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

Recognition of Chlamydia trachomatis by Toll-like receptor 9 is altered during persistence

Toll-like receptor 9 (TLR9) is an innate immune receptor that localizes to endosomes in antigen presenting cells and recognizes single stranded unmethylated CpG sites on bacterial genomic DNA (gDNA). Previous bioinformatic studies have demonstrated that the genome of the human pathogen Chlamydia trachomatis contains TLR9 stimulatory motifs, and correlative studies have implied a link between human TLR9 (hTLR9) genotype variants and susceptibility to infection. Here, we present our evaluation of the stimulatory potential of C. trachomatis gDNA and its recognition by hTLR9- and murine TLR9 (mTLR9)-expressing cells. Utilizing reporter cell lines, we demonstrate that purified gDNA from C. trachomatis can stimulate hTLR9 signaling, albeit at lower levels than gDNA prepared from other Gram-negative bacteria. Interestingly, we found that while C. trachomatis is capable of signaling through hTLR9 and mTLR9 during live infections in HEK293 reporter cell lines, signaling only occurs at later developmental time points. Chlamydia-specific induction of hTLR9 is blocked when protein synthesis is inhibited prior to the RB-to-EB conversion, exacerbated by the inhibition of lipooligosaccharide biosynthesis, and is significantly altered during the induction of aberrance/persistence. Our observations support the hypothesis that chlamydial gDNA is released during the conversion between the pathogen's replicative and infectious forms and during treatment with antibiotics targeting peptidoglycan assembly. Given that C. trachomatis inclusions do not co-localize with TLR9-containing vacuoles in the pro-monocytic cell line U937, our findings also hint that chlamydial gDNA is capable of egress from the inclusion, and traffics to TLR9-containing vacuoles via an as yet unknown pathway.

Advances in Chlamydia trachomatis Vaccination: Unveiling the Potential of Major Outer Membrane Protein Derivative Constructs

Chlamydia (C.) trachomatis, a leading cause of sexually transmitted infections (STIs) worldwide, continues to be a significant public health concern. The majority of infections are asymptomatic and, when left untreated, severe sequelae such as infertility and chronic pelvic pain can occur. Despite decades of research, an effective vaccine remains elusive. This review focuses on the potential of Major Outer Membrane Protein (MOMP)-derived constructs as promising candidates for C. trachomatis vaccination. MOMP, the most abundant protein in the outer membrane of C. trachomatis, has been a focal point of vaccine research over the years due to its antigenic properties. To overcome issues associated with the use of full MOMP as a vaccine antigen, derivative constructs have been studied. As these constructs are often not sufficiently immunogenic, antigen delivery systems or accompanying adjuvants are required. Additionally, several immunization routes have been explored with these MOMP-derived vaccine antigens, and determining the optimal route remains an ongoing area of research. Future directions and challenges in the field of C. trachomatis vaccination are discussed.

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.

Immune signature of Chlamydia vaccine CTH522/CAF®01 translates from mouse-to-human and induces durable protection in mice

The clinical development of an effective Chlamydia vaccine requires in-depth understanding of how well protective pre-clinical immune signatures translate to humans. Here, we report a comparative immunological characterization of CTH522/CAF®01 in female mice and humans. We find a range of immune signatures that translate from mouse to human, including a Th1/Th17 cytokine profile and antibody functionality. We identify vaccine-induced T cell epitopes, conserved among Chlamydia serovars, and previously found in infected individuals. Using the mouse model, we show that the common immune signature protected against ascending infection in mice, and vaccine induced antibodies could delay bacterial ascension to the oviduct, as well as development of pathology, in a T cell depleted mouse model. Finally, we demonstrate long-lasting immunity and protection of mice one year after vaccination. Based on the results obtained in the present study, we propose to further investigate CTH522/CAF®01 in a phase IIb study.

Recognition of Chlamydia trachomatis by Toll-Like Receptor 9 is altered during persistence

Toll-like receptor 9 (TLR9) is an innate immune receptor that localizes to endosomes in antigen presenting cells and recognizes single stranded unmethylated CpG sites on bacterial genomic DNA. Previous bioinformatic studies have indicated that the genome of the human pathogen Chlamydia trachomatis contains TLR9 stimulatory motifs, and correlative studies have implied a link between human TLR9 (hTLR9) genotype variants and susceptibility to infection. Here we present our evaluation of the stimulatory potential of C. trachomatis gDNA and its recognition by hTLR9- and murine TLR9 (mTLR9)-expressing cells. We confirm that hTLR9 colocalizes with chlamydial inclusions in the pro-monocytic cell line, U937. Utilizing HEK293 reporter cell lines, we demonstrate that purified genomic DNA from C. trachomatis can stimulate hTLR9 signaling, albeit at lower levels than gDNA prepared from other Gram-negative bacteria. Interestingly, we found that while C. trachomatis is capable of signaling through hTLR9 and mTLR9 during live infections in non-phagocytic HEK293 reporter cell lines, signaling only occurs at later developmental time points. Chlamydia-specific induction of hTLR9 is blocked when protein synthesis is inhibited prior to the RB-to-EB conversion and exacerbated by the inhibition of lipooligosaccharide biosynthesis. The induction of aberrance / persistence also significantly alters Chlamydia-specific TLR9 signaling. Our observations support the hypothesis that chlamydial gDNA is released at appreciable levels by the bacterium during the conversion between its replicative and infectious forms and during treatment with antibiotics targeting peptidoglycan assembly.

Efficacy of a synthetic peptide Chlamydia pecorum major outer membrane protein vaccine in a wild koala (Phascolarctos cinereus) population

Chlamydiosis is a significant disease affecting Eastern Australian koala (Phascolarctos cinereus) populations, impacting individual animal welfare and fecundity and therefore influencing population dynamics. The aim of this study was to investigate the effect of a synthetic peptide vaccine based on 4 components of the Chlamydia pecorum major outer membrane protein (MOMP), over an 18-month period in a koala population severely impacted by chlamydiosis. Wild koalas were recruited into a vaccination or a placebo treatment group on a random allocation, then followed through a period of 18 months, with recapture at 6 monthly intervals. Vaccination did not alter clinical disease expression or chlamydial shedding from the ocular or urogenital sites. Vaccination did not stimulate a significant plasma anti-MOMP IgG response, when compared to the placebo group. There was no significant effect of vaccination on IFN-γ and IL-17A mRNA expression of peripheral blood lymphocytes when stimulated with rMOMP. We have demonstrated that a synthetic peptide vaccination against chlamydiosis is not an effective management tool in a koala population with a high prevalence of C. pecorum infection and related disease. The lack of antigenic response found in this study suggests that further research utilising a larger, full-length antigen is an avenue worth investigation if we are to consider vaccination as a part of a management strategy in diseased koala populations.

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

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

DnaJ, a promising vaccine candidate against Ureaplasma urealyticum infection

Abstract

Ureaplasma urealyticum (U. urealyticum, Uu) is a common sexually transmitted pathogen that is responsible for diseases such as non-gonococcal urethritis, chorioamnionitis, and neonatal respiratory diseases. The rapid emergence of multidrug-resistant bacteria threatens the effective treatment of Uu infections. Considering this, vaccination could be an efficacious medical intervention to prevent Uu infection and disease. As a highly conserved molecular chaperone, DnaJ is expressed and upregulated by pathogens soon after infection. Here, we assessed the vaccine potential of recombinant Uu-DnaJ in a mouse model and dendritic cells. Results showed that intramuscular administration of DnaJ induced robust humoral- and T helper (Th) 1 cell-mediated immune responses and protected against genital tract infection, inflammation, and the pathologic sequelae after Uu infection. Importantly, the DnaJ protein also induced the maturation of mouse bone marrow–derived dendritic cells (BMDCs), ultimately promoting naïve T cell differentiation toward the Th1 phenotype. In addition, adoptive immunization of DnaJ-pulsed BMDCs elicited antigen-specific Immunoglobulin G2 (IgG2) antibodies as well as a Th1-biased cellular response in mice. These results support DnaJ as a promising vaccine candidate to control Uu infections.

Key points

• A novel recombinant vaccine was constructed against U. urealyticum infection.

• Antigen-specific humoral and cellular immune responses after DnaJ vaccination.

• Dendritic cells are activated by Uu-DnaJ, which results in a Th1-biased immune response.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-022-12230-4.

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

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

Combining Cellular Immunology With RNAseq to Identify Novel Chlamydia T-Cell Subset Signatures

Chlamydia trachomatis serovars A-L cause important diseases of the eyes and reproductive tract by infecting epithelium lining those organs. A major hurdle for vaccine trials is finding a surrogate biomarker for protective immunity. Investigational data argues for T-cell biomarker(s) reflecting mucosal adaption, cytokine polarization, B-cell help, antibacterial effector mechanisms, or some combination thereof. A human investigation and 2 mouse studies link IL-13 to protection from infection/immunopathology. We performed RNAseq on T cells resident in spleens and genital tracts of naturally immune mice. CD4 signatures were consistent with helper function that differed by site including a genital tract-specific Fgl2 signal. The genital tract CD8 signature featured IL-10 and promotion of healing/scarring with a unique transcription of granzyme A. The RNAseq data was used to refine previously published CD4γ13 and CD8γ13 transcriptomes derived from protective T-cell clones, potentially identifying practicable T-cell subset signatures for assessing Chlamydia vaccine candidates.

Th1/Th17 T cell Tissue-Resident Immunity Increases Protection, But Is Not Required in a Vaccine Strategy Against Genital Infection With Chlamydia trachomatis

The requirement for vaccine-induced tissue-resident immunity for protection against one or repeated infections with Chlamydia trachomatis (C.t.) is still not fully resolved. In this study, our aim was to investigate to which degree tissue-resident Th1/Th17 T cells in the genital tract (GT) could add to the protection mediated by circulating immunity. Out of several mucosal vaccine strategies, a strategy termed SIM (for simultaneous intrauterine and parenteral immunization with CAF01 adjuvanted CTH522), was superior in generating genital tract tissue-resident Th1/Th17 T cell immunity. This led to a faster and stronger local CD4 T cell response post infection, consisting of multifunctional IFNγ/TNFα-producing Th1 T cells and IFNγ/TNFα/IL-17-producing Th17 T cells, and a faster recruitment of innate immune cells. Post infection, SIM animals showed an additional significant reduction in bacterial levels compared to mice having received only a parenteral vaccine. Nevertheless, the parenteral strategy reduced bacterial levels by 75%, and interestingly, post infection, these mice generated their own vaccine-derived genital tract tissue-resident memory Th1/Th17 T cells, which upon a subsequent infection showed as fast an activation in the genital tract, as observed in SIM mice. Furthermore, in contrast to after the first infection, both groups of mice now showed a similar infection-induced boost in local vaginal IgA and IgG titers. Thus, vaccine-induced resident immunity, generated pre-infection, led to an advantage in the response against the first infection, but not the second infection, suggesting that a parenteral vaccine strategy is a suitable vaccine strategy against infections with Chlamydia trachomatis.

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

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

Chlamydia trachomatis vaccines for genital infections: where are we and how far is there to go?

INTRODUCTION

Chlamydia trachomatis is the most common sexually transmitted bacterial pathogen in the world. Antibiotic treatment does not prevent against reinfection and a vaccine is not yet available.

AREAS COVERED

We focus the review on the progress made of our understanding of the immunological responses required for a vaccine to elicit protection, and on the antigens, adjuvants, routes of immunization and delivery systems that have been tested in animal models. PubMed and Google Scholar were used to search publication on these topics for the last 5 years and recent Reviews were examined.

EXPERT OPINION

The first Phase 1 clinical trial of a C. trachomatis vaccine to protect against genital infections was successfully completed. We expect that, in the next five years, additional vaccine clinical trials will be implemented.