies, respiratory syncytial virus, staphylococcal enterotoxin, West Nile virus, and tooth decay. Animal and human efficacy data for these MAbs are discussed.

The clinical potential of passive immunization with therapeutic antibodies: focus on highly pathogenic avian influenza virus infection

ABSTRACT 

The H5N1 highly pathogenic avian influenza (HPAI) virus has been reported to infect humans and posing a significant pandemic threat. Although neuraminidase inhibitors are currently available for the treatment of human influenza, alternative strategies need to be developed for the treatment of H5N1 HPAI virus infection in humans due to the appearance of drug-resistant viruses. Recently, passive immunization with virus-specific monoclonal antibodies has been tested for H5N1 HPAI virus infection in animal models, providing evidence that antibody therapy may be a promising option for prophylaxis or treatment of this infectious disease. Here we discuss potential benefits and limitations of antibody therapy in clinical cases of H5N1 virus infection in humans.

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.

Met-CCL5 represents an immunotherapy strategy to ameliorate rabies virus infection

Background

Infection of rabies virus (RABV) causes central nervous system (CNS) dysfunction and results in high mortality in human and animals. However, it is still unclear whether and how CNS inflammation and immune response contribute to RABV infection.

Methods

Suckling mice were intracerebrally infected with attenuated RABV aG and CTN strains, followed by examination of chemokine or cytokine production, inflammatory cell infiltration and neuron apoptosis in the brain. Furthermore, the suckling mice and adult mice that were intracerebrally infected with aG and the adult mice that were intramuscularly infected with street RABV HN10 were treated with CCL5 antagonist (Met-CCL5) daily beginning on day 2 postinfection. The survival rates and inflammation responses in the CNS of these mice were analyzed.

Results

Excessive CCL5 in the CNS was associated with CNS dysfunction, inflammation, and macrophage or lymphocyte infiltration after attenuated or street RABV infection. Administration of exogenous CCL5 induced excessive infiltration of immune cells into the CNS and enhanced inflammatory chemokine and cytokine production. Met-CCL5 treatment significantly prolonged survival time of the suckling mice inoculated with aG and adult mice infected with aG and HN10.

Conclusions

These results suggest that CCL5 in the CNS is a key regulator involved in inducing rabies encephalomyelitis. Furthermore, treatment with the CCL5 antagonist Met-CCL5 prolongs survival time of the mice infected with attenuated or street RABVs, which might represent a novel therapeutic strategy to ameliorate RABV infection.

Engineering, expression in transgenic plants and characterisation of E559, a rabies virus-neutralising monoclonal antibody

Rabies post-exposure prophylaxis (PEP) currently comprises administration of rabies vaccine together with rabies immunoglobulin (RIG) of either equine or human origin. In the developing world, RIG preparations are expensive, often in short supply, and of variable efficacy. Therefore, we are seeking to develop a monoclonal antibody cocktail to replace RIG. Here, we describe the cloning, engineering and production in plants of a candidate monoclonal antibody (E559) for inclusion in such a cocktail. The murine constant domains of E559 were replaced with human IgG1κ constant domains and the resulting chimeric mouse-human genes were cloned into plant expression vectors for stable nuclear transformation of Nicotiana tabacum. The plant-expressed, chimeric antibody was purified and biochemically characterized, was demonstrated to neutralize rabies virus in a fluorescent antibody virus neutralization assay, and conferred protection in a hamster challenge model.

Protective efficacy of passive immunization with monoclonal antibodies in animal models of H5N1 highly pathogenic avian influenza virus infection

Highly pathogenic avian influenza (HPAI) viruses of the H5N1 subtype often cause severe pneumonia and multiple organ failure in humans, with reported case fatality rates of more than 60%. To develop a clinical antibody therapy, we generated a human-mouse chimeric monoclonal antibody (MAb) ch61 that showed strong neutralizing activity against H5N1 HPAI viruses isolated from humans and evaluated its protective potential in mouse and nonhuman primate models of H5N1 HPAI virus infections. Passive immunization with MAb ch61 one day before or after challenge with a lethal dose of the virus completely protected mice, and partial protection was achieved when mice were treated 3 days after the challenge. In a cynomolgus macaque model, reduced viral loads and partial protection against lethal infection were observed in macaques treated with MAb ch61 intravenously one and three days after challenge. Protective effects were also noted in macaques under immunosuppression. Though mutant viruses escaping from neutralization by MAb ch61 were recovered from macaques treated with this MAb alone, combined treatment with MAb ch61 and peramivir reduced the emergence of escape mutants. Our results indicate that antibody therapy might be beneficial in reducing viral loads and delaying disease progression during H5N1 HPAI virus infection in clinical cases and combined treatment with other antiviral compounds should improve the protective effects of antibody therapy against H5N1 HPAI virus infection.

The H5N1 highly pathogenic avian influenza virus has been circulating in poultry in Asia, the Middle East, and Africa since its first appearance in southern China in 1996. This virus occasionally infects humans with a high case mortality rate and poses a significant pandemic threat. Since neutralizing antibodies generally play a major role in protective immunity against influenza viruses, antibody therapy is a potential option for preventing highly lethal infection with the H5N1 virus in humans. Here we evaluated the protective potential of a human-mouse chimeric monoclonal antibody with strong neutralizing activity against H5N1 viruses in mouse and nonhuman primate models of lethal H5N1 virus infection. The therapeutic use of the neutralizing antibody resulted in reduced viral loads and improved survival in animals infected with highly pathogenic H5N1 viruses. It was noted that the protective effects were more prominent in immunosuppressed macaques, which might provide a model of protection against severe clinical disease in immunocompromised patients. In addition, combination therapy together with an antiviral drug reduced the selection of escape mutants. Collectively, this study suggests that antibody therapy may have beneficial effects in clinical cases of H5N1 HPAI virus infection in humans.

Alanine scanning of the rabies virus glycoprotein antigenic site III using recombinant rabies virus: implication for post-exposure treatment

The safety and availability of the human polyclonal sera that is currently utilized for post-exposure treatment (PET) of rabies virus (RABV) infection remain a concern. Recombinant monoclonal antibodies have been postulated as suitable alternatives by WHO. To this extent, CL184, the RABV human antibody combination comprising monoclonal antibodies (mAbs) CR57 and CR4098, has been developed and has delivered promising clinical data to support its use for RABV PET. For this fully human IgG1 cocktail, mAbs CR57 and CR4098 are produced in the PER.C6 human cell line and combined in equal amounts in the final product. During preclinical evaluation, CR57 was shown to bind to antigenic site I whereas CR4098 neutralization was influenced by a mutation of position 336 (N336) located within antigenic site III. Here, alanine scanning was used to analyze the influence of mutations within the potential binding site for CR4098, antigenic site III, in order to evaluate the possibility of mutated rabies viruses escaping neutralization. For this approach, twenty flanking amino acids (10 upstream and 10 downstream) of the RABV glycoprotein (G) asparagine (N336) were exchanged to alanine (or serine, if already alanine) by site-directed mutagenesis. Analysis of G expression revealed four of the twenty mutant Gs to be non-functional, as shown by their lack of cell surface expression, which is a requirement for the production of infectious RABV. Therefore, these mutants were excluded from further study. The remaining sixteen mutants were introduced in an infectious clone of RABV, and recombinant RABVs (rRABVs) were recovered and utilized for in vitro neutralization assays. All of the viruses were effectively neutralized by CR4098 as well as by CR57, indicating that single amino acid exchanges in this region does not affect the broad neutralizing capability of the CL184 mAb combination.

Monoclonal antibodies for prophylactic and therapeutic use against viral infections

Neutralizing antibodies play an essential part in antiviral immunity and are instrumental in preventing or modulating viral diseases. Polyclonal antibody preparations are increasingly being replaced by highly potent monoclonal antibodies (mAbs). Cocktails of mAbs and bispecific constructs can be used to simultaneously target multiple viral epitopes and to overcome issues of neutralization escape. Advances in antibody engineering have led to a large array of novel mAb formats, while deeper insight into the biology of several viruses and increasing knowledge of their neutralizing epitopes has extended the list of potential targets. In addition, progress in developing inexpensive production platforms will make antiviral mAbs more widely available and affordable.

Production, characterization, and antigen specificity of recombinant 62-71-3, a candidate monoclonal antibody for rabies prophylaxis in humans

Rabies kills many people throughout the developing world every year. The murine monoclonal antibody (mAb) 62-71-3 was recently identified for its potential application in rabies postexposure prophylaxis (PEP). The purpose here was to establish a plant-based production system for a chimeric mouse-human version of mAb 62-71-3, to characterize the recombinant antibody and investigate at a molecular level its interaction with rabies virus glycoprotein. Chimeric 62-71-3 was successfully expressed in Nicotiana benthamiana. Glycosylation was analyzed by mass spectroscopy; functionality was confirmed by antigen ELISA, as well as rabies and pseudotype virus neutralization. Epitope characterization was performed using pseudotype virus expressing mutagenized rabies glycoproteins. Purified mAb demonstrated potent viral neutralization at 500 IU/mg. A critical role for antigenic site I of the glycoprotein, as well as for two specific amino acid residues (K226 and G229) within site I, was identified with regard to mAb 62-71-3 neutralization. Pseudotype viruses expressing glycoprotein from lyssaviruses known not to be neutralized by this antibody were the controls. The results provide the molecular rationale for developing 62-71-3 mAb for rabies PEP; they also establish the basis for developing an inexpensive plant-based antibody product to benefit low-income families in developing countries.

Monoclonal antibodies for prophylactic and therapeutic use against viral infections

Neutralizing antibodies play an essential part in antiviral immunity and are instrumental in preventing or modulating viral diseases. Polyclonal antibody preparations are increasingly being replaced by highly potent monoclonal antibodies (mAbs). Cocktails of mAbs and bispecific constructs can be used to simultaneously target multiple viral epitopes and to overcome issues of neutralization escape. Advances in antibody engineering have led to a large array of novel mAb formats, while deeper insight into the biology of several viruses and increasing knowledge of their neutralizing epitopes has extended the list of potential targets. In addition, progress in developing inexpensive production platforms will make antiviral mAbs more widely available and affordable.

Passive immunity in the prevention of rabies

Prevention of clinical disease in those exposed to viral infection is an important goal of human medicine. Using rabies virus infection as an example, we discuss the advances in passive immunoprophylaxis, most notably the shift from the recommended polyclonal human or equine immunoglobulins to monoclonal antibody therapies. The first rabies-specific monoclonal antibodies are undergoing clinical trials, so passive immunisation might finally become an accessible, affordable, and routinely used part of global health practices for rabies. Coupled with an adequate supply of modern tissue-culture vaccines, replacing the less efficient and unsafe nerve-tissue-derived rabies vaccines, the burden of this disease could be substantially reduced.

A novel disulfide-stabilized single-chain variable antibody fragment against rabies virus G protein with enhanced in vivo neutralizing potency

Rabies is a fatal infectious disease requiring efficient protection provided by post-exposure prophylaxis (PEP) with rabies immunoglobulin (RIG). The single-chain Fv fragment (scFv) is a small engineered antigen binding protein derived from antibody variable heavy (V(H)) and light (V(L)) chains. This novel antibody format may potentially replace the current application of RIG to detect and neutralize rabies virus (RV). However, the broad use of scFvs is confined by their generally low stability. In this study, a scFv (FV57) was constructed based on the monoclonal antibody, MAB57, against RV. To enhance its stability and neutralizing potency, a disulfide-stabilized scFv, ds-FV57, was also derived by introduction of cysteines at V(H)44 and V(L)100. Furthermore, the cysteine at V(L)85 of ds-FV57 was mutated to serine to construct ds-FV57(VL85Ser) in order to avoid potential mis-formed disulfide bonds which would alter the affinity of the scFv. The stability and activity of all three proteins expressed in Escherichia coli were evaluated. All of the constructed scFvs could provide efficient protection against RV infection both in vivo and in vitro. However, the stability of ds-FV57(VL85Ser) was notably improved, and its in vitro neutralizing potency against RV infection was enhanced. Our findings from these stabilization modifications support the feasibility of developing scFvs for PEP treatment of rabies.

Postexposure treatment with the live-attenuated rabies virus (RV) vaccine TriGAS triggers the clearance of wild-type RV from the Central Nervous System (CNS) through the rapid induction of genes relevant to adaptive immunity in CNS tissues

Postexposure treatment (PET) of wild-type rabies virus (RV)-infected mice with a live-attenuated triple-glycoprotein RV variant (TriGAS) promotes survival but does not prevent the pathogenic RV from invading and replicating in the brain. Successful PET is associated with the induction of a robust virus-neutralizing antibody response and clearance of the wild-type RV from brain tissues. Comparison of the transcriptomes of normal mouse brain with those of wild-type-RV-infected mice that had received either mock or TriGAS PET treatment revealed that many of the host genes activated in the mock-treated mice represent type I interferon (IFN) response genes. This indicates that RV infection induces an early type I IFN response that is unable to control the infection. In contrast, most of the activated genes in the brain of the RV-infected, TriGAS-treated mouse play a role in adaptive immunity, including the regulation of T cell activation, T cell differentiation, and the regulation of lymphocyte and mononuclear cell proliferation. These findings were confirmed by quantitative PCR (qPCR) array studies, which showed that 3 genes in particular, encoding chemokine ligand 3 (Ccl3), natural killer cell activator 2 (interleukin 12B [IL-12B]), and granzyme A (GzmA), were activated earlier and to a greater extent in the brains of RV-infected mice treated with TriGAS than in the brains of mock-treated mice. The activation of these genes, known to play key roles in the regulation of lymphocyte and mononuclear cell proliferation, is likely an important part of the mechanism by which TriGAS mediates its PET activity.

Characterization of a human antibody fragment Fab and its calcium phosphate nanoparticles that inhibit rabies virus infection with vaccine

Recombinant antibody phage display technology has been used to mimic many aspects of the processes that govern the generation and selection of high-affinity natural human antibodies in the human immune system, especially for infectious disease prophylaxis. An anti-rabies virus immunized phage-display Fab library was constructed from peripheral blood lymphocytes from vaccinated volunteers. The immunized antibody library, with a diversity of 6.7×10(8), was used to select and produce antibodies that bound to rabies virus glycoprotein. After five rounds of immobilized fixed rabies virion panning, four unique DNA sequences were found in the higher binding clones, and only one, Fab094, showed neutralization activity. Fab094 components were analyzed by ELISA, immunoprecipitation and immunofluorescent staining. ELISA and immunofluorescence showed that Fab094 bound specifically to rabies virions. Immunoprecipitation and mass spectrometry showed that Fab094 reacted with rabies virus glycoprotein. To improve the penetration power of Fab094 antibodies, we developed Fab094 calcium phosphate nanoparticles (Fab094-CPNPs) and tested their efficacy. The rapid fluorescent focus inhibition test indicated that the neutralizing antibody titers of Fab094 and Fab094-CPNPs were reached at 200.17 IU/Kg and 246.12 IU/Kg, respectively. These findings were confirmed in vivo in a Kunming mouse challenge model. Our results demonstrate that human Fab094 and Fab094-CPNPs are efficacious candidate drugs to replace rabies immunoglobulin in post-exposure prophylaxis (PEP).

Generation and characterization of the human neutralizing antibody fragment Fab091 against rabies virus

AIM

To transform the human anti-rabies virus glycoprotein (anti-RABVG) single-chain variable fragment (scFv) into a Fab fragment and to analyze its immunological activity.

METHODS

The Fab gene was amplified using overlap PCR and inserted into the vector pComb3XSS. The recombinant vector was then transformed into E coli Top10F' for expression and purification. The purified Fab was characterized using SDS-PAGE, Western blotting, indirect ELISA, competitive ELISA, and the fluorescent antibody virus neutralization test (FAVN), respectively, and examined in a Kunming mouse challenge model in vivo.

RESULTS

A recombinant vector was constructed. The Fab was expressed in soluble form in E coli Top10F'. Specific binding of the Fab to rabies virus was confirmed by indirect ELISA and immunoprecipitation (IP). The neutralizing antibody titer of Fab was 10.26 IU/mL. The mouse group treated with both vaccine and human rabies immunoglobulin (HRIG)/Fab091 (32 IU/kg) showed protection against rabies, compared with the control group (P<0.05, Logrank test).

CONCLUSION

The antibody fragment Fab was shown to be a neutralizing antibody against RABVG. It can be used together with other monoclonal antibodies for post-exposure prophylaxis of rabies virus in future studies.

Isolation and characterization of novel human monoclonal antibodies possessing neutralizing ability against rabies virus

Rabies is a fatal viral encephalitis which is transmitted by exposure to the bite of rabid animals. Human and equine rabies immunoglobulins are indispensable pharmacological agents for severe bite exposure, as is vaccine. However, several disadvantages, including limited supply, adverse reactions, and high cost, hamper their wide application in developing countries. In the present study, two novel huMabs which neutralize rabies virus were established from vaccinated hyperimmune volunteers using the Epstein-Barr virus transformation method. One MAb (No. 254), which was subclass IgG3, effectively neutralized fixed rabies viruses of CVS, ERA, HEP-Flury, and Nishigahara strains and recognized a well-conserved epitope located in antigenic site II of the rabies virus glycoprotein. No. 254 possessed 68 ng/ml of FRNT₅₀ activity against CVS, 3.7 × 10⁻⁷ M of the Kd value, and the enhancing effect of complement-dependent virolysis. In addition, No. 254 showed effective neutralization potency in vivo in the mouse challenge test. The other MAb, 4D4, was subclass IgM and showed neutralizing activity against CVS and Nishigahara strains. 4D4 recognized a novel antigenic site which is associated with the neurovirulence of rabies, a glycoprotein located between antigenic site I and VI. Both human MAbs against rabies are expected to be utilized as a tool for future post-exposure prophylaxis.

Rupprecht C. Design of future rabies biologics and antiviral drugs

In recent years, no major paradigm shifts have occurred in the utilization of new products for the prevention and control of rabies. Development of new cost-effective rabies biologics and antiviral drugs is critical in continuing to prevent and reduce disease. Current rabies vaccines are highly effective but have developed largely based on technical improvements in the vaccine industry. In the future, alternative approaches for improved vaccines, including novel avirulent rabies virus (RABV) vectors, should be pursued. Any rabies vaccine that is effective without the need for rabies immune globulin (RIG) will contribute fundamentally to disease prevention by reducing the cost and complexity of postexposure prophylaxis (PEP). The lack of high quality, affordable RIG is a continuing problem. Virus-specific monoclonal antibodies (mAbs) will soon fulfill the PEP requirement for passive immunity, currently met with RIG. Several relevant strategies for mAb production, including use of transgenic mice, humanization of mouse mAbs, and generation of human immune libraries, are underway. As a result of successful PEP and pre-exposure prophylaxis in developed countries, until recently, no significant focused efforts have been devoted to RABV-specific antiviral agents. To date, combination therapy including broad spectrum antiviral agents has been successful in only one case, and reports of antiviral activity are often conflicting. Current antiviral strategies target either the nucleoprotein or phosphoprotein, but drugs targeting the viral polymerase should be considered. Considering the lag from creation of new concepts to experimental development and clinical trials, many years will likely elapse between today's ideas and tomorrow's practices.

The state of antibody therapy

Therapeutic antibodies are widely used in the treatment of various diseases and disease conditions, including cardiovascular diseases, autoimmune disorders, malignancies, and infections. With at least 23 therapeutic agents currently in clinical use and a successful business generating large revenues, major technological advances are now in place to improve the specificity and efficacy of those antibodies already in the market and also generate new, safe and effective macromolecules for the treatment of other ailments. This review provides a summary of the current state of antibody therapy, highlights and discusses recent developments in the field of antibody-based therapeutics production, combination therapy and shows the status of some of the agents that are in clinical trial.

Quantifying antigenic relationships among the lyssaviruses

All lyssaviruses cause fatal encephalitis in mammals. There is sufficient antigenic variation within the genus to cause variable vaccine efficacy, but this variation is difficult to characterize quantitatively: sequence analysis cannot yet provide detailed antigenic information, and antigenic neutralization data have been refractory to high-resolution robust interpretation. Here, we address these issues by using state-of-the-art antigenic analyses to generate a high-resolution antigenic map of a global panel of 25 lyssaviruses. We compared the calculated antigenic distances with viral glycoprotein ectodomain sequence data. Although 67% of antigenic variation was predictable from the glycoprotein amino acid sequence, there are in some cases substantial differences between genetic and antigenic distances, thus highlighting the risk of inferring antigenic relationships solely from sequence data at this time. These differences included epidemiologically important antigenic differences between vaccine strains and wild-type rabies viruses. Further, we quantitatively assessed the antigenic relationships measured by using rabbit, mouse, and human sera, validating the use of nonhuman experimental animals as a model for determining antigenic variation in humans. The use of passive immune globulin is a crucial component of rabies postexposure prophylaxis, and here we also show that it is possible to predict the reactivity of immune globulin against divergent lyssaviruses.

Fine mapping and interaction analysis of a linear rabies virus neutralizing epitope

A novel human antibody AR16, targeting the G5 linear epitope of rabies virus glycoprotein (RVG) was shown to have promising antivirus potency. Using AR16, the minimal binding region within G5 was identified as HDFR (residues 261-264), with key residues HDF (residues 261-263) identified by alanine replacement scanning. The key HDF was highly conserved within phylogroup I Lyssaviruses but not those in phylogroup II. Using computer-aided docking and interaction models, not only the key residues (Asp30, Asp31, Tyr32, Trp53, Asn54, Glu99, Ile101, and Trp166) of AR16 that participated in the interaction with G5 were identified, the van der Waals forces that mediated the epitope-antibody interaction were also revealed. Seven out of eight presumed key residues (Asp30, Asp31, Tyr32, Trp53, Asn54, Glu99, and Ile101) were located at the variable regions of AR16 heavy chains. A novel mAb cocktail containing AR16 and CR57, has the potential to recognize non-overlapping, non-competing epitopes, and neutralize a broad range of rabies virus.

[The use of passive rabies immunotherapy: from the past to the future]

Rabies is a fatal disease transmitted by infected animals by bite, scratch, licking on broken skin or contamination of mucosis by saliva. The regimen of post-exposure prophylaxis for people not previously vaccinated, that is currently recommended by WHO, consists of a combination of wound cleaning, active immunization and passive immunization when the exposure is of category 3. Most of the products available on the market, in particular human rabies immunoglobulins, highly purified equine rabies immunoglobulins and the derived F(ab')(2) fragments, are now characterized by high potency and safety. Although the interest of passive anti-rabies immunization was first demonstrated in the first half of the 20th century, there is still an inadequate supply of these products to the target populations mostly in developing countries. Therefore, it is urgent to set-up training and information actions for healthcare personnel on the need to use passive immunotherapy and the lack of adverse effects of the related products. For the future, we hope that a scale up of production and a lower price will improve the accessibility to these products. The development of new products based on monoclonal antibodies and molecular biology, and which may be cheaper, is promising.

Development of a mouse monoclonal antibody cocktail for post-exposure rabies prophylaxis in humans

As the demand for rabies post-exposure prophylaxis (PEP) treatments has increased exponentially in recent years, the limited supply of human and equine rabies immunoglobulin (HRIG and ERIG) has failed to provide the required passive immune component in PEP in countries where canine rabies is endemic. Replacement of HRIG and ERIG with a potentially cheaper and efficacious alternative biological for treatment of rabies in humans, therefore, remains a high priority. In this study, we set out to assess a mouse monoclonal antibody (MoMAb) cocktail with the ultimate goal to develop a product at the lowest possible cost that can be used in developing countries as a replacement for RIG in PEP. Five MoMAbs, E559.9.14, 1112-1, 62-71-3, M727-5-1, and M777-16-3, were selected from available panels based on stringent criteria, such as biological activity, neutralizing potency, binding specificity, spectrum of neutralization of lyssaviruses, and history of each hybridoma. Four of these MoMAbs recognize epitopes in antigenic site II and one recognizes an epitope in antigenic site III on the rabies virus (RABV) glycoprotein, as determined by nucleotide sequence analysis of the glycoprotein gene of unique MoMAb neutralization-escape mutants. The MoMAbs were produced under Good Laboratory Practice (GLP) conditions. Unique combinations (cocktails) were prepared, using different concentrations of the MoMAbs that were capable of targeting non-overlapping epitopes of antigenic sites II and III. Blind in vitro efficacy studies showed the MoMab cocktails neutralized a broad spectrum of lyssaviruses except for lyssaviruses belonging to phylogroups II and III. In vivo, MoMAb cocktails resulted in protection as a component of PEP that was comparable to HRIG. In conclusion, all three novel combinations of MoMAbs were shown to have equal efficacy to HRIG and therefore could be considered a potentially less expensive alternative biological agent for use in PEP and prevention of rabies in humans.

Human mortality from endemic canine rabies is estimated to be 55,000 deaths per year in Africa and Asia, yet rabies remains a neglected disease throughout most of these countries. More than 99% of human rabies cases are caused by infections resulting from a dog-bite injury. In the vast majority of human exposures to rabies, patients require post-exposure prophylaxis (PEP), which includes both passive (rabies immunoglobulin, RIG) and active immunization (rabies vaccine). The number of victims requiring PEP has increased exponentially in recent years, and human and equine RIG (HRIG and ERIG) were not sufficiently available in countries where canine rabies is endemic. Rabies virus-neutralizing monoclonal antibodies (MAbs) of mouse (Mo) origin have been identified as promising alternatives to HRIG and ERIG. We have developed and assessed both in vitro and in vivo unique mouse monoclonal antibody (MoMAb) cocktails, which are highly efficacious. Three novel combinations were shown to have an equal or superior efficacy to HRIG and therefore could be considered a potentially less expensive alternative for passive prophylactic use to prevent the development of rabies in humans, particularly where needed most in developing countries.

Recombinant human monoclonal antibodies to human cytomegalovirus glycoprotein B neutralize virus in a complement-dependent manner

Human antibodies specific for HCMV are currently considered as potential anti-HCMV therapeutic agents. In this study, we used a combinatorial human antibody library to isolate and characterize complete human monoclonal antibodies that effectively neutralize HCMV in a complement-dependent manner. One hundred and six clones were isolated in two independent screens using HCMV virions and recombinant glycoprotein B, gB654, as antigens. All of the clones recognized the same molecule gB and were classified into 14 groups based on the amino acid sequence of the V(H) region. Seven representative clones from these 14 groups had a strong gB654 binding affinity by surface plasmon resonance (SPR). A pairwise binding competition analysis suggested that there were three groups based on differences in the gB recognition sites. Although Fab fragments of the seven groups showed strong affinity for gB, none of the Fab fragments neutralized HCMV infectivity in vitro. In contrast, complete human IgG(1) antibodies of at least three groups neutralized HCMV in a complement-dependent manner. These data suggest that potent therapeutic antibodies can be obtained from a human antibody library, including most of the functional antibodies that mediate humoral immunity to the selected pathogen.

Genetic delivery of an anti-RSV antibody to protect against pulmonary infection with RSV

Respiratory syncytial virus (RSV) is a common cause of severe lower respiratory tract infections. Protection against infection with RSV can be achieved by monthly administration of the humanized monoclonal antibody palivizumab. The present study analyzes if genetic delivery of a murine version of palivizumab by single administration would achieve high-level and sustained antibody expression to protect mice against pulmonary infection with RSV. A murine version of the palivizumab antibody was constructed by replacing the human sequences with sequences from the constant region of a murine IgG1 antibody, while preserving the complementarity-determining region. As a proof-of-principle to test the validity of the strategy, the coding sequence for the heavy and light chains were cloned into a replication-defective serotype 5 human adenovirus vector (AdalphaRSV). Antibody expression and specificity for RSV was confirmed by Western analysis. To determine if AdalphaRSV would mediate production of anti-RSV antibodies in vivo, 5x10(10) particle units of AdalphaRSV or a control vector without transgene (AdNull), were administered intravenously to BALB/c mice. RSV neutralizing antibodies were detected in the serum after 4 days in mice receiving AdalphaRSV but not in AdNull-infected or naive mice (p<0.05). The mice that had received AdalphaRSV had at least 5.4-fold lower RSV titers in the lung 4 days following intranasal challenge with RSV compared to the AdNull or naive group (p<0.01). To evaluate long-term protection, the antibody construct was expressed in a non-human primate serotype rh.10 adeno-associated virus vector (AAVrh.10alphaRSV). RSV neutralizing antibodies were detected in serum and bronchoalveolar lavage fluid for up to 21 wk following intrapleural administration of AAVrh.10alphaRSV, but not with a control AAV vector expressing an unrelated transgene (AAVrh.10alpha1AT). Following challenge with RSV at 7 or 21 wk, 14.3-fold and 10.6-fold lower RSV titers were observed after 4 days in the lungs of mice that had received AAVrh.10alphaRSV compared to AAVrh.10alpha1AT (p<0.05). Together these data demonstrate that a gene transfer strategy for delivery of an anti-RSV antibody can generate protective immunity in mice against RSV infection in the respiratory tract and may provide an alternative to the administration of the antibody itself.

Lyssaviruses: current trends

Various technological developments have revitalized the approaches employed to study the disease of rabies. In particular, reverse genetics has facilitated the generation of novel viruses used to improve our understanding of the fundamental aspects of rabies virus (RABV) biology and pathogenicity and yielded novel constructs potentially useful as vaccines against rabies and other diseases. Other techniques such as high throughput methods to examine the impact of rabies virus infection on host cell gene expression and two hybrid systems to explore detailed protein-protein interactions also contribute substantially to our understanding of virus-host interactions. This review summarizes much of the increased knowledge about rabies that has resulted from such studies but acknowledges that this is still insufficient to allow rational attempts at curing those who present with clinical disease.

Human monoclonal antibody and vaccine approaches to prevent human rabies

Rabies, being a major zoonotic disease, significantly impacts global public health. It is invariably fatal once clinical signs are apparent. The majority of human rabies deaths occur in developing countries. India alone reports more than 50% of the global rabies deaths. Although it is a vaccine-preventable disease, effective rabies prevention in humans with category III bites requires the combined administration of rabies immunoglobulin (RIG) and vaccine. Cell culture rabies vaccines have become widely available in developing countries, virtually replacing the inferior and unsafe nerve tissue vaccines. Limitations inherent to the conventional RIG of either equine or human origin have prompted scientists to look for monoclonal antibody-based human RIG as an alternative. Fully human monoclonal antibodies have been found to be safer and equally efficacious than conventional RIG when tested in mice and hamsters. In this chapter, rabies epidemiology, reservoir control measures, post-exposure prophylaxis of human rabies, and combination therapy for rabies are discussed. Novel human monoclonal antibodies, their production, and the significance of plants as expression platforms are emphasized.

Genetically delivered antibody protects against West Nile virus

Gene-based delivery of recombinant antibody genes is a promising therapeutic strategy offering numerous advantages including sustained antibody levels, better safety profile and lower production cost. Here we describe generation of a recombinant antibody Fc-9E2 comprising a fusion protein between human Fc of IgG1 and a single-chain Fv derived from a hybridoma 9E2 secreting a mAb neutralizing West Nile virus (WNV). Fc-9E2 was shown to retain parental mAb's specificity and WNV-neutralizing capacity. Adenovirus-mediated in vivo delivery of the antibody gene resulted in sustained Fc-9E2 serum levels leading to abrogation of lethal WNV infection in an animal model.

A Human Monoclonal Antibody Cocktail as a Novel Component of Rabies Postexposure Prophylaxis*

The currently recommended treatment for individuals exposed to rabies virus is the combined administration of rabies vaccine and rabies immune globulin (RIG). This review sets out the criteria used to guide development of a cocktail of human monoclonal antibodies as a replacement for RIG. Using this process as a model, the general requirements for development of safe and efficacious monoclonal antibody alternatives to currently used polyclonal serum products are discussed.

Development of recombinant human polyclonal antibodies for the treatment of complex human diseases

Antibodies are a central factor in the immunity against invading pathogens, such as bacteria and viruses, as well as against malignantly transformed cells. Natural antibody responses are polyclonal, comprising antibodies against several epitopes, thus increasing the probability of eliminating the invading pathogen or malignant cell. The pharmacological advantage of polyclonality is exploited in the plasma-derived immunoglobulin products used at present to treat a number of infectious diseases. However, the use of plasma-derived products is limited by their cost, inconvenience of use and potential for transferring diseases from the donor to the patient. Symphogen has developed technologies to capture the advantages of antibody polyclonality while eliminating the potential safety risk associated with the sourcing of human material. Hence, the Symplex technology has been developed to identify diverse repertoires of target-specific, fully human antibodies. For the controlled manufacture of recombinant polyclonal antibody drugs, Symphogen has developed the Sympress technology. Combined, these two technologies allow the identification and industrial manufacturing of recombinant human polyclonal antibodies for medical use in humans. The authors believe that this new class of therapeutic antibodies will be advantageous in the treatment of complex human diseases, such as cancer and infection, as it allows the combination of several treatment modalities in one drug.