Abstract Genital infection with Chlamydia trachomatis , a gram-negative obligate intracellular bacterium, is the most common bacterial sexually transmitted infection globally. Ascension of chlamydial ...infection to the female upper genital tract can cause acute pelvic inflammatory disease, tubal factor infertility, ectopic pregnancy, and chronic pelvic pain. Shortcomings of current chlamydia control strategies, especially for low- and middle-income countries, highlight the need for an effective vaccine. Evidence from animal models, human epidemiological studies, and early trachoma vaccine trials suggest that a C. trachomatis vaccine is feasible. Vaccine development for genital chlamydial infection has been in the preclinical phase of testing for many years, but the first Phase I trials of chlamydial vaccine candidates are underway, and scientific advances hold promise for additional candidates to enter clinical evaluation in the coming years. We describe the clinical and public health need for a C. trachomatis vaccine, provide an overview of Chlamydia vaccine development efforts, and summarize current vaccine candidates in the development pipeline.
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.
Prospective studies have estimated that 10–15% of untreated chlamydia infections lead to symptomatic pelvic inflammatory disease, and 10–15% of women with symptomatic pelvic inflammatory disease, as ...well as many with subclinical pelvic inflammatory disease, will develop tubal factor infertility.2,3 Despite the high prevalence of C trachomatis infection and associated pelvic inflammatory disease, the infection can provide a detectable level of natural immunity, as evidenced by decreased infection concordance between older sex partners and lower bacterial loads in individuals with a history of previous infection.4 A recent study showed that young women in whom the infection was spontaneously cleared were able to resist reinfection, providing further evidence that protective adaptive immunity can be achieved.5 However, chronic and repeated infections are common, illustrating the need for an efficacious vaccine. ...careful evaluations of baseline immune response will be needed to ensure treatment groups are comparable. Data from mouse models indicate that partial immunity resulting from vaccination or from repeated infections alleviated by antibiotic treatment can prevent development of upper genital tract disease.10,11 Upon challenge, mice exhibit a shorter duration of infection with lower bacterial burdens and reduced ascension. ...inclusion of disease endpoints could be valuable if sterilising immunity is not achieved in vaccinated women.
Abstract Chlamydia trachomatis is the most prevalent bacterial sexually transmitted infection globally. Antibiotic treatment is highly effective, but infection is often asymptomatic resulting in most ...individuals going undetected and untreated. This untreated infection can ascend to the upper female genital tract to cause pelvic inflammatory disease, tubal factor infertility, and ectopic pregnancy. Chlamydia screening and treatment programs have failed to control this epidemic and demonstrate the need for an efficacious vaccine to prevent transmission and disease. Animal models and human epidemiological data reveal that natural immunity can provide partial or short-lived sterilizing immunity. These data further demonstrate the importance of eliciting IFNγ-producing CD4 T cells (Th1 and Th1/17 cells) that can likely synergize with antibody-mediated opsonophagocytosis to provide optimal protection. These studies have guided preclinical rational vaccine design for decades and the first Phase 1 clinical trials have recently been completed. Recent advances have led to improvements in vaccine platforms and clinically safe adjuvants that help provide a path forward. This review describes vaccine models, correlates of immunity, antigen and adjuvant selection, and future clinical testing for Chlamydia vaccine development.
Chlamydia trachomatis can cause reproductive morbidities after ascending to the upper genital tract of women, and repeated infection can lead to worse disease. Data related to protective immune ...responses at the cervical mucosa that could limit chlamydial infection to the cervix and/or prevent reinfection inform vaccine approaches and biomarkers of risk.
We measured 48 cytokines in cervical secretions from women having chlamydial cervical infection alone (n = 92) or both cervical and endometrial infection (n = 68). Univariable regression identified cytokines associated with differential odds of endometrial infection and reinfection risk, and multivariable stepwise regression identified cytokine ratios associated with differential risk.
Elevated interleukin (IL) 15/CXCL10 (odds ratio OR, 0.55 95% confidence interval {CI}, .37-.78), IL-16/tumor necrosis factor-α (OR, 0.66 95% CI, .45-.93), and CXCL14/IL-17A (OR, 0.73 95% CI, .54-.97) cytokine ratios were significantly (P ≤ .05) associated with decreased odds of endometrial infection. A higher Flt-3L/IL-14 ratio was significantly (P = .001) associated with a decreased risk of reinfection (hazard ratio, 0.71 95% CI, .58-.88).
Cytokines involved in humoral, type I interferon, and T-helper (Th) 17 responses were associated with susceptibility to C. trachomatis, whereas cytokines involved in Th1 polarization, recruitment, and activation were associated with protection against ascension and reinfection.
Identify genetic loci of enhanced susceptibility to
upper genital tract infection in women.
We performed an integrated analysis of DNA genotypes and blood-derived mRNA profiles from 200
exposed women ...to identify expression quantitative trait loci (eQTL) and determine their association with endometrial chlamydial infection using a mediation test. We further evaluated the effect of a lead eQTL on the expression of
by immune cells from women with genotypes associated with low and high whole blood expression of
, respectively.
We identified
-eQTLs modulating mRNA expression of 81 genes (eGenes) associated with altered risk of ascending infection. In women with endometrial infection, eGenes involved in proinflammatory signaling were upregulated. Downregulated eGenes included genes involved in T cell functions pivotal for chlamydial control. eGenes encoding molecules linked to metabolism of tryptophan, an essential chlamydial nutrient, and formation of epithelial tight junctions were also downregulated in women with endometrial infection. A lead eSNP rs10902226 was identified regulating
, a tetrospanin molecule important for immune cell adhesion and migration and T cell proliferation. Further
experiments showed that women with a CC genotype at rs10902226 had reduced rates of endometrial infection with increased
expression in whole blood and T cells when compared to women with a GG genotype.
We discovered genetic variants associated with altered risk for
ascension. A lead eSNP for
is a candidate genetic marker for enhanced CD4 T cell function and reduced susceptibility.
CD4 T cells and antibody are required for optimal acquired immunity to
genital tract infection, and T cell-mediated gamma interferon (IFN-γ) production is necessary to clear infection in the absence ...of humoral immunity. However, the role of T cell-independent immune responses during primary infection remains unclear. We investigated this question by inoculating wild-type and immune-deficient mice with
CM001, a clonal isolate capable of enhanced extragenital replication. Genital inoculation of wild-type mice resulted in transient dissemination to the lungs and spleen that then was rapidly cleared from these organs. However, CM001 genital infection proved lethal for
and
mice, in which IFN-γ signaling was absent, and for
mice, which lacked T and B cells and in which innate IFN-γ signaling was retained. In contrast, B cell-deficient muMT mice, which can generate a Th1 response, and T cell-deficient mice with intact B cell and innate IFN-γ signaling survived. These data collectively indicate that IFN-γ prevents lethal CM001 dissemination in the absence of T cells and suggests a B cell corequirement. Adoptive transfer of convalescent-phase immune serum but not naive IgM to
mice infected with CM001 significantly increased the survival time, while transfer of naive B cells completely rescued
mice from CM001 lethality. Protection was associated with a significant reduction in the lung chlamydial burden of genitally infected mice. These data reveal an important cooperation between T cell-independent B cell responses and innate IFN-γ in chlamydial host defense and suggest that interactions between T cell-independent antibody and IFN-γ are essential for limiting extragenital dissemination.
A vaccine is needed to combat the Chlamydia epidemic. Replication-deficient viral vectors are safe and induce antigen-specific T-cell memory. We tested the ability of intramuscular immunization with ...modified vaccinia Ankara (MVA) virus or chimpanzee adenovirus (ChAd) expressing chlamydial outer membrane protein (OmcB) or the secreted protein, chlamydial protease-like activating factor (CPAF), to enhance T-cell immunity and protection in mice previously infected with plasmid-deficient Chlamydia muridarum CM972 and elicit protection in naïve mice. MVA.OmcB or MVA.CPAF increased antigen-specific T cells in CM972-immune mice ∼150 and 50-fold, respectively, but failed to improve bacterial clearance. ChAd.OmcB/MVA.OmcB prime-boost immunization of naïve mice elicited a cluster of differentiation (CD) 8-dominant T-cell response dominated by cluster of differentiation (CD)8 T cells that failed to protect. ChAd.CPAF/ChAd.CPAF prime-boost also induced a CD8-dominant response with a marginal reduction in burden. Challenge of ChAd.CPAF-immunized mice genetically deficient in CD4 or CD8 T cells showed that protection was entirely CD4-dependent. CD4-deficient mice had prolonged infection, whereas CD8-deficient mice had higher frequencies of CPAF-specific CD4 T cells, earlier clearance, and reduced burden than wild-type controls. These data reinforce the essential nature of the CD4 T-cell response in protection from chlamydial genital infection in mice and the need for vaccine platforms that drive CD4-dominant responses.
Sexually transmitted infection (STI) of the upper reproductive tract can result in inflammation and infertility. A biomarker of STI-induced upper tract inflammation would be significant as many women ...are asymptomatic and delayed treatment increases risk of sequelae. Blood mRNA from 111 women from three cohorts was profiled using microarray. Unsupervised analysis revealed a transcriptional profile that distinguished 9 cases of STI-induced endometritis from 18 with cervical STI or uninfected controls. Using a hybrid feature selection algorithm we identified 21 genes that yielded maximal classification accuracy within our training dataset. Predictive accuracy was evaluated using an independent testing dataset of 5 cases and 10 controls. Sensitivity was evaluated in a separate test set of 12 women with asymptomatic STI-induced endometritis in whom cervical burden was determined by PCR; and specificity in an additional test set of 15 uninfected women with pelvic pain due to unknown cause. Disease module preservation was assessed in 42 women with a clinical diagnosis of pelvic inflammatory disease (PID). We also tested the ability of the biomarker to discriminate STI-induced endometritis from other diseases. The biomarker was 86.7% (13/15) accurate in correctly distinguishing cases from controls in the testing dataset. Sensitivity was 83.3% (5/6) in women with high cervical
burden and asymptomatic endometritis, but 0% (0/6) in women with low burden. Specificity in patients with non-STI-induced pelvic pain was 86.7% (13/15). Disease modules were preserved in all 8 biomarker predicted cases. The 21-gene biomarker was highly discriminatory for systemic infections, lupus, and appendicitis, but wrongly predicted tuberculosis as STI-induced endometritis in 52.4%. A 21-gene biomarker can identify asymptomatic women with STI-induced endometritis that places them at risk for chronic disease development and discriminate STI-induced endometritis from non-STI pelvic pain and other diseases.
Construction of regulatory networks using cross-sectional expression profiling of genes is desired, but challenging. The Directed Acyclic Graph (DAG) provides a general framework to infer causal ...effects from observational data. However, most existing DAG methods assume that all nodes follow the same type of distribution, which prohibit a joint modeling of continuous gene expression and categorical variables. We present a new mixed DAG (mDAG) algorithm to infer the regulatory pathway from mixed observational data containing both continuous variables (e.g. expression of genes) and categorical variables (e.g. categorical phenotypes or single nucleotide polymorphisms). Our method can identify upstream causal factors and downstream effectors closely linked to a variable and generate hypotheses for causal direction of regulatory pathways. We propose a new permutation method to test the conditional independence of variables of mixed types, which is the key for mDAG. We also utilize an
regularization in mDAG to ensure it can recover a large sparse DAG with limited sample size. We demonstrate through extensive simulations that mDAG outperforms two well-known methods in recovering the true underlying DAG. We apply mDAG to a cross-sectional immunological study of
infection and successfully infer the regularity network of cytokines. We also apply mDAG to a large cohort study, generating sensible mechanistic hypotheses underlying plasma adiponectin level. The R package mDAG is publicly available from CRAN at https://CRAN.R-project.org/package=mDAG.
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