Immunogenecity of synthetic peptides representing linear B-cell epitopes of VapA of Rhodococcus equi

An inventory of adjuvants used for vaccination in horses: the past, the present and the future

Vaccination is one of the most widely used strategies to protect horses against pathogens. However, available equine vaccines often have limitations, as they do not always provide effective, long-term protection and booster injections are often required. In addition, research efforts are needed to develop effective vaccines against emerging equine pathogens. In this review, we provide an inventory of approved adjuvants for equine vaccines worldwide, and discuss their composition and mode of action when available. A wide range of adjuvants are used in marketed vaccines for horses, the main families being aluminium salts, emulsions, polymers, saponins and ISCOMs. We also present veterinary adjuvants that are already used for vaccination in other species and are currently evaluated in horses to improve equine vaccination and to meet the expected level of protection against pathogens in the equine industry. Finally, we discuss new adjuvants such as liposomes, polylactic acid polymers, inulin, poly-ε-caprolactone nanoparticles and co-polymers that are in development. Our objective is to help professionals in the horse industry understand the composition of marketed equine vaccines in a context of mistrust towards vaccines. Besides, this review provides researchers with a list of adjuvants, either approved or at least evaluated in horses, that could be used either alone or in combination to develop new vaccines.

Adjuvanticity of a CTLA-4 3' UTR complementary oligonucleotide for emulsion formulated recombinant subunit and inactivated vaccines

Cytotoxic T-lymphocyte antigen 4 (CTLA-4) is recognized as a critical inhibitory regulator of T-cell proliferation and activation, opposing the action of CD28-mediated co-stimulation. Interfering or blocking CTLA-4 can result in continuous T-cell activation required for the full immune response to pathogenic microbes and vaccines. To test if nucleic acid-based CTLA-4 inhibitors could be developed into a novel adjuvant, we designed two oligonucleotides, CMD-1 and CMD-2, with the sequences complementary to the conserve regions identical between human and mouse CTLA-4 mRNA 3' untranslated region (3' UTR), and tested their in vitro effects on CTLA-4 production and their adjuvanticity for vaccines in mice. We found that CMD-1 inhibited the antigen-induced CTLA-4 up-regulation on the CD4⁺ T cells by interfering its mRNA expression, maintained higher levels of CD80 and CD86 on the CD11c⁺ cells and promoted the recalled proliferation of the CD4⁺ T cells and CD19⁺ B cells, and that the CMD-1 enhanced the antibody response against recombinant PCV2b capsid protein or inactivated foot-and-mouth disease virus in both ICR and BALB/c mice. These data suggest that the CMD-1 could be used as a novel vaccine adjuvant capable of inhibiting inhibitory signals rather than inducing stimulatory signals of immune cells.

Assessment of the safety and immunogenicity of Rhodococcus equi-secreted proteins combined with either a liquid nanoparticle (IMS 3012) or a polymeric (PET GEL A) water-based adjuvant in adult horses and foals--identification of promising new candidate antigens

Rhodococcus equi is the most common infectious cause of mortality in foals between 1 and 6 months of age. Because of an increase in the number of antibiotic-resistant strains, the optimization of a prophylactic strategy is a key factor in the comprehensive management of R. equi pneumonia. The objectives of this study were to assess the safety and immunogenicity of R. equi-secreted proteins (ReSP) co-administered with either the nanoparticular adjuvant Montanide™ IMS 3012 VG, or a new polymeric adjuvant Montanide™ PET GEL A, and to further investigate the most immunogenic proteins for subsequent immunization/challenge experiments in the development of a vaccine against rhodoccocal pneumonia. The approach involved two phases. The first phase aimed to investigate the safety of vaccination in six adult horses. The second phase aimed to determine the safety and immunogenicity of vaccination in twelve 3-week-old foals. We set out to develop a method based on ultrasound measurements for safety assessment in adult horses in order to evaluate any in situ changes at the injection site, in the skin or the underlying muscle, with quantitative and qualitative data revealing that administration of ReSP combined with the Pet Gel A adjuvant led to an increase in local inflammation, associated with 4- to 7-fold higher levels of anti-R. equi IgGa, IgGb and IgGT, compared to administration of ReSP associated with IMS 3012 adjuvant, but without any impact on animal demeanor. Investigations were then performed in foals with serological and clinical follow-up until 6 months of age. Interestingly, we observed in foals a much lower incidence of adverse local tissue reactions at the injection site than in adult horses, with transient and moderate swelling for the group that received ReSP combined with Pet Gel A. Immunized foals with Pet Gel A adjuvant exhibited a similar response in both IgGa and IgGT levels, but a lower response in IgGb levels, compared to adult horses, with a subisotype profile that may however reflect a bias favorable to R. equi resistance. From the crude extract of secreted proteins, dot-blot screening enabled identification of cholesterol oxidase, mycolyl transferase 3, and PSP (probable secreted protein) as the most immunogenic candidates. Taken together, these results are encouraging in developing a vaccine for foals.

Nasal vaccination with attenuated Salmonella expressing VapA: TLR2 activation is not essential for protection against R. equi infection

Virulent strains of Rhodococcus equi have a large plasmid of 80-90kb, which encodes several virulence-associated proteins (Vap), including VapA, a lipoprotein highly associated with disease. We have previously demonstrated that oral immunisation with attenuated Salmonella enterica Typhimurium strain expressing the antigen VapA (STM VapA+) induces specific and long-term humoral and cellular immunity against R. equi. It was shown that VapA activates Toll-like receptor 2 (TLR2) on macrophages by establishing an interaction that ultimately favours immunity against R. equi infection. The purpose of this study was to evaluate the immune response triggered by nasal immunisation with STM VapA+ and to determine whether TLR2 supports the vaccine effect. We developed an optimised protocol for a single nasal immunisation that conferred protection against R. equi infection in mice, which was manifested by efficient R. equi clearance in challenged animals. Nasal vaccination with STM VapA+ has also induced protection in Tlr2(-/-) mice and mice with non-functional TLR4. Moreover, spleen cells of vaccinated mice augmented T-bet expression, as well as the production of IL-12, IFN-γ, nitric oxide and hydrogen peroxide. Notably, the population of CD4(+) T cells with memory phenotype significantly increased in the spleens of vaccinated mice challenged 1 or 5 months after immunisation. In these animals, the spleen bacterial burden was also reduced. When similar experimental procedures were performed in TLR2 knockout mice, an increase in CD4(+) T cells with memory phenotype was not observed. Consequently, we conclude that nasal vaccination with attenuated Salmonella expressing the R. equi virulence factor VapA confers long-lasting protection against experimental rhodoccocosis and that TLR2 engagement was not crucial to induce this protection but may be required for a long-term immune response.

Current understanding of the equine immune response to Rhodococcus equi. An immunological review of R. equi pneumonia

Rhodococcus equi is recognised to cause chronic purulent bronchopneumonia in foals of less than 6 months of age. Virulent strains of the bacteria possess a large 80-90 kb plasmid encoding several virulence-associated proteins, including virulence-associated protein A (VapA), which is associated with disease. R. equi pneumonia can represent significant costs and wastage to the equine breeding industry, especially on stud farms where the disease is endemic. This article reviews knowledge of the equine immune response, both in the immune adult and susceptible neonate, with respect to this pathogen. Humoral immune responses are addressed, with a discussion on the use of hyperimmune and normal adult equine plasma as prophylactic tools. The role that innate immune mechanisms play in the susceptibility of some foals to R. equi infection is also highlighted. Likewise, cell-mediated immune components are reviewed, with particular attention directed towards research undertaken to develop an effective vaccine for foals. It is possible that the implementation of a single immunoprophylaxis strategy to prevent R. equi infection on farms will yield disappointing results. Combined prophylactic protocols that address husbandry practices, environmental and aerosol contamination levels, enhancement of innate immunity, good quality hyperimmune plasma for the neonate, and vaccinal efficacy in the developing foal may be required.

Comparison of Montanide adjuvants, IMS 3012 (Nanoparticle), ISA 206 and ISA 35 (Emulsion based) along with incomplete Freund's adjuvant for hyperimmunization of equines used for production of polyvalent snake antivenom

The use of adjuvant is of fundamental importance in vaccines formulations and antisera production. Currently selection and use of adjuvant systems in snake antivenom preparation has become a major issue in terms of animal welfare as well as economics. In order to minimize disadvantages associated with traditionally used Freund's adjuvant (FA) in equines and to produce potent polyvalent antivenom against four Indian snake venoms in minimum possible period, a comparison was made between various commercially available non-emulsion/emulsion based adjuvants like IMS 3012, ISA 206 and ISA 35 with Incomplete Freund's adjuvant (IFA) for their immunopotentiation capacity and safety in donor animals. The present study was conducted in 33 new horses, randomly divided into four groups and hyperimmunized using crude mixture of snake venoms, viz.; Cobra venom (CV), Russell's viper venom (RV), Krait venom (KV) and Saw-scaled viper (EV) along with four above mentioned adjuvants through subcutaneous (s.c.) route at intervals of two weeks. Periodic standard safety assessments were done. Immunopotentiation ability of each adjuvant group in terms of percent responders were estimated at 14th, 21st, 30th and 43rd week. The neutralization activity (ED(50)) of pooled sera samples by 43(rd) week, obtained with IMS 3012 group for CV, RV, KV and EV venoms were 0.133, 0.143, 0.070 and 0.270 mg venom/ml of serum respectively. The antivenom potency with IMS 3012 and overall responding horses (100%) even against weak immunogen like CV was significantly higher (p<0.05) than other three adjuvants studied. The horses of IMS 3012 group showed minimum local reactions at injection site, while horses from other three groups exhibited moderate (++) reactions; 66.7% in ISA 206, 12.5% in ISA 35 and 14.3% in IFA respectively, however these were transient and reabsorbed or healed subsequently. Finally, we conclude that, nanoparticle adjuvant IMS 3012 could be a possible alternative to the emulsion adjuvants for primary phase of immunization in antivenom preparation considering its better immunopotentiation capacity and safety in donor animals.

Synthesis of toll-like receptor-2 targeting lipopeptides as self-adjuvanting vaccines

Effective Th1- and Th2-type immune responses that result in protective immunity against pathogens can be induced by self-adjuvanting lipopeptides containing the lipid moiety dipalmitoyl-S-glyceryl cysteine (Pam2Cys). The potent immunogenicity of these lipopeptides is due to their ability to activate dendritic cells by targeting and signaling through Toll-like receptor-2 (TLR-2). In addition, the simplicity and flexibility in their design as well as their ease of chemical definition and characterisation makes them highly attractive vaccine candidates for humans and animals. We describe in this chapter the techniques involved in the synthesis of an immunocontraceptive lipopeptide vaccine as well as the experimental assays carried out to evaluate its efficiency.

Rhodococcus equi infection in foals: the science of 'rattles'

Infection with Rhodococcus (Corynebacterium) equi is a well-recognised condition in foals that represents a consistent and serious risk worldwide. The condition manifests itself primarily as one of pulmonary abscessation and bronchitis, hence the terminology of 'rattles' derived from its most obvious clinical sign, frequently terminal when first identified. This review addresses the clinical manifestation, bacteriology and pathogenesis of the condition together with recent developments providing knowledge of the organism in terms of virulence, epidemiology, transmission and immune responses. Enhanced understanding of R. equi virulence mechanisms and biology derived from the recently available genome sequence may facilitate the rational development of a vaccine and the improvement of farm management practices used to control R. equi on stud farms in the future. Reliance on vaccines alone, in the absence of management strategies to control the on-farm challenge is likely to be disappointing.

A peptide mimetic of the mycobacterial mannosylated lipoarabinomannan: characterization and potential applications

Mannosylated lipoarabinomannan (ManLAM), a complex lipoglycan, is a major component of Mycobacterium tuberculosis, the agent of tuberculosis (TB), and is an antigen used for serological diagnosis of TB. Screening random phage-display peptide libraries with anti-ManLAM mAb CS40 for peptide epitope mimics (mimotopes) led to the isolation of a panel of peptides. One of these peptides (B11) was characterized as a ManLAM mimotope: it bound the anti-ManLAM CS40 mAb and competed with ManLAM for antibody binding. Mice immunized with keyhole limpet haemocyanin-conjugated B11 peptide in a proper adjuvant developed antibodies that recognized ManLAM. Competition experiments demonstrated that the B11 peptide inhibited binding of mAb CS40 to ManLAM in a concentration-dependent manner. The data indicated that the affinity of CS40 mAb to B11 (K(D) 1.33 x 10(-8)) is higher than its affinity to ManLAM (K(D) 3.00 x 10(-7)). The sera of TB patients, as well as the sera of mice experimentally infected with M. tuberculosis, contained significant levels of antibodies that recognized both the B11 peptide and ManLAM. The specificity and sensitivity of the ELISA B11-based test were similar to those of the ELISA ManLAM-based test, indicating that the B11 antigen could be a good substitute for ManLAM serology for the diagnosis of TB.

Oral administration of a live attenuated Salmonella vaccine strain expressing the VapA protein induces protection against infection by Rhodococcus equi

Rhodococcus equi remains one of the most important pathogens of foals and vaccination strategies to prevent rhodococcosis are under increasing investigation. Attenuated Salmonella strains carrying heterologous antigens offer an advantageous alternative to conventional vaccines, especially because they induce mucosal and systemic immunity. In this work, we expressed the VapA antigen from R. equi in a Salmonella enterica Typhimurium strain, which was able to colonize and persist in the lymphoid tissue of BALB/c mice. Two days after being challenged, oral immunized mice presented a 3- to 7-fold increase in R. equi clearance. This was progressively enhanced during infection and, on the 10th day, a CFU value 50-fold lower than that recovered from non-immunized mice was attained. The number of hepatic granulomas was 2 times lower, and leukocyte infiltration was transiently detected in immunized mice, contrasting with the severe inflammation and necrosis presented by non-immunized mice. Infection with 1 x 10(7)R. equi CFU caused 100% mortality in the control groups, while all immunized mice survived. This protection was associated with the detection of high levels of anti-VapA IgG in the serum of the vaccinated mice, predominantly the IgG2a isotype. Our results suggest that attenuated Salmonella encoding VapA may be used in foals to prevent rhodococcosis.

Phenotypic and transcriptional characterization of the meningococcal PhoPQ system, a magnesium-sensing two-component regulatory system that controls genes involved in remodeling the meningococcal cell surface

We previously identified and characterized a two-component regulatory system in the meningococcus with homology to the phoP-phoQ system in salmonella and showed that allele replacement of the NMB0595 regulator gene led to loss of virulence, sensitivity to antimicrobial peptides, perturbed protein expression, and magnesium-sensitive growth. On the basis of these findings we proposed that the system should be designated the meningococcal PhoPQ system. Here we further characterized the NMB0595 mutant and demonstrated that it had increased membrane permeability and was unable to form colonies on solid media with low magnesium concentrations, features that are consistent with disruption of PhoPQ-mediated modifications to the lipooligosaccharide structure. We examined the transcriptional profiles of wild-type and NMB0595 mutant strains and found that magnesium-regulated changes in gene expression are completely abrogated in the mutant, indicating that, similar to the salmonella PhoPQ system, the meningococcal PhoPQ system is regulated by magnesium. Transcriptional profiling of the mutant indicated that, also similar to the salmonella PhoPQ system, the meningococcal system is involved in control of virulence and remodeling of the bacterial cell surface in response to the host environment. The results are consistent with the hypothesis that the PhoP homologue plays a role in the meningococcus similar to the role played by PhoP in salmonella. Elucidating the role that the PhoPQ system and PhoPQ-regulated genes play in the response of the meningococcus to the host environment may provide new insights into the pathogenic process.

Epitope mapping of Burkholderia pseudomallei serine metalloprotease: identification of serine protease epitope mimics

Filamentous phage random peptide libraries were used to identify the epitopes of Burkholderia pseudomallei protease by panning against IgG polyclonal sera that exhibited protease neutralizing properties. The isolated fusion peptides presented a consensus peptide sequence, TKSMALSG, which closely resembles part of the active site sequence, 435GTSMATPHVAG445, of B. pseudomallei serine metalloprotease. By comparing the consensus sequence, TKSMALSG, with the predicted three-dimensional molecular model of B. pseudomallei serine metalloprotease, it appears that the potential antibody binding epitope was buried within the molecule. This active site was conformational whereby one continuous sub-region (SMA) was located between two discontinuous sub-regions, supplied by the flanking residues in the same polypeptide. All phages selected from the biopanning with IgG polyclonal sera showed good binding towards the polyclonal antibodies when compared to the negative control. In addition, these peptide-bearing phages showed competitive inhibition of B. pseudomallei serine metalloprotease binding to the polyclonal IgG.

Synthetic peptides derived from SARS coronavirus S protein with diagnostic and therapeutic potential

The spike (S) protein of severe acute respiratory syndrome coronavirus (SARS-CoV) is an important viral structural protein. Based on bioinformatics analysis, 10 antigenic peptides derived from the S protein sequence were selected and synthesized. The antigenicity and immunoreactivity of all the peptides were tested in vivo and in vitro. Four peptides (P6, P8, P9 and P10) which contain B cell epitopes of the S protein were identified, and P8 peptide was confirmed in vivo to have a potential in serological diagnosis. By using a syncytia formation model, we tested the neutralization ability of all 10 peptides and their corresponding antibodies. It is interesting to find that P8 and P9 peptides inhibited syncytia formation, suggesting that the P8 and P9 spanning regions may provide a good target for anti-SARS-CoV drug design. Our data suggest that we have identified peptides derived from the S protein of SARS-CoV, which are useful for SARS treatment and diagnosis.