Heat denatured enzymatically inactive recombinant chlamydial protease-like activity factor induces robust protective immunity against genital chlamydial challenge

Role of route of delivery on Chlamydia abortus vaccine-induced immune responses and genital tract immunity in mice

We investigated if the efficacy of a Chlamydia abortus (Cab) subunit vaccine is influenced by route of administration. Thus, female CBA/J mice were immunized either by mucosal or systemic routes with Vibrio cholerae ghost (VCG)-based vaccine expressing T and B cell epitopes of Cab polymorphic membrane protein (Pmp) 18D, termed rVCG-Pmp18.3. Vaccine evaluation revealed that all routes of vaccine delivery induced a Th1-type antibody response after a prime boost or three-dose immunization regimen. Also, the intranasal and rectal mucosal and intramuscular systemic routes induced cross-reactive neutralizing antibodies against homologous and heterologous Cab strains. Irrespective of the route of immunization, the vaccine elicited a Th1-type cytokine response (IFN-γ/IL-4 >1) in immunized mice. Analysis of reduction in genital Cab burden as an index of protection showed that immunization induced substantial degrees of protection against infection, irrespective of route of delivery with the intranasal and rectal mucosal routes showing superior levels of protection 12 days postchallenge. Furthermore, there was correlation between the humoral and cellular immune response and protection was associated with the Cab-specific serum IgG antibody avidity and IFN-γ. Thus, while route of administration impacts vaccine efficacy, the rVCG-Pmp18.3-induced protective immunity against Cab respiratory infection can be accomplished by both mucosal and systemic immunization.

Low-Frequency, Sustained CD4 T-Cell Responses Chlamydia trachomatis in Women: Predominant Targeting of Chlamydial Proteaselike Activity Factor (CPAF)

BACKGROUND

Chlamydia trachomatis (CT) is a globally prevalent sexually transmitted infection that can result in pelvic inflammatory disease, ectopic pregnancy, and infertility in women. Currently, there is no prophylactic vaccine.

METHODS

This study examined T-cell immunity in a cohort of women recently infected with CT. Participants were screened against peptides spanning 33 of 894 possible CT proteins, either ex vivo or using short-term cell lines. CT-specific T cells were characterized by interferon (IFN) γ enzyme-linked immunospot (ELISPOT) assay and flow cytometry.

RESULTS

Ex vivo CT-specific T cells were rarely detected; however, in vitro expanded CT-specific T cells were detected by IFN-γ ELISPOT in 90% (27 of 30) of participants. Notably, >50% of participants had T-cell responses targeting chlamydial proteaselike activity factor (CPAF). T-cell epitopes were dispersed across the CPAF protein. Flow cytometric analysis of short-term cell lines found that CT-specific cells, mainly CD4, produced IFN-γ and tumor necrosis factor (TNF) α and were sustained over 12 months. Ex vivo analysis suggested that CT-specific T cells mostly exhibited a central memory phenotype.

CONCLUSIONS

Our results indicate that CT infection elicits low-frequency, persistent CD4 T-cell responses in most women and that the secreted protein, CPAF, is an immunoprevalent CT antigen. Altogether, these data support development and testing of CT vaccines that enhance CD4 T cells against CPAF.

Viral-vectored boosting of OmcB- or CPAF-specific T-cell responses fail to enhance protection from Chlamydia muridarum in infection-immune mice and elicits a non-protective CD8-dominant response in naïve mice

A vaccine is needed to combat the Chlamydia epidemic. Replication-deficient viral vectors are safe and induce antigen-specific T-cell memory. We tested the ability of intramuscular immunization with modified vaccinia Ankara (MVA) virus or chimpanzee adenovirus (ChAd) expressing chlamydial outer membrane protein (OmcB) or the secreted protein, chlamydial protease-like activating factor (CPAF), to enhance T-cell immunity and protection in mice previously infected with plasmid-deficient Chlamydia muridarum CM972 and elicit protection in naïve mice. MVA.OmcB or MVA.CPAF increased antigen-specific T cells in CM972-immune mice ∼150 and 50-fold, respectively, but failed to improve bacterial clearance. ChAd.OmcB/MVA.OmcB prime-boost immunization of naïve mice elicited a cluster of differentiation (CD) 8-dominant T-cell response dominated by cluster of differentiation (CD)8 T cells that failed to protect. ChAd.CPAF/ChAd.CPAF prime-boost also induced a CD8-dominant response with a marginal reduction in burden. Challenge of ChAd.CPAF-immunized mice genetically deficient in CD4 or CD8 T cells showed that protection was entirely CD4-dependent. CD4-deficient mice had prolonged infection, whereas CD8-deficient mice had higher frequencies of CPAF-specific CD4 T cells, earlier clearance, and reduced burden than wild-type controls. These data reinforce the essential nature of the CD4 T-cell response in protection from chlamydial genital infection in mice and the need for vaccine platforms that drive CD4-dominant responses.

Efficacy of Pgp3 vaccination for Chlamydia urogenital tract infection depends on its native conformation

Urogenital tract infections with Chlamydia trachomatis have frequently been detected among patients diagnosed with sexually transmitted infections, and such infections lead to inflammatory complications. Currently, no licensed chlamydial vaccine is available in clinical practice. We previously reported that immunization with recombinant C. trachomatis plasmid-encoded virulence factor Pgp3 provided cross-serovar protection against C. muridarum genital tract infection. Because Pgp3 is a homotrimer and human antisera only recognize the trimeric form of Pgp3, we compared the effects of the native conformation of Pgp3 (trimer) and heat-denatured Pgp3 (monomer) to determine whether the native conformation is dispensable for the induction of protective immunity against chlamydial vaginal challenge. Both Pgp3 trimer and monomer immunization induced corresponding specific antibody production, but only trimer-induced antibody recognized endogenous Pgp3, and trimer-immunized mouse splenocytes showed the highest IFN-γ production upon restimulation with the chlamydial elementary body or native Pgp3 in vitro. Importantly, only Pgp3 trimer-immunized mice showed shortened lower genital tract chlamydial shedding and decreased upper genital tract pathology. Thus, Pgp3-induced protective immunity against Chlamydia urogenital tract infection is highly dependent on the native conformation, which will guide the design of Pgp3-based polypeptides and multi-subunit chlamydial vaccines.

The role of an enzymatically inactive CPAF mutant vaccination in Chlamydia muridarum genital tract infection

Chlamydia trachomatis urogenital tract infection causes pelvic inflammatory disease and infertility, increases the risk of co-infection with HPV and HIV. Chlamydial vaccination is considered the most promising approach to prevent and control its infection. Among various chlamydial vaccine candidates, chlamydial protease-like activity factor (CPAF) have been reported to provide robust protective immunity against genital chlamydial infection in mice with reduced vaginal shedding and oviduct pathology. However, CPAF is a serine protease which has enzymatical activity to degrade a large number of substrates. In order to increase the safety of CPAF vaccine, in this study, we used a mutant CPAF that is deficient in enzymatical activity to determine whether proteolytic activity of CPAF affect its vaccine efficacy. The wild type or mutant CPAF immunization causes a significant lower chlamydial shedding from the vaginal and resolve the infection as early as day 20, compared to day 28 in adjuvant control mice. More important, reduced upper reproductive tract pathology were also observed in these two groups. The mutant or wild type CPAF immunization induced not only robust splenic IFN-γ and serum IgG2a but also sIgA secretion in the vaginal fluids. Furthermore, neutralization of chlamydia with immune sera did not provide protection against oviduct pathology. However, adoptive transfer of CD4⁺ splenocytes isolated from the mutant or wild type CPAF immunized mice resulted in a significant and comparable reduced oviduct pathology. Our results indicate mutant CPAF vaccination is as same efficacy as wild type, and the protection relies on CD4⁺ T cells, which will further promote the development of CPAF as clinical chlamydial vaccine.

Cellular Basis for the Enhanced Efficacy of the Fms-Like Tyrosine Kinase 3 Ligand (FL) Adjuvanted VCG-Based Chlamydia abortus Vaccine

Efficacious vaccines are needed to control genital chlamydial diseases in humans and the veterinary industry. We previously reported a C. abortus (Cab) vaccine comprising recombinant Vibrio cholerae ghosts (rVCG) expressing the conserved and immunogenic N-terminal region of the Cab polymorphic membrane protein D (rVCG-Pmp18.1) protein that protected mice against intravaginal challenge. In this study, we investigated the immunomodulatory effect of the hematopoietic progenitor activator cytokine, Fms-like tyrosine kinase 3-ligand (FL) when co-administered with the rVCG-Pmp18.1 vaccine as a strategy to enhance the protective efficacy and the potential mechanism of immunomodulation. Groups of female C57BL/6J mice were immunized and boosted twice intranasally (IN) with rVCG-PmpD18.1 with and without FL or purified rPmp18.1 or rVCG-gD2 (antigen control) or PBS (medium) per mouse. The results revealed that co-administration of the vaccine with FL enhanced antigen-specific cellular and humoral immune responses and protected against live Cab genital infection. Comparative analysis of immune cell phenotypes infiltrating mucosal and systemic immune inductive tissue sites following immunization revealed that co-administration of rVCG-Pmp18.1 with FL significantly enhanced the number of macrophages, dendritic and NK cells, γδ and NK T cells in the spleen (systemic) and iliac lymph nodes (ILN) draining the genital tract (mucosal) tissues compared to rVCG-Pmp18.1 alone. Furthermore, FL enhanced monocyte infiltration in the ILN, while CD19+ B cells and CD4+ T cells were enhanced in the spleen. These results indicate that the immunomodulatory effect of FL is associated with its ability to mobilize innate immune cells and subsequent activation of robust antigen-specific immune effectors in mucosal and systemic lymphoid tissues.

Navigating to the most promising directions amid complex fields of vaccine development: a chlamydial case study

Background: Vaccine-development research is proliferating making it difficult to determine the most promising vaccine candidates. Exemplary of this problem is vaccine development against Chlamydia, a pathogen of global public health and financial importance.Methods: We systematically extracted data from studies that included chlamydial load or host immune parameter measurements, estimating 4,453 standardized effect sizes between control and chlamydial immunization experimental groups.Results: Chlamydial immunization studies most often used (78%) laboratory mouse models. Depending on chlamydial species, single and multiple recombinant protein, viral and bacterial vectors, dendritic transfer, and dead whole pathogen were most effective at reducing chlamydial load. Immunization-driven decrease in chlamydial load was associated with increases in IFNg, IgA, IgG1, and IgG2a. Using data from individual studies, the magnitude of IgA and IgG2a increase was correlated with chlamydial load reduction. IFNg also showed this pattern for C. trachomatis, but not for C. muridarum. We also reveal the chlamydial vaccine development field to be highly bias toward studies showing these effects, limiting lessons learned from negative results.Conclusions: Most murine immunizations against Chlamydia reduced chlamydial load and increased host immune parameters. These methods are novel for vaccine development and are critical in identifying trends where large quantities of literature exist.

Intranasal immunization with recombinant chlamydial protease-like activity factor attenuates atherosclerotic pathology following Chlamydia pneumoniae infection in mice

We have shown previously that intranasal vaccination with recombinant chlamydial protease-like activity factor (rCPAF: antigen) and interleukin-12 (IL-12) as an adjuvant induces robust protection against pathological consequences of female genital tract infection with Chlamydia muridarum, a closely related species and a rodent model for the human pathogen Chlamydia trachomatis. Another related species Chlamydia pneumoniae, a human respiratory pathogen, has been associated with exacerbation of atherosclerotic pathology. CPAF is highly conserved among Chlamydia spp. leading us to hypothesize that immunization with rCPAF with IL-12 will protect against high-fat diet (HFD) and C. pneumoniae-induced acceleration of atherosclerosis. rCPAF ± IL-12 immunization induced robust splenic antigen (Ag)-specific IFN-γ and TNF-α production and significantly elevated serum total anti-CPAF Ab, IgG2c, and IgG1 antibody levels compared to mock or IL-12 alone groups. The addition of IL-12 to rCPAF significantly elevated splenic Ag-specific IFN-γ production and IgG2c/IgG1 anti-CPAF antibody ratio. Following intranasal C. pneumoniae challenge and HFD feeding, rCPAF ± IL-12-immunized mice displayed significantly enhanced splenic IFN-γ, not TNF-α, response on days 6 and 9 after challenge, and significantly reduced lung chlamydial burden on day 9 post-challenge compared to mock- or IL-12-immunized mice. Importantly, rCPAF ± IL-12-immunized mice displayed significantly reduced atherosclerotic pathology in the aortas after C. pneumoniae challenge. Serum cholesterol levels were comparable between the groups suggesting that the observed differences in pathology were due to protective immunity against the infection. Together, these results confirm and extend our previous observations that CPAF is a promising candidate antigen for a multisubunit vaccine regimen to protect against Chlamydia-induced pathologies, including atherosclerosis.

Update on Chlamydia trachomatis Vaccinology

Attempts to produce a vaccine to protect against Chlamydia trachomatis-induced trachoma were initiated more than 100 years ago and continued for several decades. Using whole organisms, protective responses were obtained. However, upon exposure to C. trachomatis, disease exacerbation developed in some immunized individuals, precluding the implementation of the vaccine. Evidence of the role of C. trachomatis as a sexually transmitted pathogen started to emerge in the 1960s, and it soon became evident that it can cause acute infections and long-term sequelae in women, men, and newborns. The main focus of this minireview is to summarize recent findings and discuss formulations, including antigens, adjuvants, routes, and delivery systems for immunization, primarily explored in the female mouse model, with the goal of implementing a vaccine against C. trachomatis genital infections.

Immunity, immunopathology, and human vaccine development against sexually transmitted Chlamydia trachomatis

This review examines the immunity, immunopathology, and contemporary problems of vaccine development against sexually transmitted Chlamydia trachomatis. Despite improved surveillance and treatment initiatives, the incidence of C. trachomatis infection has increased dramatically over the past 30 years in both the developed and developing world. Studies in animal models have shown that protective immunity to C. trachomatis is largely mediated by Th1 T cells producing IFN-γ which is needed to prevent dissemination of infection. Similar protection appears to develop in humans but in contrast to mice, immunity in humans may take years to develop. Animal studies and evidence from human infection indicate that immunity to C. trachomatis is accompanied by significant pathology in the upper genital tract. Although no credible evidence is currently available to indicate that autoimmunity plays a role, nevertheless, this underscores the necessity to design vaccines strictly based on chlamydial-specific antigens and to avoid those displaying even minimal sequence homologies with host molecules. Current advances in C. trachomatis vaccine development as well as alternatives for designing new vaccines for this disease are discussed. A novel approach for chlamydia vaccine development, based on targeting endogenous dendritic cells, is described.

TLR4-mediated immunomodulatory properties of the bacterial metalloprotease arazyme in preclinical tumor models

Despite the recent approval of new agents for metastatic melanoma, its treatment remains challenging. Moreover, few available immunotherapies induce a strong cellular immune response, and selection of the correct immunoadjuvant is crucial for overcoming this obstacle. Here, we studied the immunomodulatory properties of arazyme, a bacterial metalloprotease, which was previously shown to control metastasis in a murine melanoma B16F10-Nex2 model. The antitumor activity of arazyme was independent of its proteolytic activity, since heat-inactivated protease showed comparable properties to the active enzyme; however, the effect was dependent on an intact immune system, as antitumor properties were lost in immunodeficient mice. The protective response was IFNγ-dependent, and CD8(+) T lymphocytes were the main effector antitumor population, although B and CD4(+) T lymphocytes were also induced. Macrophages and dendritic cells were involved in the induction of the antitumor response, as arazyme activation of these cells increased both the expression of surface activation markers and proinflammatory cytokine secretion through TLR4-MyD88-TRIF-dependent, but also MAPK-dependent pathways. Arazyme was also effective in the murine breast adenocarcinoma 4T1 model, reducing primary and metastatic tumor development, and prolonging survival. To our knowledge, this is the first report of a bacterial metalloprotease interaction with TLR4 and subsequent receptor activation that promotes a proinflammatory and tumor protective response. Our results show that arazyme has immunomodulatory properties, and could be a promising novel alternative for metastatic melanoma treatment.

The p47phox deficiency significantly attenuates the pathogenicity of Chlamydia muridarum in the mouse oviduct but not uterine tissues

The Chlamydia muridarum induction of the upper genital tract pathology in mice has been used to investigate the mechanisms of chlamydial pathogenesis. We report that the NCF1 (neutrophil cytosolic factor1)-encoded p47phox (phagocyte oxidase), an essential subunit of nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase, contributes significantly to C. muridarum induction of hydrosalpinx. Mice lacking p47phox (p47phox-deficient) were no longer able to develop significant hydrosalpinx following an intravaginal infection with C. muridarum. However, there was no significant difference in uterine horn dilation (as a result of the endometrial glandular duct dilation) between the p47phox-deficient and -sufficient mice. Thus, the role of NADPH oxidase in chlamydial pathogenesis is restricted to the oviduct tissue rather than the entire upper genital tract. Interestingly, both the p47phox-deficient and -sufficient mice displayed similar levels of chlamydial live organism shedding from the lower genital tract, suggesting that the NADPH oxidase is not required for the mouse control of chlamydial infection in the lower genital tract. Furthermore, the p47phox deficiency did not affect the infectious organism burden in the upper genital tract tissues, indicating that the NADPH-oxidase activity is not necessary for the mouse prevention of chlamydial ascension from the lower to upper genital tracts. However, the p47phox-defieicnt mice displayed a significantly reduced chronic inflammatory infiltration in the oviduct but not uterine tissues, supporting the finding that the NADPH oxidase activity is required for chlamydial induction of dilation in the oviduct but not the endometrial glandular duct. Thus, we have demonstrated a significant role of the host NADPH oxidase in promoting chronic inflammatory pathology in the oviduct following chlamydial infection.

Chlamydial polymorphic membrane proteins: regulation, function and potential vaccine candidates

Pmps (Polymorphic Membrane Proteins) are a group of membrane bound surface exposed chlamydial proteins that have been characterized as autotransporter adhesins and are important in the initial phase of chlamydial infection. These proteins all contain conserved GGA (I, L, V) and FxxN tetrapeptide motifs in the N-terminal portion of each protein. All chlamydial species express Pmps. Even in the chlamydia-related bacteria Waddlia chondrophila, a Pmp-like adhesin has been identified, demonstrating the importance of Pmps in Chlamydiales biology. Chlamydial species vary in the number of pmp genes and their differentially regulated expression during the infectious cycle or in response to stress. Studies have also demonstrated that Pmps are able to induce innate immune functional responses in infected cells, including production of IL-8, IL-6 and MCP-1, by activating the transcription factor NF-κB. Human serum studies have indicated that although anti-Pmp specific antibodies are produced in response to a chlamydial infection, the response is variable depending on the Pmp protein. In C. trachomatis, PmpB, PmpC, PmpD and PmpI were the proteins eliciting the strongest immune response among adolescents with and without pelvic inflammatory disease (PID). In contrast, PmpA and PmpE elicited the weakest antibody response. Interestingly, there seems to be a gender bias for Pmp recognition with a stronger anti-Pmp reactivity in male patients. Furthermore, anti-PmpA antibodies might contribute to adverse pregnancy outcomes, at least among women with PID. In vitro studies indicated that dendritic cells infected with C. muridarum were able to present PmpG and PmpF on their MHC class II receptors and T cells were able to recognize the MHC class-II bound peptides. In addition, vaccination with PmpEFGH and Major Outer Membrane Protein (MOMP) significantly protected mice against a genital tract C. muridarum infection, suggesting that Pmps may be an important component of a multi-subunit chlamydial vaccine. Thus, Pmps might be important not only for the pathogenesis of chlamydial infection, but also as potential candidate vaccine proteins.

A T cell epitope-based vaccine protects against chlamydial infection in HLA-DR4 transgenic mice

Vaccination with recombinant chlamydial protease-like activity factor (rCPAF) has been shown to provide robust protection against genital Chlamydia infection. Adoptive transfer of IFN-γ competent CPAF-specific CD4⁺ T cells was sufficient to induce early resolution of chlamydial infection and reduction of subsequent pathology in recipient IFN-γ-deficient mice indicating the importance of IFN-γ secreting CD4⁺ T cells in host defense against Chlamydia. In this study, we identify CD4⁺ T cell reactive CPAF epitopes and characterize the activation of epitope-specific CD4⁺ T cells following antigen immunization or Chlamydia challenge. Using the HLA-DR4 (HLA-DRB1*0401) transgenic mouse for screening overlapping peptides that induced T cell IFN-γ production, we identified at least 5 CPAF T cell epitopes presented by the HLA-DR4 complex. Immunization of HLA-DR4 transgenic mice with a rCPAFep fusion protein containing these 5 epitopes induced a robust cell-mediated immune response and significantly accelerated the resolution of genital and pulmonary Chlamydia infection. rCPAFep vaccination induced CPAF-specific CD4⁺ T cells in the spleen were detected using HLA-DR4/CPAF-epitope tetramers. Additionally, CPAF-specific CD4⁺ clones could be detected in the mouse spleen following Chlamydia muridarum and a human Chlamydia trachomatis strain challenge using these novel tetramers. These results provide the first direct evidence that a novel CPAF epitope vaccine can provide protection and that HLA-DR4/CPAF-epitope tetramers can detect CPAF epitope-specific CD4⁺ T cells in HLA-DR4 mice following C. muridarum or C. trachomatis infection. Such tetramers could be a useful tool for monitoring CD4⁺ T cells in immunity to Chlamydia infection and in developing epitope-based human vaccines using the murine model.

Antibody signature of spontaneous clearance of Chlamydia trachomatis ocular infection and partial resistance against re-challenge in a nonhuman primate trachoma model

Background

Chlamydia trachomatis is the etiological agent of trachoma the world's leading cause of infectious blindness. Here, we investigate whether protracted clearance of a primary infection in nonhuman primates is attributable to antigenic variation or related to the maturation of the anti-chlamydial humoral immune response specific to chlamydial antigens.

Methodology/Principal Findings

Genomic sequencing of organisms isolated throughout the protracted primary infection revealed that antigenic variation was not related to the inability of monkeys to efficiently resolve their infection. To explore the maturation of the humoral immune response as a possible reason for delayed clearance, sera were analyzed by radioimmunoprecipitation using intrinsically radio-labeled antigens prepared under non-denaturing conditions. Antibody recognition was restricted to the antigenically variable major outer membrane protein (MOMP) and a few antigenically conserved antigens. Recognition of MOMP occurred early post-infection and correlated with reduction in infectious ocular burdens but not with infection eradication. In contrast, antibody recognition of conserved antigens, identified as PmpD, Hsp60, CPAF and Pgp3, appeared late and correlated with infection eradication. Partial immunity to re-challenge was associated with a discernible antibody recall response against all antigens. Antibody recognition of PmpD and CPAF was destroyed by heat treatment while MOMP and Pgp3 were partially affected, indicating that antibody specific to conformational epitopes on these proteins may be important to protective immunity.

Conclusions/Significance

Our findings suggest that delayed clearance of chlamydial infection in NHP is not the result of antigenic variation but rather a consequence of the gradual maturation of the C. trachomatis antigen-specific humoral immune response. However, we cannot conclude that antibodies specific for these proteins play the primary role in host protective immunity as they could be surrogate markers of T cell immunity. Collectively, our results argue that an efficacious subunit trachoma vaccine might require a combination of these antigens delivered in their native conformation.

Chlamydia trachomatis is the etiological agent of trachoma the world's leading cause of infectious blindness. In this study, we investigated whether delayed clearance of a primary infection in nonhuman primates was attributable to antigenic variation or related to gradual changes in the humoral immune response specific to chlamydial antigens. We found that antigenic variation was not related to the inability of monkeys to efficiently resolve their infection. However, exploring changes in the immune response as a possible reason for delayed clearance revealed that antibody recognition was restricted to the antigenically variable major surface protein and a few conserved polypeptides. Antibody recognition of the major antigenically variable surface protein correlated with the initial reduction in infectious burdens while recognition of conserved chlamydial antigens occurred late and correlated with infection eradication. These findings suggest that delayed clearance of chlamydial infection is not the result of antigenic variation but a consequence of a gradually evolving humoral immune response specific to different chlamydial antigens. Antibody recognition was at least partially directed against conformational epitopes, indicating that an efficacious subunit trachoma vaccine might require a combination of antigens delivered in their native conformation.

Chlamydia muridarum T cell antigens and adjuvants that induce protective immunity in mice

Major impediments to a Chlamydia vaccine lie in discovering T cell antigens and polarizing adjuvants that stimulate protective immunity. We previously reported the discovery of three T cell antigens (PmpG, PmpF, and RplF) via immunoproteomics that elicited protective immunity in the murine genital tract infection model against Chlamydia infection after adoptive transfer of antigen-pulsed dendritic cells. To expand the T cell antigen repertoire necessary for a Chlamydia vaccine, we evaluated 10 new Chlamydia T cell antigens discovered via immunoproteomics in addition to the 3 antigens reported earlier as a molecular subunit vaccine. We first tested five adjuvants, including three cationic liposome formulations (dimethyldioctadecylammonium bromide-monophosphoryl lipid A [DDA-MPL], DDA-trehalose 6,6'-dibehenate [DDA-TDB {CAF01}], and DDA-monomycolyl glycerol [DDA-MMG {CAF04}]), Montanide ISA720-CpG-ODN1826, and alum using the PmpG protein as a model T cell antigen in the mouse genital tract infection model. The results showed that the cationic liposomal adjuvants DDA-MPL and DDA-TDB elicited the best protective immune responses, characterized by multifunctional CD4(+) T cells coexpressing gamma interferon (IFN-γ) and tumor necrosis factor alpha (TNF-α), and reduced infection by more than 3 logs. Using DDA-MPL as an adjuvant, we found that 7 of 13 Chlamydia T cell antigens (PmpG, PmpE, PmpF, Aasf, RplF, TC0420, and TC0825) conferred protection better than or equal to that of the reference vaccine antigen, major outer membrane protein (MOMP). Pools of membrane/secreted proteins, cytoplasmic proteins, and hypothetical proteins were tested individually or in combination. Immunization with combinations protected as well as the best individual protein in that combination. The T cell antigens and adjuvants discovered in this study are of further interest in the development of a molecularly defined Chlamydia vaccine.

Immunity and vaccines against sexually transmitted Chlamydia trachomatis infection

PURPOSE OF REVIEW

The aim is to review recent findings on immunity and vaccine development to Chlamydia trachomatis.

RECENT FINDINGS

There is increasing knowledge on the interactions between C. trachomatis and infected host cells. During genital infection the organism avoids generating protective immunity but immune responses to a number of chlamydial proteins have been associated with reproductive tract pathology. Various vaccine and adjuvant preparations have been tried experimentally. Information generated by proteomics and complex studies of serological and T-lymphocyte immune responses points to novel vaccine candidates.

SUMMARY

C. trachomatis, an obligate intracellular bacterium, is the commonest sexually transmitted infection worldwide and is associated with reproductive pathology. To develop rational vaccines it is necessary to understand the complex lifecycle of the organism, the host immune response to infection and how these relate to disease. Infection does not prevent re-infection and antibiotic treatment prevents antibody production at a population level. It remains unclear what type of immune response would be sufficient to prevent infection and/or re-infection. Although the prevalence and demographics of infection and the severity of disease associations suggest that it would be desirable, there is no vaccine currently available. A number of studies have identified novel vaccine candidates.

Vaccination with the defined chlamydial secreted protein CPAF induces robust protection against female infertility following repeated genital chlamydial challenge

We previously have shown the efficacy of recombinant (r) chlamydial protease-like activity factor (CPAF) vaccination against hydrosalpinx development following primary genital chlamydial challenge. In this study, we evaluated further the protection induced by rCPAF vaccination against infertility. Following primary challenge, fertility levels were not significantly different between the mock- and CPAF-vaccinated and Chlamydia alone challenged mice. However, following secondary genital chlamydial challenge, mock (PBS) immunized mice displayed a significant reduction of fertility compared to age-matched naïve mice, while mice vaccinated intranasally with rCPAF+CpG displayed significant prevention of infertility. These results suggest that hydrosalpinx may be a reliable indicator of impending infertility, and that rCPAF is a promising candidate to prevent infertility resulting from repeated genital chlamydial infections.

Induction of immune memory by a multisubunit chlamydial vaccine

We tested the hypothesis that intramuscular immunization with a multisubunit chlamydial vaccine candidate will induce long lasting immune responses in mice. Accordingly, groups of female C57BL/6 mice were immunized intramuscularly with Vibrio cholerae ghosts (VCG) expressing the Poring B and polymorphic membrane protein-D proteins of Chlamydia trachomatis or a control antigen. Humoral and cell-mediated immune responses were evaluated following immunization and after live chlamydial infection. Immunization induced an anamnestic response characterized by chlamydial-specific IgG2a and IgA antibodies in sera and vaginal lavage as well as specific genital and splenic T cell responses. The results also revealed that the local mucosal and systemic cellular and humoral immune effectors induced in mice following immunization with the vaccine candidate are long lasting. Vaccinated mice cleared intravaginal challenge with 10(5) chlamydial inclusion forming units within 12 days compared to control mice, which shed up to 2 × 10(3) IFUs at this time point. Moreover, rechallenge of mice 98 days after resolution of the primary infection resulted in the recall and retention of a relatively high frequency of chlamydial-specific Th1 cells and IgG2a in the genital mucosa. These results provide the first evidence that a VCG-based multisubunit chlamydial vaccine is capable of effectively stimulating anamnestic systemic and mucosal immune responses in mice. The data support further vaccine evaluation and testing for induction of long-term protective immunity.

Towards a Chlamydia trachomatis vaccine: how close are we?

Chlamydia trachomatis is the leading cause of bacterial sexually transmitted infections and preventable blindness worldwide. The incidence of chlamydial sexually transmitted infections has increased rapidly and current antibiotic therapy has failed as an intervention strategy. The most accepted strategy for protection and/or control of chlamydial infections is a vaccine that induces both local neutralizing antibodies to prevent infections by the extracellular elementary bodies and a cell-mediated immune response to target the intracellular infection. This article will discuss the challenges in vaccine design for the prevention of chlamydial urogenital infection and/or disease, including selection of target antigens, discussion of effective delivery systems, immunization routes and adjuvants for induction of protective immunity at the targeted mucosal surface whilst minimizing severe inflammatory disease sequelae.

Vaccination against Chlamydia genital infection utilizing the murine C. muridarum model

Chlamydia trachomatis genital infection is a worldwide public health problem, and considerable effort has been expended on developing an efficacious vaccine. The murine model of C. muridarum genital infection has been extremely useful for identification of protective immune responses and in vaccine development. Although a number of immunogenic antigens have been assessed for their ability to induce protection, the majority of studies have utilized the whole organism, the major outer membrane protein (MOMP), or the chlamydial protease-like activity factor (CPAF). These antigens, alone and in combination with a variety of immunostimulatory adjuvants, have induced various levels of protection against infectious challenge, ranging from minimal to nearly sterilizing immunity. Understanding of the mechanisms of natural infection-based immunity and advances in adjuvant biology have resulted in studies that are increasingly successful, but a vaccine licensed for use in humans has not yet been brought to fruition. Here we review immunity to chlamydial genital infection and vaccine development using the C. muridarum model.

Immunization with a combination of integral chlamydial antigens and a defined secreted protein induces robust immunity against genital chlamydial challenge

We have previously demonstrated the efficacy of recombinant chlamydial protease-like activity factor (rCPAF; a secreted chlamydial protein) in inducing antigen-specific CD4+ T cell/gamma interferon (IFN-gamma)-mediated but not antibody-mediated chlamydial clearance and reduction of upper genital tract (UGT) pathological sequelae. Since chlamydial integral antigens may induce neutralizing antibody protection, we further evaluated induction of protective immunity using a combination of rCPAF and UV-inactivated chlamydial elementary bodies (UV-EB) against vaginal chlamydial challenge in comparison to immunization with the individual components or live EB. The rCPAF-UV-EB immunization induced a significantly enhanced anti-UV-EB cellular and antibody response and a reduced anti-CPAF cellular and antibody response, compared to immunization with the respective individual components. Moreover, vaccination with UV-EB and rCPAF-UV-EB induced serum antibodies that neutralized chlamydial infectivity. The rCPAF-UV-EB immunization resulted in a significant reduction of vaginal chlamydial shedding and induced earlier bacterial clearance than vaccination of mice with the individual components. Importantly, the UGT sequelae were significantly reduced in mice immunized with rCPAF or rCPAF-UV-EB, but not in those immunized with UV-EB alone, and approached the levels of protection induced by live EB. These results collectively suggest that a combination of neutralizing antibodies induced by integral chlamydial antigens and cell-mediated responses induced by secreted proteins such as CPAF induces optimal protective immunity against genital chlamydial infections.