Basics of CD8 T-cell immune responses after influenza infection and vaccination with inactivated or live attenuated influenza vaccine

The contributions of T cell-mediated immunity to protection from vaccine-preventable diseases: A primer

In the face of the ever-present burden of emerging and reemerging infectious diseases, there is a growing need to comprehensively assess individual- and population-level immunity to vaccine-preventable diseases (VPDs). Many of these efforts, however, focus exclusively on antibody-mediated immunity, ignoring the role of T cells. Aimed at clinicians, public health practioners, and others who play central roles in human vaccine research but do not have formal training in immunology, we review how vaccines against infectious diseases elicit T cell responses, what types of vaccines elicit T cell responses, and how T cell responses are measured. We then use examples to demonstrate six ways that T cells contribute to protection from VPD, including directly mediating protection, enabling antibody responses, reducing disease severity, increasing cross-reactivity, improving durability, and protecting special populations. We conclude with a discussion of challenges and solutions to more widespread consideration of T cell responses in clinical vaccinology.

Safety and Immunogenicity of a Carbohydrate Fatty Acid Monosulphate Ester Adjuvant Combined with a Low-Dose Quadrivalent Split-Virion Inactivated Influenza Vaccine: A Randomised, Observer-Blind, Active-Controlled, First-in-Human, Phase 1 Study

Seasonal influenza vaccine effectiveness is low. Carbohydrate fatty acid monosulphate ester (CMS), a new oil-in-water adjuvant, has proven potency in animal models with suggested capacity for dose-sparing. The objective was to evaluate safety and immunogenicity of CMS when added to a low-dose influenza vaccine (QIV) in humans. In a randomised, double-blind, active-controlled, first-in-human study, sixty participants (18-50 years) received either 0.5 mg CMS or 2 mg CMS with 1/5th dose QIV, or a full dose QIV without CMS. Adverse events (AE) were monitored until 7 days post-vaccination. Haemagglutinin inhibition (HI) titres in serum and CD4+ T cells in PBMCs were determined at day 0, 7, 28, and 180. Mean age was 37.6 (±10.1) years and 42/60 (70.0%) were female. Pain at injection site (42/60, 86.7%) and headache (34/60, 56.7%) were reported most and more frequently in the 2 mg CMS group. HI titres and the frequency of influenza specific CD4+ T cells were equal across strains for the three cohorts on all visits, increased until day 28 and decreased at day 180 to values higher than baseline. CMS was safe in humans. Humoral and cell-mediated immunogenicity was similar across vaccines, even with 1/5th antigen dose. CMS can have beneficial implications in low-resource settings or in a pandemic context.

Cold-adapted influenza vaccine carrying three repeats of a respiratory syncytial virus (RSV) fusion glycoprotein epitope site protects BALB/c mice and cotton rats against RSV infection

Respiratory syncytial virus is the major cause of respiratory viral infections, particularly in infants, immunocompromised populations, and the elderly (over 65 years old), the prevention of RSV infection has become a priority. In this study, we generated a chimeric influenza virus, termed LAIV/RSV/HA-3F, using reverse genetics technology which contained three repeats of the RSV fusion protein neutralizing epitope site II to the N terminal in the background of the hemagglutinin (HA) gene of cold adapted influenza vaccine A/California/7/2009 ca. LAIV/RSV/HA-3F exhibited cold-adapted (ca) and attenuated (att) phenotype. BALB/c mice immunized intranasally with LAIV/RSV/HA-3F showed robust immunogenicity, inducing viral-specific antibody responses against both influenza and RSV, eliciting RSV-specific humoral, cellular and mucosal immune responses. LAIV/RSV/HA-3F also conferred protection as indicated by reduced viral titers and improved lung histopathological alterations against live RSV virus challenge. Mechanismly, single-cell RNA sequencing (scRNA-seq) and single-cell T cell antigen receptor (TCR) sequencing were employed to characterize the immune responses triggered by chimeric RSV vaccine, displaying that LAIV/RSV/HA-3F provided protection mainly via interferon-γ (IFN-γ). Moreover, we found that LAIV/RSV/HA-3F significantly inhibited viral replication in the challenged lung and protected against subsequent RSV challenge in cotton rats without causing lung disease. Taken together, our findings demonstrated that LAIV/RSV/HA-3F has potential as a promising bivalent vaccine with dual purpose candidate for the prevention of influenza and RSV, and preclinical and clinical studies warrant further investigations.

Recombinant Hemagglutinin Protein from H9N2 Avian Influenza Virus Exerts Good Immune Effects in Mice

The H9N2 subtype of avian influenza virus (AIV) causes enormous economic losses and poses a significant threat to public health; the development of vaccines against avian influenza is ongoing. To study the immunogenicity of hemagglutinin (HA) protein, we constructed a recombinant pET-32a-HA plasmid, induced HA protein expression with isopropyl β-D-1-thiogalactopyranoside (IPTG), verified it by SDS-PAGE and Western blotting, and determined the sensitivity of the recombinant protein to acid and heat. Subsequently, mice were immunized with the purified HA protein, and the immunization effect was evaluated according to the hemagglutination inhibition (HI) titer, serum IgG antibody titer, and cytokine secretion level of the mice. The results showed that the molecular weight of the HA protein was approximately 84 kDa, and the protein existed in both soluble and insoluble forms; in addition, the HA protein exhibited good acid and thermal stability, the HI antibody titer reached 6 log2-8 log2, and the IgG-binding antibody titer was 1:1,000,000. Moreover, the levels of IL-2, IL-4, and IL-5 in the immunized mouse spleen cells were significantly increased compared with those in the control group. However, the levels of IL-1β, IL-6, IL-13, IFN-γ, IL-18, TNF-α, and GM-CSF were decreased in the immunized group. The recombinant HA protein utilized in this study exhibited good stability and exerted beneficial immune effects, providing a theoretical basis for further research on influenza vaccines.

A Live Attenuated H1N1 Influenza Vaccine Based on the Mutated M Gene

The influenza vaccines currently approved for clinical use mainly include inactivated influenza virus vaccines and live attenuated influenza vaccines (LAIVs). LAIVs have multiple advantages, such as ease of use and strong immunogenicity, and can provide cross-protection. In this study, the M gene of the PR8 virus was mutated as follows (G11T, C79G, G82C, C85G, and C1016A), and a live attenuated influenza virus containing the mutated M gene was rescued and obtained using reverse genetic technology as a vaccine candidate. The replication ability of the rescued virus was significantly weakened in both MDCK cells and mice with attenuated virulence. Studies on immunogenicity found that 1000 TCID50 of mutated PR8 (mPR8) can prime strong humoral and cellular immune responses. Single-dose immunization of 1000 TCID50 mPR8 was not only able to counter the challenge of the homologous PR8 virus but also provided cross-protection against the heterologous H9N2 virus.

An intranasal combination vaccine induces systemic and mucosal immunity against COVID-19 and influenza

Despite prolonged surveillance and interventions, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza viruses continue to pose a severe global health burden. Thus, we developed a chimpanzee adenovirus-based combination vaccine, AdC68-HATRBD, with dual specificity against SARS-CoV-2 and influenza virus. When used as a standalone vaccine, intranasal immunization with AdC68-HATRBD induced comprehensive and potent immune responses consisting of immunoglobin (Ig) G, mucosal IgA, neutralizing antibodies, and memory T cells, which protected the mice from BA.5.2 and pandemic H1N1 infections. When used as a heterologous booster, AdC68-HATRBD markedly improved the protective immune response of the licensed SARS-CoV-2 or influenza vaccine. Therefore, whether administered intranasally as a standalone or booster vaccine, this combination vaccine is a valuable strategy to enhance the overall vaccine efficacy by inducing robust systemic and mucosal immune responses, thereby conferring dual lines of immunological defenses for these two viruses.

Development of a highly sensitive TaqMan method based on multi-probe strategy: its application in ASFV detection

The establishment of high sensitive detection method for various pathogenic microorganisms remains constantly concerned. In the present study, multi-probe strategy was first systematically investigated followed by establishing a highly sensitive TaqMan real-time fluorescent quantitative PCR (qPCR) method for detecting African swine fever virus (ASFV). Briefly, four probes based on the B646L gene of ASFV were designed and the effects of different combinations of the probes in a single TaqMan qPCR assay on the detection sensitivity were investigated. As less as 0.5-5 copies/μl of the ASFV gene was detected by the established TaqMan qPCR assay. Furthermore, plasmid harboring the B646L in water samples could be concentrated 1000 times by ultrafiltration to enable a highly sensitive detection of trace viral nucleic acids. Moreover, no cross-reactivity was observed with other common clinical swine viruses such as PCV2, PCV3, PCV4, PEDV, PDCoV, CSFV, PRRSV, and PRV. When detecting 173 clinical porcine serum samples, the coincidence rate between the developed method and WOAH (World Organization of Animal Health) recommended method was 100%. This study might provide an integrated strategy to achieve higher detection sensitivity of trace pathogenic microorganisms and applicably sensitive TaqMan-based qPCR assays.

Egg microneedles for transdermal vaccination of inactivated influenza virus

The use of dissolving microneedles (DMNs) is a drug delivery technique in which drug dissolution occurs once it is administered into the skin. The skin is a remarkable site for vaccination due to its significant immunologic properties. Compared to the traditional hypodermic intramuscular (IM) injection, vaccination via DMN does not require cold chains and allows for minimal invasive drug delivery. On account of the significance of skin vaccination, preceding studies have been conducted to elucidate the importance of the DMN technology in vaccination. Most of these studies focused on formulations that maintain the activity of the vaccine, so formulations designed to be specific to the mechanical properties of the microneedle could not be used together independently. In this study, we have developed influenza vaccine loaded egg microneedles (EMN) and characterized the specificity of layer-specific functions of EMN by distinguishing between formulations that can maintain the activity of the vaccine and have the mechanical strength. By the use of in vitro tests such as ELISA and SRID assays, we quantitively evaluated the antigen activity of the formulation candidates to be 87% and 91%, respectively. In vivo tests were also conducted as mouse groups were inoculated with the formulation constructed into egg microneedles (FLU-EMN) to determine the protective efficacy against infection. The results demonstrated that FLU-EMN with functionalized formulations successfully enabled protective immune response even with a fractional dose compared to IM injection.

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.

Clade 2.3.4.4 H5 chimeric cold-adapted attenuated influenza vaccines induced cross-reactive protection in mice and ferrets

IMPORTANCE

Clade 2.3.4.4 H5Nx avian influenza viruses (AIVs) have circulated globally and caused substantial economic loss. Increasing numbers of humans have been infected with Clade 2.3.4.4 H5N6 AIVs in recent years. Only a few human influenza vaccines have been licensed to date. However, the licensed live attenuated influenza virus vaccine exhibited the potential of being recombinant with the wild-type influenza A virus (IAV). Therefore, we developed a chimeric cold-adapted attenuated influenza vaccine based on the Clade 2.3.4.4 H5 AIVs. These H5 vaccines demonstrate the advantage of being non-recombinant with circulated IAVs in the future influenza vaccine study. The findings of our current study reveal that these H5 vaccines can induce cross-reactive protective efficacy in mice and ferrets. Our H5 vaccines may provide a novel option for developing human-infected Clade 2.3.4.4 H5 AIV vaccines.

Nucleoprotein as a Promising Antigen for Broadly Protective Influenza Vaccines

Annual vaccination is considered as the main preventive strategy against seasonal influenza. Due to the highly variable nature of major viral antigens, such as hemagglutinin (HA) and neuraminidase (NA), influenza vaccine strains should be regularly updated to antigenically match the circulating viruses. The influenza virus nucleoprotein (NP) is much more conserved than HA and NA, and thus seems to be a promising target for the design of improved influenza vaccines with broad cross-reactivity against antigenically diverse influenza viruses. Traditional subunit or recombinant protein influenza vaccines do not contain the NP antigen, whereas live-attenuated influenza vaccines (LAIVs) express the viral NP within infected cells, thus inducing strong NP-specific antibodies and T-cell responses. Many strategies have been explored to design broadly protective NP-based vaccines, mostly targeted at the T-cell mode of immunity. Although the NP is highly conserved, it still undergoes slow evolutionary changes due to selective immune pressure, meaning that the particular NP antigen selected for vaccine design may have a significant impact on the overall immunogenicity and efficacy of the vaccine candidate. In this review, we summarize existing data on the conservation of the influenza A viral nucleoprotein and review the results of preclinical and clinical trials of NP-targeting influenza vaccine prototypes, focusing on the ability of NP-specific immune responses to protect against diverse influenza viruses.

Revisiting live attenuated influenza vaccine efficacy among children in developing countries

Seasonal influenza epidemics cause significant pediatric mortality and morbidity worldwide. Live attenuated influenza vaccines (LAIVs) can be administered intranasally, induce a broad and robust immune response, demonstrate higher yields during manufacturing as compared to inactivated influenza vaccines (IIVs), and thereby represent an attractive possibility for young children in developing countries. We summarize recent pediatric studies evaluating LAIV efficacy in developing countries where a large proportion of the influenza-virus-associated respiratory disease burden occurs. Recently, two randomized controlled trials (RCTs) assessing Russian-backbone trivalent LAIV in children reported contradictory results; vaccine efficacy varied between Bangladesh (41 %) and Senegal (0.0 %) against all influenza viral strains. Prior to 2013, Ann Arbor-based LAIV demonstrated superior efficacy as compared to IIV. However, due to low effectiveness of the Ann Arbor-based LAIV against influenza A(H1N1)pdm09-like viruses, the CDC Advisory Committee on Immunization Practices (ACIP) recommended against the use of LAIV during the 2016-17 and 2017-18 influenza seasons. Reduced replicative fitness of the A(H1N1)pdm09 LAIV strains is thought to have led to the low effectiveness of the Ann-Arbor-based LAIV. Once the A(H1N1)pdm09 component was updated, the ACIP reintroduced the Ann-Arbor-based LAIV as a vaccine choice for the 2018-19 influenza season. In 2021, results from a 2-year RCT evaluating the Russian-backbone trivalent LAIV in rural north India reported that LAIV demonstrated significantly lower efficacy compared to IIV, but in Year 2, the vaccine efficacy for LAIV and IIV was comparable. A profounder understanding of the mechanisms underlying varied efficacy of LAIV in developing countries is warranted. Assessing replicative fitness, in addition to antigenicity, when selecting annual A(H1N1)pdm09 components in the Russian-backbone trivalent LAIVs is essential and may ultimately, enable widespread utility in resource-poor settings.

T-Cell Immunity in COVID-19-Recovered Individuals and Individuals Vaccinated with the Combined Vector Vaccine Gam-COVID-Vac

The COVID-19 pandemic has required extensive research on the new coronavirus SARS-CoV-2 and the creation of new highly effective vaccines. The presence of T-cells in the body that respond to virus antigens suggests adequate antiviral immunity. We investigated T-cell immunity in individuals who recovered from mild and moderate COVID-19 and in individuals vaccinated with the Gam-COVID-Vac combined vector vaccine. The ELISPOT method was used to determine the number of T-cells responding with IFN-γ synthesis to stimulation by peptides containing epitopes of the S-protein or N-, M-, ORF3, and ORF7 proteins, using peripheral blood mononuclear cells (PBMCs). At the same time, the multiplex method was used to determine the accumulation of IFN-γ and other cytokines in the culture medium. According to the data obtained, the proportion of positive conclusions about the T-cell immune response to SARS-CoV-2 antigens in control, recovered, and vaccinated individuals was 12%, 70%, and 52%, respectively. At the same time, more than half of the vaccinated individuals with a T-cell response were sensitized to the antigens of N-, M-, ORF3, and ORF7 proteins not produced by Gam-COVID-Vac, indicating a high likelihood of asymptomatic SARS-CoV-2 infection. Increased IFN-γ release by single sensitized T-cells in response to specific stimulation in recovered and vaccinated individuals did not result in the accumulation of this and other cytokines in the culture medium. These findings suggest a balance between cytokine production and utilization by immunocompetent cells as a prerequisite for providing a controlled cytokine signal and avoiding a "cytokine storm".

Recombinant single-cycle influenza virus with exchangeable pseudotypes allows repeated immunization to augment anti-tumour immunity with immune checkpoint inhibitors

Virus-based tumour vaccines offer many advantages compared to other antigen-delivering systems. They generate concerted innate and adaptive immune response, and robust CD8⁺ T cell responses. We engineered a non-replicating pseudotyped influenza virus (S-FLU) to deliver the well-known cancer testis antigen, NY-ESO-1 (NY-ESO-1 S-FLU). Intranasal or intramuscular immunization of NY-ESO-1 S-FLU virus in mice elicited a strong NY-ESO-1-specific CD8⁺ T cell response in lungs and spleen that resulted in the regression of NY-ESO-1-expressing lung tumour and subcutaneous tumour, respectively. Combined administration with anti-PD-1 antibody, NY-ESO-1 S-FLU virus augmented the tumour protection by reducing the tumour metastasis. We propose that the antigen delivery through S-FLU is highly efficient in inducing antigen-specific CD8⁺ T cell response and protection against tumour development in combination with PD-1 blockade.

The role of cell-mediated immunity against influenza and its implications for vaccine evaluation

Influenza vaccines remain the most effective tools to prevent flu and its complications. Trivalent or quadrivalent inactivated influenza vaccines primarily elicit antibodies towards haemagglutinin and neuraminidase. These vaccines fail to induce high protective efficacy, in particular in older adults and immunocompromised individuals and require annual updates to keep up with evolving influenza strains (antigenic drift). Vaccine efficacy declines when there is a mismatch between its content and circulating strains. Current correlates of protection are merely based on serological parameters determined by haemagglutination inhibition or single radial haemolysis assays. However, there is ample evidence showing that these serological correlates of protection can both over- or underestimate the protective efficacy of influenza vaccines. Next-generation universal influenza vaccines that induce cross-reactive cellular immune responses (CD4+ and/or CD8+ T-cell responses) against conserved epitopes may overcome some of the shortcomings of the current inactivated vaccines by eliciting broader protection that lasts for several influenza seasons and potentially enhances pandemic preparedness. Assessment of cellular immune responses in clinical trials that evaluate the immunogenicity of these new generation vaccines is thus of utmost importance. Moreover, studies are needed to examine whether these cross-reactive cellular immune responses can be considered as new or complementary correlates of protection in the evaluation of traditional and next-generation influenza vaccines. An overview of the assays that can be applied to measure cell-mediated immune responses to influenza with their strengths and weaknesses is provided here.

Live attenuated influenza A virus vaccines with modified NS1 proteins for veterinary use

Influenza A viruses (IAV) spread rapidly and can infect a broad range of avian or mammalian species, having a tremendous impact in human and animal health and the global economy. IAV have evolved to develop efficient mechanisms to counteract innate immune responses, the first host mechanism that restricts IAV infection and replication. One key player in this fight against host-induced innate immune responses is the IAV non-structural 1 (NS1) protein that modulates antiviral responses and virus pathogenicity during infection. In the last decades, the implementation of reverse genetics approaches has allowed to modify the viral genome to design recombinant IAV, providing researchers a powerful platform to develop effective vaccine strategies. Among them, different levels of truncation or deletion of the NS1 protein of multiple IAV strains has resulted in attenuated viruses able to induce robust innate and adaptive immune responses, and high levels of protection against wild-type (WT) forms of IAV in multiple animal species and humans. Moreover, this strategy allows the development of novel assays to distinguish between vaccinated and/or infected animals, also known as Differentiating Infected from Vaccinated Animals (DIVA) strategy. In this review, we briefly discuss the potential of NS1 deficient or truncated IAV as safe, immunogenic and protective live-attenuated influenza vaccines (LAIV) to prevent disease caused by this important animal and human pathogen.

Development of a T Cell-Based COVID-19 Vaccine Using a Live Attenuated Influenza Vaccine Viral Vector

The COVID-19 pandemic emerged in 2020 and has caused an unprecedented burden to all countries in the world. SARS-CoV-2 continues to circulate and antigenically evolve, enabling multiple reinfections. To address the issue of the virus antigenic variability, T cell-based vaccines are being developed, which are directed to more conserved viral epitopes. We used live attenuated influenza vaccine (LAIV) virus vector to generate recombinant influenza viruses expressing various T-cell epitopes of SARS-CoV-2 from either neuraminidase (NA) or non-structural (NS1) genes, via the P2A self-cleavage site. Intranasal immunization of human leukocyte antigen-A*0201 (HLA-A2.1) transgenic mice with these recombinant viruses did not result in significant SARS-CoV-2-specific T-cell responses, due to the immunodominance of NP₃₆₆ influenza T-cell epitope. However, side-by-side stimulation of peripheral blood mononuclear cells (PBMCs) of COVID-19 convalescents with recombinant viruses and LAIV vector demonstrated activation of memory T cells in samples stimulated with LAIV/SARS-CoV-2, but not LAIV alone. Hamsters immunized with a selected LAIV/SARS-CoV-2 prototype were protected against challenge with influenza virus and a high dose of SARS-CoV-2 of Wuhan and Delta lineages, which was confirmed by reduced weight loss, milder clinical symptoms and less pronounced histopathological signs of SARS-CoV-2 infection in the lungs, compared to LAIV- and mock-immunized animals. Overall, LAIV is a promising platform for the development of a bivalent vaccine against influenza and SARS-CoV-2.

Mutation L319Q in the PB1 Polymerase Subunit Improves Attenuation of a Candidate Live-Attenuated Influenza A Virus Vaccine

Influenza A viruses (IAV) remain emerging threats to human public health. Live-attenuated influenza vaccines (LAIV) are one of the most effective prophylactic options to prevent disease caused by influenza infections. However, licensed LAIV remain restricted for use in 2- to 49-year-old healthy and nonpregnant people. Therefore, development of LAIV with increased safety, immunogenicity, and protective efficacy is highly desired. The U.S.-licensed LAIV is based on the master donor virus (MDV) A/Ann Arbor/6/60 H2N2 backbone, which was generated by adaptation of the virus to growth at low temperatures. Introducing the genetic signature of the U.S. MDV into the backbone of other IAV strains resulted in varying levels of attenuation. While the U.S. MDV mutations conferred an attenuated phenotype to other IAV strains, the same amino acid changes did not significantly attenuate the pandemic A/California/04/09 H1N1 (pH1N1) strain. To attenuate pH1N1, we replaced the conserved leucine at position 319 with glutamine (L319Q) in PB1 and analyzed the in vitro and in vivo properties of pH1N1 viruses containing either PB1 L319Q alone or in combination with the U.S. MDV mutations using two animal models of influenza infection and transmission, ferrets and guinea pigs. Our results demonstrated that L319Q substitution in the pH1N1 PB1 alone or in combination with the mutations of the U.S. MDV resulted in reduced pathogenicity (ferrets) and transmission (guinea pigs), and an enhanced temperature sensitive phenotype. These results demonstrate the feasibility of generating an attenuated MDV based on the backbone of a contemporary pH1N1 IAV strain. IMPORTANCE Vaccination represents the most effective strategy to reduce the impact of seasonal IAV infections. Although LAIV are superior in inducing protection and sterilizing immunity, they are not recommended for many individuals who are at high risk for severe disease. Thus, development of safer and more effective LAIV are needed. A concern with the current MDV used to generate the U.S.-licensed LAIV is that it is based on a virus isolated in 1960. Moreover, mutations that confer the temperature-sensitive, cold-adapted, and attenuated phenotype of the U.S. MDV resulted in low level of attenuation in the contemporary pandemic A/California/04/09 H1N1 (pH1N1). Here, we show that introduction of PB1 L319Q substitution, alone or in combination with the U.S. MDV mutations, resulted in pH1N1 attenuation. These findings support the development of a novel LAIV MDV based on a contemporary pH1N1 strain as a medical countermeasure against currently circulating H1N1 IAV.

Human influenza virus challenge identifies cellular correlates of protection for oral vaccination

Developing new influenza vaccines with improved performance and easier administration routes hinges on defining correlates of protection. Vaccine-elicited cellular correlates of protection for influenza in humans have not yet been demonstrated. A phase-2 double-blind randomized placebo and active (inactivated influenza vaccine) controlled study provides evidence that a human-adenovirus-5-based oral influenza vaccine tablet (VXA-A1.1) can protect from H1N1 virus challenge in humans. Mass cytometry characterization of vaccine-elicited cellular immune responses identified shared and vaccine-type-specific responses across B and T cells. For VXA-A1.1, the abundance of hemagglutinin-specific plasmablasts and plasmablasts positive for integrin α4β7, phosphorylated STAT5, or lacking expression of CD62L at day 8 were significantly correlated with protection from developing viral shedding following virus challenge at day 90 and contributed to an effective machine learning model of protection. These findings reveal the characteristics of vaccine-elicited cellular correlates of protection for an oral influenza vaccine.

Safety, Immunogenicity, and Protective Efficacy of an H5N1 Chimeric Cold-Adapted Attenuated Virus Vaccine in a Mouse Model

H5N1 influenza virus is a threat to public health worldwide. The virus can cause severe morbidity and mortality in humans. We constructed an H5N1 influenza candidate virus vaccine from the A/chicken/Guizhou/1153/2016 strain that was recommended by the World Health Organization. In this study, we designed an H5N1 chimeric influenza A/B vaccine based on a cold-adapted (ca) influenza B virus B/Vienna/1/99 backbone. We modified the ectodomain of H5N1 hemagglutinin (HA) protein, while retaining the packaging signals of influenza B virus, and then rescued a chimeric cold-adapted H5N1 candidate influenza vaccine through a reverse genetic system. The chimeric H5N1 vaccine replicated well in eggs and the Madin-Darby Canine Kidney cells. It maintained a temperature-sensitive and cold-adapted phenotype. The H5N1 vaccine was attenuated in mice. Hemagglutination inhibition (HAI) antibodies, micro-neutralizing (MN) antibodies, and IgG antibodies were induced in immunized mice, and the mucosal IgA antibody responses were detected in their lung lavage fluids. The IFN-γ-secretion and IL-4-secretion by the mouse splenocytes were induced after stimulation with the specific H5N1 HA protein. The chimeric H5N1 candidate vaccine protected mice against lethal challenge with a wild-type highly pathogenic avian H5N1 influenza virus. The chimeric H5 candidate vaccine is thus a potentially safe, attenuated, and reassortment-incompetent vaccine with circulating A viruses.

Approaches in broadening the neutralizing antibody response of the influenza vaccine

INTRODUCTION

Influenza vaccine is the mainstay for influenza prevention and elicits immune response and antigen-specific neutralizing antibodies against influenza virus. However, antigenic drift and shift can confer influenza virus to escape from the immune response induced by vaccine, and then reduce the vaccine effectiveness.

AREAS COVERED

To improve effect and neutralizing antibody response of vaccine for heterologous influenza virus, a literature review of preclinical and clinical studies published before August 2021 and searched in PubMed, which evaluated vaccine effectiveness improved by adjuvants and administration route.

EXPERT OPINION

The review showed that adjuvant, including imiquimod, GLA, MF59, and AS03, can improve the effectiveness of influenza vaccines by regulating immune system. Subjects receiving influenza vaccine combined with these adjuvants showed enhanced antibody response against homologous and heterologous virus strains compared to those vaccinated without adjuvant. This review also discussed the role of intradermal vaccination. In contrast to intramuscular vaccination, intradermal vaccination elicited a robust and prolonged antibody response against vaccine strains and drifted virus than intramuscular vaccination.

Influenza vaccine: progress in a vaccine that elicits a broad immune response

INTRODUCTION

The licensed seasonal influenza vaccines predominantly induce neutralizing antibodies against immunodominant hypervariable epitopes of viral surface proteins, with limited protection against antigenically distant influenza viruses. Strategies have been developed to improve vaccines' performance in terms of broadly reactive and long-lasting immune response induction.

AREAS COVERED

We have summarized the advancements in the development of cross-protective influenza vaccines and discussed the challenges in evaluating them in preclinical and clinical trials. Here, the literature regarding the current stage of development of universal influenza vaccine candidates was reviewed.

EXPERT OPINION

Although various strategies aim to redirect adaptive immune responses from variable immunodominant to immunosubdominant antigens, more conserved epitopes are being investigated. Approaches that improve antibody responses to conserved B cell epitopes have increased the protective efficacy of vaccines within a subtype or phylogenetic group of influenza viruses. Vaccines that elicit significant levels of T cells recognizing highly conserved viral epitopes possess a high cross-protective potential and may cover most circulating influenza viruses. However, the development of T cell-based universal influenza vaccines is challenging owing to the diversity of MHCs in the population, unpredictable degree of immunodominance, lack of adequate animal models, and difficulty in establishing T cell immunity in humans.

ABBREVIATIONS

cHA: chimeric HA; HBc: hepatitis B virus core protein; HA: hemagglutinin; HLA: human leucocyte antigen; IIV: inactivated influenza vaccine; KLH: keyhole limpet hemocyanin; LAH: long alpha helix; LAIV: live attenuated influenza vaccine; M2e: extracellular domain of matrix 2 protein; MHC: major histocompatibility complex; mRNA: messenger ribonucleic acid; NA: neuraminidase; NS1: non-structural protein 1; qNIV: quadrivalent nanoparticle influenza vaccine; T_RM: tissue-resident memory T cells; VE: vaccine effectiveness; VLP: virus-like particles; VSV: vesicular stomatitis virus.

Universal Live-Attenuated Influenza Vaccine Candidates Expressing Multiple M2e Epitopes Protect Ferrets against a High-Dose Heterologous Virus Challenge

The development of an influenza vaccine with broad protection and durability remains an attractive idea due to the high mutation rate of the influenza virus. An extracellular domain of Matrix 2 protein (M2e) is among the most attractive target for the universal influenza vaccine owing to its high conservancy rate. Here, we generated two recombinant live attenuated influenza vaccine (LAIV) candidates encoding four M2e epitopes representing consensus sequences of human, avian and swine influenza viruses, and studied them in a preclinical ferret model. Both LAIV+4M2e viruses induced higher levels of M2e-specific antibodies compared to the control LAIV strain, with the LAIV/HA+4M2e candidate being significantly more immunogenic than the LAIV/NS+4M2e counterpart. A high-dose heterosubtypic influenza virus challenge revealed the highest degree of protection after immunization with LAIV/HA+4M2e strain, followed by the NS-modified LAIV and the classical LAIV virus. Furthermore, only the immune sera from the LAIV/HA+4M2e-immunized ferrets protected mice from a panel of lethal influenza viruses encoding M genes of various origins. These data suggest that the improved cross-protection of the LAIV/HA+4M2e universal influenza vaccine candidate was mediated by the M2e-targeted antibodies. Taking into account the safety profile and improved cross-protective potential, the LAIV/HA+4M2e vaccine warrants its further evaluation in a phase I clinical trial.

African Swine Fever Virus as a Difficult Opponent in the Fight for a Vaccine-Current Data

Prevention and control of African swine fever virus (ASFV) in Europe, Asia, and Africa seem to be extremely difficult in view of the ease with which it spreads, its high resistance to environmental conditions, and the many obstacles related to the introduction of effective specific immunoprophylaxis. Biological properties of ASFV indicate that the African swine fever (ASF) pandemic will continue to develop and that only the implementation of an effective and safe vaccine will ensure a reduction in the spread of ASFV. At present, vaccines against ASF are not available. The latest approaches to the ASFV vaccine’s design concentrate on the development of either modified live vaccines by targeted gene deletion from different isolates or subunit vaccines. The construction of an effective vaccine is hindered by the complex structure of the virus, the lack of an effective continuous cell line for the isolation and propagation of ASFV, unpredictable and stain-specific phenotypes after the genetic modification of ASFV, a risk of reversion to virulence, and our current inability to differentiate infected animals from vaccinated ones. Moreover, the design of vaccines intended for wild boars and oral administration is desirable. Despite several obstacles, the design of a safe and effective vaccine against ASFV seems to be achievable.

Pollution, Inflammation, and Vaccines: A Complex Crosstalk

The importance of pollution in determining human health is becoming increasingly clear, also given the dramatic consequences it has had on recent geopolitical events. Yet, the consequences of contamination are not always straightforward. In this paper, we will discuss the effects of different pollutants on different aspects of human health, in particular on the immune system and inflammation. Different environmental pollutants can have different effects on the immune system, which can then promote complex pathologies, such as autoimmune disorders and cancer. The interaction with the microbiota also further helps to determine the consequences of contamination on wellbeing. The pollution can affect vaccination efficacy, given the widespread effects of vaccination on immunity. At the same time, some vaccinations also can exert protective effects against some forms of pollution.

Humoral and cellular immune responses in critically ill influenza A/H1N1-infected patients

There is limited knowledge of influenza-specific immune responses and their kinetics in critically ill patients. We investigated humoral and cellular immune responses after critical influenza A/H1N1 infection and hypothesized that dysfunctionality or absence of immune responses could contribute to more severe illness. We followed 12 patients hospitalized with severe influenza infection; the majority admitted to intensive care unit (ICU). Blood samples were collected at days 10 and 19 and at 5 months. Antibody responses to surface glycoproteins haemagglutinin (HA) and neuraminidase (NA) of A/H1N1pdm09 were quantified by haemagglutination inhibition (HAI), microneutralization (MN), Enzyme-linked immunosorbent assay (ELISA) and Enzyme-linked lectin assay (ELLA). Influenza-specific antibody levels and avidity were measured separately for head and stalk domains of H1. Cytokine secreting CD4⁺ and CD8⁺ T cell responses to conserved influenza epitopes (M1, NP and PB1) were analysed by FluoroSpot. Overall, the patients retained a high level of functional HA- and NA-specific antibodies over the study period. During the acute phase (up to 3 weeks from symptom onset), antibodies specific to H1 stalk increased earlier and were present in higher amount compared with H1 head-specific antibodies. The NA-specific antibodies and the non-neutralizing HA-specific antibody response for H1 head and H1 full-length showed a significant decline from acute to convalescent phase. Despite high total IgG concentrations, avidity to H1 head and H1 full-length protein remained low at all time points. Similarly, CD8⁺ T cell responses were continuously measured at low levels. In conclusion, our study found that critically ill patients were characterized by low HA-specific antibody avidity and CD8⁺ T cell response.

Systems Biological Analysis of Immune Response to Influenza Vaccination

The last decade has witnessed tremendous progress in immunology and vaccinology, owing to several scientific and technological breakthroughs. Systems vaccinology is a field that has emerged at the forefront of vaccine research and development and provides a unique way to probe immune responses to vaccination in humans. The goals of systems vaccinology are to use systems-based approaches to define signatures that can be used to predict vaccine immunogenicity and efficacy and to delineate the molecular mechanisms driving protective immunity. The application of systems biological approaches in influenza vaccination studies has enabled the discovery of early signatures that predict immunogenicity to vaccination and yielded novel mechanistic insights about vaccine-induced immunity. Here we review the contributions of systems vaccinology to influenza vaccine development and critically examine the potential of systems vaccinology toward enabling the development of a universal influenza vaccine that provides robust and durable immunity against diverse influenza viruses.

Dynamic causal modelling of immune heterogeneity

An interesting inference drawn by some COVID-19 epidemiological models is that there exists a proportion of the population who are not susceptible to infection-even at the start of the current pandemic. This paper introduces a model of the immune response to a virus. This is based upon the same sort of mean-field dynamics as used in epidemiology. However, in place of the location, clinical status, and other attributes of people in an epidemiological model, we consider the state of a virus, B and T-lymphocytes, and the antibodies they generate. Our aim is to formalise some key hypotheses as to the mechanism of resistance. We present a series of simple simulations illustrating changes to the dynamics of the immune response under these hypotheses. These include attenuated viral cell entry, pre-existing cross-reactive humoral (antibody-mediated) immunity, and enhanced T-cell dependent immunity. Finally, we illustrate the potential application of this sort of model by illustrating variational inversion (using simulated data) of this model to illustrate its use in testing hypotheses. In principle, this furnishes a fast and efficient immunological assay-based on sequential serology-that provides a (1) quantitative measure of latent immunological responses and (2) a Bayes optimal classification of the different kinds of immunological response (c.f., glucose tolerance tests used to test for insulin resistance). This may be especially useful in assessing SARS-CoV-2 vaccines.

Postvaccination graft dysfunction/aplastic anemia relapse with massive clonal expansion of autologous CD8+ lymphocytes

Acquired aplastic anemia is a T-cell–mediated autoimmune bone marrow aplasia, without a known etiologic trigger. Clonal expansion of CD8+ effector T lymphocytes can occur following vaccination and accompany graft dysfunction or aplastic anemia relapse.

Development of vaccine formulations: past, present, and future

The current situation, heavily influenced by the ongoing pandemic, puts vaccines back into the spotlight. However, the conventional and traditional vaccines present disadvantages, particularly related to immunogenicity, stability, and storage of the final product. Often, such products require the maintenance of a “cold chain,” impacting the costs, the availability, and the distribution of vaccines. Here, after a recall of the mode of action of vaccines and the types of vaccines currently available, we analyze the past, present, and future of vaccine formulation. The past focuses on conventional formulations, the present discusses the use of nanoparticles for vaccine delivery and as adjuvants, while the future presents microneedle patches as alternative formulation and administration route. Finally, we compare the advantages and disadvantages of injectable solutions, nanovaccines, and microneedles in terms of efficacy, stability, and patient-friendly design.

Different approaches to vaccine formulation development, the conventional vaccine formulations from the past, the current development of lipid nanoparticles as vaccines, and the near future microneedles formulations are discussed in this review. 

Generation and Characterization of Universal Live-Attenuated Influenza Vaccine Candidates Containing Multiple M2e Epitopes

Influenza viruses constantly evolve, reducing the overall protective effect of routine vaccination campaigns. Many different strategies are being explored to design universal influenza vaccines capable of protecting against evolutionary diverged viruses. The ectodomain of influenza A M2e protein (M2e) is among the most promising targets for universal vaccine design. Here, we generated two recombinant live attenuated influenza vaccines (LAIVs) expressing additional four M2e tandem repeats (4M2e) from the N-terminus of the viral hemagglutinin (HA) protein, in an attempt to enhance the M2e-mediated cross-protection. The recombinant H1N1+4M2e and H3N2+4M2e viruses retained growth characteristics attributable to traditional LAIV viruses and induced robust influenza-specific antibody responses in BALB/c mice, although M2e-specific antibodies were raised only after two-dose vaccination with LAIV+4M2e viruses. Mice immunized with either LAIV or LAIV+4M2e viruses were fully protected against a panel of heterologous influenza challenge viruses suggesting that antibody and cell-mediated immunity contributed to the protection. The protective role of the M2e-specific antibody was seen in passive serum transfer experiments, where enhancement in the survival rates between classical LAIV and chimeric H3N2+4M2e LAIV was demonstrated for H3N2 and H5N1 heterologous challenge viruses. Overall, the results of our study suggest that M2e-specific antibodies induced by recombinant LAIV+4M2e in addition to cellular immunity by LAIV play an important role in conferring protection against heterologous viruses.

Influenza A Virus Inhibits RSV Infection via a Two-Wave Expression of IFIT Proteins

Influenza viruses and respiratory syncytial virus (RSV) are respiratory viruses that primarily circulate worldwide during the autumn and winter seasons. Seasonal surveillance has shown that RSV infection generally precedes influenza. However, in the last four winter seasons (2016–2020) an overlap of the morbidity peaks of both viruses was observed in Israel, and was paralleled by significantly lower RSV infection rates. To investigate whether the influenza A virus inhibits RSV, human cervical carcinoma (HEp2) cells or mice were co-infected with influenza A and RSV. Influenza A inhibited RSV growth, both in vitro and in vivo. Mass spectrometry analysis of mouse lungs infected with influenza A identified a two-wave pattern of protein expression upregulation, which included members of the interferon-induced protein with the tetratricopeptide (IFITs) family. Interestingly, in the second wave, influenza A viruses were no longer detectable in mouse lungs. In addition, knockdown and overexpression of IFITs in HEp2 cells affected RSV multiplicity. In conclusion, influenza A infection inhibits RSV infectivity via upregulation of IFIT proteins in a two-wave modality. Understanding the immune system involvement in the interaction between influenza A and RSV viruses will contribute to the development of future treatment strategies against these viruses.

Systemic and respiratory T-cells induced by seasonal H1N1 influenza protect against pandemic H2N2 in ferrets

Traditional influenza vaccines primarily induce a narrow antibody response that offers no protection against heterosubtypic infections. Murine studies have shown that T cells can protect against a broad range of influenza strains. However, ferrets are a more potent model for studying immune correlates of protection in influenza infection. We therefore set out to investigate the role of systemic and respiratory T cells in the protection against heterosubtypic influenza A infections in ferrets. H1N1-priming induced systemic and respiratory T cells that responded against pandemic H2N2 and correlated with reduced viral replication and disease. CD8-positive T cell responses in the upper and lower respiratory tract were exceptionally high. We additionally confirmed that H2N2-responsive T cells are present in healthy human blood donors. These findings underline the importance of the T cell response in influenza immunity and show that T cells are a potent target for future universal influenza vaccines.

Tick-Borne Encephalitis Virus: A Quest for Better Vaccines against a Virus on the Rise

Tick-borne encephalitis virus (TBEV), a member of the family Flaviviridae, is one of the most important tick-transmitted viruses in Europe and Asia. Being a neurotropic virus, TBEV causes infection of the central nervous system, leading to various (permanent) neurological disorders summarized as tick-borne encephalitis (TBE). The incidence of TBE cases has increased due to the expansion of TBEV and its vectors. Since antiviral treatment is lacking, vaccination against TBEV is the most important protective measure. However, vaccination coverage is relatively low and immunogenicity of the currently available vaccines is limited, which may account for the vaccine failures that are observed. Understanding the TBEV-specific correlates of protection is of pivotal importance for developing novel and improved TBEV vaccines. For affording robust protection against infection and development of TBE, vaccines should induce both humoral and cellular immunity. In this review, the adaptive immunity induced upon TBEV infection and vaccination as well as novel approaches to produce improved TBEV vaccines are discussed.

African swine fever vaccines: a promising work still in progress

Abstract

African swine fever (ASF), a disease of obligatory declaration to the World Organization for Animal Health (OIE), has contributed to poverty and underdevelopment of affected areas. The presence of ASF has been historically neglected in Africa, contributing to its uncontrolled expansion and favouring its spread to continental Europe on at least three occasions, the last one in 2007 through the Republic of Georgia. Since then, African swine fever virus (ASFV) has spread to neighbouring countries, reaching the European Union in 2014, China in the summer of 2018 and spreading through Southeast Asia becoming a global problem. Lack of available vaccines against ASF makes its control even more difficult, representing today the number one threat for the swine industry worldwide and negatively affecting the global commerce equilibrium.

Main body

In this review, we intend to put in perspective the reality of ASF vaccination today, taking into account that investment into ASF vaccine development has been traditionally unattractive, overall since ASF-free areas with large swine industries applied a non-vaccination policy for diseases listed by the OIE. The dramatic situation suffered in Asia and the increasing threat that ASF represents for wealthy countries with large swine industries, has dramatically changed the perspective that both private and public bodies have about ASF vaccinology, although this is controversial. The feasibility of modifying the ASFV genome has led to safe and efficacious experimental recombinant live attenuated viruses (LAVs). The main challenge today will be confirming the safety and efficacy of these technologies in the field, accelerating transfer to the industry for official registration and commercialization. The complexity of ASFV, together with the lack of knowledge about the mechanisms involved in protection and the specific antigens involved in it, requires further investment in research and development. Although far from the efficacy achieved by LAVs, subunit vaccines are the optimal choice for the future. If the world can wait for them or not is a contentious issue.

Conclusion

Despite their inherent disadvantages, LAVs will be the first technology to reach the market, while subunit vaccines will need much further research to become a successful commercial reality.

African swine fever vaccines: a promising work still in progress

ABSTRACT

African swine fever (ASF), a disease of obligatory declaration to the World Organization for Animal Health (OIE), has contributed to poverty and underdevelopment of affected areas. The presence of ASF has been historically neglected in Africa, contributing to its uncontrolled expansion and favouring its spread to continental Europe on at least three occasions, the last one in 2007 through the Republic of Georgia. Since then, African swine fever virus (ASFV) has spread to neighbouring countries, reaching the European Union in 2014, China in the summer of 2018 and spreading through Southeast Asia becoming a global problem. Lack of available vaccines against ASF makes its control even more difficult, representing today the number one threat for the swine industry worldwide and negatively affecting the global commerce equilibrium.

MAIN BODY

In this review, we intend to put in perspective the reality of ASF vaccination today, taking into account that investment into ASF vaccine development has been traditionally unattractive, overall since ASF-free areas with large swine industries applied a non-vaccination policy for diseases listed by the OIE. The dramatic situation suffered in Asia and the increasing threat that ASF represents for wealthy countries with large swine industries, has dramatically changed the perspective that both private and public bodies have about ASF vaccinology, although this is controversial. The feasibility of modifying the ASFV genome has led to safe and efficacious experimental recombinant live attenuated viruses (LAVs). The main challenge today will be confirming the safety and efficacy of these technologies in the field, accelerating transfer to the industry for official registration and commercialization. The complexity of ASFV, together with the lack of knowledge about the mechanisms involved in protection and the specific antigens involved in it, requires further investment in research and development. Although far from the efficacy achieved by LAVs, subunit vaccines are the optimal choice for the future. If the world can wait for them or not is a contentious issue.

CONCLUSION

Despite their inherent disadvantages, LAVs will be the first technology to reach the market, while subunit vaccines will need much further research to become a successful commercial reality.

Conserved T-cell epitopes of respiratory syncytial virus (RSV) delivered by recombinant live attenuated influenza vaccine viruses efficiently induce RSV-specific lung-localized memory T cells and augment influenza-specific resident memory T-cell responses

Respiratory syncytial virus (RSV) can cause recurrent infection in people because it does not stimulate a long-lived immunological memory. There is an urgent need to develop a safe and efficacious vaccine against RSV that would induce immunological memory without causing immunopathology following natural RSV infection. We have previously generated two recombinant live attenuated influenza vaccine (LAIV) viruses that encode immunodominant T-cell epitopes of RSV M2 protein in the neuraminidase or NS1 genes. These chimeric vaccines afforded protection against influenza and RSV infection in mice, without causing pulmonary eosinophilia or inflammatory RSV disease. The current study assessed the formation of influenza-specific and RSV-specific CD4 and CD8 T-cell responses in the lungs of mice, with special attention to the lung tissue-resident memory T cell subsets (T_RM). The RSV epitopes did not affect influenza-specific CD4 effector memory T cell (Tem) levels in the lungs. The majority of these cells formed by LAIV or LAIV-RSV viruses had CD69⁺CD103^- phenotype. Both LAIV+NA/RSV and LAIV+NS/RSV recombinant viruses induced significant levels of RSV M2₈₂ epitope-specific lung-localized CD8 Tem cells expressing both CD69 and CD103 T_RM markers. Surprisingly, the CD69⁺CD103⁺ influenza-specific CD8 Tem responses were augmented by the addition of RSV epitopes, possibly as a result of the local microenvironment formed by the RSV-specific memory T cells differentiating to T_RM in the lungs of mice immunized with LAIV-RSV chimeric viruses. This study provides evidence that LAIV vector-based vaccination can induce robust lung-localized T-cell immunity to the inserted T-cell epitope of a foreign pathogen, without altering the immunogenicity of the viral vector itself.

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Two LAIV-RSV vaccine viruses induced RSV M2₈₂-specific effector memory CD8 T cells producing both IFNγ and TNFα cytokines.

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The inserted RSV epitopes did not affect influenza-specific CD4 Tem levels in the lungs of immunized mice.

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LAIV-RSV viruses induced RSV M2₈₂-specific lung-localized CD8 Tem cells expressing both CD69 and CD103 T_RM markers.

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The magnitude of RSV M2₈₂-specific CD8 Tem responses correlates with protection against RSV-induced lung pathology.

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The addition of RSV epitopes into the LAIV strain augmented CD69⁺CD103⁺ influenza-specific CD8 Tem responses in the lungs.

Prospects of and Barriers to the Development of Epitope-Based Vaccines against Human Metapneumovirus

Human metapneumovirus (HMPV) is a major cause of respiratory illnesses in children, the elderly and immunocompromised patients. Although this pathogen was only discovered in 2001, an enormous amount of research has been conducted in order to develop safe and effective vaccines to prevent people from contracting the disease. In this review, we summarize current knowledge about the most promising experimental B- and T-cell epitopes of human metapneumovirus for the rational design of HMPV vaccines using vector delivery systems, paying special attention to the conservation of these epitopes among different lineages/genotypes of HMPV. The prospects of the successful development of an epitope-based HMPV vaccine are discussed in the context of recent findings regarding HMPV’s ability to modulate host immunity. In particular, we discuss the lack of data on experimental human CD4 T-cell epitopes for HMPV despite the role of CD4 lymphocytes in both the induction of higher neutralizing antibody titers and the establishment of CD8 memory T-cell responses. We conclude that current research should be focused on searching for human CD4 T-cell epitopes of HMPV that can help us to design a safe and cross-protective epitope-based HMPV vaccine.

Recent advances in influenza vaccines

Seasonal influenza remains a major public health problem, responsible for hundreds of thousands of deaths every year, mostly of elderly people. Despite the wide availability of vaccines, there are multiple problems decreasing the effectiveness of vaccination programs. These include viral variability and hence the requirement to match strains by estimating which will become prevalent each season, problems associated with vaccine and adjuvant production, and the route of administration as well as the perceived lower vaccine efficiency in older adults. Clinical protection is still suboptimal for all of these reasons, and vaccine uptake remains too low in most countries. Efforts to improve the effectiveness of influenza vaccines include developing universal vaccines independent of the circulating strains in any particular season and stimulating cellular as well as humoral responses, especially in the elderly. This commentary assesses progress over the last 3 years towards achieving these aims. Since the beginning of 2020, an unprecedented international academic and industrial effort to develop effective vaccines against the new coronavirus SARS-CoV-2 has diverted attention away from influenza, but many of the lessons learned for the one will synergize with the other to mutual advantage. And, unlike the SARS-1 epidemic and, we hope, the SARS-CoV-2 pandemic, influenza will not be eliminated and thus efforts to improve influenza vaccines will remain of crucial importance.

Recombinant Live Attenuated Influenza Vaccine Viruses Carrying Conserved T-cell Epitopes of Human Adenoviruses Induce Functional Cytotoxic T-Cell Responses and Protect Mice against Both Infections

Human adenoviruses (AdVs) are one of the most common causes of acute respiratory viral infections worldwide. Multiple AdV serotypes with low cross-reactivity circulate in the human population, making the development of an effective vaccine very challenging. In the current study, we designed a cross-reactive AdV vaccine based on the T-cell epitopes conserved among various AdV serotypes, which were inserted into the genome of a licensed cold-adapted live attenuated influenza vaccine (LAIV) backbone. We rescued two recombinant LAIV-AdV vaccines by inserting the selected AdV T-cell epitopes into the open reading frame of full-length NA and truncated the NS1 proteins of the H7N9 LAIV virus. We then tested the bivalent vaccines for their efficacy against influenza and human AdV5 in a mouse model. The vaccine viruses were attenuated in C57BL/6J mice and induced a strong influenza-specific antibody and cell-mediated immunity, fully protecting the mice against virulent influenza virus infection. The CD8 T-cell responses induced by both LAIV-AdV candidates were functional and efficiently killed the target cells loaded either with influenza NP366 or AdV DBP418 peptides. In addition, high levels of recall memory T cells targeted to an immunodominant H2b-restricted CD8 T-cell epitope were detected in the immunized mice after the AdV5 challenge, and the magnitude of these responses correlated with the level of protection against pulmonary pathology caused by the AdV5 infection. Our findings suggest that the developed recombinant vaccines can be used for combined protection against influenza and human adenoviruses and warrant further evaluation on humanized animal models and subsequent human trials.

Insights into current clinical research on the immunogenicity of live attenuated influenza vaccines

Introduction: Live attenuated influenza vaccines (LAIVs) have been in use for more than three decades and are now licensed in many countries. There is evidence that LAIVs can have greater efficacy than inactivated influenza vaccines, especially against mismatched influenza, however, in recent years, a number of trials have found a lack of LAIV efficacy, mainly in relation to the H1N1 virus.Areas covered: In this review, we summarize the results of clinical research published in the past 5 years on the immunogenicity of LAIVs, with special attention to the mechanisms of establishing protective immunity and some factors that may influence immunogenicity and efficacy.Expert opinion: A number of recent clinical studies confirmed that the immune responses to LAIVs are multifaceted, involving different immune mechanisms. These trials suggest that the intrinsic replicative properties of each LAIV component should be taken into account, and the precise effects of adding a fourth vaccine strain to trivalent LAIV formulations are still to be identified. In addition, new data are emerging regarding the impact of pre-vaccination conditions, such as preexisting immunity or concurrent asymptomatic viral and bacterial respiratory infections, on LAIV immunogenicity, suggesting the importance of monitoring them during clinical trials or vaccination campaigns.

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.

An Inactivated Influenza Virus Vaccine Approach to Targeting the Conserved Hemagglutinin Stalk and M2e Domains

Universal influenza virus vaccine candidates that focus on the conserved hemagglutinin (HA) stalk domain and the extracellular domain of the matrix protein 2 (M2e) have been developed to increase the breadth of protection against multiple strains. In this study, we report a novel inactivated influenza virus vaccine approach that combines these two strategies. We inserted a human consensus M2e epitope into the immunodominant antigenic site (Ca2 site) of three different chimeric HAs (cHAs). Sequential immunization with inactivated viruses containing these modified cHAs substantially enhanced M2e antibody responses while simultaneously boosting stalk antibody responses. The combination of additional M2e antibodies with HA stalk antibodies resulted in superior antibody-mediated protection in mice against challenge viruses expressing homologous or heterosubtypic hemagglutinin and neuraminidase compared to vaccination strategies that targeted the HA stalk or M2e epitopes in isolation.

Recombinant live attenuated influenza vaccine viruses carrying CD8 T-cell epitopes of respiratory syncytial virus protect mice against both pathogens without inflammatory disease

Respiratory syncytial virus (RSV) is the most common cause of lower respiratory disease in young children, elderly and immunocompromised adults. There is no licensed vaccine against RSV although development of an effective and safe RSV vaccine has been a high priority for several decades. Among the various vaccine platforms, the viral-vectored RSV vaccines based on licensed cold-adapted live attenuated influenza vaccine (LAIV) might offer an advantage of inducing adequate mucosal CD8 T cell immunity at the infection site of respiratory pathogens. We constructed two recombinant LAIV viruses expressing immunodominant T-cell epitopes of RSV M2-1 protein. The results in this study provide evidence that RSV CD8 T cell epitopes delivered by LAIV viral vector could confer protection against RSV infection without causing pulmonary eosinophilia and inflammatory RSV disease in mice. In addition, these chimeric LAIV-RSV vaccines retained their attenuated phenotype and ability to protect against virulent influenza virus, thus providing a unique approach to fight against two dangerous respiratory viral pathogens using a single vaccine preparation.