Assessing the protection elicited by virus-like particles expressing the RSV pre-fusion F and tandem repeated G proteins against RSV rA2 line19F infection in mice.

Excessive pulmonary inflammation is the hallmark of respiratory syncytial virus (RSV) infection hindering efficacious RSV vaccine development. Yet, the vast majority of the experimental RSV vaccine studies use laboratory-adapted RSV strains that do not reflect the highly pathogenic and inflammatory nature of the virus found in clinical settings. Here, we re-evaluated the protective efficacy of the virus-like particle (VLP) vaccine co-expressing the pre-fusion (pre-F) protein and G protein with tandem repeats (Gt) reported in our previous study against the recombinant RSV rA2-line19F strain, which inflicts severe mucus production and inflammation in mice. VLP vaccine immunization elicited virus-specific serum antibody responses that mediated RSV rA2-line19F virus neutralization. VLP vaccine immunization promoted Th1 immune response development in the spleens and CD8 + T cell influx into the lungs of mice, which are essential for efficient viral clearance and dampened inflammatory response. When compared to the VLPs expressing only the pre-F antigen, those co-expressing both pre-F and Gt antigens conferred better protection in mice against rA2-line19F challenge infection. Overall, our data suggest that the pre-clinical VLP vaccine co-expressing RSV pre-F and Gt antigens can effectively protect mice against RSV strains that resemble pathogenic clinical isolates.

Influenza virus-like particle vaccine containing both apical membrane antigen 1 and microneme-associated antigen proteins of Plasmodium berghei confers protection in mice.

BACKGROUND: Apical membrane antigen 1 (AMA1) and microneme-associated antigen (MIC) of Plasmodium parasites are important factors involved in host cell invasion. METHODS: In this study, influenza VLP vaccines containing both codon-optimized AMA1 and MIC were generated and the vaccine efficacy was evaluated in mice. RESULTS: VLPs vaccine immunization elicited higher levels of parasite-specific IgG and IgG2a antibody responses in sera. CD4+ and CD8+ T cells and germinal center B cells in blood, inguinal lymph nodes (ILN) and spleen were found to be significantly increased. Importantly, VLPs vaccination significantly reduced the levels of pro-inflammatory cytokines IFN-γ and TNF-α, decreased parasitemia in blood, resulting in lower body weight loss and longer survival time compared to control. CONCLUSION: These results indicated that VLPs containing P. berghei AMA1 and MIC could be a candidate for malaria blood-stage vaccine design.

Protective immunity induced by CpG ODN-adjuvanted virus-like particles containing Toxoplasma gondii proteins.

AIMS: To date, a Toxoplasma gondii vaccine for clinical use remains unavailable, though multiple vaccine candidates have been suggested. In our previous studies, unadjuvanted virus-like particles (VLPs) vaccines expressing multiple T. gondii antigens were confirmed to be protective against T. gondii challenge infection. Yet, the protective efficacy of adjuvanted T. gondii VLP in comparison with the unadjuvanted counterpart requires elucidation. METHODS AND RESULTS: In the present study, mice were immunized with the multi-antigenic VLP vaccines (TG146 VLP) with or without CpG adjuvants and their protective efficacies were compared. CpG-adjuvanted TG146 VLP vaccine elicited enhanced T gondii-specific IgG and IgA antibody responses in the sera, mucosal tissue and the brain compared to unadjuvanted VLPs vaccine. Inclusion of CpG adjuvant in vaccines also induced greater CD4+ and CD8+ T-cell responses, as well as B cell and germinal centre B cell responses from splenocytes and mesenteric lymph nodes. Pro-inflammatory cytokine response and cyst counts in the brain were drastically diminished in mice immunized with CpG-adjuvanted VLP vaccines. CONCLUSION: Our results demonstrated that CpG-adjuvanted T. gondii VLPs can significantly enhance the protective efficacy of vaccines against T. gondii infection.

Systematic review and meta-analysis of the prevalence of chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME).

BACKGROUND: Chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME) has been emerging as a significant health issue worldwide. This study aimed to systemically assess the prevalence of CFS/ME in various aspects of analyses for precise assessment. METHODS: We systematically searched prevalence of CFS/ME from public databases from 1980 to December 2018. Data were extracted according to 7 categories for analysis: study participants, gender and age of the participants, case definition, diagnostic method, publication year, and country of the study conducted. Prevalence data were collected and counted individually for studies adopted various case definitions. We analyzed and estimated prevalence rates in various angles: average prevalence, pooled prevalence and meta-analysis of all studies. RESULTS: A total of 1291 articles were initially identified, and 45 articles (46 studies, 56 prevalence data) were selected for this study. Total 1085,976 participants were enrolled from community-based survey (540,901) and primary care sites (545,075). The total average prevalence was 1.40 ± 1.57%, pooled prevalence 0.39%, and meta-analysis 0.68% [95% CI 0.48-0.97]. The prevalence rates were varied by enrolled participants (gender, study participants, and population group), case definitions and diagnostic methods. For example, in the meta-analysis; women (1.36% [95% CI 0.48-0.97]) vs. men (0.86% [95% CI 0.48-0.97]), community-based samples (0.76% [95% CI 0.53-1.10]) vs. primary care sites (0.63% [95% CI 0.37-1.10]), adults ≥ 18 years (0.65% [95% CI 0.43-0.99]) vs. children and adolescents < 18 years (0.55% [95% CI 0.22-1.35]), CDC-1994 (0.89% [95% CI 0.60-1.33]) vs. Holmes (0.17% [95% CI 0.06-0.49]), and interviews (1.14% [95% CI 0.76-1.72]) vs. physician diagnosis (0.09% [95% CI 0.05-0.13]), respectively. CONCLUSIONS: This study comprehensively estimated the prevalence of CFS/ME; 0.89% according to the most commonly used case definition CDC-1994, with women approximately 1.5 to 2 folds higher than men in all categories. However, we observed the prevalence rates are widely varied particularly by case definitions and diagnostic methods. An objective diagnostic tool is urgently required for rigorous assessment of the prevalence of CFS/ME.

Orally administered recombinant baculovirus vaccine elicits partial protection against avian influenza virus infection in mice.

Avian influenza outbreaks have placed a tremendous economic burden on the poultry industry, necessitating the need for an effective vaccine. Although multiple vaccine candidates are available, its development is hindered by several drawbacks associated with the vaccine platforms and as such, more improvements to the vaccines are needed. Therefore, in this study, the vaccine efficacy in the murine models was assessed prior to evaluation in chickens. An oral recombinant baculovirus (rBV) vaccine expressing influenza hemagglutinin (HA) (A/H5N1) was generated and its efficacy was investigated against homologous avian influenza infection in mice. Our results confirmed that oral administration of rBVs enhanced the level of virus-specific antibodies in the sera following boost immunization. Upon challenge infection with a lethal dose of highly pathogenic avian influenza virus (HPAI, H5N1) virus, a marked increase in mucosal IgG and IgA were observed. Drastically increased antibody secretory cell responses from the bone marrow cells and splenocytes of vaccinated mice were observed, in addition to the strongly elicited germinal center responses in the lungs and the spleens. Vaccinated mice showed significantly reduced lung pro-inflammatory cytokine responses, lung viral loads, body weight loss, and mortality. Though mice were only partially protected upon challenge infection, these results highlight the potential of orally administered rBVs expressing the HA as a vaccine candidate for controlling avian influenza outbreaks.

Virus-like particle vaccine displaying Toxoplasma gondii apical membrane antigen 1 induces protection against T. gondii ME49 infection in mice.

Toxoplasmosis is an intracellular parasitic disease caused by the protozoa Toxoplasma gondii, which affects about half of the world's population. In spite of the strenuous endeavors, a T. gondii vaccine for clinical use remains unreported to date. In the present study, we generated virus-like particles (VLPs) containing T. gondii apical membrane antigen 1 (AMA1) and assessed its efficacy in a murine model. VLPs were characterized using western blot and TEM. T. gondii-specific IgG and IgA antibody responses in sera, germinal center B cell responses in spleen, brain cyst counts and their sizes were determined. Elevated T. gondii-specific IgG and IgA antibody responses were observed from the sera of AMA1 VLP-immunized mice. Immunization with AMA1 VLPs enhanced T. gondii-specific antibody-secreting cell responses and germinal center B cell responses upon antigen stimulation. Brain tissue analysis revealed that AMA1 VLP-immunization reduced cyst formation and its size compared to control. Also, VLP-immunized mice were less susceptible to body weight loss and displayed enhanced survival rate compared to the control group. Our results demonstrated that the immune response induced by T. gondii AMA1 VLPs confer partial protection against T. gondii infection and provides important insight into potential T. gondii vaccine design strategy.

Toxoplasma gondii virus-like particle vaccination alleviates inflammatory response in the brain upon T gondii infection.

AIMS: Neuroinflammation can manifest upon infection with the neurotropic parasite Toxoplasma gondii (ME49), which can lead to brain injury and cognitive dysfunction. Rhoptry organelle proteins (ROPs) secreted by T gondii play critical roles in host invasion. METHODS AND RESULTS: In this study, influenza virus-like particles (VLPs) expressing T gondii ROP4 or ROP13 were generated to assess vaccination-induced changes in intracranial pro-inflammatory cytokines and antibody responses upon T gondii challenge infection. Compared to ROP13 VLPs, ROP4VLPs vaccination significantly limited the production of pro-inflammatory cytokines IFN-γ and IL-6 in the brains of mice. Reduced pro-inflammatory cytokine responses by ROP4 VLPs and ROP13 VLPs correlated with significantly increased T gondii-specific IgG and IgA antibody responses in the brain, as well as IgG, IgG1 and IgM antibody responses in the sera. CONCLUSION: We concluded that influenza T gondii VLP vaccination induces antibody responses in sera and brain, which may contribute to the significant reduction of neuroinflammation during T gondii infection.

Virus-like particles expressing Plasmodium berghei MSP-8 induce protection against P. berghei infection.

AIMS: Merozoite surface protein 8 (MSP-8) of Plasmodium parasites plays an important role in erythrocyte invasion and is a potential malaria vaccine candidate. METHODS AND RESULTS: In this study, virus-like particles (VLPs) expressing MSP-8 of Plasmodium berghei on the surface of influenza virus matrix protein 1 (M1) core protein were generated for vaccine efficacy assessment. Mice were intramuscularly (IM) immunized with MSP-8 VLPs twice and challenge-infected with P. berghei. We found that VLP vaccination elicited higher levels of P. berghei-specific IgG antibody response in the sera, along with blood CD4+ and CD8+ T-cell response enhancement compared to the naïve control mice. CD4+ and CD8+ effector memory T-cell and memory B-cell responses in the spleen were found to be higher in VLP-immunized mice compared to control mice. VLP vaccination significantly reduced inflammatory cytokine (IFN-γ) response in the spleen and parasitemia levels in blood compared to naïve control mice. CONCLUSIONS: These results indicate that MSP-8 containing virus-like particles could be a vaccine candidate for blood-stage vaccine design.

Protection induced by malaria virus-like particles containing codon-optimized AMA-1 of Plasmodium berghei.

BACKGROUND: Despite the extensive endeavours, developing an effective malaria vaccine remains as a great challenge. Apical membrane antigen 1 (AMA-1) located on the merozoite surface of parasites belonging to the genus Plasmodium is involved in red blood cell invasion. METHODS: Influenza virus-like particle (VLP) vaccines containing codon-optimized or native (non-codon optimized) AMA-1 from Plasmodium berghei were generated. VLP-induced protective immunity was evaluated in a mouse model. RESULTS: Mice immunized with VLP vaccine containing the codon-optimized AMA-1 elicited higher levels of P. berghei-specific IgG and IgG2a antibody responses compared to VLPs containing non-codon optimized AMA-1 before and after challenge infection. Codon-optimized AMA-1 VLP vaccination induced higher levels of CD4+ T cells, CD8+ T cells, B cells, and germinal centre cell responses compared to non-codon optimized AMA-1 VLPs. Importantly, the codon-optimized AMA-1 VLP vaccination showed lower body weight loss, longer survival and a significant decrease in parasitaemia compared to non-codon optimized VLP vaccination. CONCLUSION: Overall, VLP vaccine expressing codon-optimized AMA-1 induced better protective efficacy than VLPs expressing the non-codon optimized AMA-1. Current findings highlight the importance of codon-optimization for vaccine use and its potential involvement in future malaria vaccine design strategies.

Immune Correlates of Protection Induced by Virus-Like Particles Containing 2009 H1N1 Pandemic Influenza HA, NA or M1 Proteins.

Influenza virus-like particle (VLPs) vaccines are a promising alternative to conventional egg-based vaccines. Evaluation of vaccine efficacy induced by HA-M1 VLPs, NA-M1 VLPs or M1 VLPs against virus challenge infection would provide important insight into vaccine design strategy. In this study, we generated VLPs containing hemagglutinin (HA), neuraminidase (NA) or M1 proteins derived from the A/California/04/09. Mice were immunized intramuscularly with HA-M1, NA-M1 or M1 VLPs and protective immunity was evaluated by assessing lung virus loads against low (5LD50) or high (100LD50) lethal dose of homologous virus challenges. High levels of virus-specific serum IgG antibody responses were induced in mice after HA-M1 VLPs immunization, whereas low or no IgG antibody responses were detected from immunization with NA-M1 VLPs or M1 VLPs, independently. Mice that were immunized with HA-M1 VLPs showed below the limit of detection on lung virus loads against low dose (5LD50) of challenge and significant reduction against high dose (100LD50) of challenge infection. Mice that were immunized with NA-M1 or M1 VLPs also displayed reduced lung viral loads compared to naïve control. In vitro cultures of cells from mouse spleen and bone marrow revealed that HA-M1 VLPs and NA-M1 VLPs induced higher levels of antibody-secreting cell (ASC) responses compared to naïve control, whereas M1 VLPs showed no ASC responses. HA-M1, NA-M1 or M1 VLPs immunization demonstrated varying degree of protection with respect to body weight changes and survival rates, which are consistent with the levels of antibody responses in sera and ASC responses from spleen and bone marrow.

Parasite Infiltration and Apoptosis in Spleen upon Toxoplasma gondii Infection.

Toxoplasma gondii infection induces parasite infiltration and apoptosis in the spleen. However, dose-dependent parasite infiltration, apoptosis, body weight alternations and survival in mice remain largely unknown. In this study, mice were intraperitoneally infected with 10, 30 or 100 tachyzoites of T. gondii, respectively. Parasite infiltration and apoptosis in the spleen were analyzed on days 3, 7, and 9 post-infection by immunohistochemistry and flow cytometry. Significantly higher levels of T. gondii infiltration and apoptosis in the spleen were found in 30 and 100 tachyzoites infected mice compared to 10 tachyzoites infected mice on days 7 and 9 post-infection. Although 30 and 100 tachyzoites infected mice showed significant body weight loss compared to 10 tachyzoites infected mice, all of the 100, 30, and 10 tachyzoites infected mice died by days 12, 15, and 17, each respectively. Interestingly, T. gondii infiltration in 10 tachyzoites infected mice were limited to capsule area of the spleen on day 9 post-infection. Several areas of parasite infiltrations were found in the 30 tachyzoites infected mice, where noticeable levels of splenic capsule de-adhesion occurred. These results indicated that parasite infiltration and apoptosis in the spleen, as well as body weight loss (survival) are closely correlated with infection dosage. The level of T. gondii infiltration and apoptosis in the spleen and splenic de-adhesion were dependent on the parasite dose.

Previous Infection with Plasmodium berghei Confers Resistance to Toxoplasma gondii Infection in Mice.

Both Plasmodium spp. and Toxoplasma gondii are important apicomplexan parasites, which infect humans worldwide. Genetic analyses have revealed that 33% of amino acid sequences of inner membrane complex from the malaria parasite Plasmodium berghei is similar to that of Toxoplasma gondii. Inner membrane complex is known to be involved in cell invasion and replication. In this study, we investigated the resistance against T. gondii (ME49) infection induced by previously infected P. berghei (ANKA) in mice. Levels of T. gondii-specific IgG, IgG1, IgG2a, and IgG2b antibody responses, CD4+ and CD8+ T cell populations were found higher in the mice infected with P. berghei (ANKA) and challenged with T. gondii (ME49) compared to that in control mice infected with T. gondii alone (ME49). P. berghei (ANKA) + T. gondii (ME49) group showed significantly reduced the number and size of T. gondii (ME49) cysts in the brains of mice, resulting in lower body weight loss compared to ME49 control group. These results indicate that previous exposure to P. berghei (ANKA) induce resistance to subsequent T. gondii (ME49) infection.

Virus-like Particle Vaccine Containing Toxoplasma gondii Rhoptry Protein 13 Induces Protection against T. gondii ME49 Infection in Mice.

Toxoplasma gondii can infect humans worldwide, causing serious diseases in pregnant women and immunocompromised individuals. T. gondii rhoptry protein 13 (ROP13) is known as one of the key proteins involved in host cell invasion. In this study, we generated virus-like particles (VLPs) vaccine expressing T. gondii rhoptry ROP13 and investigated VLPs vaccine efficacy in mice. Mice immunized with ROP13 VLPs vaccine elicited significantly higher levels of T. gondii-specific IgG, IgG1, IgG2a, and IgA antibody responses following boost immunization and challenge infection, whereas antibody inductions were insignificant upon prime immunization. Differing immunization routes resulted in differing antibody induction, as intranasal immunization (IN) induced greater antibody responses than intramuscular immunization (IM) after boost and challenge infection. IN immunization induced significantly higher levels of IgG and IgA antibody responses from feces, antibody-secreting cells (ASCs), CD4+ T, CD8+ T cells and germinal center B cell responses in the spleen compared to IM immunization. Compared to IM immunization, IN immunization resulted in significantly reduced cyst counts in the brain as well as lesser body weight loss, which contributed to better protection. All of the mice immunized through either route survived, whereas all naïve control mice perished. These results indicate that the ROP13 VLPs vaccine could be a potential vaccine candidate against T. gondii infection.

Correlates of Immune Response in Trichinella spiralis Infection.

Trichinella spiralis infection induces Trichinella-specific IgG antibody and high level of blood eosinophil. However, the kinetics induced by different parasite burdens during infectious periods remains unclear. In this study, rats were infected with 100, 1000, or 3000 larvae of T. spiralis (100 TS, 1000 TS, or 3000 TS). Correlates of eosinophils, antibody responses, and Regulated on Activation, Normal T Cell Expressed and Secreted (RANTES) with worm burdens were evaluated at 1 week, 2 weeks, 1 month, and 2 months postinfection. Heavy infections (1000 TS and 3000 TS) showed significantly higher levels of eosinophil, IgG, and IgG1 antibody responses at 2 weeks postinfection compared to light infection (100 TS). The highest RANTES mRNA expression was also found in the heavy infection group (3000 TS). The results indicate, at early stage of infection (week 2), heavy infection induced higher levels of IgG, IgG1, eosinophil, and RANTES responses. However, at late stage of infection (month 2), there were no correlates of immunity with parasite burdens. Higher levels of IgG and IgG1 antibody responses are critical in heavy T. spiralis infection. These results provide important information in evaluating immune responses by T. spiralis infective stage during the T. spiralis infection.

Virus-Like Particles Expressing Toxoplasma gondii Rhoptry Protein 18 Induces Better Protection Than Rhoptry Protein 4 against T. gondii Infection.

Toxoplasma gondii is a ubiquitous protozoan parasite responsible for causing toxoplasmosis. Preventive measures for toxoplasmosis are currently lacking and as such, development of novel vaccines are of urgent need. In this study, we generated 2 virus-like particles (VLPs) vaccines expressing T. gondii rhoptry protein 4 (ROP4) or rhoptry protein 18 (ROP18) using influenza matrix protein (M1) as a core protein. Mice were intranasally immunized with VLPs vaccines and after the last immunization, mice were challenged with ME49 cysts. Protective efficacy was assessed and compared by determining serum antibody responses, body weight changes and the reduction of cyst counts in the brain. ROP18 VLPs-immunized mice induced greater levels of IgG and IgA antibody responses than those immunized with ROP4 VLPs. ROP18 VLPs immunization significantly reduced body weight loss and the number of brain cysts in mice compared to ROP4 VLPs post-challenge. These results indicate that T. gondii ROP18 VLPs elicited better protective efficacy than ROP4 VLPs, providing important insight into vaccine design strategy.

Influenza M1 Virus-Like Particles Consisting of Toxoplasma gondii Rhoptry Protein 4.

Toxoplasma gondii infections occur throughout the world, and efforts are needed to develop various vaccine candidates expressing recombinant protein antigens. In this study, influenza matrix protein (M1) virus-like particles (VLPs) consisting of T. gondii rhoptry antigen 4 (ROP4 protein) were generated using baculovirus (rBV) expression system. Recombinant ROP4 protein with influenza M1 were cloned and expressed in rBV. SF9 insect cells were coinfected with recombinant rBVs expressing T. gondii ROP4 and influenza M1. As the results, influenza M1 VLPs showed spherical shapes, and T. gondii ROP4 protein exhibited as spikes on VLP surface under transmission electron microscopy (TEM). The M1 VLPs resemble virions in morphology and size. We found that M1 VLPs reacted with antibody from T. gondii-infected mice by western blot and ELISA. This study demonstrated that T. gondii ROP4 protein can be expressed on the surface of influenza M1 VLPs and the M1 VLPs containing T. gondii ROP4 reacted with T. gondii-infected sera, indicating the possibility that M1 VLPs could be used as a coating antigen for diagnostic and/or vaccine candidate against T. gondii infection.

Immune Correlates of Resistance to Trichinella spiralis Reinfection in Mice.

The immune correlate of host resistance induced by reinfection of Trichinella spiralis remains unclear. In this study, we investigated immune correlates between the resistance and serum IgG antibody level, CD23+ IgM+ B cells, and eosinophil responses induced by T. spiralis reinfection. Mice were primarily infected with 10 or 100 T. spiralis larvae (10 TS, 100 TS), respectively, and after 4 weeks, they were challenge infected with 100 T. spiralis larvae (10-100 TS, 100-100 TS). Upon challenge infections, 10-100 TS mice induced significantly higher levels of T. spiralis-specific total IgG antibody responses in sera and antibody secreting cell responses in spleens compared to 100-100 TS mice, resulting in significantly reduced worm burdens in 10-100 TS mice (60% and 70% reductions for adult and larvae, respectively). Higher levels of eosinophils were found in mice primarily infected with 10 TS compared to those of 100 TS at week 8 upon challenge. CD23+ IgM+ B cells were found to be increased significantly in mice primarily infected with 10 TS. These results indicate that primary infection of 10 larvae of T. spiralis, rather than 100 larvae, induces significant resistance against reinfection which closely correlated with T. spiralis-specific IgG, eosinophil, and CD23+ IgM+ B cell responses.

Correction: Virus-Like Nanoparticle Vaccine Confers Protection against Toxoplasma gondii.

[This corrects the article DOI: 10.1371/journal.pone.0161231.].

Virus-Like Particles Assembled Using Respiratory Syncytial Virus Matrix Protein Elicit Protective Immunity in Mice.

Purpose: Heterologous virus-like particle (VLP) assembly involving influenza or the Newcastle disease virus matrix protein (M) has been extensively used to explore the efficacies of VLP vaccines against the respiratory syncytial virus (RSV). Here, we attempted to generate homologous RSV VLPs by expressing the pre-fusion (pre-F) or the glycoprotein (G) on the RSV M protein and evaluated their protective efficacy in mice. Methods: We generated VLPs using the baculovirus expression system in Spodoptera frugiperda (Sf9) insect cells. Recombinant baculoviruses expressing the RSV pre-F, G, and M antigens were inoculated into Sf9 cells, and particles were self-assembled. Mice were immunized with either pre-F or G-expressing VLPs, and immune parameters were assessed to determine protection. Results: Our findings show that successful VLP assembly can be achieved by utilizing recombinant baculoviruses expressing the RSV pre-F or G proteins with the native matrix protein. Mice immunized with either pre-F or the G antigen-expressing VLPs elicited robust serum-mediated virus neutralization. VLP immunization evoked Th1-biased RSV-specific antibody responses in the sera of mice. Following challenge infection with the RSV A2 strain, immunized mice experienced lesser eosinophil and IL-4 accumulation in the lungs, though a substantial increase in TNF-α secretion was observed from CD4+ T cells. Interestingly, splenic antibody-secreting cell responses were substantially enhanced against RSV F antigen, but not against the RSV G antigen following immunization and challenge infection. Immunizing mice with the VLPs significantly inhibited pulmonary histopathology development, as indicated by the diminished inflammatory immune cell influx and mucin secretion. Conclusion: Combined, these vaccine-induced immune responses contributed to successfully inhibiting the RSV replication in the lungs of mice and demonstrated that RSV VLP assembly using insect cell-derived homologous RSV matrix protein is a feasible approach.

Virus-like Particle Vaccine Expressing the Respiratory Syncytial Virus Pre-Fusion and G Proteins Confers Protection against RSV Challenge Infection.

Respiratory syncytial virus (RSV) causes severe lower respiratory tract disease in children and the elderly. However, there are no effective antiviral drugs or licensed vaccines available for RSV infection. Here, RSV virus-like particle (VLP) vaccines expressing Pre-F, G, or Pre-F and G proteins on the surface of influenza virus matrix protein 1 (M1) were produced using the baculovirus expression system, and their protective efficacy was evaluated in mice. The morphology and successful assembly of VLPs were confirmed by transmission electron microscope (TEM) and Western blot. High levels of serum IgG antibody response were detected in VLP-immunized mice, and significantly higher levels of IgG2a and IgG2b were found in the Pre-F+G VLP immunization group compared to the unimmunized control. Serum-neutralizing activity was higher in the VLP immunization groups compared to the naïve group, with Pre-F+G VLPs demonstrating superior neutralizing activity to the single antigen-expressing VLP groups. Pulmonary IgA and IgG responses were generally comparable across the immunization groups, with VLPs expressing the Pre-F antigen eliciting higher IFN-γ in spleens. The frequencies of eosinophils and IL-4-producing CD4+ T cell populations were substantially lower in the lungs of VLP-immunized mice, with the PreF+G vaccine inducing a significant increase in CD4+ and CD8+ T cells. VLP immunization significantly decreased the viral titer and inflammation in the lungs of mice, with Pre-F+G VLPs conferring the best protection. In conclusion, our present study suggests that the Pre-F+G VLPs could be a potential vaccine candidate against RSV infection.