High Protective Efficacy Research Articles

A prospective cohort study comparing efficacy of 1 dose of quadrivalent human papillomavirus vaccine to 2 and 3 doses at an average follow up of 12 years postvaccination.

While recommending a human papillomavirus (HPV) single-dose vaccination schedule in 2022, the World Health Organization highlighted the need for long-term follow-up studies to monitor waning of protection. We report on vaccine efficacy against HPV infections in 1-, 2-, and 3-dose schedules and protection against cervical precancers at a median follow-up of 12 years postvaccination. This randomized multicenter study in India was originally designed to vaccinate unmarried girls aged 10-18 years with either 2 or 3 doses of quadrivalent HPV vaccine. A ministerial decree to halt vaccination in trials resulted in the creation of cohorts receiving different doses, including just a single dose. Cohorts were assessed for incident and persistent infections by genotyping cervical samples collected yearly for 4 consecutive years after participants were married. Cervical screening with an HPV test was initiated at age 25 years for married participants. Age- and site-matched unvaccinated married women were recruited to be compared with vaccinated cohorts. Vaccine efficacy was assessed using proportional incidence ratios. The number of participants in the 1-, 2- (at 0 and 6 months), and 3-dose cohorts was 4949, 4980, and 4348, respectively. Of the recipients, 71%-82% in the different cohorts were eligible to provide samples for genotyping. Vaccine efficacy against persistent HPV 16 and 18 infection was 92.0% (95% confidence interval [CI] = 87.0% to 95.0%) in 3022 recipients of the single dose; and comparable with that observed in the 2-dose arm (94.8%, 95% CI = 90.0% to 97.3%) and the 3-dose arm (95.3%, 95% CI = 90.9% to 97.5%). No high-grade precancer associated with HPV 16 and 18 was detected among vaccinated participants compared with 8 precancers detected among the unvaccinated women. This observational cohort study has established that a single dose of HPV vaccine provides high protective efficacy against persistent HPV 16 and 18 infections and associated neoplasia 15 years postvaccination.

Why does malaria transmission continue at high levels despite universal vector control? Quantifying persistent malaria transmission by Anopheles funestus in Western Province, Zambia

BackgroundSome settings continue to experience a high malaria burden despite scale-up of malaria vector control to high levels of coverage. Characterisation of persistent malaria transmission in the presence of standard control measures, also termed residual malaria transmission, to understand where and when individuals are exposed to vector biting is critical to inform refinement of prevention and control strategies.MethodsSecondary analysis was performed using data collected during a phase III cluster randomized trial of attractive targeted sugar bait stations in Western Province, Zambia. Two seasonal cohorts of children aged 1–14 years were recruited and monitored monthly during the malaria transmission season, concurrent with entomological surveillance using a combination of human landing catch (HLC) and Centres for Disease Control (CDC) light traps at randomly selected households in study clusters. Behavioural data from cohort participants were combined with measured Anopheles funestus landing rates and sporozoite positivity to estimate the human behaviour-adjusted entomological inoculation rate (EIR).ResultsBehavioural data from 1237 children over 5456 child-visits in 20 entomology surveillance clusters were linked with hourly landing rates from 8131 female An. funestus trapped by HLC. Among all An. funestus tested by enzyme-linked immunosorbent assay (ELISA), 3.3% were sporozoite-positive. Mean EIR directly measured from HLC was 0.07 infectious bites per person per night (ib/p/n). When accounting for child locations over the evening and night, the mean behaviour-adjusted EIR was 0.02 ib/p/n. Children not sleeping under insecticide-treated nets (ITNs) experienced 13.6 infectious bites per person per 6 month season, 8% of which occurred outdoors, while ITN users received 1.3 infectious bites per person per 6 month season, 86% of which were received outdoors. Sleeping under an ITN can prevent approximately 90% of potential An. funestus bites among children.ConclusionsIn this setting ITNs have a high personal protective efficacy owing to peak An. funestus biting occurring indoors while most individuals are asleep. However, despite high household possession of ITNs (>90%) and high individual use (>70%), children in this setting experience more than one infectious bite per person per 6 month transmission season, sufficient to maintain high malaria transmission and burden. New tools and strategies are required to reduce the malaria burden in such settings.Graphical

New Engineered-Chimeric Botulinum Neurotoxin Mutant Acts as an Effective Bivalent Vaccine Against Botulinum Neurotoxin Serotype A and E.

Botulinum neurotoxins (BoNTs), including serotypes A and E, are potent biotoxins known to cause human poisoning. In addition to the critical protective antigen found in the full BoNT molecule, the receptor binding domain (Hc domain), BoNTs also harbour another essential protective antigen-the light chain-translocation domain (L-HN domain). Leveraging these pivotal protective antigens, we genetically engineered a series of inactivated chimeric molecules incorporating L-HN and Hc domains of BoNT/A and E. The structure of these chimeric molecules, mirror BoNT/A and E, but are devoid of enzyme activity. Experimental findings demonstrated that a lead candidate mEL-HN-mAHc harnessing the inactivated protease LCHN/E with the mutated gangliosides binding site Hc/A (mE-mA) elicited robust immune protection against BoNT/A and E simultaneously in a mouse model, requiring low immune dosages and minimal immunisations. Moreover, mE-mA exhibited high protective efficacy against BoNT/A and E in guinea pigs and New Zealand white rabbits, resulting in elevated neutralising antibody titres. Furthermore, mE-mA proved to be a more stable and safer vaccine compared to formaldehyde-inactivated toxoid. Our data underscore the genetically engineered mE-mA as a highly effective bivalent vaccine against BoNT/A and E, paving the way for the development of polyvalent vaccines against biotoxins.

Electrochemical, Structural and Thermodynamic Investigations of Methanolic Parsley Extract as a Green Corrosion Inhibitor for C37 Steel in HCl

Phytochemical-rich natural extracts have recently attracted intense attention as green corrosion inhibitors and costly benign coating components for the protection of metallic structures of immense commercial importance. Herein, various methods were applied to assess the corrosion protection efficiency of a methanolic extract of parsley (Petroselinum crispum) (PCE) on carbon steel C37 in 1 M HCl. Initially, the chemical profile of PCE was analyzed using gas chromatography/mass spectrometry (GC/MS), and myristicin and apiol were identified as the main components. The results from the weight loss, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP) techniques revealed a substantial reduction in the corrosion rate upon the use of PCE, with a maximum inhibition efficiency of 92% at 1 g L−1 PCE. To optimize the performance, the corrosion behavior was investigated over a temperature range of 303–333 K and for concentrations of 0.1–1 g L−1. The inhibition effectiveness increased at higher concentrations of PCE, whilst it decreased when the temperature was elevated. The query suggests that the adsorption process involves both physical and chemical mechanisms. The adsorption of PCE onto C37 was well described by the Langmuir adsorption isotherm. The data were used to determine the activation energy and thermodynamic parameters. The PCE coating acted as a mixed-type inhibitor, hampering both cathodic and anodic corrosion reactions. SEM further confirmed the formation of a protective coating film on the steel surface when exposed to PCE. UV-Vis and XRD were implemented to understand the inhibition mechanism and formed products at the microscopic and spectroscopic levels. Hence, the green PCE inhibitor may potentially be applied in corrosion mitigation due to its high corrosion protection efficacy and its environmentally benign nature.

Protective efficacy against two different viral hemorrhagic septicemia virus (VHSV) isolates belonging to genotype IVa depending on various dose-boost immunizations of rVHSV-GΔTM in olive flounder

Viral vector-based vaccines are promising candidates that deliver antigens of interest into hosts. Particularly, a single-cycle virus possesses the immunogenicity of a live virus vaccine and safety of an inactivated virus vaccine because they do not produce progeny virion after infection. The rVHSV-GΔTM single-cycle, which removes the transmembrane region and C-terminal cytoplasmic region of the G gene from the KJ2008 isolate, virus demonstrates its superiority as a vaccine in controlling the viral hemorrhagic septicemia virus (VHSV) in olive flounder, although research for establishing its suitability is still lacking. Therefore, we established optimal usage through various concentrations and booster immunizations in olive flounder and confirmed the cross-protective effect against KJ2008 and GCVP-02 belonging to different subclades of the glycoprotein genotype IVa. The olive flounder were intramuscular prime or boost immunized from 1 × 102 pfu/fish to 1 × 104 pfu/fish of rVHSV-GΔTM. After four weeks of immunization, each group was challenged with KJ2008 and GCVP-02 isolates. In the prime immunization group, protective efficacy against the GCVP-02 isolate was relatively low compared with the KJ2008 isolate, but the boost immunization group showed improved protective efficacy in both isolates. Our findings suggest that the rVHSV-GΔTM single-cycle virus vaccine based on the KJ2008 isolate can be effective in controlling VHSV in the fish culture industry because it showed a protective efficacy even against other isolates and high protective efficacy upon boosting.

A vaccine targeting antigen-presenting cells through CD40 induces protective immunity against Nipah disease

Nipah virus (NiV) has been recently ranked by the World Health Organization as being among the top eight emerging pathogens likely to cause major epidemics, whereas no therapeutics or vaccines have yet been approved. We report a method to deliver immunogenic epitopes from NiV through the targeting of the CD40 receptor of antigen-presenting cells by fusing a selected humanized anti-CD40 monoclonal antibody to the Nipah glycoprotein with conserved NiV fusion and nucleocapsid peptides. In the African green monkey model, CD40.NiV induces specific immunoglobulin A (IgA) and IgG as well as cross-neutralizing responses against circulating NiV strains and Hendra virus and Tcell responses. Challenge experiments using a NiV-B strain demonstrate the high protective efficacy of the vaccine, with all vaccinated animals surviving and showing no significant clinical signs or virus replication, suggesting that the CD40.NiV vaccine conferred sterilizing immunity. Overall, results obtained with the CD40.NiV vaccine are highly promising in terms of the breadth and efficacy against NiV.

Shigella virulence protein VirG is a broadly protective antigen and vaccine candidate

Diarrhea caused by Shigella has been associated with high morbidity and mortality in young children worldwide. There are no licensed vaccines, and those clinically advanced have restricted coverage as they elicit serotype-specific immunity while disease is caused by multiple circulating serotypes. Our group had previously reported a close association between serum antibodies to the Shigella virulence factor VirG (or IcsA) and clinical protection in infected individuals. VirG is highly conserved among Shigella strains and appealing as a broad-spectrum vaccine candidate. In this study, we investigated the immunogenicity and protective capacity of VirG as a subunit vaccine in mice. The surface-exposed alpha (α) domain of VirG (VirGα) was produced as a recombinant protein. This region has almost identical immune reactivity to full-length VirG. Administered intramuscularly with alum, VirGα elicited robust immune responses and high protective efficacy against S. flexneri 2a and S. sonnei. Almost complete protection was afforded by VirGα given intranasally with the E. coli double mutant heat-labile toxin (dmLT). VirGα-specific antibodies recognized VirG expressed on live Shigella, and blocked Shigella adhesion and invasion to human colonic cells. These results show for the first time that VirGα is a promising cross-protective vaccine candidate to prevent Shigella infection.

Effect of temperature on the protective efficacy of a live attenuated vaccine against herpesviral haematopoietic necrosis in goldfish.

The live attenuated vaccine P7-P8 strain against herpesviral haematopoietic necrosis, which is caused by cyprinid herpesvirus 2 (CyHV-2), exhibits high protective efficacy in goldfish at 25°C, the predominant temperature for this disease; however, the effect of water temperature during the vaccination period on efficacy has not been determined. In this study, an in vitro experiment revealed that the vaccine strain grew between 15 and 30°C in the goldfish cell line RyuF-2. Subsequent in vivo efficacy tests were conducted with vaccination temperatures ranging from 15 to 30°C. During the vaccination period, organs were sampled to determine the vaccine growth dynamics. Blood plasma was collected to assess anti-CyHV-2 antibody titres. The protective efficacy of the vaccine at 15, 20, 25, and 30°C after subsequent virulent CyHV-2 challenge resulted in a relative percentage survival of 73.3%, 77.8%, 100%, and 77.8%, respectively, which indicated that the vaccine is effective over this temperature range. The vaccine virus load in the spleen was lowest at 15°C (103.7 DNA copies/mg) and highest at 25°C (106.5 DNA copies/mg). This indicates that the vaccine virus load over 104 DNA copies/mg may elicit sufficient acquired immunity. No significant differences in antibody titre were observed between groups, which suggests that cell-mediated immunity can be fundamentally involved in protection.

Recombinant chimpanzee adenovirus expressing spike protein protects chickens against infectious bronchitis virus

Infectious bronchitis (IB) is an acute and highly contagious disease caused by avian infectious bronchitis virus (IBV), resulting in significant economic losses in the global poultry industry. In this study, we utilized a replication-incompetent adenovirus vector derived from chimpanzees for the first time to express the S gene of IBV. The adenovirus was successfully rescued and demonstrated convenient production, good growth performance, and stability on HEK293 A cells. Morphologically, the recombinant adenovirus (named PAD-S) appeared normal under transmission electron microscopy, and efficient expression of the exogenous gene was confirmed through immunofluorescence analysis and immunoblotting. Administration of PAD-S via ocular and nasal routes induced a strong immune response in the chicken population, as evidenced by specific antibody and cytokine measurements. PAD-S was unable to replicate within chickens and showed low pre-existing immunity, demonstrating high safety and environmental friendliness. The robust immune response triggered by PAD-S immunization effectively suppressed viral replication in various tissues, alleviating clinical symptoms and tissue damage, thus providing complete protection against viral challenges in the chicken population. In conclusion, this study successfully developed an IBV candidate vaccine strain that possesses biosafety, high protective efficacy, and ease of production.

Emulsion and liposome-based adjuvanted R21 vaccine formulations mediate protection against malaria through distinct immune mechanisms

Adjuvanted protein vaccines offer high efficacy, yet most potent adjuvants remain proprietary. Several adjuvant compounds are being developed by the Vaccine Formulation Institute in Switzerland for global open access clinical use. In the context of the R21 malaria vaccine, in a mouse challenge model, we characterize the efficacy and mechanism of action of four Vaccine Formulation Institute adjuvants: two liposomal (LQ and LMQ) and two squalene emulsion-based adjuvants (SQ and SMQ), containing QS-21 saponin (Q)and optionally a synthetic TLR4 agonist (M). Two R21 vaccine formulations, R21/LMQ and R21/SQ, offer the highest protection (81%-100%), yet they trigger different innate sensing mechanisms in macrophages with LMQ, but not SQ, activating the NLRP3 inflammasome. The resulting invivo adaptive responses have a different TH1/TH2 balance and engage divergent innate pathways while retaining high protective efficacy. We describe how modular changes in vaccine formulation allow for the dissection of the underlying immune pathways, enabling future mechanistically informed vaccine design.

Molecular determinants of cross-reactivity and potency by VH3-33 antibodies against the Plasmodium falciparum circumsporozoite protein

IGHV3-33-encoded antibodies are prevalent in the human humoral response against the Plasmodium falciparum circumsporozoite protein (PfCSP). Among VH3-33 antibodies, cross-reactivity between PfCSP major repeat (NANP), minor (NVDP), and junctional (NPDP) motifs is associated with high affinity and potent parasite inhibition. However, the molecular basis of antibody cross-reactivity and the relationship with efficacy remain unresolved. Here, we perform an extensive structure-function characterization of 12 VH3-33 anti-PfCSP monoclonal antibodies (mAbs) with varying degrees of cross-reactivity induced by immunization of mice expressing a human immunoglobulin gene repertoire. We identify residues in the antibody paratope that mediate cross-reactive binding and delineate four distinct epitope conformations induced by antibody binding, with one consistently associated with high protective efficacy and another that confers comparably potent inhibition of parasite liver invasion. Our data show a link between molecular features of cross-reactive VH3-33 mAb binding to PfCSP and mAb potency, relevant for the development of antibody-based interventions against malaria.

Variations in O-Glycosylation Patterns Influence Viral Pathogenicity, Infectivity, and Transmissibility in SARS-CoV-2 Variants.

The highly glycosylated S protein plays a vital role in host cell invasion, making it the principal target for vaccine development. Differences in mutations observed on the spike (S) protein of SARS-CoV-2 variants may result in distinct glycosylation patterns, thus influencing immunological evasion, infectivity, and transmissibility. The glycans can mask key epitopes on the S1 protein and alter its structural conformation, allowing the virus to escape the immune system. Therefore, we comprehensively characterize O-glycosylation in eleven variants of SARS-CoV-2 S1 subunits to understand the differences observed in the biology of the variants. In-depth characterization was performed with a double digestion strategy and an efficient LC-MS/MS approach. We observed that O-glycosylation is highly conserved across all variants in the region between the NTD and RBD, whereas other domains and regions exhibit variation in O-glycosylation. Notably, omicron has the highest number of O-glycosylation sites on the S1 subunit. Also, omicron has the highest level of sialylation in the RBD and RBM functional motifs. Our findings may shed light on how differences in O-glycosylation impact viral pathogenicity in variants of SARS-CoV-2 and facilitate the development of a robust vaccine with high protective efficacy against the variants of concern.

Efficient showering vaccination with a live attenuated vaccine against herpesviral hematopoietic necrosis in goldfish

Herpesviral hematopoietic necrosis caused by cyprinid herpesvirus 2 (CyHV-2) frequently affects farmed goldfish Carassius auratus and gibel carp C. auratus gibelio, leading to significant economic damage. In our previous study, a live attenuated vaccine, called the P7-P8 vaccine strain, was developed by propagating virulent CyHV-2 in two non-natural host cell lines. The vaccine demonstrated high protective efficacy in goldfish with no signs of virulence reversion. Methods that reduce the costs of the procedure, including labor costs, are warranted for the practical application of this vaccine in goldfish aquaculture. The aim of this study was to explore alternative vaccination protocols for the P7-P8 strain in goldfish. First, we tested the previous standard administration protocol which is the bath vaccination with 1: 1000 diluted vaccine cultures for 2 h. In the simple first step to reduce vaccine virus culture, we examined the bathing protocol with more-diluted virus culture (ranging from 1: 1000 to 1: 81,000). The relative percentage survival (RPS) after the virulent virus immersion challenge for 2 h at 21 days post-vaccination was remarkably decreased in a dose-dependent manner; a dilution of 1: 3000 resulted in a 19% reduction from that used in the standard bathing protocol. Therefore, alternative methods (dipping and showering vaccination protocols) were tested using a 1: 100 dilution vaccine culture (10-fold more concentrated than the standard protocol) with short exposure times. Dipping vaccination for 10 s, 1 min, 2 min, and 5 min showed sufficient RPS of 82.4%–100%. The 10 s process was repeated six times using the same vaccine solution, resulting in an RPS >89%. In the showering vaccination protocol, the vaccine solution (1: 100 dilution; 1 mL, 3 mL, or 5 mL) was showered onto 20 goldfish on a net and held for 10 s, resulting in an RPS of >89%. We selected the showering vaccination as the suitable vaccination protocol. The effectiveness of this vaccination protocol was tested using the virus challenge by employing the cohabitation method with infected fish. The results showed high protective efficacy with an RPS of 65%–100%. This study demonstrated that the showering vaccination protocol, which uses small amounts of vaccine culture and produces less waste vaccine solution with short labor time, may be considered as a suitable alternative to the standard bath method in goldfish aquaculture.

Active inoculation with an inactivated Coxsackievirus A2 vaccine induces neutralizing antibodies and protects mice against lethal infection

Coxsackievirus A2 (CVA2) is one of the causative agents of hand-foot-and-mouth disease (HFMD), which poses a great challenge for global public health. However, presently, there are no available commercial vaccines or antivirals to prevent CVA2 infection. Here, we present an inactivated Vero cell-based whole CVA2 vaccine candidate and evaluate its safety and efficacy in this study. Neonatal BALB/c mice were vaccinated at 5 and 7 days old, respectively, and then challenged with either homologous or heterologous strain of CVA2 at a lethal dose at 10 days old. The inactivated whole CVA2 vaccine candidate showed a high protective efficacy. Additionally, our inactivated vaccine stimulated the production of CVA2-specific IgG1 and IgG2a antibodies in vivo and high titers of neutralization antibodies (NtAbs) in the serum of immunized mice. Maternal immunization with the inactivated CVA2 vaccine provided full protection to pups against lethal infection. Compared with mice inoculated with only alum, the viral loads were decreased, and pathological changes were relieved in tissue samples of immunized mice. Moreover, the transcription levels of some genes related to cytokines (IFN-γ and TNF-α, MCP-1, IL-6, CXCL-10 etc.) were significantly reduced. The number of immune cells and levels of cytokines in peripheral blood of mice inoculated with only alum were higher than that of immunized mice. It is noteworthy that this vaccine showed a good cross-immunity efficacy against Enterovirus A71 (EVA71) challenge. In conclusion, our findings suggest that this experimental inactivated CVA2 vaccine is a promising component of polyvalent vaccines related to HFMD in the near future.

Impact of the TLR4 agonist BECC438 on a novel vaccine formulation against Shigella spp.

Shigellosis (bacillary dysentery) is a severe gastrointestinal infection with a global incidence of 90 million cases annually. Despite the severity of this disease, there is currently no licensed vaccine against shigellosis. Shigella's primary virulence factor is its type III secretion system (T3SS), which is a specialized nanomachine used to manipulate host cells. A fusion of T3SS injectisome needle tip protein IpaD and translocator protein IpaB, termed DBF, when admixed with the mucosal adjuvant double-mutant labile toxin (dmLT) from enterotoxigenic E. coli was protective using a murine pulmonary model. To facilitate the production of this platform, a recombinant protein that consisted of LTA-1, the active moiety of dmLT, and DBF were genetically fused, resulting in L-DBF, which showed improved protection against Shigella challenge. To extrapolate this protection from mice to humans, we modified the formulation to provide for a multivalent presentation with the addition of an adjuvant approved for use in human vaccines. Here, we show that L-DBF formulated (admix) with a newly developed TLR4 agonist called BECC438 (a detoxified lipid A analog identified as Bacterial Enzymatic Combinatorial Chemistry candidate #438), formulated as an oil-in-water emulsion, has a very high protective efficacy at low antigen doses against lethal Shigella challenge in our mouse model. Optimal protection was observed when this formulation was introduced at a mucosal site (intranasally). When the formulation was then evaluated for the immune response it elicits, protection appeared to correlate with high IFN-γ and IL-17 secretion from mucosal site lymphocytes.

Immunogenicity and Efficacy of a Feed-Based Bivalent Vaccine against Streptococcosis and Motile Aeromonad Septicemia in Red Hybrid Tilapia (Oreochromis sp.).

Streptococcosis and motile Aeromonad septicemia (MAS) are the main bacterial diseases in tilapia culture worldwide, causing significant economic losses. Vaccination is an effective method of preventing diseases and contributes to economic sustainability. This study investigated the immuno-protective efficacy of a newly developed feed-based bivalent vaccine against streptococcosis and MAS in red hybrid tilapia. The feed-based bivalent vaccine pellet was developed by incorporating the formalin-killed S. agalactiae and A. hydrophila antigens into a commercial feed pellet with palm oil as the adjuvant. The bivalent vaccine was subjected to feed quality analyses. For immunological analyses, 900 fish (12.94 ± 0.46 g) were divided into two treatment groups in triplicate. Fish in Group 1 were unvaccinated (control), while those in Group 2 were vaccinated with the bivalent vaccine. The bivalent vaccine was delivered orally at 5% of the fish's body weight for three consecutive days on week 0, followed by boosters on weeks 2 and 6. Lysozyme and enzyme-linked immunosorbent assays (ELISAs) on serum, gut lavage, and skin mucus were performed every week for 16 weeks. Lysozyme activity in vaccinated fish was significantly (p ≤ 0.05) higher than in unvaccinated fish following vaccination. Similarly, the IgM antibody levels of vaccinated fish were significantly (p ≤ 0.05) higher after vaccination. The bivalent vaccine provided high protective efficacy against S. agalactiae (80.00 ± 10.00%) and A. hydrophila (90.00 ± 10.00%) and partial cross-protective efficacy against S. iniae (63.33 ± 5.77%) and A. veronii (60.00 ± 10.00%). During the challenge test, fewer clinical and gross lesions were observed in vaccinated fish compared with unvaccinated fish. Histopathological assessment showed less severe pathological changes in selected organs than the unvaccinated fish. This study showed that vaccination with a feed-based bivalent vaccine improves immunological responses in red hybrid tilapia, and thus protects against streptococcosis and MAS.

Fructose potentiates the protective efficiency of live Edwardsiella tarda cell vaccine.

Vaccination is an effective measure to prevent infection by pathogens. Live vaccines have higher protective efficacy than inactivated vaccines. However, how live vaccines interact with the host from a metabolic perspective is unknown. The present study aimed to explore whether a live Edwardsiella tarda vaccine regulates host metabolism and whether this regulation is related to the protective efficacy of the vaccine. Therefore, a gas chromatography mass spectrometry (GC-MS)-based metabolomics approach was used to investigate the metabolomic profile of mice serum after vaccination with live E. tarda vaccine. Fructose was identified as a key biomarker that contributes to the immune protection induced by the live vaccine. Moreover, co-administration of exogenous fructose and the live vaccine synergistically promoted survival of mice and fish after bacterial challenge. These results indicate that metabolites, especially fructose, can potentiate the live E. tarda vaccine to increase its protective efficiency.

Development of Next Generation Vaccines against SARS-CoV-2 and Variants of Concern.

SARS-CoV-2 has caused the COVID-19 pandemic, with over 673 million infections and 6.85 million deaths globally. Novel mRNA and viral-vectored vaccines were developed and licensed for global immunizations under emergency approval. They have demonstrated good safety and high protective efficacy against the SARS-CoV-2 Wuhan strain. However, the emergence of highly infectious and transmissible variants of concern (VOCs) such as Omicron was associated with considerable reductions in the protective efficacy of the current vaccines. The development of next-generation vaccines that could confer broad protection against both the SARS-CoV-2 Wuhan strain and VOCs is urgently needed. A bivalent mRNA vaccine encoding the Spike proteins of both the SARS-CoV-2 Wuhan strain and the Omicron variant has been constructed and approved by the US FDA. However, mRNA vaccines are associated with instability and require an extremely low temperature (-80 °C) for storage and transportation. They also require complex synthesis and multiple chromatographic purifications. Peptide-based next-generation vaccines could be developed by relying on in silico predictions to identify peptides specifying highly conserved B, CD4+ and CD8+ T cell epitopes to elicit broad and long-lasting immune protection. These epitopes were validated in animal models and in early phase clinical trials to demonstrate immunogenicity and safety. Next-generation peptide vaccine formulations could be developed to incorporate only naked peptides, but they are costly to synthesize and production would generate extensive chemical waste. Continual production of recombinant peptides specifying immunogenic B and T cell epitopes could be achieved in hosts such as E. coli or yeast. However, recombinant protein/peptide vaccines require purification before administration. The DNA vaccine might serve as the most effective next-generation vaccine for low-income countries, since it does not require an extremely low temperature for storage or need extensive chromatographic purification. The construction of recombinant plasmids carrying genes specifying highly conserved B and T cell epitopes meant that vaccine candidates representing highly conserved antigenic regions could be rapidly developed. Poor immunogenicity of DNA vaccines could be overcome by the incorporation of chemical or molecular adjuvants and the development of nanoparticles for effective delivery.

Recombinant Pichinde viral vector expressing tuberculosis antigens elicits strong T cell responses and protection in mice.

Tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) remains a major global health threat. The only available vaccine Bacille Calmette-Guérin (BCG) does not prevent adult pulmonary TB. New effective TB vaccines should aim to stimulate robust T cell responses in the lung mucosa to achieve high protective efficacy. We have previously developed a novel viral vaccine vector based on recombinant Pichinde virus (PICV), a non-pathogenic arenavirus with low seroprevalence in humans, and have demonstrated its efficacy to induce strong vaccine immunity with undetectable anti-vector neutralization activity. Using this tri-segmented PICV vector (rP18tri), we have generated viral vectored TB vaccines (TBvac-1, TBvac-2, and TBvac-10) encoding several known TB immunogens (Ag85B, EsxH, and ESAT-6/EsxA). A P2A linker sequence was used to allow for the expression of two proteins from one open-reading-frame (ORF) on the viral RNA segments. The immunogenicity of TBvac-2 and TBvac-10 and the protective efficacy of TBvac-1 and TBvac-2 were evaluated in mice. Both viral vectored vaccines elicited strong antigen-specific CD4 and CD8 T cells through intramuscular (IM) and intranasal (IN) routes as evaluated by MHC-I and MHC-II tetramer analyses, respectively. The IN inoculation route helped to elicit strong lung T cell responses. The vaccine-induced antigen-specific CD4 T cells are functional, expressing multiple cytokines as detected by intracellular cytokine staining. Finally, immunization with TBvac-1 or TBvac-2, both expressing the same trivalent antigens (Ag85B, EsxH, ESAT6/EsxA), reduced Mtb lung tissue burden and dissemination in an aerosol challenge mouse model. The novel PICV vector-based TB vaccine candidates can express more than two antigens via the use of P2A linker sequence and elicit strong systemic and lung T cell immunity with protective efficacy. Our study suggests the PICV vector as an attractive vaccine platform for the development of new and effective TB vaccine candidates.

Response regulator KdpE contributes to Aeromonas dhakensis virulence

Aeromonas dhakensis is an emerging pathogen that is harmful to humans and aquaculture in tropical areas. The aim of this study was to understand the role of the two-component signal transduction system KdpDE in regulating the virulence of this species. A ΔkdpE mutant was generated via a markerless knockout. Phenotype analysis showed that the mutant was attenuated in growth, biofilm formation, mobility, ECPase activity, and resistance to H2O2 and antimicrobial peptides under conditions of potassium depletion. A challenge experiment to analyze the virulence of A. dhakensis in zebrafish, via intraperitoneal injection, demonstrated that the clinicopathological signs of infection were dropsy, tail and/or fin bleeding, hepatonecrosis, spleen congestion, and nephrohemia. The LD50 value of the mutant (9.02 × 106 CFU/ml) was 15.6-fold higher than that of the wild-type strain (5.77 × 105 CFU/ml). The survival rate of zebrafish was higher after double immunization (76.7%) than after single immunization with the mutant (36.7%). These data reveal for the first time that KdpDE is associated with the virulence of A. dhakensis. The ΔkdpE mutant is attenuated in virulence and shows high protective efficacy in adult zebrafish after double immunization, and is therefore a promising attenuated vaccine candidate.