Correlates of protection induced by vaccination

Immune imprinting: The persisting influence of the first antigenic encounter with rapidly evolving viruses

Immune imprinting is a phenomenon that stems from the fundamentals of immunological memory. Upon recurrent exposures to an evolving pathogen, the immune system must weigh the benefits of rapidly recalling established antibody repertoires with greater affinity to the initial variant or invest additional time and energy in producing de novo responses specific to the emerging variant. In this review, we delve into the mechanistic complexities of immune imprinting and its role in shaping subsequent immune responses, both de novo and recall, against rapidly evolving respiratory viruses such as influenza and coronaviruses. By exploring the duality of immune imprinting, we examine its potential to both enhance or hinder immune protection against disease, while emphasizing the role of host and viral factors. Finally, we explore how different vaccine platforms may affect immune imprinting and comment on vaccine strategies that can favor de novo variant-specific antibody responses.

A phase 4, open-label study to evaluate the safety and immunogenicity of DTaP5-HBV-IPV-Hib in children previously vaccinated with DTaP2-HBV-IPV-Hib or DTaP5-HBV-IPV-Hib (V419-016)

DTaP5-HBV-IPV-Hib (Vaxelis®) is a hexavalent combination vaccine (HV) indicated in infants and toddlers for the prevention of diphtheria, tetanus, pertussis, hepatitis B, poliomyelitis, and invasive disease due to Haemophilus influenzae type b. Switching between HVs during the childhood vaccination series is sometimes necessary due to, for example, vaccine availability, health-care provider preference, and/or tender awards. The purpose of this study was to describe the safety, tolerability, and immunogenicity of a booster dose of Vaxelis® in participants who previously received a primary infant series of either DTaP2-HBV-IPV-Hib (Hexyon®) or Vaxelis®. Healthy participants approximately 11-13 months of age who previously received a two-dose primary series of Hexyon® (HHV group) or Vaxelis® (VVV group) all received a Vaxelis® booster dose. Immunogenicity was evaluated by measuring antibody levels to individual vaccine antigens approximately 30 days following booster vaccination. Safety was evaluated as the proportion of participants with adverse events (AEs). The proportions of participants with antibody-specific responses for antigens contained in both Vaxelis® and Hexyon® at 30 days post-toddler-booster vaccination with Vaxelis® were comparable between groups, and higher in the VVV group for Vaxelis® antigens PRN and FIM2/3. The overall proportions of participants with AEs were generally comparable between groups. Following a booster dose of Vaxelis®, immune responses were comparable between groups for all shared antigens, and higher in the VVV group for antigens found only in Vaxelis®. The booster was well tolerated in both groups. These data support the use of Vaxelis® as a booster in mixed HV regimens.

Serological investigation on the prevalence of poliovirus in Guangdong province: A cross-sectional study

In 2019, we conducted a cross-sectional study for polio virus seroprevalence in Guangdong province, China. We assessed the positivity rates of poliomyelitis NA and GMT in serum across various demographic groups, and the current findings were compared with pre-switch data from 2014. Using multistage random sampling method, four counties/districts were randomly selected per city, and within each, one general hospital and two township hospitals were chosen. Healthy individuals coming for medical checkups or vaccination were invited. A total of 1318 individual samples were collected and tested. In non-newborn population, age-dependent positivity rates ranged from 77.8% to 100% for PV1 NA and 70.3% to 98.9% for PV3 NA (p < .01). The lowest GMT values for both types (17.03 and 8.46) occurred in the 20 to <30 years age group, while peak GMTs for PV1 and PV3 were observed in 1 to <2 (340.14) and 0 to <1-year (168.90) age groups, respectively. GMTs for PV1 (P = .002) and PV3 (P = .007) in Eastern Guangdong were lower than those in the other three regions. Male participants showed higher GMTs than females (P = .016 and .033, respectively). In newborn population, both males and females showed higher PV1 NA positivity rates and GMTs compared to PV3 (p < .05). Post-switch PV3 NA positivity rates were higher than pre-switch rates (p = .016). GMTs of both PV1 and PV3 were significantly higher post-switch (p < .001). The positivity rates of NAs and GMTs remain high level, which play an important role in resisting poliomyelitis infection. Effect of the converted immunization program was more pronounced than that before.

Serological assessment of the durability of vaccine-mediated protection against SARS-CoV-2 infection

Virus-neutralizing antibodies are often accepted as a correlate of protection against infection, though questions remain about which components of the immune response protect against SARS-CoV-2 infection. In this small observational study, we longitudinally measured spike receptor binding domain (RBD)-specific and nucleocapsid (NP)-specific serum IgG in a human cohort immunized with the Pfizer BNT162b2 vaccine. NP is not encoded in the vaccine, so an NP-specific response is serological evidence of natural infection. A greater than fourfold increase in NP-specific antibodies was used as the serological marker of infection. Using the RBD-specific IgG titers prior to seroconversion for NP, we calculated a protective threshold for RBD-specific IgG. On average, the RBD-specific IgG response wanes below the protective threshold 169 days following vaccination. Many participants without a history of a positive test result for SARS-CoV-2 infection seroconverted for NP-specific IgG. As a group, participants who seroconverted for NP-specific IgG had significantly higher levels of RBD-specific IgG following NP-seroconversion. RBD-specific IgG titers may serve as one correlate of protection against SARS-CoV-2 infection. These titers wane below the proposed protective threshold approximately six months following immunization. Based on serological evidence of infection, the frequency of breakthrough infections and consequently the level of SARS-CoV-2-specific immunity in the population may be higher than what is predicted based on the frequency of documented infections.

Synthesis and Structure Optimization of Star Copolymers as Tunable Macromolecular Carriers for Minimal Immunogen Vaccine Delivery

Minimal immunogen vaccines are being developed to focus antibody responses against otherwise challenging targets, including human immunodeficiency virus (HIV), but multimerization of the minimal peptide immunogen on a carrier platform is required for activity. Star copolymers comprising multiple hydrophilic polymer chains ("arms") radiating from a central dendrimer unit ("core") were recently reported to be an effective platform for arraying minimal immunogens for inducing antibody responses in mice and primates. However, the impact of different parameters of the star copolymer (e.g., minimal immunogen density and hydrodynamic size) on antibody responses and the optimal synthetic route for controlling those parameters remains to be fully explored. We synthesized a library of star copolymers composed of poly[N-(2-hydroxypropyl)methacrylamide] hydrophilic arms extending from poly(amidoamine) dendrimer cores with the aim of identifying the optimal composition for use as minimal immunogen vaccines. Our results show that the length of the polymer arms has a crucial impact on the star copolymer hydrodynamic size and is precisely tunable over a range of 20-50 nm diameter, while the dendrimer generation affects the maximum number of arms (and therefore minimal immunogens) that can be attached to the surface of the dendrimer. In addition, high-resolution images of selected star copolymer taken by a custom-modified environmental scanning electron microscope enabled the acquisition of high-resolution images, providing new insights into the star copolymer structure. Finally, in vivo studies assessing a star copolymer vaccine comprising an HIV minimal immunogen showed the criticality of polymer arm length in promoting antibody responses and highlighting the importance of composition tunability to yield the desired biological effect.

Saponin nanoparticle adjuvants incorporating Toll-like receptor agonists drive distinct immune signatures and potent vaccine responses

Over the past few decades, the development of potent and safe immune-activating adjuvant technologies has become the heart of intensive research in the constant fight against highly mutative and immune evasive viruses such as influenza, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and human immunodeficiency virus (HIV). Herein, we developed a highly modular saponin-based nanoparticle platform incorporating Toll-like receptor agonists (TLRas) including TLR1/2a, TLR4a, and TLR7/8a adjuvants and their mixtures. These various TLRa-saponin nanoparticle adjuvant constructs induce unique acute cytokine and immune-signaling profiles, leading to specific T helper responses that could be of interest depending on the target disease for prevention. In a murine vaccine study, the adjuvants greatly improved the potency, durability, breadth, and neutralization of both COVID-19 and HIV vaccine candidates, suggesting the potential broad application of these adjuvant constructs to a range of different antigens. Overall, this work demonstrates a modular TLRa-SNP adjuvant platform that could improve the design of vaccines and affect modern vaccine development.

Determination of DTaP vaccine potency by multiplex immunogenicity testing using electrochemiluminescence

Lot release testing of diphtheria, tetanus and acellular pertussis vaccines traditionally relied on in vivo protection models involving challenge of laboratory animals with toxins. Meanwhile, many labs have switched to serological testing of these vaccines, which is often performed in separate in vivo assays, even if all components were formulated into one vaccine product. Here we describe the results of simultaneous serological potency determination of diphtheria (D), tetanus (T) and acellular pertussis (aP) antigens obtained following immunization of guinea pigs with multicomponent pediatric and booster vaccines from different manufacturers. The 4th World Health Organization (WHO) International Standard (IS) for diphtheria toxoid (No. 07/216) and the 4th WHO IS for tetanus toxoid (No. 08/218) were used as reference preparations. For aP, a pediatric vaccine batch containing the antigens pertussis toxoid, filamentous hemagglutinin, pertactin and fimbriae proteins type 2/3 was established as internal control. Quantification of IgG against D, T and aP antigens in guinea pig sera was performed using a hexaplex electrochemiluminescence immunoassay. We further provide proof-of-concept using experimental vaccine samples lacking or containing reduced amounts of diphtheria toxoid in the presence of full amounts of tetanus and pertussis antigens and alum adjuvant. Importantly, the assay confirmed dose-response relationships for all antigens tested and was able to detect diphtheria out-of-specification batches. The results confirmed the suitability of the protocol for combined serology batch release testing of DTaP combination vaccines as first measure towards implementation of full in vitro testing of DTaP vaccines. This report summarizes the data and the protocol used for validation prior to implementation of this method in routine batch release testing of DTaP vaccines, which led to replacement of in vivo challenge experiments in our laboratory following the 3 R (replace, reduce, refine) principle.

Picrasidine S Induces cGAS-Mediated Cellular Immune Response as a Novel Vaccine Adjuvant

New adjuvants that trigger cellular immune responses are urgently needed for the effective development of cancer and virus vaccines. Motivated by recent discoveries that show activation of type I interferon (IFN-I) signaling boosts T cell immunity, this study proposes that targeting this pathway can be a strategic approach to identify novel vaccine adjuvants. Consequently, a comprehensive chemical screening of 6,800 small molecules is performed, which results in the discovery of the natural compound picrasidine S (PS) as an IFN-I inducer. Further analysis reveals that PS acts as a powerful adjuvant, significantly enhancing both humoral and cellular immune responses. At the molecular level, PS initiates the activation of the cGAS-IFN-I pathway, leading to an enhanced T cell response. PS vaccination notably increases the population of CD8+ central memory (TCM)-like cells and boosts the CD8+ T cell-mediated anti-tumor immune response. Thus, this study identifies PS as a promising candidate for developing vaccine adjuvants in cancer prevention.

Comparison of uridine and N1-methylpseudouridine mRNA platforms in development of an Andes virus vaccine

The rodent-borne Andes virus (ANDV) causes a severe disease in humans. We developed an ANDV mRNA vaccine based on the M segment of the viral genome, either with regular uridine (U-mRNA) or N1-methylpseudouridine (m1Ψ-mRNA). Female mice immunized by m1Ψ-mRNA developed slightly greater germinal center (GC) responses than U-mRNA-immunized mice. Single cell RNA and BCR sequencing of the GC B cells revealed similar levels of activation, except an additional cluster of cells exhibiting interferon response in animals vaccinated with U-mRNA but not m1Ψ-mRNA. Similar immunoglobulin class-switching and somatic hypermutations were observed in response to the vaccines. Female Syrian hamsters were immunized via a prime-boost regimen with two doses of each vaccine. The titers of glycoprotein-binding antibodies were greater for U-mRNA construct than for m1Ψ-mRNA construct; however, the titers of ANDV-neutralizing antibodies were similar. Vaccinated animals were challenged with a lethal dose of ANDV, along with a naïve control group. All control animals and two animals vaccinated with a lower dose of m1Ψ-mRNA succumbed to infection whereas other vaccinated animals survived without evidence of virus replication. The data demonstrate the development of a protective vaccine against ANDV and the lack of a substantial effect of m1Ψ modification on immunogenicity and protection in rodents.

Immunologic Predictors of Vaccine Responsiveness in Patients With Lymphoma and Chronic Lymphocytic Leukemia

Patients with B-cell lymphomas have altered cellular components of vaccine responses due to malignancy and therapy, and the optimal timing of vaccination relative to therapy remains unknown. Severe acute respiratory syndrome coronavirus 2 vaccines created an opportunity for new insights in vaccine timing because patients were challenged with a novel antigen across multiple phases of treatment. We studied serologic messenger RNA vaccine response in retrospective and prospective cohorts with lymphoma and chronic lymphocytic leukemia, paired with clinical and research immune parameters. Reduced serologic response was observed more frequently during active treatment, but nonresponse was also common within observation and posttreatment groups. Total immunoglobulin A and immunoglobulin M correlated with successful vaccine response. In individuals treated with anti-CD19-directed chimeric antigen receptor-modified T cells, nonresponse was associated with reduced B and T follicular helper cells. Predictors of vaccine response varied by disease and therapeutic group, and therefore further studies of immune health during and after cancer therapies are needed to individualize vaccine timing.

Serosurveillance for Measles and Rubella

Measles and rubella remain global health threats, despite the availability of safe and effective vaccines. Estimates of population immunity are crucial for achieving elimination goals and assessing the impact of vaccination programs, yet conducting well-designed serosurveys can be challenging, especially in resource-limited settings. In this review, we provide a comprehensive assessment of 130 measles and rubella studies published from January 2014 to January 2024. Methodologies and design aspects of serosurveys varied greatly, including sample size, assay type, and population demographics. Most studies utilized enzyme immunoassays for IgG detection. Sample sizes showed diverse sampling methods but favored convenience sampling despite its limitations. Studies spanned 59 countries, predominantly including adults, and revealed disparities in seroprevalence across demographics, regions, and notably among migrants and women. Age-related declines in antibodies were observed, particularly among infants, and correlations between vaccination status and seropositivity varied. We conclude with an outlook on measles and rubella serosurveillance, emphasizing the need for proper survey design and the advantages of standardized, multiplex serology assays.

Advanced Therapies for Human Immunodeficiency Virus

Human Immunodeficiency Virus (HIV) remains a significant global health challenge with approximately 38 million people currently having the virus worldwide. Despite advances in treatment development, the virus persists in the human population and still leads to new infections. The virus has a powerful ability to mutate and hide from the human immune system in reservoirs of the body. Current standard treatment with antiretroviral therapy effectively controls viral replication but requires lifelong adherence and does not eradicate the virus. This review explores the potential of Advanced Therapy Medicinal Products as novel therapeutic approaches to HIV, including cell therapy, immunisation strategies and gene therapy. Cell therapy, particularly chimeric antigen receptor T cell therapy, shows promise in preclinical studies for targeting and eliminating HIV-infected cells. Immunisation therapies, such as broadly neutralising antibodies are being investigated to control viral replication and reduce reservoirs. Despite setbacks in recent trials, vaccines remain a promising avenue for HIV therapy development. Gene therapy using technologies like CRISPR/Cas9 aims to modify cells to resist HIV infection or eliminate infected cells. Challenges such as off-target effects, delivery efficiency and ethical considerations persist in gene therapy for HIV. Future directions require further research to assess the safety and efficacy of emerging therapies in clinical trials. Combined approaches may be necessary to achieve complete elimination of the HIV reservoir. Overall, advanced therapies offer new hope for advancing HIV treatment and moving closer to a cure.

GB and gH/gL fusion machinery: a promising target for vaccines to prevent Epstein-Barr virus infection

Epstein‒Barr virus (EBV) is a double-stranded DNA virus belonging to the family Orthoherpesviridae that is associated with the development of various tumors, such as lymphoma, nasopharyngeal carcinoma, and gastric cancer. There are no uniformly effective treatments for human EBV infection, and vaccines and immunotherapies are currently the main research directions. The glycoproteins gB and gH/gL are surface glycoproteins that are common to all herpesviruses, with subtle differences in structure and function between different viruses. The core membrane fusion machinery constituted by EBV gB and gH/gL is an important target of neutralizing antibodies in epithelial EBV infection due to its essential role in the fusion of viral and target cell membranes. In this article, we review the main modes of EBV infection, the structure and function of the core fusion machinery gB and gH/gL, and the development of neutralizing antibodies and prophylactic vaccines based on this target.

Surface Display of Duck Hepatitis A Virus Type 1 VP1 Protein on Bacillus subtilis Spores Elicits Specific Systemic and Mucosal Immune Responses on Mice

Duck viral hepatitis, primarily caused by duck hepatitis A virus type 1 (DHAV-1), poses a significant threat to the global duck industry. Bacillus subtilis is commonly utilized as a safe probiotic in the development of mucosal vaccines. In this study, a recombinant strain of B. subtilis, designated as B. subtilis RV, was constructed to display the DHAV-1 capsid protein VP1 on its spore surface using the outer coat protein B as an anchoring agent. The immunogenicity of this recombinant strain was evaluated in a mouse model through mixed feeding immunization. The results indicated that B. subtilis RV could elicit specific systemic and mucosal immune responses in mice, as evidenced by the high levels of serum IgG, intestinal secretory IgA, and potent virus-neutralizing antibodies produced. Furthermore, the recombinant strain significantly upregulated the expression levels of IL-2, IL-6, IL-10, TNF-α, and IFN-γ in the intestinal mucosa. Thus, the recombinant strain maintained the balance of the Th1/Th2 immune response and demonstrated an excellent mucosal immune adjuvant function. In summary, this study suggests that B. subtilis RV can be a novel alternative for effectively controlling DHAV-1 infection as a vaccine-based feed additive.

Effectiveness and duration of protection of primary and booster immunisation against meningococcal serogroup C disease with meningococcal conjugate C and ACWY vaccines: Systematic review

OBJECTIVES

To estimate vaccine effectiveness (VE) and duration of protection of single primary and booster immunisation with meningococcal C (MenC) and ACWY (MenACWY) conjugate vaccines in preventing MenC invasive meningococcal disease (IMD).

METHODS

We performed a systematic review on studies of VE and immunogenicity (rSBA/hSBA titers) of participants aged 12-23 months for primary and 6-18 years for booster immunisation (last search: 18 August 2023). Risk of bias and certainty of evidence were evaluated (PROSPERO: CRD42020178773).

RESULTS

We identified 10 studies. Two studies reported VE of primary immunisation with MenC vaccines ranging between 90% (74.9 - 96.1) and 84.1% (41.5 - 95.7) for periods of 2 and 7 years, respectively. Eight studies reported immunogenicity of primary immunisation with MenC and/or MenACWY vaccines, of which two reported -in addition- on booster immunisation. The percentage of participants with protective rSBA titers was high after primary immunisation but waned over the following 6 years. A single booster at the age of 7 years or older seems to prolong protection for several years.

CONCLUSIONS

A single dose of MenC or MenACWY vaccine at 12-23 months of age provides robust protection against MenC IMD. Data on booster immunisation are sparse, but indicate prolonged protection for three years at least.

Opposing effects of pre-existing antibody and memory T cell help on the dynamics of recall germinal centers

Re-exposure to an antigen generates abundant antibody responses and drives the formation of secondary germinal centers (GCs). Recall GCs in mice consist almost entirely of naïve B cells, whereas recall antibodies derive overwhelmingly from memory B cells. Here, we examine this division between cellular and serum compartments. After repeated immunization with the same antigen, tetramer analyses of recall GCs revealed a marked decrease in the ability of B cells in these structures to bind the antigen. Boosting with viral variant proteins restored antigen binding in recall GCs, as did genetic ablation of primary-derived antibody-secreting cells through conditional deletion of Prdm1, demonstrating suppression of GC recall responses by pre-existing antibodies. In hapten-carrier experiments in which B and T cell specificities were uncoupled, memory T cell help allowed B cells with undetectable antigen binding to access GCs. Thus, antibody-mediated feedback steers recall GC B cells away from previously targeted epitopes and enables specific targeting of variant epitopes, with implications for vaccination protocols.

Current challenges and improvements in assessing the immunogenicity of bacterial vaccines

The increase in antimicrobial-resistant bacterial strains has highlighted the need for a new vaccine strategy. The primary goal of a candidate vaccine is to prevent disease, by inducing a persistent immunologic memory, through the activation of pathogen-specific immune response. Antibody titer is the main parameter used to assess the immunogenicity of bacterial vaccine candidates and it is the most widely used as a correlate of protection. On the other hand, the antibody titer alone cannot provide complete information on all the activity mediated by antibodies which can only be assessed by functional assays, like the serum bactericidal assay and the opsonophagocytosis assay. However, due to the involvement of many biological factors, these assays are difficult to standardize. Some improvements have been achieved in recent years, but further optimizations are needed to minimize inter- and intra-laboratories variability and to allow the applicability of these functional assays for the vaccine immunogenicity assessment on a larger scale.

Recombinant H77C gpE1/gpE2 heterodimer elicits superior HCV cross-neutralisation than H77C gpE2 alone

BACKGROUND & AIMS

An optimal HCV vaccine requires the induction of antibodies that neutralise the infectivity of many heterogenous viral isolates. In this study, we have focused on determining the optimal recombinant envelope glycoprotein component to elicit cross-neutralising antibodies against global HCV genotypes. We compared the immunoreactivity and antigenicity of the HCV genotype 1a strain H77C-derived envelope glycoprotein heterodimer gpE1/gpE2 with that of recombinant gpE2 alone.

METHODS

Characterisation of the envelope glycoproteins was accomplished by determining their ability to bind to a panel of broadly cross-neutralising monoclonal antibodies. Immunogenicity was determined by testing the ability of vaccine antisera to neutralise the infectivity in vitro of a panel of pseudotyped HCV particles in which gpE1/gpE2 derived from representative isolates of the major global HCV genotypes were displayed.

RESULTS

gpE1/gpE2 binds to more diverse broadly cross-neutralising antibodies than gpE2 alone and elicits a broader profile of cross-neutralising antibodies in animals, especially against more heterologous, non-1a genotypes. While not all heterologous HCV strains can be potently inhibited in vitro by gpE1/gpE2 antisera derived from a single HCV strain, the breadth of heterologous cross-neutralisation is shown to be substantial.

CONCLUSIONS

Our work supports the inclusion of gpE1/gpE2 in an HCV vaccine in order to maximise the cross-neutralisation of heterogenous HCV isolates. Our data also offers future directions in formulating a cocktail of gpE1/gpE2 antigens from a small selection of HCV genotypes to further enhance cross-neutralisation of global HCV strains and hopefully advance the development of a globally effective HCV vaccine.

IMPACT AND IMPLICATIONS

An HCV vaccine is urgently required to prevent the high global incidence of HCV infection and disease. Since HCV is a highly heterogeneous virus, it is desirable for a vaccine to elicit antibodies that neutralise the infectivity of most global strains. To this end, we have compared the immunoreactivity and antigenicity of recombinant H77C E1E2 heterodimer with that of H77C E2 alone and show that the former exhibits more cross-neutralising epitopes and demonstrates a broader cross-neutralisation profile in vitro. In addition, our data suggests a way to further broaden cross-neutralisation using a combination of E1E2 antigens derived from a few different HCV clades. Our work is relevant for the development of an effective global HCV vaccine.

Comparison of Anti-Hepatitis A Antibody Pharmacokinetics in Healthy Australian Subjects Receiving Standard or Weight-Based Dosing of Polyvalent Immunoglobulin

This randomized controlled trial compared two dosing regimens of the polyvalent immunoglobulin available for hepatitis A post-exposure prophylaxis in Australia. Participants were randomized to receive either 270 IU (standard dose) or 3.375 IU/kg (dose by weight). Quantitative serial serum hepatitis A antibody concentrations were measured at baseline and then on days 1, 3, 7, 28, and 50. Fifteen participants completed the trial. Serum hepatitis A antibody concentrations were not different between the study groups at any time point. Pharmacokinetic parameters estimated from participant data were not different between the study groups. The hepatitis A antibody level of all participants exceeded 10 mIU/mL at day 50. While no difference between dosing regimens was found in this study, further research should examine dosing at the lower limit of current Australian recommendations before making policy decisions.

Modulation of T-Cell-Dependent Humoral Immune Response to Influenza Vaccine by Multiple Antioxidant/Immunomodulatory Micronutrient Supplementation

Notwithstanding prevalence gaps in micronutrients supporting immune functions, the significance of their deficits/supplementation for the efficacy of vaccines is underinvestigated. Thus, the influence of supplementation combining vitamins C and D, zinc, selenium, manganese, and N-acetyl cysteine on immune correlates/surrogates of protection conferred by a quadrivalent influenza vaccine (QIV) in mice was investigated. The supplementation starting 5 days before the first of two QIV injections given 28 days apart increased the serum titres of total and neutralizing IgG against each of four influenza strains from QIV. Accordingly, the frequencies of germinal center B cells, follicular CD4+ T helper (Th) cells, and IL-21-producing Th cells increased in secondary lymphoid organs (SLOs). Additionally, the supplementation improved already increased IgG response to the second QIV injection by augmenting not only neutralizing antibody production, but also IgG2a response, which is important for virus clearance, through favoring Th1 differentiation as indicated by Th1 (IFN-γ)/Th2 (IL-4) signature cytokine level ratio upon QIV restimulation in SLO cell cultures. This most likely partly reflected antioxidant action of the supplement as indicated by splenic redox status analyses. Thus, the study provides a solid scientific background for further research aimed at repurposing the use of this safe and inexpensive micronutrient combination to improve response to the influenza vaccine.

Saponin Nanoparticle Adjuvants Incorporating Toll-Like Receptor Agonists Drive Distinct Immune Signatures and Potent Vaccine Responses

Over the past few decades, the development of potent and safe immune-activating adjuvant technologies has become the heart of intensive research in the constant fight against highly mutative and immune evasive viruses such as influenza, SARS-CoV-2, and HIV. Herein, we developed a highly modular saponin-based nanoparticle platform incorporating toll-like receptor agonists (TLRas) including TLR1/2a, TLR4a, TLR7/8a adjuvants and their mixtures. These various TLRa-SNP adjuvant constructs induce unique acute cytokine and immune-signaling profiles, leading to specific Th-responses that could be of interest depending on the target disease for prevention. In a murine vaccine study, the adjuvants greatly improved the potency, durability, breadth, and neutralization of both COVID-19 and HIV vaccine candidates, suggesting the potential broad application of these adjuvant constructs to a range of different antigens. Overall, this work demonstrates a modular TLRa-SNP adjuvant platform which could improve the design of vaccines for and dramatically impact modern vaccine development.

Teaser

Saponin-TLRa nanoadjuvants provide distinct immune signatures and drive potent, broad, durable COVID-19 and HIV vaccine responses.

A cocktail nanovaccine targeting key entry glycoproteins elicits high neutralizing antibody levels against EBV infection

Epstein-Barr virus (EBV) infects more than 95% of adults worldwide and is closely associated with various malignancies. Considering the complex life cycle of EBV, developing vaccines targeting key entry glycoproteins to elicit robust and durable adaptive immune responses may provide better protection. EBV gHgL-, gB- and gp42-specific antibodies in healthy EBV carriers contributed to sera neutralizing abilities in vitro, indicating that they are potential antigen candidates. To enhance the immunogenicity of these antigens, we formulate three nanovaccines by co-delivering molecular adjuvants (CpG and MPLA) and antigens (gHgL, gB or gp42). These nanovaccines induce robust humoral and cellular responses through efficient activation of dendritic cells and germinal center response. Importantly, these nanovaccines generate high levels of neutralizing antibodies recognizing vulnerable sites of all three antigens. IgGs induced by a cocktail vaccine containing three nanovaccines confer superior protection from lethal EBV challenge in female humanized mice compared to IgG elicited by individual NP-gHgL, NP-gB and NP-gp42. Importantly, serum antibodies elicited by cocktail nanovaccine immunization confer durable protection against EBV-associated lymphoma. Overall, the cocktail nanovaccine shows robust immunogenicity and is a promising candidate for further clinical trials.

Vaccination with nanoparticles displaying gH/gL from Epstein-Barr virus elicits limited cross-protection against rhesus lymphocryptovirus

Epstein-Barr virus (EBV) is associated with infectious mononucleosis, cancer, and multiple sclerosis. A vaccine that prevents infection and/or EBV-associated morbidity is an unmet need. The viral gH/gL glycoprotein complex is essential for infectivity, making it an attractive vaccine target. Here, we evaluate the immunogenicity of a gH/gL nanoparticle vaccine adjuvanted with the Sigma Adjuvant System (SAS) or a saponin/monophosphoryl lipid A nanoparticle (SMNP) in rhesus macaques. Formulation with SMNP elicits higher titers of neutralizing antibodies and more vaccine-specific CD4+ T cells. All but one animal in the SMNP group were infected after oral challenge with the EBV ortholog rhesus lymphocryptovirus (rhLCV). Their immune plasma had a 10- to 100-fold lower reactivity against rhLCV gH/gL compared to EBV gH/gL. Anti-EBV neutralizing monoclonal antibodies showed reduced binding to rhLCV gH/gL, demonstrating that EBV gH/gL neutralizing epitopes are poorly conserved on rhLCV gH/gL. Prevention of rhLCV infection despite antigenic disparity supports clinical development of gH/gL nanoparticle vaccines against EBV.

Identifying Key Drivers of Efficient B Cell Responses: On the Role of T Help, Antigen-Organization, and Toll-like Receptor Stimulation for Generating a Neutralizing Anti-Dengue Virus Response

T help (Th), stimulation of toll-like receptors (pathogen-associated molecular patterns, PAMPs), and antigen organization and repetitiveness (pathogen-associated structural patterns, PASPs) were shown numerous times to be important in driving B-cell and antibody responses. In this study, we dissected the individual contributions of these parameters using newly developed "Immune-tag" technology. As model antigens, we used eGFP and the third domain of the dengue virus 1 envelope protein (DV1 EDIII), the major target of virus-neutralizing antibodies. The respective proteins were expressed alone or genetically fused to the N-terminal fragment of the cucumber mosaic virus (CMV) capsid protein-nCMV, rendering the antigens oligomeric. In a step-by-step manner, RNA was attached as a PAMP, and/or a universal Th-cell epitope was genetically added for additional Th. Finally, a PASP was added to the constructs by displaying the antigens highly organized and repetitively on the surface of CMV-derived virus-like particles (CuMV VLPs). Sera from immunized mice demonstrated that each component contributed stepwise to the immunogenicity of both proteins. All components combined in the CuMV VLP platform induced by far the highest antibody responses. In addition, the DV1 EDIII induced high levels of DENV-1-neutralizing antibodies only if displayed on VLPs. Thus, combining multiple cues typically associated with viruses results in optimal antibody responses.

Predicting Efficacy of a Purified Inactivated Zika Virus Vaccine in Flavivirus-Naïve Humans Using an Immunological Correlate of Protection in Non-Human Primates

A traditional phase 3 clinical efficacy study for a Zika vaccine may be unfeasible because of the current low transmission of Zika virus (ZIKV). An alternative clinical development approach to evaluate Zika vaccine efficacy (VE) is therefore required, delineated in the US FDA's Accelerated Approval Program for licensure, which utilizes an anti-Zika neutralizing antibody (Zika NAb) titer correlated with non-human primate (NHP) protection as a surrogate endpoint. In this accelerated approval approach, the estimation of VE would be inferred from the percentage of phase 3 trial participants achieving the established surrogate endpoint. We provide a statistical framework to predict the probability of protection for human participants vaccinated with a purified inactivated ZIKV vaccine (TAK-426), in the absence of VE measurements, using NHP data under a single-correlate model. Based on a logistic regression (LR) with bias-reduction model, a probability of 90% protection in humans is expected with a ZIKV NAb geometric mean titer (GMT) ≥ 3.38 log10 half-maximal effective concentration (EC50). The predicted probability of protection of TAK-426 against ZIKV infection was determined using the two-parameter LR model that fit the calculated VE in rhesus macaques and the flavivirus-naïve phase 1 trial participants' ZIKV NAb GMTs log10 EC50, measured by a ZIKV reporter virus particle assay, at 1 month post dose 2. The TAK-426 10 µg dose predicted a probability of protection from infection of 98% among flavivirus-naïve phase 1 trial participants.

Immunogenicity, reactogenicity, and IgE-mediated immune responses of a mixed whole-cell and acellular pertussis vaccine schedule in Australian infants: A randomised, double-blind, noninferiority trial

BACKGROUND

In many countries, infant vaccination with acellular pertussis (aP) vaccines has replaced use of more reactogenic whole-cell pertussis (wP) vaccines. Based on immunological and epidemiological evidence, we hypothesised that substituting the first aP dose in the routine vaccination schedule with wP vaccine might protect against IgE-mediated food allergy. We aimed to compare reactogenicity, immunogenicity, and IgE-mediated responses of a mixed wP/aP primary schedule versus the standard aP-only schedule.

METHODS AND FINDINGS

OPTIMUM is a Bayesian, 2-stage, double-blind, randomised trial. In stage one, infants were assigned (1:1) to either a first dose of a pentavalent wP combination vaccine (DTwP-Hib-HepB, Pentabio PT Bio Farma, Indonesia) or a hexavalent aP vaccine (DTaP-Hib-HepB-IPV, Infanrix hexa, GlaxoSmithKline, Australia) at approximately 6 weeks old. Subsequently, all infants received the hexavalent aP vaccine at 4 and 6 months old as well as an aP vaccine at 18 months old (DTaP-IPV, Infanrix-IPV, GlaxoSmithKline, Australia). Stage two is ongoing and follows the above randomisation strategy and vaccination schedule. Ahead of ascertainment of the primary clinical outcome of allergist-confirmed IgE-mediated food allergy by 12 months old, here we present the results of secondary immunogenicity, reactogenicity, tetanus toxoid IgE-mediated immune responses, and parental acceptability endpoints. Serum IgG responses to diphtheria, tetanus, and pertussis antigens were measured using a multiplex fluorescent bead-based immunoassay; total and specific IgE were measured in plasma by means of the ImmunoCAP assay (Thermo Fisher Scientific). The immunogenicity of the mixed schedule was defined as being noninferior to that of the aP-only schedule using a noninferiority margin of 2/3 on the ratio of the geometric mean concentrations (GMR) of pertussis toxin (PT)-IgG 1 month after the 6-month aP. Solicited adverse reactions were summarised by study arm and included all children who received the first dose of either wP or aP. Parental acceptance was assessed using a 5-point Likert scale. The primary analyses were based on intention-to-treat (ITT); secondary per-protocol (PP) analyses were also performed. The trial is registered with ANZCTR (ACTRN12617000065392p). Between March 7, 2018 and January 13, 2020, 150 infants were randomised (75 per arm). PT-IgG responses of the mixed schedule were noninferior to the aP-only schedule at approximately 1 month after the 6-month aP dose [GMR = 0·98, 95% credible interval (0·77 to 1·26); probability (GMR > 2/3) > 0·99; ITT analysis]. At 7 months old, the posterior median probability of quantitation for tetanus toxoid IgE was 0·22 (95% credible interval 0·12 to 0·34) in both the mixed schedule group and in the aP-only group. Despite exclusions, the results were consistent in the PP analysis. At 6 weeks old, irritability was the most common systemic solicited reaction reported in wP (65 [88%] of 74) versus aP (59 [82%] of 72) vaccinees. At the same age, severe systemic reactions were reported among 14 (19%) of 74 infants after wP and 8 (11%) of 72 infants after aP. There were 7 SAEs among 5 participants within the first 6 months of follow-up; on blinded assessment, none were deemed to be related to the study vaccines. Parental acceptance of mixed and aP-only schedules was high (71 [97%] of 73 versus 69 [96%] of 72 would agree to have the same schedule again).

CONCLUSIONS

Compared to the aP-only schedule, the mixed schedule evoked noninferior PT-IgG responses, was associated with more severe reactions, but was well accepted by parents. Tetanus toxoid IgE responses did not differ across the study groups.

TRIAL REGISTRATION

Trial registered at the Australian and New Zealand Clinical 207 Trial Registry (ACTRN12617000065392p).

Assessing vaccine-induced immunity against pneumococcus, hepatitis A and B over a 9-year follow-up in pediatric liver transplant recipients: A nationwide retrospective study

Pediatric liver transplant recipients are particularly at risk of infections. The most cost-effective way to prevent infectious complications is through vaccination, which can potentially prevent infections due to hepatitis B (HBV) virus, hepatitis A virus (HAV), and invasive pneumococcal diseases. Here, we performed a retrospective analysis of HBV, HAV, and pneumococcal immunity in pediatric liver transplant recipients between January 1, 2009, and December 31, 2020, to collect data on immunization and vaccine serology. A total of 94% (58/62) patients had available vaccination records. At transplant, 90% (45/50) were seroprotected against HBV, 63% (19/30) against HAV, and 78% (18/23) had pneumococcal immunity, but immunity against these 3 pathogens remained suboptimal during the 9-year follow-up. A booster vaccine was administered to only 20% to 40% of patients. Children who had received >4 doses of HBV vaccine and > 2 doses of HAV vaccine pretransplant displayed a higher overall seroprotection over time post-solid organ transplant. Our findings suggest that a serology-based approach should be accompanied by a more systematic follow-up of vaccination, with special attention paid to patients with an incomplete vaccination status at time of transplant.

Heterogeneity and Hierarchy of Immune Response to Primary Immunization in HIV-Infected Children on HAART and the Impact of an Additional Dose of Vaccine

The nature of vaccine response inferiority is not well studied in children living with HIV (CLHIV). The authors investigated Hepatitis B Virus (HBV) and Diphtheria/Pertussis/Tetanus toxoid (DPT) vaccination responses following primary immunization in CLHIV (n = 42) and healthy controls (HC) (n = 38) and the effect of an additional vaccine dose. Antibody responses, CD4 and HBV-specific T/B cells were analysed using CMIA/ELISA and flow-cytometry. CLHIV had significantly lower baseline median antibody titres for all vaccines than HC (p <0.02). Differential seroprotection rates observed in CLHIV were, 4.8% for pertussis; 9.5% for HBV; 26.2% for diphtheria and 66.7% for tetanus. WHO staging significantly influenced anti-HBs levels (p = 0.0095). HBsAg-specific CD4+T-cells were significantly higher in CLHIV than HC (p = 0.042). An additional vaccine dose (HBV and Tdap) conferred a higher protection rate for tetanus and diphtheria (p <0.040) in CLHIV. These findings suggest that CLHIV exhibit a hierarchy of vaccine responses affecting antibody levels and protection rate, which was rescued by administering additional vaccine dose.

COVID-19 Vaccination Strategies in the Endemic Period: Lessons from Influenza

Coronavirus disease 2019 (COVID-19) is a highly contagious zoonotic respiratory disease with many similarities to influenza. Effective vaccines are available for both; however, rapid viral evolution and waning immunity make them virtually impossible to eradicate with vaccines. Thus, the practical goal of vaccination is to reduce the incidence of serious illnesses and death. Three years after the introduction of COVID-19 vaccines, the optimal vaccination strategy in the endemic period remains elusive, and health authorities worldwide have begun to adopt various approaches. Herein, we propose a COVID-19 vaccination strategy based on the data available until early 2024 and discuss aspects that require further clarification for better decision making. Drawing from comparisons between COVID-19 and influenza vaccination strategies, our proposed COVID-19 vaccination strategy prioritizes high-risk groups, emphasizes seasonal administration aligned with influenza vaccination campaigns, and advocates the co-administration with influenza vaccines to increase coverage.

Serological Correlates of Protection Induced by COVID-19 Vaccination in the Working Age Population: A Systematic Review and Meta-Analysis

COVID-19 vaccines represent effective public health measures in contrasting the pandemic worldwide. However, protection at the individual-level, which is of crucial importance from an occupational health perspective, is commonly assessed by a serological correlate of protection (CoP) for SARS-CoV-2, which has not yet been determined. The emergence of variants of concern (VOCs) that have shown high rates of breakthrough infections has further complicated the understanding of immune protection against infection. To define a potential serological correlate of protection induced by the COVID-19 vaccination, a systematic review and meta-analysis was performed to summarize the evidence concerning the binding antibody concentration corresponding to a protective effect. Eighteen and four studies were included in the qualitative and quantitative analyses, respectively. The protection against infection was shown for anti-receptor-binding domain (RBD) titers ranging from 154 to 168.2 binding antibody units (BAU)/mL during the pre-Omicron period, while ranging from 1235 to 3035 BAU/mL in the Omicron period. Pooling the results from the studies concerning anti-RBD and anti-Spike antibody titer, we found a mean of 1341.5 BAU/mL and 1400.1 BAU/mL, respectively. These findings suggest that although a fixed serological threshold corresponding to protection against different SARS-CoV-2 variants is not yet definable, higher binding antibody concentrations are associated with increased protective effects.

Antecedents of major depressive, bipolar, and psychotic disorders: A systematic review and meta-analysis of prospective studies

Major depressive, bipolar, or psychotic disorders are preceded by earlier manifestations in behaviours and experiences. We present a synthesis of evidence on associations between person-level antecedents (behaviour, performance, psychopathology) in childhood, adolescence, or early adulthood and later onsets of major depressive disorder, bipolar disorder, or psychotic disorder based on prospective studies published up to September 16, 2022. We screened 11,342 records, identified 460 eligible publications, and extracted 570 risk ratios quantifying the relationships between 52 antecedents and onsets in 198 unique samples with prospective follow-up of 122,766 individuals from a mean age of 12.4 to a mean age of 24.8 for 1522,426 person years of follow-up. We completed meta-analyses of 12 antecedents with adequate data. Psychotic symptoms, depressive symptoms, anxiety, disruptive behaviors, affective lability, and sleep problems were transdiagnostic antecedents associated with onsets of depressive, bipolar, and psychotic disorders. Attention-deficit/hyperactivity and hypomanic symptoms specifically predicted bipolar disorder. While transdiagnostic and diagnosis-specific antecedents inform targeted prevention and help understand pathogenic mechanisms, extensive gaps in evidence indicate potential for improving early risk identification.

Raising Epidemiological Awareness: Assessment of Measles/MMR Susceptibility in Highly Vaccinated Clusters within the Hungarian and Croatian Population-A Sero-Surveillance Analysis

Perceptions of the complete eradication of vaccine-preventable diseases such as measles, mumps, and rubella (MMR) may foster complacency and compromise vaccination efforts. Decreased measles vaccination rates during the COVID-19 pandemic have heightened the risk of outbreaks, even in adequately vaccinated populations. To address this, we have aligned with ECDC recommendations, leveraging previous cross-border sero-epidemiological assessments between Pécs, Hungary, and Osijek, Croatia, to identify latent risk groups and uncover potential parallels between our nations. Testing 2680 Hungarian and 1764 Croatian serum samples for anti-MMR IgG via ELISAs revealed anti-measles seropositivity ratios below expectations in Croatian cohorts aged ~20-30 (75.7%), ~30-40 (77.5%) and ~40-50 years (73.3%). Similarly, Hungarian samples also showed suboptimal seropositivity ratios in the ~30-40 (80.9%) and ~40-50 (87.3%) age groups. Considering mumps- and rubella-associated seropositivity trends, in both examined populations, individuals aged ~30-50 years exhibited the highest vulnerability. Additionally, we noted congruent seropositivity trends across both countries, despite distinct immunization and epidemiological contexts. Therefore, we propose expanding research to encompass the intricate dynamics of vaccination, including waning long-term immunity. This understanding could facilitate targeted interventions and bolster public awareness. Our findings underscore persistent challenges in attaining robust immunity against measles despite vaccination endeavors.

Correlates of protection against symptomatic SARS-CoV-2 in vaccinated children

The paucity of information on longevity of vaccine-induced immune responses and uncertainty of the correlates of protection hinder the development of evidence-based COVID-19 vaccination policies for new birth cohorts. Here, to address these knowledge gaps, we conducted a cohort study of healthy 5-12-year-olds vaccinated with BNT162b2. We serially measured binding and neutralizing antibody titers (nAbs), spike-specific memory B cell (MBC) and spike-reactive T cell responses over 1 year. We found that children mounted antibody, MBC and T cell responses after two doses of BNT162b2, with higher antibody and T cell responses than adults 6 months after vaccination. A booster (third) dose only improved antibody titers without impacting MBC and T cell responses. Among children with hybrid immunity, nAbs and T cell responses were highest in those infected after two vaccine doses. Binding IgG titers, MBC and T cell responses were predictive, with T cells being the most important predictor of protection against symptomatic infection before hybrid immunity; nAbs only correlated with protection after hybrid immunity. The stable MBC and T cell responses over time suggest sustained protection against symptomatic SARS-CoV-2 infection, even when nAbs wane. Booster vaccinations do not confer additional immunological protection to healthy children.

Mucosal vaccines for viral diseases: Status and prospects

Virus-associated infectious diseases are highly detrimental to human health and animal husbandry. Among all countermeasures against infectious diseases, prophylactic vaccines, which developed through traditional or novel approaches, offer potential benefits. More recently, mucosal vaccines attract attention for their extraordinary characteristics compared to conventional parenteral vaccines, particularly for mucosal-related pathogens. Representatively, coronavirus disease 2019 (COVID-19), a respiratory disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), further accelerated the research and development efforts for mucosal vaccines by thoroughly investigating existing strategies or involving novel techniques. While several vaccine candidates achieved positive progresses, thus far, part of the current COVID-19 mucosal vaccines have shown poor performance, which underline the need for next-generation mucosal vaccines and corresponding platforms. In this review, we summarized the typical mucosal vaccines approved for humans or animals and sought to elucidate the underlying mechanisms of these successful cases. In addition, mucosal vaccines against COVID-19 that are in human clinical trials were reviewed in detail since this public health event mobilized all advanced technologies for possible solutions. Finally, the gaps in developing mucosal vaccines, potential solutions and prospects were discussed. Overall, rational application of mucosal vaccines would facilitate the establishing of mucosal immunity and block the transmission of viral diseases.

Selection of positive controls and their impact on anti-drug antibody assay performance

Development of assays to reliably identify and characterize anti-drug antibodies (ADAs) depends on positive control anti-idiotype (anti-id) reagents, which are used to demonstrate that the standards recommended by regulatory authorities are met. This work employs a set of therapeutic antibodies under clinical development and their corresponding anti-ids to investigate how different positive control reagent properties impact ADA assay development. Positive controls exhibited different response profiles and apparent assay analytical sensitivity values depending on assay format. Neither anti-id affinity for drug, nor sensitivity in direct immunoassays related to sensitivity in ADA assays. Anti-ids were differentially able to detect damage to drug conjugates used in bridging assays and were differentially drug tolerant. These parameters also failed to relate to assay sensitivity, further complicating selection of anti-ids for use in ADA assay development based on functional characteristics. Given this variability among anti-ids, alternative controls that could be employed across multiple antibody drugs were investigated as a more uniform means to define ADA detection sensitivity across drug products and assay protocols, which could help better relate assay results to clinical risks of ADA responses. Overall, this study highlights the importance of positive control selection to reliable detection and clinical interpretation of the presence and magnitude of ADA responses.

Therapeutic vaccines for herpesviruses

Herpesviruses establish latent infections, and most reactivate frequently, resulting in symptoms and virus shedding in healthy individuals. In immunocompromised patients, reactivating virus can cause severe disease. Persistent EBV has been associated with several malignancies in both immunocompromised and nonimmunocompromised persons. Reactivation and shedding occur with most herpesviruses, despite potent virus-specific antibodies and T cell immunity as measured in the blood. The licensure of therapeutic vaccines to reduce zoster indicates that effective therapeutic vaccines for other herpesviruses should be feasible. However, varicella-zoster virus is different from other human herpesviruses in that it is generally only shed during varicella and zoster. Unlike prophylactic vaccines, in which the correlate of immunity is antibody function, T cell immunity is the correlate of immunity for the only effective therapeutic herpesvirus vaccine-zoster vaccine. While most studies of therapeutic vaccines have measured immunity in the blood, cellular immunity at the site of reactivation is likely critical for an effective therapeutic vaccine for certain viruses. This Review summarizes the status of therapeutic vaccines for herpes simplex virus, cytomegalovirus, and Epstein-Barr virus and proposes approaches for future development.

High-resolution African HLA resource uncovers HLA-DRB1 expression effects underlying vaccine response

How human genetic variation contributes to vaccine effectiveness in infants is unclear, and data are limited on these relationships in populations with African ancestries. We undertook genetic analyses of vaccine antibody responses in infants from Uganda (n = 1391), Burkina Faso (n = 353) and South Africa (n = 755), identifying associations between human leukocyte antigen (HLA) and antibody response for five of eight tested antigens spanning pertussis, diphtheria and hepatitis B vaccines. In addition, through HLA typing 1,702 individuals from 11 populations of African ancestry derived predominantly from the 1000 Genomes Project, we constructed an imputation resource, fine-mapping class II HLA-DR and DQ associations explaining up to 10% of antibody response variance in our infant cohorts. We observed differences in the genetic architecture of pertussis antibody response between the cohorts with African ancestries and an independent cohort with European ancestry, but found no in silico evidence of differences in HLA peptide binding affinity or breadth. Using immune cell expression quantitative trait loci datasets derived from African-ancestry samples from the 1000 Genomes Project, we found evidence of differential HLA-DRB1 expression correlating with inferred protection from pertussis following vaccination. This work suggests that HLA-DRB1 expression may play a role in vaccine response and should be considered alongside peptide selection to improve vaccine design.

Humoral and cellular immune responses induced by serogroup W135 meningococcal conjugate and polysaccharide vaccines

Investigating the mechanisms by which W135 meningococcal conjugate (PSW135-TT) activates adaptive immune responses in mice can provide a comprehensive understanding of the immune mechanisms of bacterial polysaccharide conjugate vaccines. We compared B-cell and T-cell immune responses immunized with W135 meningococcal capsular polysaccharides (PSW135), tetanus toxoid (TT) and PSW135-TT in mice. The results showed that PSW135-TT could induce higher PSW135-specific and TT-specific IgG antibodies with a significant enhancement after two doses. All serum antibodies immunized with PSW135- TT had strong bactericidal activity, whereas none of the serum antibodies immunized with PSW135 had bactericidal activity. Besides, IgM and IgG antibodies immunized with PSW135-TT after two doses were positively correlated with the titer of bactericidal antibodies. We also found Th cells favored Th2 humoral immune responses in PSW135-TT, PSW135, and TT-immunized mice, especially peripheral blood lymphocytes. Furthermore, PSW135-TT and TT could effectively activate bone marrow derived dendritic cells (BMDCs) and promote BMDCs to highly express major histocompatibility complex Ⅱ (MHCⅡ), CD86 and CD40 molecules in mice, whereas PSW135 couldn't. These data verified the typical characteristics of PSW135-TT and TT as T cell dependent antigen (TD-Ag) and PSW135 as T cell independent antigen (TI-Ag), which will be very helpful for further exploration of the immune mechanism of polysaccharide-protein conjugate vaccines and improvement of the quality of bacterial polysaccharide conjugate vaccines in future.

Adaptive immune responses to two-dose COVID-19 vaccine series in healthy Canadian adults ≥ 50 years: a prospective, observational cohort study

To evaluate immune responses to COVID-19 vaccines in adults aged 50 years and older, spike protein (S)-specific antibody concentration, avidity, and function (via angiotensin-converting enzyme 2 (ACE2) inhibition surrogate neutralization and antibody dependent cellular phagocytosis (ADCP)), as well as S-specific T cells were quantified via activation induced marker (AIM) assay in response to two-dose series. Eighty-four adults were vaccinated with either: mRNA/mRNA (mRNA-1273 and/or BNT162b2); ChAdOx1-S/mRNA; or ChAdOx1-S/ChAdOx1-S. Anti-S IgG concentrations, ADCP scores and ACE2 inhibiting antibody concentrations were highest at one-month post-second dose and declined by four-months post-second dose for all groups. mRNA/mRNA and ChAdOx1-S/mRNA schedules had significantly higher antibody responses than ChAdOx1-S/ChAdOx1-S. CD8+ T-cell responses one-month post-second dose were associated with increased ACE2 surrogate neutralization. Antibody avidity (total relative avidity index) did not change between one-month and four-months post-second dose and did not significantly differ between groups by four-months post-second dose. In determining COVID-19 correlates of protection, a measure that considers both antibody concentration and avidity should be considered.

A TriAdj-Adjuvanted Chlamydia trachomatis CPAF Protein Vaccine Is Highly Immunogenic in Pigs

Chlamydia trachomatis (Ct) infections are the most common sexually transmitted infection (STI). Despite effective antibiotics for Ct, undetected infections or delayed treatment can lead to infertility, ectopic pregnancies, and chronic pelvic pain. Besides humans, chlamydia poses similar health challenges in animals such as C. suis (Cs) in pigs. Based on the similarities between humans and pigs, as well as their chlamydia species, we use pigs as a large biomedical animal model for chlamydia research. In this study, we used the pig model to develop a vaccine candidate against Ct. The vaccine candidate consists of TriAdj-adjuvanted chlamydial-protease-like activity factor (CPAF) protein. We tested two weekly administration options-twice intranasal (IN) followed by twice intramuscular (IM) and twice IM followed by twice IN. We assessed the humoral immune response in both serum using CPAF-specific IgG (including antibody avidity determination) and also in cervical and rectal swabs using CPAF-specific IgG and IgA ELISAs. The systemic T-cell response was analyzed following in vitro CPAF restimulation via IFN-γ and IL-17 ELISpots, as well as intracellular cytokine staining flow cytometry. Our data demonstrate that while the IN/IM vaccination mainly led to non-significant systemic immune responses, the vaccine candidate is highly immunogenic if administered IM/IN. This vaccination strategy induced high serum anti-CPAF IgG levels with strong avidity, as well as high IgA and IgG levels in vaginal and rectal swabs and in uterine horn flushes. In addition, this vaccination strategy prompted a pronounced cellular immune response. Besides inducing IL-17 production, the vaccine candidate induced a strong IFN-γ response with CD4 T cells. In IM/IN-vaccinated pigs, these cells also significantly downregulated their CCR7 expression, a sign of differentiation into peripheral-tissue-homing effector/memory cells. Conclusively, this study demonstrates the strong immunogenicity of the IM/IN-administered TriAdj-adjuvanted Ct CPAF vaccine candidate. Future studies will test the vaccine efficacy of this promising Ct vaccine candidate. In addition, this project demonstrates the suitability of the Cs pre-exposed outbred pig model for Ct vaccine development. Thereby, we aim to open the bottleneck of large animal models to facilitate the progression of Ct vaccine candidates into clinical trials.

Dengue virus IgG and serotype-specific neutralizing antibody titers measured with standard and mature viruses are associated with protection

Recent work demonstrates the limitations of the standard dengue virus (DENV) neutralization assay to predict protection against dengue. We perform studies to compare how a commercial IgG ELISA, envelope domain III (EDIII) or non-structural protein 1 (NS1) binding antibodies, and titers from plaque reduction neutralization tests (PRNTs) using reference standard and clinical mature viruses are associated with dengue disease. Healthy children (n = 1,206) in Cebu, Philippines were followed for 5 years. High ELISA values (≥3) were associated with reduced dengue probability relative to naïve children (3% vs. 10%, p = 0.008), but antibody binding EDIII or NS1 from each serotype had no association. High standard and mature geometric mean PRNT titers were associated with reduced dengue disease overall (p < 0.01), and high DENV2 and DENV3 titers in both assays provided protection against the matched serotype (p < 0.02). However, while 52% of dengue cases had standard virus PRNT titers > 100, only 2% of cases had mature virus PRNT titers > 100 (p < 0.001), indicating a lower, more consistent threshold for protection. Each assay may be useful for different purposes as correlates of protection in population and vaccine trials.

Vaccines Induce Homeostatic Immunity, Generating Several Secondary Benefits

The optimal immune response eliminates invading pathogens, restoring immune equilibrium without inflicting undue harm to the host. However, when a cascade of immunological reactions is triggered, the immune response can sometimes go into overdrive, potentially leading to harmful long-term effects or even death. The immune system is triggered mostly by infections, allergens, or medical interventions such as vaccination. This review examines how these immune triggers differ and why certain infections may dysregulate immune homeostasis, leading to inflammatory or allergic pathology and exacerbation of pre-existing conditions. However, many vaccines generate an optimal immune response and protect against the consequences of pathogen-induced immunological aggressiveness, and from a small number of unrelated pathogens and autoimmune diseases. Here, we propose an "immuno-wave" model describing a vaccine-induced "Goldilocks immunity", which leaves fine imprints of both pro-inflammatory and anti-inflammatory milieus, derived from both the innate and the adaptive arms of the immune system, in the body. The resulting balanced, 'quiet alert' state of the immune system may provide a jump-start in the defense against pathogens and any associated pathological inflammatory or allergic responses, allowing vaccines to go above and beyond their call of duty. In closing, we recommend formally investigating and reaping many of the secondary benefits of vaccines with appropriate clinical studies.

Outer membrane vesicles derived from Bordetella pertussis are potent adjuvant that drive Th1-biased response

For several years, we have been committed to exploring the potential of Bordetella pertussis-derived outer membrane vesicles (OMVBp) as a promising third-generation vaccine against the reemerging pertussis disease. The results of our preclinical trials not only confirm its protective capacity against B. pertussis infection but also set the stage for forthcoming human clinical trials. This study delves into the examination of OMVBp as an adjuvant. To accomplish this objective, we implemented a two-dose murine schedule to evaluate the specific immune response induced by formulations containing OMVBp combined with 3 heterologous immunogens: Tetanus toxoid (T), Diphtheria toxoid (D), and the SARS-CoV-2 Spike protein (S). The specific levels of IgG, IgG1, and IgG2a triggered by the different tested formulations were evaluated using ELISA in dose-response assays for OMVBp and the immunogens at varying levels. These assays demonstrated that OMVBp exhibits adjuvant properties even at the low concentration employed (1.5 μg of protein per dose). As this effect was notably enhanced at medium (3 μg) and high concentrations (6 μg), we chose the medium concentration to determine the minimum immunogen dose at which the OMV adjuvant properties are significantly evident. These assays demonstrated that OMVBp exhibits adjuvant properties even at the lowest concentration tested for each immunogen. In the presence of OMVBp, specific IgG levels detected for the lowest amount of antigen tested increased by 2.5 to 10 fold compared to those found in animals immunized with formulations containing adjuvant-free antigens (p<0.0001). When assessing the adjuvant properties of OMVBp compared to the widely recognized adjuvant alum, we detected similar levels of specific IgG against D, T and S for both adjuvants. Experiments with OMVs derived from E. coli (OMVE.coli) reaffirmed that the adjuvant properties of OMVs extend across different bacterial species. Nonetheless, it's crucial to highlight that OMVBp notably skewed the immune response towards a Th1 profile (p<0.05). These collective findings emphasize the dual role of OMVBp as both an adjuvant and modulator of the immune response, positioning it favorably for incorporation into combined vaccine formulations.

Four statistical frameworks for assessing an immune correlate of protection (surrogate endpoint) from a randomized, controlled, vaccine efficacy trial

A central goal of vaccine research is to characterize and validate immune correlates of protection (CoPs). In addition to helping elucidate immunological mechanisms, a CoP can serve as a valid surrogate endpoint for an infectious disease clinical outcome and thus qualifies as a primary endpoint for vaccine authorization or approval without requiring resource-intensive randomized, controlled phase 3 trials. Yet, it is challenging to persuasively validate a CoP, because a prognostic immune marker can fail as a reliable basis for predicting/inferring the level of vaccine efficacy against a clinical outcome, and because the statistical analysis of phase 3 trials only has limited capacity to disentangle association from cause. Moreover, the multitude of statistical methods garnered for CoP evaluation in phase 3 trials renders the comparison, interpretation, and synthesis of CoP results challenging. Toward promoting broader harmonization and standardization of CoP evaluation, this article summarizes four complementary statistical frameworks for evaluating CoPs in a phase 3 trial, focusing on the frameworks' distinct scientific objectives as measured and communicated by distinct causal vaccine efficacy parameters. Advantages and disadvantages of the frameworks are considered, dependent on phase 3 trial context, and perspectives are offered on how the frameworks can be applied and their results synthesized.

A comprehensive method for the phenotypical and functional characterization of recalled human memory B and T cells specific to vaccine antigens

Current methodologies for assessing vaccine effectiveness and longevity primarily center on measuring vaccine-induced neutralizing antibodies in serum or plasma. However, these methods overlook additional parameters such as the presence of memory B cells, even as antibody levels wane, and the pivotal role played by memory T cells in shaping antigen-specific memory B cell responses. Several studies have employed a combination of polyclonal activators, such as CpG and R848, along with various cytokines to provoke the recall of memory B cells from peripheral blood mononuclear cells (PBMCs) into antibody-secreting cells (ASCs). Other studies have examined the use of live attenuated viruses to stimulate antigen-specific memory T cells within PBMCs into effector T cells that produce Th1/Th2 cytokines. However, these studies have not fully elucidated the distinct effects of these polyclonal activators on individual subsets, nor have they evaluated whether the vaccine antigen alone is sufficient to trigger the recall of memory T cells. Thus, in this study, we directly compared the capacity of two B cell polyclonal activators to induce the transition of existing vaccine-specific memory cells present in peripheral blood samples into ASCs. Simultaneously, we also assessed the transition of existing memory T cells into effector subsets in response to vaccine antigens. Our findings demonstrate that both polyclonal activator combinations, CpG with IL-6 and IL-15, as well as R848 with IL-2, effectively induce the terminal differentiation of memory B cells into ASCs. Notably, CpG treatment preferentially expanded naïve and non-class-switched B cells, while R848 expanded class-switched memory cells, plasmablasts, and plasma cells. Consequently, R848 treatment led to a greater overall production of total and antigen-specific IgG immunoglobulins. Additionally, the exposure of isolated PBMCs to vaccine antigens alone proved sufficient for recalling the rare antigen-specific memory T cells into effector subsets, predominantly consisting of IFN-γ-producing CD4 T cells and TNF-β-producing CD8 T cells. This study not only establishes a rationale for the selection of methods to expand and detect antigen-specific lymphocyte subsets but also presents a means to quantify vaccine effectiveness by correlating serum antibody levels with preexisting memory cells within peripheral blood samples.

Exploring the path to polio eradication: insights from consecutive seroprevalence surveys among Pakistani children

Introduction

After trivalent oral poliovirus vaccine (tOPV) cessation, Pakistan has maintained immunity to type 2 poliovirus by administering inactivated polio vaccine (IPV) in routine immunization, alongside monovalent OPV type 2 (mOPV2) and IPV in supplementary immunization activities (SIAs). This study assesses the change in poliovirus type 2 immunity after tOPV withdrawal and due to SIAs with mOPV2 and IPV among children aged 6-11 months.

Methods

Three cross-sectional sequential serological surveys were conducted in 12 polio high-risk areas of Pakistan. 25 clusters from each geographical stratum were selected utilizing probability proportional to size.

Results

Seroprevalence of type 2 poliovirus was 49%, with significant variation observed among surveyed areas; <30% in Pishin, >80% in Killa Abdullah, Mardan & Swabi, and Rawalpindi. SIAs with IPV improved immunity from 38 to 57% in Karachi and 60 to 88% in Khyber. SIAs with IPV following mOPV2 improved immunity from 62 to 65% in Killa Abdullah, and combined mOPV2 and IPV SIAs in Pishin improved immunity from 28 to 89%. Results also reflected that immunity rates for serotypes 1 and 3 were consistently above 90% during all three phases and across all geographical areas.

Conclusion

The study findings highlight the importance of implementing effective vaccination strategies to prevent the re-emergence of poliovirus. Moreover, the results provide crucial information for policymakers working toward achieving global polio eradication.

Vaccine Responses in Patients with Liver Cirrhosis: From the Immune System to the Gut Microbiota

Vaccines prevent a significant number of deaths annually. However, certain populations do not respond adequately to vaccination due to impaired immune systems. Cirrhosis, a condition marked by a profound disruption of immunity, impairs the normal immunization process. Critical vaccines for cirrhotic patients, such as the hepatitis A virus (HAV), hepatitis B virus (HBV), influenza, pneumococcal, and coronavirus disease 19 (COVID-19), often elicit suboptimal responses in these individuals. The humoral response, essential for immunization, is less effective in cirrhosis due to a decline in B memory cells and an increase in plasma blasts, which interfere with the creation of a long-lasting response to antigen vaccination. Additionally, some T cell subtypes exhibit reduced activation in cirrhosis. Nonetheless, the persistence of memory T cell activity, while not preventing infections, may help to attenuate the severity of diseases in these patients. Alongside that, the impairment of innate immunity, particularly in dendritic cells (DCs), prevents the normal priming of adaptive immunity, interrupting the immunization process at its onset. Furthermore, cirrhosis disrupts the gut-liver axis balance, causing dysbiosis, reduced production of short-chain fatty acids (SCFAs), increased intestinal permeability, and bacterial translocation. Undermining the physiological activity of the immune system, these alterations could impact the vaccine response. Enhancing the understanding of the molecular and cellular factors contributing to impaired vaccination responses in cirrhotic patients is crucial for improving vaccine efficacy in this population and developing better prevention strategies.

Epitope Mapping of Japanese Encephalitis Virus Neutralizing Antibodies by Native Mass Spectrometry and Hydrogen/Deuterium Exchange

Japanese encephalitis virus (JEV) remains a global public health concern due to its epidemiological distribution and the existence of multiple strains. Neutralizing antibodies against this infection have shown efficacy in in vivo studies. Thus, elucidation of the epitopes of neutralizing antibodies can aid in the design and development of effective vaccines against different strains of JEV. Here, we describe a combination of native mass spectrometry (native-MS) and hydrogen/deuterium exchange mass spectrometry (HDX-MS) to complete screening of eight mouse monoclonal antibodies (MAbs) against JEV E-DIII to identify epitope regions. Native-MS was used as a first pass to identify the antibodies that formed a complex with the target antigen, and it revealed that seven of the eight monoclonal antibodies underwent binding. Native mass spectra of a MAb (JEV-27) known to be non-binding showed broad native-MS peaks and poor signal, suggesting the protein is a mixture or that there are impurities in the sample. We followed native-MS with HDX-MS to locate the binding sites for several of the complex-forming antibodies. This combination of two mass spectrometry-based approaches should be generally applicable and particularly suitable for screening of antigen-antibody and other protein-protein interactions when other traditional approaches give unclear results or are difficult, unavailable, or need to be validated.

Predicting Vaccine Effectiveness for Hospitalization and Symptomatic Disease for Novel SARS-CoV-2 Variants Using Neutralizing Antibody Titers

The emergence of new virus variants, including the Omicron variant (B.1.1.529) of SARS-CoV-2, can lead to reduced vaccine effectiveness (VE) and the need for new vaccines or vaccine doses if the extent of immune evasion is severe. Neutralizing antibody titers have been shown to be a correlate of protection for SARS-CoV-2 and other pathogens, and could be used to quickly estimate vaccine effectiveness for new variants. However, no model currently exists to provide precise VE estimates for a new variant against severe disease for SARS-CoV-2 using robust datasets from several populations. We developed predictive models for VE against COVID-19 symptomatic disease and hospitalization across a 54-fold range of mean neutralizing antibody titers. For two mRNA vaccines (mRNA-1273, BNT162b2), models fit without Omicron data predicted that infection with the BA.1 Omicron variant increased the risk of hospitalization 2.8-4.4-fold and increased the risk of symptomatic disease 1.7-4.2-fold compared to the Delta variant. Out-of-sample validation showed that model predictions were accurate; all predictions were within 10% of observed VE estimates and fell within the model prediction intervals. Predictive models using neutralizing antibody titers can provide rapid VE estimates, which can inform vaccine booster timing, vaccine design, and vaccine selection for new virus variants.