A synthetic peptide corresponding to the cleavage region of VP3 from rotavirus SA11 induces neutralizing antibodies

Conserved Binding Regions Provide the Clue for Peptide-Based Vaccine Development: A Chemical Perspective

Synthetic peptides have become invaluable biomedical research and medicinal chemistry tools for studying functional roles, i.e., binding or proteolytic activity, naturally-occurring regions’ immunogenicity in proteins and developing therapeutic agents and vaccines. Synthetic peptides can mimic protein sites; their structure and function can be easily modulated by specific amino acid replacement. They have major advantages, i.e., they are cheap, easily-produced and chemically stable, lack infectious and secondary adverse reactions and can induce immune responses via T- and B-cell epitopes. Our group has previously shown that using synthetic peptides and adopting a functional approach has led to identifying Plasmodium falciparumconserved regions binding to host cells. Conserved high activity binding peptides’ (cHABPs) physicochemical, structural and immunological characteristics have been taken into account for properly modifying and converting them into highly immunogenic, protection-inducing peptides (mHABPs) in the experimental Aotus monkey model. This article describes stereo–electron and topochemical characteristics regarding major histocompatibility complex (MHC)-mHABP-T-cell receptor (TCR) complex formation. Some mHABPs in this complex inducing long-lasting, protective immunity have been named immune protection-inducing protein structures (IMPIPS), forming the subunit components in chemically synthesized vaccines. This manuscript summarizes this particular field and adds our recent findings concerning intramolecular interactions (H-bonds or π-interactions) enabling proper IMPIPS structure as well as the peripheral flanking residues (PFR) to stabilize the MHCII-IMPIPS-TCR interaction, aimed at inducing long-lasting, protective immunological memory.

Prospects for vaccines against rotaviruses

Candidate vaccines against rotavirus-caused diarrhoea have been under development for more than ten years. Recent research has helped to identify virological and immunological parameters which are most likely to be correlates of protection from rotavirus infection and disease. Large double-blind, placebo-controlled trials in the United States and Venezuela have resulted in successful protection from severe disease and dehydration after immunisation with live-attenuated rhesus rotavirus-based monovalent and tetravalent vaccine candidates. The tetravalent vaccine is now submitted for regulatory approval in the United States. The anticipated widespread use of such a vaccine will need careful safety and effectiveness surveillance as the enormous diversity of rotavirus antigenicity may affect efficacy in different geographical regions. To proceed from licensure to reduction of disease a series of goals must be achieved: the vaccine must be recommended by major immunisation advisory committees, be financed in both the public and private sectors, be integrated into existing vaccination schedules, be promoted, find parental acceptance and achieve a high level of coverage. Copyright 1998 John Wiley & Sons, Ltd.

Studies on the single-shelled rotavirus receptor with a synthetic peptide derived from the cytoplasmic domain of NS28

The nonstructural glycoprotein NS28 of rotaviruses plays an important part in the assembly of double-shelled rotaviruses. C-terminal domains of the protein function as a receptor for single-shelled rotavirus particles at the membrane of the rough endoplasmic reticulum. In the present report we describe studies performed with a synthetic peptide corresponding to amino acid (aa) 160 to 169, the most hydrophilic C-terminal epitope of NS28. An antipeptide serum raised against this peptide demonstrated that this epitope was accessible in infected MA104 cells. Moreover, polymeric peptide was demonstrated to aggregate single-shelled rotavirus particles. This aggregation could be almost completely inhibited by preincubation with monomeric peptide. Our results clearly demonstrate that the epitope corresponding to aa 160-169 is able to bind single-shelled rotavirus particles.

The rotavirus genus

Human rotaviruses, discovered nearly 20 years ago, have been proven to be major cause of paediatric diarrhoeal disease morbidity and mortality. The clinical significance of these viruses stimulated basic studies on their biology, molecular and antigenic properties and epidemiology. General features, clinical relevance, epidemiologic pattern and laboratory diagnosis of human rotavirus infections are here reviewed.

Rotavirus vaccines and vaccination potential

The development of a successful rotavirus vaccine is a complex problem. Our review of rotavirus vaccine development shows that many challenges remain, and priorities for future studies need to be established. For example, the evaluation of administration of a vaccine with OPV or breast milk might receive less emphasis until a vaccine is made that shows clear efficacy against all virus serotypes. Samples remaining from previous trials should be analyzed to determine epitope-specific serum and coproantibody responses to clarify why only some trials were successful. Detailed evaluation of the antigenic properties of the viruses circulating and causing illness in vaccinated children also should be performed for comparisons with the vaccine strains. In future trials, sample collection should include monitoring for asymptomatic infections and cellular immune responses should be analyzed. The diversity of rotavirus serotype distribution must be monitored before, during, and after a trial in the study population and placebo recipients must be matched carefully to vaccine recipients. Epidemiologic and molecular studies should be expanded to document, or disprove, the possibility of animal to human rotavirus transmission, because, if this occurs, vaccine protection may be more difficult in those areas of the world where cohabitation with animals occurs. We also need to have an accurate assessment of the rate of protection that follows natural infections. Is it realistic to try to achieve 90% protective efficacy with a vaccine if natural infections with these enteric pathogens only provide 60% or 70% protection? Subunit vaccines should be considered to be part of vaccine strategies, especially if maternal antibody interferes with the take of live vaccines. The constraints on development of new vaccines are not likely to come from molecular biology. The challenge remains whether the biology and immunology of rotavirus infections can be understood and exploited to permit effective vaccination. Recent advances in developing small animal models for evaluation of vaccine efficacy should facilitate future vaccine development and understanding of the protective immune response(s) (Ward et al. 1990b; Conner et al. 1993).

Recognition of SV40-VP2 in the infected cell by antipeptide antibodies

Antipeptide antibodies were elicited against two synthetic peptides corresponding to amino acids 47-55 and 98-103 of the structural protein VP 2 of SV 40. The induced antibodies proved to be VP 2-specific in an immunoblot. In immunofluorescence these antibodies showed a discrete nuclear and perinuclear staining pattern. In immune electron microscopy studies the induced antibodies did not bind to major virions suggesting that VP 2 is not present at the surface of SV 40 particles.

Monoclonal antipeptide antibodies recognize epitopes upon VP4 and VP7 of simian rotavirus SA11 in infected MA104 cells

To study morphogenetic events of rotavirus SA11-infected MA104 cells with strictly defined reagents we produced monoclonal antibodies against synthetic peptides from both outer capsid proteins VP4 (aa residues 228-241: QNTRNIVPVSIVSR) and VP7 (aa residues 319-326: SAAFYYRV) of simian rotavirus SA11. Two of the selected monoclonal antibodies proved to be reactive with determinants of SA11-infected MA104 rhesus monkey kidney cells, with purified SA11 as well as with the particular peptides used for immunization. The anti-VP4 antibody had a demonstrable neutralizing titer of 200 (50% focus reduction) whereas the anti-VP7 MuMAb revealed no detectable neutralizing activity. In peptide-inhibition experiments, the corresponding peptide inhibited its MuMAb whereas the noncorresponding peptide had no effect on antibody binding to intracellular viral antigen. Localization of VP7 was preceded by VP4 as shown by immunofluorescence microscopy.

Antibody-dependent cellular cytotoxicity (ADCC) is directed against immunodominant epitopes of the envelope proteins of human immunodeficiency virus 1 (HIV-1)

In this study, epitopes of HIV envelope proteins that are involved in ADCC were identified. Peripheral blood mononuclear cells (PBMC) were obtained from adults with asymptomatic HIV infection or early symptoms of AIDS. These PBMC, which were reported to be "armed" in vivo with HIV-specific antibodies, were used as effector cells in 51Cr release assays. Target cells consisted of CD4 lymphocytes from healthy seronegative donors, coated with the IIIB strain of HIV-1 or with one of seven synthetic peptides. Cytotoxicity was detected against CD4 lymphocytes coated with HIV-1 IIIB or with the peptides env aa 507-518, corresponding to the carboxy-terminus of gp120, and env aa 597-611, corresponding to the region of the cysteine loop of gp41. The magnitude of target cell lysis was directly related to the quantity of peptide used. In contrast, target cells coated with the peptide gag aa 129-135, corresponding to the p17/p24 cleavage region of the gag precursor, were not killed. The same immunodominant regions which were involved in ADCC were recognized in enzyme-linked immunoabsorbent assays (ELISA) by the majority of 107 sera from HIV-infected adults. We conclude that the immunodominant epitopes located at the carboxy-terminus of gp120 and the cysteine loop of gp41 serve as recognition structure for antibodies, capable of mediating ADCC against HIV-infected cells.

Serotype-specific epitope(s) present on the VP8 subunit of rotavirus VP4 protein

cDNA clones representing the VP8 and VP5 subunits of VP4 of symptomatic human rotavirus strain KU (VP7 serotype 1 and VP4 serotype 1A) or DS-1 (VP7 serotype 2 and VP4 serotype 1B) or asymptomatic human rotavirus strain 1076 (VP7 serotype 2 and VP4 serotype 2) were constructed and inserted into the pGEMEX-1 plasmid and expressed in Escherichia coli. Immunization of guinea pigs with the VP8 or VP5 protein of each strain induced antibodies that neutralized the rotavirus from which the VP4 subunits were derived. In a previous study (M. Gorziglia, G. Larralde, A.Z. Kapikian, and R. M. Chanock, Proc. Natl. Acad. Sci. USA 87:7155-7159, 1990), three distinct serotypes and one subtype of VP4 outer capsid protein were identified among 17 human rotavirus strains that had previously been assigned to five distinct VP7 serotypes. The results obtained by cross-immunoprecipitation and by neutralization assay with antisera to the VP8- and VP5-expressed proteins suggest that the VP8 subunit of VP4 contains the major antigenic site(s) responsible for serotype-specific neutralization of rotavirus via VP4, whereas the VP5 subunit of VP4 is responsible for much of the cross-reactivity observed among strains that belong to different VP4 serotypes.

Operational overlapping of cross-reactive and serotype-specific neutralization epitopes on VP7 of human rotavirus serotype 3

VP7-specific neutralizing monoclonal antibodies (N-MAbs) to serotype 3 human rotavirus were produced to analyze serotype 3-specific and cross-reactive neutralization epitopes on VP7. On the basis of the reactivity patterns in neutralization tests with various human and animal strains, a total of 10 N-MAbs could be classified into four groups; five antibodies specific to serotype 3 were divided into two groups, and five antibodies consisted of two groups which are cross-reactive with strain 69 M (serotype 8) or strain WI61 (serotype 9). Seven N-MAbs showed the same reactivity patterns to the virus strains in both neutralization tests and enzyme-linked immunosorbent assay (ELISA), while three N-MAbs specific to serotype 3 in neutralization showed a cross-reactivity with the serotype 8 strain in ELISA. Neutralization-resistant mutants of serotype 3 strains P and YO were selected by the N-MAbs. Cross-neutralization tests between the mutants and the MAbs indicated the presence of two serotype-specific (S1 and S2) and three cross-reactive (C1, C2, and C3) epitope groups. S1, S2, and C3 epitope groups overlapped operationally each other, and the S1 epitope group had an overlapping with the C1 epitope group. However, C2 epitope group identified by the MAbs which neutralized serotypes 3 and 9, had no operational overlapping with any other epitope groups.

Neutralization epitopes on rotavirus SA11 4fM outer capsid proteins

The VP7 and VP4 genes of seven antigenic mutants of simian rotavirus SA11 4fM (serotype 3) selected after 39 passages in the presence of SA11 4fM hyperimmune antiserum, were sequenced. Nucleotide sequence analysis indicated the following. (i) Twice as many amino acid substitutions occurred in the VP7 protein than in VP4, which has a molecular weight twice that of VP7. (ii) Most amino acid changes that occurred clustered in six variable regions of VP7 and in two variable regions of VP4; these variable regions may represent immunodominant epitopes. (iii) Most amino acid substitutions that occurred in VP7 and VP4 of these mutants were also observed in antigenic mutants selected with neutralizing monoclonal antibodies (NMAbs); however, some amino acid substitutions occurred that were not selected for NMAbs. (iv) On VP7, some of the neutralization epitopes appeared to be interrelated because amino acid substitution in one site affected binding of specific NMAbs to other sites, while other neutralization epitopes on VP7 appeared to be independent, in that amino acid substitution in one site did not affect the binding of NMAbs to another distant site.

Polypeptide composition of rotavirus empty capsids and their possible use as a subunit vaccine

Two types of empty capsid particles that differed with respect to the presence of the two outer shell proteins were isolated from MA-104 cells infected with bovine rotavirus V1005. Three previously uncharacterized polypeptides, I, II, and III, migrating between VP2 and VP6, were detected in empty capsids but not in single- and double-shelled rotavirus particles. Peptide mapping revealed that all three proteins were related to VP2. Polypeptides I, II, and III could be generated by in vitro trypsin digestion of empty capsids not exposed to trypsin in the infection medium. Labeled polypeptides appeared in empty capsids before they were detected in intracellular single- or double-shelled rotavirus particles. Empty capsids were also observed in MA-104 cells infected with bovine rotaviruses UK and NCDV, simian rotavirus SA11, and human rotavirus KU. VP7-containing empty capsid is the minimal subunit vaccine for cows; we failed to induce a substantial neutralizing antibody increase with VP7 purified under denaturating or nondenaturating conditions or with synthetic peptides corresponding to two regions of VP7.

Priming for rotavirus neutralizing antibodies by a VP4 protein-derived synthetic peptide

In the rotavirus SA11 surface protein VP4, the trypsin cleavage sites associated with the enhancement of infectivity are flanked by two amino acid regions that are highly conserved among different rotaviruses. We have tested the ability of synthetic peptides that mimic these two regions to induce and prime for a rotavirus neutralizing antibody response in mice. After the peptide immunization schedule, both peptides induced peptide antibodies, but neither was able to induce virus antibodies, as measured by an enzyme-linked immunosorbent assay or a neutralization assay. However, when the peptide-inoculated mice were subsequently injected with intact SA11 virus, a rapid and high neutralizing antibody response was observed in mice that had previously received the peptide comprising amino acids 220 to 233 of the VP4 protein. This neutralizing activity was serotype specific; however, this peptide was also able to efficiently prime the immune system of mice for a neutralizing antibody response to the heterotypic rotavirus ST3 when the ST3 virus was used for the secondary inoculation.

Rotavirus gene structure and function

Knowledge of the structure and function of the genes and proteins of the rotaviruses has expanded rapidly. Information obtained in the last 5 years has revealed unexpected and unique molecular properties of rotavirus proteins of general interest to virologists, biochemists, and cell biologists. Rotaviruses share some features of replication with reoviruses, yet antigenic and molecular properties of the outer capsid proteins, VP4 (a protein whose cleavage is required for infectivity, possibly by mediating fusion with the cell membrane) and VP7 (a glycoprotein), show more similarities with those of other viruses such as the orthomyxoviruses, paramyxoviruses, and alphaviruses. Rotavirus morphogenesis is a unique process, during which immature subviral particles bud through the membrane of the endoplasmic reticulum (ER). During this process, transiently enveloped particles form, the outer capsid proteins are assembled onto particles, and mature particles accumulate in the lumen of the ER. Two ER-specific viral glycoproteins are involved in virus maturation, and these glycoproteins have been shown to be useful models for studying protein targeting and retention in the ER and for studying mechanisms of virus budding. New ideas and approaches to understanding how each gene functions to replicate and assemble the segmented viral genome have emerged from knowledge of the primary structure of rotavirus genes and their proteins and from knowledge of the properties of domains on individual proteins. Localization of type-specific and cross-reactive neutralizing epitopes on the outer capsid proteins is becoming increasingly useful in dissecting the protective immune response, including evaluation of vaccine trials, with the practical possibility of enhancing the production of new, more effective vaccines. Finally, future analyses with recently characterized immunologic and gene probes and new animal models can be expected to provide a basic understanding of what regulates the primary interactions of these viruses with the gastrointestinal tract and the subsequent responses of infected hosts.