Protection against infertility in a BALB/c mouse salpingitis model by intranasal immunization with the mouse pneumonitis biovar of Chlamydia trachomatis

Forty years of development of salpingitis animal modeling

This review summarizes and examines research in the area of salpingitis animal modeling in the last 40 years, focusing primarily on Chlamydia trachomatis animal models, which are the most numerous in the literature. Early animal models are examined, followed by a discussion of study parameters and their impact on modeling success, subsequent considerations of fertility measures in modeling, explorations of treatment options, and finally exploring recent directions with a brief discussion of models using other bacterial pathogens.

Evaluation of Four Adjuvant Combinations, IVAX-1, IVAX-2, CpG-1826+Montanide ISA 720 VG and CpG-1018+Montanide ISA 720 VG, for Safety and for Their Ability to Elicit Protective Immune Responses in Mice against a Respiratory Challenge with Chlamydia muridarum

There is an urgent need to produce a vaccine for Chlamydia trachomatis infections. Here, using the Chlamydia muridarum major outer membrane protein (MOMP) as an antigen, four adjuvant combinations IVAX-1 (MPLA+CpG-1018+AddaVax), IVAX-2 (MPLA+CpG-1018+AS03), CpG-1826+Montanide ISA 720 VG (CpG-1826+Mont) and CpG-1018+Montanide ISA 720 VG (CpG-1018+Mont), were tested for their local reactogenicity and ability to elicit protection in BALB/c mice against a respiratory challenge with C. muridarum. Immunization with IVAX-1 or IVAX-2 induced no significant local reactogenicity following intramuscular immunization. In contrast, vaccines containing Montanide resulted in the formation of a local granuloma. Based on the IgG2a/IgG1 ratio in serum, the four adjuvant combinations elicited Th1-biased responses. IVAX-1 induced the highest in vitro neutralization titers while CpG-1018+Mont stimulated the lowest. As determined by the levels of IFN-γ produced by T-cells, the most robust cellular immune responses were elicited in mice immunized with CpG-1018+Mont, while the weakest responses were mounted by mice receiving IVAX-1. Following the respiratory challenge, mice immunized with CpG-1018+Mont lost the least amount of body weight and had the lowest number of C. muridarum inclusion-forming units (IFUs) in the lungs, while those receiving IVAX-2 had lost the most weight and had the highest number of IFUs in their lungs. Animals vaccinated with CpG-1826+Mont had the lightest lungs while those immunized using IVAX-2 had the heaviest. To conclude, due to their safety and adjuvanticity, IVAX formulations should be considered for inclusion in human vaccines against Chlamydia.

A modular vaccine platform enabled by decoration of bacterial outer membrane vesicles with biotinylated antigens

Engineered outer membrane vesicles (OMVs) derived from Gram-negative bacteria are a promising technology for the creation of non-infectious, nanoparticle vaccines against diverse pathogens. However, antigen display on OMVs can be difficult to control and highly variable due to bottlenecks in protein expression and localization to the outer membrane of the host cell, especially for bulky and/or complex antigens. Here, we describe a universal approach for avidin-based vaccine antigen crosslinking (AvidVax) whereby biotinylated antigens are linked to the exterior of OMVs whose surfaces are remodeled with multiple copies of a synthetic antigen-binding protein (SNAP) comprised of an outer membrane scaffold protein fused to a biotin-binding protein. We show that SNAP-OMVs can be readily decorated with a molecularly diverse array of biotinylated subunit antigens, including globular and membrane proteins, glycans and glycoconjugates, haptens, lipids, and short peptides. When the resulting OMV formulations are injected in mice, strong antigen-specific antibody responses are observed that depend on the physical coupling between the antigen and SNAP-OMV delivery vehicle. Overall, these results demonstrate AvidVax as a modular platform that enables rapid and simplified assembly of antigen-studded OMVs for application as vaccines against pathogenic threats.

Chitosan particle stabilized Pickering emulsion/interleukin-12 adjuvant system for Pgp3 subunit vaccine elicits immune protection against genital chlamydial infection in mice

Considering the shortcomings in current chlamydia infection control strategies, a major challenge in curtailing infection is the implementation of an effective vaccine. The immune response induced by C. trachomatis plasmid encoded Pgp3 was insufficient against C. trachomatis infection, which requires adjuvant applications to achieve the robust immune response induced by Pgp3. There is increasing promising in developing adjuvant systems relying on the delivery potential of Pickering emulsions and the immunomodulatory effects of interleukin (IL)-12. Here, owing to the polycationic nature, chitosan particles tended to absorb on the oil/water interphase to prepare the optimized chitosan particle-stabilized Pickering emulsion (CSPE), which was designed as a delivery system for Pgp3 protein and IL-12. Our results showed that the average droplets size of CSPE was 789.47 ± 44.26 nm after a series of optimizations and about 90% antigens may be absorbed by CSPE owing to the positively charged surface (33.2 ± 3mV), and CSPE promoted FITC-BSA proteins uptake by macrophages. Furthermore, as demonstrated by Pgp3-specific antibody production and cytokine secretion, CSPE/IL-12 system enhanced significantly higher levels of Pgp3-specific IgG, IgG1, IgG2a, sIgA and significant cytokines secretion of IFN-γ, IL-2, TNF-α, IL-4. Similarly, vaginal chlamydial shedding and hydrosalpinx pathologies were markedly reduced in mice immunized with Pgp3/CSPE/IL-12. Collectively, vaccination with Pgp3/CSPE/IL-12 regimen elicited robust cellular and humoral immune response in mice resulting in an obvious reduction of live chlamydia load in the vaginal and inflammatory pathologies in the oviduct, which further propells the development of vaccines against C. trachomatis infection.

Role of TRAIL-R in Primary and Secondary Genital and Respiratory Chlamydia muridarum Infections in Mice

The tumor necrosis factor (TNF)-related apoptosis-inducing ligand receptor (TRAIL-R) suppresses inflammation and could therefore affect the course of Chlamydia infections and their long-term sequelae. Wild-type (WT) and TRAIL-R-/- C57BL/6 mice were inoculated vaginally with Chlamydia muridarum; the course of the infection was followed with vaginal cultures and the presence of hydrosalpinx determined. To evaluate the role of TRAIL-R following a secondary infection, the mice were vaginally reinfected. WT and TRAIL-R-/- male mice were also infected and reinfected in the respiratory tract, and the course of the diseases and the infections were followed. Following the primary and secondary vaginal infection, no significant differences in vaginal shedding or hydrosalpinx formation were observed between the WT and TRAIL-R-/- mice. The WT and TRAIL-R-/- mice mounted antibody responses in serum and vaginal washes that were not significantly different. After the primary and secondary intranasal infections of the male mice, changes in body weight were determined, and no significant differences were observed between the WT and TRAIL-R-/- mice. Ten days after the primary and the secondary infections, the weight of the lungs and number of C. muridarum inclusion forming units (IFU) were determined. The lungs of the WT mice weighed less compared with the TRAIL-R-/- mice following a primary infection but not after a secondary infection. No differences in the number of C. muridarum IFU in the lungs were observed between the two groups of mice. In conclusion, despite playing a role in inflammation cell-signaling pathways in vitro, TRAIL-R does not appear to play a major role in the susceptibility, clinical outcomes, or long-term sequelae of C. muridarum infections in vivo. IMPORTANCE TNF-related apoptosis-inducing ligand receptor (TRAIL-R) is involved in suppressing inflammatory responses. Bacterial pathogens such as Chlamydia spp. elicit inflammatory responses in humans following genital, ocular, and respiratory infections. The inflammatory responses are important to control the spread of Chlamydia. However, in certain instances, these inflammatory responses can produce long-term sequelae, including fibrosis. Fibrosis, or scarring, in the genital tract, eye, and respiratory system results in functional deficiencies, including infertility, blindness, and chronic obstructive lung disease, respectively. The goal of this study was to determine if mice deficient in TRAIL-R infected in the genital and respiratory tracts with Chlamydia spp. suffer more or less severe infections, infertility, or lung diseases than wild-type mice. Our results show no differences between the immune responses, infection severity, and long-term sequelae between TRAIL-R knockout and wild-type animals following a genital or a respiratory infection with Chlamydia.

Chlamydia trachomatis vaccine development - a view on the current challenges and how to move forward

INTRODUCTION

Chlamydia trachomatis is the most common sexually transmitted bacterial pathogen in the world. A licensed vaccine is not yet available, but the first vaccines have entered clinical trials.

AREAS COVERED

: We describe the progress that has been made in our understanding of the type of immunity that a protective vaccine should induce, and the challenges that vaccine developers face. We also focus on the clinical development of a chlamydia vaccine. The first chlamydia vaccine candidate has now been tested in a clinical phase-I trial, and another phase-I trial is currently running. We discuss what it will take to continue this development and what future trial setups could look like.

EXPERT OPINION

The chlamydia field is coming of age and the first phase I clinical trial of a C. trachomatis vaccine has been successfully completed. We expect and hope that this will motivate various stakeholders to support further development of chlamydia vaccines in humans.

Induction of Protection in Mice against a Chlamydia muridarum Respiratory Challenge by a Vaccine Formulated with the Major Outer Membrane Protein in Nanolipoprotein Particles

Chlamydia trachomatis is a sexually transmitted bacterium that infects over 130 million individuals worldwide annually. To implement a vaccine, we developed a cell-free co-translational system to express the Chlamydia muridarum major outer membrane protein (MOMP). This approach uses a nanolipoprotein particles (tNLP) made from ApoA1 protein, amphiphilic telodendrimer and lipids that self-assemble to form 10-25 nm discs. These tNLP provide a protein-encapsulated lipid support to solubilize and fold membrane proteins. The cell-free system co-translated MOMP and ApoA1 in the presence of telodendrimer mixed with lipids. The MOMP-tNLP complex was amenable to CpG and FSL-1 adjuvant addition. To investigate the ability of MOMP-tNLP+CpG+FSL-1 to induce protection against an intranasal (i.n.) C. muridarum challenge, female mice were vaccinated intramuscularly (i.m.) or i.n. and i.m. simultaneously 4 weeks apart. Following vaccination with MOMP-tNLP+CpG+FSL-1, mice mounted significant humoral and cell-mediated immune responses. Following the i.n. challenge, mice vaccinated with MOMP-tNLP+CpG+FSL-1 i.n. + i.m. group were protected as determined by the percentage change in body weight and by the number of C. muridarum inclusion forming units (IFU) recovered from the lungs. To our knowledge, this is the first time a MOMP-based vaccine formulated in tNLP has been shown to protect against C. muridarum.

Chlamydia-Specific IgA Secretion in the Female Reproductive Tract Induced via Per-Oral Immunization Confers Protection against Primary Chlamydia Challenge

Chlamydia trachomatis is an obligate intracellular pathogen that causes sexually transmitted disease. In women, chlamydial infections may cause pelvic inflammatory disease (PID), ectopic pregnancy, and infertility. The role of antibodies in protection against a primary Chlamydia infection is unclear and was a focus of this work. Using the C. muridarum mouse infection model, we show that intestinal mucosa is infected via intranasal (i.n.) or per-oral (p.o.) Chlamydia inoculation and that unlike the female reproductive tract (FRT) mucosa, it halts systemic Chlamydia dissemination. Moreover, p.o. immunization or infection with Chlamydia confers protection against per-vaginal (p.v.) challenge, resulting in significantly decreased bacterial burden in the FRT, accelerated Chlamydia clearance, and reduced hydrosalpinx pathology. In contrast, subcutaneous (s.c.) immunization conferred no protection against the p.v. challenge. Both p.o. and s.c. immunizations induced Chlamydia-specific serum IgA. However, IgA was found only in the vaginal washes and fecal extracts of p.o.-immunized animals. Following a p.v. challenge, unimmunized control and s.c.-s.c.-immunized animals developed Chlamydia-specific intestinal IgA yet failed to develop IgA in the FRT, indicating that IgA response in the FRT relies on the FRT to gastrointestinal tract (GIT) antigen transport. Vaginal secretions of p.o.-immunized animals neutralize Chlamydia in vivo, resulting in significantly lower Chlamydia burden in the FRT and Chlamydia transport to the GIT. We also show that infection of the GIT is not necessary for induction of protective immunity in the FRT, a finding that is important for the development of p.o. subunit vaccines to target Chlamydia and possibly other sexually transmitted pathogens.

Vaccination with the recombinant major outer membrane protein elicits long-term protection in mice against vaginal shedding and infertility following a Chlamydia muridarum genital challenge

Implementation of a vaccine is likely the best approach to curtail Chlamydia trachomatis infections. The aim of this study was to determine the ability of a vaccine formulated with the recombinant major outer membrane protein (MOMP) and Th1 and Th2 adjuvants, delivered by combinations of systemic and mucosal routes, to elicit long-term protection in mice against a genital challenge with Chlamydia muridarum. As a negative control, mice were vaccinated with the recombinant Neisseria gonorrhoeae porinB, and the positive control group was immunized with C. muridarum live elementary bodies (EB). The four vaccines formulated with MOMP, as determined by the titers of IgG and neutralizing antibodies in serum, proliferative responses of T-cells stimulated with EB and levels of IFN-γ in the supernatants, elicited robust humoral and cellular immune responses over a 6-month period. Groups of mice were challenged genitally at 60, 120, or 180 days postimmunization. Based on the number of mice with positive vaginal cultures, number of positive cultures, length of time of shedding, and number of inclusion forming units recovered, MOMP vaccinated groups were significantly protected. To assess fertility, when the vaginal cultures became negative, female mice were caged with male mice and the outcome of the pregnancy evaluated. As determined by the number of pregnant mice and the number of embryos, two of the vaccine formulations protected mice up to 180 days postimmunization. To our knowledge this is the first subunit of Chlamydia vaccine that has elicited in mice significant long-term protection against a genital challenge.

Induction of protection in mice against a respiratory challenge by a vaccine formulated with exosomes isolated from Chlamydia muridarum infected cells

The goal of this study was to determine if exosomes, isolated from Chlamydia muridarum infected HeLa cells (C. muridarum-exosomes), induce protective immune responses in mice following vaccination using CpG plus Montanide as adjuvants. Exosomes, collected from uninfected HeLa cells and PBS, formulated with the same adjuvants, were used as negative controls. Mass spectrometry analyses identified 113 C. muridarum proteins in the C. muridarum-exosome preparation including the major outer membrane protein and the polymorphic membrane proteins. Vaccination with C. muridarum-exosomes elicited robust humoral and cell-mediated immune responses to C. muridarum elementary bodies. Following vaccination, mice were challenged intranasally with C. muridarum. Compared to the negative controls, mice immunized with C. muridarum-exosomes were significantly protected as measured by changes in body weight, lungs' weight, and number of inclusion forming units recovered from lungs. This is the first report, of a vaccine formulated with Chlamydia exosomes, shown to elicit protection against a challenge.

Protection against a chlamydial respiratory challenge by a chimeric vaccine formulated with the Chlamydia muridarum major outer membrane protein variable domains using the Neisseria lactamica porin B as a scaffold

Chlamydia trachomatis is the most frequently detected sexually transmitted bacterial pathogen in the world. Attempts to control these infections with screening programs and antibiotics have failed and, therefore, a vaccine is the best approach to control this epidemic. The Chlamydia major outer membrane protein (MOMP) is the most protective subunit vaccine so far tested. Protection induced by MOMP is, in part, dependent on its tertiary structure. We have previously described new recombinant antigens composed of the Neisseria lactamica PorB engineered to express the variable domains (VD) from Chlamydia muridarum MOMP. Here we tested antigens containing each individual MOMP VD and different VD combinations. Following immunization, mice were challenged intranasally with C. muridarum. Our results show that three constructs, PorB/VD1-3, PorB/VD1-4, and PorB/VD1-2-4, elicited high serum IgG titers in vivo, significant IFN-γ levels upon T cells re-stimulation in vitro, and evidence of protective immunity in vivo. PorB/VD1-3, PorB/VD1-4, and PorB/VD1-2-4 immunized mice lost less body weight, had lighter lungs, and decreased numbers of inclusion forming units (IFUs) in lungs than other PorB/VD construct tested and mock PBS-immunized mice. These results suggest that this approach may be a promising alternative to the use of MOMP in a Chlamydia vaccine.

Protection of outbred mice against a vaginal challenge by a Chlamydia trachomatis serovar E recombinant major outer membrane protein vaccine is dependent on phosphate substitution in the adjuvant

Chlamydia trachomatis is the most common bacterial sexually-transmitted pathogen for which there is no vaccine. We previously demonstrated that the degree of phosphate substitution in an aluminum hydroxide adjuvant in a TLR-4-based C. trachomatis serovar E (Ser E) recombinant major outer membrane protein (rMOMP) formulation had an impact on the induced antibody titers and IFN-γ levels. Here, we have extended these observations using outbreed CD-1 mice immunized with C. trachomatis Ser E rMOMP formulations to evaluate the impact on bacterial challenge. The results confirmed that the rMOMP vaccine containing the adjuvant with the highest phosphate substitution induced the highest neutralizing antibody titers while the formulation with the lowest phosphate substitution induced the highest IFN-γ production. The most robust protection was observed in mice vaccinated with the formulation containing the adjuvant with the lowest phosphate substitution, as shown by the number of mice with positive vaginal cultures, number of positive cultures and number of C. trachomatis inclusion forming units recovered. This is the first report showing that vaccination of an outbred strain of mice with rMOMP induces protection against a vaginal challenge with C. trachomatis.

A Recombinant Chlamydia trachomatis MOMP Vaccine Elicits Cross-serogroup Protection in Mice Against Vaginal Shedding and Infertility

BACKGROUND

Chlamydia trachomatis is the most common sexually transmitted bacterial pathogen worldwide. Here, we determined the ability of a C. trachomatis recombinant major outer membrane protein (rMOMP) vaccine to elicit cross-serogroup protection.

METHODS

Female C3H/HeN mice were vaccinated by mucosal and systemic routes with C. trachomatis serovar D (UW-3/Cx) rMOMP and challenged in the ovarian bursa with serovars D (UW-3/Cx), D (UCI-96/Cx), E (IOL-43), or F (N.I.1). CpG-1826 and Montanide ISA 720 were used as adjuvants.

RESULTS

Immune responses following vaccination were more robust against the most closely related serovars. Following a genital challenge (as determined by number of mice with positive vaginal cultures, number of positive cultures, number of inclusion forming units recovered, and number of days with positive cultures) mice challenged with C. trachomatis serovars of the same complex were protected but not those challenged with serovar F (N.I.1) from a different subcomplex. Females were caged with male mice. Based on fertility rates, number of embryos, and hydrosalpinx formation, vaccinated mice were protected against challenges with serovars D (UW-3/Cx), D (UCI-96/Cx), and E (IOL-43) but not F (N.I.1).

CONCLUSIONS

This is the first subunit vaccine shown to protect mice against infection, pathology, and infertility caused by different C. trachomatis serovars.

Spectroscopic analysis of chlamydial major outer membrane protein in support of structure elucidation

Chlamydial major outer membrane protein (MOMP) is the major protein constituent of the bacterial pathogen Chlamydia trachomatis. Chlamydia trachomatis Serovars D–K are the leading cause of genital tract infections which can lead to infertility or ectopic pregnancies. A vaccine against Chlamydia is highly desirable but currently not available. MOMP accounts for ~ 60% of the chlamydial protein mass and is considered to be one of the lead vaccine candidates against C. trachomatis. We report on the spectroscopic analysis of C. trachomatis native MOMP Serovars D, E, F, and J as well as C. muridarum MOMP by size exclusion chromatography multi angle light scattering (SEC MALS), circular dichroism (CD) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR‐FTIR). MOMP was purified from the native bacterium grown in either adherent HeLa cells or in different suspension cell lines. Our results confirm that MOMP forms homo‐trimers in detergent micelles. The secondary structure composition of C. trachomatis MOMP was conserved across serovars, but different from composition of C. muridarum MOMP with a 13% (CD) to 18% (ATR‐FTIR) reduction in β‐sheet conformation for C. trachomatis MOMP. When Serovar E MOMP was isolated from suspension cell lines the α‐helix content increased by 7% (CD) to 13% (ATIR‐FTIR). Maintenance of a native‐like tertiary and quaternary structure in subunit vaccines is important for the generation of protective antibodies. This biophysical characterization of MOMP presented here serves, in the absence of functional assays, as a method for monitoring the structural integrity of MOMP.

Characterization of the Horizontal and Vertical Sexual Transmission of Chlamydia Genital Infections in a New Mouse Model

Chlamydia trachomatis is the most common sexually transmitted bacterial pathogen worldwide, and there is a need to control this epidemic. So far there is no established animal model in which both the horizontal and the vertical transmission of Chlamydia can be studied. To implement a horizontal sexual transmission model, male mice were inoculated in the meatus urethra with Chlamydia muridarum and they were caged with naive female mice. Urine and vaginal swab specimens were collected for culture. To study vertical transmission, newborns were euthanized and specimens were cultured. As controls, females were mated with sham-infected male mice. All C. muridarum-inoculated male mice had positive urine cultures. As determined by serology, all females caged with C. muridarum-inoculated males became infected, and 93% of them had positive vaginal swab specimen cultures. More females mated with C. muridarum-infected male mice (35%) than females mated with sham-infected male mice (0%) were infertile (P < 0.05). Also, C. muridarum-infected females delivered significantly fewer pups (3.8 ± 3.2/mouse) than control females (6.3 ± 1.6/mouse) (P < 0.05). Of the newborn mice, 32% were C. muridarum positive either in the lungs or in the intestines. Female mice housed with sham-infected males had no positive vaginal swab specimen cultures or C. muridarum-positive pups. This new mouse model of horizontal and vertical sexual transmission of Chlamydia closely parallels C. trachomatis sexual transmission in humans and may be a good model system to better understand the pathogenesis of these infections.

Seventy Years of Chlamydia Vaccine Research - Limitations of the Past and Directions for the Future

Chlamydia is a major bacterial pathogen that infects humans, as well as a wide range of animals, including marsupials, birds, cats, pigs, cattle, and sheep. Antibiotics are the only treatment currently available, however, with high rates of re-infection, there is mounting pressure to develop Chlamydia vaccines. In this review, we analyzed how Chlamydia vaccine trials have developed over the past 70 years and identified where future trials need to be focused. There has been a strong bias toward studies targeting C. muridarum and C. trachomatis within mice and a lack of studies matching chlamydial species to their end target host. Even though a large number of specific antigenic targets have been studied, the results from whole-cell vaccine targets show slightly more promising results overall. There has also been a strong bias toward systemic vaccine delivery systems, despite the finding that mucosal delivery systems have shown more promising outcomes. However, the only successful vaccines with matched chlamydial species/infecting host are based on systemic vaccine delivery methods. We highlight the extensive work done with mouse model trials and indicate that whole cell antigenic targets are capable of inducing an effective response, protecting from disease and reducing shedding rates. However, replication of these results using antigen preparations more conducive to commercial vaccine production has proven difficult. To date, the Major Outer Membrane Protein (MOMP) has emerged as the most suitable substitute for whole cell targets and its delivery as a combined systemic and mucosal vaccine is most effective. Finally, although mouse model trials are useful, differences between hosts and infecting chlamydial strains are preventing vaccine formulations from mouse models to be translated into larger animals or intended hosts.

The Chlamydia M278 Major Outer Membrane Peptide Encapsulated in the Poly(lactic acid)-Poly(ethylene glycol) Nanoparticulate Self-Adjuvanting Delivery System Protects Mice Against a Chlamydia muridarum Genital Tract Challenge by Stimulating Robust Systemic and Local Mucosal Immune Responses

Recently, we reported that our PPM chlamydial nanovaccine [a biodegradable co-polymeric PLA-PEG (poly(lactic acid)-poly(ethylene glycol))-encapsulated M278 peptide (derived from the major outer membrane protein (MOMP) of Chlamydia)] exploits the caveolin-mediated endocytosis pathway for endosomal processing and MHC class II presentation to immune-potentiate Chlamydia-specific CD4⁺ T-cell immune effector responses. In the present study, we employed the Chlamydia muridarum mouse infection model to evaluate the protective efficacy of PPM against a genital tract challenge. Our results show that mice immunized with PPM were significantly protected against a homologous genital tract challenge evidently by reduced vaginal bacterial loads. Protection of mice correlated with enhanced Chlamydia-specific adaptive immune responses predominated by IFN-γ along with CD4⁺ T-cells proliferation and their differentiation to CD4⁺ memory (CD44^high CD62L^high) and effector (CD44^high CD62L^low) T-cell phenotypes. We observed the elevation of M278- and MOMP-specific serum antibodies with high avidity in the ascending order IgG1 > IgG2b > IgG2a. A key finding was the elevated mucosal IgG1 and IgA antibody titers followed by an increase in MOMP-specific IgA after the challenge. The Th1/Th2 antibody titer ratios (IgG2a/IgG1 and IgG2b/IgG1) revealed that PPM evoked a Th2-directed response, which skewed to a Th1-dominated antibody response after the bacterial challenge of mice. In addition, PPM immune sera neutralized the infectivity of C. muridarum in McCoy cells, suggesting the triggering of functional neutralizing antibodies. Herein, we reveal for the first time that subcutaneous immunization with the self-adjuvanting biodegradable co-polymeric PPM nanovaccine immune-potentiated robust CD4⁺ T cell-mediated immune effector responses; a mixed Th1 and Th2 antibody response and local mucosal IgA to protect mice against a chlamydial genital tract challenge.

Transcervical Inoculation with Chlamydia trachomatis Induces Infertility in HLA-DR4 Transgenic and Wild-Type Mice

Chlamydia trachomatis is the leading cause of infection-induced infertility in women. Attempts to control this epidemic with screening programs and antibiotic therapy have failed. Currently, a vaccine to prevent C. trachomatis infections is not available. In order to develop an animal model for evaluating vaccine antigens that can be applied to humans, we used C. trachomatis serovar D (strain UW-3/Cx) to induce infertility in mice whose major histocompatibility complex class II antigen was replaced with the human leukocyte antigen DR4 (HLA-DR4). Transcervical inoculation of medroxyprogesterone-treated HLA-DR4 transgenic mice with 5 × 10⁵C. trachomatis D inclusion forming units (IFU) induced a significant reduction in fertility, with a mean number of embryos/mouse of 4.4 ± 1.3 compared to 7.8 ± 0.5 for the uninfected control mice (P < 0.05). A similar fertility reduction was elicited in the wild-type (WT) C57BL/6 mice (4.3 ± 1.4 embryos/mouse) compared to the levels of the WT controls (9.1 ± 0.4 embryos/mouse) (P < 0.05). Following infection, WT mice mounted more robust humoral and cellular immune responses than HLA-DR4 mice. As determined by vaginal shedding, HLA-DR4 mice were more susceptible to a transcervical C. trachomatis D infection than WT mice. To assess if HLA-DR4 transgenic and WT mice could be protected by vaccination, 10⁴ IFU of C. trachomatis D was delivered intranasally, and mice were challenged transcervically 6 weeks later with 5 × 10⁵ IFU of C. trachomatis D. As determined by severity and length of vaginal shedding, WT C57BL/6 and HLA-DR4 mice were significantly protected by vaccination. The advantages and limitations of the HLA-DR4 transgenic mouse model for evaluating human C. trachomatis vaccine antigens are discussed.

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.

Computational modeling of TC0583 as a putative component of the Chlamydia muridarum V-type ATP synthase complex and assessment of its protective capabilities as a vaccine antigen

Numerous Chlamydia trachomatis proteins have been identified as potential subunit vaccines, of which the major outer-membrane protein (MOMP) has, so far, proven the most efficacious. Recently, subunit A of the V-type ATP synthase (ATPase; TC0582) complex was shown to elicit partial protection against infection. Computational modeling of a neighboring gene revealed a novel subunit of the V-type ATPase (TC0583). To determine if this newly identified subunit could induce protection and/or enhance the partial protection provided by subunit A alone, challenge studies were performed using a combination of these recombinant proteins. The TC0583 subunit alone and concurrently with TC0582, was used to vaccinate BALB/c mice utilizing CpG-1826 and Montanide ISA 720 VG as adjuvants. Vaccinated animals were challenged intranasally with Chlamydia muridarum and the course of the infection was followed. Mice immunized with individual antigens showed minimal alleviation of body weight reduction; however, mice immunized with TC0583 and TC0582 in combination, displayed weight loss levels close to those observed with MOMP. Importantly, immunization with a combination of recombinant subunit proteins reduced chlamydial inclusion forming units by approximately a log-fold. These protection levels support that, these highly conserved Chlamydia proteins, in combination with other antigens, may serve as potential vaccine candidates.

A vaccine formulated with the major outer membrane protein can protect C3H/HeN, a highly susceptible strain of mice, from a Chlamydia muridarum genital challenge

C3H/HeN female mice were vaccinated with native Chlamydia muridarum major outer membrane protein (MOMP), using Montanide+CpG or Alum+CpG as adjuvants. Negative control groups were immunized with ovalbumin (OVA) and the same adjuvants. As positive control, mice were inoculated intranasally with live Chlamydia. Mice were challenged in the ovarian bursa with 10(5) C. muridarum inclusion forming units. Six weeks after the genital challenge the animals were caged with male mice and monitored for pregnancy. Mice vaccinated with MOMP+Montanide+CpG developed high levels of C. muridarum-specific antibodies, with a high IgG2a/IgG1 ratio and neutralizing titres. Animals immunized using Alum+CpG had low antibody levels. Cellular immune responses were significantly higher in mice vaccinated with MOMP and Montanide+CpG, but not with Alum+CpG, when compared with negative controls. Following the genital challenge, only 20% (4/20) of mice vaccinated with MOMP+CpG+Montanide had positive vaginal cultures whereas 100% (9/9) of mice immunized with MOMP+CpG+Alum had positive cultures. Of the positive control animals inoculated with live Chlamydia only 15% (3/20) had positive vaginal cultures. In contrast, 100% (20/20) of mice immunized with OVA+CpG+Montanide, or minimal essential medium, had positive cultures. Following mating, 80% (16/20) of mice vaccinated with MOMP+CpG+Montanide, and 85% (17/20) of animals inoculated intranasally with live C. muridarum carried embryos in both uterine horns. No protection against infertility was observed in mice immunized with MOMP and CpG+Alum or OVA. In conclusion, this is the first time that a subunit vaccine has been shown to elicit a protective immune response in the highly susceptible C3H/HeN strain of mice against an upper genital challenge.

Comparison of subcutaneous versus intranasal immunization of male koalas (Phascolarctos cinereus) for induction of mucosal and systemic immunity against Chlamydia pecorum

Chlamydia pecorum infections are debilitating in the koala, contributing significantly to morbidity and mortality, with current antibiotic treatments having minimal success and adversely affecting gut microflora. This, combined with the sometimes-asymptomatic nature of the infection, suggests that an efficacious anti-chlamydial vaccine is required to control chlamydial infections in the koala. To date vaccination studies have focused primarily on female koalas, however, given the physiological differences between male and female reproductive tracts, we tested the efficacy of a vaccine in 12 captive male koalas. We evaluated the potential of both subcutaneous and intranasal vaccine delivery to elicit mucosal immunity in male koalas. Our results showed that both intranasal and subcutaneous delivery of a vaccine consisting of C. pecorum major outer membrane protein (MOMP) and the adjuvant immunostimulating complex (ISC) induced significant immune responses in male koalas. Subcutaneous immunization elicited stronger cell-mediated responses in peripheral blood lymphocytes (PBL), and greater plasma antibody levels whereas the intranasal immunization elicited stronger humoral responses in urogenital tract (UGT) secretions. This is the first time a Chlamydia vaccine has been tested in the male koala and the first assessment of a mucosal vaccination route in this species. Our results suggest that vaccination of male koalas can elicit mucosal immunity and could contribute to the long-term survivability of wild populations of the koala.

Increased immunoaccessibility of MOMP epitopes in a vaccine formulated with amphipols may account for the very robust protection elicited against a vaginal challenge with Chlamydia muridarum

There is a need to implement a vaccine to protect against Chlamydia trachomatis infections. To test a new vaccine, mice were immunized with the Chlamydia muridarum native major outer membrane protein (nMOMP) solubilized with either amphipol A8-35 or the detergent Z3-14. OVA was used as a negative control, and mice were inoculated intranasally with C. muridarum as positive controls. Animals vaccinated with nMOMP mounted strong Chlamydia-specific humoral and cell-mediated immune responses. Mice vaccinated with nMOMP/A8-35 had a higher ratio of Abs to denatured elementary bodies (EB) over live EB, recognized more synthetic MOMP peptides and had higher neutralizing titers than sera from mice immunized with nMOMP/Z3-14. T cell lymphoproliferative responses and levels of IFN-γ were also higher in mice vaccinated with nMOMP/A8-35 than with nMOMP/Z3-14. Following immunization, animals were challenged intravaginally with C. muridarum. On the basis of the number of mice with positive vaginal cultures, length of vaginal shedding, total number of positive vaginal cultures, and number of Chlamydia inclusion forming units recovered, nMOMP/A8-35 elicited a more robust protection than nMOMP/Z3-14. By depleting T cells with Abs, we determined that CD4(+) and not CD8(+) T cells mediated the protection elicited by nMOMP/A8-35. Mice were subsequently mated, and based on the number of pregnant mice and number of embryos, animals that were vaccinated with nMOMP/A8-35 or nMOMP/Z3-14 had fertility rates equivalent to the positive control group immunized with live EB and the fertility controls. In conclusion, increased accessibility of epitopes in the nMOMP/A8-35 preparation may account for the very robust protection against infection and disease elicited by this vaccine.

A vaccine formulated with a combination of TLR-2 and TLR-9 adjuvants and the recombinant major outer membrane protein elicits a robust immune response and significant protection against a Chlamydia muridarum challenge

Chlamydia trachomatis is the most common sexually transmitted bacterial pathogen in the World and there is a need for a vaccine. To enhance the immunogenicity of a vaccine formulated with the Chlamydia muridarum (Cm) mouse pneumonitis recombinant major outer membrane protein (MOMP), we used combinations of Pam2CSK4 + CpG-1826 and Montanide ISA 720 VG + CpG-1826 as adjuvants. Neisseria gonorrhoeae recombinant porin B (Ng-PorB) was used as the antigen control with the same adjuvants. Female BALB/c mice were immunized twice in the nares (i.n.) or in the colon (cl.) and were boosted twice by the intramuscular plus subcutaneous (i.m. + s.c.) routes. Based on the IgG2a/IgG1 ratio in sera, mice immunized with MOMP + Pam2CSK4 + CpG-1826 showed a strong Th2 response while animals vaccinated with MOMP + Montanide ISA 720 VG + CpG-1826 had a Th1 response. Both groups of mice also developed robust Cm-specific T cell proliferation and high levels of IFN-γ. Four weeks after the last immunization, the mice were challenged i.n. with 10(4) inclusion-forming units (IFU) of Cm. Using changes in body weight and number of IFU recovered from the lungs at 10 days post-challenge mice immunized i.n. + i.m./s.c. with MOMP + Pam2CSK4 + CpG-1826 were better protected than other groups. In conclusion, MOMP adjuvanted with Pam2CSK4 + CpG-1826, elicits strong humoral and cellular immune responses and induces significant protection against Chlamydia.

Assessment of the role in protection and pathogenesis of the Chlamydia muridarum V-type ATP synthase subunit A (AtpA) (TC0582)

A novel Chlamydia muridarum antigen (TC0582) was used to vaccinate BALB/c mice. Mice were also immunized with other components of the ATP synthase complex (TC0580, TC0581, and TC0584), or with the major outer membrane protein (MOMP). TC0582 was also formulated in combination with TC0580, TC0581 or MOMP. TC0582 alone, or in combination with the other antigens, elicited strong Chlamydia-specific humoral and cellular immune responses. Vaccinated animals were challenged intranasally and the course of the infection was followed for 10 days. Based on percentage change in body weight, lung weight, and number of Chlamydia inclusion forming units recovered from the lungs, mice immunized with TC0582, TC0581 or MOMP, as single antigens, showed significant protection. Mice immunized with combinations of two antigens were also protected but the level of protection was not additive. TC0582 has sequence homology with the eukaryotic ATP synthase subunit A (AtpA). Therefore, to determine if immunization with TC0582, or with Chlamydia, elicited antibodies that cross-reacted with the mouse AtpA, the two proteins were printed on a microarray. Sera from mice immunized with TC0582 and/or live Chlamydia, strongly reacted with TC0582 but did not recognize the mouse AtpA. In conclusion, TC0582 may be considered as a Chlamydia vaccine candidate.

The duration of Chlamydia muridarum genital tract infection and associated chronic pathological changes are reduced in IL-17 knockout mice but protection is not increased further by immunization

IL-17 is believed to be important for protection against extracellular pathogens, where clearance is dependent on neutrophil recruitment and local activation of epithelial cell defences. However, the role of IL-17 in protection against intracellular pathogens such as Chlamydia is less clear. We have compared (i) the course of natural genital tract C. muridarum infection, (ii) the development of oviduct pathology and (iii) the development of vaccine-induced immunity against infection in wild type (WT) BALB/c and IL-17 knockout mice (IL-17-/-) to determine if IL-17-mediated immunity is implicated in the development of infection-induced pathology and/or protection. Both the magnitude and duration of genital infection was significantly reduced in IL-17-/- mice compared to BALB/c. Similarly, hydrosalpinx was also greatly reduced in IL-17-/- mice and this correlated with reduced neutrophil and macrophage infiltration of oviduct tissues. Matrix metalloproteinase (MMP) 9 and MMP2 were increased in WT oviducts compared to IL-17-/- animals at day 7 post-infection. In contrast, oviducts from IL-17-/- mice contained higher MMP9 and MMP2 at day 21. Infection also elicited higher levels of Chlamydia-neutralizing antibody in serum of IL-17-/- mice than WT mice. Following intranasal immunization with C. muridarumMajor Outer Membrane Protein (MOMP) and cholera toxin plus CpG adjuvants, significantly higher levels of chlamydial MOMP-specific IgG and IgA were found in serum and vaginal washes of IL-17-/- mice. T cell proliferation and IFNγ production by splenocytes was greater in WT animals following in vitro re-stimulation, however vaccination was only effective at reducing infection in WT, not IL-17-/- mice. Intranasal or transcutaneous immunization protected WT but not IL-17-/- mice against hydrosalpinx development. Our data show that in the absence of IL-17, the severity of C. muridarum genital infection and associated oviduct pathology are significantly attenuated, however neither infection or pathology can be reduced further by vaccination protocols that effectively protect WT mice.

Vaccination with major outer membrane protein proteosomes elicits protection in mice against a Chlamydia respiratory challenge

Vaccines formulated with the Chlamydia muridarum native major outer membrane protein (nMOMP) have so far been shown to elicit the most robust protection against this pathogen. nMOMP is a membrane protein and therefore, detergents are used to keep it in solution. Detergents however, have toxic effects. To address this limitation, we tested a nMOMP proteosome vaccine and compared its ability to elicit protection against nMOMP solubilized in the detergent Z3-14. The two preparations were formulated with or without CpG + Montanide (C/M). As a control antigen we used ovalbumin. Mice vaccinated with nMOMP developed strong humoral and cell mediated Chlamydia-specific immune responses. Based on the IgG2a/IgG1 levels in serum and amounts of IFN-γ in splenocytes supernatants the immune responses were predominantly Th1-biased. The animals were subsequently challenged intranasally with 2 × 10(3)Chlamydia inclusion forming units (IFU) and the course of the infection was followed for 10 days when the mice were euthanized. Based on changes in body weight, weight of the lungs and number of IFU recovered from the lungs, mice immunized with nMOMP-Ps and nMOMP + Z3-14 adjuvanted with C/M showed the most robust protection. In summary, nMOMP-Ps should be considered as Chlamydia vaccine candidates.

Mechanism of T-cell mediated protection in newborn mice against a Chlamydia infection

To determine the immune components needed for protection of newborn mice against Chlamydia muridarum, animals born to Chlamydia-immunized and to sham-immunized dams were infected intranasally with C. muridarum at 2 post-natal days. T-cells isolated from immunized or sham-immunized adult mice were adoptively transferred to newborn mice at the time of infection. Also, to establish what cytokines are involved in protection, IFN-γ, TNF-α, IL-10, and IL-12 were passively transferred to newborn mice. To assess the Chlamydia burden in the lungs mice were euthanized at 12 post-natal days. When T-cells from immunized adult mice were transferred, mice born to and fed by immunized dams were significantly protected as evidenced by the reduced number of Chlamydia isolated from the lungs compared to mice born to and fed by sham-immunized dams. Transfer of IFN-γ and TNF-α also significantly reduced the number of Chlamydia in the lungs of mice born to immunized dams. Transfer of IL-10 or IL-12 did not result in a significant reduction of Chlamydia. In vitro T-cell proliferation data suggest that neonatal antigen presenting cells can present Chlamydia antigens to adult T-cells. In conclusion, maternal antibodies and Chlamydia specific T-cells or Th1 cytokines are required for protection of neonates against this pathogen.

Vaccination with the recombinant major outer membrane protein elicits antibodies to the constant domains and induces cross-serovar protection against intranasal challenge with Chlamydia trachomatis

To determine the ability of the major outer membrane protein (MOMP) to elicit cross-serovar protection, groups of mice were immunized by the intramuscular (i.m.) and subcutaneous (s.c.) routes with recombinant MOMP (rMOMP) from Chlamydia trachomatis serovars D (UW-3/Cx), E (Bour), or F (IC-Cal-3) or Chlamydia muridarum strain Nigg II using CpG-1826 and Montanide ISA 720 VG as adjuvants. Negative-control groups were immunized i.m. and s.c. with Neisseria gonorrhoeae recombinant porin B (Ng-rPorB) or i.n. with Eagle's minimal essential medium (MEM-0). Following vaccination, the mice developed antibodies not only against the homologous serovar but also against heterologous serovars. The rMOMP-vaccinated animals also mounted cell-mediated immune responses as assessed by a lymphoproliferative assay. Four weeks after the last immunization, mice were challenged i.n. with 10(4) inclusion-forming units (IFU) of C. muridarum. The mice were weighed for 10 days and euthanized, and the number of IFU in their lungs was determined. At 10 days postinfection (p.i.), mice immunized with the rMOMP of C. muridarum or C. trachomatis D, E, or F had lost 4%, 6%, 8%, and 8% of their initial body weight, respectively, significantly different from the negative-control groups (Ng-rPorB, 13%; MEM-0, 19%; P < 0.05). The median number of IFU recovered from the lungs of mice immunized with C. muridarum rMOMP was 0.13 × 10(6). The median number of IFU recovered from mice immunized with rMOMP from serovars D, E, and F were 0.38 × 10(6), 7.56 × 10(6), and 11.94 × 10(6) IFU, respectively. All the rMOMP-immunized animals had significantly less IFU than the Ng-rPorB (40 × 10(6))- or MEM-0 (70 × 10(6))-immunized mice (P < 0.05). In conclusion, vaccination with rMOMP can elicit protection against homologous and heterologous Chlamydia serovars.

Differences in infectivity and induction of infertility: a comparative study of Chlamydia trachomatis strains in the murine model

Chlamydia trachomatis, although commonly asymptomatic in women, can result in chronic sequelae, such as pelvic inflammatory disease, ectopic pregnancy and infertility. However, a clear relationship has not been determined between specific serovars and the ability to lead to upper genital tract infection or infertility. Thus, in order to investigate differences in pathogenicity, C3H/HeN mice were infected in the ovarian bursa with the C. trachomatis strains D (UW-3/Cx), F (N.I.1), F (IC-Cal-3) and E (Bour). Differences both in the amount of vaginal shedding as well as subsequent fertility rates were observed between D (UW-3/Cx) and F (N.I.1) compared to F (IC-Cal-3) and E (Bour). Approximately 50% of the mice infected with the D (UW-3/Cx) and F (N.I.1) strains had vaginal shedding for up to 3-4 weeks after infection and fertility rates of less than 25%. Furthermore, mice inoculated with D (UW-3/Cx) and F (N.I.1) showed infertility even in the absence of medroxy progesterone acetate (MPA) treatment. In contrast, both MPA and non-MPA treated mice infected with F (IC-Cal-3) or E (Bour) did not show vaginal shedding and had fertility rates between 45 and 88%. Mutations in the CT135 open reading frame have been associated with virulence. However, no nucleotide differences were found among the four isolates for CT135. This murine model of infection with C. trachomatis may help with the understanding of disease pathology in humans and ultimately vaccine development.

Proteomic identification of immunodominant chlamydial antigens in a mouse model

Chlamydia trachomatis is the most common bacterial sexually transmitted pathogen in the world. To identify new vaccine candidates a protein microarray was constructed by expressing the open reading frames (ORFs) from Chlamydia mouse pneumonitis (MoPn). C57BL/6, C3H/HeN and BALB/c mice were immunized either intranasally or intravaginally with live MoPn elementary bodies (EB). Two additional groups were immunized by the intramuscular plus subcutaneous routes with UV-treated EB, using CpG and Montanide as adjuvants to favor a Th1 response, or Alum, to elicit a Th2 response. Serum samples collected from the three strains of mice were tested in the microarray. The array included the expression of 909 proteins from the 921 ORFs of the MoPn genome and plasmid. A total of 530 ORFs were recognized by at least one serum sample. Of these, 36 reacted with sera from the three strains of mice immunized with live EB. These antigens included proteins that were previously described as immunogenic such as MOMP and HSP60. In addition, we uncovered new immunogens, including 11 hypothetical proteins. In summary, we have identified new immunodominant chlamydial proteins that can be tested for their ability to induce protection in animal models and subsequently in humans.

A TLR2 agonist is a more effective adjuvant for a Chlamydia major outer membrane protein vaccine than ligands to other TLR and NOD receptors

Chlamydia trachomatis (Ct) is the most common sexually transmitted bacterial pathogen in the World and there is an urgent need for a vaccine to prevent these infections. To determine what type of adjuvant can better enhance the immunogenicity of a Chlamydia vaccine, we formulated the recombinant major outer membrane protein (Ct-rMOMP) with several ligands for Toll-like receptors (TLR) and the nucleotide-binding oligomerization domain (NOD) including Pam(2)CSK(4) (TLR2/TLR6), Poly (I:C) (TLR3), monophosphoryl lipid A (TLR4), flagellin (TLR5), imiquimod R837 (TLR7), imidazoquinoline R848 (TRL7/8), CpG-1826 (TLR9), M-Tri-(DAP) (NOD1/NOD2) and muramyldipeptide (NOD2). Groups of female BALB/c mice were immunized intramuscularly (i.m.) three times with the Ct-rMOMP and each one of those adjuvants. Four weeks after the last immunization the mice were challenged intranasally (i.n.) with 10(4)C. trachomatis mouse pneumonitis (MoPn) inclusion forming units (IFU). As negative antigen control, mice were immunized with the Neisseria gonorrhoeae recombinant porin B (Ng-rPorB) and the same adjuvants. As a positive vaccine control, mice were inoculated i.n. with 10(4)IFU of MoPn. The humoral and cell mediated immune responses were determined the day before the challenge. Following the challenge the mice were weighed daily and, at 10 days post-challenge (p.c.), they were euthanized, their lungs weighted and the number of IFU in the lungs counted. As determined by the IgG2a/IgG1 ratio in the sera, mice immunized with Ct-rMOMP+Pam(2)CSK(4) showed a strong Th2 biased humoral immune response. Furthermore, these mice developed a robust cellular immune response with high Chlamydia-specific T cell proliferation and levels of IFN-γ production. In addition, based on changes in body weight, weight of the lungs and number of IFU recovered from the lungs, the mice immunized with Ct-rMOMP+Pam(2)CSK(4), were better protected against the i.n. challenge than any group of mice immunized with Ct-rMOMP and the other adjuvants. In conclusion, Pam(2)CSK(4) should be evaluated as a candidate adjuvant for a C. trachomatis vaccine.

Induction of protection against vaginal shedding and infertility by a recombinant Chlamydia vaccine

A vaccine formulated with the Chlamydia muridarum recombinant major outer membrane protein, plus the adjuvants CpG and Montanide, was tested for its ability to protect BALB/c mice against a vaginal challenge. Mice were immunized by mucosal [intravaginal (i.vag.) plus colonic (col.), or intranasal (i.n.) plus sublingual (s.l.)], or systemic [intramuscular (i.m.) plus subcutaneous (s.c.)] routes, and a combination of mucosal priming and systemic boosting routes. A negative control group was vaccinated with the Neisseria gonorrhoeae porin B (Ng-rPorB) and a positive control group was inoculated in the nares with live Chlamydia. The strongest Chlamydia-specific humoral and cell-mediated immune responses were observed in the groups immunized by a combination of mucosal and systemic routes. Following the vaginal challenge, groups immunized using mucosal priming followed by systemic immunization had a significant decrease in the number of mice with positive vaginal cultures. For example, of the mice immunized i.n./s.l.+i.m./s.c., 24% had positive cultures during the six weeks of the experiment versus 69% for the negative control group immunized with Ng-rPorB (P<0.05). Similarly, the groups of mice primed by the mucosal routes and boosted by the systemic routes had significantly less IFU in the vaginal cultures when compared to the Ng-rPorB animals (P<0.05). These combination groups were also protected against infertility. The two groups had fertility rates of 100% (i.n./s.l.+i.m./s.c.) and 81% (i.vag./col.+i.m./s.c.) equivalent to the positive-control group immunized with live Chlamydia (100% fertility; P>0.05). These results show the importance of the schedule and routes of vaccination and represent the first study to show protection against infertility by a Chlamydia recombinant subunit vaccine.

Amphipols stabilize the Chlamydia major outer membrane protein and enhance its protective ability as a vaccine

The native major outer membrane protein (nMOMP) from Chlamydia was purified in its trimeric form using the zwitterionic detergent Z3-14. In aliquots from this preparation, Z3-14 was exchanged for amphipol (APol) A8-35. CD analysis showed that trapping with A8-35 improved the thermostability of nMOMP without affecting its secondary structure. Recombinant MOMP (rMOMP) was also formulated with Z3-14 or A8-35. Four groups of mice were vaccinated with nMOMP/Z3-14, nMOMP/A8-35, rMOMP/Z3-14 or rMOMP/A8-35 using CpG and Montanide as adjuvants. A positive control group was inoculated intranasally with live Chlamydia and a negative control group with culture medium. Mice were challenged intranasally with live Chlamydia and protection was assessed based on changes in body weight, the weight of the lungs and the number of chlamydial inclusion forming units recovered from the lungs 10 days after the challenge. Overall, vaccines formulated with nMOMP elicited better protection than those using rMOMP. Furthermore, the protection afforded by nMOMP/A8-35 was more robust than that achieved with nMOMP/Z3-14. In contrast, no differences in protection were observed between rMOMP/Z3-14 and rMOMP/A8-35 preparations. These findings suggest that the higher protection conferred by nMOMP/A8-35 complexes most likely results from a better preservation of the native structure of MOMP and/or from a more efficient presentation of the antigen to the immune system, rather than from an adjuvant effect of the amphipol. Thus, amphipols can be used in vaccine formulations to stabilize a membrane-protein component and enhance its immunogenicity.

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.

Identification of immunodominant antigens by probing a whole Chlamydia trachomatis open reading frame proteome microarray using sera from immunized mice

Chlamydia trachomatis infections can lead to severe chronic complications, including trachoma, ectopic pregnancy, and infertility. The only effective approach to disease control is vaccination. The goal of this work was to identify new potential vaccine candidates through a proteomics approach. We constructed a protein chip array (Antigen Discovery, Inc.) by expressing the open reading frames (ORFs) from C. trachomatis mouse pneumonitis (MoPn) genomic and plasmid DNA and tested it with serum samples from MoPn-immunized mice. Two groups of BALB/c female mice were immunized either intranasally or intravaginally with live elementary bodies (EB). Another two groups were immunized by a combination of the intramuscular and subcutaneous routes with UV-treated EB (UV-EB), using either CpG and Montanide as adjuvants to favor a Th1 response or alum to elicit a Th2 response. Serum samples collected at regular intervals postimmunization were tested in the proteome array. The microarray included the expression products of 909 proteins from a total of 921 ORFs of the Chlamydia MoPn genome and plasmid. A total of 185 immunodominant proteins elicited an early and sustained antibody response in the mice immunized with live EB, and of these, 71 were also recognized by the sera from mice immunized with UV-EB. The reactive antigens included some proteins that were previously described as immunogenic, such as the major outer membrane protein, OmpB, Hsp60, and IncA and proteins from the type III secretion system. In addition, we identified in mice several new immunogens, including 75 hypothetical proteins. In summary, we have identified a new group of immunodominant chlamydial proteins that can be tested for their ability to induce protection.

A new murine model for testing vaccines against genital Chlamydia trachomatis infections in males

Two groups of 50 BALB/c male mice were immunized with live Chlamydia trachomatis mouse pneumonitis (MoPn) using the intranasal (i.n.) or the meatus urethra (intraurethral: i.u.) routes. As a control group, 100 male mice were sham-immunized in parallel. Both groups of animals vaccinated with live organisms developed strong Chlamydia-specific humoral and cell mediated immune responses. Based on the IgG2a/IgG1 ratio and the levels of IFN-γ both groups mounted a Th1 immune response. At six weeks following the immunization, all mice were challenged in the meatus urethra. The urethra, urinary bladder, testes and epididymides were harvested at weekly intervals and tested for the presence of C. trachomatis. Based on the culture results from these four organs both groups of Chlamydia-immunized mice showed significant protection. In the group immunized i.u., 10% (5/50) had positive cultures, while in the group immunized i.n. 28% (14/50) had positive cultures during the 5 weeks of observation. In contrast, in the sham-immunized animals 47% (47/100) had positive cultures (P<0.005) during the study period. In addition, the number of positive organs, the length of time that the animal had positive cultures, and the total number of inclusion forming units (IFU) recovered were overall significantly lower in the i.u. or i.n. groups in comparison with the sham-immunized animals. However, in relation to the i.u. immunized group, the protection elicited in the i.n. group was delayed and not as robust. In conclusion, immunization of mice in the meatus urethra may provide the gold standard for testing Chlamydia vaccines in a male model.

Enhancement of the protective efficacy of a Chlamydia trachomatis recombinant vaccine by combining systemic and mucosal routes for immunization

Chlamydia trachomatis causes respiratory and sexually transmitted infections. Here, we tested a vaccine formulated with the recombinant major outer membrane protein from C. trachomatis mouse pneumonitis (CT-MoPn) for its ability to protect mice against an intranasal (i.n.) challenge. The adjuvants CpG and Montanide were used for systemic routes, intramuscular (i.m.) and subcutaneous (s.c.), and cholera toxin for mucosal routes, sublingual (s.l.) and colonic (c.l.). Mucosal immunizations were performed either alone or in combination with systemic routes. Mice inoculated i.n. with 10(4) inclusion-forming units (IFU) of CT-MoPn served as a positive control and the Neisseria gonorrhoeae recombinant porin B (Ng-rPorB) as the negative antigen control. Immunized animals were challenged i.n. with 10(4)IFU of CT-MoPn. Following immunization the combination groups showed high chlamydial serum IgG titers (s.l.+i.m.+s.c. 25,600; c.l+i.m.+s.c. 102,400) and the IgG2a/IgG1 ratios indicated a Th1 response. Following the i.n. challenge the s.l.+i.m.+s.c. group showed the best protection as demonstrated by an increase in body weight of 0.3% over the 10 day course of infection. A statistically significant difference was found when compared with the Ng-rPorB immunized animals that had lost 20% of their original body weight (P<0.05). In addition, the repeated measures ANOVA test showed significant difference in body weight change for the combined immunized groups vs their mucosal counterparts and also the systemic immunized group. A statistically significant difference (P<0.05) was also observed in the number of IFUs recovered from the lungs when the s.l.+i.m.+s.c. (2.8×10(6)) and c.l.+i.m.+s.c. (3.4×10(6)) groups were compared to their respective mucosal only groups (s.l.: 61.9×10(6) and c.l: 136.2×10(6)) and the control Ng-rPorB immunized mice (198.2×10(6)) (P<0.05). In conclusion, a combined systemic plus mucosal vaccination provides better protection against a respiratory challenge with C. trachomatis than either systemic or mucosal immunizations alone.

CD4+ T cells and antibody are required for optimal major outer membrane protein vaccine-induced immunity to Chlamydia muridarum genital infection

Despite effective antimicrobial chemotherapy, control of Chlamydia trachomatis urogenital infection will likely require a vaccine. We have assessed the protective effect of an outer membrane protein-based vaccine by using a murine model of chlamydial genital infection. Female mice were first vaccinated with Chlamydia muridarum major outer membrane protein (MOMP) plus the adjuvants CpG-1826 and Montanide ISA 720; then they were challenged with C. muridarum. Vaccinated mice shed 2 log(10) to 3 log(10) fewer inclusion-forming units (IFU) than ovalbumin-vaccinated or naïve animals, resolved infection sooner, and had a lower incidence of hydrosalpinx. To determine the relative contribution of T cells to vaccine-induced protection, mice were vaccinated, depleted of CD4(+) or CD8(+) T cells, and then challenged vaginally with C. muridarum. Depletion of CD4(+) T cells, but not depletion of CD8(+) T cells, diminished vaccine-induced protection, with CD4-depleted mice shedding 2 log(10) to 4 log(10) more IFU than CD8-depleted or nondepleted mice. The contribution of antibodies to vaccine-induced protection was demonstrated by the absence of protective immunity in vaccinated B-cell-deficient mice and by a 2 log(10) to 3 log(10) decrease in bacterial shedding by mice passively administered an anti-MOMP serum. Thus, optimal protective immunity in this model of vaccine-induced protection depends on contributions from both CD4(+) T cells and antibody.

Maternal immunity partially protects newborn mice against a Chlamydia trachomatis intranasal challenge

To determine the role of maternal immunity in protecting newborn mice against a Chlamydia trachomatis infection, female BALB/c mice were immunized intranasally (i.n.) with 10⁴ inclusion forming units (IFU) of the C. trachomatis mouse pneumonitis biovar (MoPn). As a control, another group of female mice was sham-immunized i.n. with HeLa cell extracts. Immunized animals mounted strong immune responses as evidenced by high Chlamydia-specific antibody titers in serum and milk. Newborn mice born from immunized and sham-immunized dams were challenged i.n. with 10³IFU of MoPn at two post-natal days (PND). Following inoculation, newborn mice were euthanized at 7- and 18-PND and the lungs, spleen and intestine were cultured for Chlamydia. Overall, no significant differences were observed between the mice born from and fed by immunized dams and mice born from and fed by sham-immunized dams. Of the mice born from immunized dams, 75 and 25% had positive lung cultures at 7- and 18-PND, respectively. Of the mice born from sham-immunized dams, 82 and 50% had positive lung cultures for those same days. When the number of IFU recovered from the lungs and spleens was compared between the two groups no significant differences were observed. However, when the number of IFU recovered from the small intestine was compared, significant differences were observed between the two groups of newborn mice (2×10⁵ versus 32×10⁶ at 7-PND and 9.2×10⁶ versus 85×10⁶ at 18-PND). In conclusion, maternal immunity plays a limited role in protecting newborn mice against a Chlamydia infection.

Protection against Chlamydia promoted by a subunit vaccine (CTH1) compared with a primary intranasal infection in a mouse genital challenge model

BACKGROUND

The chlamydial proteins CT443 (OmcB) and CT521 (rl16) have previously been identified as human B and/or T cell targets during a chlamydial infection in humans. Here we compare the protective effector mechanism promoted by a fusion protein composed of CT521 and CT443 (CTH1) with a primary intranasal Chlamydia muridarum infection known to provide high levels of protection against a genital chlamydial challenge.

METHODOLOGY/PRINCIPAL FINDINGS

The fusion protein CTH1, adjuvanted with a strong Th1 inducing cationic adjuvant (CAF01), significantly reduced the bacterial shedding compared to a control group in both a C. trachomatis Serovar D and C. muridarum challenge model. The CTH1/CAF01 vaccine was found to induce polyfunctional T cells consisting of TNFalpha/IL-2 and TNFalpha/IL-2/IFN-gamma positive cells and high titers of CTH1 specific IgG2a and IgG1. By depletion experiments the protection in the C. muridarum challenge model was demonstrated to be mediated solely by CD4(+) T cells. In comparison, an intranasal infection with C. muridarum induced a T cell response that consisted predominantly of TNFalpha/IFN-gamma co-expressing effector CD4(+) T cells and an antibody response consisting of C. muridarum specific IgG1, IgG2a but also IgA. This response was associated with a high level of protection against challenge-a protection that was only partially dependent on CD4(+) T cells. Furthermore, whereas the antibody response induced by intranasal infection was strongly reactive against the native antigens displayed in the chlamydial elementary body, only low levels of antibodies against this preparation were found after CTH1/CAF01 immunization.

CONCLUSIONS/SIGNIFICANCE

Our data demonstrate that CTH1 vaccination promotes a CD4(+) T cell dependent protective response but compared with intranasal C. muridarum infection lacks a CD4 independent protective mechanism for complete protection.

Identification of immunodominant antigens of Chlamydia trachomatis using proteome microarrays

Chlamydia trachomatis is the most common bacterial sexually transmitted pathogen in the world. In order to control this infection there is an urgent need to formulate a vaccine. Identification of protective antigens is required to implement a subunit vaccine. To identify potential antigen vaccine candidates, three strains of mice, BALB/c, C3H/HeN and C57BL/6, were inoculated with live and inactivated C. trachomatis mouse pneumonitis (MoPn) by different routes of immunization. Using a protein microarray, serum samples collected after immunization were tested for the presence of antibodies against specific chlamydial antigens. A total of 225 open reading frames (ORF) of the C. trachomatis genome were cloned, expressed, and printed in the microarray. Using this protein microarray, a total of seven C. trachomatis dominant antigens were identified (TC0052, TC0189, TC0582, TC0660, TC0726, TC0816 and, TC0828) as recognized by IgG antibodies from all three strains of animals after immunization. In addition, the microarray was probed to determine if the antibody response exhibited a Th1 or Th2 bias. Animals immunized with live organisms mounted a predominant Th1 response against most of the chlamydial antigens while mice immunized with inactivated Chlamydia mounted a Th2-biased response. In conclusion, using a high throughput protein microarray we have identified a set of novel proteins that can be tested for their ability to protect against a chlamydial infection.

C3H male mice with severe combined immunodeficiency cannot clear a urethral infection with a human serovar of Chlamydia trachomatis

The pathogenesis of an infection of the male genitourinary tract of mice with a human serovar of Chlamydia trachomatis has not been characterized. To establish a new model, we inoculated C3H/HeN (H-2(k)) mice in the meatus urethra with C. trachomatis serovar D. To determine the 50% infectious dose (ID(50)), male mice were inoculated with doses ranging from 10(2) to 10(6) inclusion-forming units (IFU). The mice were euthanized 10 days post infection (p.i.), and the urethra, bladder, epididimydes, and testes were cultured for Chlamydia. Positive cultures were obtained from the urethra, urinary bladder, and epididimydes, and the ID(50) was determined to be 5 x 10(4) IFU/mouse. Subsequently, to characterize the course of the infection, wild-type (WT) and C3H animals with severe combined immunodeficiency (SCID animals) were inoculated with 10(6) IFU/mouse (20 times the ID(50)). In the WT mice, the infection peaked in the second week, and by 42 days p.i., it was cleared. In contrast, most of the SCID mice continued to have positive cultures at 60 days p.i. C. trachomatis-specific antibodies were first detected in WT animals' sera at 21 days p.i. and increased until 42 days p.i. The immunoglobulin G2a (IgG2a) titers were 32-fold higher than those of IgG1, indicative of a Th1-biased immune response. A lymphoproliferative assay using splenocytes showed a significant cell-mediated immune response in the WT mice. As expected, no humoral or cell-mediated immune responses were observed in the SCID animals. In conclusion, inoculation of WT male mice in the meatus urethra with a human serovar of C. trachomatis resulted in a limited infection mainly localized to the lower genitourinary tract. On the other hand, SCID animals could not clear the infection, suggesting that in male mice, the adaptive immune response is necessary to control an infection with a C. trachomatis human serovar.

Induction of protective immunity by vaccination against Chlamydia trachomatis using the major outer membrane protein adjuvanted with CpG oligodeoxynucleotide coupled to the nontoxic B subunit of cholera toxin

The present study was undertaken to test the efficacy of immunization with the native major outer membrane protein (nMOMP) of Chlamydia trachomatis mouse pneumonitis (MoPn) serovar in combination with a novel immunostimulatory adjuvant consisting of CpG oligodeoxynucleotide (ODN) linked to the nontoxic B subunit of cholera toxin (CTB-CpG) to elicit a protective immune response to C. trachomatis. High levels of Chlamydia-specific IgG antibodies were detected in the sera from BALB/c mice immunized intramuscularly and subcutaneously (i.m.+s.c.) with the nMOMP/CTB-CpG vaccine or with nMOMP adjuvanted with a mixture of CT and CpG ODN (CT+CpG). Further, these immunization schemes gave rise to significant T-cell-mediated Chlamydia-specific immune responses. No Chlamydia-specific humoral or cell-mediated immune responses were detected in the control mice vaccinated with ovalbumin together with either CTB-CpG or CT+CpG. Following an intranasal challenge with C. trachomatis the groups of mice immunized with nMOMP plus CTB-CpG, CT+CpG or live C. trachomatis were found to be protected based on their change in body weight and lung weight as well as number of inclusion forming unit recovered from the lungs, as compared with control groups immunized with ovalbumin plus either adjuvants. Interestingly, IFN-gamma-producing CD4(+), but not CD8(+), T-cells showed a significant correlation with the outcomes of the challenge. In conclusion, nMOMP in combination with the novel adjuvant CTB-CpG elicited a significant antigen-specific antibody and cell-mediated immune responses as well as protection against a pulmonary challenge with C. trachomatis.

Protection against an intranasal challenge by vaccines formulated with native and recombinant preparations of the Chlamydia trachomatis major outer membrane protein

To compare the ability of a native and a recombinant preparation of the major outer membrane protein of Chlamydia trachomatis mouse pneumonitis (MoPn; Ct-nMOMP and Ct-rMOMP) to protect against an intranasal (i.n.) challenge, BALB/c mice were vaccinated by the intramuscular (i.m.) and subcutaneous (s.c.) routes using CpG-1826 and Montanide ISA 720 as adjuvants. Animals inoculated i.n. with live elementary bodies (EB) of Chlamydia served as a positive control. Negative control groups were immunized with either Neisseria gonorrhoeae recombinant porin B (Ng-rPorB) or with minimal essential medium (MEM-0). Mice immunized with Ct-rMOMP, Ct-nMOMP and EB developed a strong immune response as shown by high levels of Chlamydia specific antibodies in serum and a strong T-cell lymphoproliferative response. Following the i.n. challenge with 10(4) inclusion forming units (IFU) of C. trachomatis, mice immunized with Ct-nMOMP or Ct-rMOMP lost significantly less weight than the negative control animals immunized with Ng-rPorB or MEM-0 (P<0.05). However, mice vaccinated with the Ct-nMOMP lost less weight than those immunized with the Ct-rMOMP (P<0.05). Mice were euthanized at 10 days following the challenge, their lungs weighed and the number of IFU of Chlamydia determined. Based on the lung weight and number of IFU recovered, significant protection was observed in the groups of mice immunized with both Ct-nMOMP and the Ct-rMOMP (P<0.05). Nevertheless, significantly better protection was achieved with the Ct-nMOMP in comparison with the Ct-rMOMP (P<0.05). In conclusion, vaccination with a preparation of the nMOMP elicited a more robust protection than immunization with rMOMP, suggesting that the conformational structure of MOMP is critical for inducing strong protection.

Protection of wild-type and severe combined immunodeficiency mice against an intranasal challenge by passive immunization with monoclonal antibodies to the Chlamydia trachomatis mouse pneumonitis major outer membrane protein

Monoclonal antibodies (MAbs) to the Chlamydia trachomatis mouse pneumonitis (MoPn) major outer membrane protein (MOMP) were characterized for their ability to neutralize the infectivity of this organism in vitro and in vivo. One of the MAbs (MoPn-23) recognizes a nonlinear epitope in the MOMP, MAb MoPn-40 binds to a linear epitope in the variable domain 1 (VD1), and MAb MoPn-32 recognizes the chlamydial lipopolysaccharide. MAb MoPn-23 neutralized 50% of the infectivity of Chlamydia, as measured in vitro by using HAK (Fc gammaIII(-)) and HeLa-229 (Fc gammaIII(+)) cells at a concentration 100 times lower than MAb MoPn-40. MAb MoPn-32 had no neutralizing ability. In comparison to the control normal mouse immunoglobulin G, passive immunization of BALB/c mice with MAb MoPn-23 resulted in a highly significant protection against an intranasal (i.n.) challenge as determined by the change in body weight, the weight of the lungs, and the yield of Chlamydia inclusion-forming units (IFU) from the lungs. Passive immunization with MAb MoPn-40 resulted in a lower degree of protection, and MAb MoPn-32 afforded no protection. MAb MoPn-23 was also tested for its ability to protect wild-type (WT) and severe combined immunodeficient (SCID) C.B-17 mice against an i.n. challenge. Protection based on total body weight, lung weight, and yield of Chlamydia IFU was as effective in SCID as in WT C.B-17 mice. In conclusion, antibodies to MOMP can protect mice against a chlamydial infection in the presence or absence of T and B cells.