Search Results (332)

To address the lack of a commercially available vaccine for goose circovirus (GoCV), we developed and evaluated a prokaryotically expressed subunit vaccine targeting the viral capsid (Cap) protein. A truncated Cap protein (GoCV-ΔCap) was expressed in Escherichia coli (E. coli) and formulated with aluminum hydroxide as a subunit vaccine (GoCVsubvac). Goslings were primed intramuscularly (i.m.) with high (75 µg) or low (15 µg) doses GoCVsubvac, followed by a boost 14 days later. At 14 days post-boost, goslings were challenged with GoCV and were administered a bivalent inactivated vaccine against Newcastle disease virus (NDV) and H9-subtype Avian influenza virus (AIV). Using our established gosling pathogenicity model, vaccine efficacy was evaluated via body weight, lesions, viral load, antibody titers, cytokine responses, and interference with NDV/AIV immunity. Results demonstrated that the GoCV-ΔCap vaccine, especially the high-dose formulation, provided effective immunoprotection. It elicited robust humoral and cellular immune responses, reduced lymphoid pathology, and decreased the viral detection rate in lymphoid tissues from 100% (5/5) in infected controls to 40% (2/5). Importantly, it alleviated GoCV-induced immunosuppression and preserved the immunogenicity of co-administered vaccines. This novel subunit vaccine is a promising candidate for controlling GoCV disease (GoCVD). Full article

Toxoplasma gondii is an obligate intracellular protozoan parasite that causes toxoplasmosis, posing a significant threat to human health and livestock production worldwide. Although monovalent DNA or mRNA vaccines often confer only partial protection, whether these platforms can be effectively integrated into a heterologous prime–boost regimen against T. gondii remains to be fully elucidated. Here, we constructed GRA35-encoding DNA and mRNA vaccines and evaluated their immunogenicity and protective efficacy, administered either alone or in heterologous prime–boost combinations, in C57BL/6 and BALB/c mice. Both vaccines induced strong antigen-specific immune responses, with the heterologous prime–boost regimen eliciting the strongest effects and conferring the most robust and consistent protection across both mouse strains. Immunization triggered a predominantly Th1-skewed response characterized by significantly elevated IFN-γ production, accompanied by balanced antigen-specific IgG responses. Moreover, vaccinated mice developed rapid and potent cytotoxic T lymphocyte (CTL) responses. Following challenge with the RH and PRU strains, vaccinated mice exhibited prolonged survival and significantly reduced brain cyst burdens following PRU challenge compared with control groups. Collectively, these findings indicate that GRA35-based nucleic acid vaccines, particularly when administered in a heterologous prime–boost regimen, elicit multifaceted protective immune responses and represent promising vaccine candidates against T. gondii infection. Full article

Background: Respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract infections and poses a substantial disease burden to infants, older adults, and immunocompromised populations. Methods: In this study, a recombinant vaccinia virus (rMVA-RSV preF) was constructed based on the modified vaccinia virus Ankara (MVA) platform by inserting a stabilized prefusion F protein gene of RSV into the MVA genome. The immunogenicity of rMVA-RSV preF and preF protein was evaluated in Balb/c mice under different vaccination regimens. Results: A heterologous prime–boost regimen, priming with rMVA-RSV preF and boosting with AS01E-adjuvanted preF protein, elicited robust cellular and humoral immune responses with a Th1 bias. This regimen significantly enhanced immunogenicity compared to homologous vaccination. Conclusions: There is a lack of data from further challenge studies to support the efficacy of the rMVA-RSV preF vaccine in terms of protection, but our findings demonstrate a favorable immunogenicity profile of the rMVA-RSV preF vaccine, supporting its further development as a promising RSV vaccine candidate. Full article

Background/Objectives: Pathogenic mammarenaviruses cause severe hemorrhagic and neurologic disease in humans. Machupo virus (MACV), a New World (NW) mammarenavirus, causes Bolivian hemorrhagic fever in humans, and there are no approved vaccines. Methods: Here, we describe and compare the immunogenicity of three vaccines expressing the MACV glycoprotein complex (GPC) in C57BL/6 mice: a recombinant vesicular stomatitis virus (rVSV) and two different lipid nanoparticle (LNP)-encapsulated nucleoside-modified mRNA (mRNA-LNP) vaccines. The first mRNA-LNP vaccine, designated MACV mRNA, expresses the full-length MACV GPC. The second mRNA-LNP vaccine, called MACV VLP mRNA, encodes MACV GPC with appended sequences that induce the budding of virus-like particles (VLPs) with MACV GPC on the surface. This is the first description of any mRNA-LNP vaccine for MACV and the first comparison of mRNA and rVSVs as vaccine candidates for MACV. Results: We find that two doses of either MACV mRNA or MACV VLP mRNA are required for the induction of robust humoral and cellular immune responses including total MACV GPC IgG, neutralizing antibodies, cross-reactive antibodies that bind the related Junín virus GPC, and MACV-specific T-cell responses. To further investigate vaccination strategies for MACV, we also evaluated a heterologous prime-boost regimen involving the MACV mRNA vaccine coupled with the rVSV-based MACV vaccine. We find that the highest levels of MACV GPC-specific IgG and neutralizing titers were achieved when heterologous mRNA and rVSV prime-boost regimens were employed. Conclusions: These results elucidate differences in the immune response to different vaccine platforms for MACV and can inform future vaccine development for NW arenaviruses. Full article

Background/objectives: SARS-CoV-2 antibodies wane after natural infections and vaccinations. COVID-19 booster vaccination enhances the durability and functionality of antibodies against emerging SARS-CoV-2 variants. Data on booster-induced antibody durability in sub-Saharan Africa remain sparse. Comparative analysis of vaccine-induced responses between heterologous and homologous vaccination regimens remains limited. This study evaluated longitudinal RBD-specific IgG responses following homologous and heterologous COVID-19 booster vaccination in previously vaccinated adults. Methods: Adults with prior mRNA or adenoviral-vectored vaccination were boosted with either Pfizer (mRNA) or Janssen (adenoviral-vectored) vaccines. Plasma IgG binding to Wuhan, Delta, and Omicron RBDs was measured pre-booster and at 3, 6, and 9 months. A total of 181 participants were enrolled between November 2022 and October 2023. Results: More than 60% of participants had detectable pre-booster RBD- and N-antigen-specific IgG. Booster vaccination substantially increased Wuhan-specific RBD-IgG at three months, with limited boosting of Delta and Omicron responses. Antibody levels waned to pre-booster concentrations by month nine. Heterologous boosting with a viral-vectored prime followed by Pfizer mRNA significantly enhanced both peak RBD-IgG levels and durability. Conclusions: These longitudinal data provide rare real-world evidence on booster immunogenicity in African adults and demonstrate that heterologous regimens confer a short- to intermediate-term advantage in antibody magnitude compared to a homologous regimen. This benefit was most pronounced within the first six months post-boost. The findings support additional booster dosing to strengthen protection against emerging variants in sub-Saharan Africa. Full article

Background/Objectives: Eliciting robust immune responses against the hepatitis B virus (HBV) through therapeutic vaccination holds promise for curing chronic hepatitis B. We previously developed the heterologous protein prime/viral vector boost clinical vaccine candidate, TherVacB. Here, we evaluated a replication-competent chimeric vesicular stomatitis virus vector (VSV-GP) as an alternative viral vector boost vaccine. Methods: A recombinant VSV-GP vector co-expressing HBV surface and core antigens (VSV-GP-HBs/c) was generated and characterized for antigen expression. Its immunogenicity, antiviral efficacy, and durability were assessed in HBV-naïve and HBV-carrier mice, using protein primed, viral vector-primed, and multi-viral vector boost regimens. Results: VSV-GP-HBs/c efficiently expressed both HBV antigens in vitro. A single immunization with VSV-GP-HBs/c induced only weak HBV-specific immune responses in vivo. Replacing protein priming with VSV-GP-HBs/c resulted in modest immune activation and limited antiviral effects in HBV-carrier mice. In contrast, substituting the modified vaccinia virus Ankara (MVA)-HBs/c boost in the TherVacB regimen with VSV-GP-HBs/c elicited robust HBV-specific antibody responses and strong CD4 and CD8 T-cell immunity, assessed by intracellular IFN-γ staining after peptide stimulation. This regimen achieved a substantial reduction in serum HBsAg levels, numbers of HBV-positive hepatocytes, and intrahepatic HBV-DNA, with antiviral efficacy comparable to that of the classical TherVacB regimen. Notably, a second viral vector boost did not enhance HBV-specific immunity or antiviral efficacy; instead, it promoted dominant vector-specific CD8 T-cell responses. Long-term analyses performed 10 weeks after the last vaccination further demonstrated that a single protein-prime/VSV-GP-HBs/c boost was sufficient to achieve sustained antiviral control. Conclusions: These findings identify VSV-GP-HBs/c as an effective boost vector for therapeutic hepatitis B vaccination and establish protein priming followed by a single viral vector boost as an optimal strategy for sustained antiviral immunity. Full article

Pigeon Newcastle disease poses a persistent threat to the global pigeon industry, underscoring the need for effective vaccination strategies. While both inactivated and DNA vaccines offer distinct advantages, the immunogenicity of a combined heterologous regimen remains underexplored. This study evaluated and compared three immunization strategies in pigeons: a DNA vaccine encoding the NDV F protein fused with chicken IL-18, an inactivated vaccine from a local virulent strain, and a DNA prime-inactivated boost regimen. The preparation workflows for both vaccine platforms are described in detail to provide methodological context for the immunological comparison. Critically, the prime–boost regimen elicited significantly higher hemagglutination inhibition (HI) antibody titers than either vaccine administered alone, demonstrating a clear synergistic effect. These findings highlight the complementary roles of the two platforms and provide a strong immunological rationale for further evaluation of this sequential strategy. Future studies incorporating viral challenge experiments and long-term immune monitoring are needed to determine whether the enhanced HI antibody response translates into protective efficacy under field conditions. Full article

Background/Objectives: Epidemiological studies have proven that coxsackievirus B3 (CVB3) is the major virus that causes acute and chronic myocarditis and pancreatitis. Currently, there are no antiviral therapeutic drugs or vaccines that are available for use as clinical therapeutics or vaccines. Subunit polypeptides-based vaccines, especially when combined with adjuvants, represent safe and effective vaccine platforms because they are considered to be better immunogens. The viral capsid protein VP1 of CVB3 is the most immunogenic viral polypeptide, providing opportunities for its use in designing subunit polypeptide vaccines. In the present study, we designed and produced a CVB3 vaccine candidate based on the recombinant expression of the major immunogenic viral protein VP1 of a wild-type CVB3 strain. Methods: We assessed its induced humoral and cellular immune responses and then evaluated its protective immunity against pathogenic CVB3 strain challenges in a Balb/c mouse model. Neutralizing specific antibodies and cytokine interferon gamma (INF-γ) production were determined in the sera of both prime- and prime-boost-immunized mice with the vaccine candidate. Results: Our results demonstrate that the recombinant rVP1 expressed in a eukaryotic insect cell baculovirus vector system elicited cellular and humoral immune responses, protecting Balb/c mice from lethal challenges. Conclusions: Hence, the vaccine produced based on the recombinant expression of VP1 is a promising and potential candidate against natural CVB3 infections. Full article

Highly pathogenic avian influenza A/H5N1 remains a persistent threat to public health and poultry production. H5N1 antigens are typically poorly immunogenic and require effective adjuvants for antigen dose-sparing. Here, we evaluated chitosan microparticles (CSMs) and nanoparticles (CSNs) as polymeric nano-adjuvants for an H5N1 influenza vaccine, focusing on the roles of antigen dose and particle size. A purified hemagglutinin antigen was adsorbed onto chitosan particles at doses ranging from 0.15 to 5.0 µg. Both CSNs and CSMs showed consistently high loading efficiency (97–99%). BALB/c mice were immunized intramuscularly in a prime–boost schedule. Chitosan nanoparticles significantly enhanced IgG and hemagglutination inhibition (HI) titers at low antigen doses compared with aluminum hydroxide and antigen-only controls (p < 0.05). Immune responses reached saturation at a 1.5 µg dose of antigen for chitosan nanoparticles and 3.0 µg for chitosan microparticles. IgG subtype analysis suggested a balanced IgG1/IgG2a profile. Collectively, these findings support chitosan-based polymeric nanoparticles as promising adjuvants enabling dose-sparing H5N1 vaccination. Full article

Background/Objectives: Porcine epidemic diarrhea (PED) is a highly contagious enteric disease caused by porcine epidemic diarrhea virus (PEDV) and is associated with severe clinical signs and high mortality in neonatal piglets. Vaccination is an important strategy for PED control through the induction of humoral immunity. This study aimed to compare immune responses induced by inactivated and live-attenuated PEDV vaccines and to evaluate a heterologous prime-boost vaccination strategy in PEDV-naïve replacement gilts. Methods: Twenty-four PEDV-naïve replacement gilts were randomly assigned to four groups: unvaccinated control, inactivated vaccine administered twice (K/K), live-attenuated vaccine administered twice (L/L), and live-attenuated priming followed by an inactivated booster (L/K). Pigs received two intramuscular vaccinations at 16 weeks of age and two weeks later. Serum samples collected up to 42 days post-vaccination were analyzed for PEDV-specific IgG and IgA antibodies by ELISA, and serum-neutralizing antibody titers were determined using a serum neutralization test. Results: The L/K regimen induced the highest PEDV-specific IgG responses, with peak levels at day 28 post-vaccination that were significantly higher than those in the K/K and control groups. Serum-neutralizing antibody titers were significantly higher in the L/K and L/L groups than in the K/K and control groups. Serum IgA responses were low and transient across all vaccination groups. Conclusions: A heterologous prime-boost vaccination strategy using a live-attenuated PEDV vaccine followed by an inactivated booster induces strong systemic humoral immune responses in replacement gilts and represents a promising approach for PEDV vaccination programs. Full article

Background/Objectives: Adjuvants, added to vaccines to enhance immune responses, are central to shaping the magnitude and durability of immunity, yet their precise mechanisms remain incompletely defined. This study evaluated how diverse adjuvant combinations influence HPV vaccine immunogenicity in non-human primates, with a particular focus on impacts on hematopoietic biology—megakaryocytes and platelets—and broader innate and adaptive pathways. Methods: Eight adjuvanted formulations, each incorporating distinct immunomodulatory components and delivery platforms, were compared against an alum-only control in non-human primates. Longitudinal antibody titers (HPV16-specific) were measured up to 54 weeks, and blood transcriptomes were profiled at Day 1 and Day 7 after both prime and boost doses to assess pathway-level enrichment and gene-expression patterns. Results: Several adjuvant combinations significantly increased antibody titers at 54 weeks compared with alum alone. Formulations containing cationic lipid or monophosphoryl lipid A (MPL) were associated with enhanced antibody responses. Early upregulation of immune-related genes across innate and adaptive pathways was also observed, with some combinations (e.g., inclusion of QS21 or ISCOMs) showing similar trends. Distinct group- and time-dependent transcriptional signatures were observed, with higher-responding formulations exhibiting stronger enrichment in pathogen-influenced signaling and cellular/humoral immune programs. Conclusions: Adjuvant selection and formulation strategy substantially modulate vaccine immunogenicity and early transcriptional programs, including innate, adaptive, and hematopoietic pathways. While individual adjuvants differentially regulate immune and platelet-associated genes, common pathway-level patterns emerge across formulations. These findings suggest candidate mechanisms for prolonged vaccine efficacy and provide actionable insights to guide rational adjuvant design for sustained immune protection. Full article

Background/Objectives: SARS-CoV-2, the causative agent of COVID-19, has been responsible for more than seven million deaths worldwide since its emergence. The Bacillus Calmette–Guérin (BCG) vaccine, used for over 100 years to prevent tuberculosis, induces a Th1-prominent immune response that is important for protection against Mycobacterium tuberculosis, other mycobacteria, and intracellular pathogens. BCG has also been shown to induce innate immune memory and heterologous protection against non-related infections. Additionally, BCG has been used as a vector to express heterologous proteins, showing protective effects against various diseases, particularly respiratory viral infections, including SARS-CoV-2. In this report, we constructed two recombinant BCG strains as potential vaccine candidates based on the receptor-binding domain (RBD) of the Spike antigen: one expressing only the RBD protein (rBCG-RBD) and another expressing the RBD protein in fusion with the LTB (Escherichia coli Labile Toxin subunit B) adjuvant (rBCG-LTB-RBD). Methods: We evaluated the induction of SARS-CoV-2-specific humoral and cellular immune responses using these vaccine candidates in a prime–boost strategy with a booster dose using the rRBD protein (produced in cell culture) and the Alum adjuvant. Antisera were evaluated for neutralization of the Wuhan and Omicron SARS-CoV-2 pseudotyped virus. Results: Either immunization scheme (rBCG-RBD/rRBD or rBCG-LTB-RBD/rRBD) induced high IgG antibody titers, with antibody neutralization against a Wuhan SARS-CoV-2 pseudotyped virus after 10 weeks. The antibody levels induced by rBCG-RBD/rRBD were maintained for up to 9 months. Interestingly, only the sera from mice receiving the prime–boost with rBCG-LTB-RBD/rRBD showed cross-reactive neutralization against the Omicron SARS-CoV-2 pseudotyped virus. Immunization with rBCG-RBD or rBCG-LTB-RBD and a rRBD booster dose promoted the induction of specific CD4+ and CD8+ T cells producing Th1/Th2 cytokines (IL-4, TNF-α and IFN-γ). Conclusions: Our study highlights the potential of the prime–boost immunization strategy using rBCG-RBD/rRBD to induce long-term immunity and rBCG-LTB-RBD/rRBD to induce cross-protection against different variants, both of which could serve as promising vaccine candidates. Full article

Background: Developing an effective vaccine is crucial for the prevention and control of AIDS. Viral vector-based vaccines, particularly those utilizing homologous or heterologous prime-boost strategies, represent an important direction in current HIV vaccine research. Methods: In this study, replication-defective chimeric adenovirus Ad5F35 and modified vaccinia virus Ankara (rMVA) vector vaccines expressing the HIV-1 AEgp145 were successfully constructed, designated as Ad5F35-AEgp145 and rMVA-AEgp145, respectively. Sixty BALB/c mice were randomly divided into three groups: Ad5F35 alone, rMVA prime/Ad5F35 boost, and PBS control. The mice were immunized intramuscularly at weeks 0 and 3, and humoral and cellular immune responses were assessed at 4, 8, 12, and 16 weeks after the initial immunization. Results: The homologous Ad5F35 and heterologous rMVA/Ad5F35 vaccination regimens elicited comparable levels of HIV Env-specific cellular immune responses, peaking at 2100 ± 222 SFCs/million splenocytes and 2200 ± 619 SFCs/million splenocytes, respectively (p > 0.05). Compared to the heterologous regimen, the homologous Ad5F35 regimen induced significantly higher levels of gp120-binding antibodies at weeks 4 and 8 post-initial immunization, with geometric mean titers of 1:25,600 ± 7011 versus 1:1280 ± 150.7 and 1:10,240 ± 4048 versus 1:2560 ± 391.9, respectively. Furthermore, neutralizing activity at week 8 was significantly higher in the homologous group, with a 50% neutralization titers of 1:45 compared to 1:12 in the heterologous group (p < 0.01). Conclusion: This study demonstrates that the Ad5F35-AEgp145 vaccine, whether administered alone or in combination with rMVA-AEgp145, effectively induces strong and comparable cellular immune responses targeting HIV-1 Env in mice. While both regimens are effective, homologous immunization elicits moderately higher levels of antibody responses. These findings provide an important foundation for the further investigation of vector-based HIV vaccine formulations. Full article

Background: Emerging immune-evasive viral variants threaten the efficacy of current vaccines, underscoring the need for strategies that elicit broad and durable protection. Heterologous prime–boost regimens combining distinct vaccine platforms can enhance humoral and cellular immunity through complementary mechanisms. Methods: Using an intramuscular immunization scheme aligned with clinical vaccination practice, CD-1 mice received homologous or heterologous prime–boost regimens combining a replication-deficient Orf virus (Parapoxvirus orf, ORFV)-based spike vaccine (ORFV-S) with the licensed adjuvanted recombinant protein vaccine VidPrevtyn Beta. Spike-specific humoral and cellular immune responses were assessed. Results: ORFV-S alone induced potent and broad spike-specific IgG responses and achieved the strongest ACE2-binding inhibition across variants of concern. ORFV-S priming followed by VidPrevtyn Beta boosting markedly enhanced the magnitude and cross-variant breadth of antibody responses compared with homologous protein vaccination. Both homologous ORFV-S and heterologous regimens incorporating ORFV-S elicited strong CD4⁺ and CD8⁺ T-cell responses, whereas VidPrevtyn Beta alone induced only modest T-cell activity, demonstrating that ORFV-S effectively complements protein-based vaccines. Conclusions: The ORFV-S vector represents a potent vaccine platform capable of inducing broad humoral and cellular immunity. Its use in heterologous prime–boost combinations enhances both antibody magnitude and breadth beyond homologous protein vaccination, supporting its application in vaccination strategies against evolving viral pathogens. Full article

Background/Objectives: Tuberculosis (TB) remains the leading cause of death from a single infectious agent worldwide. In line with the World Health Organization’s (WHO) goal to end TB by 2035, the rapid development and clinical implementation of new, effective vaccines is urgently needed. To support global TB control efforts, we developed a novel candidate subunit multistage vaccine. Methods: This vaccine incorporates multiple Mycobacterium tuberculosis antigens expressed during both dormant and active stages of infection, fused into a single recombinant protein (ESAT6-CFP10-Ag85A-Rv2660c-Rv1813c). The antigen was encapsulated in biodegradable poly(D,L-lactide-co-glycolide) (PLGA) nanoparticles along with the pattern recognition receptor (PRR) agonists monophosphoryl lipid A (MPLA) and muramyl dipeptide (MDP), which function as adjuvants. Results: Using a mixed intramuscular/nasal prime-boost regimen, the vaccine elicited a mixed Th1/Th17 cell-mediated immune response, as well as a robust humoral response characterized by sustained systemic IgG (lasting at least one year) and prominent local secretory IgA. The vaccine demonstrated protective efficacy as a prophylactic booster following BCG priming in both murine and guinea pig models and was also effective in a therapeutic setting in a murine infection model. Conclusions: The results of this study provide empirical evidence that multistage tuberculosis vaccines represent a promising strategy for achieving global TB control. Full article