A CD8+ T cell heptaepitope minigene vaccine induces protective immunity against Chlamydia pneumoniae

Update on treatment and preventive interventions against COVID-19: an overview of potential pharmacological agents and vaccines

The outbreak of coronavirus disease 2019 (COVID-19) triggered by the new member of the coronaviridae family, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has created an unprecedented challenge for global health. In addition to mild to moderate clinical manifestations such as fever, cough, and fatigue, severe cases often developed lethal complications including acute respiratory distress syndrome (ARDS) and acute lung injury. Given the alarming rate of infection and increasing trend of mortality, the development of underlying therapeutic and preventive treatment, as well as the verification of its effectiveness, are the top priorities. Current research mainly referred to and evaluated the application of the empirical treatment based on two precedents, severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS), including antiviral drugs targeting different stages of virus replication, immunotherapy modulating the overactivated inflammation response, and other therapies such as herbal medicine and mesenchymal stem cells. Besides, the ongoing development of inventing prophylactic interventions such as various vaccines by companies and institutions worldwide is crucial to decline morbidity and mortality. This review mainly focused on promising candidates for the treatment of COVID-19 and collected recently updated evidence relevant to its feasibility in clinical practice in the near future.

The relationship between Chlamydia pneumoniae infection and CD4/CD8 ratio, lymphocyte subsets in middle-aged and elderly individuals

Chlamydia pneumoniae (C. pneumoniae) is a common respiratory pathogen associated with many inflammatory diseases. There are few data concerning the lymphocyte subsets in middle-aged and elderly individuals with C. pneumoniae infection. A total of 191 patients were included in this study. The study population was categorized into the middle-aged group (40-64 years old) and the elderly group (65-89 years old). Lymphocyte subsets in peripheral blood were examined with multi-colored flow cytometry. Immunological monitoring included lymphocyte subsets, C. pneumoniae IgG and IgM serology. In the middle-aged group, 69.83% individuals presented IgG positivity, which was associated with the inverted CD4/CD8 ratio. Individuals with C. pneumoniae IgG positivity also presented an increased percentage of CD8⁺CD28^- cells and a decreased CD4/CD8 ratio when compared to weakly-positive individuals. In the elderly group, C. pneumoniae IgG positivity was associated with a significant increase in the percentage of CD3⁺CD56⁺CD45⁺ (NKT) cells. In conclusion, altered lymphocyte homeostasis was shown in middle-aged individuals with C. pneumoniae IgG positivity. The senescent phenotypes of T cells might be associated with C. pneumoniae infection in middle-aged individuals.

Rapid In Vivo Assessment of Adjuvant's Cytotoxic T Lymphocytes Generation Capabilities for Vaccine Development

The assessment of modern sub-unit vaccines reveals that the generation of neutralizing antibodies is important but not sufficient for adjuvant selection. Therefore, adjuvants with both humoral and cellular immuno-stimulatory capabilities that are able to promote cytotoxic T lymphocytes (CTL) responses are urgently needed. Thus, faithful monitoring of adjuvant candidates that induce cross-priming and subsequently enhance CTL generation represents a crucial step in vaccine development. In here we present an application for a method that uses SIINFEKL-specific (OT-I) T cells to monitor the cross-presentation of the model antigen ovalbumin (OVA) in vivo in the presence of different adjuvant candidates. This method represents a rapid test to select adjuvants with the best cross-priming capabilities. The proliferation of CD8⁺ T cells is the most valuable indication of cross-priming and it is also regarded as a correlate of adjuvant-induced cross-presentation. This feature can be evaluated in different immune organs like lymph nodes and spleen. The extent of the CTL generation can also be monitored, thereby giving insights on the nature of a local (draining lymph node mainly) or a systemic response (distant lymph nodes and/or spleen). This technique further allows multiple modifications for testing drugs that can inhibit specific cross-presentation pathways and also offers the possibility to be used in different strains of conventional and genetically modified mice. In summary, the application that we present here will be useful for vaccine laboratories in industry or academia that develop or modify chemical adjuvants for vaccine research and development.

Immunogenicity evaluation of a rationally designed polytope construct encoding HLA-A*0201 restricted epitopes derived from Leishmania major related proteins in HLA-A2/DR1 transgenic mice: steps toward polytope vaccine

Background

There are several reports demonstrating the role of CD8 T cells against Leishmania species. Therefore peptide vaccine might represent an effective approach to control the infection. We developed a rational polytope-DNA construct encoding immunogenic HLA-A2 restricted peptides and validated the processing and presentation of encoded epitopes in a preclinical mouse model humanized for the MHC-class-I and II.

Methods and Findings

HLA-A*0201 restricted epitopes from LPG-3, LmSTI-1, CPB and CPC along with H-2Kd restricted peptides, were lined-up together as a polytope string in a DNA construct. Polytope string was rationally designed by harnessing advantages of ubiquitin, spacers and HLA-DR restricted Th1 epitope. Endotoxin free pcDNA plasmid expressing the polytope was inoculated into humanized HLA-DRB1*0101/HLA-A*0201 transgenic mice intramuscularly 4 days after Cardiotoxin priming followed by 2 boosters at one week interval. Mice were sacrificed 10 days after the last booster, and splenocytes were subjected to ex-vivo and in-vitro evaluation of specific IFN-γ production and in-vitro cytotoxicity against individual peptides by ELISpot and standard chromium-51(⁵¹Cr) release assay respectively. 4 H-2Kd and 5 HLA-A*0201 restricted peptides were able to induce specific CD8 T cell responses in BALB/C and HLA-A2/DR1 mice respectively. IFN-γ and cytolytic activity together discriminated LPG-3-P1 as dominant, LmSTI-1-P3 and LmSTI-1-P6 as subdominant with both cytolytic activity and IFN-γ production, LmSTI-1-P4 and LPG-3-P5 as subdominant with only IFN-γ production potential.

Conclusions

Here we described a new DNA-polytope construct for Leishmania vaccination encompassing immunogenic HLA-A2 restricted peptides. Immunogenicity evaluation in HLA-transgenic model confirmed CD8 T cell induction with expected affinities and avidities showing almost efficient processing and presentation of the peptides in relevant preclinical model. Further evaluation will determine the efficacy of this polytope construct protecting against infectious challenge of Leishmania. Fortunately HLA transgenic mice are promising preclinical models helping to speed up immunogenicity analysis in a human related mouse model.

Protective immunity against lethal F. tularensis holarctica LVS provided by vaccination with selected novel CD8+ T cell epitopes

Recently we described an unbiased bacterial whole-genome immunoinformatic analysis aimed at selection of potential CTL epitopes located in "hotspots" of predicted MHC-I binders. Applying this approach to the proteome of the facultative intra-cellular pathogen Francisella tularensis resulted in identification of 170 novel CTL epitopes, several of which were shown to elicit highly robust T cell responses. Here we demonstrate that by DNA immunization using a short DNA fragment expressing six of the most prominent identified CTL epitopes a potent and specific CD8+ T cell responses is being induced, to all encoded epitopes, a response not observed in control mice immunized with the DNA vector alone Moreover, this CTL-specific mediated immune response prevented disease development, allowed for a rapid clearance of the bacterial infection and provided complete protection against lethal challenge (10LD50) with F. tularensis holarctica Live Vaccine Strain (LVS) (a total to 30 of 30 immunized mice survived the challenge while all control DNA vector immunized mice succumbed). Furthermore, and in accordance with these results, CD8 deficient mice could not be protected from lethal challenge after immunization with the CTL-polyepitope. Vaccination with the DNA poly-epitope construct could even protect mice (8/10) against the more demanding pulmonary lethal challenge of LVS. Our approach provides a proof-of-principle for selecting and generating a multi-epitpoe CD8 T cell-stimulating vaccine against a model intracellular bacterium.

Novel approaches in polyepitope T-cell vaccine development against HIV-1

RV144 clinical trial was modestly effective in preventing HIV infection. New alternative approaches are needed to design improved HIV-1 vaccines and their delivery strategies. One of these approaches is construction of synthetic polyepitope HIV-1 immunogen using protective T- and B-cell epitopes that can induce broadly neutralizing antibodies and responses of cytotoxic (CD8(+) CTL) and helpers (CD4(+) Th) T-lymphocytes. This approach seems to be promising for designing of new generation of vaccines against HIV-1, enables in theory to cope with HIV-1 antigenic variability, focuses immune responses on protective determinants and enables to exclude from the vaccine compound that can induce autoantibodies or antibodies enhancing HIV-1 infectivity. Herein, the authors will focus on construction and rational design of polyepitope T-cell HIV-1 immunogens and their delivery, including: advantages and disadvantages of existing T-cell epitope prediction methods; features of organization of polyepitope immunogens, which can generate high-level CD8(+) and CD4(+) T-lymphocyte responses; the strategies to optimize efficient processing, presentation and immunogenicity of polyepitope constructs; original software to design polyepitope immunogens; and delivery vectors as well as mucosal strategies of vaccination. This new knowledge may bring us a one step closer to developing an effective T-cell vaccine against HIV-1, other chronic viral infections and cancer.

Effect of age and vaccination on extent and spread of Chlamydia pneumoniae infection in C57BL/6 mice

Background

Chlamydia pneumoniae is an obligate intracellular respiratory pathogen for humans. Infection by C. pneumoniae may be linked etiologically to extra-respiratory diseases of aging, especially atherosclerosis. We have previously shown that age promotes C. pneumoniae respiratory infection and extra-respiratory spread in BALB/c mice.

Findings

Aged C57BL/6 mice had a greater propensity to develop chronic and/or progressive respiratory infections following experimental intranasal infection by Chlamydia pneumoniae when compared to young counterparts. A heptavalent CTL epitope minigene (CpnCTL7) vaccine conferred equal protection in the lungs of both aged and young mice. This vaccine was partially effective in protecting against C. pneumoniae spread to the cardiovascular system of young mice, but failed to provide cardiovascular protection in aged animals.

Conclusions

Our findings suggest that vaccine strategies that target the generation of a C. pneumoniae-specific CTL response can protect the respiratory system of both young and aged animals, but may not be adequate to prevent dissemination of C. pneumoniae to the cardiovascular system or control replication in those tissues in aged animals.

Possibilities for therapeutic interventions in disrupting Chlamydophila pneumoniae involvement in atherosclerosis

Strong sero-epidemiologic, pathologic, and experimental evidence suggests that Chlamydophila pneumoniae (Cpn) infection may play a causative role in the development of atherosclerosis. Cpn is an obligate intracellular gram-negative bacterium that is responsible for 10% of cases of community-acquired pneumonia. In addition to its presence in the respiratory tract, live Cpn has been found within atherosclerotic plaques. Experimental findings have established Cpn's ability to infect vascular cells and elicit important atherogenic responses. Furthermore, Cpn infection can promote atherosclerotic development in different animal models. To date however, large-scale antibiotic clinical trials have not been effective in preventing major cardiovascular events. It is becoming apparent that Cpn undergoes a persistent state of infection, which is refractory to current chlamydial antibiotics. New treatment strategies that are effective toward acute and persistent forms of Cpn infection are needed in order to effectively eradicate the bacterium within the vascular wall. Possible therapeutics targets include Cpn-specific proteins and machinery directly involved in their survival, replication and maintenance. Alternatively, selectively targeting host cell pathways and machinery required for Cpn's actions in vascular cells also represent potential treatment strategies for atherosclerosis.

Chlamydia vaccine candidates and tools for chlamydial antigen discovery

The failure of the inactivated Chlamydia-based vaccine trials in the 1960s has led researchers studying Chlamydia to take cautious and rational approaches to develop safe and effective chlamydial vaccines. Subsequent research efforts focused on three areas. The first is the analysis of the immunobiology of chlamydial infection in animal models, with supporting clinical studies, to identify the immune correlates of both protective immunity and pathological responses. Second, recent radical improvements in genomics, proteomics and associated technologies have assisted in the implementation of creative approaches to search for suitable vaccine candidates. Third, progress in the analysis of host response and adjuvanticity regulating both innate and adaptive immunity at the mucosal site of infection has led to progress in the design of optimal delivery and adjuvant systems for enhancing protective immunity. Considerable progress has been made in the first two areas but research efforts to better define the factors that regulate immunity at mucosal sites of infection and to develop strategies to boost protective immunity via immunomodulation, effective delivery systems and potent adjuvants, have remained elusive. In this article, we will summarize progress in these areas with a focus on chlamydial vaccine antigen discovery, and discuss future directions towards the development of a safe and effective chlamydial vaccine.

Role of CD8(+)T cells in the host response to Chlamydia

Chlamydia infections constitute a major public health problem. Although multiple arms of the immune system participate in the control of Chlamydia in infected hosts, T lymphocytes are essential. This review focuses on the roles that CD8(+)T cells may play in immunoprotection and immunopathology following recognition of Chlamydia-infected cells.

The safety of two Bacillus probiotic strains for human use

Probiotics based on Bacillus strains have been increasingly proposed for prophylactic and therapeutic use against several gastro-intestinal diseases. We studied safety for two Bacillus strains included in a popular East European probiotic. Bacillus subtilis strain that was sensitive to all antibiotics listed by the European Food Safety Authority. Bacillus licheniformis strain was resistant to chloramphenicol and clindamycin. Both were non-hemolytic and did not produce Hbl or Nhe enterotoxins. No bceT and cytK toxin genes were found. Study of acute toxicity in BALB/c mice demonstrated no treatment-related deaths. The oral LD(50) for both strains was more than 2 x 10(11) CFU. Chronic toxicity studies were performed on mice, rabbits, and pigs and showed no signs of toxicity or histological changes in either organs or tissues. We demonstrated that while certain risks may exist for the B. licheniformis strain considering antibiotic resistance, B. subtilis strain may be considered as non-pathogenic and safe for human consumption.

CD8+ T cell protective immunity against Chlamydia pneumoniae includes an H2-M3-restricted response that is largely CD4+ T cell-independent

CD8+ T cells are important for immunity to the intracellular bacterial pathogen Chlamydia pneumoniae (Cpn). Recently, we reported that type 1 CD8+ (Tc1) from Cpn-infected B6 mice recognize peptides from multiple Cpn Ags in a classical MHC class Ia-restricted fashion. In this study, we show that Cpn infection also induces nonclassical MHC class Ib-(H2-M3)-restricted CD8+ T cell responses. H2-M3-binding peptides representing the N-terminal formylated sequences from five Cpn Ags sensitized target cells for lysis by cytolytic effectors from the spleens of infected B6 mice. Of these, only peptides fMFFAPL (P1) and fMLYWFL (P4) stimulated IFN-gamma production by infection-primed splenic and pulmonary CD8+ T cells. Studies with Cpn-infected Kb-/-/Db-/- mice confirmed the Tc1 cytokine profile of P1- and P4-specific CD8+ T cells and revealed the capacity of these effectors to exert in vitro H2-M3-restricted lysis of Cpn-infected macrophages and in vivo pulmonary killing of P1- and P4-coated splenocytes. Furthermore, adoptive transfer of P1- and P4-specific CD8+ T cells into naive Kb-/-/Db-/- mice reduced lung Cpn loads following challenge. Finally, we show that in the absence of MHC class Ia-restricted CD8+ T cell responses, CD4+ T cells are largely expendable for the control of Cpn growth, and for the generation, memory maintenance, and secondary expansion of P1- and P4-specific CD8+ T cells. These results suggest that H2-M3-restricted CD8+ T cells contribute to protective immunity against Cpn, and that chlamydial Ags presented by MHC class Ib molecules may represent novel targets for inclusion in anti-Cpn vaccines.

Chlamydia pneumoniae inclusion membrane protein Cpn0585 interacts with multiple Rab GTPases

Chlamydiae are intracellular bacteria that develop within a membrane-bound vacuole called an inclusion. To ensure that the inclusion is a safe niche for chlamydial replication, chlamydiae exploit a number of host cell processes, including membrane-trafficking pathways. Recently, several Rab GTPases were found to associate with the inclusions of various chlamydial species. Here we report that Cpn0585, a Chlamydia pneumoniae inclusion membrane protein (Inc), interacts with multiple Rab GTPases. The results from yeast two-hybrid experiments revealed that an amino-terminally truncated form of Cpn0585 (Cpn0585(102-651)) interacts with Rab1, Rab10, and Rab11 but not with Rab4 or Rab6. Cpn0585-Rab GTPase interactions are direct and GTP dependent as shown in glutathione S-transferase pull-down assays using native and recombinant Cpn0585. In C. pneumoniae-infected HEp-2 cells transfected with enhanced green fluorescent protein (EGFP)-tagged Rab GTPases, the colocalization with Cpn0585 at the inclusion membrane was partial for EGFP-Rab1 and EGFP-Rab10, but extensive for wild-type EGFP-Rab11A and the constitutively active GTPase-deficient EGFP-Rab11AQ70L. Moreover, Cpn0585 colocalized with EGFP-Rab11AQ70L as early as 2 h postinfection. Upon delivery into live C. pneumoniae-infected cells, Cpn0585(628-651)-specific antibodies bound to the inclusion membrane, demonstrating that the Rab GTPase-interacting domain of Cpn0585 faces the host cell cytosol. Finally, ectopic expression of Cpn0585(102-651) partially inhibited the development of C. pneumoniae inclusions in EGFP. but not in EGFP-Rab11AQ70L-expressing HEp-2 cells. Collectively, these data suggest that Cpn0585 is involved in the recruitment of Rab GTPases to the inclusion membrane and that interfering with this function may adversely impact the fitness of the C. pneumoniae inclusion for chlamydial replication.

Pneumococcal capsular polysaccharide vaccine-mediated protection against serotype 3 Streptococcus pneumoniae in immunodeficient mice

Pneumococcal capsular polysaccharide (PPS) vaccines are less immunogenic in immunocompromised than immunocompetent individuals. However, neither the efficacy of PPS vaccines in immunocompromised individuals nor the host cellular subsets required for vaccine efficacy against pneumococcal disease have been directly investigated. In this study, we vaccinated CD4-deficient (CD4(-/-)), CD8-deficient (CD8(-/-)), and secretory immunoglobulin M-deficient (sIgM(-/-)) mice and wild-type C57BL/6 (Wt) mice with a conjugate of PPS of serotype 3 and tetanus toxoid (PPS3-TT) and determined the antibody response and efficacy of vaccination against systemic and pulmonary challenge with serotype 3 pneumococcus in immunized and control mice. Our results showed that the isotype and predominant IgG subclass of the PPS3 response differed between immunodeficient mouse strains and between immunodeficient and Wt mice, with CD8(-/-) mice having the most robust response. Vaccination protected Wt, CD4(-/-), and sIgM(-/-) mice from death resulting from both systemic and pulmonary challenge, whereas CD8(-/-) mice were protected only from systemic and not from pulmonary challenge. Passive vaccination with PPS3-TT-induced sera from Wt, CD4(-/-), CD8(-/-), and sIgM(-/-) mice protected naïve Wt mice from death due to pulmonary challenge; however, CD8(-/-) mice were not protected by sera from Wt or CD8(-/-) mice. Our findings suggest that PPS-based vaccines can be effective in the setting of CD4 T-cell deficiency but that CD8 T cells could be required for vaccine-mediated protection against pulmonary challenge with serotype 3 pneumococcus.

Distinct NKT cell subsets are induced by different Chlamydia species leading to differential adaptive immunity and host resistance to the infections

We investigated the role of NKT cells in immunity to Chlamydia pneumoniae and Chlamydia muridarum infections using a combination of knockout mice and specific cellular activation approaches. The NKT-deficient mice showed exacerbated susceptibility to C. pneumoniae infection, but more resistance to C. muridarum infection. Activation of NKT reduced C. pneumoniae in vivo growth, but enhanced C. muridarum infection. Cellular analysis of invariant NKT cells revealed distinct cytokine patterns following C. pneumoniae and C. muridarum infections, i.e., predominant IFN-gamma in the former, while predominant IL-4 in the latter. The cytokine patterns of CD4(+) and CD8(+) T cells matched those of NKT cells. Our data provide in vivo evidence for a functionally diverse role of NKT cells in immune response to two intracellular bacterial pathogens. These results suggest that distinct NKT subsets are induced by even biologically closely related pathogens, thus leading to differential adaptive immune response and infection outcomes.

Localization of the hypothetical protein Cpn0585 in the inclusion membrane of Chlamydia pneumoniae-infected cells

Cpn0585, encoded by a hypothetical open reading frame in Chlamydia pneumoniae genome, was detected in the inclusion membrane during C. pneumoniae infection using both polyclonal and monoclonal antibodies raised with Cpn0585 fusion protein. The anti-Cpn0585 antibodies specifically recognized the endogenous Cpn0585 without cross-reacting with IncA (a known inclusion membrane protein of C. pneumoniae) or other control antigens. A homologue of Cpn0585 in the C. caviae species (encoded by the ORF CCA00156) was also localized in the inclusion membrane of the C. caviae-infected cells. The Cpn0585 protein became detectable 24h while CCA00156 as early as 8h after infection. Once expressed, both proteins remained in the inclusion membrane throughout the rest of infection course.

Community-acquired pneumonia: paving the way towards new vaccination concepts

Despite the availability of antimicrobial agents and vaccines, community-acquired pneumonia remains a serious problem. Severe forms tend to occur in very young children and among the elderly, since their immune competence is eroded by immaturity and immune senescence, respectively. The main etiologic agents differ according to patient age and geographic area. Streptococcus pneumoniae, Haemophilus influenzae, respiratory syncytial virus (RSV) and parainfluenza virus type 3 (PIV-3) are the most important pathogens in children, whereas influenza viruses are the leading cause of fatal pneumonia in the elderly. Effective vaccines are available against some of these organisms. However, there are still many agents against which vaccines are not available or the existent ones are suboptimal. To tackle this problem, empiric approaches are now being systematically replaced by rational vaccine design. This is facilitated by the growing knowledge in the fields of immunology, microbial pathogenesis and host response to infection, as well as by the availability of sophisticated strategies for antigen selection, potent immune modulators and efficient antigen delivery systems. Thus, a new generation of vaccines with improved safety and efficacy profiles compared to old and new agents is emerging. In this chapter, an overview is provided about currently available and new vaccination concepts.

Host-Cell Survival and Death During Chlamydia Infection

Different Chlamydia trachomatis strains are responsible for prevalent bacterial sexually-transmitted disease and represent the leading cause of preventable blindness worldwide. Factors that predispose individuals to disease and mechanisms by which chlamydiae cause inflammation and tissue damage remain unclear. Results from recent studies indicate that prolonged survival and subsequent death of infected cells and their effect on immune effector cells during chlamydial infection may be important in determining the outcome. Survival of infected cells is favored at early times of infection through inhibition of the mitochondrial pathway of apoptosis. Death at later times displays features of both apoptosis and necrosis, but pro-apoptotic caspases are not involved. Most studies on chlamydial modulation of host-cell death until now have been performed in cell lines. The consequences for pathogenesis and the immune response will require animal models of chlamydial infection, preferably mice with targeted deletions of genes that play a role in cell survival and death.

Discovery of a vaccine antigen that protects mice from Chlamydia pneumoniae infection

Chlamydiae are atypical intracellular bacteria that infect via mucosal surfaces causing, for example, trachoma, pneumonia, cervicitis, urethritis and infertility. Existing antibiotics are only partially effective and no vaccines are available. Using surface expressed or secreted proteins previously identified by genomics and proteomics we tested five as vaccines against intranasal challenge with Chlamydia pneumoniae. One antigen, LcrE, induced CD4+ and CD8+ T cell activation, type 1 cytokine secretion and neutralising antibodies and was completely effective in eliminating infection. Such antigens are highly conserved and essential to all Chlamydial species. The discovery of an effective vaccine for Chlamydiae pneumoniae has potential wide benefits for human health.