Immunization with the Chlamydia trachomatis mouse pneumonitis major outer membrane protein can elicit a protective immune response against a genital challenge

Safety and efficacy of C. muridarum vaccines adjuvanted with CpG-1826 and four concentrations of Montanide-ISA-720-VG

It is recommended that the adjuvant Montanide ISA 720 VG be used at a concentration of 70% v/v. At this concentration, Montanide causes at the site of immunization a local granuloma that can last for several weeks. To determine the safety and protective efficacy of a Chlamydia muridarum MOMP vaccine, formulated with CpG-1826 and four different concentrations of Montanide (70%, 50%, 30% and 10%), BALB/c (H-2d) female mice were immunized twice intramuscularly. Local reactogenicity was significant for vaccines formulated with 70% or 50% Montanide but not for those inoculated with 30% or 10% Montanide. Robust humoral and cell mediated memory immune responses were elicited by the 70%, 50% and 30% Montanide formulations. Mice were challenged intranasally with 104 C. muridarum inclusion forming units (IFU). Based on changes in body weight, lungs's weight and number of IFU recovered, mice vaccinated with the 70%, 50% and 30% Montanide formulations were significantly protected, but not mice receiving 10% Montanide. To conclude, we recommend the 30% Montanide concentration to be tested in humans and animal models to determine its safety and efficacy, in comparison to the 70% Montanide concentration currently used. The 30% Montanide formulation could significantly facilitate licensing of this adjuvant for human use.

Protective anti-chlamydial vaccine regimen-induced CD4+ T cell response mediates early inhibition of pathogenic CD8+ T cell response following genital challenge

We have demonstrated previously that TNF-α-producing CD8+ T cells mediate chlamydial pathogenesis, likely in an antigen (Ag)-specific fashion. Here we hypothesize that inhibition of Ag-specific CD8+ T cell response after immunization and/or challenge would correlate with protection against oviduct pathology induced by a protective vaccine regimen. Intranasal (i.n.) live chlamydial elementary body (EB), intramuscular (i.m.) live EB, or i.n. irrelevant antigen, bovine serum albumin (BSA), immunized animals induced near-total protection, 50% protection, or no protection, respectively against oviduct pathology following i.vag. C. muridarum challenge. In these models, we evaluated Ag-specific CD8+ T cell cytokine response at various time-periods after immunization or challenge. The results show protective efficacy of vaccine regimens correlated with reduction of Ag-specific CD8+ T cell TNF-α responses following i.vag. chlamydial challenge, not after immunization. Depletion of CD4+ T cells abrogated, whereas adoptive transfer of Ag-specific CD4+ T cells induced the significant reduction of Ag-specific CD8+ T cell TNF-α response after chlamydial challenge. In conclusion, protective anti-chlamydial vaccine regimens induce Ag-specific CD4+ T cell response that mediate early inhibition of pathogenic CD8+ T cell response following challenge and may serve as a predictive biomarker of protection against Chlamydia -induced chronic pathologies.

Evaluation of three formulations based on Polymorphic membrane protein D in mice infected with Chlamydia trachomatis

The significant impact of Chlamydia trachomatis(Ct) infections worldwide highlights the need to develop a prophylactic vaccine that elicits effective immunity and protects the host from the immunopathological effects of Ct infection. The aim of this study was to evaluate a vaccine based on a fragment of the Polymorphic membrane protein D (FPmpD) of C. trachomatis as an immunogen using a heterologous DNA prime-protein boost strategy in female mice Three different formulations were evaluated as protein boost: free recombinant FPmpD (rFPmpD) or rFPmpD formulated with a liposomal adjuvant alternatively supplemented with CpG or a cationic gemini lipopeptide as immunostimulants. The three candidates induced an increase in the cervicovaginal and systemic titers of anti-rFPmpD antibodies in two strains of mice (BALB/c and C57BL/6), with no evidence of fertility alterations. The three formulations induced a rapid and robust humoral immune response upon the Ct challenge. However, the booster with free rFPmpD more efficiently reduced the shedding of infective Ct and prevented the development of immunopathology. The formulations containing adjuvant induced a strong inflammatory reaction in the uterine tissue. Hence, the prime-boost strategy with the adjuvant-free FPmpD vaccine formulation might constitute a promissory candidate to prevent C. trachomatis intravaginal infection.

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.

Epitope-Based Vaccines against the Chlamydia trachomatis Major Outer Membrane Protein Variable Domain 4 Elicit Protection in Mice

Chlamydia trachomatis (Ct) is the most common bacterial sexual transmitted pathogen, yet a vaccine is not currently available. Here, we used the immunogenic bacteriophage MS2 virus-like particle (VLP) technology to engineer vaccines against the Ct major outer membrane protein variable domain 4 (MOMP-VD4), which contains a conserved neutralizing epitope (TTLNPTIAG). A previously described monoclonal antibody to the MOMP-VD4 (E4 mAb) is capable of neutralizing all urogenital Ct serovars and binds this core epitope, as well as several non-contiguous amino acids. This suggests that this core epitope may require conformational context in order to elicit neutralizing antibodies to Ct. In order to identify immunogens that could elicit neutralizing antibodies to the TTLNPTIAG epitope, we used two approaches. First, we used affinity selection with a bacteriophage MS2-VLP library displaying random peptides in a constrained, surface-exposed loop to identify potential E4 mAb mimotopes. After four rounds of affinity selection, we identified a VLP-displayed peptide (HMVGSTKWTN) that could bind to the E4 mAb and elicited serum IgG that bound weakly to Ct elementary bodies by ELISA. Second, two versions of the core conserved TTLNPTIAG epitope (TTLNPTIAG and TTLNPTIAGA) were recombinantly expressed on the coat protein of the MS2 VLP in a constrained, surface-exposed loop. Mouse immune sera IgG bound to Ct elementary bodies by ELISA. Immunization with these MS2 VLPs provided protection from vaginal Chlamydia infection in a murine challenge model. These data suggest that short peptide epitopes targeting the MOMP-VD4 could be appropriate for Ct vaccine design when displayed on an immunogenic bacteriophage VLP vaccine platform.

A Review of the Challenges and Complexities in the Diagnosis, Etiology, Epidemiology, and Pathogenesis of Pelvic Inflammatory Disease

Pelvic inflammatory disease (PID) is a syndrome that causes substantial morbidity, including chronic pelvic pain, to women globally. While limited data are available from low- and middle-income countries, national databases from the United States and Europe suggest that PID incidence may be decreasing but the rate of decrease may differ by the etiologic cause. Recent studies of women with PID have reported that fewer than half of women receiving a diagnosis of PID have gonococcal or chlamydial infection, while Mycoplasma genitalium, respiratory pathogens, and the constellation of bacteria associated with bacterial vaginosis may account for a substantial fraction of PID cases. The clinical diagnosis of PID is nonspecific, creating an urgent need to develop noninvasive tests to diagnose PID. Advances in serologic testing for Chlamydia trachomatis and Neisseria gonorrhoeae could advance epidemiologic studies, while the development of vaccines against these sexually transmitted pathogens could affect incident PID and associated morbidity.

Chlamydia trachomatis Cross-Serovar Protection during Experimental Lung Reinfection in Mice

Chlamydia trachomatis causes most bacterial sexually transmitted diseases worldwide. Different major outer membrane proteins (MOMPs) define various serovars of this intracellular pathogen: In women, D to L3 can cause urethritis, cervicitis, salpingitis, and oophoritis, and, thus, infertility. Protective immunity might be serovar-specific since chlamydial infection does not appear to induce an effective acquired immunity and reinfections occur. A better understanding of induced cross-serovar protection is essential for the selection of suitable antigens in vaccine development. In our mouse lung infection screening model, we evaluated the urogenital serovars D, E, and L2 in this regard. Seven weeks after primary infection or mock-infection, respectively, mice were infected a second time with the identical or one of the other serovars. Body weight and clinical score were monitored for 7 days. Near the peak of the second lung infection, bacterial load, myeloperoxidase, IFN-γ, and TNF-α in lung homogenate, as well as chlamydia-specific IgG levels in blood were determined. Surprisingly, compared with mice that were infected then for the first time, almost independent of the serovar combination used, all acquired parameters of disease were similarly diminished. Our reinfection study suggests that efficient cross-serovar protection could be achieved by a vaccine combining chlamydial antigens that do not include nonconserved MOMP regions.

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.

Prophylactic Multi-Subunit Vaccine against Chlamydia trachomatis: In Vivo Evaluation in Mice

Chlamydia trachomatis is the most frequent sexually-transmitted disease-causing bacterium. Urogenital serovars of this intracellular pathogen lead to urethritis and cervicitis. Ascending infections result in pelvic inflammatory disease, salpingitis, and oophoritis. One of 200 urogenital infections leads to tubal infertility. Serovars A–C cause trachoma with visual impairment. There is an urgent need for a vaccine. We characterized a new five-component subunit vaccine in a mouse vaccination-lung challenge infection model. Four recombinant Pmp family-members and Ctad1 from C. trachomatis serovar E, all of which participate in adhesion and binding of chlamydial elementary bodies to host cells, were combined with the mucosal adjuvant cyclic-di-adenosine monophosphate. Intranasal application led to a high degree of cross-serovar protection against urogenital and ocular strains of C. trachomatis, which lasted at least five months. Critical evaluated parameters were body weight, clinical score, chlamydial load, a granulocyte marker and the cytokines IFN-γ/TNF-α in lung homogenate. Vaccine antigen-specific antibodies and a mixed Th1/Th2/Th17 T cell response with multi-functional CD4⁺ and CD8⁺ T cells correlate with protection. However, serum-transfer did not protect the recipients suggesting that circulating antibodies play only a minor role. In the long run, our new vaccine might help to prevent the feared consequences of human C. trachomatis infections.

A Chlamydia trachomatis VD1-MOMP vaccine elicits cross-neutralizing and protective antibodies against C/C-related complex serovars

Ocular and urogenital infections with Chlamydia trachomatis (C.t.) are caused by a range of different serovars. The first C.t. vaccine in clinical development (CTH522/CAF®01) induced neutralizing antibodies directed to the variable domain 4 (VD4) region of major outer membrane protein (MOMP), covering predominantly B and intermediate groups of serovars. The VD1 region of MOMP contains neutralizing B-cell epitopes targeting serovars of the C and C-related complex. Using an immuno-repeat strategy, we extended the VD1 region of SvA and SvJ to include surrounding conserved segments, extVD1^A and extVD1^J, and repeated this region four times. The extVD1^A*4 was most immunogenic with broad cross-surface and neutralizing reactivity against representative members of the C and C-related complex serovars. Importantly, in vitro results for extVD1^A*4 translated into in vivo biological effects, demonstrated by in vivo neutralization of SvA and protection/cross-protection against intravaginal challenge with both SvA and the heterologous SvIa strain.

Mycoplasma pneumoniae Infections: Pathogenesis and Vaccine Development

Mycoplasma pneumoniae is a major causative agent of community-acquired pneumonia which can lead to both acute upper and lower respiratory tract inflammation, and extrapulmonary syndromes. Refractory pneumonia caused by M. pneumonia can be life-threatening, especially in infants and the elderly. Here, based on a comprehensive review of the scientific literature related to the respective area, we summarize the virulence factors of M. pneumoniae and the major pathogenic mechanisms mediated by the pathogen: adhesion to host cells, direct cytotoxicity against host cells, inflammatory response-induced immune injury, and immune evasion. The increasing rate of macrolide-resistant strains and the harmful side effects of other sensitive antibiotics (e.g., respiratory quinolones and tetracyclines) in young children make it difficult to treat, and increase the health risk or re-infections. Hence, there is an urgent need for development of an effective vaccine to prevent M. pneumoniae infections in children. Various types of M. pneumoniae vaccines have been reported, including whole-cell vaccines (inactivated and live-attenuated vaccines), subunit vaccines (involving M. pneumoniae protein P1, protein P30, protein P116 and CARDS toxin) and DNA vaccines. This narrative review summarizes the key pathogenic mechanisms underlying M. pneumoniae infection and highlights the relevant vaccines that have been developed and their reported effectiveness.

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.

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.

Improved protection against Chlamydia muridarum using the native major outer membrane protein trapped in Resiquimod-carrying amphipols and effects in protection with addition of a Th1 (CpG-1826) and a Th2 (Montanide ISA 720) adjuvant

A new vaccine formulated with the Chlamydia muridarum native major outer membrane protein (nMOMP) and amphipols was assessed in an intranasal (i.n.) challenge mouse model. nMOMP was trapped either in amphipol A8-35 (nMOMP/A8-35) or in A8-35 conjugated with Resiquimod (nMOMP/Resiq-A8-35), a TLR7/8 agonist added as adjuvant. The effects of free Resiquimod and/or additional adjuvants, Montanide ISA 720 (TLR independent) and CpG-1826 (TLR9 agonist), were also evaluated. Immunization with nMOMP/A8-35 alone administered i.n. was used as negative adjuvant-control group, whereas immunizations with C. muridarum elementary bodies (EBs) and MEM buffer, administered i.n., were used as positive and negative controls, respectively. Vaccinated mice were challenged i.n. with C. muridarum and changes in body weight, lungs weight and recovery of Chlamydia from the lungs were evaluated. All the experimental groups showed protection when compared with the negative control group. Resiquimod alone produced weak humoral and cellular immune responses, but both Montanide and CpG-1826 showed significant increases in both responses. The addition of CpG-1826 alone switched immune responses to be Th1-biased. The most robust protection was elicited in mice immunized with the three adjuvants and conjugated Resiquimod. Increased protection induced by the Resiquimod covalently linked to A8-35, in the presence of Montanide and CpG-1826 was established based on a set of parameters: (1) the ability of the antibodies to neutralize C. muridarum; (2) the increased proliferation of T-cells in vitro accompanied by higher production of IFN-γ, IL-6 and IL-17; (3) the decreased body weight loss over the 10 days after challenge; and (4) the number of IFUs recovered from the lungs at day 10 post challenge. In conclusion, a vaccine formulated with the C. muridarum nMOMP bound to amphipols conjugated with Resiquimod enhances protective immune responses that can be further improved by the addition of Montanide and CpG-1826.

Comparison of Chlamydia outer membrane complex to recombinant outer membrane proteins as vaccine

The Chlamydial outer membrane complex (COMC) from the elementary body (EB) is a protein rich insoluble outer membrane shell from which cytosolic proteins have been extracted with detergent. In this study we conducted mass spectrometry experiments to detect proteins in the COMC prepared from C. muridarum EB. Proteomic analysis showed that the COMC contained 75 proteins that included 10 outer membrane proteins (OMPs) such as the major outer membrane protein (MOMP) and polymorphic membrane proteins (Pmps) that were previously identified as CD4 T cell vaccine candidates. We tested the vaccine efficacy of COMC in comparison to individual or combination of recombinant OMPs formulated with Th1 polarizing adjuvant DDA/MPL in two murine genital tract models (C. muridarum and C. trachomatis) by measuring organismal shedding, tubal pathology and immune responses including neutralizing antibodies. In the C. muridarum model, the COMC vaccine generated broadly reactive immune responses against multiple outer membrane proteins, high levels of EB binding and neutralizing antibody and exhibited superior protection against genital infection and pathology when compared to the recombinant PmpG vaccine. Denaturing the COMC by boiling significantly reduced protection. In the C. trachomatis model, the COMC vaccine also conferred greater protection compared to individual or multiple recombinant outer membrane proteins. Immunization with multiple COMCs from C. trachomatis serovars D, F and J generated neutralizing antibodies against multiple C. trachomatis serovars. We conclude that broader immunogenicity and generation of neutralizing antibody may explain the superior efficacy of COMC vaccine. The study suggests that conformationally intact proteins will be necessary for a successful recombinant OMP vaccine.

Parenteral vaccination protects against transcervical infection with Chlamydia trachomatis and generate tissue-resident T cells post-challenge

The optimal protective immunity against Chlamydia trachomatis (C.t.) is still not fully resolved. One of the unresolved issues concerns the importance of resident immunity, since a recent study showed that optimal protection against a transcervical (TC) infection required genital tissue-resident memory T cells. An important question in the Chlamydia field is therefore if a parenteral vaccine strategy, inducing only circulating immunity primed at a nonmucosal site, should be pursued by Chlamydia vaccine developers. To address this question we studied the protective efficacy of a parenteral Chlamydia vaccine, formulated in the Th1/Th17 T cell-inducing adjuvant CAF01. We found that a parenteral vaccination induced significant protection against a TC infection and against development of chronic pathology. Protection correlated with rapid recruitment of Th1/Th17 T cells to the genital tract (GT), which efficiently prevented infection-driven generation of low quality Th1 or Th17 T cells, and instead maintained a pool of high quality multifunctional Th1/Th17 T cells in the GT throughout the infection. After clearance of the infection, a pool of these cells settled in the GT as tissue-resident Th1 and Th17 cells expressing CD69 but not CD103, CD49d, or CCR7, where they responded rapidly to a reinfection. These results show that a nonmucosal parenteral strategy inducing Th1 and Th17 T cells mediates protection against both infection with C.t. as well as development of chronic pathology, and lead to post-challenge protective tissue-resident memory immunity in the genital tract.

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.

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.

Unusual Self-Assembly of the Recombinant Chlamydia trachomatis Major Outer Membrane Protein-Based Fusion Antigen CTH522 Into Protein Nanoparticles

Sexually transmitted Chlamydia trachomatis infects more than 100 million people annually, and untreated chlamydia infections can cause severe complications. Therefore, there is an urgent need for a chlamydia vaccine. The Ctrachomatis major outer membrane protein (MOMP) is highly immunogenic but is a challenging vaccine candidate by being an integral membrane protein, and the immunogenicity depends on a correctly folded structure. We investigated the biophysical properties of the recombinant MOMP-based fusion antigen CTH522, which is tested in early human clinical trials. It consists of a truncated and cysteine-free version of MOMP fused to 4 variable domains from serovars D-G. In the native state, CTH522 did not exist as a monomer but showed an unusual self-assembly into nanoparticles with a negative zeta potential. In contrast to the β-barrel structure of MOMP, native CTH522 contained no well-defined secondary structural elements, and no thermal transitions were measurable. Chemical unfolding resulted in monomers that upon removal of the denaturant self-assembled into higher order structures, comparable to the structure of the native protein. The conformation of CTH522 in nanoparticles is thus not entirely random and contains structural elements stabilized via denaturant-disruptable hydrophobic interactions. In conclusion, CTH522 has an unusual quaternary structure of supramolecular self-assemblies.

Cell-free production of a functional oligomeric form of a Chlamydia major outer-membrane protein (MOMP) for vaccine development

Chlamydia is a prevalent sexually transmitted disease that infects more than 100 million people worldwide. Although most individuals infected with Chlamydia trachomatis are initially asymptomatic, symptoms can arise if left undiagnosed. Long-term infection can result in debilitating conditions such as pelvic inflammatory disease, infertility, and blindness. Chlamydia infection, therefore, constitutes a significant public health threat, underscoring the need for a Chlamydia-specific vaccine. Chlamydia strains express a major outer-membrane protein (MOMP) that has been shown to be an effective vaccine antigen. However, approaches to produce a functional recombinant MOMP protein for vaccine development are limited by poor solubility, low yield, and protein misfolding. Here, we used an Escherichia coli-based cell-free system to express a MOMP protein from the mouse-specific species Chlamydia muridarum (MoPn-MOMP or mMOMP). The codon-optimized mMOMP gene was co-translated with Δ49apolipoprotein A1 (Δ49ApoA1), a truncated version of mouse ApoA1 in which the N-terminal 49 amino acids were removed. This co-translation process produced mMOMP supported within a telodendrimer nanolipoprotein particle (mMOMP-tNLP). The cell-free expressed mMOMP-tNLPs contain mMOMP multimers similar to the native MOMP protein. This cell-free process produced on average 1.5 mg of purified, water-soluble mMOMP-tNLP complex in a 1-ml cell-free reaction. The mMOMP-tNLP particle also accommodated the co-localization of CpG oligodeoxynucleotide 1826, a single-stranded synthetic DNA adjuvant, eliciting an enhanced humoral immune response in vaccinated mice. Using our mMOMP-tNLP formulation, we demonstrate a unique approach to solubilizing and administering membrane-bound proteins for future vaccine development. This method can be applied to other previously difficult-to-obtain antigens while maintaining full functionality and immunogenicity.

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.

Recombinant expression of Chlamydia trachomatis major outer membrane protein in E. Coli outer membrane as a substrate for vaccine research

Background

Chlamydia trachomatis is a human pathogen which causes a number of pathologies, including genital tract infections in women that can result in tubal infertility. Prevention of infection and disease control might be achieved through vaccination; however, a safe, efficacious and cost-effective vaccine against C. trachomatis infection remains an unmet medical need. C. trachomatis major outer membrane protein (MOMP), a β-barrel integral outer membrane protein, is the most abundant antigen in the outer membrane of the bacterium and has been evaluated as a subunit vaccine candidate. Recombinant MOMP (rMOMP) expressed in E. coli cytoplasm forms inclusion bodies and rMOMP extracted from inclusion bodies results in a reduced level of protection compared to the native MOMP in a mouse challenge model.

Results

We sought to target the recombinant expression of MOMP to the E. coli outer membrane (OM). Successful surface expression was achieved with codon harmonization, utilization of low copy number vectors and promoters with moderate strength, suitable leader sequences and optimization of cell culture conditions. rMOMP was extracted from E. coli outer membrane, purified, and characterized biophysically. The OM expressed and purified rMOMP is immunogenic in mice and elicits antibodies that react to the native antigen, Chlamydia elementary body (EB).

Conclusions

C. trachomatis MOMP was functionally expressed on the surface of E. coli outer membrane. The OM expressed and purified rMOMP elicits antibodies that react to the native antigen, Chlamydia EB, in a mouse immunogenicity model. Surface expression of MOMP could provide useful reagents for vaccine research, and the methodology could serve as a platform to produce other outer membrane proteins recombinantly.

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.

Genital Chlamydia trachomatis: understanding the roles of innate and adaptive immunity in vaccine research

Chlamydia trachomatis is the leading cause of bacterial sexually transmitted disease worldwide, and despite significant advances in chlamydial research, a prophylactic vaccine has yet to be developed. This Gram-negative obligate intracellular bacterium, which often causes asymptomatic infection, may cause pelvic inflammatory disease (PID), ectopic pregnancies, scarring of the fallopian tubes, miscarriage, and infertility when left untreated. In the genital tract, Chlamydia trachomatis infects primarily epithelial cells and requires Th1 immunity for optimal clearance. This review first focuses on the immune cells important in a chlamydial infection. Second, we summarize the research and challenges associated with developing a chlamydial vaccine that elicits a protective Th1-mediated immune response without inducing adverse immunopathologies.

A Multi-Component Prime-Boost Vaccination Regimen with a Consensus MOMP Antigen Enhances Chlamydia trachomatis Clearance

BACKGROUND

A vaccine for Chlamydia trachomatis is of urgent medical need. We explored bioinformatic approaches to generate an immunogen against C. trachomatis that would induce cross-serovar T-cell responses as (i) CD4(+) T cells have been shown in animal models and human studies to be important in chlamydial protection and (ii) antibody responses may be restrictive and serovar specific.

METHODS

A consensus antigen based on over 1,500 major outer membrane protein (MOMP) sequences provided high epitope coverage against the most prevalent C. trachomatis strains in silico. Having designed the T-cell immunogen, we assessed it for immunogenicity in prime-boost regimens. This consensus MOMP transgene was delivered using plasmid DNA, Human Adenovirus 5 (HuAd5) or modified vaccinia Ankara (MVA) vectors with or without MF59(®) adjuvanted recombinant MOMP protein.

RESULTS

Different regimens induced distinct immune profiles. The DNA-HuAd5-MVA-Protein vaccine regimen induced a cellular response with a Th1-biased serum antibody response, alongside high serum and vaginal MOMP-specific antibodies. This regimen significantly enhanced clearance against intravaginal C. trachomatis serovar D infection in both BALB/c and B6C3F1 mouse strains. This enhanced clearance was shown to be CD4(+) T-cell dependent. Future studies will need to confirm the specificity and precise mechanisms of protection.

CONCLUSION

A C. trachomatis vaccine needs to induce a robust cellular response with broad cross-serovar coverage and a heterologous prime-boost regimen may be an approach to achieve this.

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.

Subunit vaccines for the prevention of mucosal infection with Chlamydia trachomatis

Chlamydia trachomatis is the most common preventable cause of tubal infertility in women. In high-income countries, despite public health control efforts, C. trachomatis case rates continue to rise. Most medium and low-income countries lack any Chlamydia control program; therefore, a vaccine is essential for the control of Chlamydia infections. A rationally designed Chlamydia vaccine requires understanding of the immunological correlates of protective immunity, pathological responses to this mucosal pathogen, identification of optimal vaccine antigens and selection of suitable adjuvant delivery systems that engender protective immunity. Fortunately, Chlamydia vaccinology is facilitated by genomic knowledge and by murine models that reproduce many of the features of human C. trachomatis infection. This article reviews recent progress in these areas with a focus on subunit vaccine development.

Chlamydia trachomatis: Protective Adaptive Responses and Prospects for a Vaccine

Chlamydia trachomatis is the most common cause of sexually transmitted bacterial infection globally. These infections translate to a significant public health burden, particularly women's healthcare costs due to serious disease sequelae such as pelvic inflammatory disease (PID), tubal factor infertility, chronic pelvic pain, and ectopic pregnancy. There is no evidence that natural immunity can provide complete, long-term protection necessary to prevent chronic pathology, making human vaccine development critical. Vaccine design will require careful consideration of protective versus pathological host-response mechanisms in concert with elucidation of optimal antigens and adjuvants. Evidence suggests that a Th1 response, facilitated by IFN-γ-producing CD4 T cells, will be instrumental in generating long-term, sterilizing immunity. Although the role of antibodies is not completely understood, they have exhibited a protective effect by enhancing chlamydial clearance. Future work will require investigation of broadly neutralizing antibodies and antibody-augmented cellular immunity to successfully design a vaccine that potently elicits both arms of the immune response. Sterilizing immunity is the ultimate goal. However, vaccine-induced partial immunity that prevents upper genital tract infection and inflammation would be cost-effective compared to current screening and treatment strategies. In this chapter, we examine evidence from animal and human studies demonstrating protective adaptive immune responses to Chlamydia and discuss future challenges and prospects for vaccine development.

A multi-subunit Chlamydia vaccine inducing neutralizing antibodies and strong IFN-γ⁺ CMI responses protects against a genital infection in minipigs

Chlamydia is the most widespread sexually transmitted bacterial disease and a prophylactic vaccine is highly needed. Ideally, this vaccine is required to induce a combined response of Th1 cell-mediated immune (CMI) response in concert with neutralizing antibodies. Using a novel Göttingen minipig animal model, we evaluated the immunogenicity and efficacy of a multi-subunit vaccine formulated in the strong Th1-inducing adjuvant CAF01. We evaluated a mixture of two fusion proteins (Hirep1 and CTH93) designed to promote either neutralizing antibodies or cell-mediated immunity, respectively. Hirep1 is a novel immunogen based on the variant domain (VD) 4 region from major outer membrane protein (MOMP) serovar (Sv) D, SvE and SvF, and CTH93 is a fusion molecule of three antigens (CT043, CT414 and MOMP). Pigs were immunized twice intramuscularly with either Hirep1+CTH93/CAF01, UV-inactivated Chlamydia trachomatis SvD bacteria (UV-SvD/CAF01) or CAF01. The Hirep1+CTH93/CAF01 vaccine induced a strong CMI response against the vaccine antigens and high titers of antibodies, particularly against the VD4 region of MOMP. Sera from Hirep1+CTH93/CAF01 immunized pigs neutralized C. trachomatis SvD and SvF infectivity in vitro. Both Hirep1+CTH93/CAF01 and UV-SvD/CAF01 vaccination protected pigs against a vaginal C. trachomatis SvD infection. In conclusion, the Hirep1+CTH93/CAF01 vaccine proved highly immunogenic and equally protective as UV-SvD/CAF01 showing promise for the development of a subunit vaccine against Chlamydia.

Protection Against Chlamydia trachomatis Infection and Upper Genital Tract Pathological Changes by Vaccine-Promoted Neutralizing Antibodies Directed to the VD4 of the Major Outer Membrane Protein

The VD4 region from the Chlamydia trachomatis major outer membrane protein contains important neutralizing B-cell epitopes of relevance for antibody-mediated protection against genital tract infection. We developed a multivalent vaccine construct based on VD4s and their surrounding constant segments from serovars D, E, and F. Adjuvanted with cationic liposomes, this construct promoted strong immune responses to serovar-specific epitopes, the conserved LNPTIAG epitope and neutralized serovars D, E, and F. Vaccinated mice were protected against challenge, with protection defined as reduced bacterial numbers in vagina and prevention of pathological changes in the upper genital tract. Adoptive transfer of serum and T-cell depletion experiments demonstrated a dominant role for antibodies and CD4(+) T cells in the protective immune response. Integrating a multivalent VD4 construct into the sequence of the major outer membrane protein resulted in a protective and broadly neutralizing vaccine. Our findings emphasize the important role of antibodies in protection against Chlamydia trachomatis.

Evaluation of a multisubunit recombinant polymorphic membrane protein and major outer membrane protein T cell vaccine against Chlamydia muridarum genital infection in three strains of mice

An efficacious vaccine is needed to control Chlamydia trachomatis infection. In the murine model of Chlamydia muridarum genital infection, multifunctional mucosal CD4 T cells are the foundation for protective immunity, with antibody playing a secondary role. We previously identified four Chlamydia outer membrane proteins (PmpE, PmpF, PmpG and PmpH) as CD4 T cell vaccine candidates using a dendritic cell-based immunoproteomic approach. We also demonstrated that these four polymorphic membrane proteins (Pmps) individually conferred protection as measured by accelerated clearance of Chlamydia infection in the C57BL/6 murine genital tract model. The major outer membrane protein, MOMP is also a well-studied protective vaccine antigen in this system. In the current study, we tested immunogenicity and protection of a multisubunit recombinant protein vaccine consisting of the four Pmps (PmpEFGH) with or without the major outer membrane protein (MOMP) formulated with a Th1 polarizing adjuvant in C57BL/6, Balb/c and C3H mice. We found that C57BL/6 mice vaccinated with PmpEFGH+MOMP elicited more robust cellular immune responses than mice immunized with individual protein antigens. Pmps elicited more variable cellular immune responses than MOMP among the three strains of mice. The combination vaccine accelerated clearance in the three strains of mice although at different rates. We conclude that the recombinant outer membrane protein combination constitutes a promising first generation Chlamydia vaccine construct that should provide broad immunogenicity in an outbred population.

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.

Chlamydia trachomatis recombinant MOMP encapsulated in PLGA nanoparticles triggers primarily T helper 1 cellular and antibody immune responses in mice: a desirable candidate nanovaccine

We recently demonstrated by in vitro experiments that PLGA (poly D, L-lactide-co-glycolide) potentiates T helper 1 (Th1) immune responses induced by a peptide derived from the recombinant major outer membrane protein (rMOMP) of Chlamydia trachomatis, and may be a promising vaccine delivery system. Herein we evaluated the immune-potentiating potential of PLGA by encapsulating the full-length rMOMP (PLGA-rMOMP), characterizing it in vitro, and investigating its immunogenicity in vivo. Our hypothesis was that PLGA-rMOMP triggers Th1 immune responses in mice, which are desirable prerequisites for a C. trachomatis candidate nanovaccine. Physical-structural characterizations of PLGA-rMOMP revealed its size (approximately 272 nm), zeta potential (−14.30 mV), apparent spherical smooth morphology, and continuous slow release pattern. PLGA potentiated the ability of encapsulated rMOMP to trigger production of cytokines and chemokines by mouse J774 macrophages. Flow cytometric analyses revealed that spleen cells from BALB/c mice immunized with PLGA-rMOMP had elevated numbers of CD4+ and CD8+ T cell subsets, and secreted more rMOMP-specific interferon-gamma (Th1) and interleukin (IL)-12p40 (Th1/Th17) than IL-4 and IL-10 (Th2) cytokines. PLGA-rMOMP-immunized mice produced higher serum immunoglobulin (Ig)G and IgG2a (Th1) than IgG1 (Th2) rMOMP-specific antibodies. Notably, sera from PLGA-rMOMP-immunized mice had a 64-fold higher Th1 than Th2 antibody titer, whereas mice immunized with rMOMP in Freund’s adjuvant had only a four-fold higher Th1 than Th2 antibody titer, suggesting primarily induction of a Th1 antibody response in PLGA-rMOMP-immunized mice. Our data underscore PLGA as an effective delivery system for a C. trachomatis vaccine. The capacity of PLGA-rMOMP to trigger primarily Th1 immune responses in mice promotes it as a highly desirable candidate nanovaccine against C. trachomatis.

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.

Chlamydia trachomatis control requires a vaccine

As the most common reported communicable disease in North America and Europe, Chlamydia trachomatis is the focus of concerted public health control efforts based on screening and treatment. Unexpectedly control efforts are accompanied by rising reinfection rates attributed in part to arresting the development of herd immunity. Shortening the duration of infection through the testing and treatment program is the root cause behind the arrested immunity hypothesis and because of this a vaccine will be essential to control efforts. Advances in Chlamydia vaccinomics have revealed the C. trachomatis antigens that can be used to constitute a subunit vaccine and a vaccine solution appears to be scientifically achievable. We propose that an accelerated C. trachomatis vaccine effort requires coordinated partnership among academic, public health and private sector players together with a commitment to C. trachomatis vaccine control as a global public health priority.

Chlamydia vaccines: recent developments and the role of adjuvants in future formulations

Bacteria of the genus Chlamydia cause a plethora of ocular, genital and respiratory diseases that continue to pose a considerable public health challenge worldwide. The major diseases are conjunctivitis and blinding trachoma, non-gonococcal urethritis, cervicitis, pelvic inflammatory disease, ectopic pregnancy, tubal factor infertility and interstitial pneumonia. The rampart asymptomatic infections prevent timely and effective antibiotic treatments, and quite often clinical presentation of sequelae is the first evidence of an infection. Besides, significant broad coverage in population screening and treatment is economically and logistically impractical, and mass education for public awareness has been ineffective. The current medical opinion is that an efficacious prophylactic vaccine is the best approach to protect humans from chlamydial infections. Unfortunately, a human vaccine has yet to be realized despite successful veterinary vaccines. Fortunately, recent advances in chlamydial immunobiology, cell biology, molecular pathogenesis, genomics, antigen discovery and animal models of infections are hastening progress toward an efficacious vaccine. Thus, it is established that Chlamydia immunity is mediated by T cells and a complementary antibody response, and several potential vaccine candidates have been identified. However, further advances are needed in effective vaccine delivery systems and safe potent adjuvants to boost and sustain immune responses for long-lasting protective immunity. This article focuses on the current status of human chlamydial vaccine research, specifically how application of new delivery systems and human compatible adjuvants could lead to a timely achievement of efficacious Chlamydia vaccines. The ranking of the candidate vaccine antigens for human vaccine development will await the availability of results from studies in which the antigens are tested by comparable experimental standards, such as antigen-adjuvant combination, route of delivery and possible toxicity.

A novel chimeric MOMP antigen expressed in Escherichia coli, Arabidopsis thaliana, and Daucus carota as a potential Chlamydia trachomatis vaccine candidate

The major outer membrane protein (MOMP) of Chlamydia trachomatis is a highly antigenic and hydrophobic transmembrane protein. Our attempts to express the full-length protein in a soluble form in Escherichia coli and in transgenic plants failed. A chimeric gene construct of C. trachomatis serovar E MOMP was designed in order to increase solubility of the MOMP protein but with retained antigenicity. The designed construct was successfully expressed in E. coli, in Arabidopsis thaliana, and in Daucus carota. The chimeric MOMP expressed in and purified from E. coli was used as antigen for production of antibodies in rabbits. The anti-chimeric MOMP antibodies recognized the corresponding protein in both E. coli and in transgenic plants, as well as in inactivated C. trachomatis elementary bodies. Transgenic Arabidopsis and carrots were characterized for the number of MOMP chimeric genetic inserts and for protein expression. Stable integration of the transgene and the corresponding protein expression were demonstrated in Arabidopsis plants over at least six generations. Transgenic carrots showed a high level of expression of the chimeric MOMP - up to 3% of TSP.

Chlamydia trachomatis vaccine research through the years

Chlamydia trachomatis is a Gram-negative obligate intracellular bacterium. It is the leading cause of bacterial sexual transmitted infections (STIs). World Health Organization figures estimated that over 90 million new cases of genital C. trachomatis infections occur worldwide each year. A vaccination program is considered to be the best approach to reduce the prevalence of C. trachomatis infections, as it would be much cheaper and have a greater impact on controlling C. trachomatis infections worldwide rather than a screening program or treating infections with antibiotics. Currently, there are no vaccines available which effectively protect against a C. trachomatis genital infection despite the many efforts that have been made throughout the years. In this paper, the many attempts to develop a protective vaccine against a genital C. trachomatis infection will be reviewed.

Evaluation of a broadly protective Chlamydia-cholera combination vaccine candidate

The need to simultaneously target infections with epidemiological overlap in the population with a single vaccine provides the basis for developing combination vaccines. Vibrio cholerae ghosts (rVCG) offer an attractive approach for developing vaccines against a number of human and animal pathogens. In this study, we constructed a multisubunit vaccine candidate co-expressing the serovar D-derived Porin B and polymorphic membrane protein-D proteins of Chlamydia trachomatis and evaluated its ability to simultaneously induce broad-based chlamydial immunity and elicit a vibriocidal antibody response to the Vibrio carrier envelope. Intramuscular (IM) immunization with the vaccine candidate elicited high levels of antigen-specific genital mucosal and systemic Th1 cell-mediated and humoral immune responses against heterologous serovars and strains, including serovars E-H and L. Also, in addition to the multisubunit vaccine, the single subunit constructs conferred significant cross protection against the heterologous mouse strain, Chlamydia muridarum. Furthermore, all mice immunized with rVCG vaccine constructs responded with a significant rise in vibriocidal antibody titer, the surrogate marker for protection in cholera. These findings demonstrate the ability of the multisubunit vaccine to induce cross protective chlamydial as well as vibriocidal immunity and establish the possibility of developing a broadly efficacious Chlamydia-cholera combination vaccine.

Management of Chlamydia trachomatis genital tract infection: screening and treatment challenges

Chlamydia trachomatis is a prevalent sexually transmitted infection that can lead to serious reproductive morbidity. Management and control of C. trachomatis is a challenge, largely due to its asymptomatic nature and our incomplete understanding of its natural history. Although chlamydia screening programs have been implemented worldwide, several countries have observed increasing rates of reported chlamydia cases. We reviewed the literature relating to the long-term complications of C. trachomatis, as well as screening strategies, treatment, and prevention strategies for reducing chlamydia in the population. Articles from 1950-2010 were identified through a Medline search using the keyword "Chlamydia trachomatis" combined with "screening", "pelvic inflammatory disease", "endometritis", "salpingitis", "infertility", "ectopic pregnancy", "urethritis", "epididymitis", "proctitis", "prostatitis", "reinfection", "cost-effectiveness", "treatment", "vaccines", or "prevention". Progression of C. trachomatis varies, and recurrent infections are common. Currently, there is limited evidence on the effectiveness of chlamydia screening. Higher quality studies are needed to determine the efficacy of more frequent screening, on a broader range of sequelae, including infertility and ectopic pregnancy, in addition to pelvic inflammatory disease. Studies should focus on delineating the natural history of recurrent infections, paying particular attention to treatment failures. Furthermore, alternatives to screening, such as vaccines, should continue to be explored.

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.

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.

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.