Immune Correlates Of Protection Research Articles

Antibody-Dependent, Gamma Interferon-Independent Sterilizing Immunity Induced by a Subunit Malaria Vaccine.

The development of effective malaria vaccines is hampered by incomplete understanding of the immunological correlates of protective immunity. Recently, the moderate clinical efficacy of the Plasmodium falciparum circumsporozoite protein (CSP)-based RTS,S/AS01E vaccine in phase 3 studies highlighted the urgency to design and test more efficacious next-generation malaria vaccines. In this study, we report that immunization with recombinant CSP from Plasmodium yoelii (rPyCSP), when delivered in Montanide ISA 51, induced sterilizing immunity against sporozoite challenge in C57BL/6 and BALB/c strains of mice. This immunity was antibody dependent, as evidenced by the complete loss of immunity in B-cell-knockout (KO) mice and by the ability of immune sera to neutralize sporozoite infectivity in mice. Th2-type isotype IgG1 antibody levels were associated with protective immunity. The fact that immunized gamma interferon (IFN-γ)-KO mice and wild-type (WT) mice have similar levels of protective immunity and the absence of IFN-γ-producing CD4+ and CD8+ T cells in protected mice, as shown by flow cytometry, indicate that the immunity is IFN-γ independent. Protection against sporozoite challenge correlated with higher frequencies of CD4+ T cells that express interleukin-2 (IL-2), IL-4, and tumor necrosis factor alpha (TNF-α). In the RTS,S study, clinical immunity was associated with higher IgG levels and frequencies of IL-2- and TNF-α-producing CD4+ T cells. The other hallmarks of immunity in our study included an increased number of follicular B cells but a loss in follicular T helper cells. These results provide an excellent model system to evaluate the efficacy of novel adjuvants and vaccine dosage and determine the correlates of immunity in the search for superior malaria vaccine candidates.

Functional antibodies as immunological endpoints to evaluate protective immunity against Shigella

ABSTRACTThe development, clinical advancement and licensure of vaccines, and monitoring of vaccine effectiveness could be expedited and simplified by the ability to measure immunological endpoints that can predict a favorable clinical outcome. Antigen-specific and functional antibodies have been described in the context of naturally acquired immunity and vaccination against Shigella, and their presence in serum has been associated with reduced risk of disease in human subjects. The relevance of these antibodies as correlates of protective immunity, their mechanistic contribution to protection (e.g. target antigens, interference with pathogenesis, and participation in microbial clearance), and factors that influence their magnitude and makeup (e.g. host age, health condition, and environment) are important considerations that need to be explored. In addition to facilitating vaccine evaluation, immunological correlates of protection could be useful for identifying groups at risk and advancing immune therapies. Herein we discuss the precedent and value of functional antibodies as immunological endpoints to predict vaccine efficacy and the relevance of functional antibody activity to evaluate protective immunity against shigellosis.

Evidence for Residual Immunity to Smallpox After Vaccination and Implications for Re-emergence.

Smallpox has been eradicated but advances in synthetic biology have increased the risk of its re-emergence. Residual immunity in individuals who were previously vaccinated may mitigate the impact of an outbreak, but there is a high degree of uncertainty about the duration and degree of residual immunity. Both cell-mediated and humoral immunity are thought to be important but the exact mechanisms of protection are unclear. Guidelines usually suggest vaccine-induced immunity wanes to zero after 3-10 years post vaccination, whereas other estimates show long term immunity over decades. A systematic review of the literature was conducted to quantify the duration and extent of residual immunity to smallpox after vaccination. Twenty-nine papers related to quantifying residual immunity to smallpox after vaccination were identified: neutralizing antibody levels were used as immune correlates of protection in 11/16 retrospective cross-sectional studies, 2/3 epidemiological studies, 6/7 prospective vaccine trials and 0/3 modeling studies. Duration of protection of >20 years was consistently shown in the 16 retrospective cross-sectional studies, while the lowest estimated duration of protection was 11.7 years among the modeling studies. Childhood vaccination conferred longer duration of protection than vaccination in adulthood, and multiple vaccinations did not appear to improve immunity. Most studies suggest a longer duration of residual immunity (at least 20 years) than assumed in smallpox guidelines. Estimates from modeling studies were less but still greater than the 3-10 years suggested by the WHO Committee on International Quarantine or US CDC guidelines. These recommendations were probably based on observations and studies conducted while smallpox was endemic. The cut-off values for pre-existing antibody levels of >1:20 and >1:32 reported during the period of endemic smallpox circulation may not be relevant to the contemporary population, but have been used as a threshold for identifying people with residual immunity in post-eradication era studies. Of the total antibodies produced in response to smallpox vaccination, neutralizing antibodies have shown to contribute significantly to immunological memory. Although the mechanism of immunological memory and boosting is unclear, revaccination is likely to result in a more robust response. There is a need to improve the evidence base for estimates on residual immunity to better inform planning and preparedness for re-emergent smallpox.

Survey of cellular immune responses to human cytomegalovirus infection in the microenvironment of the uterine-placental interface.

Congenital human cytomegalovirus (HCMV) infection is a leading cause of birth defects, yet there are no established treatments for preventing maternal-fetal transmission. During first trimester, HCMV replicates in basal decidua that functions as a reservoir for virus and source of transmission to the attached placenta and fetal hemiallograft but also contains immune cells, including natural killer cells, macrophages, and T cell subsets, that respond to pathogens, protecting the placenta and fetus. However, the specific cellular and cytokine responses to infection are unknown, nor are the immune correlates of protection that guide development of therapeutic strategies. Here we survey immune cell phenotypes in intact explants of basal decidua infected with a clinical pathogenic HCMV strain ex vivo and identify specific changes occurring in response to infection in the tissue environment. Using 4-color immunofluorescence microscopy, we found that at 3days postinfection, virus replicates in decidual stromal cells and epithelial cells of endometrial glands. Infected cells and effector memory CD8+ T cells (TEM) in contact with them make IFN-γ. CD8+ TEM cells produce granulysin and cluster at sites of infection in decidua and the epithelium of endometrial glands. Quantification indicated expansion of two immune cell subtypes-CD8+ TEM cells and, to a lesser extent, iNKT cells. Approximately 20% of immune cells were found in pairs in both control and infected decidua, suggesting frequent cross-talk in the microenvironment of decidua. Our findings indicate a complex immune microenvironment in basal decidua and suggest CD8+ TEM cells play a role in early responses to decidual infection in seropositive women.

Clinically Relevant Immune Responses against Cytomegalovirus: Implications for Precision Medicine.

Immune responses to human cytomegalovirus (CMV) can be used to assess immune fitness in an individual. Further to its clinical significance in posttransplantation settings, emerging clinical and translational studies provide examples of immune correlates of protection pertaining to anti-CMV immune responses in the context of cancer or infectious diseases, e.g., tuberculosis. In this viewpoint, we provide a brief overview about CMV-directed immune reactivity and immune fitness in a clinical context and incorporate some of our own findings obtained from peripheral blood or tumour-infiltrating lymphocytes (TIL) from patients with advanced cancer. Observations in patients with solid cancers whose lesions contain both CMV and tumour antigen-specific T-cell subsets are highlighted, due to a possible CMV-associated “bystander” effect in amplifying local inflammation and subsequent tumour rejection. The role of tumour-associated antibodies recognising diverse CMV-derived epitopes is also discussed in light of anti-cancer immune responses. We discuss here the use of anti-CMV immune responses as a theranostic tool—combining immunodiagnostics with a personalised therapeutic potential—to improve treatment outcomes in oncological indications.

Immune Protection of SIV Challenge by PD-1 Blockade During Vaccination in Rhesus Monkeys.

Though immune correlates for protection are still under investigation, potent cytotoxic T lymphocyte responses are desirable for an ideal HIV-1 vaccine. PD-1 blockade enhances SIV-specific CD8+ T cells. However, little information has been reported about how it affects the immunogenicity and protection of prophylactic SIV vaccines in nonhuman primates. Here, we show that PD-1 blockade during vaccination substantially improved protective efficacy in SIV challenged macaques. The PD-1 pathway was blocked using a monoclonal antibody specific to human PD-1. Administration of this antibody effectively augmented and sustained vaccine-induced SIV-specific T cell responses for more than 42 weeks after first immunization in rhesus monkeys, as compared with SIV vaccination only. Importantly, after intrarectally repeated low-dosage challenge with highly pathogenic SIVmac239, monkeys with PD-1 blockade during vaccination achieved full protection against incremental viral doses of up to 50,000 TICD50. These findings highlight the importance of PD-1 blockade during vaccination for the development of HIV vaccines.

Mycobacterium Growth Inhibition Assay of Human Alveolar Macrophages as a Correlate of Immune Protection Following Mycobacterium bovis Bacille Calmette-Guérin Vaccination.

In order to eliminate tuberculosis (TB), an effective vaccine is urgently needed to prevent infection with Mycobacterium tuberculosis. A key obstacle for the development of novel TB vaccines is the lack of surrogate markers for immune protection against M. tuberculosis. We investigated growth rates of M. tuberculosis in the mycobacterial growth inhibition assay (MGIA) as a marker for mycobacterial growth control of human bronchoalveolar lavage (BALC) and peripheral blood mononuclear cells (PBMC) before and after vaccination with Mycobacterium bovis Bacille Calmette-Guérin (BCG) of healthy adult volunteers. Vaccination induced a positive response (p < 0.001) to purified protein derivate (PPD) in 58.8% of the individuals in an interferon-γ release assay-ELISpot. Intraindividual evaluation of the MGIA growth rates before and after M. bovis BCG-vaccination revealed no significant difference in time to culture positivity before and after vaccination in BALC (p = 0.604) and PBMC (p = 0.199). The magnitude of the PPD-response induced by M. bovis BCG-vaccination did not correlate with growth control in BALC and PBMC (correlation = 0.468, 95% CI: -0.016 to 0.775). In conclusion, M. bovis BCG-vaccination-induced mycobacterial-specific cytokine immune response does not result in functional immune control against M. tuberculosis in the MGIA.

Antibody to Poly-N-acetyl glucosamine provides protection against intracellular pathogens: Mechanism of action and validation in horse foals challenged with Rhodococcus equi.

Immune correlates of protection against intracellular bacterial pathogens are largely thought to be cell-mediated, although a reasonable amount of data supports a role for antibody-mediated protection. To define a role for antibody-mediated immunity against an intracellular pathogen, Rhodococcus equi, that causes granulomatous pneumonia in horse foals, we devised and tested an experimental system relying solely on antibody-mediated protection against this host-specific etiologic agent. Immunity was induced by vaccinating pregnant mares 6 and 3 weeks prior to predicted parturition with a conjugate vaccine targeting the highly conserved microbial surface polysaccharide, poly-N-acetyl glucosamine (PNAG). We ascertained antibody was transferred to foals via colostrum, the only means for foals to acquire maternal antibody. Horses lack transplacental antibody transfer. Next, a randomized, controlled, blinded challenge was conducted by inoculating at ~4 weeks of age ~106 cfu of R. equi via intrabronchial challenge. Eleven of 12 (91%) foals born to immune mares did not develop clinical R. equi pneumonia, whereas 6 of 7 (86%) foals born to unvaccinated controls developed pneumonia (P = 0.0017). In a confirmatory passive immunization study, infusion of PNAG-hyperimmune plasma protected 100% of 5 foals against R. equi pneumonia whereas all 4 recipients of normal horse plasma developed clinical disease (P = 0.0079). Antibodies to PNAG mediated killing of extracellular and intracellular R. equi and other intracellular pathogens. Killing of intracellular organisms depended on antibody recognition of surface expression of PNAG on infected cells, along with complement deposition and PMN-assisted lysis of infected macrophages. Peripheral blood mononuclear cells from immune and protected foals released higher levels of interferon-γ in response to PNAG compared to controls, indicating vaccination also induced an antibody-dependent cellular release of this critical immune cytokine. Overall, antibody-mediated opsonic killing and interferon-γ release in response to PNAG may protect against diseases caused by intracellular bacterial pathogens.

Human cytomegalovirus (HCMV)-specific T cell but not neutralizing or IgG binding antibody responses to glycoprotein complexes gB, gHgLgO, and pUL128L correlate with protection against high HCMV viral load reactivation in solid-organ transplant recipients.

Immune correlates of protection against human cytomegalovirus (HCMV) infection are still debated. This study aimed to investigate which arm of the immune response plays a major role in protection against HCMV infection in kidney transplant recipients (n = 40) and heart transplant recipients (n = 12). Overall, patients were divided into 2 groups: one including 37 patients with low viral load (LVL), and the other including 15 patients with high viral load (HVL). All LVL patients resolved the infection spontaneously, whereas HVL patients were all treated with one or more courses of antivirals. In HVL patients, viral DNAemia, which was more than 100 times higher than LVL, appeared and peaked at significantly earlier times, but disappeared much later than in LVL patients. During a 1-year follow-up, all LVL patients had levels of HCMV-specific CD4+ (and CD8+ ) T cells significantly higher than HVL patients. On the contrary, titers of neutralizing antibodies and enzyme-linked immunosorbent assay-IgG antibodies to gB, gHgLgO, and pentamer gHgLpUL128L were overlapping in the 2 patient groups. In conclusion, while a valid HCMV-specific T-cell response was detected in more than 90% of LVL patients, >90% of HVL patients lacked an adequate T-cell response. Antibody responses did not appear to be associated directly or indirectly with protection.

The Hurdles From Bench to Bedside in the Realization and Implementation of a Universal Influenza Vaccine.

Influenza viruses circulate worldwide causing annual epidemics that have a substantial impact on public health. This is despite vaccines being in use for over 70 years and currently being administered to around 500 million people each year. Improvements in vaccine design are needed to increase the strength, breadth, and duration of immunity against diverse strains that circulate during regular epidemics, occasional pandemics, and from animal reservoirs. Universal vaccine strategies that target more conserved regions of the virus, such as the hemagglutinin (HA)-stalk, or recruit other cellular responses, such as T cells and NK cells, have the potential to provide broader immunity. Many pre-pandemic vaccines in clinical development do not utilize new vaccine platforms but use “tried and true” recombinant HA protein or inactivated virus strategies despite substantial leaps in fundamental research on universal vaccines. Significant hurdles exist for universal vaccine development from bench to bedside, so that promising preclinical data is not yet translating to human clinical trials. Few studies have assessed immune correlates derived from asymptomatic influenza virus infections, due to the scale of a study required to identity these cases. The realization and implementation of a universal influenza vaccine requires identification and standardization of set points of protective immune correlates, and consideration of dosage schedule to maximize vaccine uptake.

Development of a high-throughput flexible quantitative suspension array assay for IgG against multiple Plasmodium falciparum antigens

BackgroundAntibody responses to Plasmodium falciparum play a critical role in disease control. Finding reliable IgG biomarkers of protection is complicated by a parasite proteome of over 5000 proteins, some with polymorphisms. Studies of anti-malarial naturally acquired and vaccine immunity would benefit from a standard high-throughput immunoassay to measure multiple antibodies. A multiplex quantitative suspension assay to measure antigen-specific IgGs was developed and its precision (reproducibility and repeatability), dynamic range, limits of detection and quantification, and non-specific binding to different P. falciparum proteins tested. A set of 288 human plasma samples from a malaria-endemic region were analysed twice by two different operators. Another set of samples from 9 malaria-naïve and 10 malaria-exposed individuals were repetitively assayed during 22 consecutive days. Positive controls, negative controls, blanks and microspheres coated with bovine serum albumin were included in all assays.ResultsThe multiplex quantitative suspension assay demonstrated low non-specific signal and good estimates of precision and reproducibility between operators. The overall mean of non-specific binding measured in 288 plasma samples was 32.83 to ± 44.81 median fluorescence intensity (MFI). Repeatability was 7.66% ± 15.89 between triplicates for all antigens and samples, being lower in samples from malaria-exposed than malaria-naïve individuals. No evidence of significantly different variance across days in MFI or arbitrary units (AU)/mL was found, assuming homogeneity of variance between days of analysis. Intra-class correlation coefficient between 22 days of analysis was 0.98 (0.97–0.98) for MFI units and 0.9 (0.87–0.93) for AU/mL. Reproducibility between operators for all samples and antigens had an overall adjusted correlation of 0.929 for MFI and 0.836 for AU/mL.ConclusionsThis high-throughput multiplex immunoassay is simple and highly reproducible. This represents an asset for malaria vaccine studies involving CSP-specific antibodies and selected antigens for sero-epidemiological purposes. Measuring a multiplex antigen panel in a single reaction will help to assess not only vaccine immunogenicity but also potential malaria vaccine effects on naturally acquired immune responses. This will accelerate the identification of immune correlates of protection, down-selection of vaccine formulations, antigen discovery and guide second-generation vaccine design.

Vaccine-induced antibodies to herpes simplex virus glycoprotein D epitopes involved in virus entry and cell-to-cell spread correlate with protection against genital disease in guinea pigs.

Herpes simplex virus type 2 (HSV-2) glycoprotein D (gD2) subunit antigen is included in many preclinical candidate vaccines. The rationale for including gD2 is to produce antibodies that block crucial gD2 epitopes involved in virus entry and cell-to-cell spread. HSV-2 gD2 was the only antigen in the Herpevac Trial for Women that protected against HSV-1 genital infection but not HSV-2. In that trial, a correlation was detected between gD2 ELISA titers and protection against HSV-1, supporting the importance of antibodies. A possible explanation for the lack of protection against HSV-2 was that HSV-2 neutralization titers were low, four-fold lower than to HSV-1. Here, we evaluated neutralization titers and epitope-specific antibody responses to crucial gD2 epitopes involved in virus entry and cell-to-cell spread as correlates of immune protection against genital lesions in immunized guinea pigs. We detected a strong correlation between neutralizing antibodies and protection against genital disease. We used a high throughput biosensor competition assay to measure epitope-specific responses to seven crucial gD2 linear and conformational epitopes involved in virus entry and spread. Some animals produced antibodies to most crucial epitopes while others produced antibodies to few. The number of epitopes recognized by guinea pig immune serum correlated with protection against genital lesions. We confirmed the importance of antibodies to each crucial epitope using monoclonal antibody passive transfer that improved survival and reduced genital disease in mice after HSV-2 genital challenge. We re-evaluated our prior study of epitope-specific antibody responses in women in the Herpevac Trial. Humans produced antibodies that blocked significantly fewer crucial gD2 epitopes than guinea pigs, and antibody responses in humans to some linear epitopes were virtually absent. Neutralizing antibody titers and epitope-specific antibody responses are important immune parameters to evaluate in future Phase I/II prophylactic human vaccine trials that contain gD2 antigen.

Lessons Learned in Developing a Commercial FIV Vaccine: The Immunity Required for an Effective HIV-1 Vaccine.

The feline immunodeficiency virus (FIV) vaccine called Fel-O-Vax® FIV is the first commercial FIV vaccine released worldwide for the use in domestic cats against global FIV subtypes (A–E). This vaccine consists of inactivated dual-subtype (A plus D) FIV-infected cells, whereas its prototype vaccine consists of inactivated dual-subtype whole viruses. Both vaccines in experimental trials conferred moderate-to-substantial protection against heterologous strains from homologous and heterologous subtypes. Importantly, a recent case-control field study of Fel-O-Vax-vaccinated cats with outdoor access and ≥3 years of annual vaccine boost, resulted in a vaccine efficacy of 56% in Australia where subtype-A viruses prevail. Remarkably, this protection rate is far better than the protection rate of 31.2% observed in the best HIV-1 vaccine (RV144) trial. Current review describes the findings from the commercial and prototype vaccine trials and compares their immune correlates of protection. The studies described in this review demonstrate the overarching importance of ant-FIV T-cell immunity more than anti-FIV antibody immunity in affording protection. Thus, future efforts in developing the next generation FIV vaccine and the first effective HIV-1 vaccine should consider incorporating highly conserved protective T-cell epitopes together with the conserved protective B-cell epitopes, but without inducing adverse factors that eliminate efficacy.

Analyzing the Human Serum Antibody Responses to a Live Attenuated Tetravalent Dengue Vaccine Candidate.

Dengue virus serotypes 1-4 (DENV-1-4) are the most common vector-borne viral pathogens of humans and the etiological agents of dengue fever and dengue hemorrhagic syndrome. A live-attenuated tetravalent dengue vaccine (TDV) developed by Takeda Vaccines has recently progressed to phase 3 safety and efficacy evaluation. We analyzed the qualitative features of the neutralizing antibody (nAb) response induced in naive and DENV-immune individuals after TDV administration. Using DENV-specific human monoclonal antibodies (mAbs) and recombinant DENV displaying different serotype-specific Ab epitopes, we mapped the specificity of TDV-induced nAbs against DENV-1-3. Nearly all subjects had high levels of DENV-2-specific nAbs directed to epitopes centered on domain III of the envelope protein. In some individuals, the vaccine induced nAbs that tracked with a DENV-1-specific neutralizing epitope centered on domain I of the envelope protein. The vaccine induced binding Abs directed to a DENV-3 type-specific neutralizing epitope, but findings of mapping of DENV-3 type-specific nAbs were inconclusive. Here we provide qualitative measures of the magnitude and epitope specificity of the nAb responses to TDV. This information will be useful for understanding the performance of TDV in clinical trials and for identifying correlates of protective immunity.

Human antibodies activate complement against Plasmodium falciparum sporozoites, and are associated with protection against malaria in children

BackgroundAntibodies targeting Plasmodium falciparum sporozoites play a key role in human immunity to malaria. However, antibody mechanisms that neutralize sporozoites are poorly understood. This has been a major constraint in developing highly efficacious vaccines, as we lack strong correlates of protective immunity.MethodsWe quantified the ability of human antibodies from malaria-exposed populations to interact with human complement, examined the functional effects of complement activity against P. falciparum sporozoites in vitro, and identified targets of functional antibodies. In children and adults from malaria-endemic regions, we determined the acquisition of complement-fixing antibodies to sporozoites and their relationship with antibody isotypes and subclasses. We also investigated associations with protective immunity in a longitudinal cohort of children (n = 206) residing in a malaria-endemic region.ResultsWe found that antibodies to the major sporozoite surface antigen, circumsporozoite protein (CSP), were predominately IgG1, IgG3, and IgM, and could interact with complement through recruitment of C1q and activation of the classical pathway. The central repeat region of CSP, included in leading vaccines, was a key target of complement-fixing antibodies. We show that antibodies activate human complement on P. falciparum sporozoites, which consequently inhibited hepatocyte cell traversal that is essential for establishing liver-stage infection, and led to sporozoite death in vitro. The natural acquisition of complement-fixing antibodies in malaria-exposed populations was age-dependent, and was acquired more slowly to sporozoite antigens than to merozoite antigens. In a longitudinal cohort of children, high levels of complement-fixing antibodies were significantly associated with protection against clinical malaria.ConclusionsThese novel findings point to complement activation by antibodies as an important mechanism of anti-sporozoite human immunity, thereby enabling new strategies for developing highly efficacious malaria vaccines. We also present evidence that complement-fixing antibodies may be a valuable correlate of protective immunity in humans.

Correlates of protective immunity for fish vaccines

Vaccination is one of the most effective disease control strategies that has contributed to the significant reduction of disease outbreaks and antibiotics usage in salmonid aquaculture. To date, licensing of fish vaccines is to a limited extent based on in vitro correlates of protection, as done for many mammalian vaccines. This is because the immunological mechanisms of vaccine protection have not been clearly elucidated for most fish vaccines. Herein, we provide an overview of the different steps required to establish correlates of protective immunity required to serve as benchmarks in optimizing vaccine production in aquaculture. We highlight the importance of optimizing challenge models needed to generate consistent results used during vaccine development as a basis for establishing immune correlates of protection. Data generated this far shows that antibodies are potentially the most reliable correlates of protective immunity for fish vaccines. Our findings also show that antigen dose can be optimized to serve as a correlate of protection for fish vaccines. Further, there is need to establish signatures of T-cell protective immunity when antibodies fail to serve as proxies of immune protection, particularly for vaccines against intracellular pathogens. We can anticipate that documentation of efficacy for future vaccines in aquaculture, particularly batch testing will be based on in vitro correlates of protective immunity.

Epitope-Specific Humoral Responses to Human Cytomegalovirus Glycoprotein-B Vaccine With MF59: Anti-AD2 Levels Correlate With Protection From Viremia.

The human cytomegalovirus (HCMV) virion envelope protein glycoprotein B (gB) is essential for viral entry and represents a major target for humoral responses following infection. Previously, a phase 2 placebo-controlled clinical trial conducted in solid organ transplant candidates demonstrated that vaccination with gB plus MF59 adjuvant significantly increased gB enzyme-linked immunosorbent assay (ELISA) antibody levels whose titer correlated directly with protection against posttransplant viremia. The aim of the current study was to investigate in more detail this protective humoral response in vaccinated seropositive transplant recipients. We focused on 4 key antigenic domains (AD) of gB (AD1, AD2, AD4, and AD5), measuring antibody levels in patient sera and correlating these with posttransplant HCMV viremia. Vaccination of seropositive patients significantly boosted preexisting antibody levels against the immunodominant region AD1 as well as against AD2, AD4, and AD5. A decreased incidence of viremia correlated with higher antibody levels against AD2 but not with antibody levels against the other 3 ADs. Overall, these data support the hypothesis that antibodies against AD2 are a major component of the immune protection of seropositives seen following vaccination with gB/MF59 vaccine and identify a correlate of protective immunity in allograft patients.

Human dengue virus serotype 2 neutralizing antibodies target two distinct quaternary epitopes.

Dengue virus (DENV) infection causes dengue fever, dengue hemorrhagic fever and dengue shock syndrome. It is estimated that a third of the world’s population is at risk for infection, with an estimated 390 million infections annually. Dengue virus serotype 2 (DENV2) causes severe epidemics, and the leading tetravalent dengue vaccine has lower efficacy against DENV2 compared to the other 3 serotypes. In natural DENV2 infections, strongly neutralizing type-specific antibodies provide protection against subsequent DENV2 infection. While the epitopes of some human DENV2 type-specific antibodies have been mapped, it is not known if these are representative of the polyclonal antibody response. Using structure-guided immunogen design and reverse genetics, we generated a panel of recombinant viruses containing amino acid alterations and epitope transplants between different serotypes. Using this panel of recombinant viruses in binding, competition, and neutralization assays, we have finely mapped the epitopes of three human DENV2 type-specific monoclonal antibodies, finding shared and distinct epitope regions. Additionally, we used these recombinant viruses and polyclonal sera to dissect the epitope-specific responses following primary DENV2 natural infection and monovalent vaccination. Our results demonstrate that antibodies raised following DENV2 infection or vaccination circulate as separate populations that neutralize by occupying domain III and domain I quaternary epitopes. The fraction of neutralizing antibodies directed to different epitopes differs between individuals. The identification of these epitopes could potentially be harnessed to evaluate epitope-specific antibody responses as correlates of protective immunity, potentially improving vaccine design.

Immunogenicity of HPV prophylactic vaccines: Serology assays and their use in HPV vaccine evaluation and development

When administered as standard three-dose schedules, the licensed HPV prophylactic vaccines have demonstrated extraordinary immunogenicity and efficacy. We summarize the immunogenicity of these licensed vaccines and the most commonly used serology assays, with a focus on key considerations for one-dose vaccine schedules.Although immune correlates of protection against infection are not entirely clear, both preclinical and clinical evidence point to neutralizing antibodies as the principal mechanism of protection. Thus, immunogenicity assessments in vaccine trials have focused on measurements of antibody responses to the vaccine. Non-inferiority of antibody responses after two doses of HPV vaccines separated by 6 months has been demonstrated and this evidence supported the recent WHO recommendations for two-dose vaccination schedules in both boys and girls 9–14 years of age. There is also some evidence suggesting that one dose of HPV vaccines may provide protection similar to the currently recommended two-dose regimens but robust data on efficacy and immunogenicity of one-dose vaccine schedules are lacking. In addition, immunogenicity has been assessed and reported using different methods, precluding direct comparison of results between different studies and vaccines. New head-to-head vaccine trials evaluating one-dose immunogenicity and efficacy have been initiated and an increase in the number of trials relying on immunobridging is anticipated. Therefore, standardized measurement and reporting of immunogenicity for the up to nine HPV types targeted by the current vaccines is now critical. Building on previous HPV serology assay standardization and harmonization efforts initiated by the WHO HPV LabNet in 2006, new secondary standards, critical reference reagents and testing guidelines will be generated as part of a new partnership to facilitate harmonization of the immunogenicity testing in new HPV vaccine trials.

Hepcidin deficiency and iron deficiency do not alter tuberculosis susceptibility in a murine M.tb infection model.

Tuberculosis (TB), caused by the macrophage-tropic pathogen Mycobacterium tuberculosis (M.tb) is a highly prevalent infectious disease. Since an immune correlate of protection or effective vaccine have yet to be found, continued research into host-pathogen interactions is important. Previous literature reports links between host iron status and disease outcome for many infections, including TB. For some extracellular bacteria, the iron regulatory hormone hepcidin is essential for protection against infection. Here, we investigated hepcidin (encoded by Hamp1) in the context of murine M.tb infection. Female C57BL/6 mice were infected with M.tb Erdman via aerosol. Hepatic expression of iron-responsive genes was measured by qRT-PCR and bacterial burden determined in organ homogenates. We found that hepatic Hamp1 mRNA levels decreased post-infection, and correlated with a marker of BMP/SMAD signalling pathways. Next, we tested the effect of Hamp1 deletion, and low iron diets, on M.tb infection. Hamp1 knockout mice did not have a significantly altered M.tb mycobacterial load in either the lungs or spleen. Up to 10 weeks of dietary iron restriction did not robustly affect disease outcome despite causing iron deficiency anaemia. Taken together, our data indicate that unlike with many other infections, hepcidin is decreased following M.tb infection, and show that hepcidin ablation does not influence M.tb growth in vivo. Furthermore, because even severe iron deficiency did not affect M.tb mycobacterial load, we suggest that the mechanisms M.tb uses to scavenge iron from the host must be extremely efficient, and may therefore represent potential targets for drugs and vaccines.