Features of T-cell recognition and antigen structure useful in the design of vaccines to elicit T-cell immunity

Hydrogen Peroxide, Povidone-Iodine and Chlorhexidine Fail to Eradicate Staphylococcus aureus Biofilm from Infected Implant Materials

Hydrogen peroxide, povidone-iodine, and chlorhexidine are antiseptics that are commonly added to irrigants to either prevent or treat infection. There are little clinical data available that demonstrate efficacy of adding antiseptics to irrigants in the treatment of periprosthetic joint infection after biofilm establishment. The objective of the study was to assess the bactericidal activity of the antiseptics on S. aureus planktonic and biofilm. For planktonic irrigation, S. aureus was exposed to different concentrations of antiseptics. S. aureus biofilm was developed by submerging a Kirschner wire into normalized bacteria and allowing it to grow for forty-eight hours. The Kirschner wire was then treated with irrigation solutions and plated for CFU analysis. Hydrogen peroxide, povidone-iodine, and chlorhexidine were bactericidal against planktonic bacteria with over a 3 log reduction (p < 0.0001). Unlike cefazolin, the antiseptics were not bactericidal (less than 3 log reduction) against biofilm bacteria but did have a statistical reduction in biofilm as compared to the initial time point (p < 0.0001). As compared to cefazolin treatment alone, the addition of hydrogen peroxide or povidone-iodine to cefazolin treatment only additionally reduced the biofilm burden by less than 1 log. The antiseptics demonstrated bactericidal properties with planktonic S. aureus; however, when used to irrigate S. aureus biofilms, these antiseptics were unable to decrease biofilm mass below a 3 log reduction, suggesting that S. aureus biofilm has a tolerance to antiseptics. This information should be considered when considering antibiotic tolerance in established S. aureus biofilm treatment.

Phlebotomus papatasi SP15: mRNA expression variability and amino acid sequence polymorphisms of field populations

Background

The Phlebotomus papatasi salivary protein PpSP15 was shown to protect mice against Leishmania major, suggesting that incorporation of salivary molecules in multi-component vaccines may be a viable strategy for anti-Leishmania vaccines.

Methods

Here, we investigated PpSP15 predicted amino acid sequence variability and mRNA profile of P. papatasi field populations from the Middle East. In addition, predicted MHC class II T-cell epitopes were obtained and compared to areas of amino acid sequence variability within the secreted protein.

Results

The analysis of PpSP15 expression from field populations revealed significant intra- and interpopulation variation.. In spite of the variability detected for P. papatasi populations, common epitopes for MHC class II binding are still present and may potentially be used to boost the response against Le. major infections.

Conclusions

Conserved epitopes of PpSP15 could potentially be used in the development of a salivary gland antigen-based vaccine.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-015-0914-2) contains supplementary material, which is available to authorized users.

In vitro immunogenic and immunostimulatory effects of zwitterionized 23-valent pneumococcal polysaccharide vaccine compared with nonzwitterionized vaccine

BACKGROUND

It was hypothesized that the observed slight immunostimulatory effect of the 23-valent pneumococcal polysaccharide (pneumo-23) vaccine might be due to the presence of low levels of zwitterionic motifs. Therefore, it was hypothesized further that introducing zwitterionic motifs experimentally into polysaccharides of pneumo-23 vaccine might render it an effective immunostimulatory agent.

OBJECTIVE

This study was conducted to assess the in vitro immunostimulatory effect of zwitterionized pneumo-23 (Z-P23) vaccine compared with the nonzwitterionized commercial pneumo-23 (C-P23) vaccine.

METHODS

In vitro proliferation, ELISA-based in vitro cytokine synthesis (interleukin [IL]-2, interferon [IFN]-γ, and IL-10), and immunofluorescence microscopy-based immune cell profiling (CD4(+), CD8(+), and CD21(+) cells) assays were used to evaluate the immunostimulatory effect of Z-P23 on peripheral blood mononuclear cells (PBMC) of immunosuppressed cancer (IC) patients and healthy control subjects in comparison with PBMC exposed to C-P23, concanavalin A (positive control), and phosphate-buffered saline (PBS) (negative control).

RESULTS

Z-P23 induced proliferation of PBMC in the IC (81.1%) and control (75.1%) groups significantly higher than that achieved with concanavalin A in the IC group (51.0%; P = 0.01) but not in the control group (89.2%; P = NS). This was also significantly higher than that achieved with C-P23 in the IC (4.8%; P < 0.001) and control (6.2%; P < 0.001) groups. Z-P23 induced IL-2 and IFN-γ synthesis in the IC group (0.61 and 0.45 ng/mL, respectively) significantly more than that with C-P23 (0.4 and 0.45 ng/mL; P = 0.002 and P <0.001), concanavalin A (0.45 and 0.31 ng/mL; P = 0.021 and P = 0.03), and PBS (0.41 and 0.29 ng/mL; P = 0.005 and P = 0.04) but not the control group. Z-P23 induced expansion of CD4(+), CD8(+), and CD21(+) lymphocytes (39.3%, 42.7%, and 8.1%, respectively) in the IC group higher than that with C-P23 (28.3%, 30.1%, and 5.5%; P = 0.01, P = 0.003, and P = NS), concanavalin A (27.2%, 35.8%, and 4.1%; P = 0.02, P = 0.048, and P = 0.035), and PBS (25.6%, 31.9%, and 4.2%; P = 0.018, P = 0.02, and P = 0.045).

CONCLUSION

The in vitro immunostimulatory potential of Z-P23 was clearly observed on PBMC of IC patients as well as, to a lesser extent, healthy control subjects, stimulating the synthesis of core cytokines of T-helper 1, and primarily inducing CD4(+) and CD8(+)T cells.

Oral administration of Lactococcus lactis expressing Helicobacter pylori Cag7-ct383 protein induces systemic anti-Cag7 immune response in mice

To express the 3′‐region (1152 bp) of the cag7 gene of Helicobacter pylori 51 strain, encoding the C‐terminal 383 amino acid (ct383 aa) region of Cag7 protein that is known to cover the needle region of T4SS, in a live delivery vehicle Lactococcus lactis, the cag7‐ct383 gene was amplified by PCR. DNA sequence analysis revealed that the amino acid sequence of Cag7‐ct383 of H. pylori 51 shared 98.4% and 97.4% identity with H. pylori 26695 and J99, respectively. Intramuscular injection of the GST‐Cag7‐ct383 fusion protein into a rat could raise the anti‐Cag7 antibody, indicating the immunogenicity of the Cag7‐ct383 protein. When the cag7‐ct383 gene was cloned in Escherichia coli–L. lactis shuttle vector (pMG36e) and transformed into L. lactis, the transformant could produce the Cag7‐ct383 protein, as evidenced by Western blot analysis. The Cag7‐ct383 protein level in the L. lactis transformant reached a maximum at the early stationary phase without extracellular secretion. The oral administration of the L. lactis transformant into mice generated anti‐Cag7 antibody in serum in five of five mice. These results suggest that L. lactis transformant expressing Cag7‐ct383 protein may be applicable as an oral vaccine to induce mucosal and systemic immunity to H. pylori.

The [173–196] fragment of ovalbumin suppresses ovalbumin-specific rat IgE responses

Peptides and protein hydrolysates are attractive tools for the induction of tolerance or regulation of targeted B and/or T cell responses. In vivo, peptides are mainly produced by the action of digestive enzymes or following the processing of exogenous antigens by antigen-presenting cells (APCs). In vitro, these molecules are generally produced by enzymatic digestion and chemical hydrolysis of proteins. We investigated the T and B cell determinants of the major food allergen ovalbumin (nOVA) in rat by analyzing (1) the stimulatory effect of nOVA peptides generated by cyanogen bromide (CNBr) cleavage on nOVA-specific T cells, and (2) the potential of CNBr-derived OVA fractions to induce oral tolerance to nOVA. Peptide fractions of the CNBr-hydrolysated OVA were isolated by high-pressure liquid chromatography and tested for their ability to stimulate nOVA-specific T cells isolated from rats parenterally immunized with nOVA. The nOVA fractions containing the stimulatory determinants were then intragastrically administered to rat to test their potential to induce oral tolerance. The hole CNBr hydolysate stimulated proliferation of nOVA-specific T cells. Three out of the five HPLC-purified peptidic fractions were also able to stimulate proliferation and cytokine production by nOVA-specific T cells. A peptide fraction exhibiting a single peak by HPLC contained the 173-196 nOVA segment and stimulated nOVA-specific T cells. This segment also promoted oral tolerance to nOVA and reduced IgE responses. CNBr hydrolysis releases several peptides with stimulatory effect on nOVA-specific T cells including a new nOVA [173-196] T cell determinant which induces oral tolerance to nOVA.

Th1 T Cell Responses to HIV-1 Gag Protein Delivered by a Listeria monocytogenes Vaccine Are Similar to Those Induced by Endogenous Listerial Antigens

Listeria monocytogenes is a facultative intracellular bacterium that lives and grows in the cytoplasm of the host cell. The hallmark of a listerial infection is a cell-mediated immune response to its own secreted virulence factors. Thus, L. monocytogenes vaccines engineered to secrete HIV proteins may be ideal vectors for boosting cellular immune responses against HIV. Using strains of L. monocytogenes that stably express and secrete HIV Gag (Lm-Gag) to deliver this Ag to the immune system, we have previously shown strong MHC class I-restricted cytotoxic T cell responses to this protein. In this study, we examine MHC class II-restricted T cell responses to HIV-Gag delivered by Lm-Gag. We demonstrate the induction of CD4+ T cells that are HIV-Gag specific and identify three epitopes in two strains of mice, BALB/c (H-2d) and C57BL/6 (H-2b), two of which are both H-2d and H-2b restricted, but are not immunodominant for both haplotypes. In addition, we show that the CD4+ T cells induced are of the Th1 phenotype that produce IFN-γ at levels similar to CD4+ T cells induced to endogenous listerial Ags. These studies suggest that chromosomally modified strains of L. monocytogenes may be useful as vaccine vectors for the induction of Th1 T cell responses against HIV.

T-lymphocyte responses in guinea pigs vaccinated with foot-and-mouth disease virus

The guinea pig provides an alternative experimental model for analysis of the immune response against foot-and-mouth disease virus (FMDV). The cellular immune response against FMDV in this experimental animal is unknown and was analyzed by in vivo and in vitro studies. In guinea pigs immunized with an FMDV A5 vaccine, a marked change in T-lymphocyte count appeared. For analyzing which functional T-cell compartment was affected, immunofluorescence studies, using monoclonal antibodies directed against differentiation antigens on guinea pig lymphoid cells, were performed. The proliferating T-cells were predominantly CD4-positive and, therefore, helper cells. T-cells from these animals were re-stimulated in vitro with homologous inactivated virus. The antigen-specific proliferative response of the T-cells in vitro was measured using the thymidine incorporation assay. A proliferative response to FMDV was observed that depended on the dose of the antigen. High concentration of virus had an inhibitory effect on T-cell proliferation. These data indicate that the guinea pig is a useful model for analysis of T-cell mediated mechanisms in the pathogenesis and immunity of foot-and-mouth disease.

Towards vaccine optimisation

New molecular technologies have accelerated the search for sub-unit candidate vaccines. However, once identified the use of a candidate antigen must be optimised to reap the maximum benefit from the eventual vaccine. This optimisation should take into account both the needs of the target population, and the various ways of potentiating the protective immune response induced. One must be sure that the final product will be used. Hence, vaccine optimisation should strive toward meeting the needs of a specific epidemiological problem within the economic constraints of a given situation. This may be possible using novel delivery systems designed to limit the number of doses needed, improve the stability or facilitate the delivery of a particular vaccine. In meeting the needs of a target population in a field situation, one must also keep in mind certain safety factors that go beyond the usual regulatory constraints. The immune response to vaccine candidates can be potentiated in many ways. The ability to preferentially induce specific protective effector mechanisms: i.e., antibody isotypes, T-cell subsets, and T-cell sub-subsets, is becoming a reality. Carrier molecules designed to avoid the problems of epitope suppression and competition, and perhaps an eventual "carrier jam," are being developed. Adjuvants and immunostimulants may also help, but the critical issue here remains their acceptability for use in man. Finally novel strategies for the induction of the immune response may also potentiate the immune response in the optimisation of vaccines.

Identification of a bluetongue virus serotype 1-specific ovine helper T-cell determinant in outer capsid protein VP2

Ovine T-cell lines (including one clone [101A]), which are specific for Bluetongue virus serotype 1 (BTV1), have been established and characterized. Although these T-cell lines react with different isolates of BTV1 (including those from South Africa, Australia, Nigeria, and Cameroon), they do not react with heterologous BTV serotypes. Antigen specificity of these T-cells was studied using purified virus particles, infectious subviral particles (ISVP) and cores, or using individual BTV structural proteins that were either isolated by SDS-PAGE or expressed by recombinant strains of vaccinia virus. The results showed that each of the T-cell lines reacted with outer capsid protein VP2 (the BTV protein exhibiting most serotype-specific variation and the major neutralization antigen). However, all of the uncloned T-cell lines also reacted with either the core structural proteins or the outer capsid protein VP5. In contrast, the T-cell clone 101A only reacted with outer capsid protein VP2. Cell surface marker analysis showed that 101A has a helper T-cell phenotype (CD5+, CD4+, CD8-, T-19-). The T-cell lines and clone 101A all produced large amounts of interleukin 2 (IL-2) when stimulated with purified BTV1 virus particles, or with VP2 (up to 120 IU/ml from 2 x 10(5) T-cells). BTV serotype-specific antigenic sites, for B cells and at least one site for ovine helper T-cells, are therefore located within VP2.

Defining minimal requirements for antibody production to peptide antigens

The role that individual determinants play in modulating the immune response of an organism to a pathogen is often obscured because of the complexity of the pathogen. In order to gain a better appreciation of the role of individual determinants in the immune response, a pathogen may be dissociated into smaller components, for example peptides representing specific epitopes. These isolated components are often poorly immunogenic and historically have required the use of adjuvants to stimulate antibody production. This report defines the minimal essential requirements for antibody production to a peptide in this system. These are the ability to stimulate both B- and T-helper lymphocytes, anchorage in a phospholipid complex and multivalency within the complex. When these conditions are met, no additional adjuvants are necessary. This procedure has allowed us to identify three distinct T-helper cell epitopes from HIV gp160. In addition, this information has been used to produce a simple, totally synthetic and highly immunogenic preparation for the production of antibodies to peptides.

Development and application of synthetic peptides as vaccines

Vaccination against bacterial and viral diseases has been one of the major achievements in medicine and immunology since the beginning of this century. Extensive vaccination programs have been able to control or, in the case of smallpox, virtually wipe out some of the most dangerous infectious diseases e.g. poliomyelitis, measles, whooping cough, diphtheria and tetanus. However, as this success has been limited mainly to the developed, affluent countries, infectious diseases still remain the worlds largest health problem. Furthermore, vaccines against human parasites are non-existent. Recent advances in immunology and molecular biology including recombinant DNA technology have provided the basis for new approaches to vaccine development.

Identification of T-cell epitopes and use in construction of synthetic vaccines

The T cell is central to the immune system response to foreign antigens, and understanding the mechanism of T cell response to antigen is crucial for vaccine development. Short subpeptides of foreign antigen can prime the T cells to respond to the whole antigen, in some cases as well as or better than immunization with the whole antigen itself. Antigenic sites located first in the murine model are also antigenic in the human, suggesting that the structural features of antigenic sites are species-independent. The amphipathic helix hypothesis has proven useful in developing an algorithm that has successfully located immunodominant sites in important proteins, thus reducing substantially the experimental time and effort required to locate those sites. Other algorithms have also been used successfully, but in all cases there are proven T-cell sites not accounted for by the algorithm. A data base showing T-cell response to collections of peptides uniformly distributed along protein antigens would be very useful in subsequent efforts to characterize the physical and chemical properties of T-cell antigenic sites.

The main obstacle to a malaria vaccine: the malaria parasite

The challenge to development of a malaria vaccine will be the variability of the sequences of target antigens. We discuss the variability in the T cell epitopes on the circumsporozoite protein of Plasmodium falciparum and the rapid selection of mutants after immunization with a protein from the asexual erythrocytic stage of P. knowlesi.