Monoclonal antibodies to the glycoprotein of vesicular stomatitis virus: comparative neutralizing activity.

Nineteen independently isolated hybridomas producing monoclonal antibodies to the glycoprotein of vesicular stomatitis virus were isolated and studied for their capacity to neutralize viral infectivity. By measuring competitive binding of 125I-labeled monoclonal antibodies in a radioimmunoassay. 11 different, non-cross-reacting antigenic determinants were identified on the vesicular stomatitis virus G protein. All monoclonal antibodies reacting with determinants 1, 2, 3, and 4 resulted in viral neutralization, whereas those binding to the other seven determinants did not neutralize infectivity. The mixture of two monoclonal antibodies binding to different determinants resulted in a more rapid neutralization than either antibody alone, suggesting that different antibodies can exert a synergistic effect on viral neutralization. Kinetic experiments revealed biphasic neutralization curves similar to those expected for heterologous antibody. No evidence could be obtained to relate biphasic kinetics of viral neutralization to heterogeneous populations either of antibody molecules or of virus. The possible significance of the kinetic data with monoclonal antibodies is discussed.     

Characterization of the structural proteins of the murine coronavirus strain A59 using monoclonal antibodies

Monoclonal antibodies reacting with the A59 strain of mouse hepatitis virus (MHV-A59) were characterized and those specific to the E2 major envelope glycoprotein were studied in detail. Antibodies were tested for their ability to neutralize viral infectivity (N+ characteristic) and prevent viral-induced cell-to-cell fusion (F+ characteristic). All four possible combinations of activities reflecting E2 functions were found, i.e., N+F+, N-F-, N+F-, and N-F+. In addition, competitive binding studies with these monoclonal antibodies revealed two nonoverlapping antigenic regions. The first region, designated A, was recognized by antibodies which included each of the four functional types. Region B was identified by a single monoclonal antibody with N-F- activities. The existence of antibodies which only neutralize virus or only block viral-induced fusion implies that the structures on E2 which serve as targets for neutralization and which induce fusion are not identical. The critical determinants for neutralization and fusion must be closely related topographically on E2 since both N+F- and N-F+ antibodies recognize the same antigenic region.     

Development and characterization of monoclonal antibodies against Rift Valley fever virus nucleocapsid protein generated by DNA immunization

This paper describes the generation of monoclonal antibodies directed to immunogenic nucleoprotein N epitopes of Rift Valley fever virus (RVFV), and their application in diagnostics, both for antibody detection in competitive ELISA and for antigen capture in a sandwich ELISA. Monoclonal antibodies (mAbs) were generated after DNA immunization of Balb/c mice and characterized by Western blot, ELISA and cell immunostaining assays. At least three different immunorelevant epitopes were defined by mAb competition assays. Interestingly, two of the mAbs generated were able to distinguish between RVFV strains from Egyptian or South African lineages. These monoclonal antibodies constitute useful tools for diagnosis, especially for the detection of serum anti-RVFV antibodies from a broad range of species by means of competitive ELISA.     

Epitope mapping and characterization of the infectious hematopoietic necrosis virus glycoprotein, using fusion proteins synthesized in Escherichia coli.

A characterization of the antigenic determinants (epitopes) of the glycoprotein (G) of infectious hematopoietic necrosis virus was made by expressing different regions of the G gene in Escherichia coli. A cDNA copy of the G gene was divided into four fragments by TaqI digestion, and the fragments were subcloned into pATH vectors, placing the expression of each G gene fragment under control of the trpE promoter. The resulting plasmids, pXL2, pXL3, and pXL7, encoded trpE-G fusion proteins subsequently detected with anti-infectious hematopoietic necrosis virus sera by Western immunoblots. A comparison of reactivities of the fusion proteins encoded by these plasmids was made by Western immunoblot and radioimmunoassay with a number of anti-G specific monoclonal antibodies (MAbs). The nonneutralizing MAb 136J reacted with the trpE-G fusion protein encoded by pXL3 and fusion proteins encoded by plasmids p52G and p618G, which were described in previous studies (R. D. Gilmore, Jr., H. M. Engelking, D. S. Manning, and J. C. Leong. Bio/Technology 6:295-300, 1988). Another nonneutralizing MAb, 2F, bound to the pXL3 fusion protein, and the neutralizing MAb RB/B5 recognized the pXL7 fusion protein. All fusion proteins were tested as vaccines in rainbow trout fry. Although significant protection was induced by all fusion proteins, the pXL3 fusion protein was most effective as a vaccine.     

Antigenic structure of the flavivirus envelope protein E at the molecular level, using tick-borne encephalitis virus as a model.

A model of the tick-borne encephalitis virus envelope protein E is presented that contains information on the structural organization of this flavivirus protein and correlates epitopes and antigenic domains to defined sequence elements. It thus reveals details of the structural and functional characteristics of the corresponding protein domains. The localization of three antigenic domains (composed of 16 distinct epitopes) within the primary structure was performed by (i) amino-terminal sequencing of three immunoreactive fragments of protein E and (ii) sequencing the protein E-coding regions of seven antigenic variants of tick-borne encephalitis virus that had been selected in the presence of neutralizing monoclonal antibodies directed against the E protein. Further information about variable and conserved regions was obtained by a comparative computer analysis of flavivirus E protein amino acid sequences. The search for potential T-cell determinants revealed at least one sequence compatible with an amphipathic alpha-helix which is conserved in all flaviviruses sequenced so far. By combining these data with those on the location of disulfide bridges (T. Nowak and G. Wengler, Virology 156:127-137, 1987) and the structural characteristics of epitopes, such as dependency on conformation or on intact disulfide bridges or both, a model was established that goes beyond the location of epitopes in the primary sequence and reveals features of the folding of the polypeptide chain, including the generation of discontinuous protein domains.     

Antigenic properties and cellular localization of herpes simplex virus glycoprotein H synthesized in a mammalian cell expression system.

Herpes simplex virus type 1 glycoprotein H (HSV-1 gH) was synthesized in an inducible mammalian cell expression system, and its properties were examined. The gH coding sequence, together with the stable 5' untranslated leader sequence from xenopus beta-globin, was placed under control of the strong promoter from the human cytomegalovirus major immediate-early gene in an amplifiable plasmid which contains the simian virus 40 (SV40) virus origin for replication (ori). This expression vector was transfected into ts COS cells constitutively expressing a temperature-sensitive SV40 T antigen which allows utilization of the SV40 ori at permissive temperatures. The results of transient expression assays at the permissive temperature showed that HSV-1 gH could be synthesized in greater amounts than those produced by a high-multiplicity virus infection. The proteins produced were detected in Western blots (immunoblots) with a HSV-1 gH-specific polyclonal serum raised against a TrpE-gH fusion protein. The transfected gH had an apparent molecular weight of approximately 105,000, intermediate in size to those of the precursor (100,000) and fully processed forms (110,000) of HSV-1 gH from infections. Antigenicity was investigated by reactions with three virus-neutralizing monoclonal antibodies specific for conformational epitopes on gH. Only one of these monoclonal antibodies could immunoprecipitate the synthesized gH. However, equal recognition of the transfected gH was achieved by superinfection with virus. In addition, detectable amounts of gH were not expressed on the cell surface unless the cells were superinfected with virus. Studies with a temperature-sensitive mutant, ts1201, defective in encapsidation showed that the changes in antigenic structure and cell surface expression caused by superinfection with virus were not due simply to incorporation of gH into virions. These results suggest that gH requires additional virus gene products for cell surface localization and formation of an antigenic structure important for its function in mediating infectivity.     

Monoclonal antibody-defined epitope map of expressed rubella virus protein domains.

An expanded library of murine monoclonal antibodies (MAbs) was generated by infecting BALB/C mice with the Therien strain of rubella virus (RV) and selecting secreting hybrids by enzyme-linked immunosorbent assay (ELISA) using purified virion targets. A panel of plasmids containing specified RV cDNA fragments was also constructed by using a variety of strategies with pGE374- and pGE374-derived expression vectors. Hybrid RecA-RV-beta-galactosidase (LacZ)- or RecA-RV-truncated LacZ-containing proteins collectively representing the entire open reading frame of the structural proteins of RV were overexpressed in Escherichia coli. Bacterial lysates were then probed by ELISA with selected MAbs and by immunoblot following separation by electrophoresis under denaturing conditions. With this approach, MAbs that appeared to react with linear determinants defined epitopes localized within the following domains: MAbs C-1, C-2, and C-8 bind epitopes within the predicted amino-terminal 21 amino acids of the capsid region C9 to C29; MAb C-9 binds to a domain bounded by C64 and C97; MAbs E2-1 through E2-6 bind to the E2 glycoprotein backbone region from E2(1) to E2(115); MAbs E1-18 and E1-20 bind to the E1 glycoprotein region from E1(202) to E1(283). MAb E1-18 neutralizes RV infectivity; MAb E1-20 neutralizes infectivity and modestly inhibits hemagglutination. Analyses with selected synthetic peptides have confirmed several of the molecular domains deduced with the expressed proteins. These plasmid constructions and peptides have proven useful in beginning to unravel the molecular organization of several antigenic sites of this human pathogen.     

Identification of amino acids recognized by syncytium-inhibiting and neutralizing monoclonal antibodies to the human parainfluenza type 3 virus fusion protein.

Neutralizing monoclonal antibodies specific for the fusion (F) glycoprotein of human parainfluenza type 3 virus (PIV3) were used to select neutralization-resistant antigenic variants. Sequence analysis of the F genes of the variants indicated that their resistance to antibody binding, antibody-mediated neutralization or to both was a result of specific amino acid substitutions within the neutralization epitopes of the F1 and F2 subunits. Comparison of the locations of PIV3 neutralization epitopes with those of Newcastle disease and Sendai viruses indicated that the antigenic organization of the fusion proteins of paramyxoviruses is similar. Furthermore, some of the PIV3 epitopes recognized by syncytium-inhibiting monoclonal antibodies are located in an F1 cysteine cluster region which corresponds to an area of the measles virus F protein involved in fusion activity.     

Development and characterization of monoclonal antibodies against Rift Valley fever virus nucleocapsid protein generated by DNA immunization

This paper describes the generation of monoclonal antibodies directed to immunogenic nucleoprotein N epitopes of Rift Valley fever virus (RVFV), and their application in diagnostics, both for antibody detection in competitive eLISA and for antigen capture in a sandwich eLISA. Monoclonal antibodies (mAbs) were generated after DNA immunization of Balb/c mice and characterized by western blot, ELISA and cell immunostaining assays. At least three different immunorelevant epitopes were defined by mAb competition assays. Interestingly, two of the mAbs generated were able to distinguish between RVFV strains from egyptian or South African lineages. these monoclonal antibodies constitute useful tools for diagnosis, especially for the detection of serum anti-RVFV antibodies from a broad range of species by means of competitive ELISA.Key words: RVF, nucleoprotein, competitive ELISA, RVFV lineages     

Inactivation of retroviruses with preservation of structural integrity by targeting the hydrophobic domain of the viral envelope

We describe a new approach for the preparation of inactivated retroviruses for vaccine application. The lipid domain of the viral envelope was selectively targeted to inactivate proteins and lipids therein and block fusion of the virus with the target cell membrane. In this way, complete elimination of the infectivity of human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) could be achieved with preservation of antigenic determinants on the surface of the viral envelope. Inactivation was accomplished by modification of proteins and lipids in the viral envelope using the hydrophobic photoinduced alkylating probe 1,5 iodonaphthylazide (INA). Treatment of HIV and SIV isolates with INA plus light completely blocked fusion of the viral envelope and abolished infectivity. The inactivated virus remained structurally unchanged, with no detectable loss of viral proteins. Modifications to envelope and nucleocapsid proteins were detected by changes in their elution pattern on reverse-phase high-performance liquid chromatography. These modifications had no effect on primary and secondary structure epitopes as determined by monoclonal antibodies. Likewise, the inactivated HIV reacted as well as the live virus with the conformation-sensitive and broadly neutralizing anti-HIV type 1 monoclonal antibodies 2G12, b12, and 4E10. Targeting the lipid domain of biological membranes with hydrophobic alkylating compounds could be used as a general approach for inactivation of enveloped viruses and other pathogenic microorganisms for vaccine application.     

Protective effects of glycoprotein-specific monoclonal antibodies on the course of experimental mumps virus meningoencephalitis.

Newborn Syrian hamsters were challanged with an intracerebral inoculum containing 128 50% lethal doses of the Kilham strain of mumps virus and treated 24 h later with a single intraperitoneal injection of mouse monoclonal antibody. Monoclonal antibodies reactive with epitopes on the fusion glycoprotein of mumps virus could not inhibit hemagglutination or neutralize infectivity in vitro and failed to provide biologically important protection against the in vivo infection. In contrast, monoclonal antibodies reactive with epitopes on the hemagglutinin-neuraminidase glycoprotein of mumps virus inhibited hemagglutination and neutralized infectivity in vitro and protected infected animals from the otherwise lethal central nervous system virus infection. Similar protection was provided by both purified immunoglobulin and F(ab')2 fragments. Immuno-cytochemical and virological studies showed diminished virus antigen and virus titers in the brains of successfully treated animals. It appears that a topographically restricted region of the hemagglutinin-neuraminidase molecule of the Kilham strain of mumps virus is of critical importance for immune recognition by the infected host.     

Neutralization epitopes of the F glycoprotein of respiratory syncytial virus: effect of mutation upon fusion function.

Eighteen neutralizing monoclonal antibodies (MAbs) specific for the fusion glycoprotein of the A2 strain of respiratory syncytial virus (RSV) were used to construct a detailed topological and operational map of epitopes involved in neutralization and fusion. Competitive binding assays identified three nonoverlapping antigenic sites (A, B, and C) and one bridge site (AB). Thirteen MAb-resistant mutants (MARMs) were selected, and the neutralization patterns of the MAbs with either MARMs or RSV clinical strains identified a minimum of 16 epitopes. MARMs selected with antibodies to six of the site A and AB epitopes displayed a small-plaque phenotype, which is consistent with an alteration in a biologically active region of the F molecule. Analysis of MARMs also indicated that these neutralization epitopes occupy topographically distinct but conformationally interdependent regions with unique biological and immunological properties. Antigenic variation in F epitopes was examined by using 23 clinical isolates (18 subgroup A and 5 subgroup B) in cross-neutralization assays with the 18 anti-F MAbs. This analysis identified constant, variable, and hypervariable regions on the molecule and indicated that antigenic variation in the neutralization epitopes of the RSV F glycoprotein is the result of a noncumulative genetic heterogeneity. Of the 16 eptiopes, 8 were conserved on all or all but 1 of 23 subgroup A or subgroup B clinical isolates.     

Modifications of the human immunodeficiency virus envelope glycoprotein enhance immunogenicity for genetic immunization

In this study, we have investigated the effect of specific mutations in human immunodeficiency virus type 1 (HIV-1) envelope (Env) on antibody production in an effort to improve humoral immune responses to this glycoprotein by DNA vaccination. Mice were injected with plasmid expression vectors encoding HIV Env with modifications in regions that might affect this response. Elimination of conserved glycosylation sites did not substantially enhance humoral or cytotoxic-T-lymphocyte (CTL) immunity. In contrast, a modified gp140 with different COOH-terminal mutations intended to mimic a fusion intermediate and stabilize trimer formation enhanced humoral immunity without reducing the efficacy of the CTL response. This mutant, with deletions in the cleavage site, fusogenic domain, and spacing of heptad repeats 1 and 2, retained native antigenic conformational determinants as defined by binding to known monoclonal antibodies or CD4, oligomer formation, and virus neutralization in vitro. Importantly, this modified Env, gp140 Delta CFI, stimulated the antibody response to native gp160 while it retained its ability to induce a CTL response, a desirable feature for an AIDS vaccine.     

Use of simian virus 40 large T-beta-galactosidase fusion proteins in an immunochemical analysis of simian virus 40 large T antigen.

Simian virus 40 large T antigen is a multifunctional protein that is encoded by the early region of the viral genome. We constructed fusion proteins between simian virus 40 large T antigen and beta-galactosidase by cloning HindIII fragments A and D of the virus into the HindIII sites of expression vectors pUR290, pUR291, and pUR292. Large amounts of the fusion protein were synthesized when the DNA fragment encoding part of simian virus 40 large T antigen was in frame with the lacZ gene of the expression vector. Using Western blotting and a competition radioimmunoassay, we assessed the binding of existing anti-T monoclonal and polyclonal antibodies to the two fusion proteins. Several monoclonal antibodies reacted with the protein encoded by the fragment A construction, but none reacted with the protein encoded by the fragment D construction. However, mice immunized with pure beta-galactosidase-HindIII fragment D fusion protein produced good levels of anti-T antibodies, which immunoprecipitated simian virus 40 large T antigen from lytically infected cells, enabling derivation of monoclonal antibodies to this region of large T antigen. Therefore, the fusion proteins allowed novel epitopes to be discovered on large T antigen and permitted the precise localization of epitopes recognized by existing antibodies. The same approach can also be used to produce antibodies against defined regions of any gene.     

Antigenic and functional organization of human parainfluenza virus type 3 fusion glycoprotein.

Twenty-six monoclonal antibodies (MAbs) (14 neutralizing and 12 nonneutralizing) were used to examine the antigenic structure, biological properties, and natural variation of the fusion (F) glycoprotein of human type 3 parainfluenza virus (PIV3). Analysis of laboratory-selected antigenic variants and of PIV3 clinical isolates indicated that the panel of MAbs recognizes at least 20 epitopes, 14 of which participate in neutralization. Competitive binding assays indicated that the 14 neutralization epitopes are organized into three nonoverlapping antigenic sites (A, B, and C) and one bridge site (AB) and that the 6 nonneutralization epitopes form four sites (D, E, F, and G). Most of the neutralizing MAbs were involved in nonreciprocal competitive binding reactions, suggesting that they induce conformational changes in other neutralization epitopes. Fusion-inhibition and complemented-enhanced neutralization assays indicated that antigenic sites AB, B, and C may correspond to functional domains of the F molecule. Our results indicated that antibody binding alone is not sufficient for virus neutralization and that many anti-F MAbs neutralize by mechanisms not involving fusion-inhibition. The degree of antigenic variation in the F epitopes of clinical strains was examined by binding and neutralization tests. It appears that PIV3 frequently develops mutations that produce F epitopes which efficiently bind antibodies, but are completely resistant to neutralization by these antibodies.     

Monoclonal antibodies identify individual determinants on mouse mammary tumor virus glycoprotein gp52 with group, class, or type specificity

Hybrid cell lines producing monoclonal antibodies against the C3H strain of mouse mammary tumor virus (C3H MMTV) were prepared by the fusion of mouse myeloma cells with the lymphocytes of BALB/c mice that were immunized with C3H MMTV. Approximately 10% of the hybrid cells initially plated after cell fusion produced immunoglobulins that reacted in antibody-binding assays with C3H MMTV; 40 of these cells were cloned, and 6 eventually yielded stable cell lines. High concentrations of monoclonal antibodies (5 to 20 mg/ml) were obtained from serum and ascites fluid of syngeneic mice inoculated with the hybrid cells. All of the monoclonal antibodies were directed against the envelope glycoprotein gp52. Three of the hybrid cell lines produced immunoglobulins of the immunoglobulin M subclass and three produced immunoglobulin G2a. The monoclonal antibodies showed limited charge heterogeneity in light and heavy chains when analyzed by high-resolution, two-dimensional gel electrophoresis. Three serologically distinct specificities were observed when these ascites fluids were tested against different strains of MMTV. The antigenic determinants detected were the following: (i) a type-specific determinant unique to the C3H strain of MMTV; (ii) class-specific determinants shared between C3H and GR MMTVs; and (iii) a group-specific determinant found on C3H, GR, RIII, and the endogenous C3H (C3Hf) MMTVs. Because monoclonal antibodies recognize single antigenic determinants, these results demonstrate for the first time that the three patterns of antigenic reactivity for MMTV are related to individual determinants on the gp52 molecule and also clearly show that one strain of MMTV can be distinguished from other strains.     

Antigenic Structure of Human Respiratory Syncytial Virus Fusion Glycoprotein

New series of escape mutants of human respiratory syncytial virus were prepared with monoclonal antibodies specific for the fusion (F) protein. Sequence changes selected in the escape mutants identified two new antigenic sites (V and VI) recognized by neutralizing antibodies and a group-specific site (I) in the F1 chain of the F molecule. The new epitopes, and previously identified antigenic sites, were incorporated into a refined prediction of secondary-structure motifs to generate a detailed antigenic map of the F glycoprotein.