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Biomedical subjects

Francis O Eko

Publications and source records attributed to Francis O Eko.

15 recordsLinked to original sources
PubMed2006

A recombinant multivalent combination vaccine protects against Chlamydia and genital herpes.

Chlamydia trachomatis and Herpes simplex virus type 2 (HSV-2) genital infections pose a considerable public health challenge worldwide. Considering the high incidence of coinfections by the two pathogens, a combination vaccine that can be administered as a single regimen would be highly desirable. Recombinant Vibrio cholerae ghosts (rVCG) offer an attractive approach for the induction of humoral and cellular immune responses against human and animal pathogens. In this study, we evaluated a bivalent combination vaccine formulation comprising rVCG expressing chlamydial MOMP and HSV-2 glycoprotein D in mice for immunogenicity and protective efficacy against genital challenge with either pathogen. Mice immunized with the combination vaccine elicited secretory IgA and IgG2a antibodies to both chlamydial and HSV-2 antigens in serum and vaginal secretions. Robust antigen-specific mucosal and systemic T helper type 1 responses were induced in mice as measured by increased interferon-gamma levels produced by immune T cells in response to restimulation with target antigen in vitro. In addition, mice immunized with the combination vaccine were prophylactically protected from genital challenge with high doses of live Chlamydia and HSV-2. Thus, the combination vaccine regimen delivered by rVCG elicited adequate immune effectors that simultaneously protected against the individual pathogens.

Animals↗
PubMed2005

Molecular basis for the potency of IL-10-deficient dendritic cells as a highly efficient APC system for activating Th1 response.

Identification and targeting of novel immunobiological factors that regulate the induction of Th1 cells are crucial for designing effective vaccines against certain intracellular pathogens, including Chlamydia. IL-10-deficient dendritic cells (DC) are potent APCs and effective cellular vaccines that activate a high frequency of specific Th1 cells. To elucidate the molecular basis for the potency of the IL-10-deficient APC system, we tested the hypothesis that Chlamydia Ag-primed IL-10 knockout (IL-10KO) DC are quantitatively and qualitatively distinct in their metabolic characteristics relating to T cell activation. Using a combination of RT-PCR, two-dimensional gel electrophoresis, and MALDI-TOF-based proteomics analyses, the transcriptional and translational activities of Chlamydia-pulsed DC from wild-type and IL-10KO mice were assessed. IL-10 deficiency caused early maturation and activation of pulsed DC (i.e., high CD11c, CD40, CD80, CD83, CD86, IL-1, IL-12, and the T cell-attracting chemokine CCL27/CTACK) and consequently an enhanced ability to process and present Ags for a rapid and robust T cell activation. Supporting comparative proteomics revealed further that IL-10 deficient DC possess specific immunobiological properties, e.g., the T cell-attracting chemokine CCL27/CTACK, calcium-dependent protein kinase, and the IL-1/IL-12 inducer, NKR-P1A (CD161), which differentiated them immunologically from wild-type DC that express molecules relating to anti-inflammatory, differentiative, and metabolic processes, e.g., the anti-IL-12 molecule peroxisome proliferator-activated receptor-alpha and thymidine kinase. Collectively, these results provide a molecular basis for the high Th1-activating capacity of IL-10KO APC and may provide unique immunomodulation targets when designing vaccines against pathogens controlled by T cell immunity.

Animals↗
PubMed2005

Host inflammatory response and development of complications of Chlamydia trachomatis genital infection in CCR5-deficient mice and subfertile women with the CCR5delta32 gene deletion.

T cell immunity protects against diseases caused by the obligate intracellular bacterium Chlamydia trachomatis. Incidentally, host inflammatory response that includes T cells appears to also contribute to the pathogenesis of chlamydial diseases such as trachoma and tubal factor infertility (TFI). Therefore, designing effective prevention strategies requires a delineation of immune processes responsible for pathology and those mediating immunity, and identification of the immunogenetic factors predisposing to complication development. The chemokine receptor CCR5 is crucial for T cell activation and function since its deficiency causes suppression of T cell response. We investigated the hypothesis that the clearance of genital chlamydial infection in CCR5-deficient mice could be delayed in the short term; however, a beneficial effect could include protection against inflammation-related complications such as TFI. In a translational study in humans, we investigated the effect of a functional 32 bp deletion in the CCR5 gene on the risk of developing tubal pathology in Dutch Caucasian women with immunologic evidence [i.e., immunoglobulin G (IgG) responses] of chlamydial infection. When genitally-infected wild-type (WT) and CCR5 knockout (CCR5KO) mice were evaluated for microbiologic shedding of chlamydiae, there was a greater intensity of infection and delayed resolution in the knockout mice. However, compared to WT mice, the fertility of infected CCR5KO mice (measured by pregnancy rate) was only mildly affected in the short term and unaffected in the long term (70% vs 30% reduction in the short term, and 50 vs 0% in the long term, respectively). Immunobiologic analysis revealed that the diminished capacity of CCR5KO to control acute chlamydial infection correlated with the relatively low chemokine [interferon-inducible protein 10 (IP-10) and regulated upon activation normal cell expressed and secreted (RANTES)] and cytokine (mainly interferon-gamma and tumor necrosis factor-alpha) expression corresponding to a poor early T-helper I response. However, the reduced incidence of complications in the CCR5KO mice appears to correlate with the low activity of long term inflammatory mediators. Besides, the translational studies in humans revealed that among patients with positive anti-chlamydial IgG responses, tubal pathology correlated with a low incidence of CCR5delta32 deletion (7%), while women without tubal pathology had higher incidence of the CCR5delta32 deletion (31%) as compared to controls (19%). Thus, in mice and humans the inflammation associated with CCR5 function may predispose to development of complications of chlamydial infection, such as TFI.

Animals↗
PubMed2004

A novel recombinant multisubunit vaccine against Chlamydia.

The administration of an efficacious vaccine is the most effective long-term measure to control the oculogenital infections caused by Chlamydia trachomatis in humans. Chlamydia genome sequencing has identified a number of potential vaccine candidates, and the current challenge is to develop an effective delivery vehicle for induction of a high level of mucosal T and complementary B cell responses. Vibrio cholerae ghosts (VCG) are nontoxic, effective delivery vehicles with potent adjuvant properties, and are capable of inducing both T cell and Ab responses in mucosal tissues. We investigated the hypothesis that rVCG could serve as effective delivery vehicles for single or multiple subunit chlamydial vaccines to induce a high level of protective immunity. rVCG-expressing chlamydial outer membrane proteins were produced by a two-step genetic process, involving cloning of Omp genes in V. cholerae, followed by gene E-mediated lysis of the cells. The immunogenicity and vaccine efficacy of rVCG-expressing single and multiple subunits were compared. Immunologic analysis indicated that i.m. immunization of mice with either vaccine construct induced a strong mucosal and systemic specific Th1 response against the whole chlamydial organism. However, there was an immunogenic advantage associated with the multiple subunit vaccine that induced a higher frequency of Th1 cells and a relatively greater ability to confer protective immunity, compared with the single subunit construct. These results support the operational theory that the ability of a vaccine to confer protective immunity against Chlamydia is a function of the level of Th1 response elicited.

Animals↗
PubMed2004

Antibody regulation of Tcell immunity: implications for vaccine strategies against intracellular pathogens.

Intracellular microbial pathogens cause a plethora of diseases that pose a huge public health challenge. Efficacious prophylactic vaccines are needed to protect the population from this myriad of infectious diseases. Contemporary approaches to vaccine design are guided by the immunobiological paradigm that extracellular pathogens are controlled principally by humoral immunity, involving specific antibodies, whereas host protection against intracellular pathogens requires effectors of cell-mediated immunity. However, this distinct T-helper (Th) type 1 and 2 paradigm of host defense has encountered a major challenge due to the reality that most antigens or vaccines induce mixed immune responses comprising of both humoral and CMI effectors. Besides, the true functional independence of antibodies and T-cells under in vivo physiologic conditions is uncertain. Recent findings have revealed that antibodies exert a significant immunoregulatory effect on T-cell immunity. Thus, a robust and protective T-cell memory response against microbial pathogens such as Chlamydia and Mycobacteria require an effective primary humoral immune response characterized by specific antibody isotypes whose role is to modulate Th1 activation via Fc receptors (FcR) by facilitating a rapid uptake, processing and presentation of pathogen-derived antigens for an enhanced T-cell response. These findings have crystallized into a paradigm shift in host defense wherein different components of the apparently disparate mixed immune responses elicited against a microbial pathogen function concertedly to maximize the principal effector mechanism. This review focuses on the essential role of both arms of the immune system in controlling intracellular microbial pathogens, especially the regulatory role of FcR-mediated antibody function in optimizing the induction of a protective Th1 response. The immunobiological implications are discussed in the context of vaccine design, delivery and evaluation against intracellular microbial pathogens of bacteria, fungi and parasitic origin.

Animals↗
PubMed2004

Antigen discovery and delivery of subunit vaccines by nonliving bacterial ghost vectors.

The bacterial ghost (BG) platform system is a novel vaccine delivery system endowed with intrinsic adjuvant properties. BGs are nonliving Gram-negative bacterial cell envelopes which are devoid of their cytoplasmic contents, yet maintain their cellular morphology and antigenic structures, including bioadhesive properties. The main advantages of BGs as carriers of subunit vaccines include their ability to stimulate a high immune response and to target the carrier itself to primary antigen-presenting cells. The intrinsic adjuvant properties of BGs enhance the immune response to target antigens, including T-cell activation and mucosal immunity. Since native and foreign antigens can be carried in the envelope complex of BGs, combination vaccines with multiple antigens of diverse origin can be presented to the immune system simultaneously. Beside the capacity of BGs to function as carriers of protein antigens, they also have a high loading capacity for DNA. Thus, loading BGs with recombinant DNA takes advantage of the excellent bioavailability for DNA-based vaccines and the high expression rates of the DNA-encoded antigens in target cell types such as macrophages and dendritic cells. There are many spaces within BGs including the inner and outer membranes, the periplasmic space and the internal lumen which can carry antigens, DNA or mediators of the immune response. All can be used for subunit antigen to design new vaccine candidates with particle presentation technology. In addition, the fact that BGs can also carry piggyback large-size foreign antigen particles, increases the technologic usefulness of BGs as combination vaccines against viral and bacterial pathogens. Furthermore, the BG antigen carriers can be stored as freeze-dried preparations at room temperature for extended periods without loss of efficacy. The potency, safety and relatively low production cost of BGs offer a significant technical advantage over currently utilized vaccine technologies.

Adjuvants, Immunologic↗
PubMed2004

Developing effective delivery systems for Chlamydia vaccines.

Members of the genus Chlamydia cause a plethora of ocular, genital and respiratory diseases, with severe complications, such as blinding trachoma, pelvic inflammatory disease, ectopic pregnancy and tubal factor infertility, interstitial pneumonia, and chronic diseases that may include atherosclerosis, multiple sclerosis, adult-onset asthma and Alzheimer's disease. The current medical opinion is that an effective prophylactic vaccine would constitute the best approach to protect the human population from the most severe consequences of these infections. There are three essential and mutually inclusive areas of challenge confronting researchers developing Chlamydia vaccines. These are to define the elements of protective immunity and the basis of vaccine evaluation, the judicious selection of an immunogenic and safe antigen(s) to form the basis of a subunit vaccine, and to develop effective delivery systems that boost the immune response to achieve long-lasting protective immunity. The development of delivery vehicles and adjuvants to boost protective long-term immunity against chlamydiae currently poses the greatest challenge in vaccine research. However, enormous progress is being made in the construction of novel delivery systems, such as DNA and plasmid expression systems, viral vectors, and living and non-living bacterial delivery systems, and the use of chemical adjuvants. In addition, there is increasing effort being made in designing delivery strategies involving specific immunomodulatory procedures that modify the cytokine and chemokine environment, upregulate co-stimulatory molecules and target vaccines to specific mucosal sites. These efforts will likely culminate in an efficacious chlamydial vaccine in the near future.

Adult↗
PubMed2003

Evaluation of the protective efficacy of Vibrio cholerae ghost (VCG) candidate vaccines in rabbits.

An effective Vibrio cholerae vaccine is needed to reduce the morbidity and mortality caused by this pathogen. Despite the availability of current oral vaccines with measurable efficacy, there is need for more effective vaccines with broad-spectrum efficacy in target populations. Recent studies have shown that bacterial ghosts, produced by the expression of cloned lysis gene E, possess adjuvant properties and are immunogenic. In this study, ghosts were prepared from V. cholerae O1 or O139 and evaluated as vaccines in the reversible intestinal tie adult rabbit diarrhea (RITARD) model. Rabbits were orally immunized with different doses of V. cholerae ghost (VCG) formulations. The vaccine formulations elicited high levels of serum vibriocidal titers against indicator strains. The magnitude of the response was measured as the geometric mean titer (GMT) increase for all rabbits in relation to prevaccination titers. The induction of cross protection was evidenced by the ability of serum from VCG-immunized rabbits to mediate complement-dependent killing of both the homologous and the heterologous strains. Immunized rabbits were protected against intraduodenal challenge 30 days after primary immunization. Protective immunity against challenge appeared to be dose dependent and was associated with marked inhibition of colonization. These results indicate that VCGs represent a novel approach to cholera vaccine development and constitute an effective vaccine delivery vehicle.

Animals↗
PubMed2003

Fc receptor-mediated antibody regulation of T cell immunity against intracellular pathogens.

Immunity to intracellular microbial pathogens, including Chlamydia species, is controlled primarily by cell-mediated effector mechanisms, yet, the absence of antibodies results in inefficient microbial clearance. We investigated the hypothesis that certain Fc receptor functions promote the rapid induction of elevated T helper type 1 (Th1) response, which effectively clears chlamydiae. FcR(-/-) mice exhibited a delayed and reduced frequency of Chlamydia-specific Th1 cells, compared to FcR(+/+) mice. In vitro, antichlamydial antibodies increased the rate of Th1 activation by FcR(+/+) but not FcR(-/-) antigen-presenting cells. FcR(-/-) dendritic cells and the T cell-associated IgG2A and IgA mediate enhanced Th1 activation by antibodies. Immunization with chlamydia-antibody complexes induced elevated and protective Th1 response. These results provide a mechanistic basis for requiring both T cell and humoral immune responses in protective immunity and vaccine evaluation. Findings offer a paradigm in host defense wherein different effector components function indirectly to maximize the principal effector mechanism.

Animals↗
PubMed2003

Recombinant Vibrio cholerae ghosts as a delivery vehicle for vaccinating against Chlamydia trachomatis.

An efficacious vaccine is needed to control the morbidity and burden of rising healthcare costs associated with genital Chlamydia trachomatis infection. Despite considerable efforts, the development of reliable chlamydial vaccines using conventional strategies has proven to be elusive. The 40kDa major outer membrane protein (MOMP) of C. trachomatis is so far the most promising candidate for a subunit vaccine. The lack of satisfactory protective immunity with MOMP-based vaccine regimens to date would suggest that either MOMP alone is inadequate as a vaccine candidate or better delivery systems are needed to optimize the effect of MOMP. Recombinant Vibrio cholerae ghosts (rVCG) are attractive for use as non-living vaccines because they possess strong adjuvant properties and are excellent vehicles for delivery of antigens of vaccine relevance to mucosal sites. The suitability of the ghost technology for designing an anti-chlamydial vaccine was evaluated by constructing a rVCG vector-based candidate vaccine expressing MOMP (rVCG-MOMP) and assessing vaccine efficacy in a murine model of C. trachomatis genital infection. Intramuscular delivery of the rVCG-MOMP vaccine induced elevated local genital mucosal as well as systemic Th1 responses. In addition, immune T cells from immunized mice could transfer partial protection against a C. trachomatis genital challenge to nai;ve mice. These results suggest that rVCG expressing chlamydial proteins may constitute a suitable subunit vaccine for inducing an efficient mucosal T cell response that protects against C. trachomatis infection. Altogether, the potency and relatively low production cost of rVCG offer a significant technical advantage as a chlamydial vaccine.

Animals↗
PubMed2003

Contemporary approaches to designing and evaluating vaccines against Chlamydia.

The clinically relevant pathologic consequences of primary ocular, genital, or respiratory human infection by members of the genus Chlamydia are conjunctivitis, cervicitis, urethritis and sinusitis. The major complications and sometimes debilitating evolutionary outcomes of these infections include: trichiasis and cicatrizing trachoma, endometritis or pelvic inflammatory disease and involuntary tubal factor infertility and bronchopulmonary pneumonia. These diseases, in addition to other chlamydia-associated chronic syndromes (e.g., artherosclerosis, multiple sclerosis and Alzheimer's disease), pose serious public healthcare and huge budgetary concerns. The current medical opinion is that an efficacious prophylactic vaccine is a sine qua non--to control the morbidity of chiamydial infection in the human population. The research goal for an efficacious human chlamydial vaccine has faced key challenges to define the elements of protective immunity to facilitate vaccine evaluation, the judicious selection of appropriate vaccine candidates that possess stable antigenic and immunologic properties and the development of effective delivery vehicles and adjuvants to boost immune effectors to achieve long-term protective immunity. Progress in the functional immunobiology of Chlamydia has established the essential immunologic paradigms for vaccine selection and evaluation, including the obligatory requirement for a vaccine to induce T-helper Type 1 immune response that controls chlamydiae. Recent advances in chlamydial genomics and proteomics should enhance the identification of likely chlamydial gene products that fulfill the antigenic requirements of putative vaccine candidates. Major inroads are however needed in the construction and development of novel and effective delivery systems, such as vectors and adjuvants. This review summarizes the status of contemporary chlamydial vaccine research and promising trends fueling the growing optimism for an efficacious vaccine. The unified approach to vaccines for the genus Chlamydia is validated by the several conserved genes and common immunogenic proteins among member species and the similarity of immune effectors controlling Chlamydia species in animals and humans.

Adjuvants, Immunologic↗
PubMed2003

Bacterial ghosts as carrier and targeting systems for mucosal antigen delivery.

The application of new strategies to develop effective vaccines is essential in modern medicine. The bacterial ghost system is a novel vaccine delivery system endowed with intrinsic adjuvant properties. Bacterial ghosts are nonliving gram-negative bacterial cell envelopes devoid of cytoplasmic contents while maintaining their cellular morphology and native surface antigenic structures including bioadhesive properties. They are produced by PhiX174 protein E-mediated lysis of gram-negative bacteria. The intrinsic adjuvant properties of bacterial ghost preparations enhance immune responses against envelope-bound antigens, including T-cell activation and mucosal immunity. Since native and foreign antigens can be expressed in the envelope complex of ghosts before E-mediated lysis, multiple antigens of various origin can be presented to the immune system simultaneously. In addition, the extended bacterial ghost system represents a platform technology for specific targeting of DNA-encoded antigens to primary antigen-presenting cells. The potency, safety and relatively low production cost of bacterial ghosts offer a significant technical advantage, especially when used as combination vaccines.

Adjuvants, Immunologic↗
PubMed2002

Fc receptor regulation of protective immunity against Chlamydia trachomatis.

The prevailing paradigm for designing potentially efficacious vaccines against the obligate intracellular bacterium, Chlamydia trachomatis, advocates regimens capable of inducing a mucosal antigen-specific T helper type 1 (Th1) response. However, recent reports indicate that rapid and efficient clearance of a secondary infection also requires certain B-cell functions. We investigated the hypothesis that Fc receptor (FcR)-mediated antibody effector mechanisms are important B-cell-related functions involved in controlling a chlamydial genital reinfection. Microbiological analysis of genital chlamydial infection in FcR knockout (FcRKO) mice lacking the activatory FcgammaRI (CD64) and FcRgammaIII (CD16), as well as the inhibitory FcgammaRIIB1 (CD32), revealed a greater intensity of secondary infection (i.e. bacterial shedding) in FcRminus sign/minus sign as compared to FcR+/+ mice; however, the course of the primary infection was indistinguishable in both animals. Pathologically, FcRKO mice suffered greater ascending infection than immunocompetent wild-type (WT) mice after a secondary infection. Immunological evaluation indicated that the presence of specific anti-chlamydial antibodies enhanced chlamydial antigen presentation for induction of a Th1 response by FcR+/+, but not FcRminus sign/minus sign, antigen-presenting cells. In addition, specific anti-chlamydial antibodies augmented both macrophage killing of infected epithelial cells by antibody-dependent cellular cytotoxicity (ADCC) and macrophage inhibition of productive growth of chlamydiae in co-cultures. These results indicate that B cells participate in anti-chlamydial immunity via FcR-mediated effector functions of antibodies, which are operative during reinfections. Such effector functions include ADCC, and possibly enhanced uptake, processing and presentation of chlamydial antigens for rapid induction of a Th1 response, all facilitating the early clearance of an infection. These findings suggest that a future anti-chlamydial vaccine should elicit both humoral and T-cell-mediated immune responses for optimal memory response and vaccine efficacy.

Animals↗
PubMed2002

Chemokine and chemokine receptor dynamics during genital chlamydial infection.

Current design strategies for vaccines against certain microbial pathogens, including Chlamydia trachomatis, require the induction and targeting of specific immune effectors to the local sites of infection known as the mucosal effector sites. Chemokines and their receptors are important mediators of leukocyte trafficking and of the controlled recruitment of specific leukocyte clonotypes during host defense against infections and during inflammation. We analyzed the dynamics of chemokine and chemokine receptor expression in genital mucosae during genital chlamydial infection in a murine model to determine how these molecular entities influence the development of immunity and the clearance of infection. A time course study revealed an increase of up to threefold in the levels of expression of RANTES, monocyte chemotactic protein 1 (MCP-1), gamma-interferon-inducible protein 10 (IP-10), macrophage inflammatory protein 1alpha (MIP-1alpha), and intercellular adhesion molecule type 1 (ICAM-1) after genital infection with the C. trachomatis agent of mouse pneumonitis. Peak levels of expression of RANTES, MCP-1, and MIP-1alpha occurred by day 7 after primary infection, while those of IP-10 and ICAM-1 peaked by day 21. Expression levels of these molecules decreased by day 42 after primary infection, by which time all animals had resolved the infection, suggesting an infection-driven regulation of expression. A rapid upregulation of expression of these molecules was observed after secondary infection. The presence of cells bearing the chemokine receptors CCR5 and CXCR3, known to be preferentially expressed on Th1 and dendritic cells, was also synchronous with the kinetics of immune induction in the genital tract and clearance of infection. Results demonstrated that genital chlamydial infection is associated with a significant induction of chemokines and chemokine receptors that are involved in the recruitment of Th1 cells into the site of infection. Future studies will focus on how selective modulation of chemokines and their receptors can be used to optimize long-term immunity against CHLAMYDIA:

Animals↗