Correlates of immune protection induced by live, attenuated, cold-adapted, trivalent, intranasal influenza virus vaccine

Systems immunology analysis of human immune organoids identifies host-specific correlates of protection to different influenza vaccines

Vaccines are an essential tool to significantly reduce pathogen-related morbidity and mortality. However, our ability to rationally design vaccines and identify correlates of protection remains limited. Here, we employed an immune organoid approach to capture human adaptive immune response diversity to influenza vaccines and systematically identify host and antigen features linked to vaccine response variability. Our investigation identified established and unique immune signatures correlated with neutralizing antibody responses across seven different influenza vaccines and antigens. Unexpectedly, heightened ex vivo tissue frequencies of T helper (Th)1 cells emerged as both a predictor and a correlate of neutralizing antibody responses to inactivated influenza vaccines (IIVs). Secondary analysis of human public data confirmed that elevated Th1 signatures are associated with antibody responses following in vivo vaccination. These findings demonstrate the utility of human in vitro models for identifying in vivo correlates of protection and establish a role for Th1 functions in influenza vaccination.

Intranasal recombinant protein subunit vaccine targeting TLR3 induces respiratory tract IgA and CD8 T cell responses and protects against respiratory virus infection

BACKGROUND

Intranasal vaccines against respiratory viruses are desired due to ease of administration and potential to protect against virus infection of the upper respiratory tract.

METHODS

We tested a cationic liposomal adjuvant delivering the TLR3 agonist Poly (I:C) (CAF®09b) for intranasal administration, by formulating this with SARS-CoV-2 spike trimeric protein and assessing airway mucosal immune responses in mice. The vaccine was further evaluated in SARS-CoV-2 virus challenge models, using mice expressing the human ACE2 receptor and Syrian hamsters.

FINDINGS

The intranasal vaccine elicited both serum neutralising antibody responses and IgA responses in the upper respiratory tract. Uniquely, it also elicited high-magnitude CD4 and CD8 T cell responses in the lung parenchyma and nasal-associated lymphoid tissue. In contrast, parenteral administration of the same vaccine, or the mRNA-1273 (Spikevax®) vaccine, led to systemic antibody responses and vaccine-induced CD4 T cells were mainly found in circulation. The intranasal vaccine protected against homologous SARS-CoV-2 (Wuhan-Hu-1) challenge in K18-hACE2 mice, preventing weight loss and virus infection in the upper and lower airways. In Syrian hamsters, the vaccine prevented weight loss and significantly reduced virus load after challenge with the homologous strain and Omicron BA.5.

INTERPRETATION

This study demonstrates that intranasal subunit vaccines containing TLR3-stimulating cationic liposomes effectively induce airway IgA and T cell responses, which could be utilised in future viral pandemics.

FUNDING

This work was primarily supported by the European Union Horizon 2020 research and innovation program under grant agreement no. 101003653.

Hemagglutination-Inhibition Antibodies and Protection against Influenza Elicited by Inactivated and Live Attenuated Vaccines in Children

BACKGROUND

Hemagglutinin (HA)-inhibiting antibodies contribute to the immune defense against influenza infection. However, there are insufficient data on the extent of correlation between vaccine-elicited HA antibodies and protection in children against different influenza strains, particularly when comparing live attenuated influenza vaccines (LAIV) versus inactivated influenza vaccines (IIV).

METHODS

We measured postvaccination hemagglutination-inhibition (HAI) titers in 3-15-year-old participants of a cluster-randomized controlled trial of trivalent LAIV(3) versus IIV(3) in Canadian Hutterite colonies. We assessed HAI titers as predictors of symptomatic, reverse transcription polymerase chain reaction (RT-PCR)-confirmed influenza over 3 influenza seasons using Cox proportional hazards regression models with vaccine type as a covariate.

RESULTS

For each log2 unit increase in postvaccination HAI against A/H1N1 in 2013-2014, A/H3N2 2014-2015, and B/Yamagata in 2013-2014 (each the predominant circulating strain for the respective influenza season), the reduction in the risk of confirmed influenza was equal to 29.6% (95% confidence interval [CI], 17.1%-39.5%), 34.8% (95% CI, 17.2%-47.9%), and 31.8% (95% CI, 23.8%-38.5%), respectively. No reduction in the risk of influenza was observed with B/Yamagata-specific HAI titers in 2012-2013, which was dominated by a mixture of Yamagata and Victoria strains. Despite the overall lower HAI titers in the LAIV3 group, both H1N1 and H3N2 HAI titers were associated with protection against subtype matched influenza.

CONCLUSIONS

Both LAIV3- and IIV3-elicited HA antibodies are associated with protection against influenza infection in seasons when the vaccine strains match the circulating influenza strain subtypes, supporting the use of HAI as a correlate of protection for both vaccine types in children.

Intranasal M2SR (M2-Deficient Single Replication) Influenza Vaccine Induces Broadly Reactive Mucosal Antibody Production in Adults

Intranasal H3N2 M2SR vaccine induced cross-reactive mucosal IgA antibodies against a panel of H3N2 hemagglutinins, ranging from 1968 to 2014, in adults independent of baseline immune status. The breadth extended to potential pandemic strain H7N9, presumably through the hemagglutinin stem.

Intranasal M2SR (M2-deficient single replication) influenza virus vaccine induces robust immune responses in animal models and humans. A high-throughput multiplexed platform was used to analyze hemagglutinin-specific mucosal antibody responses in adults after a single dose of H3N2 M2SR. Nasal swab specimens were analyzed for total and hemagglutinin-specific IgA. Significant dose-dependent increases in mucosal antibody responses to vaccine-matched and drifted H3N2 hemagglutinin were observed in persons vaccinated with M2SR regardless of baseline serum and mucosal immune status. These data suggest that M2SR induces broadly cross-reactive mucosal immune responses, which may provide better protection against drifted and newly emerging influenza strains.

Expression and delivery of HA1-M2e antigen using an innovative attenuated Salmonella-mediated delivery system confers promising protection against H9N2 avian influenza challenge

This study explores a dual expression vector system for delivering prokaryotic and eukaryotic antigens to improve conventional vaccination strategies. To enhance immune protection against H9N2 avian influenza virus (AIV), which threatens poultry and humans, we used the previously constructed pJHL270 and pJHL305 plasmids with the Ptrc and CMV promoters to stimulate MHC class II and I responses through exogenous and endogenous antigenic presentation. Salmonella Gallinarum (SG), a delivery vector, was engineered to have defective lipopolysaccharide structures through lon, pagL, and rfaL deletion. It demonstrated a safety profile with lower induction of inflammatory cytokines than the wild-type strain. Bioinformatics tools predicted that the HA1 and M2e sequences, which were designed as consensus sequences of South Korean strains (2000-2021), would have high antigenicity and favorable structures. In vitro expression of the vaccine constructs was validated by western blotting. Birds immunized with attenuated SG harboring pJHL270 (JOL3025) or pJHL305 (JOL3027) containing HA-M2e showed significant increases in serum IgY and mucosal IgA antibodies, indicating strong humoral and mucosal immune responses, comparable with inactivated commercial vaccine. Post-immunization, we found a substantial rise in the hemagglutination inhibition titer, suggesting effective prevention of viral attachment and robust cell-mediated immunity, with a 1.96-fold and 2.80-fold increase in CD4+ and CD8+ T cells, respectively, for JOL3025 and a 1.75-fold and 2.49-fold increase for JOL3027. Furthermore, MHC class I and II expression increased 1.35-fold and 1.63-fold, for JOL3025, and 1.61-fold and 1.68-fold, respectively, for JOL3027. The IL-4 and IFN-γ levels were elevated, indicating a balanced Th-1 and Th-2 response. Post-challenge, birds immunized with vaccine candidates or the commercial vaccine exhibited minimal to no clinical signs, reduced lesions, lower lung viral titers, and negligible impacts on egg production compared to controls. In conclusion, both plasmids successfully delivered HA1-M2e immunogens through the engineered SG strains, eliciting strong humoral, mucosal, and cell-mediated immune responses and co-stimulating MHC class I and II antigen presentation pathways to provide effective protection against H9N2 AIV with minimal adverse effects.

An Optimised Live Attenuated Influenza Vaccine Ferret Efficacy Model Successfully Translates H1N1 Clinical Data

Between 2013 and 2016, the A/H1N1pdm09 component of the live attenuated influenza vaccine (LAIV) produced instances of lower-than-expected vaccine effectiveness. Standard pre-clinical ferret models, using a human-like vaccine dose and focusing on antigenic match to circulating wildtype (wt) strains, were unable to predict these fluctuations. By optimising the vaccine dose and utilising clinically relevant endpoints, we aimed to develop a ferret efficacy model able to reproduce clinical observations. Ferrets were intranasally vaccinated with 4 Log10 FFU/animal (1000-fold reduction compared to clinical dose) of seven historical LAIV formulations with known (19-90%) H1N1 vaccine efficacy or effectiveness (VE). Following homologous H1N1 wt virus challenge, protection was assessed based on primary endpoints of wt virus shedding in the upper respiratory tract and the development of fever. LAIV formulations with high (82-90%) H1N1 VE provided significant protection from wt challenge, while formulations with reduced (19-32%) VE tended not to provide significant protection. The strongest correlation observed was between reduction in wt shedding and VE (R2 = 0.75). Conversely, serum immunogenicity following vaccination was not a reliable indicator of protection (R2 = 0.37). This demonstrated that, by optimisation of the vaccine dose and the use of non-serological, clinically relevant protection endpoints, the ferret model could successfully translate clinical H1N1 LAIV VE data.

Inno4Vac Workshop Report Part 1: Controlled Human Influenza Virus Infection Model (CHIVIM) Strain Selection and Immune Assays for CHIVIM Studies, November 2021, MHRA, UK

Controlled human infection models (CHIMs) are a critical tool for the understanding of infectious disease progression, characterising immune responses to infection and rapid assessment of vaccines or drug treatments. There is increasing interest in using CHIMs for vaccine development and an obvious need for widely available and fit-for-purpose challenge agents. Inno4Vac is a large European consortium working towards accelerating and de-risking the development of new vaccines, including the development of CHIMs for influenza, respiratory syncytial virus and Clostridioides difficile. This report (in two parts) summarises a workshop held at the MHRA in 2021, focused on how to select CHIM candidate strains of influenza and respiratory syncytial virus (RSV) based on desirable virus characteristics and which immune assays would provide relevant information for assessing pre-existing and post-infection immune responses and defining correlates of protection. This manuscript (Part 1) summarises presentations and discussions centred around influenza CHIMs and immune assays (a second manuscript summarises RSV CHIM and immune assays: Inno4Vac workshop report Part 2: RSV CHIM strain selection and immune assays for RSV CHIM studies, November 2021, MHRA, UK).

Meeting Report From "Correlates of Protection for Next Generation Influenza Vaccines: Lessons Learned From the COVID-19 Pandemic"

BACKGROUND

This report summarizes the discussions and conclusions from the "Correlates of Protection for Next Generation Influenza Vaccines: Lessons Learned from the COVID-19 Pandemic" meeting, which took place in Seattle, USA, from March 1, 2023, to March 3, 2023.

CONCLUSIONS

Discussions around influenza virus correlates of protection and their use continued from where the discussion had been left off in 2019. While there was not much progress in the influenza field itself, many lessons learned during the coronavirus disease 2019 (COVID-19) pandemic, especially the importance of mucosal immunity, were discussed and can directly be applied to influenza correlates of protection.

Safety and immunogenicity of the intranasal H3N2 M2-deficient single-replication influenza vaccine alone or coadministered with an inactivated influenza vaccine (Fluzone High-Dose Quadrivalent) in adults aged 65-85 years in the USA: a multicentre, randomised, double-blind, double-dummy, phase 1b trial

BACKGROUND

Older adults (aged ≥65 years) show increased susceptibility to severe disease with influenza virus infection, accounting for 70-85% of annual influenza-related fatalities in the USA. Stimulating mucosal antibodies and T cells might enhance the low vaccine effectiveness seen in older adults for currently licensed inactivated influenza vaccines, which induce mainly serum antibodies. We aimed to evaluate the safety and immunogenicity of the intranasal H3N2 M2-deficient single-replication (M2SR) vaccine, alone or coadministered with a licensed inactivated influenza vaccine (Fluzone High-Dose Quadrivalent; hereafter referred to as Fluzone HD), in older adults.

METHODS

In this multicentre, randomised, double-blind, double-dummy, phase 1b trial, individuals aged 65-85 years who were considered healthy or with stable chronic conditions with no recent (<6 months) influenza vaccinations were recruited from five clinical trial sites in the USA and randomly assigned (3:3:3:1) using a permuted block design to receive the H3N2 M2SR vaccine and Fluzone HD, the H3N2 M2SR vaccine and placebo, Fluzone HD and placebo, or placebo alone. All participants received a single intranasal spray and a single intramuscular injection, whether active or placebo, to maintain masking. The primary outcome was to assess the safety of H3N2 M2SR, administered alone or with Fluzone HD, in the safety analysis set, which included all participants who were randomly assigned and received treatment. Serum and mucosal antibodies were assessed as a secondary endpoint, and cell-mediated immunity as an exploratory endpoint, in participants in the per-protocol population, which included individuals in the safety analysis set without major protocol deviations. This trial is registered with ClinicalTrials.gov, NCT05163847.

FINDINGS

Between June 14 and Sept 15, 2022, 305 participants were enrolled and randomly assigned to receive the H3N2 M2SR vaccine plus placebo (n=89), H3N2 M2SR vaccine plus Fluzone HD (n=94), Fluzone HD plus placebo (n=92), or placebo alone (n=30). All randomly assigned participants were included in the safety analysis set. The most frequently reported local symptoms up to day 8 in groups that received M2SR were rhinorrhoea (43% [38 of 89] in the H3N2 M2SR plus placebo group and 38% [36 of 94] in the H3N2 M2SR plus Fluzone HD group), nasal congestion (51% [45 of 89] and 35% [33 of 94]), and injection-site pain (8% [seven of 89] and 49% [46 of 94]), and the most frequently reported solicited systemic symptoms were sore throat (28% [25 of 89]) for M2SR and decreased activity (26% [24 of 94]) for the M2SR plus Fluzone HD group. In the Fluzone HD plus placebo group, the most frequently reported local symptom was injection-site pain (48% [44 of 92]) and systemic symptom was muscle aches (22% [20 of 92]). The frequency of participants with any treatment-emergent adverse event related to vaccination was low across all groups (2-5%). One serious adverse event was reported, in a participant in the Fluzone HD plus placebo group. M2SR with Fluzone HD induced seroconversion (≥four-fold increase in haemagglutination inhibition antibodies from baseline to day 29) in 44 (48%) of 91 participants, compared with 28 (31%) of 90 participants who seroconverted in the Fluzone HD plus placebo group (p=0·023). M2SR with Fluzone HD also induced mucosal and cellular immune responses.

INTERPRETATION

The H3N2 M2SR vaccine coadministered with Fluzone HD in older adults was well tolerated and provided enhanced immunogenicity compared with Fluzone HD administered alone, suggesting potential for improved efficacy of influenza vaccination in this age group. Additional studies are planned to assess efficacy.

FUNDING

US Department of Defense.

Safety, reactogenicity and immunogenicity of an intranasal seasonal influenza vaccine adjuvanted with gram-positive matrix (GEM) particles (FluGEM): A randomized, double-blind, controlled, ascending dose study in healthy adults and elderly

BACKGROUND

Intranasal administration of respiratory vaccines offers many advantages such as eliciting both systemic and mucosal immunity at the point of viral entry. Immunogenicity of intranasal vaccination can be improved through the use of adjuvants. Bacteria-like particles derived fromLactococcus lactishave the potential to serve as a vaccine adjuvant.This clinical study investigated the safety, reactogenicity and immunogenicity of intranasal seasonal influenza vaccine adjuvanted with gram-positive matrix particles (FluGEM®).

METHODS

This was a first-in-human, randomized, double-blind, controlled, dose-escalation study performed at the Centre for Human Drug Research (CHDR), the Netherlands. Participants aged 18-49 were randomized in a 3:1 ratio to receive FluGem® in ascending doses (two-dose regimens) together with a standard trivalent inactivated influenza vaccine or unadjuvanted TIV only. Primary outcomes were safety and tolerability. Secondary outcomes were serum hemagglutination inhibition (HI) antibody titers and mucosal IgA. The most immunogenic dose was used in an additionalelderly cohort (>65 years).

RESULTS

Ninty participants were included. Intranasal FluGem®was safe and well tolerated. The majority of adverse events were mild (97.4 %) with (un)solicited adverse events comparable across all dose levels and control groups. All groups showed geometric mean increases ≥ 2.5-fold. Seroconversion (≥40 % participants) was achieved at both day 21 (single-dose) and 42 (two-dose) for the 1.25 mg dose and on day 42 (two-dose only) for the 2.5 mg dose. Highest geometric mean IgA increases were observed in the 1.25 mg group on day 21. Immunogenicity was less pronounced in elderly.

CONCLUSIONS

Intranasal vaccination of FluGEM®was safe and tolerable in healthy adult volunteers aged 18-49 years and 65 and older. Highest immunogenicity was observed for 1.25 mg and 2.5 mg doses (compared to 5 mg) suggesting a potential non-linear dose-response relationship.More research is needed to further investigate the capabilities of bacteria-like peptides as adjuvants.

Development of Cross-Reactive Live Attenuated Influenza Vaccine Candidates against Both Lineages of Influenza B Virus

BACKGROUND

Influenza viruses continue to cause a significant social and economic burden globally. Vaccination is recognized as the most effective measure to control influenza. Live attenuated influenza vaccines (LAIVs) are an effective means of preventing influenza, especially among children. A reverse genetics (RG) system is required to rapidly update the antigenic composition of vaccines, as well as to design LAIVs with a broader spectrum of protection. Such a system has been developed for the Russian LAIVs only for type A strains, but not for influenza B viruses (IBV).

METHODS

All genes of the B/USSR/60/69 master donor virus (B60) were cloned into RG plasmids, and the engineered B60, as well as a panel of IBV LAIV reassortants were rescued from plasmid DNAs encoding all viral genes. The engineered viruses were evaluated in vitro and in a mouse model.

RESULTS

The B60 RG system was successfully developed, which made it possible to rescue LAIV reassortants with the desired antigenic composition, including hybrid strains with hemagglutinin and neuraminidase genes belonging to the viruses from different IBV lineages. The LAIV candidate carrying the HA of the B/Victoria-lineage virus and NA from the B/Yamagata-lineage virus demonstrated optimal characteristics in terms of safety, immunogenicity and cross-protection, prompting its further assessment as a broadly protective component of trivalent LAIV.

CONCLUSIONS

The new RG system for B60 MDV allowed the rapid generation of type B LAIV reassortants with desired genome compositions. The generation of hybrid LAIV reassortants with HA and NA genes belonging to the opposite IBV lineages is a promising approach for the development of IBV vaccines with broad cross-protection.

The potential of saliva as an accessible and sensitive sample type for the detection of respiratory pathogens and host immunity

Despite its prominence in early scientific records, the usefulness of saliva as a respiratory specimen has been de-emphasised over the past century. However, due to its low cost and reliance on specific supply chains and the non-invasive nature of its collection, its benefits over swab-based specimens are again becoming increasingly recognised. These benefits were highlighted over the course of the COVID-19 pandemic, where saliva emerged as a more practical, clinically non-inferior sample type for the detection of SARS-CoV-2 and saw numerous saliva-based diagnostic tests approved for clinical use. Looking forward, as saliva uniquely contains both respiratory secretions and immunological components, it has potentially wide applications, ranging from clinical diagnostics to post-vaccine disease burden and immunity surveillance. This Personal View seeks to summarise the existing evidence for the use of saliva in detecting respiratory pathogens, beyond SARS-CoV-2, as well as detailing methodological factors that can influence sample quality and thus, clinical utility.

Role of Acacia catechu and Scutellaria baicalensis in Enhancing Immune Function Following Influenza Vaccination of Healthy Adults: A Randomized, Triple-Blind, Placebo-Controlled Clinical Trial

OBJECTIVE

The study aimed to examine the role of an Acacia catechu and Scutellaria baicalensis formulation, UP446, on supporting immune function in response to influenza vaccination.

METHODS

A randomized, triple-blind, placebo-controlled, parallel study consisted of a 56-day intervention period with a 28-day pre-vaccination period, an influenza vaccination on Day 28 and 28-day post-vaccination period. Fifty healthy adults 40-80 years of age who had not received their flu vaccine were randomized to either UP446 or Placebo. At baseline, Days 28 and 56, immune and oxidative stress markers were measured in blood and a quality of life questionnaire was administered. Participants completed the Wisconsin Upper Respiratory Symptom Survey (WURSS)-24 daily.

RESULTS

In the post-vaccination period, total IgA and IgG levels increased in participants supplemented with UP446 vs. those on Placebo (p ≤ 0.026). As well, influenza B-specific IgG increased 19.4% from Day 28 to 56 and 11.6% from baseline at Day 56 (p ≤ 0.0075). Serum glutathione peroxidase (GSH-Px) was increased in the pre-vaccination period and from baseline at Day 56 with UP446 supplementation (p ≤ 0.0270).

CONCLUSION

These results suggest a 56-day supplementation with UP446 was beneficial in mounting a robust humoral response following vaccination. Increasing GSH-Px in the pre-vaccination period may help improve antioxidant functions and potentially mitigate the oxidative stress induced following vaccination.

Influenza vaccine format mediates distinct cellular and antibody responses in human immune organoids

Highly effective vaccines elicit specific, robust, and durable adaptive immune responses. To advance informed vaccine design, it is critical that we understand the cellular dynamics underlying responses to different antigen formats. Here, we sought to understand how antigen-specific B and T cells were activated and participated in adaptive immune responses within the mucosal site. Using a human tonsil organoid model, we tracked the differentiation and kinetics of the adaptive immune response to influenza vaccine and virus modalities. Each antigen format elicited distinct B and T cell responses, including differences in their magnitude, diversity, phenotype, function, and breadth. These differences culminated in substantial changes in the corresponding antibody response. A major source of antigen format-related variability was the ability to recruit naive vs. memory B and T cells to the response. These findings have important implications for vaccine design and the generation of protective immune responses in the upper respiratory tract.

A single intranasal administration of AdCOVID protects against SARS-CoV-2 infection in the upper and lower respiratory tracts

The coronavirus disease 2019 (COVID-19) pandemic has illustrated the critical need for effective prophylactic vaccination to prevent the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Intranasal vaccination is an attractive approach for preventing COVID-19 as the nasal mucosa is the site of initial SARS-CoV-2 entry and viral replication prior to aspiration into the lungs. We previously demonstrated that a single intranasal administration of a candidate adenovirus type 5-vectored vaccine encoding the receptor-binding domain of the SARS-CoV-2 spike protein (AdCOVID) induced robust immunity in both the airway mucosa and periphery, and completely protected K18-hACE2 mice from lethal SARS-CoV-2 challenge. Here we show that a single intranasal administration of AdCOVID limits viral replication in the nasal cavity of K18-hACE2 mice. AdCOVID also induces sterilizing immunity in the lungs of mice as reflected by the absence of infectious virus. Finally, AdCOVID prevents SARS-CoV-2 induced pathological damage in the lungs of mice. These data show that AdCOVID not only limits viral replication in the respiratory tract, but it also prevents virus-induced inflammation and immunopathology following SARS-CoV-2 infection.

Intranasal M2SR (M2-Deficient Single Replication) H3N2 Influenza Vaccine Provides Enhanced Mucosal and Serum Antibodies in Adults

BACKGROUND

We previously demonstrated that an intranasal dose of 108 50% tissue culture infectious dose (TCID50) M2-deficient single replication (M2SR) influenza vaccine protected against highly drifted H3N2 influenza challenge in a subset of subjects who demonstrated ≥2-fold increase in microneutralization (MN) antibodies to Belgium2015 (the challenge strain) after vaccination. Here, we describe a phase 1b, observer-blinded, dose-escalation study demonstrating an increased proportion of responders with this signal of immune protection.

METHODS

Serosusceptible subjects aged 18-49 years were randomized to receive 2 doses (108-109 TCID50) of M2SR or placebo administered 28 days apart. Clinical specimens were collected before and after each dose. The primary objective was to demonstrate safety of M2SR vaccines.

RESULTS

The vaccine was well tolerated at all dose levels. Against Belgium2015, ≥ 2-fold increases in MN antibodies were noted among 40% (95% confidence interval [CI], 24.9%-56.7%) of subjects following a single 108 TCID50 M2SR dose and among 80.6% (95% CI, 61.4%-92.3%) after 109 dose (P < .001). A single 109 TCID50 dose of M2SR generated ≥4-fold hemagglutination inhibition antibody seroconversion against the vaccine strain in 71% (95% CI, 52.0%-85.8%) of recipients. Mucosal and cellular immune responses were also induced.

CONCLUSIONS

These results indicate that M2SR may provide substantial protection against infection with highly drifted strains of H3N2 influenza.

CLINICAL TRIALS REGISTRATION

NCT03999554.

Development and characterization of influenza M2 ectodomain and/or hemagglutinin stalk-based dendritic cell-targeting vaccines

A universal influenza vaccine is required for broad protection against influenza infection. Here, we revealed the efficacy of novel influenza vaccine candidates based on Ebola glycoprotein dendritic cell (DC)-targeting domain (EΔM) fusion protein technology. The four copies of ectodomain matrix protein of influenza (tM2e) or M2e hemagglutinin stalk (HA stalk) peptides (HM2e) were fused with EΔM to generate EΔM-tM2e or EΔM-HM2e, respectively. We demonstrated that EΔM-HM2e- or EΔM-tM2e-pseudotyped viral particles can efficiently target DC/macrophages in vitro and induced significantly high titers of anti-HA and/or anti-M2e antibodies in mice. Significantly, the recombinant vesicular stomatitis virus (rVSV)-EΔM-tM2e and rVSV-EΔM-HM2e vaccines mediated rapid and potent induction of M2 or/and HA antibodies in mice sera and mucosa. Importantly, vaccination of rVSV-EΔM-tM2e or rVSV-EΔM-HM2e protected mice from influenza H1N1 and H3N2 challenges. Taken together, our study suggests that rVSV-EΔM-tM2e and rVSV-EΔM-HM2e are promising candidates that may lead to the development of a universal vaccine against different influenza strains.

CAvant® WO-60 as an Effective Immunological Adjuvant for Avian Influenza and Newcastle Disease Vaccine

Despite the immunogenicity of vaccines currently used in poultry, several pathogens, including avian influenza virus (AIV) and Newcastle disease virus (NDV), cause enormous economic losses to the global poultry industry. The efficacy of vaccines can be improved by the introduction of effective adjuvants. This study evaluated a novel water-in-oil emulsion adjuvant, CAvant® WO-60, which effectively enhanced both the immunogenicity of conserved influenza antigen sM2HA2 and inactivated whole H9N2 antigen (iH9N2). CAvant® WO-60 induced both humoral and cell-mediated immunity in mice and provided 100% protection from challenge with 10 LD50 of A/Aquatic bird/Korea/W81/2005 (H5N2) and A/Chicken/Korea/116/2004 (H9N2) AIV. Importantly, immunization of chickens with iH9N2 plus inactivated NDV LaSota (iNDV) bivalent inactivated vaccine emulsified in CAvant® WO-60 induced seroprotective levels of antigen-specific antibody responses. Taken together, these results suggested that CAvant® WO-60 is a promising adjuvant for poultry vaccines.

Safety and Immunogenicity of M2-Deficient, Single Replication, Live Influenza Vaccine (M2SR) in Adults

M2SR (M2-deficient single replication) is an investigational live intranasal vaccine that protects against multiple influenza A subtypes in influenza-naïve and previously infected ferrets. We conducted a phase 1, first-in-human, randomized, dose-escalation, placebo-controlled study of M2SR safety and immunogenicity. Adult subjects received a single intranasal administration with either placebo or one of three M2SR dose levels (10⁶, 10⁷ or 10⁸ tissue culture infectious dose (TCID₅₀)) expressing hemagglutinin and neuraminidase from A/Brisbane/10/2007 (H3N2) (24 subjects per group). Subjects were evaluated for virus replication, local and systemic reactions, adverse events (AE), and immune responses post-vaccination. Infectious virus was not detected in nasal swabs from vaccinated subjects. At least one AE (most commonly mild nasal rhinorrhea/congestion) was reported among 29%, 58%, and 83% of M2SR subjects administered a low, medium or high dose, respectively, and among 46% of placebo subjects. No subject had fever or a severe reaction to the vaccine. Influenza-specific serum and mucosal antibody responses and B- and T-cell responses were significantly more frequent among vaccinated subjects vs. placebo recipients. The M2SR vaccine was safe and well tolerated and generated dose-dependent durable serum antibody responses against diverse H3N2 influenza strains. M2SR demonstrated a multi-faceted immune response in seronegative and seropositive subjects.

Live Attenuated Cold-Adapted Influenza Vaccines

Live attenuated, cold-adapted influenza vaccines exhibit several desirable characteristics, including the induction of systemic, mucosal, and cell-mediated immunity resulting in breadth of protection, ease of administration, and yield. Seasonal live attenuated influenza vaccines (LAIVs) were developed in the United States and Russia and have been used in several countries. In the last decade, following the incorporation of the 2009 pandemic H1N1 strain, the performance of both LAIVs has been variable and the U.S.-backbone LAIV was less effective than the corresponding inactivated influenza vaccines. The cause appears to be reduced replicative fitness of some H1N1pdm09 viruses, indicating a need for careful selection of strains included in multivalent LAIV formulations. Assays are now being implemented to select optimal strains. An improved understanding of the determinants of replicative fitness of vaccine strains and of vaccine effectiveness of LAIVs is needed for public health systems to take full advantage of these valuable vaccines.

Single-Dose Intranasal Administration of AdCOVID Elicits Systemic and Mucosal Immunity against SARS-CoV-2 and Fully Protects Mice from Lethal Challenge

The coronavirus disease 2019 (COVID-19) pandemic has highlighted the urgent need for effective prophylactic vaccination to prevent the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Intranasal vaccination is an attractive strategy to prevent COVID-19 as the nasal mucosa represents the first-line barrier to SARS-CoV-2 entry. The current intramuscular vaccines elicit systemic immunity but not necessarily high-level mucosal immunity. Here, we tested a single intranasal dose of our candidate adenovirus type 5-vectored vaccine encoding the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein (AdCOVID) in inbred, outbred, and transgenic mice. A single intranasal vaccination with AdCOVID elicited a strong and focused immune response against RBD through the induction of mucosal IgA in the respiratory tract, serum neutralizing antibodies, and CD4+ and CD8+ T cells with a Th1-like cytokine expression profile. A single AdCOVID dose resulted in immunity that was sustained for over six months. Moreover, a single intranasal dose completely protected K18-hACE2 mice from lethal SARS-CoV-2 challenge, preventing weight loss and mortality. These data show that AdCOVID promotes concomitant systemic and mucosal immunity and represents a promising vaccine candidate.

Single Replication M2SR Influenza Vaccine Induced Immune Responses Associated with Protection Against Human Challenge with Highly Drifted H3N2 Influenza Strain

Background

Current influenza vaccines are strain specific and demonstrate low vaccine efficacy against H3N2 influenza disease, especially when vaccine is mismatched to circulating virus. The novel influenza vaccine candidate, M2-deficient single replication (M2SR), induces a broad, multi-effector immune response.

Methods

A phase 2 challenge study was conducted to assess the efficacy of an M2SR vaccine expressing hemagglutinin and neuraminidase from A/Brisbane/10/2007 (Bris2007 M2SR H3N2; clade 1). Four weeks after vaccination, recipients were challenged with antigenically distinct H3N2 virus (A/Belgium/4217/2015, clade 3C.3b) and assessed for infection and clinical symptoms.

Results

Adverse events after vaccination were mild and similar in frequency for placebo and M2SR recipients. A single dose of Bris2007 M2SR induced neutralizing antibody to the vaccine (48% of recipients) and challenge strain (27% of recipients). Overall, 54% of M2SR recipients were infected after challenge, compared with 71% of placebo recipients. The subset of M2SR recipients with a vaccine-induced microneutralization response against the challenge virus had reduced rates of infection after challenge (38% vs 71% of placebo recipients; P = .050) and reduced illness.

Conclusions

Study participants with vaccine-induced neutralizing antibodies were protected against infection and illness after challenge with an antigenically distinct virus. This is the first demonstration of vaccine-induced protection against a highly drifted H3N2 challenge virus.

Durability of Immunity to SARS-CoV-2 and Other Respiratory Viruses

Even in nonpandemic times, respiratory viruses account for a vast global burden of disease. They remain a major cause of illness and death and they pose a perpetual threat of breaking out into epidemics and pandemics. Many of these respiratory viruses infect repeatedly and appear to induce only narrow transient immunity, but the situation varies from one virus to another. In the absence of effective specific treatments, understanding the role of immunity in protection, disease, and resolution is of paramount importance. These problems have been brought into sharp focus by the coronavirus disease 2019 (COVID-19) pandemic. Here, we summarise what is now known about adaptive immunity to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and draw comparisons with immunity to other respiratory viruses, focusing on the longevity of protective responses.

The COVID-19 Vaccine Landscape

The history of vaccine development spans centuries. At first, whole pathogens were used as vaccine agents, either inactivated or attenuated, to reduce virulence in humans. Safety and tolerability were increased by including only specific proteins as antigens and using cell culture methods, while novel vaccine strategies, like nucleic acid- or vector-based vaccines, hold high promise for the future. Vaccines have generally not been employed as the primary tools in outbreak response, but this might change since advances in medical technology in the last decades have made the concept of developing vaccines against novel pathogens a realistic strategy. Wandering the uncharted territory of a novel pathogen, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), we can learn from other human Betacoronaviridae that emerged in the last decades, SARS-CoV-1 and MERS-CoV. We can identify the most likely target structures of immunity, establish animal models that emulate human disease and immunity as closely as possible, and learn about complex mechanisms of immune interaction such as cross-reactivity or antibody-dependent enhancement (ADE). However, significant knowledge gaps remain. What are the correlates of protection? How do we best induce immunity in vulnerable populations like the elderly? Will the immunity induced by vaccination (or by natural infection) wane over time? To date, at least 149 vaccine candidates against SARS-CoV-2 are under development. At the time of writing, at least 17 candidates have already progressed past preclinical studies (in vitro models and in vivo animal experiments) into clinical development. This chapter will provide an overview of this rapidly developing field.

Safety and Immunogenicity of a Novel Intranasal Influenza Vaccine (NasoVAX): A Phase 2 Randomized, Controlled Trial

Annual influenza vaccination greatly reduces morbidity and mortality, but effectiveness remains sub-optimal. Weaknesses of current vaccines include low effectiveness against mismatched strains, lack of mucosal and other effective tissue-resident immune responses, weak cellular immune responses, and insufficiently durable immune responses. The safety and immunogenicity of NasoVAX, a monovalent intranasal influenza vaccine based on a replication-deficient adenovirus type 5 platform, were evaluated in a placebo-controlled single ascending-dose study. Sixty healthy adults (18-49 years) received a single intranasal dose of 1×109 viral particles (vp), 1 × 1010 vp, or 1 × 1011 vp of NasoVAX or placebo. NasoVAX was well-tolerated and elicited robust influenza-specific systemic and mucosal immune responses. The highest NasoVAX dose and the approved Fluzone® influenza vaccine elicited comparable hemagglutination inhibition (HAI) geometric mean titers (152.8 vs. 293.4) and microneutralization (MN) geometric mean titers (142.5 vs. 162.8), with NasoVAX HAI titers maintained more than 1-year on average following a single dose. Hemagglutinin-specific T cells responses were also documented in peripheral mononuclear cell (PBMC) preparations. Consistent with the intranasal route of administration, NasoVAX elicited antigen-specific mucosal IgA responses in the nasopharyngeal cavity with an increase of approximately 2-fold over baseline GMT at the mid- and high-doses. In summary, NasoVAX appeared safe and elicited a broad immune response, including humoral, cellular, and mucosal immunity, with no impact of baseline anti-adenovirus antibody at the most immunogenic dose.

Immunity and Protective Efficacy of Mannose Conjugated Chitosan-Based Influenza Nanovaccine in Maternal Antibody Positive Pigs

Parenteral administration of killed/inactivated swine influenza A virus (SwIAV) vaccine in weaned piglets provides variable levels of immunity due to the presence of preexisting virus specific maternal derived antibodies (MDA). To overcome the effect of MDA on SwIAV vaccine in piglets, we developed an intranasal deliverable killed SwIAV antigen (KAg) encapsulated chitosan nanoparticles called chitosan-based NPs encapsulating KAg (CS NPs-KAg) vaccine. Further, to target the candidate vaccine to dendritic cells and macrophages which express mannose receptor, we conjugated mannose to chitosan (mCS) and formulated KAg encapsulated mCS nanoparticles called mannosylated chitosan-based NPs encapsulating KAg (mCS NPs-KAg) vaccine. In MDA-positive piglets, prime-boost intranasal inoculation of mCS NPs-KAg vaccine elicited enhanced homologous (H1N2-OH10), heterologous (H1N1-OH7), and heterosubtypic (H3N2-OH4) influenza virus-specific secretory IgA (sIgA) antibody response in nasal passage compared to CS NPs-KAg vaccinates. In vaccinated upon challenged with a heterologous SwIAV H1N1, both mCS NPs-KAg and CS NPs-KAg vaccinates augmented H1N2-OH10, H1N1-OH7, and H3N2-OH4 virus-specific sIgA antibody responses in nasal swab, lung lysate, and bronchoalveolar lavage (BAL) fluid; and IgG antibody levels in lung lysate and BAL fluid samples. Whereas, the multivalent commercial inactivated SwIAV vaccine delivered intramuscularly increased serum IgG antibody response. In mCS NPs-KAg and CS NPs-KAg vaccinates increased H1N2-OH10 but not H1N1-OH7 and H3N2-OH4-specific serum hemagglutination inhibition titers were observed. Additionally, mCS NPs-KAg vaccine increased specific recall lymphocyte proliferation and cytokines IL-4, IL-10, and IFNγ gene expression compared to CS NPs-KAg and commercial SwIAV vaccinates in tracheobronchial lymph nodes. Consistent with the immune response both mCS NPs-KAg and CS NPs-KAg vaccinates cleared the challenge H1N1-OH7 virus load in upper and lower respiratory tract more efficiently when compared to commercial vaccine. The virus clearance was associated with reduced gross lung lesions. Overall, mCS NP-KAg vaccine intranasal immunization in MDA-positive pigs induced a robust cross-reactive immunity and offered protection against influenza virus.

Influenza in Children

Influenza poses a significant disease burden on children worldwide, with high rates of hospitalization and substantial morbidity and mortality. Although the clinical presentation of influenza in children has similarities to that seen in adults, there are unique aspects to how children present with infection that are important to recognize. In addition, children play a significant role in viral transmission within communities. Growing evidence supports the idea that early influenza infection can uniquely establish lasting immunologic memory, making an understanding of how viral immunity develops in this population critical to better protect children from infection and to facilitate efforts to develop a more universally protective influenza vaccine.

Repurposing of Miltefosine as an Adjuvant for Influenza Vaccine

We previously reported that topical imiquimod can improve the immunogenicity of the influenza vaccine. This study investigated another FDA-approved drug, miltefosine (MTF), as a vaccine adjuvant. Mice immunized with an influenza vaccine with or without MTF adjuvant were challenged by a lethal dose of influenza virus 3 or 7 days after vaccination. Survival, body weight, antibody response, histopathological changes, viral loads, cytokine levels, and T cell frequencies were compared. The MTF-adjuvanted vaccine (MTF-VAC) group had a significantly better survival rate than the vaccine-only (VAC) group, when administered 3 days (80% vs. 26.7%, p = 0.0063) or 7 days (96% vs. 65%, p = 0.0041) before influenza virus challenge. Lung damage was significantly ameliorated in the MTF-VAC group. Antibody response was significantly augmented in the MTF-VAC group against both homologous and heterologous influenza strains. There was a greater T follicular helper cell (T_FH) response and an enhanced germinal center (GC) reaction in the MTF-VAC group. MTF-VAC also induced both T_H1 and T_H2 antigen-specific cytokine responses. MTF improved the efficacy of the influenza vaccine against homologous and heterologous viruses by improving the T_FH and antibody responses. Miltefosine may also be used for other vaccines, including the upcoming vaccines for COVID-19.

Single-dose intranasal administration of AdCOVID elicits systemic and mucosal immunity against SARS-CoV-2 in mice

The coronavirus disease 2019 (COVID-19) pandemic has highlighted the urgent need for effective preventive vaccination to reduce burden and spread of severe acute respiratory syndrome (SARS) coronavirus 2 (SARS-CoV-2) in humans. Intranasal vaccination is an attractive strategy to prevent COVID-19 as the nasal mucosa represents the first-line barrier to SARS-CoV-2 entry before viral spread to the lung. Although SARS-CoV-2 vaccine development is rapidly progressing, the current intramuscular vaccines are designed to elicit systemic immunity without conferring mucosal immunity. Here, we show that AdCOVID, an intranasal adenovirus type 5 (Ad5)-vectored vaccine encoding the receptor binding domain (RBD) of the SARS-CoV-2 spike protein, elicits a strong and focused immune response against RBD through the induction of mucosal IgA, serum neutralizing antibodies and CD4+ and CD8+ T cells with a Th1-like cytokine expression profile. Therefore, AdCOVID, which promotes concomitant systemic and local mucosal immunity, represents a promising COVID-19 vaccine candidate.

Environmental Lead Exposure and Influenza and Respiratory Syncytial Virus Diagnoses in Young Children: A Test-Negative Case-Control Study

Experimental and epidemiological evidence suggests that environmental toxicants may influence susceptibility to influenza and respiratory syncytial virus (RSV). The objective of the present study was to estimate the association between blood lead concentrations and the odds of child influenza or RSV infection. A test-negative, case-control study was conducted among 617 children, <4 years of age, tested for influenza/RSV from 2012-2017 in Rochester, NY. There were 49 influenza cases (568 controls) and 123 RSV cases (494 controls). Blood lead concentrations reported in children's medical records were linked with influenza/RSV lab test results. Covariables were collected from medical records, birth certificates, and U.S. census data. In this sample, evidence of an association between blood lead levels and RSV or influenza diagnosis was not observed. Children with a lead level ≥1 μg/dL vs. <1 μg/dL had an adjusted odds ratio (aOR) and 95% confidence limit of 0.95 (0.60, 1.49) for RSV and 1.34 (0.65, 2.75) for influenza. In sex-specific analyses, boys with lead concentrations ≥1 μg/dL vs. <1 μg/dL had an aOR = 1.89 (1.25, 2.86) for influenza diagnosis, while the estimates were inconsistent for girls. These results are suggestive of sex-specific associations between blood lead levels and the risk of influenza, although the sample size was small.

The Effect of Preexisting Immunity on Virus Detection and Immune Responses in a Phase II, Randomized Trial of a Russian-Backbone, Live, Attenuated Influenza Vaccine in Bangladeshi Children

Background

In a 2012 Phase II clinical trial, 300 Bangladeshi children aged 24 to 59 months with no prior influenza vaccine exposure were randomized to receive a single intranasally-administered dose of either trivalent, Russian-backbone, live, attenuated influenza vaccine (LAIV) or placebo. Protocol-defined analyses, presented in the companion manuscript, demonstrate decreased viral detection and immunogenicity for A/H1N1pdm09, relative to the A/H3N2 and B strains. This post hoc analysis of the trial data aims to investigate the LAIV strain differences by testing the hypothesis that preexisting humoral and mucosal immunity may influence viral recovery and immune responses after LAIV receipt.

Methods

We used logistic regressions to evaluate the relations between markers of preexisting immunity (ie, hemagglutination inhibition [HAI], microneutralization, and immunoglobulin G and immunoglobulin A (both serum and mucosal antibodies) and LAIV viral recovery in the week post-vaccination. We then tested for potential effect modification by baseline HAI titers (ie, <10 versus ≥10) and week 1 viral recovery on the LAIV-induced serum and mucosal immune responses, measured between days 0 and 21 post-vaccination.

Results

Higher levels of preexisting immunity to influenza A/H3N2 and B were strongly associated with strain-specific prevention of viral shedding upon LAIV receipt. While evidence of LAIV immunogenicity was observed for all 3 strains, the magnitudes of immune responses were most pronounced in children with no evidence of preexisting HAI and in those with detectable virus.

Conclusions

The results provide evidence for a bidirectional association between viral replication and immunity, and underscore the importance of accounting for preexisting immunity when evaluating virologic and immunologic responses to LAIVs.

Clinical Trials Registration

NCT01625689.

Influenza hemagglutinin antigenic distance measures capture trends in HAI differences and infection outcomes, but are not suitable predictive tools

Vaccination is the most effective method to combat influenza. Vaccine effectiveness is influenced by the antigenic distance between the vaccine strain and the actual circulating virus. Amino acid sequence based methods of quantifying the antigenic distance were designed to predict influenza vaccine effectiveness in humans. The use of these antigenic distance measures has been proposed as an additive method for seasonal vaccine selection. In this report, several antigenic distance measures were evaluated as predictors of hemagglutination inhibition titer differences and clinical outcomes following influenza vaccination or infection in mice or ferrets. The antigenic distance measures described the increasing trend in the change of HAI titer, lung viral titer and percent weight loss in mice and ferrets. However, the variability of outcome variables produced wide prediction intervals for any given antigenic distance value. The amino acid substitution based antigenic distance measures were no better predictors of viral load and weight loss than HAI titer differences, the current predictive measure of immunological correlate of protection for clinical signs after challenge.

IgA Responses Following Recurrent Influenza Virus Vaccination

Influenza is a highly contagious viral respiratory disease that affects millions of people worldwide each year. Annual vaccination is recommended by the World Health Organization to reduce influenza severity and limit transmission through elicitation of antibodies targeting mainly the hemagglutinin glycoprotein of the influenza virus. Antibodies elicited by current seasonal influenza vaccines are predominantly strain-specific. However, continuous antigenic drift by circulating influenza viruses facilitates escape from pre-existing antibodies requiring frequent reformulation of the seasonal influenza vaccine. Traditionally, immunological responses to influenza vaccination have been largely focused on IgG antibodies, with almost complete disregard of other isotypes. In this report, young adults (18–34 years old) and elderly (65–85 years old) subjects were administered the split inactivated influenza vaccine for 3 consecutive seasons and their serological IgA and IgG responses were profiled. Moreover, correlation analysis showed a positive relationship between vaccine-induced IgA antibody titers and traditional immunological endpoints, exposing vaccine-induced IgA antibodies as an important novel immune correlate during influenza vaccination.

Impact of influenza vaccine-modified infectivity on attack rate, case fatality ratio and mortality

Generally, vaccines are designed to provide protection against infection (susceptibility), disease (symptoms and transmissibility), and/or complications. In a recent study of influenza vaccination, it was observed that vaccinated yet infected individuals experienced increased transmission levels. In this paper, using a mathematical model of infection and transmission, we study the impact of vaccine-modified effects, including susceptibility and infectivity, on important epidemiological outcomes of an immunization program. The balance between vaccine-modified susceptibility, infectivity and recovery needed in preventing an influenza outbreak, or in mitigating the health outcomes of the outbreak is studied using the SIRV-type of disease transmission model. We also investigate the impact of influenza vaccination program on the infection risk of vaccinated and non-vaccinated individuals.

Effect of Previous-Season Influenza Vaccination on Serologic Response in Children During 3 Seasons, 2013-2014 Through 2015-2016

BACKGROUND

The effects of repeated influenza vaccination in children are not well understood. In this study, we evaluated previous vaccination effects on antibody response after vaccination with trivalent inactivated influenza vaccine (IIV) or quadrivalent live-attenuated influenza vaccine (LAIV) among school-aged children (5-17 years) across 3 seasons.

METHODS

Children were enrolled in the fall of 2013, 2014, and 2015. The participants received IIV or LAIV according to parent preference (2013-2014) or our randomization scheme (2014-2015). All study children received IIV in 2015-2016. Hemagglutination-inhibition assays measured antibody response to egg-grown vaccine strains from prevaccination and postvaccination serum samples. Geometric mean titers (GMTs) and increases in GMTs from before to after vaccination (geometric mean fold rise [GMFR]) were estimated from repeated-measures linear mixed models.

RESULTS

We enrolled 161 children in 2013-2014, 128 in 2014-2015, and 126 in 2015-2016. Among the IIV recipients, responses to the influenza A(H1N1)pdm09 and B vaccine strains were lowest among children who had received a previous-season IIV. The GMFRs for strains A(H1N1)pdm09 and B were 1.5 to 2.3 for previous-season IIV and 4.3 to 12.9 for previous-season LAIV or no previous vaccine. GMFRs were lower for strain A(H3N2), and differences according to previous-season vaccination history were smaller and not significant in most seasons. Most children had a post-IIV vaccination titer of ≥40 for vaccine strains in all seasons, regardless of previous-season vaccination history. Little to no increase in antibody levels was observed after vaccination with LAIV.

CONCLUSIONS

Serologic response to vaccination was greatest for IIV, but previous-season vaccination modified IIV response to A(H1N1)pdm09 and B. Influenza A(H3N2) responses were low in all groups, and LAIV generated minimal serologic response against all strains.

The Current and Future State of Vaccines, Antivirals and Gene Therapies Against Emerging Coronaviruses

Emerging coronaviruses (CoV) are constant global public health threats to society. Multiple ongoing clinical trials for vaccines and antivirals against CoVs showcase the availability of medical interventions to both prevent and treat the future emergence of highly pathogenic CoVs in human. However, given the diverse nature of CoVs and our close interactions with wild, domestic and companion animals, the next epidemic zoonotic CoV could resist the existing vaccines and antivirals developed, which are primarily focused on Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) and Middle East Respiratory Syndrome Coronavirus (MERS CoV). In late 2019, the novel CoV (SARS-CoV-2) emerged in Wuhan, China, causing global public health concern. In this review, we will summarize the key advancements of current vaccines and antivirals against SARS-CoV and MERS-CoV as well as discuss the challenge and opportunity in the current SARS-CoV-2 crisis. At the end, we advocate the development of a "plug-and-play" platform technologies that could allow quick manufacturing and administration of broad-spectrum countermeasures in an outbreak setting. We will discuss the potential of AAV-based gene therapy technology for in vivo therapeutic antibody delivery to combat SARS-CoV-2 outbreak and the future emergence of severe CoVs.

Understanding Immunity in Children Vaccinated With Live Attenuated Influenza Vaccine

Live attenuated influenza vaccine (LAIV), or FluMist, was approved for use in the United States in 2003. This vaccine, administered intranasally, offers the advantage of stimulating immunity at the site of infection in the upper respiratory tract and, by mimicking natural infection, has the potential to elicit a multifaceted immune response. However, the development of immunity following LAIV administration requires viral replication, causing vaccine effectiveness to be impacted by both the replicative fitness of the attenuated viruses being administered and the degree of the host's preexisting immunity. In this review, we discuss the current state of knowledge regarding the mechanisms of protection elicited by LAIV in children, contrast this with immune protection that develops upon vaccination with inactivated influenza vaccines, and briefly discuss both the potential advantages as well as challenges offered by this vaccination platform.

MiRNA Targeted NP Genome of Live Attenuated Influenza Vaccines Provide Cross-Protection against a Lethal Influenza Virus Infection

The miRNA-based strategy has been used to develop live attenuated influenza vaccines. In this study, the nucleoprotein (NP) genome segment of the influenza virus was inserted by different perfect miRNA-192-5p target sites, and the virus was rescued by standard reverse genetics method, so as to verify the virulence and protective efficacy of live attenuated vaccine in cells and mice. The results showed there was no significant attenuation in 192t virus with one perfect miRNA-192-5p target site, and 192t-3 virus with three perfect miRNA target sites. However, 192t-6 virus with 6 perfect miRNA target sites and 192t-9 virus with 9 perfect miRNA target sites were both significantly attenuated after infection, and their virulence were similar to that of temperature-sensitive (TS) influenza A virus (IAV) which is a temperature-sensitive live attenuated influenza vaccine. Mice were immunized with different doses of 192t-6, 192t-9, and TS IAV. Four weeks after immunization, the IgG in serum and IgA in lung homogenate were increased in the 192t-6, 192t-9, and TS IAV groups, and the numbers of IFN-γ secreting splenocytes were also increased in a dose-dependent manner. Finally, 192t-6, and 192t-9 can protect the mice against the challenge of homologous PR8 H1N1 virus and heterosubtypic H3N2 influenza virus. MiRNA targeted viruses 192t-6 and 192t-9 were significantly attenuated and showed the same virulence as TS IAV and played a role in the cross-protection.

Differences in nasal immunoglobulin A responses to influenza vaccine strains after live attenuated influenza vaccine (LAIV) immunization in children

Different vaccine strains included in the live attenuated influenza vaccine (LAIV) have variable efficacy. The reasons for this are not clear and may include differences in immunogenicity. We report a Phase IV open-label study on the immunogenicity of a single dose of quadrivalent LAIV (Fluenz™ Tetra) in children during the 2015/16 season, to investigate the antibody responses to different strains. Eligible children were enrolled to receive LAIV; nasal samples were collected before and approximately 4 weeks after immunization. There was a significant increase in nasal immunoglobulin (Ig)A to the H3N2, B/Victoria lineage (B/Brisbane) and B/Yamagata lineage (B/Phuket) components, but not to the H1N1 component. The fold change in nasal IgA response was inversely proportional to the baseline nasal IgA titre for H1N1, H3N2 and B/Brisbane. We investigated possible associations that may explain baseline nasal IgA, including age and prior vaccination status, but found different patterns for different antigens, suggesting that the response is multi-factorial. Overall, we observed differences in immune responses to different viral strains included in the vaccine; the reasons for this require further investigation.

A Live Attenuated Influenza Vaccine Elicits Enhanced Heterologous Protection When the Internal Genes of the Vaccine Are Matched to Those of the Challenge Virus

Influenza A virus (IAV) causes significant morbidity and mortality, despite the availability of viral vaccines. The efficacy of live attenuated influenza vaccines (LAIVs) has been especially poor in recent years. One potential reason is that the master donor virus (MDV), on which all LAIVs are based, contains either the internal genes of the 1960 A/Ann Arbor/6/60 or the 1957 A/Leningrad/17/57 H2N2 viruses (i.e., they diverge considerably from currently circulating strains). We previously showed that introduction of the temperature-sensitive (ts) residue signature of the AA/60 MDV into a 2009 pandemic A/California/04/09 H1N1 virus (Cal/09) results in only 10-fold in vivo attenuation in mice. We have previously shown that the ts residue signature of the Russian A/Leningrad/17/57 H2N2 LAIV (Len LAIV) more robustly attenuates the prototypical A/Puerto Rico/8/1934 (PR8) H1N1 virus. In this work, we therefore introduced the ts signature from Len LAIV into Cal/09. This new Cal/09 LAIV is ts in vitro, highly attenuated (att) in mice, and protects from a lethal homologous challenge. In addition, when our Cal/09 LAIV with PR8 hemagglutinin and neuraminidase was used to vaccinate mice, it provided enhanced protection against a wild-type Cal/09 challenge relative to a PR8 LAIV with the same attenuating mutations. These findings suggest it may be possible to improve the efficacy of LAIVs by better matching the sequence of the MDV to currently circulating strains.IMPORTANCE Seasonal influenza infection remains a major cause of disease and death, underscoring the need for improved vaccines. Among current influenza vaccines, the live attenuated influenza vaccine (LAIV) is unique in its ability to elicit T-cell immunity to the conserved internal proteins of the virus. Despite this, LAIV has shown limited efficacy in recent years. One possible reason is that the conserved, internal genes of all current LAIVs derive from virus strains that were isolated between 1957 and 1960 and that, as a result, do not resemble currently circulating influenza viruses. We have therefore developed and tested a new LAIV, based on a currently circulating pandemic strain of influenza. Our results show that this new LAIV elicits improved protective immunity compared to a more conventional LAIV.

Nasal priming with immunobiotic lactobacilli improves the adaptive immune response against influenza virus

The nasal priming with Lactobacillus rhamnosus CRL1505 modulates the respiratory antiviral innate immune response and improves protection against influenza virus (IFV) challenge in mice. However, the potential beneficial effect of the CRL1505 strain on the adaptive immune response triggered by IFV infection or vaccination was not evaluated before. In this work, we demonstrated that nasally administered L. rhamnosus CRL1505 is able to improve both the humoral and cellular adaptive immune responses induced by IFV infection or vaccination. Higher levels of IFV-specific IgA and IgG as well as IFN-γ were found in the serum and the respiratory tract of CRL1505-treated mice after IFV challenge. Lactobacilli treated mice also showed reduced concentrations of IL-17 and improved levels of IL-10 during IFV infection. The differential balance of inflammatory and regulatory cytokines induced by L. rhamnosus CRL1505 contributed to the protection against IFV by favoring an effective effector immune response without inducing inflammatory-mediated lung damage. The optimal immunomodulatory effect of the CRL1505 strain was achieved with viable bacteria. However, non-viable L. rhamnosus CRL1505 was also efficient in improving the adaptive immune responses generated by IFV challenges and therefore, emerged as an interesting alternative for vaccination of immunocompromised hosts. Similar to other immunomodulatory properties of lactobacilli, it was shown here that the adjuvant effect in the context of IFV vaccination was a strain dependent ability, since differences were found when L. rhamnosus CRL1505 and the immunomodulatory strain L. rhamnosus IBL027 were compared. This investigation represents a thorough exploration of the role of immunobiotic lactobacilli in improving humoral and cellular adaptive immune responses against IFV in the context of both infection and vaccination.

Co-encapsulation of synthetic lipidated TLR4 and TLR7/8 agonists in the liposomal bilayer results in a rapid, synergistic enhancement of vaccine-mediated humoral immunity

To increase vaccine immunogenicity, modern vaccines incorporate adjuvants, which serve to enhance immune cross-protection, improve humoral and cell-mediated immunity, and promote antigen dose sparing. Pattern recognition receptors (PRRs), including the Toll-like receptor (TLR) family are promising targets for development of agonist formulations for use as vaccine adjuvants. Combinations of co-delivered TLR4 and TLR7/8 ligands have been demonstrated to have synergistic effects on innate and adaptive immune response. Here, we create liposomes that stably co-encapsulate CRX-601, a synthetic TLR4 agonist, and UM-3004, a lipidated TLR7/8 agonist, within the liposomal bilayer in order to achieve co-delivery, allow tunable physical properties, and induce in vitro and in vivo immune synergy. Co-encapsulation demonstrates a synergistic increase in IL-12p70 cytokine output in vitro from treated human peripheral blood mononuclear cells (hPBMCs). Further, co-encapsulated formulations give significant improvement of early IgG2a antibody titers in BALB/c mice following primary vaccination when compared to single agonist or dual agonists delivered in separate liposomes. This work demonstrates that co-encapsulation of TLR4 and lipidated TLR7/8 agonists within the liposomal bilayer leads to innate and adaptive immune synergy which biases a Th1 immune response. Thus, liposomal co-encapsulation may be a useful and flexible tool for vaccine adjuvant formulation containing multiple TLR agonists.

Updates on immunologic correlates of vaccine-induced protection

Correlates of protection (CoPs) are increasingly important in the development and licensure of vaccines. Although the study of CoPs was initially directed at identifying a single immune function that could explain vaccine efficacy, it has become increasingly clear that there are often multiple functions responsible for efficacy. This review is meant to supplement prior articles on the subject, illustrating both simple and complex CoPs.

Comparative Immunogenicity of the 2014-2015 Northern Hemisphere Trivalent IIV and LAIV against Influenza A Viruses in Children

Both inactivated influenza vaccines (IIV) and live-attenuated influenza vaccines (LAIV) have been recommended for administration to children. Children are a high-risk group for severe influenza, and a major source of transmission. Therefore, prevention of infection by vaccination is particularly important. However, efficacy and immunogenicity of these vaccines are known to vary by season and geographic location. We compared the immunogenicity of the 2014–2015 Northern Hemisphere trivalent IIV and LAIV against influenza A virus in Canadian Hutterite children aged 2 to 17 using hemagglutination inhibition (HAI) assays, and enzyme-linked immunosorbent assays to measure hemagglutinin-specific serum IgA and mucosal IgA. Both vaccine formulations induced significant increases in HAI titers against H1N1 and H3N2 vaccine strains. Serum IgA titers against H3N2 were significantly boosted by both IIV and LAIV, while only IIV induced a significant increase in serum IgA specific to the H1N1 vaccine strain. While HAI titers correlated with protection conferred by IIV, mucosal IgA titers correlated with protection conferred by LAIV (mucosal IgA titers could not be established as a correlate for IIV due to sample size limitations). IIV and LAIV were previously reported to be equally efficacious in this cohort, although the immunogenicity of IIV was generally superior.

Influenza and Antibody-Dependent Cellular Cytotoxicity

Despite the availability of yearly vaccinations, influenza continues to cause seasonal, and pandemic rises in illness and death. An error prone replication mechanism results in antigenic drift and viral escape from immune pressure, and recombination results in antigenic shift that can rapidly move through populations that lack immunity to newly emergent strains. The development of a “universal” vaccine is a high priority and many strategies have been proposed, but our current understanding of influenza immunity is incomplete making the development of better influenza vaccines challenging. Influenza immunity has traditionally been measured by neutralization of virions and hemagglutination inhibition, but in recent years there has been a growing appreciation of other responses that can contribute to protection such as antibody-dependent cellular cytotoxicity (ADCC) that can kill influenza-infected cells. ADCC has been shown to provide cross-strain protection and to assist in viral clearance, making it an attractive target for “universal” vaccine designs. Here we provide a brief overview of the current state of influenza research that leverages “the other end of the antibody.”