Novel monoclonal antibodies that bind to wild and fixed rabies virus strains

Pseudotyped Viruses for Lyssavirus

Lyssaviruses, which belong to the family Rhabdoviridae, are enveloped and bullet-shaped ssRNA viruses with genetic diversity. All members of Lyssavirus genus are known to infect warm-blooded animals and cause the fatal disease rabies. The rabies virus (RABV) in lyssavirus is the major pathogen to cause fatal rabies. The pseudotyped RABV is constructed to study the biological functions of G protein and evaluation of anti-RABV products including vaccine-induced antisera, rabies immunoglobulins (RIG), neutralizing mAbs, and other antiviral inhibitors. In this chapter, we focus on RABV as a representative and describe the construction of RABV G protein bearing pseudotyped virus and its applications. Other non-RABV lyssaviruses are also included.

Antigenic variations of recent street rabies virus

The genetic and/or antigenic differences between street rabies virus (RABV) and vaccine strains could potentially affect effectiveness of rabies vaccines. As such, it is important to continue monitoring the glycoprotein (G) of the street isolates. All RABVG sequences in public database were retrieved and analysed. Using a pseudovirus system, we investigated 99 naturally occurring mutants for their reactivities to well-characterized neutralizing monoclonal antibodies (mAbs) and vaccine-induced antisera. A divergence in G sequences was found between vaccine strains and recent street isolates, with mutants demonstrating resistance to neutralizing mAbs and vaccine-induced antibodies. Moreover, antigenic variants were observed in a wide range of animal hosts and geographic locations, with most of them emerging since 2010. As the number of antigenic variants has increased in recent years, close monitoring on street isolates should be strengthened.

Development and evaluation of an anti-rabies virus phosphoprotein-specific monoclonal antibody for detection of rabies neutralizing antibodies using RFFIT

BACKGROUND

Rabies is a major public health problem with a fatality rate close to 100%; however, complete prevention can be achieved through pre- or post-exposure prophylaxis. The rapid fluorescent focus inhibition test (RFFIT) is one of the recommended testing methods to determine the production of neutralizing antibodies after vaccination. Here, we report the development of a new monoclonal antibody (mAb) designed to react specifically with Rabies virus (RABV) phosphoprotein (P protein), and the evaluation of its applicability to the RFFIT and its effectiveness as a diagnostic reagent for human rabies.

METHODOLOGY/PRINCIPAL FINDINGS

The mAb KGH P 16B8 was produced to target the P protein of the Korean KGH RABV strain. An indirect immunofluorescence assay (IFA) was conducted to detect various strains of RABV in various cell lines. Alexa-conjugated KGH P 16B8 (16B8-Alexa) was developed for the RFFIT. The IFA test could detect RABV up to a 1:2,500 dilution, with a detection limit comparable to that of a commercial diagnostic reagent. The sensitivity, specificity, positive predictive value, and negative predictive value of the RFFIT using 16B8-Alexa in 414 clinical specimens were 98.67%, 99.47%, 99.55%, and 98.42%, respectively. The results of the RFFIT with 16B8-Alexa were strongly correlated with those obtained using an existing commercial diagnostic reagent (r = 0.995, p<0.001).

CONCLUSIONS/SIGNIFICANCE

The mAb developed in this study shows high sensitivity and specificity, confirming its clinical utility with the RFFIT to measure the rabies neutralizing antibody titer and establish a diagnosis in human. Thus, 16B8-Alexa is expected to serve as an alternative diagnostic reagent that is widely accessible, with potentially broad applications beyond those of the RFFIT in Korea. Further studies with 16B8-Alexa should provide insight into the immunological mechanism of the P protein of Korean RABV.

Efficient generation of monoclonal antibodies against major structural proteins of rabies virus with suckling mouse brain antigen

The rabies virus is a neurotropic virus that causes fatal disease in humans and animals. However, not all commercial antibodies against rabies virus (RABV) structural proteins are generally available, and production of high-quality monoclonal antibodies (MAbs) requires high purification of virus particles and special facilities and is time-consuming. By using RABV-infected suckling mouse brain as antigens in this study, 11 hybridoma cells secreting MAbs against RABV were obtained, which showed strong reactivity with RABV-infected Vero cells in immunofluorescence assay. Among the 11 MAbs, three MAbs (1B11, 1C8, and 8H12) showed a neutralizing effect to RABV, while MAb 4B7 recognized the recombinant nucleoprotein (N) of RABV expressed in Vero cells; seven MAbs (1H3, 3H7, 4E7, 4G3, 5A10, 6C9, and 7B3) reacted specifically with phosphoprotein (P) of RABV. The MAbs developed in this study will be useful in establishing a diagnostic test and study on the interactions between RABV and its host.

Presence of cross-reactions with other viral encephalitides in the indirect fluorescent-antibody test for diagnosis of rabies

The antemortem diagnosis of rabies in humans employs techniques that require accuracy, speed, and sensitivity. A combination of histochemical analysis, in vitro virus isolation, immunological methods, and molecular amplification procedures are utilized in efforts to diagnose the disease. Modern medicine now offers potentially life-saving treatment for a disease that was considered invariably fatal once clinical signs develop. However, medical intervention efforts require a rapid and accurate diagnosis as early in the course of clinical disease as possible. Indirect fluorescent-antibody (IFA) testing on cerebrospinal fluid and serum specimens provides rapid results, but the specificity of the assay has not been well studied. Because false-positive IFA results could significantly affect patient treatment and outcomes, it is critical to understand the specificity of this assay. In this study, IFA testing was performed on 135 cerebrospinal fluid and serum specimens taken from patients with viral encephalitis or a presumed viral infection involving an agent other than rabies virus. Results indicate that false-positive results can occur in interpreting the rabies IFA test. Staining patterns morphologically similar to antirabies staining were observed in 7 of the 135 cerebrospinal fluid specimens examined. In addition, a majority of the cerebrospinal fluid specimens tested from patients with encephalitis presented immunoglobulin that bound to antigens present in the cell culture substrate. Of marked concern was the frequent presence of cross-reactive antibodies in encephalitis cases associated with West Nile and Powassan flaviviruses. Because IFA testing for rabies on human specimens may result in false-positive results, it should not be used as the sole basis for initiating antirabies treatment.

Biotechnology advances: a perspective on the diagnosis and research of Rabies Virus

Rabies is a widespread zoonotic disease responsible for approximately 55,000 human deaths/year. The direct fluorescent antibody test (DFAT) and the mouse inoculation test (MIT) used for rabies diagnosis, have high sensitivity and specificity, but are expensive and time-consuming. These disadvantages and the identification of new strains of the virus encourage the use of new techniques that are rapid, sensitive, specific and economical for the detection and research of the Rabies Virus (RABV). Real-time RT-PCR, phylogeographic analysis, proteomic assays and DNA recombinant technology have been used in research laboratories. Together, these techniques are effective on samples with low virus titers in the study of molecular epidemiology or in the identification of new disease markers, thus improving the performance of biological assays. In this context, modern advances in molecular technology are now beginning to complement more traditional approaches and promise to revolutionize the diagnosis of rabies. This brief review presents some of the recent molecular tools used for RABV analysis, with emphasis on rabies diagnosis and research.

Preparation and identification of anti-rabies virus monoclonal antibodies

To provide a foundation for the development of rapid and specific methods for the diagnosis of rabies virus infection, anti-rabies virus monoclonal antibodies were prepared and rabies virus nucleoprotein and human rabies virus vaccine strain (PV strain) were used as immunogens to immunize 6-8 week old female BALB/c mice. Spleen cells and SP2/0 myeloma cells were fused according to conventional methods: the monoclonal cell strains obtained were selected using the indirect immunofluorescence test; this was followed by preparation of monoclonal antibody ascitic fluid; and finally, systematic identification of subclass, specificity and sensitivity was carried out. Two high potency and specific monoclonal antibodies against rabies virus were obtained and named 3B12 and 4A12, with ascitic fluid titers of 1:8000 and 1:10000, respectively. Both belonged to the IgG2a subclass. These strains secrete potent, stable and specific anti-rabies virus monoclonal antibodies, which makes them well suited for the development of rabies diagnosis reagents.