Can successful vaccines teach us how to induce efficient protective immune responses?

Advancing Toward HIV-1 Vaccine Efficacy through the Intersections of Immune Correlates

Interrogating immune correlates of infection risk for efficacious and non-efficacious HIV-1 vaccine clinical trials have provided hypotheses regarding the mechanisms of induction of protective immunity to HIV-1. To date, there have been six HIV-1 vaccine efficacy trials (VAX003, Vaxgen, Inc., San Francisco, CA, USA), VAX004 (Vaxgen, Inc.), HIV-1 Vaccine Trials Network (HVTN) 502 (Step), HVTN 503 (Phambili), RV144 (sponsored by the U.S. Military HIV Research Program, MHRP) and HVTN 505). Cellular, humoral, host genetic and virus sieve analyses of these human clinical trials each can provide information that may point to potentially protective mechanisms for vaccine-induced immunity. Critical to staying on the path toward development of an efficacious vaccine is utilizing information from previous human and non-human primate studies in concert with new discoveries of basic HIV-1 host-virus interactions. One way that past discoveries from correlate analyses can lead to novel inventions or new pathways toward vaccine efficacy is to examine the intersections where different components of the correlate analyses overlap (e.g., virus sieve analysis combined with humoral correlates) that can point to mechanistic hypotheses. Additionally, differences in durability among vaccine-induced T- and B-cell responses indicate that time post-vaccination is an important variable. Thus, understanding the nature of protective responses, the degree to which such responses have, or have not, as yet, been induced by previous vaccine trials and the design of strategies to induce durable T- and B-cell responses are critical to the development of a protective HIV-1 vaccine.

Exposure to SIV in utero results in reduced viral loads and altered responsiveness to postnatal challenge

HIV disease progression appears to be driven by increased immune activation. Given observations that fetal exposure to infectious pathogens in utero can result in reduced immune responses, or tolerance, to those pathogens postnatally, we hypothesized that fetal exposure to HIV may render the fetus tolerant to the virus, thus reducing damage caused by immune activation during infection later in life. To test this hypothesis, fetal rhesus macaques (Macaca mulatta) were injected with the attenuated virus SIVmac1A11 in utero and challenged with pathogenic SIVmac239 1 year after birth. SIVmac1A11-injected animals had significantly reduced plasma RNA viral loads (P < 0.02) up to 35 weeks after infection. Generalized estimating equations analysis was performed to identify immunologic and clinical measurements associated with plasma RNA viral load. A positive association with plasma RNA viral load was observed with the proportion of CD8(+) T cells expressing the transcription factor, FoxP3, and the proportion of CD4(+) T cells producing the lymphoproliferative cytokine, IL-2. In contrast, an inverse relationship was found with the frequencies of circulating CD4(+) and CD8(+) T cells displaying intermediate expression of the proliferation marker, Ki-67. Animals exposed to simian immunodeficiency virus (SIV) in utero appeared to have enhanced SIV-specific immune responses, a lower proportion of CD8(+) T cells expressing the exhaustion marker PD-1, and more circulating TH17 cells than controls. Although the development of tolerance was not demonstrated, these data suggest that rhesus monkeys exposed to SIVmac1A11 in utero had distinct immune responses associated with the control of viral replication after postnatal challenge.

Predicting clinical severity based on substitutions near epitope A of influenza A/H3N2

Epitopes are the main targets for specific antibodies in the host defense systems. Recent studies have shown that amino acid (aa) substitutions located within the influenza A/H3N2 hemagglutinin 1 (HA1) epitopes A-E, particularly in A and B, result in antigenic drift. Viruses with such drift mutations may have resulted in more severe influenza-related illness during influenza epidemics between late 2012 and early 2015. We sought to quantify vaccine mismatches in epitopes A-E of the HA1 protein, and correlate these with the severity of the patient's illness. The influenza A/H3N2 clinical samples were collected between April 2009 and November 2013 (n=206). Patients were clinically stratified into groups with mild, moderate, and severe influenza-like illness (ILI). The impact of the number of aa mismatches in each of epitopes A-E, gender, age groups (⩽18, 19-64, ⩾65 years), and comorbidities on the likelihood that patients would suffer moderate and/or severe ILI due to influenza A/H3N2 infection were assessed. A higher number of aa mismatches in epitope A between the vaccine and locally circulating viruses correlated with more severe influenza infection, although this correlation was most significant with pre-existing comorbidities. A practical application of this finding would be to monitor patients (especially those in high-risk groups) infected with such viruses more closely, as they are at increased risk of developing more serious disease. Epidemiologically, it was of interest to note that viruses from subclade 3A of Victoria/208 strain were not detected in Singapore between 2009 and 2012. By contrast, these viruses were detected at a prevalence of up to 40% in the 2011-2012 influenza seasons in other regions of the Northern and Southern hemispheres. Such findings support the rationale for more regionally customized seasonal influenza vaccine compositions to optimize the protection of the population against locally circulating virus strains.

Novel vaccine concept based on back-boost effect in viral infection

A novel vaccine concept is discussed based on recent evidence of a "back-boost" effect in Influenza infection. The initial immune response to the infection is imprinted through an immune memory pathway. The immune memory in the back-boost mechanism could be used in reversed order as a "forward-boost" in the proposed vaccine concept.

Immunotherapeutic approaches for cancer therapy: An updated review

In spite of specific immune effector mechanisms raised against tumor cells, there are mechanisms employed by the tumor cells to keep them away from immune recognition and elimination; some of these mechanisms have been identified, while others are still poorly understood. Manipulation or augmentation of specific antitumor immune responses are now the preferred approaches for treatment of malignancies, and traditional therapeutic approaches are being replaced by the use of agents which potentiate immune effector mechanisms, broadly called "immunotherapy". Cancer immunotherapy is generally classified into two main classes including active and passive methods. Interventions to augment the immune system of the patient, for example, vaccination or adjuvant therapy, actively promote antitumor effector mechanisms to improve cancer elimination. On the other hand, administration of specific monoclonal antibodies (mAbs) against different tumor antigens and adoptive transfer of genetically-modified specific T cells are currently the most rapidly developing approaches for cancer targeted therapy. In this review, we will discuss the different modalities for active and passive immunotherapy for cancer.

Enabling skin vaccination using new delivery technologies

The skin is known to be a highly immunogenic site for vaccination, but few vaccines in clinical use target skin largely because conventional intradermal injection is difficult and unreliable to perform. Now, a number of new or newly adapted delivery technologies have been shown to administer vaccine to the skin either by non-invasive or minimally invasive methods. Non-invasive methods include high-velocity powder and liquid jet injection, as well as diffusion-based patches in combination with skin abrasion, thermal ablation, ultrasound, electroporation, and chemical enhancers. Minimally invasive methods are generally based on small needles, including solid microneedle patches, hollow microneedle injections, and tattoo guns. The introduction of these advanced delivery technologies can make the skin a site for simple, reliable vaccination that increases vaccine immunogenicity and offers logistical advantages to improve the speed and coverage of vaccination.

Avidity of anti-circumsporozoite antibodies following vaccination with RTS,S/AS01E in young children

Background

The nature of protective immune responses elicited by immunization with the candidate malaria vaccine RTS,S is still incompletely understood. Antibody levels correlate with protection against malaria infection, but considerable variation in outcome is unexplained (e.g., children may experience malaria despite high anti-circumsporozoite [CS] titers).

Methods and Findings

We measured the avidity index (AI) of the anti-CS antibodies raised in subgroup of 5–17 month old children in Kenya who were vaccinated with three doses of RTS,S/AS01_E between March and August 2007. We evaluated the association between the AI and the subsequent risk of clinical malaria. We selected 19 cases (i.e., with clinical malaria) and 42 controls (i.e., without clinical malaria), matching for anti-CS antibody levels and malaria exposure. We assessed their sera collected 1 month after the third dose of the vaccine, in March 2008 (range 4–10 months after the third vaccine), and at 12 months after the third vaccine dose. The mean AI was 45.2 (95% CI: 42.4 to 48.1), 45.3 (95% CI: 41.4 to 49.1) and 46.2 (95% CI; 43.2 to 49.3) at 1 month, in March 2008 (4–10 months), and at 12 months after the third vaccination, respectively (p = 0.9 by ANOVA test for variation over time). The AI was not associated with protection from clinical malaria (OR = 0.90; 95% CI: 0.49 to 1.66; p = 0.74). The AI was higher in children with high malaria exposure, as measured using the weighted local prevalence of malaria, compared to those with low malaria exposure at 1 month post dose 3 (p = 0.035).

Conclusion

Our data suggest that in RTS,S/AS01_E-vaccinated children residing in malaria endemic countries, the avidity of anti-circumsporozoite antibodies, as measured using an elution ELISA method, was not associated with protection from clinical malaria. Prior natural malaria exposure might have primed the response to RTS,S/AS01_E vaccination.

Nasal immunization of mice with AFCo1 or AFPL1 plus capsular polysaccharide Vi from Salmonella typhi induces cellular response and memory B and T cell responses

The response to infection against Salmonella involves both B and T cell mediated immunity. An effective immunization can activate an adequate immune response capable to control the primary infection and protect against a secondary infection. Mucosal vaccination, by inducing local pathogen-specific immune responses, has the potential to counter mucosally transmitted pathogens at the portal of entry, thereby increasing the efficacy of vaccines. The aim of this work was to explore the efficacy of AFCo1 or AFPL1, as mucosal adjuvants to stimulate cell immunity and memory responses against Vi polysaccharide antigen of Salmonella typhi (PsVi). Mice immunized with 3 intranasal doses exhibited high levels of PsVi-specific IgG (p<0.05), IgG2a and IgG2c subclasses. Also, an amplified recall response after a booster immunization with a plain polysaccharide vaccine was induced. Avidities index were higher in mice immunized with adjuvanted formulations at different chaotropic concentrations. Furthermore, IL-12 and IFN-γ levels in nasally vaccinated mice with both adjuvants were induced. Moreover, priming with 3 doses followed by booster immunization with VaxTyVi(®) resulted in high levels of anti-Vi specific IgG, IgG subclasses and antibody avidity. Long lived plasma cells in bone marrow, memory B cells and long-term memory T cells after booster dose were induced. The combined formulation of Vi polysaccharide with mucosal adjuvants provides an improved immunogenicity, in particular with regard to cellular responses and long lasting cells responses.

Combined meningococcal serogroup A and W135 outer-membrane vesicles activate cell-mediated immunity and long-term memory responses against non-covalent capsular polysaccharide A

Outer-membrane vesicles (OMVs) have inherent adjuvant properties, and many vaccines use OMV as vaccine components. Utilizing the adjuvant properties of OMV could lead to the formulation of vaccines that are less expensive and potentially more immunogenic than covalently conjugated polysaccharide vaccines. We evaluated the adjuvant effect in Balb/c mice of combinations of OMV from Neisseria meningitidis serogroup A and W135 as compared to that of the non-covalently conjugated capsular polysaccharide A. Both antigens were adsorbed onto aluminum hydroxide. The mice were given a booster dose of plain polysaccharide A to stimulate an immunologic memory response. Subclasses determination and cytokine assays demonstrated the capacity of OMV to induce a IgG2a/IgG2b isotype profile and IFN-γ production, suggesting the induction of a Th1 pattern immune response. Lymphoproliferative responses to OMVs were high, with affinity maturation of antibodies observed. Bactericidal titers after the booster dose were also observed. Memory B cells and long-term memory T cells were also detected. The results of this study indicate that combined meningococcal serogroup A and W135 OMV can activate cell-mediated immunity and induce a long-term memory response.

FCGR2C polymorphisms associate with HIV-1 vaccine protection in RV144 trial

The phase III RV144 HIV-1 vaccine trial estimated vaccine efficacy (VE) to be 31.2%. This trial demonstrated that the presence of HIV-1-specific IgG-binding Abs to envelope (Env) V1V2 inversely correlated with infection risk, while the presence of Env-specific plasma IgA Abs directly correlated with risk of HIV-1 infection. Moreover, Ab-dependent cellular cytotoxicity responses inversely correlated with risk of infection in vaccine recipients with low IgA; therefore, we hypothesized that vaccine-induced Fc receptor-mediated (FcR-mediated) Ab function is indicative of vaccine protection. We sequenced exons and surrounding areas of FcR-encoding genes and found one FCGR2C tag SNP (rs114945036) that associated with VE against HIV-1 subtype CRF01_AE, with lysine at position 169 (169K) in the V2 loop (CRF01_AE 169K). Individuals carrying CC in this SNP had an estimated VE of 15%, while individuals carrying CT or TT exhibited a VE of 91%. Furthermore, the rs114945036 SNP was highly associated with 3 other FCGR2C SNPs (rs138747765, rs78603008, and rs373013207). Env-specific IgG and IgG3 Abs, IgG avidity, and neutralizing Abs inversely correlated with CRF01_AE 169K HIV-1 infection risk in the CT- or TT-carrying vaccine recipients only. These data suggest a potent role of Fc-γ receptors and Fc-mediated Ab function in conferring protection from transmission risk in the RV144 VE trial.

Safety and immunogenicity of co-administered MF59-adjuvanted 2009 pandemic and plain 2009-10 seasonal influenza vaccines in rheumatoid arthritis patients on biologicals

Rheumatoid arthritis (RA) patients under immunosuppressive therapy are particularly susceptible to infections, mainly of the respiratory tract, thus vaccination may represent a strategy to reduce their incidence in this vulnerable population. In the 2009-10 influenza season, the safety and immunogenicity of co-administered non-adjuvanted seasonal and MF59-adjuvanted pandemic influenza vaccines were evaluated in this study in 30 RA patients under therapy with anti-tumour necrosis factor (TNF)-α agents or Abatacept and in 13 healthy controls (HC). Patients and HC underwent clinical and laboratory evaluation before (T0), 1 (T1) and 6 months (T2) after vaccinations. No severe adverse reactions, but a significant increase in total mild side effects in patients versus HC were observed. Both influenza vaccines fulfilled the three criteria of the Committee for Proprietary Medicinal Products (CPMP). Seroconversion rate for any viral strain in patients and HC was, respectively, 68 versus 45 for H1-A/Brisbane/59/07, 72 versus 81 for H3-A/Brisbane/10/07, 68 versus 54 for B/Brisbane/60/08 and 81 versus 54 for A/California/7/2009. A slight increase in activated interferon (IFN)-γ-, TNF-α- or interleukin (IL)-17A-secreting T cells at T1 compared to T0, followed by a reduction at T2 in both patients and HC, was registered. In conclusion, simultaneous administration of adjuvanted pandemic and non-adjuvanted seasonal influenza vaccines is safe and highly immunogenic. The largely overlapping results between patients and HC, in terms of antibody response and cytokine-producing T cells, may represent further evidence for vaccine safety and immunogenicity in RA patients on biologicals.

Challenges to the development of vaccines to hepatitis C virus that elicit neutralizing antibodies

Despite 20 years of research, a vaccine to prevent hepatitis C virus (HCV) infection has not been developed. A vaccine to prevent HCV will need to induce broadly reactive immunity able to prevent infection by the 7 genetically and antigenically distinct genotypes circulating world-wide. HCV encodes two surface exposed glycoproteins, E1 and E2 that function as a heterodimer to mediate viral entry. Neutralizing antibodies (NAbs) to both E1 and E2 have been described with the major NAb target being E2. The function of E2 is to attach virions to host cells via cell surface receptors that include, but is not limited to, the tetraspanin CD81 and scavenger receptor class B type 1. However, E2 has developed a number of immune evasion strategies to limit the effectiveness of the NAb response and possibly limit the ability of the immune system to generate potent NAbs in natural infection. Hypervariable regions that shield the underlying core domain, subdominant neutralization epitopes and glycan shielding combine to make E2 a difficult target for the immune system. This review summarizes recent information on the role of NAbs to prevent HCV infection, the targets of the NAb response and structural information on glycoprotein E2 in complex with neutralizing antibodies. This new information should provide a framework for the rational design of new vaccine candidates that elicit highly potent broadly reactive NAbs to prevent HCV infection.

In-utero exposure to maternal HIV infection alters T-cell immune responses to vaccination in HIV-uninfected infants

OBJECTIVE

In sub-Saharan Africa, HIV-exposed uninfected (HEU) infants have higher morbidity and mortality than HIV-unexposed infants. To evaluate whether immune dysfunction contributes to this vulnerability of HEU infants, we conducted a longitudinal, observational cohort study to assess T-cell immune responses to infant vaccines (Mycobacterium bovis BCG and acellular pertussis) and staphylococcal enterotoxin B (SEB). In total, 46 HEU and 46 HIV-unexposed infants were recruited from Khayelitsha, Cape Town.

METHODS

Vaccine-specific T-cell proliferation (Ki67 expression) and intracellular expression of four cytokines [interferon-γ, interleukin (IL)-2, IL-13 and IL-17] were measured after whole blood stimulation with antigens at 6 and 14 weeks of age.

RESULTS

HEU infants demonstrated elevated BCG-specific CD4 and CD8 T-cell proliferative responses at 14 weeks (P  = 0.041 and 0.002, respectively). These responses were significantly increased even after adjusting for birth weight, feeding mode and gestational age. Similar to BCG, increased CD4 and CD8 T-cell proliferation was evident in response to SEB stimulation (P  = 0.004 and 0.002, respectively), although pertussis-specific T cells proliferated comparably between the two groups. Within HEU infants, maternal CD4 cell count and length of antenatal antiretroviral exposure had no effect on T-cell proliferation to BCG or SEB. HIV exposure significantly diminished measurable cytokine polyfunctionality in response to BCG, Bordetella pertussis and SEB stimulation.

CONCLUSION

These data show for the first time, when adjusting for confounders, that exposure to HIV in utero is associated with significant alterations to CD4 and CD8T-cell immune responses in infants to vaccines and nonspecific antigens.

Reconstructing a B-Cell Clonal Lineage. II. Mutation, Selection, and Affinity Maturation

Affinity maturation of the antibody response is a fundamental process in adaptive immunity during which B-cells activated by infection or vaccination undergo rapid proliferation accompanied by the acquisition of point mutations in their rearranged immunoglobulin (Ig) genes and selection for increased affinity for the eliciting antigen. The rate of somatic hypermutation at any position within an Ig gene is known to depend strongly on the local DNA sequence, and Ig genes have region-specific codon biases that influence the local mutation rate within the gene resulting in increased differential mutability in the regions that encode the antigen-binding domains. We have isolated a set of clonally related natural Ig heavy chain-light chain pairs from an experimentally infected influenza patient, inferred the unmutated ancestral rearrangements and the maturation intermediates, and synthesized all the antibodies using recombinant methods. The lineage exhibits a remarkably uniform rate of improvement of the effective affinity to influenza hemagglutinin (HA) over evolutionary time, increasing 1000-fold overall from the unmutated ancestor to the best of the observed antibodies. Furthermore, analysis of selection reveals that selection and mutation bias were concordant even at the level of maturation to a single antigen. Substantial improvement in affinity to HA occurred along mutationally preferred paths in sequence space and was thus strongly facilitated by the underlying local codon biases.

Attenuation of human enterovirus 71 high-replication-fidelity variants in AG129 mice

In a screen for ribavirin resistance, a novel high-fidelity variant of human enterovirus 71 (EV71) with the single amino acid change L123F in its RNA-dependent RNA polymerase (RdRp or 3D) was identified. Based on the crystal structure of EV71 RdRp, L123 locates at the entrance of the RNA template binding channel, which might form a fidelity checkpoint. EV71 RdRp-L123F variants generated less progeny in a guanidine resistance assay and virus populations with lower mutation frequencies in cell culture passage due to their higher replication fidelity. However, compared with wild-type viruses, they did not show growth defects. In vivo infections further revealed that high-fidelity mutations L123F and G64R (previously reported) negatively impacted EV71 fitness and greatly reduced viral pathogenicity alone or together in AG129 mice. Interestingly, a variant with double mutations, RG/B4-G64R/L123F (where RG/B4 is an EV71 genotype B4 virus constructed by reverse genetics [RG])showed higher fidelity in vitro and less virulence in vivo than any one of the above two single mutants. The 50% lethal dose (LD50) of the double mutant increased more than 500 times compared with the LD50 of wild-type RG/B4 in mice. The results indicated that these high-fidelity variants exhibited an attenuated pathogenic phenotype in vivo and offer promise as a live attenuated EV71 vaccine.

IMPORTANCE

The error-prone nature of the RNA-dependent RNA polymerase (RdRp) of RNA viruses during replication results in quasispecies and aids survival of virus populations under a wide range of selective pressures. Virus variants with higher replication fidelity exhibit lower genetic diversity and attenuated pathogenicity in vivo. Here, we identified a novel high-fidelity mutation L123F in the RdRp of human enterovirus 71 (EV71). We further elucidated that EV71 variants with the RdRp-L123F mutation and/or the previously identified high-fidelity mutation RdRp-G64R were attenuated in an AG129 mouse model. As EV71 has emerged as a serious worldwide health threat, especially in developing countries in the Asia-Pacific region, we urgently need EV71 vaccines. Learning from the poliovirus vaccination, we prefer live attenuated EV71 vaccines to inactivated EV71 vaccines in order to effectively control EV71 outbreaks at low cost. Our results imply a new means of attenuating EV71 and reducing its mutation rate at the same time.

Long-term protection in children with meningococcal C conjugate vaccination: lessons learned

Owing to an increase in group C disease, extensive prelicensure studies have been funded by both the UK Department of Health and vaccine manufacturers. These demonstrated the safety and immunogenicity of three candidate meningococcal group C conjugate (MCC) vaccines (two conjugated to CRM(197) and one to tetanus toxoid) in the targeted age groups. Induction of immunological memory in infants and young children was also demonstrated by either a low dose of polysaccharide challenge following primary immunization with MCC or by an increase in avidity indices post-primary to pre-challenge. Immune memory after infant immunization persisted to at least 4 years of age, although antibody persistence in this age group was poor. MCC vaccine was introduced into the UK routine immunization schedule at 2, 3 and 4 months of age in 1999, with a catch-up as a single dose to all children aged 1-18 years with two doses for infants aged 5-11 months. The number of group C cases fell rapidly in the targeted age groups and early analyzes showed high vaccine effectiveness in all age groups together with significant herd immunity. However, when effectiveness was measured again more than 1 year after vaccination, there was a significant decline in all age groups, most marked in infants vaccinated in the routine infant immunization program, for whom there was no demonstrable efficacy after only 1 year and then in toddlers for whom efficacy declined to 61% (95% confidence interval: -327-94) from 88% (95% confidence interval: 65-96) in the first year. However, good disease control was maintained in the UK with only low numbers of vaccine failures. The assumption that immune memory was predictive of long-term protection is incorrect, at least after vaccination in infancy. Persistence of antibody and herd immunity may be more relevant for long-term disease control.

Short communication: antibody responses to human immunodeficiency virus envelope from infections with multiple subtypes utilize the 1F7-idiotypic repertoire

A common idiotype of anti-HIV antibodies (Abs), designated as 1F7, was recently observed on anti-HIV broadly neutralizing Abs (BnAbs). The presence of the 1F7-idiotype on BnAbs suggests that continuous selection of 1F7-idiotypic Abs may allow these clones to achieve the somatic hypermutation necessary for broad neutralization. As the selection of type-specific BnAbs occurs in the setting of infections with a wide array of HIV subtypes, we investigated Abs from subjects infected with diverse subtypes for the selection of 1F7-idiotypic Abs. We observed the 1F7-idiotype on antiviral Abs in infections with various HIV subtypes. Furthermore, gp140-specific 1F7-idiotypic Abs recognized the gp140 antigens from several HIV subtypes. These results demonstrate that the 1F7-idiotype is a common characteristic of Abs from infections with diverse HIV subtypes, and suggests that early cross-reactivity of 1F7-idiotypic clones may act in conjunction with somatic hypermutation to produce BnAbs.

Harnessing DNA-induced immune responses for improving cancer vaccines

DNA vaccines have emerged as an attractive strategy to promote protective cellular and humoral immunity against the encoded antigen. DNA vaccines are easy to generate, inexpensive to produce and purify at large-scale, highly stable and safe. In addition, plasmids used for DNA vaccines act as powerful "danger signals" by stimulating several DNA-sensing innate immune receptors that promote the induction of protective adaptive immunity. The induction of tumor-specific immune responses represents a major challenge for DNA vaccines because most of tumor-associated antigens are normal non-mutated self-antigens. As a consequence, induction of potentially self-reactive T cell responses against such poorly immunogenic antigens is controlled by mechanisms of central and peripheral tolerance as well as tumor-induced immunosuppression. Although several DNA vaccines against cancer have reached clinical testing, disappointing results have been observed. Therefore, the development of new adjuvants that strongly stimulate the induction of antitumor T cell immunity and counteract immune-suppressive regulation is an attractive approach to enhance the potency of DNA vaccines and overcome tumor-associated tolerance. Understanding the DNA-sensing signaling pathways of innate immunity that mediate the induction of T cell responses elicited by DNA vaccines represents a unique opportunity to develop novel adjuvants that enhance vaccine potency. The advance of DNA adjuvants needs to be complemented with the development of potent delivery systems, in order to step toward successful clinical application. Here, we briefly discuss recent evidence showing how to harness DNA-induced immune response to improve the potency of cancer vaccines and counteract tumor-associated tolerance.

The role of social contacts and original antigenic sin in shaping the age pattern of immunity to seasonal influenza

Recent serological studies of seasonal influenza A in humans suggest a striking characteristic profile of immunity against age, which holds across different countries and against different subtypes of influenza. For both H1N1 and H3N2, the proportion of the population seropositive to recently circulated strains peaks in school-age children, reaches a minimum between ages 35–65, then rises again in the older ages. This pattern is little understood. Variable mixing between different age classes can have a profound effect on disease dynamics, and is hence the obvious candidate explanation for the profile, but using a mathematical model of multiple influenza strains, we see that age dependent transmission based on mixing data from social contact surveys cannot on its own explain the observed pattern. Instead, the number of seropositive individuals in a population may be a consequence of ‘original antigenic sin’; if the first infection of a lifetime dominates subsequent immune responses, we demonstrate that it is possible to reproduce the observed relationship between age and seroprevalence. We propose a candidate mechanism for this relationship, by which original antigenic sin, along with antigenic drift and vaccination, results in the age profile of immunity seen in empirical studies.

The way in which a population builds immunity to influenza affects outbreak size and the emergence of new strains. However, although age-specific immunity has been widely discussed for the 2009 influenza pandemic, the age profile of immunity to seasonal influenza remains little understood. In contrast to many infections, the proportion of people immune to recent strains peaks in school-age children then reaches a minimum between ages 35–65, before rising again in older age groups. Our results suggest that rather than variable mixing between different age groups being solely responsible, the pattern may be shaped by an effect known as ‘original antigenic sin’, by which the first infection of a lifetime dictates subsequent immune responses: instead of developing antibodies to every new virus that is encountered, the immune system may reuse the response to a similar virus it has already seen. The framework we describe, which extends theoretical models to allow for comparison with data, also opens the possibility of investigating the mechanisms behind patterns of immunity to other evolving pathogens.

Developing a neonatal HIV vaccine: insights from macaque models of pediatric HIV/AIDS

PURPOSE OF REVIEW

This review analyzes recent findings from nonhuman primate models of HIV/AIDS that are most relevant to developing active neonatal vaccine strategies against HIV breast milk transmission. We focus on studies published from 2005 to early 2007 that have characterized simian immunodeficiency virus or simian/human immunodeficiency virus transmission and the efficacy of HIV vaccine strategies in neonatal macaques.

RECENT FINDINGS

Nonhuman primate models of natural HIV breast milk transmission recapitulate many features of infection in human infants; however, the variation in timing and overall low rate of infection in these models precludes their use in conducting vaccine studies. Oral inoculation of infant macaques with defined viral inocula results in reliable transmission and is an efficient model for evaluating neonatal HIV vaccine strategies. All HIV vaccine strategies tested in neonatal macaques are immunogenic, but only a subset of these vaccines confer significant protection against virus acquisition or simian AIDS after oral challenge.

SUMMARY

Candidate HIV vaccine strategies can elicit virus-specific humoral and cell-mediated immune responses in newborn primates; however, vaccine immunogenicity in infant macaques is not a reliable criterion for predicting a vaccine's efficacy against oral virus challenge exposure.

Immunology of infants through adolescents: responses to emulate for HIV vaccines

PURPOSE OF REVIEW

The major target groups for an HIV vaccine include breastfeeding infants and adolescents. Differential immune maturity in these age groups may significantly impact vaccine efficacy, and should be taken into account when developing vaccines. Here we review these differences, with an emphasis on the immune response to vaccines for HIV and other pathogens. Recommendations for potential adaptation of current HIV vaccines are also made.

RECENT FINDINGS

An effective neonatal vaccine needs to be immunogenic in the presence of maternal antibody, and must induce cytotoxic T-lymphocyte responses, neutralizing antibody responses, both systemic and mucosal. There is renewed hope in the possibility of stimulating neutralizing antibodies with HIV vaccination. DNA vaccines are promising for neonates, but will need appropriate boosting. Certain adjuvants and vector delivery systems are more suitable for neonates. Adolescents may have stronger immune responses to HIV vaccines than adults, and will also require induction of mucosal neutralizing humoral and cellular immunity.

SUMMARY

Some current HIV vaccine strategies may need adaptation for neonates and suitable product development should be accelerated. Vaccines could induce better responses in adolescents and therefore should not be discarded prematurely. Development of vaccines that have potential for these age groups is an urgent global priority.

Measurements of immune responses for establishing correlates of vaccine protection against HIV

Well-defined correlates of protective immunity are an essential component of rational vaccine development. Despite years of basic science and three HIV vaccine efficacy trials, correlates of immunological protection from HIV infection remain undefined. In December 2010, a meeting of scientists engaged in basic and translational work toward developing HIV-1 vaccines was convened. The goal of this meeting was to discuss current opportunities and optimal approaches for defining correlates of protection, both for ongoing and future HIV-1 vaccine candidates; specific efforts were made to engage young scientists. We discuss here the highlights from the meeting regarding the progress made and the way forward for a protective HIV-1 vaccine.

Can mucosal adjuvants contribute to the induction of immunological memory induced via unconjugated T-cell-independent antigens?

Vaccination remains the most cost-effective method for preventing infectious diseases. Key to vaccine design is the development of immunological memory, which is an essential property of the adaptive immune system. Bacterial polysaccharide conjugate vaccines are the gold standard currently used to confer protection of the host by inducing humoral immune responses against T-cell-independent antigens. Conjugate vaccines are effective, but we propose that local mucosal immune responses are likely to also play an important role in inducing immunity, and they have been less explored than systemic and adaptive immune responses. Adjuvants have been used to improve the immune response to vaccine antigens, however, no mucosal adjuvant has been licensed for human use. Here we describe the recent progress in the use of mucosal adjuvants to achieve significant immune responses against T-cell-independent antigens. We also introduce the idea that studying the mechanisms that induce cell sub-populations with strong immunological memory may facilitate the design of novel vaccine formulations, in particular in cases of B-cell unresponsiveness to thymus-independent stimuli.

Measurement of the plasma levels of antibodies against the polymorphic vaccine candidate apical membrane antigen 1 in a malaria-exposed population

Background

Establishing antibody correlates of protection against malaria in human field studies and clinical trials requires, amongst others, an accurate estimation of antibody levels. For polymorphic antigens such as apical membrane antigen 1 (AMA1), this may be confounded by the occurrence of a large number of allelic variants in nature.

Methods

To test this hypothesis, plasma antibody levels in an age-stratified cohort of naturally exposed children from a malaria-endemic area in Southern Ghana were determined by indirect ELISA. Titres against four single PfAMA1 alleles were compared with those against three different allele mixtures presumed to have a wider repertoire of epitope specificities. Associations of antibody levels with the incidence of clinical malaria as well as with previous exposure to parasites were also examined.

Results

Antibody titres against PfAMA1 alleles generally increased with age/exposure while antibody specificity for PfAMA1 variants decreased, implying that younger children (≤ 5 years) elicit a more strain-specific antibody response compared to older children. Antibody titre measurements against the FVO and 3D7 AMA1 alleles gave the best titre estimates as these varied least in pair-wise comparisons with titres against all PfAMA1 allele mixtures. There was no association between antibody levels against any capture antigen and either clinical malaria incidence or parasite density.

Conclusions

The current data shows that levels of naturally acquired antigen-specific antibodies, especially in infants and young children, are dependent on the antigenic allele used for measurement. This may be relevant to the interpretation of antibody titre data from measurements against single PfAMA1 alleles, especially in studies involving infants and young children who have experienced fewer infections.

Optimizing vaccine-induced CD8(+) T-cell immunity: focus on recombinant adenovirus vectors

Recombinant adenoviruses have emerged as promising viral vectors for CD8(+) T-cell vaccines. Our studies have indicated that unlike most acute infections, the CD8(+) T-cell memory population elicited by recombinant human adenovirus serotype 5 (rHuAd5) displays a dominant effector memory phenotype. Persistent, low-level transgene expression from the rHuAd5 vector sustains the CD8(+) T-cell memory population and a nonhematopoietic cell compartment appears to be involved in long-term presentation of adenoviral antigens. Although we are beginning to learn more about the factors that control the maintenance and functionality of memory CD8(+) T cells, we do not yet fully understand what comprises a protective CD8(+) T-cell response. Results from upcoming Phase II clinical trials will be important for determining whether rHuAd5 T-cell vaccines are effective in humans and should help identify correlates of CD8(+) T-cell protection.

The Importance of Animal Models in the Development of Vaccines

Efficient translation of basic vaccine research into clinical therapies greatly depends upon the availability of appropriate animal models. Testing novel vaccine candidates in animal models is a critical step in the development of modern vaccines. Animal models are being used to assess the quality and quantity of the immune response, to identify the optimal route of delivery and formulation, to determine protection from infection and disease transmission, and to evaluate the safety and toxicity of the vaccine formulation. Animal models help to make the translation from basic research to clinical application, and they often allow prediction of the vaccine potential, which helps in predicting the financial risks for vaccine manufacturers. Choosing an appropriate animal model has become increasingly important for the field, as each model has its own advantages and disadvantages. In this review, the criteria for selecting the right animal model, the advantages and disadvantages of various animal models, as well as the future needs for animal models are being discussed.

Age profile of immunity to influenza: effect of original antigenic sin

When multiple infections are possible during an individual's lifetime, as with influenza, a host's history of infection and immunity will determine the result of future exposures. In turn, the suite of varying individual infection histories will shape the population level dynamics of the disease. Exploring the consequences of precisely how immunity is acquired using mathematical models has proven challenging though: if n strains have circulated previously, there are 2(n) combinations of past infection to consider. However, by using an age-structured mathematical model of a disease with multiple strains, we can examine the population immune profile without explicitly keeping track of all possible infection histories. This framework allows previously unknown consequences of assumptions about immune acquisition to be observed. In particular, we see that 'original antigenic sin' can reduce immunity in some age groups: these immune blind spots could be responsible for the unexpectedly high severity of certain past influenza epidemics.

OBTENÇÃO E CARACTERIZAÇÃO DE IMUNÓGENO CONJUGADO DE LIPOPOLISSACARÍDEO DE PSEUDOMONAS AERUGINOSA E ALBUMINA BOVINA

RESUMO A Pseudomonas aeruginosa é agente etiológico de infecções oportunistas, principalmente em pacientes imunocomprometidos. Suas características inerentes em desenvolver resistência aos mais variados tipos de antibacterianos a torna um ponto crítico no controle de infecções. Em animais, os problemas com multirresistência ocorrem principalmente em casos de otite, cistite, úveo-conjuntivite, endometrite e mastite, não havendo vacina comercialmente disponível. No intuito de melhorar a imunogenicidade desse antígeno, foi testada a técnica de conjugação do lipopolissacarídeo (LPS) de P. aeruginosa à albumina bovina (BSA) por aminação redutiva direta utilizando .-periodato de sódio. A conjugação foi avaliada por cromatografia de gel-permeação, dosando-se açúcar e proteína totais, e tanto o LPS quanto a BSA foram identificados em proporções semelhantes. A imunização de camundongos com a vacina conjugada LPS-BSA conferiu títulos de anticorpos aglutinantes contra P. aeruginosa inferiores aos obtidos com a mistura de LPS e BSA livres. Foram 65% e 86% menores na 6ª e na 10ª semanas após o procedimento de hiperimunização, respectivamente. Isto indica que a reação de conjugação resultou em um produto imunogênico, porém, sua qualidade precisará ser melhorada.

Concomitant administration of Mycobacterium bovis BCG with the meningococcal C conjugate vaccine to neonatal mice enhances antibody response and protective efficacy

Mycobacterium bovis BCG is administered to human neonates in many countries worldwide. The objective of the study was to assess if BCG could act as an adjuvant for polysaccharide-protein conjugate vaccines in newborns and thereby induce protective immunity against encapsulated bacteria in early infancy when susceptibility is high. We assessed whether BCG could enhance immune responses to a meningococcal C (MenC) conjugate vaccine, MenC-CRM(197), in mice primed as neonates, broaden the antibody response from a dominant IgG1 toward a mixed IgG1 and IgG2a/IgG2b response, and increase protective efficacy, as measured by serum bactericidal activity (SBA). Two-week-old mice were primed subcutaneously (s.c.) with MenC-CRM(197). BCG was administered concomitantly, a day or a week before MenC-CRM(197). An adjuvant effect of BCG was observed only when it was given concomitantly with MenC-CRM(197), with increased IgG response (P = 0.002) and SBA (8-fold) after a second immunization with MenC-CRM(197) without BCG, indicating increased T-cell help. In neonatal mice (1 week old) primed s.c. with MenC-CRM(197) together with BCG, MenC-polysaccharide (PS)-specific IgG was enhanced compared to MenC-CRM(197) alone (P = 0.0015). Sixteen days after the second immunization with MenC-CRM(197), increased IgG (P < 0.05), IgG1 (P < 0.05), IgG2a (P = 0.06), and IgG2b (P < 0.05) were observed, and only mice primed with MenC-CRM(197) plus BCG showed affinity maturation and detectable SBA (SBA > 128). Thus, vaccination with a meningococcal conjugate vaccine (and possibly with other conjugates) may benefit from concomitant administration of BCG in the neonatal period to accelerate and enhance production of protective antibodies, compared to the current infant administration of conjugate which follows BCG vaccination at birth.

Differences in the priming effect of various clades/subclades of inactivated H5N1 vaccine for booster injection with heterologous clades of vaccine strains

The prime-boost response induced by different combinations of four H5N1 vaccines (NIBRG-14 (clade 1), Indo05/2005(H5N1)/PR8-IBCDC-RG2 (clade 2.1), A/Bar-Headed Goose/Qinhai Lake/1A/05 SJ163222 (clade 2.2), and Anhui01/2005(H5N1)-PR8-IBCDC-RG5 (clade 2.3.4)) was evaluated in mice. Clade 1-primed BALB/c mice showed a booster response to all of the other three H5N1 vaccines. Clade 2.2 vaccine was also a good priming vaccine. However, mice primed with clade 2.1 or clade 2.3.4 vaccine did not respond to booster injection with clade 1 vaccine, suggesting that priming might actually inhibit the booster response with some combinations of vaccines belonging to different clades. Analysis of the mechanism involved showed that lymphocytes from primed mice secreted comparable amounts of cytokines with any combination of priming and booster vaccines. Therefore, impairment of B cell immunity specific to certain booster strains may have been involved.

Design of a protective single-dose intranasal nanoparticle-based vaccine platform for respiratory infectious diseases

Despite the successes provided by vaccination, many challenges still exist with respect to controlling new and re-emerging infectious diseases. Innovative vaccine platforms composed of adaptable adjuvants able to appropriately modulate immune responses, induce long-lived immunity in a single dose, and deliver immunogens in a safe and stable manner via multiple routes of administration are needed. This work describes the development of a novel biodegradable polyanhydride nanoparticle-based vaccine platform administered as a single intranasal dose that induced long-lived protective immunity against respiratory disease caused by Yesinia pestis, the causative agent of pneumonic plague. Relative to the responses induced by the recombinant protein F1-V alone and MPLA-adjuvanted F1-V, the nanoparticle-based vaccination regimen induced an immune response that was characterized by high titer and high avidity IgG1 anti-F1-V antibody that persisted for at least 23 weeks post-vaccination. After challenge, no Y. pestis were recovered from the lungs, livers, or spleens of mice vaccinated with the nanoparticle-based formulation and histopathological appearance of lung, liver, and splenic tissues from these mice post-vaccination was remarkably similar to uninfected control mice.

Sustained high levels of interleukin-6 contribute to the pathogenesis of enterovirus 71 in a neonate mouse model

Enterovirus 71 (EV71) is the major causative agent of hand, foot, and mouth disease (HFMD) in young children and has been consistently associated with the most severe complications of the disease, including central nervous system inflammation and pulmonary edema. Increasing frequency and amplitude of EV71 outbreaks have raised awareness and concerns worldwide. Previous reports proposed that overwhelming virus replication combined with the induction of massive proinflammatory cytokines is responsible for the pathogenicity of EV71. Specifically, elevated interleukin-6 (IL-6) levels were observed consistently in patients and strongly correlated with disease severity. In this study, we show in the neonate mouse model that sustained high levels of IL-6 produced upon EV71 infection lead to severe tissue damage and eventually death of the animals. Administration of anti-IL-6 neutralizing antibodies after the onset of the clinical symptoms successfully improved the survival rates and clinical scores of the infected hosts. Compared to untreated infected controls, anti-IL-6-treated mice displayed reduced tissue damage, absence of splenic atrophy, and increased immune cell activation. In addition, markedly elevated systemic levels of IL-10 were measured in the protected animals. Furthermore, there was no significant difference in virus titers between anti-IL-6-treated mice and untreated mice, indicating that the anti-IL-6 antibody-mediated protection is independent of the virus load. Our findings thus demonstrate that IL-6 plays a major role in EV71-induced immunopathogenesis. As there is still neither vaccine nor treatment available against EV71, anti-IL-6 antibody treatment represents a potential therapeutic approach to providing protection from the most severe complications of the disease.

Contributions of humoral and cellular immunity to vaccine-induced protection in humans

Vaccines play a vital role in protecting the host against infectious disease. The most effective licensed vaccines elicit long-term antigen-specific antibody responses by plasma cells in addition to the development of persisting T cell and B cell memory. The relative contributions of these different immune cell subsets are context-dependent and vary depending on the attributes of the vaccine (i.e., live/attenuated, inactivated, and subunit) as well as the biology of the pathogen in question. For relatively simple vaccines against bacterial antigens (e.g., tetanus toxin) or invariant viruses, the immunological correlates of protection are well-characterized. For more complex vaccines against viruses, especially those that mutate or cause latent infections, it is more difficult to define the specific correlates of immunity. This often requires observational/natural history studies, clinical trials, or experimental evaluation in relevant animal models in order for immunological correlates to be determined or extrapolated. In this review, we will discuss the relative contributions of virus-specific T cell and B cell responses to vaccine-mediated protection against disease.

T cells and follicular dendritic cells in germinal center B-cell formation and selection

Germinal centers (GCs) are specialized microenvironments formed after infection where activated B cells can mutate their B-cell receptors to undergo affinity maturation. A stringent process of selection allows high affinity, non-self-reactive B cells to become long-lived memory B cells and plasma cells. While the precise mechanism of selection is still poorly understood, the last decade has advanced our understanding of the role of T cells and follicular dendritic cells (FDCs) in GC B-cell formation and selection. T cells and non-T-cell-derived CD40 ligands on FDCs are essential for T-dependent (TD) and T-independent GC formation, respectively. TD-GC formation requires Bcl-6-expressing T cells capable of signaling through SAP, which promotes formation of stable T:B conjugates. By contrast, differentiation of B blasts along the extrafollicular pathway is less dependent on SAP. T-follicular helper (Tfh) cell-derived CD40L, interleukin-21, and interleukin-4 play important roles in GC B-cell proliferation, survival, and affinity maturation. A role for FDC-derived integrin signals has also emerged: GC B cells capable of forming an immune synapse with FDCs have a survival advantage. This emerges as a powerful mechanism to ensure death of B cells that bind self-reactive antigen, which would not normally be presented on FDCs.

Mycobacterium tuberculosis directs immunofocusing of CD8+ T cell responses despite vaccination

Vaccines that elicit T cell responses try to mimic protective memory T cell immunity after infection by increasing the frequency of Ag-specific T cells in the immune repertoire. However, the factors that determine immunodominance during infection and after vaccination and the relation between immunodominance and protection are incompletely understood. We previously identified TB10.4(20-28) as an immunodominant epitope recognized by H2-K(d)-restricted CD8(+) T cells after M. tuberculosis infection. Here we report a second epitope, EspA(150-158), that is recognized by a substantial number of pulmonary CD8(+) T cells. The relative abundance of these T cells in the naive repertoire only partially predicts their relative frequency after M. tuberculosis infection. Furthermore, although vaccination with recombinant vaccinia virus expressing these epitopes changes their relative immunodominance in the preinfection T cell repertoire, this change is transient after challenge with M. tuberculosis. We speculate that factors intrinsic to the chronic nature of M. tuberculosis infection establishes the hierarchy of immunodominance and may explain the failure of some vaccines to provide protection.

IgG transmitted from allergic mothers decreases allergic sensitization in breastfed offspring

BACKGROUND

The mechanism(s) responsible for the reduced risk of allergic disease in breastfed infants are not fully understood. Using an established murine model of asthma, we demonstrated previously that resistance to allergic airway disease transmitted from allergic mothers to breastfed offspring requires maternal B cell-derived factors.

OBJECTIVE

The aim of this study was to investigate the role of offspring neonatal Fc receptor for IgG uptake by intestinal epithelial cells (FcRn) in this breast milk transferred protection from allergy.

METHODS

Allergic airway disease was induced during pregnancy in C57BL/6 female mice. These allergic mothers foster nursed naive FcRn+/- or FcRn-/- progeny born to FcRn+/- females that were mated to C57BL/6J-FcRn-/- male mice. In offspring deficient in FcRn, we expected reduced levels of systemic allergen-specific IgG1, a consequence of decreased absorption of maternal IgG from the lumen of the neonatal gastrointestinal tract. Using this model, we were able to investigate how breast milk IgG affected offspring responses to allergic sensitization.

RESULTS

Levels of maternal antibodies absorbed from the breast milk of allergic foster mothers were determined in weanling FcRn-sufficient or -deficient mice. Maternal transmission of allergen-specific IgG1 to breastfed FcRn-/- offspring was at levels 103-104 lower than observed in FcRn+/- or FcRn+/+ mice. Five weeks after weaning, when offspring were 8 wk old, mice were sensitized and challenged to evaluate their susceptibility to develop allergic airway disease. Protection, indicated by reduced parameters of disease (allergen-specific IgE in serum, eosinophilic inflammation in the airways and lung) were evident in FcRn-sufficient mice nursed as neonates by allergic mothers. In contrast, FcRn-deficient mice breastfed by the same mothers acquired limited, if any, protection from development of allergen-specific IgE and associated pathology.

CONCLUSIONS

FcRn expression was a major factor in determining how breastfed offspring of allergic mothers acquired levels of systemic allergen-specific IgG1 sufficient to inhibit allergic sensitization in this model.

Defining the humoral immune response to infectious agents using high-density protein microarrays

A major component of the adaptive immune response to infection is the generation of protective and long-lasting humoral immunity. Traditional approaches to understanding the host's humoral immune response are unable to provide an integrated understanding of the antibody repertoire generated in response to infection. By studying multiple antigenic responses in parallel, we can learn more about the breadth and dynamics of the antibody response to infection. Measurement of antibody production following vaccination is also a gauge for efficacy, as generation of antibodies can protect from future infections and limit disease. Protein microarrays are well suited to identify, quantify and compare individual antigenic responses following exposure to infectious agents. This technology can be applied to the development of improved serodiagnostic tests, discovery of subunit vaccine antigen candidates, epidemiologic research and vaccine development, as well as providing novel insights into infectious disease and the immune system. In this review, we will discuss the use of protein microarrays as a powerful tool to define the humoral immune response to bacteria and viruses.

Humoral and cellular immune responses to measles and tetanus: the importance of elapsed time since last exposure and the nature of the antigen

OBJECTIVE

This study aims to assess the cellular and humoral immune response pre- and post-vaccine rechallenge in healthy adults with previous exposure to measles (virus or vaccine) and different time intervals since last tetanus vaccine.

METHODS

Humoral immunity was tested by ELISA, and cellular immunity was tested by intracellular interferon gamma detection after in vitro stimulation with antigens.

RESULTS

While cellular immunity was comparable among vaccinated individuals and those who had measles, higher antibody levels were found in those who had the disease in the past. Both antibodies and CD4(+) T cell tetanus immune responses depended on elapsed time since last immunization. Following a vaccine booster, an increase in cellular immunity and antibodies was observed to both tetanus and measles. Measles humoral response was much more intense among individuals previously exposed to a wild virus.

CONCLUSIONS

In an era when natural boosters are less frequent, an immune surveillance might be necessary to investigate waning immunity as occurs for tetanus.

Carrier induced epitopic suppression of antibody responses induced by virus-like particles is a dynamic phenomenon caused by carrier-specific antibodies

Pre-existing immunity against vaccine carrier proteins has been reported to inhibit the immune response against antigens conjugated to the same carrier by a process termed carrier induced epitopic suppression (CIES). Hence understanding the phenomenon of CIES is of major importance for the development of conjugate vaccines. Virus-like particles (VLPs) are a novel class of potent immunological carriers which have been successfully used to enhance the antibody response to virtually any conjugated antigen. In the present study we investigated the impact of a pre-existing VLP-specific immune response on the development of antibody responses against a conjugated model peptide after primary, secondary and tertiary immunization. Although VLP-specific immune responses led to reduced peptide-specific antibody titers, we showed that CIES against peptide-VLP conjugates could be overcome by high coupling densities, repeated injections and/or higher doses of conjugate vaccine. Furthermore we dissected VLP-specific immunity by adoptively transferring VLP-specific antibodies, B-cells or T(helper) cells separately into naïve mice and found that the observed CIES against peptide-VLP conjugates was mainly mediated by carrier-specific antibodies.

Rational antibody-based HIV-1 vaccine design: current approaches and future directions

Many antiviral vaccines elicit neutralizing antibodies as a correlate of protection. For HIV, given the huge variability of the virus, it is widely believed that the induction of a broadly neutralizing antibody (bNAb) response will be crucial in a successful vaccine against the virus. Unfortunately, despite many efforts, the development of an immunogen that elicits bNAbs remains elusive. However, recent structural studies of HIV-1 Env proteins, generation of novel bNAbs, maturation of technologies for the isolation of further antibodies, insights into the requirements for antibody-mediated protection, and novel vaccination approaches are providing grounds for renewed optimism.

Mechanisms of anti-D action in the prevention of hemolytic disease of the fetus and newborn: what can we learn from rodent models?

PURPOSE OF REVIEW

Hemolytic disease of the fetus and newborn can be effectively prevented by administration of anti-D to the mother. In this setting, the IgG purified from the plasma of D-alloimmunized donors prevents the maternal immune response to D-positive red blood cells (RBC). Several monoclonal anti-D antibodies have recently been developed for potential use in the setting of hemolytic disease of the fetus and newborn; the functional assays used to assess the potential success of these antibodies have often assumed antigen clearance as the predominant mechanism of anti-D. Unfortunately, the in-vivo success of these monoclonal antibodies has thus far been limited. A similar inhibitory effect of IgG has been observed in animal models with a vast array of different antigens, referred to as antibody-mediated immune suppression (AMIS). Here, studies of AMIS are reviewed and the relevance of these findings for anti-D-mediated immunoprophylaxis is discussed.

RECENT FINDINGS

In animal models of AMIS, IgG-mediated antigen clearance was not sufficient for prevention of the antibody response to RBC. Furthermore, anti-RBC IgG inhibited B-cell priming to foreign RBC, but failed to prevent a T-cell response and immunological memory.

SUMMARY

The applicability of AMIS models for determining the true mechanism of anti-D, though uncertain, may nevertheless provide knowledge as to potential mechanisms of action of anti-RBC antibodies.

How to design effective vaccines: lessons from an old success story

Evaluation of: Gaucher D, Therrien R, Kettaf N et al. Yellow fever vaccine induces integrated multilineage and polyfunctional immune responses. J. Exp. Med. 205(13), 3119-3131 (2008). Despite the successful development of vaccines that are able to elicit potent and protective immune responses, the majority of vaccines were developed empirically and the mechanistic events leading to protective immune responses are often poorly understood. This impedes the development of new prophylactic as well as therapeutic vaccines for infectious diseases and cancer. Gaucher et al. took advantage of the effective yellow fever vaccine 17D to prospectively identify key immunological responses elicited by the vaccine using functional genomics and flow cytometric analysis. The results of the study clearly indicate 'that the immune response to a strong vaccine is preceded by the coordinated induction of master transcription factors that lead to the development of a broad, polyfunctional and persistent immune response integrating all effector cells of the immune system'.