Subunit vaccines for the prevention of mucosal infection with Chlamydia trachomatis

Disease burden and macrolide resistance of Mycoplasma pneumoniae infection in adults in the Asia-Pacific region

OBJECTIVES

In the Asia-Pacific region, Mycoplasma pneumoniae (MP) could be a notable pathogen responsible for adult community-acquired pneumonia (CAP), with varying prevalence rates. This comprehensive review aimed to explore the epidemiology, clinical manifestations, macrolide resistance, and molecular characteristics of MP in adults across several countries in Asia.

METHODS

PubMed, Embase, and Google Scholar were searched for relevant articles from 2010-2023 based on the following keywords: adult and Mycoplasma pneumoniae.

RESULTS

The prevalence of MP in CAP patients in these countries ranged from 2.1% in Korea to 25.5% in Japan. Macrolide resistance was prominent, particularly in China, with rates ranging 26.9-100%. Clinical manifestations of MP infection included protean extrapulmonary manifestations, and complications such as rhabdomyolysis and thrombocytopenia. Molecular characteristics, especially the multiple locus variable-number tandem-repeat analysis type 4/5/7/2, remained predominant across various countries, emphasising the importance of ongoing surveillance.

CONCLUSIONS

This review highlights the urgent need for continued monitoring of MP infections, macrolide resistance, and molecular characteristics to inform effective prevention and treatment strategies in the Asia-Pacific region.

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.

Antibody responses to Chlamydia trachomatis vaccine candidate antigens in Chlamydia-infected women and correlation with antibody-mediated phagocytosis of elementary bodies

Murine research has revealed a significant role for antibody responses in protection against Chlamydia reinfection. To explore potential humoral immune markers of protection elicited by Chlamydia trachomatis (CT) antigens in humans in the context of presumed clinical correlates of protection, we used both an IgG1-based ELISA and a conventional total IgG ELISA to evaluate antibody responses. We evaluated responses to five CT outer membrane proteins (PmpE, PmpF, PmpG, PmpH, and MOMP), along with other promising CT antigens (Pgp3 and HSP60), negative control antigens (RecO and AtpE), and CT elementary bodies (EBs) in sera from a well-characterized cohort of 60 women with different CT infection outcomes, including two outcomes that are likely clinical correlates of protective immunity: spontaneous resolution of infection and absence of reinfection after treatment. Furthermore, we used a flow cytometry-based assay to measure antibody-mediated phagocytosis by neutrophils in these sera. Results demonstrated that IgG1 ELISA displayed higher sensitivity than conventional total IgG ELISA in assessing antibody responses to CT EBs and antigens. Pgp3 IgG1 ELISA exhibited the highest sensitivity compared to IgG1 ELISA incorporating CT EBs or other antigens, confirming Pgp3 IgG1 ELISA as an ideal assay for CT antibody detection. Most (95%) sera from women with CT infection outcomes exhibited antibody-mediated phagocytosis of CT EBs, which was significantly correlated with IgG1 antibody responses to MOMP, Pgp3, HSP60, and PmpF. However, neither IgG1 responses to CT antigens and EBs nor antibody-mediated phagocytosis were associated with clinical correlates of protection. These findings suggest that neither CT IgG1 antibody detection nor antibody-mediated phagocytosis will be useful as immune correlates of protection against CT infection in humans.

A novel chimeric recombinant FliC-Pgp3 vaccine promotes immunoprotection against Chlamydia muridarum infection in mice

The Pgp3 subunit vaccine elicits immune protection against Chlamydia trachomatis infection, but additional adjuvants are still required to enhance its immunoprotective efficacy. Flagellin can selectively stimulate immunity and act as an adjuvant. In this research, the FliC-Pgp3 recombinant was successfully expressed and purified. Tri-immunization with the FliC-Pgp3 vaccine in Balb/C mice induced rapid and persistent germinal center B-cell response and Tfh differentiation, promoting a significantly higher IgG antibody titer compared to the Pgp3 group. FliC-Pgp3 immunization primarily induced Th1-type cellular immunity, leading to higher levels of IFN-γ, TNF-α, and IL-2 secreted by CD4+ T cells than in Pgp3-vaccinated mice. Chlamydia muridarum challenge results showed that FliC-Pgp3-vaccinated mice exhibited more rapid clearance of Chlamydia muridarum colonization in the lower genital tract, ensuring a lower hydrosalpinx rate and cumulative score. Histological analysis showed reduced dilation and inflammatory infiltration in the oviduct and uterine horn of FliC-Pgp3-vaccinated mice compared to the PBS and Pgp3 control. Importantly, tri-immunization with FliC-Pgp3 effectively activated CD4+ T cells and dendritic cells, as confirmed by the adoptive transfer, resulting in better immune protection in recipient mice. In summary, the novel FliC-Pgp3 chimeric is hoped to be a novel vaccine with improved immunoprotection against Chlamydia muridarum.

Prevention strategies for sexually transmitted infections, HIV, and viral hepatitis in Europe

The current prevention efforts for STIs, HIV and viral hepatitis in the WHO European Region, especially in the Central and Eastern subregions, are hindered by healthcare disparities, data gaps, and limited resources. In this comprehensive narrative review, we aim to highlight both achievements and persisting challenges while also exploring new developments that could significantly impact the prevention of these infections in the near future. While pre-exposure prophylaxis (PrEP) for HIV has been broadly approved and implemented in 38 out of 53 countries in the region, challenges remain, including cost, limited licensing, and incomplete adherence. We explore innovative approaches like on-demand PrEP, long-acting injectable cabotegravir, and intravaginal rings that have shown promising results, alongside the use of six-monthly lenacapavir, the outcomes of which are pending. Additionally, the potential of doxycycline post-exposure prophylaxis has been discussed, revealing efficacy in reducing chlamydia and syphilis risk, but effectiveness against gonorrhoea being contingent on tetracycline resistance rates, and the need of further data to determine potential resistance development in other bacteria and its impact on the gut microbiome. We examine successful vaccination campaigns against HBV and HPV, the ongoing development of vaccines for chlamydia, syphilis, herpesvirus, and gonorrhoea, and challenges in HIV vaccine research, including lines of research with significant potential like sequential immunization, T-cell responses, and mRNA technology. This review underscores the research endeavors that pave the way for a more resilient and robust approach to combating STIs, HIV, and viral hepatitis in the region.

Production of a promising modular proteinaceous self-assembled delivery system for vaccination

Recently, there have been enormous advances in nano-delivery materials, especially safer and more biocompatible protein-based nanoparticles. Generally, proteinaceous nanoparticles (such as ferritin and virus-like particles) are self-assembled from some natural protein monomers. However, to ensure their capability of assembly, it is difficult to upgrade the protein structure through major modifications. Here, we have developed an efficient orthogonal modular proteinaceous self-assembly delivery system that could load antigens with an attractive coupling strategy. In brief, we constructed a nanocarrier by fusing two orthogonal domains-a pentameric cholera toxin B subunit and a trimer forming peptide-and an engineered streptavidin monomer for binding biotinylated antigens. After successfully preparing the nanoparticles, the receptor-binding domain of SARS-CoV-2 spike protein and influenza virus haemagglutination antigen are used as model antigens for further evaluation. We found that the biotinylated antigen is able to bind to the nanoparticles with high affinity and achieve efficient lymph node drainage when loaded on the nanoparticles. Then, T cells are greatly activated and the formation of germinal centers is observed. Experiments of two mouse models demonstrate the strong antibody responses and prophylactic effects of these nanovaccines. Thus, we establish a proof-of-concept for the delivery system with the potential to load diverse antigen cargos to generate high-performance nanovaccines, thereby offering an attractive platform technology for nanovaccine preparation.

Heterologous prime-boost vaccination based on Polymorphic protein D protects against intravaginal Chlamydia trachomatis infection in mice

The control of the worldwide spread of sexually transmitted Chlamydia trachomatis (Ct) infection urgently demands the development of a preventive vaccine. In this work, we designed a vaccine based on a fragment of polymorphic protein D (FPmpD) that proved to be immunogenic enough to generate a robust systemic and mucosal IgG humoral immune response in two strains of mice. We used a heterologous prime-boost strategy, including simultaneous systemic and mucosal administration routes. The high titers of anti-PmpD antibodies elicited by this immunization scheme did not affect murine fertility. We tested the vaccine in a mouse model of Ct intravaginal infection. Anti-PmpD antibodies displayed potent neutralizing activity in vitro and protective effects in uterine tissues in vivo. Notably, the humoral immune response of PmpD-vaccinated mice was faster and stronger than the primary immune response of non-vaccinated mice when exposed to Ct. FPmpD-based vaccine effectively reduced Ct shedding into cervicovaginal fluids, bacterial burden at the genitourinary tract, and overall infectivity. Hence, the FPmpD-based vaccine might constitute an efficient tool to protect against Ct intravaginal infection and decrease the infection spreading.

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

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

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.

Intranasal immunization with inactivated chlamydial elementary bodies formulated in VCG-chitosan nanoparticles induces robust immunity against intranasal Chlamydia psittaci challenge

Vaccines based on live attenuated Chlamydia elementary bodies (EBs) can cause disease in vaccinated animals and the comparably safer inactivated whole EBs are only marginally protective. Recent studies show that a vaccine formulation comprising UV-inactivated EBs (EB) and appropriate mucosal delivery systems and/or adjuvants induced significant protective immunity. We tested the hypothesis that intranasal delivery of UV-inactivated C. psittaci EB formulated in Vibrio cholerae ghosts (VCG)-chitosan nanoparticles will induce protective immunity against intranasal challenge in SPF chickens. We first compared the impact of VCG and CpG adjuvants on protective immunity following IN mucosal and IM systemic delivery of EB formulated in chitosan hydrogel/microspheres. Immunologic analysis revealed that IN immunization in the presence of VCG induced higher levels of IFN-γ response than IM delivery or the CpG adjuvanted groups. Also, vaccine efficacy evaluation showed enhanced pharyngeal bacterial clearance and protection against lung lesions with the VCG adjuvanted vaccine formulation, thereby establishing the superior adjuvanticity of VCG over CpG. We next evaluated the impact of different concentrations of VCG on protective immunity following IN mucosal immunization. Interestingly, the adjuvanticity of VCG was concentration-dependent, since protective immunity induced following IN mucosal immunization showed dose-dependent immune responses and protection. These studies reveal that formulation of inactivated chlamydial antigens with adjuvants, such as VCG and chitosan increases their ability to induce protective immune responses against challenge.

Encapsulation of Recombinant MOMP in Extended-Releasing PLGA 85:15 Nanoparticles Confer Protective Immunity Against a Chlamydia muridarum Genital Challenge and Re-Challenge

Recently we reported the immune-potentiating capacity of a Chlamydia nanovaccine (PLGA-rMOMP) comprising rMOMP (recombinant major outer membrane protein) encapsulated in extended-releasing PLGA [poly (D, L-lactide-co-glycolide) (85:15)] nanoparticles. Here we hypothesized that PLGA-rMOMP would bolster immune-effector mechanisms to confer protective efficacy in mice against a Chlamydia muridarum genital challenge and re-challenge. Female BALB/c mice received three immunizations, either subcutaneously (SC) or intranasally (IN), before receiving an intravaginal challenge with C. muridarum on day 49 and a re-challenge on day 170. Both the SC and IN immunization routes protected mice against genital challenge with enhanced protection after a re-challenge, especially in the SC mice. The nanovaccine induced robust antigen-specific Th1 (IFN-γ, IL-2) and IL-17 cytokines plus CD4+ proliferating T-cells and memory (CD44high CD62Lhigh) and effector (CD44high CD62Llow) phenotypes in immunized mice. Parallel induction of antigen-specific systemic and mucosal Th1 (IgG2a, IgG2b), Th2 (IgG1), and IgA antibodies were also noted. Importantly, immunized mice produced highly functional Th1 avidity and serum antibodies that neutralized C. muridarum infectivity of McCoy fibroblasts in-vitro that correlated with their respective protection levels. The SC, rather than the IN immunization route, triggered higher cellular and humoral immune effectors that improved mice protection against genital C. muridarum. We report for the first time that the extended-releasing PLGA 85:15 encapsulated rMOMP nanovaccine confers protective immunity in mice against genital Chlamydia and advances the potential towards acquiring a nano-based Chlamydia vaccine.

Modulation of Immune Response to Chlamydia muridarum by Host miR-135a

Previously, our laboratory established the role of small, noncoding RNA species, i.e., microRNA (miRNA) including miR-135a in anti-chlamydial immunity in infected hosts. We report here chlamydial infection results in decreased miR-135a expression in mouse genital tissue and a fibroblast cell line. Several chemokine and chemokine receptor genes (including CXCL10, CCR5) associated with chlamydial pathogenesis were identified in silico to contain putative miR-135a binding sequence(s) in the 3' untranslated region. The role of miR-135a in the host immune response was investigated using exogenous miR-135a mimic to restore the immune phenotype associated with decreased miR-135a following Chlamydia muridarum (Cm) infection. We observed miR-135a regulation of Cm-primed bone marrow derived dendritic cells (BMDC) via activation of Cm-immune CD4⁺ T cells for clonal expansion and CCR5 expression. Using a transwell cell migration assay, we explore the role of miR-135a in regulation of genital tract CXCL10 expression and recruitment of CXCR3⁺ CD4⁺ T cells via the CXCL10/CXCR3 axis. Collectively, data reported here support miR-135a affecting multiple cellular processes in response to chlamydial infection.

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.

A nanovaccine formulation of Chlamydia recombinant MOMP encapsulated in PLGA 85:15 nanoparticles augments CD4+ effector (CD44high CD62Llow) and memory (CD44high CD62Lhigh) T-cells in immunized mice

Vaccine developmental strategies are utilizing antigens encapsulated in biodegradable polymeric nanoparticles. Here, we developed a Chlamydia nanovaccine (PLGA-rMOMP) by encapsulating its recombinant major outer membrane protein (rMOMP) in the extended-releasing and self-adjuvanting PLGA [poly (D, L-lactide-co-glycolide) (85:15)] nanoparticles. PLGA-rMOMP was small (nanometer size), round and smooth, thermally stable, and exhibited a sustained release of rMOMP. Stimulation of mouse primary dendritic cells (DCs) with PLGA-rMOMP augmented endosome processing, induced Th1 cytokines (IL-6 and IL-12p40), and expression of MHC-II and co-stimulatory (CD40, CD80, and CD86) molecules. BALB/c mice immunized with PLGA-rMOMP produced enhanced CD4⁺ T-cells-derived memory (CD44^high CD62L^high), and effector (CD44^high CD62L^low) phenotypes and functional antigen-specific serum IgG antibodies. In vivo biodistribution of PLGA-rMOMP revealed its localization within lymph nodes, suggesting migration from the injection site via DCs. Our data provide evidence that the PLGA (85:15) nanovaccine activates DCs and augments Chlamydia-specific rMOMP adaptive immune responses that are worthy of efficacy testing.

A Nonsurgical Embryo Transfer Technique for Fresh and Cultured Blastocysts in Rats

The use of a nonsurgical embryo transfer technique in rodents eliminates the potential pain, distress, and health complications that may result from a surgical procedure and as such, represents a refinement in rodent assisted reproductive techniques. A nonsurgical technique has not been previously developed for use with rat embryos. Here we describe an efficient method to deliver either fresh or cultured blastocyst stage embryos to the uterine horn of pseudopregnant female rats using a rat nonsurgical embryo transfer (rNSET) device. The rNSET device is composed of a Teflon catheter and a hub that attaches to a 2 μL pipette. Oxytocin is used to dilate the cervix before the delivery of blastocysts, allowing passage of the rNSET catheter directly into the uterine horn for embryo delivery. The efficiency of recovery of pups after nonsurgical embryo transfer is similar to the efficiency after surgical embryo transfer. Furthermore, the technique is not stressful to the subjects, as demonstrated by the absence of a decrease in weight or increase in fecal corticosterone level in recipients of embryos delivered nonsurgically, without the use of anesthesia or analgesia.

Suppressors of Cytokine Signaling (SOCS)1 and SOCS3 Proteins Are Mediators of Interleukin-10 Modulation of Inflammatory Responses Induced by Chlamydia muridarum and Its Major Outer Membrane Protein (MOMP) in Mouse J774 Macrophages

The immunopathology of chlamydial diseases is exacerbated by a broad-spectrum of inflammatory mediators, which we reported are inhibited by IL-10 in macrophages. However, the chlamydial protein moiety that induces the inflammatory mediators and the mechanisms by which IL-10 inhibits them are unknown. We hypothesized that Chlamydia major outer membrane protein (MOMP) mediates its disease pathogenesis, and the suppressor of cytokine signaling (SOCS)1 and SOCS3 proteins are mediators of the IL-10 inhibitory actions. Our hypothesis was tested by exposing mouse J774 macrophages to chlamydial stimulants (live Chlamydia muridarum and MOMP) with and without IL-10. MOMP significantly induced several inflammatory mediators (IL-6, IL-12p40, CCL5, CXCL10), which were dose-dependently inhibited by IL-10. Chlamydial stimulants induced the mRNA gene transcripts and protein expression of SOCS1 and SOCS3, with more SOCS3 expression. Notably, IL-10 reciprocally regulated their expression by reducing SOCS1 and increasing SOCS3. Specific inhibitions of MAPK pathways revealed that p38, JNK, and MEK1/2 are required for inducing inflammatory mediators as well as SOCS1 and SOCS3. Chlamydial stimulants triggered an M1 pro-inflammatory phenotype evidently by an enhanced nos2 (M1 marker) expression, which was skewed by IL-10 towards a more M2 anti-inflammatory phenotype by the increased expression of mrc1 and arg1 (M2 markers) and the reduced SOCS1/SOCS3 ratios. Neutralization of endogenously produced IL-10 augmented the secretion of inflammatory mediators, reduced SOCS3 expression, and skewed the chlamydial M1 to an M2 phenotype. Inhibition of proteasome degradation increased TNF but decreased IL-10, CCL5, and CXCL10 secretion by suppressing SOCS1 and SOCS3 expressions and dysregulating their STAT1 and STAT3 transcription factors. Our data show that SOCS1 and SOCS3 are regulators of IL-10 inhibitory actions, and underscore SOCS proteins as therapeutic targets for IL-10 control of inflammation for Chlamydia and other bacterial inflammatory diseases.

Evaluation of a tandem Chlamydia psittaci Pgp3 multiepitope peptide vaccine against a pulmonary chlamydial challenge in mice

Chlamydia psittaci is the pathogen of psittacosis, and it has emerged as a significant public health threat. Because most infections are easily overlooked, a vaccine is recognized as the best solution to control the spread of C. psittaci. Our previous study showed that Pgp3 protein is efficacious as a subunit vaccine while not the best candidate due to the negative effects. Thus, in this study, we tested the ability of a tandem epitope vaccine candidate designated SP based on Pgp3-dominant epitopes to induce protective immunity against pulmonary chlamydial infection. BALB/c mice were intraperitoneally inoculated with multiepitope peptide antigens followed by intranasal infection with C. psittaci. We found that the multiepitope peptide antigens induced strong humoral and cellular immune responses with high Th1-related (IFN-γ and IL-2) and proinflammatory (IL-6) cytokine levels. Meanwhile, the pathogen burden and inflammatory infiltration were significantly reduced in lungs of SP-immunized mice after chlamydial challenge. In addition, the IFN-γ and IL-6 secretion levels in the infected lungs were substantially reduced. Overall, our findings demonstrate that the peptide vaccine SP plays a significant role with good immunogenicity and protective efficacy against C. psittaci lung infection in BALB/c mice, providing important insights towards understanding the potential of peptide vaccines as new vaccine antigens for inducing protective immunity against chlamydial infection.

Proteome array of antibody responses to Chlamydia trachomatis infection in nonhuman primates

AIMS

Nonhuman primates have been used to investigate pathogenic mechanisms and evaluate immune responses following Chlamydia trachomatis inoculation. This study aimed to systemically profile antibody responses to C. trachomatis infection in nonhuman primates.

MATERIALS AND METHODS

Sera were obtained from 4 pig-tailed and 8 long-tailed macaques which were intravaginally or ocularly infected with live C. trachomatis organisms, and analyzed by C. trachomatis proteome array of antigens.

KEY FINDINGS

The sera from 12 macaques recognized total 172 C. trachomatis antigens. While 84 antigens were recognized by pig-tailed macaques intravaginally infected with serovar D strain, 125 antigens were recognized by long-tailed macaques ocularly infected with serovar A, and 37 antigens were recognized by both. Ocular inoculation with virulent A2497 strain induced antibodies to more antigens. Among the antigens uniquely recognized by A2497 strain infected macaques, outer membrane complex B antigen (OmcB) induced robust antibody response. Although macaques infected by less virulent A/HAR-13 strain failed to develop antibodies to OmcB, reinfection by A2497 strain induced high levels of antibodies to OmcB.

SIGNIFICANCE

Proteome array has revealed a correlation of chlamydial infection invasiveness with chlamydial antigen immunogenicity, and identified antibody responses to OmcB potentially as biomarkers for invasive infection with C. trachomatis.

The ΦCPG1 chlamydiaphage can infect Chlamydia trachomatis and significantly reduce its infectivity

Recent years have seen a significant increase in rates of persistent, antibiotic-resistant infection of Chlamydia trachomatis (CT) infections, representing an increasingly serious public health threat. At present there are no effective vaccines or antibodies available to treat CT, prompting the need for novel treatment strategies. One potential solution to this issue is the use of ΦCPG1, a chlamydia-specific lytic phage which has over 90% nucleotide sequence identity with other chlamydiaphages. Previous work has shown the Vp1 capsid protein of ΦCPG1 to exhibit broad inhibitory activity against all CT serotypes, inhibiting CT-mediated host cell toxicity. Patients with CT infections exhibit circulating antibodies against this Vp1 protein, suggesting that this or similar phages may be present in vivo in the context of CT infections, even though no phages have been specifically detected to date. Given these previous findings, we hypothesized that the ΦCPG1 chlamydiaphage may be able to infect CT, thereby inhibiting its growth and proliferation. To test this, we generated a recombinant pGFP-ΦCPG1 phage which we used to explore its effects on CT and chlamydia conjunctivitis of guinea pigs (GPIC). We found that pGFP insertion did not alter the packaging or infectivity of ΦCPG1, and that this recombinant phage was readily able to infect CT and GPIC and inhibit CT and GPIC in a dose-dependent fashion. This inhibition was most pronounced during the mid and late stages of the CT infection, disrupting the reticular body (RB) to EB transition, leading to the formation of enlarged RBs. These results indicate that ΦCPG1 is able to infect CT, highlighting this phage as a novel potential therapeutic agent for treating chlamydia infections. In addition, by engineering pGFP to express ΦCPG1, we have produced an valuable experimental tool useful for future studies of drug resistance, pathogenicity, and vaccine research aimed at improving CT treatment.

Co-delivery of amphipol-conjugated adjuvant with antigen, and adjuvant combinations, enhance immune protection elicited by a membrane protein-based vaccine against a mucosal challenge with Chlamydia

INTRODUCTION

Chlamydial infections are spread worldwide and a vaccine is needed to control this pathogen. The goals of this study were to determine if the delivery of an adjuvant associated to the antigen, via a derivatized amphipol, and adjuvant combinations improve vaccine protection.

METHODS

A novel approach, trapping the Chlamydia muridarum (Cm) native MOMP (nMOMP) with amphipols (A8-35), bearing a covalently conjugated peptide (EP67), was used. Adjuvants incorporated were: EP67 either conjugated to A8-35, which was used to trap nMOMP (nMOMP/EP67-A8-35), or free as a control, added to nMOMP/A8-35 complexes (nMOMP/A8-35+EP67); Montanide ISA 720 to enhance humoral responses, and CpG-1826 to elicit robust cell-mediated immunity (CMI). BALB/c mice were immunized by mucosal and systemic routes. Intranasal immunization with live Cm was used as positive control and three negative controls were included. Mice were challenged intranasally with Cm and changes in body weight, lungs weight and number of Cm-inclusion forming units (IFU) recovered from the lungs were evaluated to establish protection. To assess local responses levels of IFN- γ and Cm-specific IgA were determined in lungs' supernatants.

RESULTS

Structural assays demonstrated that nMOMP secondary structure and thermal stability were maintained when A8-35 was covalently modified. Mice vaccinated with nMOMP/EP67-A8-35 were better protected than animals immunized with nMOMP/A8-35+EP67. Addition of Montanide enhanced Th2 responses and improved protection. Including CpG-1826 further broadened, intensified and switched to Th1-biased immune responses. With delivery of nMOMP and the three adjuvants, as determined by changes in body weight, lungs weight and number of IFU recovered from lungs, protection at 10 days post-challenge was equivalent to that induced by immunization with live Cm.

CONCLUSIONS

Covalent association of EP67 to A8-35, used to keep nMOMP water-soluble, improves protection over that conferred by free EP67. Adjuvant combinations including EP67+Montanide+CpG-1826, by broadening and intensifying cellular and humoral immune responses, further enhanced protection.

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.

Future of human Chlamydia vaccine: potential of self-adjuvanting biodegradable nanoparticles as safe vaccine delivery vehicles

INTRODUCTION

There is a persisting global burden and considerable public health challenge by the plethora of ocular, genital and respiratory diseases caused by members of the Gram-negative bacteria of the genus Chlamydia. The major diseases are conjunctivitis and blinding trachoma, non-gonococcal urethritis, cervicitis, pelvic inflammatory disease, ectopic pregnancy, tubal factor infertility, and interstitial pneumonia. The failures in screening and other prevention programs led to the current medical opinion that an efficacious prophylactic vaccine is the best approach to protect humans from chlamydial infections. Unfortunately, there is no human Chlamydia vaccine despite successful veterinary vaccines. A major challenge has been the effective delivery of vaccine antigens to induce safe and effective immune effectors to confer long-term protective immunity. The dawn of the era of biodegradable polymeric nanoparticles and the adjuvanted derivatives may accelerate the realization of the dream of human vaccine in the foreseeable future.

AREAS COVERED

This review focuses on the current status of human chlamydial vaccine research, specifically the potential of biodegradable polymeric nanovaccines to provide efficacious Chlamydia vaccines in the near future.

EXPERT COMMENTARY

The safety of biodegradable polymeric nanoparticles-based experimental vaccines with or without adjuvants and the array of available chlamydial vaccine candidates would suggest that clinical trials in humans may be imminent. Also, the promising results from vaccine testing in animal models could lead to human vaccines against trachoma and reproductive diseases simultaneously.

Development of a Chlamydia trachomatis vaccine for urogenital infections: novel tools and new strategies point to bright future prospects

INTRODUCTION

The "cloaked" bacterial pathogen that is Chlamydia trachomatis continues to cause sexually transmitted infections (STIs) that adversely affect the health and well-being of children, adolescents and adults globally. The reproductive disease sequelae follow unresolved or untreated chronic or recurrent asymptomatic C.trachomatis infections of the lower female genital tract (FGT) and can include pelvic pain, pelvic inflammatory disease (PID) and ectopic pregnancy. Tubal Factor Infertility (TFI) can also occur since protective and long-term natural immunity to chlamydial infection is incomplete, allowing for ascension of the organism to the upper FGT. Developing countries including the WHO African (8.3 million cases) and South-East Asian regions (7.2 million cases) bear the highest burden of chlamydial STIs.

AREAS COVERED

Genetic advances for Chlamydia have provided tools for transformation (including dendrimer-enabled transformation), lateral gene transfer and chemical mutagenesis. Recent progress in these areas is reviewed with a focus on vaccine development for Chlamydia infections of the female genital tract.

EXPERT COMMENTARY

A vaccine that can elicit immuno-protective responses whilst avoiding adverse immuno-pathologic host responses is required. The current technological advances in chlamydial genetics and proteomics, as well as novel and improved adjuvants and delivery systems, provide new hope that the elusive chlamydial vaccine is an imminent and realistic goal.

Chlamydia abortus Pmp18.1 Induces IL-1β Secretion by TLR4 Activation through the MyD88, NF-κB, and Caspase-1 Signaling Pathways

The polymorphic membrane protein D (Pmp18D) is a 160-kDa outer membrane protein that is conserved and plays an important role in Chlamydia abortus pathogenesis. We have identified an N-terminal fragment of Pmp18D (designated Pmp18.1) as a possible subunit vaccine antigen. In this study, we evaluated the vaccine potential of Pmp18.1 by investigating its ability to induce innate immune responses in dendritic cells and the signaling pathway(s) involved in rPmp18.1-induced IL-1β secretion. We next investigated the immunomodulatory impact of VCG, in comparison with the more established Th1-promoting adjuvants, CpG and FL, on rPmp18.1-mediated innate immune activation. Finally, the effect of siRNA targeting TLR4, MyD88, NF-κB p50, and Caspase-1 mRNA in DCs on IL-1β cytokine secretion was also investigated. Bone marrow-derived dendritic cells (BMDCs) were stimulated with rPmp18.1 in the presence or absence of VCG or CpG or FL and the magnitude of cytokines produced was assessed using a multiplex cytokine ELISA assay. Expression of costimulatory molecules and Toll-like receptors (TLRs) was analyzed by flow cytometry. Quantitation of intracellular levels of myeloid differentiation factor 88 (MyD88), nuclear factor kappa beta (NF-κB p50/p65), and Caspase-1 was evaluated by Western immunoblotting analysis while NF-κB p65 nuclear translocation was assessed by confocal microscopy. The results showed DC stimulation with rPmp18.1 provoked the secretion of proinflammatory cytokines and upregulated expression of TLRs and co-stimulatory molecules associated with DC maturation. These responses were significantly (p ≤ 0.001) enhanced by VCG but not CpG or FL. In addition, rPmp18.1 activated the expression of MyD88, NF-κB p50, and Caspase-1 as well as the nuclear expression of NF-κB p65 in treated DCs. Furthermore, targeting TLR4, MyD88, NF-κB p50, and Caspase-1 mRNA in BMDCs with siRNA significantly reduced their expression levels, resulting in decreased IL-1β cytokine secretion, strongly suggesting their involvement in the rPmp18.1-induced IL-1β cytokine secretion. Taken together, these results indicate that C. abortus Pmp18.1 induces IL-1β secretion by TLR4 activation through the MyD88, NF-κB as well as the Caspase-1 signaling pathways and may be a potential C. abortus vaccine candidate. The vaccine potential of Pmp18.1 will subsequently be evaluated in an appropriate animal model, using VCG as an immunomodulator, following immunization and challenge.

Dendrimer-conjugated peptide vaccine enhances clearance of Chlamydia trachomatis genital infection

Peptide-based vaccines have emerged in recent years as promising candidates in the prevention of infectious diseases. However, there are many challenges to maintaining in vivo peptide stability and enhancement of peptide immunogenicity to generate protective immunity which enhances clearance of infections. Here, a dendrimer-based carrier system is proposed for peptide-based vaccine delivery, and shows its anti-microbial feasibility in a mouse model of Chlamydia trachomatis. Chlamydiae are the most prevalent sexually transmitted bacteria worldwide, and also the causal agent of trachoma, the leading cause of preventable infectious blindness. In spite of the prevalence of this infectious agent and the many previous vaccine-related studies, there is no vaccine commercially available. The carrier system proposed consists of generation 4, hydroxyl-terminated, polyamidoamine (PAMAM) dendrimers (G4OH), to which a peptide mimic of a chlamydial glycolipid antigen-Peptide 4 (Pep4, AFPQFRSATLLL) was conjugated through an ester bond. The ester bond between G4OH and Pep4 is expected to break down mainly in the intracellular environment for antigen presentation. Pep4 conjugated to dendrimer induced Chlamydia-specific serum antibodies after subcutaneous immunizations. Further, this new vaccine formulation significantly protected immunized animals from vaginal challenge with infectious Chlamydia trachomatis, and it reduced infectious loads and tissue (genital tract) damage. Pep4 conjugated to G4OH or only mixed with peptide provided enhanced protection compared to Pep4 and adjuvant (i.e. alum), suggesting a potential adjuvant effect of the PAMAM dendrimer. Combined, these results demonstrate that hydroxyl-terminated PAMAM dendrimer is a promising polymeric nanocarrier platform for the delivery of peptide vaccines and this approach has potential to be expanded to other infectious intracellular bacteria and viruses of public health significance.

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.

Chlamydial Type III Secretion System Needle Protein Induces Protective Immunity against Chlamydia muridarum Intravaginal Infection

Chlamydia trachomatis imposes serious health problems and causes infertility. Because of asymptomatic onset, it often escapes antibiotic treatment. Therefore, vaccines offer a better option for the prevention of unwanted inflammatory sequelae. The existence of serologically distinct serovars of C. trachomatis suggests that a vaccine will need to provide protection against multiple serovars. Chlamydia spp. use a highly conserved type III secretion system (T3SS) composed of structural and effector proteins which is an essential virulence factor. In this study, we expressed the T3SS needle protein of Chlamydia muridarum, TC_0037, an ortholog of C. trachomatis CdsF, in a replication-defective adenoviral vector (AdTC_0037) and evaluated its protective efficacy in an intravaginal Chlamydia muridarum model. For better immune responses, we employed a heterologous prime-boost immunization protocol in which mice were intranasally primed with AdTC_0037 and subcutaneously boosted with recombinant TC_0037 and Toll-like receptor 4 agonist monophosphoryl lipid A mixed in a squalene nanoscale emulsion. We found that immunization with TC_0037 antigen induced specific humoral and T cell responses, decreased Chlamydia loads in the genital tract, and abrogated pathology of upper genital organs. Together, our results suggest that TC_0037, a highly conserved chlamydial T3SS protein, is a good candidate for inclusion in a Chlamydia vaccine.

Future prospects for new vaccines against sexually transmitted infections

PURPOSE OF REVIEW

This review provides an update on the need, development status, and important next steps for advancing development of vaccines against sexually transmitted infections (STIs), including herpes simplex virus (HSV), Neisseria gonorrhoeae (gonorrhea), Chlamydia trachomatis (chlamydia), and Treponema pallidum (syphilis).

RECENT FINDINGS

Global estimates suggest that more than a million STIs are acquired every day, and many new and emerging challenges to STI control highlight the critical need for development of new STI vaccines. Several therapeutic HSV-2 vaccine candidates are in Phase I/II clinical trials, and one subunit vaccine has shown sustained reductions in genital lesions and viral shedding, providing hope that an effective HSV vaccine is on the horizon. The first vaccine candidate for genital chlamydia infection has entered Phase I trials, and several more are in the pipeline. Use of novel technological approaches will likely see viable vaccine candidates for gonorrhea and syphilis in the future. The global STI vaccine roadmap outlines key activities to further advance STI vaccine development.

SUMMARY

Major progress is being made in addressing the large global unmet need for STI vaccines. With continued collaboration and support, these critically important vaccines for global sexual and reproductive health can become a reality.

Protection against genital tract Chlamydia trachomatis infection following intranasal immunization with a novel recombinant MOMP VS2/4 antigen

The asymptomatic nature of most Chlamydia trachomatis infections and the lack of appropriate effects by current prevention and management call for vaccine development. We evaluated a recombinant subunit vaccine candidate based on the major outer membrane protein variable segments 2 and 4 (MOMP VS2/4). To achieve maximal immunogenicity and ease of production and purification, MOMP VS2/4 was constructed by using highly immunogenic sequences of MOMP only, thereby minimizing the presence of hydrophobic regions, and spacing the immunogenic epitopes with a flexible amino acid sequence. A purification tag was also added. The MOMP VS2/4 was given intranasally, with or without intravaginal boost, with cholera toxin (CT) adjuvant to C57BL/6 mice, which were screened for immunogenicity and protection against a live challenge infection with C. trachomatis serovar D. Bacterial shedding, cell-mediated responses, and antibody responses were monitored. Immunized mice exhibited significantly less bacterial shedding and were better protected against infertility as compared to unimmunized control mice. Immunizations stimulated both systemic and local specific antibody (IgG1, IgG2c, and IgA) responses, and primed T cells that produced interferon-γ and interleukins 13 and 17 upon challenge with recall antigen. Thus, MOMP VS2/4, in combination with CT adjuvant, stimulated Th1, Th2, and Th17 effector cells, and generated protective immunity associated with less pathology. We regard MOMP VS2/4 as a promising candidate for further development into a mucosal chlamydial vaccine.