Vascular endothelial growth factor A polymorphism and risk of Kaposi's sarcoma herpesvirus viremia in kidney allograft recipients.

BACKGROUND: Kaposi's sarcoma herpesvirus (KSHV) causes Kaposi's sarcoma (KS), primary effusion lymphoma, and multicentric Castleman's disease in immunocompromised patients including allograft recipients. Detection of KSHV DNA in blood, as well as host genetic polymorphisms has been found to be associated with an increased risk for KS. We investigated an association between single nucleotide polymorphisms (SNPs) in vascular endothelial growth factor A (VEGFA) gene region and KSHV viremia in kidney transplant recipients (KTR) in Saudi Arabia. METHODS: In total, 152 KTR who have survived kidney transplantation for at least 6 months were included in the study. KSHV viremia was determined by real-time polymerase chain reaction (PCR). Genotyping of SNPs in the VEGFA region was performed by PCR and direct sequencing, as well as by restriction fragment length polymorphism. RESULTS: KSHV DNA was detected in 28.9% (n = 44) of the study population. The A-allele at position C172A VEGFA gene promoter region was found to be associated with KSHV viremia (odd ratio [OR] = 4.8, P = 0.005). In addition, the G-allele at position C+405G in the 5'-untranslated region was associated with KSHV viremia in women, but not in men (OR = 3.98, P = 0.004). CONCLUSIONS: Our results suggest an association of VEGFA polymorphisms with KSHV viremia among KTR in this study population. A limitation of our study is that the results can only be predicated for patients 6 months after kidney transplantation and should be validated in another cohort with larger sample size.

Seroepidemiological study of Toxoplasma gondii infection in the human population in the Eastern Region.

OBJECTIVE: Toxoplasma gondii is an an obligate intracellular protozoan parasite that causes toxoplasmosis. The infection is worldwide, particularly in warm and moist climates. Few studies have been conducted on the prevalence of subclinical or overt disease in Saudi Arabia. No population-based study was conducted or the seroprevalence of toxoplasmosis in humans in Saudi Arabia and this initiated the present study. The present study aimed at studying seroprevalence of Toxoplasma IgG and IgM antibodies in sera from 5 areas in the Eastern Region of Saudi Arabia. METHODS: A population based epidemiological approach, prevalence according to lifestyle (urban or rural), gender (male or female) occupation and age. RESULTS: Inactive toxoplasmosis (IgG levels) is of rather high prevalence in the human population in the Eastern Region of Saudi Arabia (25%). On the other hand, active toxoplasmosis (acquired during pregnancy) is of rather low prevalence in this study (5%). Active toxoplasmosis (IgM levels) is positively related to the level of exposure, high in farmers and employees in village rural areas and low in children and students in urban areas. CONCLUSION: Patients with active toxoplasmosis are to be treated and made aware of their situation. Hygienic conditions in areas of rather high prevalence of active toxoplasmosis are to be more strictly imposed to minimize transmission of the disease.

Protection against measles virus-induced encephalitis by anti-mimotope antibodies: the role of antibody affinity.

Synthetic peptides mimicking a conformational B-cell epitope (M2) of the measles virus fusion protein (MVF) were used for the immunization of BALB/c mice and the anti-peptide and anti-virus antibody titers induced were compared. Of the panel of tested peptides, a chimeric peptide consisting of two copies of a T-helper epitope (residues 288-302 of MVF) and one copy of the mimotope M2 (TTM2) and a multiple antigen peptide with eight copies of M2 (MAP-M2) induced the highest titers of anti-M2 and anti-MV antibodies. Furthermore, peptides TTM2 and MAP-M2 induced antibodies with highest affinity for the mimotope and highest avidity for measles virus. Immunization with the MAP-M2 construct induced high titers of high-affinity anti-M2 antibody despite the absence of a T-helper epitope, and lymphocyte proliferation data suggest that the addition of M2 to the MAP resulted in the generation of a structure capable of stimulating T-cell help. Sera with anti-M2 reactivity were pooled according to affinity values for binding to M2, and high- and low-affinity pools were tested for their ability to prevent MV-induced encephalitis in a mouse model. The high-affinity serum pool conferred protection in 100% of mice, whereas the lower affinity pool conferred protection to only 50% of animals. These results indicate the potential of mimotopes for use as synthetic peptide immunogens and highlight the importance of designing vaccines to induce antibodies of high affinity.

CTL epitopes identified with a defective recombinant adenovirus expressing measles virus nucleoprotein and evaluation of their protective capacity in mice.

Cytotoxic T-lymphocyte (CTL) responses to measles virus (MV) play an important role in recovery from infection, with one of the major target proteins for CTL activity being the nucleoprotein (Np). In this report, a replication-deficient adenovirus-5 recombinant, expressing for MV Np (Rad68) was tested for in vivo priming of MV Np-specific CTL responses in BALB/c and CBA mice. In both strains of mice strong Np-specific CTL responses were induced and these responses were shown to be MHC class I restricted. Using overlapping 15mer peptides spanning residues 1-505 of MV Np a single epitope comprising residues 281-295 was identified in BALB/c mice whereas, in CBA mice two epitopes comprising residues 51-65 and 81-95, were identified. These epitopes were found to contain class I motifs for H-2L(d) and H-2K(k) MHC molecules, respectively. Immunization of BALB/c and CBA mice with the respective CTL epitopes resulted in the in vivo induction of peptide-and MV Np-specific CTL responses. In addition, the identified H-2K(k) restricted CTL epitopes conferred some protection against encephalitis induced following intracerebral challenge with a lethal dose of canine distemper virus (the Np of which shares 70% sequence homology with MV Np). These findings highlight the potential of using well-defined CTL epitopes to control virus infection.

Synergistic effect of immunization with a peptide cocktail inducing antibody, helper and cytotoxic T-cell responses on protection against respiratory syncytial virus.

Respiratory syncytial virus (RSV)-specific cytotoxic T lymphocytes (CTL) or neutralizing antibodies can protect against RSV infection when induced separately by immunization with synthetic peptides. In the work described here, RSV-specific neutralizing antibodies and CTLs were induced after immunization with a cocktail of peptides consisting of a B-cell mimotope (S1S-MAP), a T-helper epitope (SH:45-60) and a CTL epitope linked to a fusion (F) peptide (F/M2:81-95) that were comparable to those induced by the peptides alone. Following challenge, a 190-fold reduction in RSV titre was observed in the lungs of peptide cocktail-immunized mice. The combination of RSV-specific humoral and cellular immunity induced by the peptide cocktail was thus more effective at clearing RSV than peptide-induced humoral or cellular immunity alone.

Protective cytotoxic T lymphocyte responses against paramyxoviruses induced by epitope-based DNA vaccines: involvement of IFN-gamma.

Plasmid DNA vectors have been constructed with minigenes encoding a single cytotoxic T lymphocyte (CTL) epitope from either the M2 protein of respiratory syncytial virus (RSV) or from the nucleoprotein of measles virus (MV) with or without a signal sequence (also called secretory or leader sequence). Following intradermal immunization, plasmids in which the CTL epitopes were expressed in-frame with the signal sequence were more effective at inducing peptide- and virus-specific CTL responses than plasmids expressing CTL epitopes without the signal sequence. This immunization resulted in protection against MV-induced encephalitis and a significant reduction in viral load following RSV challenge. The reduction of viral load following RSV challenge was abrogated by prior injection with anti-IFN-gamma antibodies. These results highlight the ability of epitope-based DNA immunization to induce protective immune responses to well-defined epitopes and indicate the potential of this approach for the development of vaccines against infectious diseases.

Protection against measles virus-induced encephalitis by antibodies from mice immunized intranasally with a synthetic peptide immunogen.

Balb/c mice were immunized intranasally (i.n.) with a chimeric synthetic peptide containing two copies of a T- and one copy of a B-cell epitope (TTB) from measles virus (MV) fusion protein, plus cholera toxin B (CTB) adjuvant. The antibodies induced cross-reacted with, and neutralized MV and on passive transfer, protected mice against encephalitis induced by neuroadapated MV. Immunization with TTB alone induced antibodies which increased survival but not significantly compared to controls. Furthermore, i.n. immunization with TTB plus CTB induced TTB-specific IgA antibodies in saliva and nasal washes. Co-administration of CTB increased the affinity of antibodies to the B-cell epitope of TTB and caused a relative increase in the level of anti-peptide antibodies of the IgG2a subclass and the overall titre of IgG antibodies. These results indicate the potential of the i.n. route for immunization with synthetic peptide immunogens for induction of both local and systemic anti-peptide antibody responses.

A peptide mimic of a protective epitope of respiratory syncytial virus selected from a combinatorial library induces virus-neutralizing antibodies and reduces viral load in vivo.

Respiratory syncytial virus (RSV) is the most important cause of bronchiolitis and pneumonia in infants and young children worldwide. As yet, there is no effective vaccine against RSV infection, and previous attempts to develop a formalin-inactivated vaccine resulted in exacerbated disease in recipients subsequently exposed to the virus. In the work described here, a combinatorial solid-phase peptide library was screened with a protective monoclonal antibody (MAb 19) to identify peptide mimics (mimotopes) of a conserved and conformationally-determined epitope of RSV fusion (F) protein. Two sequences identified (S1 [HWYISKPQ] and S2 [HWYDAEVL]) reacted specifically with MAb 19 when they were presented as solid-phase peptides. Furthermore, after amino acid substitution analyses, three sequences derived from S1 (S1S [HWSISKPQ], S1K [KWYISKPQ], and S1P [HPYISKPQ]), presented as multiple antigen peptides (MAPs), also showed strong reactivity with MAb 19. The affinity constants of the binding of MAb 19, determined by surface plasmon resonance analyses, were 1.19 x 10(9) and 4.93 x 10(9) M(-1) for S1 and S1S, respectively. Immunization of BALB/c mice with these mimotopes, presented as MAPs, resulted in the induction of anti-peptide antibodies that inhibited the binding of MAb 19 to RSV and neutralized viral infection in vitro, with titers equivalent to those in sera from RSV-infected animals. Following RSV challenge of S1S mimotope-immunized mice, a 98.7% reduction in the titer of virus in the lungs was observed. Furthermore, there was a greatly reduced cell infiltration in the lungs of immunized mice compared to that in controls. These results indicate the potential of peptide mimotopes to protect against RSV infection without exacerbating pulmonary pathology.

Fine specificity of the antibody response to a synthetic peptide from the fusion protein and protection against measles virus-induced encephalitis in a mouse model.

A synthetic peptide representing residues 397-420 from the measles virus (MV) fusion (F) protein was tested for its structure, immunogenicity and protective capacity against intracerebral challenge with a neuroadapted strain of MV. Analysis of the peptide by mass spectrometry showed that it was linear, despite the presence of two cysteine residues in the sequence. Circular dichroism spectroscopy highlighted a weak preference for the peptide to adopt an alpha-helical conformation. The peptide was shown to be immunogenic in BALB/c and C57BL/6 mice after intraperitoneal immunization in Freund's adjuvant, and anti-peptide antibodies from both strains of mice reacted with the MV as a solid phase antigen on an ELISA plate. When the fine specificity of the anti-peptide antibody response was examined using overlapping 8-mer peptides, serum antibodies from BALB/c mice recognized the region between residues 407-417 whereas antibodies from C57BL/6 mice recognized the region 408-420 of the 397-420 peptide sequence. Although anti-397-420 antibodies had no demonstrable neutralizing activity, protection against challenge with a neuroadapted strain of MV was demonstrated following active immunization with peptide in C57BL/6 mice or after passive transfer of anti-peptide antibodies in BALB/c mice. These findings highlight the importance of the 397-420 region in the induction of protective antibodies in the MV encephalitis mouse model, and suggest that this epitope might be a good candidate for inclusion in a future MV synthetic peptide vaccine.

Identification of an immunodominant neutralizing and protective epitope from measles virus fusion protein by using human sera from acute infection.

Polyclonal sera obtained from African children with acute measles were used to screen a panel of 15-mer overlapping peptides representing the sequence of measles virus (MV) fusion (F) protein. An immunodominant antigenic region from the F protein (p32; amino acids 388 to 402) was found to represent an amino acid sequence within the highly conserved cysteine-rich domain of the F protein of paramyxoviruses. Epitope mapping of this peptide indicated that the complete 15-amino-acid sequence was necessary for high-affinity interaction with anti-MV antibodies. Immunization of two strains of mice with the p32 peptide indicated that it was immunogenic and could induce antipeptide antibodies which cross-reacted with and neutralized MV infectivity in vitro. Moreover, passive transfer of antipeptide antibodies conferred significant protection against fatal rodent-adapted MV-induced encephalitis in susceptible mice. These results indicate that this epitope represents a candidate for inclusion in a future peptide vaccine for measles.

Peptide mimics of a conformationally constrained protective epitopes of respiratory syncytial virus fusion protein.

AIMS: To identify peptides that mimic (mimotopesi conformational and protective epitopes of RSV fusion protein and to assess their efficacy as immunogens and potential vaccines. MATERIAL AND METHODS: An 8-mer solid-phase (TG resin) library was screened with a neutralising and protective RSV fusion protein specific monoclonal antibodies (Mab-19). After selection of positive beads, reactive sequences were identified by microsequencing and 8-mer peptides were synthesised. Improvement of binding was analysed by amino acid replacement using the SPOTs method. RESULTS: Mabs were not able to bind to the free and soluble peptides, nor did these peptides induce anti-RSV specific antibodies. However, several peptides re-synthesised on a TG resin (to produce de-protected 8-mer peptides linked to the resin) or as SPOTs reacted specifically. Therefore it was critical to be able to reproduce this conformation in order to use these mimotopes as immunogens and potential vaccines. Using C-terminal constrained versions of the mimotopes, strong binding of one of the Mabs to the peptides was demonstrated by surface-plasmon resonance. Immunisation of Balb/c mice with these peptide-mimics produced anti-sera that: (1) reacted specifically with RSV; (2) inhibited the binding of the Mab to the virus; (3) neutralised RSV in vitro with high titres (range: 80-640); and (4) reduce significantly the viral load in the lungs of mice challenged with RSV (P < 0.01). CONCLUSIONS: This report demonstrates for the first time that: (1) a protective epitope of the conserved RSV fusion protein can be mimicked by synthetic peptides; and (2) immunisations with these mimotopes induced specific anti-RSV neutralising antibodies and reduced viral load in vivo. These results represent a novel concept for the development of a vaccine against RSV.

Immunological analysis of the protective responses to the chimeric synthetic peptide representing T- and B-cell epitopes from the fusion protein of measles virus.

The role of different adjuvant formulations and routes of immunization on the antibody responses and protection induced in mice was determined by a synthetic peptide representing T- and B- cell epitopes from the measles virus (MV) fusion (F) protein (TTB peptide) which has previously been shown to induce protective responses against MV encephalitis in mice. When the peptide TTB was administered in Freud's complete adjuvant (FCA), Freud's incomplete adjuvant (FIA), alum or with IL-2, anti-peptide antibody responses and anti-MV antibody responses were detected. Interestingly, immunization with TTB without adjuvant resulted in the induction of anti-peptide antibody responses which did not cross react with the MV. The use of FIA as an adjuvant led to a significantly higher IgG2a antibody response compared with FCA and alum, whereas alum led to a significantly lower IgG3 response. Immunization with TTB in FCA, FIA and alum led to the generation of high affinity antibodies (with alum generating the highest affinity), whereas immunization of peptide with IL-2 or in PBS resulted in the induction of antibodies of lower affinity. Only the FCA, FIA and alum formulations led to the induction of protective responses in mice against MV-induced encephalitis. When the subcutaneous route (s.c.) of immunization was compared with the intraperitoneal route (i.p.), s.c. immunization with the TTB peptide led to higher anti-peptide and anti-MV antibody responses and higher affinity antibodies compared to those induced following i.p. immunization. Mice receiving the TTB peptide via the s.c. route had a higher percentage survival after MV challenge than those immunized via the i.p. route. These results show that the nature of the adjuvant used as well as the route of immunization play an important role in the induction of protective anti-TTB peptide antibody responses against MV-induced encephalitis in mice.

A mimotope from a solid-phase peptide library induces a measles virus-neutralizing and protective antibody response.

A solid-phase 8-mer random combinatorial peptide library was used to generate a panel of mimotopes of an epitope recognized by a monoclonal antibody to the F protein of measles virus (MV). An inhibition immunoassay was used to show that these peptides were bound by the monoclonal antibody with different affinities. BALB/c mice were coimmunized with the individual mimotopes and a T-helper epitope peptide (from MV fusion protein), and the reactivity of the induced anti-mimotope antibodies with the corresponding peptides and with MV was determined. The affinities of the antibodies with the homologous peptides ranged from 8.9 x 10(5) to 4.4 x 10(7) liters/mol. However, only one of the anti-mimotope antibodies cross-reacted with MV in an enzyme-linked immunosorbent assay and inhibited MV plaque formation. Coimmunization of mice with this mimotope and the T-helper epitope peptide induced an antibody response which conferred protection against fatal encephalitis induced following challenge with MV and with the structurally related canine distemper virus. These results indicate that peptide libraries can be used to identify mimotopes of conformational epitopes and that appropriate immunization with these mimotopes can induce protective antibody responses.

Protection against morbillivirus-induced encephalitis by immunization with a rationally designed synthetic peptide vaccine containing B- and T-cell epitopes from the fusion protein of measles virus.

Synthetic peptides representing T- and B-cell epitopes from the fusion (F) protein of measles virus (MV) were tested for their ability to induce a protective immune response against intracerebral challenge with neuroadapted strains of MV and canine distemper virus (CDV) in mice. Of the panel of peptides tested, only a chimeric peptide consisting of two copies of a promiscuous T-cell epitope (representing residues 288 to 302 of MV F protein) synthesized at the amino terminus of a B-cell epitope (representing residues 404 to 414 of MV F protein) was able to induce a protective response against challenge with MV and CDV in inbred mice. The protective response induced by this peptide (TTB) was associated with a significant reduction in mortality, histological absence of acute encephalitis, and greatly reduced titers of virus in the brains of TTB-immune mice following challenge compared with the results for nonimmunized controls. A chimeric peptide comprising one copy of the T-cell epitope and one copy of the B-cell epitope (TB) did not induce a protective response. A comparison of the antibody responses induced by the two chimeras suggested that differences in protective efficacy following immunization may be a result of the higher affinity of the antibody induced by the TTB peptide than that of the antibody induced by the TB peptide. In addition, differences in the immunoglobulin G subclass of the antipeptide antibody responses were observed, and these may play a role in the differences in protection observed. These results indicate that appropriately designed synthetic peptides have potential as vaccines for the induction of cross-reactive protection against morbilliviruses.

The potential of immunization with synthetic peptides to overcome the immunosuppressive effect of maternal anti-measles virus antibodies in young mice.

In this paper, we describe the results of experiments designed to test the hypothesis that immunogenic synthetic peptides representing non-immunodominant B- and T-cell epitopes of measles virus (MV) proteins can overcome the suppressive effect of maternal antibodies and induce anti-MV antibodies in young mice in the presence of maternal antibody to the virus. We have established a mouse model of immunosuppression by maternal antibody of both anti-MV and anti-peptide antibody responses in the young. Results obtained with this model immunization of young mice with a cocktail of synthetic peptides can overcome the suppression by maternal anti-MV antibodies and results in the induction of anti-peptide antibodies which recognize the virus. This work indicates that appropriately selected synthetic peptides have potential as vaccines which can be immunogenic and induce antibodies reactive with the virus-virus antibodies. in the presence of maternal anit-virus antibodies.

Analysis of the antigenic profile of measles virus haemagglutinin in mice and humans using overlapping synthetic peptides.

In this study, a panel of 55 synthetic peptides representing 92.2% of the haemagglutinin (H) glycoprotein of measles virus (MV) were used to study the antigenic profile of the H molecule of anti-MV antibodies raised in mice and late convalescent human sera. In addition the immunogenicity of these peptides was tested in two mouse strains. Mouse anti-MV antibodies had different fine specificity of binding to the peptides depending on the mouse strain. Thus in BALB/c (H-2d) mice, anti-MV antibodies recognised six peptides representing residues 103-117; 123-137; 242-255; 293-307 and 463-477. In TO (H-2s) mice, anti-MV antibodies recognised peptides representing residues 49-72 and 463-477. When the immunogenicity of the peptides was tested, 29 were immunogenic in BALB/c mice and 34 were immunogenic in TO mice. Several of the anti-peptide antisera were found to cross-react with MV, depending on the solid phase assay system used but none were able to inhibit virus infectivity in vitro. The reactivity of a panel of late convalescent human sera with the peptides was heterogeneous and the extent of the binding to the peptides was related to the titre of anti-MV. However, human sera recognized certain peptides more frequently than others, in particular peptides at the carboxyl-terminus.

Identification of helper T cell antigenic sites in mice from the haemagglutinin glycoprotein of measles virus.

The aim of this study was to define the helper T cell epitopes on the haemagglutinin (H) of measles virus (MV) in BALB/c (H-2d) and TO (H-2s) mice. A panel of 55 synthetic peptides (15-mers, overlapping by five amino acids) representing 92.2% of the H protein were synthesized and tested for immunogenicity and ability to stimulate MV-primed lymphocytes in vitro. The results obtained show that mouse lymphocytes respond to defined regions of the H protein which differ according to mouse strain. Virus-primed lymphocytes from BALB/c mice responded in vitro to peptides 7, 38, 39 and 44 whereas lymphocytes from virus-primed TO mice responded only to peptide 39. When mice of both strains were immunized with the peptides, a number of peptides induced proliferative responses, showing that the T cell repertoire for epitopes on the H protein is broader than that following immunization with virus. In BALB/c mice, lymphocytes primed to peptides 37, 39, 40, 42 and 43 responded in vitro to MV and in TO mice, lymphocytes primed to peptides 14, 32, 39, 40 and 49 responded to the virus. Thus in both strains of mice peptide 39 behaved as a dominant T cell epitope following immunization with virus or peptides. When the results obtained experimentally were compared with sequences predicted to be T cell epitopes by a number of algorithms, the concordance was limited.

Antibody responses to non-immunogenic synthetic peptides induced by co-immunization with immunogenic peptides.

Chimeric peptides comprising B- and T-helper cell epitopes from the proteins of infectious agents represent immunogens with potential for use as new vaccines. However, it has become clear that the orientation of the epitopes, the presence of spacer residues and the number of copies of the epitopes influence the specificity, levels and affinity of the antibody produced following immunization with such constructs. Furthermore, the response to peptides is under genetic control leading to major histocompatibility complex (MHC)-linked non-responsiveness. In this study, we have investigated the potential of co-immunization of immunogenic peptides (to provide T-cell help) with non-immunogenic peptides (representing B-cell epitopes) to overcome the non-response to the latter. For this purpose, we have employed peptides representing T- and B-cell epitopes derived from the sequences of the fusion and haemagglutinin glycoproteins of measles virus. The results obtained show that simple co-immunization of a B-cell epitope with a T-cell epitope results in the production of antibody to the B-cell epitope without the requirement for covalent linkage of the two peptides. This approach could thus be used to overcome the problem of poor immunogenicity of peptides and will be of potential value in the design of immunization strategies using synthetic immunogens.