Correlates of protection induced by vaccination

Variable epitope libraries: new vaccine immunogens capable of inducing broad human immunodeficiency virus type 1-neutralizing antibody response

The extreme antigenic variability of human immunodeficiency virus (HIV) leads to immune escape of the virus, representing a major challenge in the design of effective vaccine. We have developed a novel concept for immunogen construction based on introduction of massive mutations within the epitopes targeting antigenically variable pathogens and diseases. Previously, we showed that these immunogens carrying large combinatorial libraries of mutated epitope variants, termed as variable epitope libraries (VELs), induce potent, broad and long lasting CD8+IFN-γ+ T-cell response. Moreover, we demonstrated that these T cells recognize more than 50% of heavily mutated variants (5 out of 10 amino acid positions were mutated in each epitope variant) of HIV-1 gp120 V3 loop-derived cytotoxic T lymphocyte epitope (RGPGRAFVTI) in mice. The constructed VELs had complexities of 10000 and 12500 individual members, generated as plasmid DNA or as M13 phage display combinatorial libraries, respectively, and with structural composition RGPGXAXXXX or XGXGXAXVXI, where X is any of 20 natural amino acids. Here, we demonstrated that sera from mice immunized with these VELs are capable of neutralizing 5 out of 10 viral isolates from Tier 2 reference panel of subtype B envelope clones, including HIV-1 isolates which are known to be resistant to neutralization by several potent monoclonal antibodies, described previously. These data indicate the feasibility of the application of immunogens based on VEL concept as an alternative approach for the development of molecular vaccines against antigenically variable pathogens.

Influenza vaccine for pregnant women in resource-constrained countries: a review of the evidence to inform policy decisions

Seasonal influenza is responsible for three to five million severe cases of disease annually, and up to 500,000 deaths worldwide. Pregnant women and infants suffer disproportionately from severe outcomes of influenza. The excellent safety profile and reliable immunogenicity of inactivated influenza vaccine support WHO recommendations that pregnant women be vaccinated to decrease complications of influenza disease during pregnancy. Nevertheless, influenza vaccine is not routinely used in most low-and middle-income countries and is not widely used in pregnant women worldwide. Two recent prospective, controlled trials of maternal influenza vaccination in Bangladesh and US Native American reservations demonstrated that inactivated influenza vaccine given to pregnant women can decrease laboratory-confirmed influenza virus infection in their newborn children. These studies support consideration of the feasibility of targeted influenza vaccine programs in resource-constrained countries. Platforms exist for the delivery of influenza vaccine to pregnant women worldwide. Even in the least developed countries, an estimated 70% of women receive antenatal care, providing an opportunity for targeted influenza vaccination. Challenges to the introduction of maternal influenza vaccination in resource-constrained countries exist, including issues regarding vaccine formulation, availability, and cost. Nonetheless, maternal influenza vaccination remains an important and potentially cost-effective approach to decrease influenza morbidity in two high-risk groups - pregnant women and young infants.

Upregulation of IL-21 receptor on B cells and IL-21 secretion distinguishes novel 2009 H1N1 vaccine responders from nonresponders among HIV-infected persons on combination antiretroviral therapy

Mechanisms underlying failure of novel 2009 H1N1 influenza vaccine-induced Ab responses in HIV-infected persons are poorly understood. This study prospectively evaluated 16 HIV-infected patients on combination antiretroviral therapy and eight healthy controls (HC) who received a single 15 μg dose of nonadjuvanted novel 2009 H1N1 influenza vaccine during the 2009 H1N1 epidemic. Peripheral blood was collected at baseline (T0) and at 7 d (T1) and 28 d (T2) postvaccination for evaluation of immune responses. Prevaccination hemagglutination inhibition Ab titer was <1:20 in all except one study participant. At T2, all HC and 8 out of 16 patients (50%) developed a vaccine-induced Ab titer of ≥ 1:40. Vaccine responder (R) and vaccine nonresponder patients were comparable at T0 in age, CD4 counts, virus load, and B cell immunophenotypic characteristics. At T2, HC and R patients developed an expansion of phenotypic and functional memory B cells and ex vivo H1N1-stimulated IgG Ab-secreting cells in an ELISPOT assay. The memory B cell response was preceded by a significant expansion of plasmablasts and spontaneous H1N1-specific Ab-secreting cells at T1. At T2, HC and R patients also exhibited significant increases in serum IL-21 levels and in the frequency and mean fluorescence intensity of IL-21R-expressing B cells, which correlated with serum H1N1 Ab titers. Vaccine nonresponder patients failed to develop the above-described vaccine-induced immunologic responses. The novel association of novel 2009 H1N1 vaccine-induced Ab responses with IL-21/IL-21R upregulation and with development of memory B cells and plasmablasts has implications for future research in vaccine design.

Role of immune mechanisms in induction of HIV-1 broadly neutralizing antibodies

Although antibodies can be elicited by HIV-1 infection or immunization, those that are broadly neutralizing (bnAbs) are undetectable in most individuals, and when they do arise in HIV-1 infection, only do so years after transmission. Until recently, the reasons for difficulty in inducing such bnAbs have been obscure. Recent technological advances in isolating bnAbs from rare patients have increased our knowledge of their specificities and features, and along with gene-targeting studies, have also begun uncovering evidence of immunoregulatory roadblocks preventing their induction. One crucial avenue towards developing an effective HIV-1 vaccine is to harness this emerging information into the rational design of immunogens and formulation of adjuvants, such that structural and immunological hurdles to routinely eliciting bnAbs can be overcome.

Vaccine potential of Nipah virus-like particles

Nipah virus (NiV) was first recognized in 1998 in a zoonotic disease outbreak associated with highly lethal febrile encephalitis in humans and a predominantly respiratory disease in pigs. Periodic deadly outbreaks, documentation of person-to-person transmission, and the potential of this virus as an agent of agroterror reinforce the need for effective means of therapy and prevention. In this report, we describe the vaccine potential of NiV virus-like particles (NiV VLPs) composed of three NiV proteins G, F and M. Co-expression of these proteins under optimized conditions resulted in quantifiable amounts of VLPs with many virus-like/vaccine desirable properties including some not previously described for VLPs of any paramyxovirus: The particles were fusogenic, inducing syncytia formation; PCR array analysis showed NiV VLP-induced activation of innate immune defense pathways; the surface structure of NiV VLPs imaged by cryoelectron microscopy was dense, ordered, and repetitive, and consistent with similarly derived structure of paramyxovirus measles virus. The VLPs were composed of all the three viral proteins as designed, and their intracellular processing also appeared similar to NiV virions. The size, morphology and surface composition of the VLPs were consistent with the parental virus, and importantly, they retained their antigenic potential. Finally, these particles, formulated without adjuvant, were able to induce neutralizing antibody response in Balb/c mice. These findings indicate vaccine potential of these particles and will be the basis for undertaking future protective efficacy studies in animal models of NiV disease.

Immunogenicity and safety of an investigational fully liquid hexavalent combination vaccine versus licensed combination vaccines at 6, 10, and 14 weeks of age in healthy South African infants

BACKGROUND

Assessment of primary vaccination of a new fully liquid, hexavalent investigational DTaP-IPV-Hep B-PRP-T vaccine (Hexaxim) in South African infants.

METHODS

Infants were randomized to the following at 6, 10, and 14 weeks of age (Expanded Program on Immunization schedule): DTaP-IPV-Hep B-PRP-T (Group 1; N = 286); DTwP-Hib, hepatitis B, and OPV vaccines (Group 2; N = 286); or DTaP-IPV-Hep B-PRP-T vaccine with hepatitis B vaccine at birth (Group 3; N = 143). Antibody titers were measured before vaccination (pertussis toxoid, filamentous hemagglutinin) and postprimary vaccination (all valences). Noninferiority analyses were performed for Group 1 versus Group 2 for seroprotection rates. Safety was evaluated from parental reports.

RESULTS

Noninferiority (Group 1 minus Group 2) was demonstrated for anti-HBs, -PRP, -diphtheria, -tetanus, and -polio 1, 2, 3 (lower 95% confidence interval for the difference was -8.20 to 3.46). Anti-HBs antibody titers ≥10 mIU/mL and anti-PRP ≥0.15 μg/mL were ≥95.4% in each group. Seroprotection rates were also high for the other antigens. Seroconversion rates (4-fold increase from pre- to postvaccination) were 93.6%, 83.2%, and 95.1% in Groups 1, 2, and 3, respectively, for anti-pertussis toxoid and 93.1%, 57.7%, and 90.0% for anti-filamentous hemagglutinin. Anti-HBs GMTs were 330, 148, and 1913 mIU/mL for Groups 1, 2, and 3, respectively. Reactogenicity was similar in each group. Fever ≥39.0°C occurred in 1.7%, 0.4%, and 0.0% of infants in Groups 1, 2, and 3, respectively; no extensive limb swelling, hypotonic-hyporesponsive episodes, or vaccine-related serious adverse events were reported.

CONCLUSIONS

The new, fully liquid, investigational hexavalent vaccine in the Expanded Program on Immunization schedule, with/without hepatitis B at birth, is highly immunogenic and safe compared with control vaccines, warranting further development.

Immunogenicity and safety study of a new DTaP-IPV-Hep B-PRP-T combined vaccine compared to a licensed DTaP-IPV-Hep B//PRP-T comparator, both concomitantly administered with a 7-valent pneumococcal conjugate vaccine at 2, 4, and 6 months of age in Thai infants

OBJECTIVE

To assess a new, fully-liquid, hexavalent DTaP-IPV-Hep B-PRP-T vaccine (diphtheria toxoid (D), tetanus toxoid (T), acellular pertussis (aP), inactivated poliovirus (IPV), hepatitis B (Hep B), and Haemophilus influenzae type b polysaccharide conjugated to tetanus protein (PRP-T) antigens) compared to a licensed DTaP-IPV-Hep B//PRP-T vaccine following primary series co-administration with a 7-valent pneumococcal conjugate vaccine (PCV7).

METHODS

This was a randomized, phase III, observer-blind study in Thai infants (N=412), who received DTaP-IPV-Hep B-PRP-T or DTaP-IPV-Hep B//PRP-T at 2, 4, and 6 months of age, co-administered with PCV7. All received Hep B at birth. Non-inferiority for Hep B ≥ 10 mIU/ml and PRP ≥0.15μg/ml was analyzed (DTaP-IPV-Hep B-PRP-T relative to DTaP-IPV-Hep B//PRP-T) at 1 month post-primary. Seroprotection/seroconversion and geometric mean titers (GMTs) were analyzed descriptively for all hexavalent components. Safety was evaluated from parental reports.

RESULTS

Anti-Hep B and anti-PRP antibody seroprotection rates were high for DTaP-IPV-Hep B-PRP-T (n=189) and DTaP-IPV-Hep B//PRP-T (n=190), and non-inferiority was demonstrated. Anti-D and anti-T ≥ 0.01 IU/ml, anti-polio types 1, 2, and 3 ≥ 8 (1/dil), and anti-PT and anti-FHA seroconversion were high and similar in each group. For DTaP-IPV-Hep B-PRP-T and DTaP-IPV-Hep B//PRP-T, anti-Hep B ≥ 100 mIU/ml was 98.4% and 99.5% (GMTs 2477 and 2442 mIU/ml), respectively; anti-PRP ≥ 1.0 μg/ml was 85.2% and 71.1% (GMTs 5.07 and 2.41 μg/ml), respectively. Safety profiles were comparable. There were no vaccine-related serious adverse events.

CONCLUSIONS

Following co-administration with PCV7 the investigational DTaP-IPV-Hep B-PRP-T vaccine was safe and immunogenic. Non-inferiority to DTaP-IPV-Hep B//PRP-T was shown for Hep B and PRP.

Enhancing effects of adjuvanted 2009 pandemic H1N1 influenza A vaccine on memory B-cell responses in HIV-infected individuals

OBJECTIVE

To assess the humoral immune response to low-dose AS03-adjuvanted and standard-dose nonadjuvanted 2009 pandemic H1N1 influenza A vaccine in HIV-infected aviremic individuals receiving antiretroviral therapy and in uninfected individuals.

DESIGN

A three-arm study.

SETTING

Two clinics: one at the National Institutes of Health in Bethesda, Maryland, USA; and the other at the Maple Leaf Medical Clinic in Toronto, Ontario, Canada.

PARTICIPANTS

HIV-infected and HIV-uninfected adults.

INTERVENTION

Single intramuscular 15 μg dose of the monovalent inactivated 2009 pandemic H1N1 influenza A vaccine without adjuvant or 3.75 μg dose of the same strain with adjuvant AS03.

MAIN OUTCOMES

Immunogenicity, as measured by hemagglutination inhibition (HAI) antibody titers and vaccine-specific memory B-cell responses.

RESULTS

A total of 74 participants were enrolled. Twenty-one HIV-infected individuals received the low-dose adjuvanted 2009 pandemic H1N1 influenza A vaccine. Twenty-nine HIV-infected and 24 HIV-uninfected individuals received the standard-dose nonadjuvanted vaccine. There were no significant differences in antibody responses at 9 weeks postvaccination among the three groups studied. However, the IgG memory B-cell response against the vaccine was significantly higher in the HIV-infected group that received the low-dose adjuvanted vaccine when compared to the HIV-infected and uninfected groups that received the standard-dose nonadjuvanted vaccine. Conclusions remained unchanged after regression adjustment for age, gender, CD4 T-cell count, and baseline HAI titer.

CONCLUSION

These data suggest that adjuvants could be used to expand coverage through dose sparing and improve humoral immune responses in immunocompromised individuals.

Comparison of a bacteriophage-delivered DNA vaccine and a commercially available recombinant protein vaccine against hepatitis B

A bacteriophage lambda DNA vaccine expressing the small surface antigen (HBsAg) of hepatitis B was compared with Engerix B, a commercially available vaccine based on the homologous recombinant protein (r-HBsAg). Rabbits (five per group) were vaccinated intramuscularly at weeks 0, 5 and 10. Antibody responses against r-HBsAg were measured by indirect enzyme-linked immunosorbent assay, by limiting dilutions and by subtyping. Specific lymphocyte proliferation in vitro was also measured. After one vaccination, three of the five phage-vaccinated rabbits showed a strong antibody response, whereas no r-HBsAg-vaccinated animals responded. Following two vaccinations, all phage-vaccinated animals responded and antibody levels remained high throughout the experiment (220 days total). By 2 weeks after the second vaccination, antibody responses were significantly higher (P<0.05) in the phage-vaccinated group in all tests. After three vaccinations, one out of five r-HBsAg-vaccinated rabbit still failed to respond. The recognized correlate of protection against hepatitis B infection is an antibody response against the HBsAg antigen. When combined with the fact that phage vaccines are potentially cheap to produce and stable at a range of temperatures, the results presented here suggest that further studies into the use of phage vaccination against hepatitis B are warranted.

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.

Vaccine adjuvants: putting innate immunity to work

Adjuvants enhance immunity to vaccines and experimental antigens by a variety of mechanisms. In the past decade, many receptors and signaling pathways in the innate immune system have been defined and these innate responses strongly influence the adaptive immune response. The focus of this review is to delineate the innate mechanisms by which adjuvants mediate their effects. We highlight how adjuvants can be used to influence the magnitude and alter the quality of the adaptive response in order to provide maximum protection against specific pathogens. Despite the impressive success of currently approved adjuvants for generating immunity to viral and bacterial infections, there remains a need for improved adjuvants that enhance protective antibody responses, especially in populations that respond poorly to current vaccines. However, the larger challenge is to develop vaccines that generate strong T cell immunity with purified or recombinant vaccine antigens.

Some unmet challenges in the immunology of viral infections

Viral immunology is a rapidly evolving field. Major strides have been made in our understanding of innate and adaptive immune responses to viruses, largely based on highly reductionistic animal infection models, but more recently in humans, with validation that fundamental immunological concepts do in fact translate into clinical science well. From these studies there has emerged an appreciation of the enormous complexity of the immune response to viral infections as well as the diverse array of strategies developed by viruses to deal with immune detection. In this review, we highlight some of the major challenges we face in unraveling this complexity and summarize current efforts under way to improve the efficacy of viral vaccines.

Evaluating the orthopoxvirus type I interferon-binding molecule as a vaccine target in the vaccinia virus intranasal murine challenge model

The biological threat imposed by orthopoxviruses warrants the development of safe and effective vaccines. We developed a candidate orthopoxvirus DNA-based vaccine, termed 4pox, which targets four viral structural components, A33, B5, A27, and L1. While this vaccine protects mice and nonhuman primates from lethal infections, we are interested in further enhancing its potency. One approach to enhance potency is to include additional orthopoxvirus immunogens. Here, we investigated whether vaccination with the vaccinia virus (VACV) interferon (IFN)-binding molecule (IBM) could protect BALB/c mice against lethal VACV challenge. We found that vaccination with this molecule failed to significantly protect mice from VACV when delivered alone. IBM modestly augmented protection when delivered together with the 4pox vaccine. All animals receiving the 4pox vaccine plus IBM lived, whereas only 70% of those receiving a single dose of 4pox vaccine survived. Mapping studies using truncated mutants revealed that vaccine-generated antibodies spanned the immunoglobulin superfamily domains 1 and 2 and, to a lesser extent, 3 of the IBM. These antibodies inhibited IBM cell binding and IFN neutralization activity, indicating that they were functionally active. This study shows that DNA vaccination with the VACV IBM results in a robust immune response but that this response does not significantly enhance protection in a high-dose challenge model.