Heterologous immunization targeting the CST1 antigen confers better protection than ROP18 in mice.

Aim: To evaluate the protective efficacy induced by heterologous immunization with recombinant baculoviruses or virus-like particles targeting the CST1 and ROP18 antigens of Toxoplasma gondii.Materials & methods: Recombinant baculovirus and virus-like particle vaccines expressing T. gondii CST1 or ROP18 antigens were developed to evaluate protective immunity in mice upon challenge infection with 450 Toxoplasma gondii (ME49).Results: Immunization with CST1 or ROP18 vaccines induced similar levels of T. gondii-specific IgG and IgA responses. Compared with ROP 18, CST1 vaccine showed better antibody-secreting cell response, germinal center B cell activation, and significantly reduced brain cyst burden and body weight loss.Conclusion: Our findings suggest that CST1 heterologous immunization elicited better protection than ROP18, providing important insight into improving the toxoplasmosis vaccine design strategy.

[Box: see text].

Cell-targeted gene modification by delivery of CRISPR-Cas9 ribonucleoprotein complexes in pseudotyped lentivirus-derived nanoparticles.

To fully utilize the potential of CRISPR-Cas9-mediated genome editing, time-restricted and targeted delivery is crucial. By modulating the pseudotype of engineered lentivirus-derived nanoparticles (LVNPs), we demonstrate efficient cell-targeted delivery of Cas9/single guide RNA (sgRNA) ribonucleoprotein (RNP) complexes, supporting gene modification in a defined subset of cells in mixed cell populations. LVNPs pseudotyped with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein resulted in angiotensin-converting enzyme 2 (ACE2)-dependent insertion or deletion (indel) formation in an ACE2+/ACE2- population of cells, whereas Nipah virus glycoprotein pseudotyping resulted in Ephrin-B2/B3-specific gene knockout. Additionally, LVNPs pseudotyped with Edmonston strain measles virus glycoproteins (MV-H/F) delivered Cas9/sgRNA RNPs to CD46+ cells with and without additional expression of SLAM (signaling lymphocytic activation molecule; CD150). However, an engineered SLAM-specific measles virus pseudotype (measles virus-hemagglutinin/fusion [MV-H/F]-SLAM) efficiently targeted LVNPs to SLAM+ cells. Lentiviral vectors (LVs) pseudotyped with MV-H/F-SLAM efficiently transduced >80% of interleukin (IL)-4/IL-21-stimulated primary B cells cultured on CD40 ligand (CD40L)-expressing feeder cells. Notably, LVNPs pseudotyped with MV-H/F and MV-H/F-SLAM reached indel rates of >80% and >60% in stimulated primary B cells, respectively. Collectively, our findings demonstrate the modularity of LVNP-directed delivery of ready-to-function Cas9/sgRNA complexes. Using a panel of different pseudotypes, we provide evidence that LVNPs can be engineered to induce effective indel formation in a subpopulation of cells defined by the expression of surface receptors.

Strengthening global health resilience: Marburg virus-like particle vaccines and the One Health approach.

The Marburg virus (MARV), belonging to the Filoviridae family, poses a significant global health threat, emphasizing the urgency to develop Marburg virus-like particle (VLP) vaccines for outbreak mitigation. The virus's menacing traits accentuate the need for such vaccines, which can be addressed by VLPs that mimic its structure safely, potentially overcoming past limitations. Early Marburg vaccine endeavors and their challenges are examined in the historical perspectives section, followed by an exploration of VLPs as transformative tools, capable of eliciting immune responses without conventional risks. Noteworthy milestones and achievements in Marburg VLP vaccine development, seen through preclinical and clinical trials, indicate potential cross-protection. Ongoing challenges, encompassing durability, strain diversity, and equitable distribution, are addressed, with proposed innovations like novel adjuvant, mRNA technology, and structure-based design poised to enhance Marburg VLP vaccines. This review highlights the transformative potential of Marburg VLPs in countering the virus, showcasing global collaboration, regulatory roles, and health equity for a safer future through the harmonious interplay of science, regulation, and global efforts.

Insect cell production of chimeric virus-like particles based on human immunodeficiency virus GAG proteins and yellow fever virus envelope protein.

The yellow fever virus (YFV) is a single stranded RNA virus belonging to the genus Orthoflavivirus that is capable of zoonotic transmissions that infect nonhuman and human primates. It is endemic in Brazil with recurrent epidemics of the disease, and it is transmitted through mosquitoes. The detection and immunization against YFV and other flaviviruses are fundamental for the management of the impacts of the disease in human environments. In an ongoing effort to develop new approaches for diagnostics and immunizations, we expressed VLPs displaying the yellow fever virus envelope protein (YFE) using recombinant baculovirus in insect cells. By co-expressing HIV-1 Pr55Gag protein (GAG) together with YFE we were able to generate chimeric VLPs containing a GAG core together with an envelope containing the YFE protein. The YFE and the chimeric GAG-YFE VLPs have potential as vaccine candidates and as reagents for serological assays in the detection of these viruses in human sera.

Enhancing NA immunogenicity through novel VLP designs.

Current influenza virus vaccines poorly display key neuraminidase (NA) epitopes and do not robustly induce NA-reactive antibodies; instead, they focus on the induction of hemagglutinin (HA)-reactive antibodies. Next-generation influenza vaccines should be optimized in order to activate NA-reactive B cells and to induce a broadly cross-reactive and protective antibody response. We aimed at enhancing the immunogenicity of the NA on vaccines by two strategies: (i) modifying the HA:NA ratio of the vaccine preparation and (ii) exposing epitopes on the lateral surface or beneath the head of the NA by extending the NA stalk. The H1N1 glycoproteins from the influenza virus A/California/04/2009 strain were displayed on human immunodeficiency virus 1 (HIV-1) gag-based virus-like particles (VLP). Using the baculovirus insect cell expression system, we biased the quantity of surface glycoproteins employing two different promoters, the very late baculovirus p10 promoter and the early and late gp64 promoter. This led to a 1:1 to 2:1 HA:NA ratio, which was approximately double or triple the amount of NA as present on the wild-type influenza A virus (HA:NA ratio 3:1 to 5:1). Furthermore, by insertion of 15 amino acids from the A-New York/61/2012 strain (NY12) which prolongates the NA stalk (NA long stalk; NA-LS), we intended to improve the accessibility of the NA. Six different types of VLPs were produced and purified using a platform downstream process based on Capto-Core 700™ followed by Capto-Heparin™ affinity chromatography combined with ultracentrifugation. These VLPs were then tested in a mouse model. Robust titers of antibodies that inhibit the neuraminidase activity were elicited even after vaccination with two low doses (0.3 µg) of the H1N1 VLPs without compromising the anti-HA responses. In conclusion, our results demonstrate the feasibility of the two developed strategies to retain HA immunogenicity and improve NA immunogenicity as a future influenza vaccine candidate.

Characterization of a triple-type chimeric vaccine against human papillomavirus types 18, 45, and 59.

Persistent infection with high-risk human papillomavirus (HPV) types can lead to the development of cancer in HPV-infected tissues, including the cervix, oropharynx, anus, penis, vagina, and vulva. While current HPV vaccines cover approximately 90 % of cervical cancers, nearly 10 % of cases associated with HPV types not included in the vaccines remain unaddressed, notably HPV59. This study describes the development of a chimeric virus-like particle (VLP) targeting HPV18/45/59, proposed as a vaccine candidate for high-risk HPV type (HPV59) currently lacking commercial vaccines. Given that the majority of neutralizing antibody epitopes are located on the surface loops, we engineered a strategic swap of these loops between the closely related HPV18 and HPV45. This methodology was then extended to incorporate surface loops of HPV59, resulting in the lead candidate construct of the H18-45BCEF-59HI chimeric VLP with two surface loops swapping from HPV45 to HPV18. Characterization confirmed that H18-45BCEF-59HI closely resembled the wild-type (WT) backbone types in particle size and morphology, as verified by Transmission Electron Microscopy (TEM), High-Performance Size-Exclusion Chromatography (HPSEC), and Analytical Ultracentrifugation (AUC), and demonstrated similar thermal stability as evidenced by Differential Scanning Calorimetry (DSC). Immunization studies in mice with the chimeric VLPs assessed their immunogenicity, revealing that the H18-45EF-59HI chimeric VLP exhibited optimal cross-neutralization. Additionally, when produced in a Good Manufacturing Practice (GMP)-like facility, the H18-45BCEF-59HI VLP was selected as a promising vaccine candidate for the prevention of HPV18/45/59 infection. This study not only offers a potential solution to the current vaccination gap but also provides a foundational approach for the design of vaccines targeting viruses with multiple subtypes or variants.

Lipid A-modified Escherichia coli can produce porcine parvovirus virus-like particles with high immunogenicity and minimal endotoxin activity.

BACKGROUND: A cost-effective Escherichia coli expression system has gained popularity for producing virus-like particle (VLP) vaccines. However, the challenge lies in balancing the endotoxin residue and removal costs, as residual endotoxins can cause inflammatory reactions in the body. RESULTS: In this study, porcine parvovirus virus-like particles (PPV-VLPs) were successfully assembled from Decreased Endotoxic BL21 (BL21-DeE), and the effect of structural changes in the lipid A of BL21 on endotoxin activity, immunogenicity, and safety was investigated. The lipopolysaccharide purified from BL21-DeE produced lower IL-6 and TNF-α than that from wild-type BL21 (BL21-W) in both RAW264.7 cells and BALB/c mice. Additionally, mice immunized with PPV-VLP derived form BL21-DeE (BL21-DeE-VLP) showed significantly lower production of inflammatory factors and a smaller increase in body temperature within 3 h than those immunized with VLP from BL21-W (BL21-W-VLP) and endotoxin-removed VLP (ReE-VLP). Moreover, mice in the BL21-DeE-VLP immunized group had similar levels of serum antibodies as those in the BL21-W-VLP group but significantly higher levels than those in the ReE-VLP group. Furthermore, the liver, lungs, and kidneys showed no pathological damage compared with the BL21-W-VLP group. CONCLUSION: Overall, this study proposes a method for producing VLP with high immunogenicity and minimal endotoxin activity without chemical or physical endotoxin removal methods. This method could address the issue of endotoxin residues in the VLP and provide production benefits.

A nucleoside-modified mRNA vaccine forming rabies virus-like particle elicits strong cellular and humoral immune responses against rabies virus infection in mice.

Rabies is a lethal zoonotic disease that threatens human health. As the only viral surface protein, the rabies virus (RABV) glycoprotein (G) induces main neutralizing antibody (Nab) responses; however, Nab titre is closely correlated with the conformation of G. Virus-like particles (VLP) formed by the co-expression of RABV G and matrix protein (M) improve retention and antigen presentation, inducing broad, durable immune responses. RABV nucleoprotein (N) can elicit humoral and cellular immune responses. Hence, we developed a series of nucleoside-modified RABV mRNA vaccines encoding wild-type G, soluble trimeric RABV G formed by an artificial trimer motif (tG-MTQ), membrane-anchored prefusion-stabilized G (preG). Furthermore, we also developed RABV VLP mRNA vaccine co-expressing preG and M to generate VLPs, and VLP/N mRNA vaccine co-expressing preG, M, and N. The RABV mRNA vaccines induced higher humoral and cellular responses than inactivated rabies vaccine, and completely protected mice against intracerebral challenge. Additionally, the IgG and Nab titres in RABV preG, VLP and VLP/N mRNA groups were significantly higher than those in G and tG-MTQ groups. A single administration of VLP or VLP/N mRNA vaccines elicited protective Nab responses, the Nab titres were significantly higher than that in inactivated rabies vaccine group at day 7. Moreover, RABV VLP and VLP/N mRNA vaccines showed superior capacities to elicit potent germinal centre, long-lived plasma cell and memory B cell responses, which linked to high titre and durable Nab responses. In summary, our data demonstrated that RABV VLP and VLP/N mRNA vaccines could be promising candidates against rabies.

Chemically Tagging Cargo for Specific Packaging inside and on the Surface of Virus-like Particles.

Virus-like particles (VLPs) have untapped potential for packaging and delivery of macromolecular cargo. To be a broadly useful platform, there needs to be a strategy for attaching macromolecules to the inside or the outside of the VLP with minimal modification of the platform or cargo. Here, we repurpose antiviral compounds that bind to hepatitis B virus (HBV) capsids to create a chemical tag to noncovalently attach cargo to the VLP. Our tag consists of a capsid assembly modulator, HAP13, connected to a linker terminating in maleimide. Our cargo is a green fluorescent protein (GFP) with a single addressable cysteine, a feature that can be engineered in many proteins. The HAP-GFP construct maintained HAP's intrinsic ability to bind HBV capsids and accelerate assembly. We investigated the capacity of HAP-GFP to coassemble with HBV capsid protein and bind to preassembled capsids. HAP-GFP binding was concentration-dependent, sensitive to capsid stability, and dependent on linker length. Long linkers had the greatest activity to bind capsids, while short linkers impeded assembly and damaged intact capsids. In coassembly reactions, >20 HAP-GFP molecules were presented on the outside and inside of the capsid, concentrating the cargo by more than 100-fold compared to bulk solution. We also tested an HAP-GFP with a cleavable linker so that external GFP molecules could be removed, resulting in exclusive internal packaging. These results demonstrate a generalizable strategy for attaching cargo to a VLP, supporting development of HBV as a modular VLP platform.

Green Routes: Exploring Protein-Based Virus-like Nanoparticle Transport and Immune Activation in Nicotiana benthamiana for Biotechnological Applications.

Viral, bacterial, fungal, and nematode infections cause significant agricultural losses, with limited treatment options, necessitating novel approaches to enhance plant defense systems and protection against pathogens. Virus-like nanoparticles (VLPs), extensively used in animal and human therapies (e.g., vaccines and immune enhancers), hold potential for novel agricultural solutions and advancing plant nanotechnology. This study employed various methodologies, including VLP production, confocal microscopy, and real-time qPCR. Our findings demonstrated the presence of 30 nm Qß-VLPs, fluorescently labeled, within the intercellular space of Nicotiana benthamiana leaves one hour post-infiltration. Furthermore, infiltration with Qß-VLPs led to an upregulation of key defense genes (NbPR1a, NbPR5, NbNPR, NbERF1, NbMYC2, and NbLRR2) in treated plants. Using RT-qPCR, a significant increase in the relative expression levels of defense genes was observed, with sustained high levels of NbERF1 and NbLRR2 even after 24 h. These findings suggest that Qß-VLPs effectively upregulate genes crucial for pathogen defense in N. benthamiana, initiating PAMP-triggered immunity and launching signaling cascades that enhance defense mechanisms. This innovative application of VLPs to activate plant defense programs advances plant nanobiotechnology, offering new agricultural solutions.

Sequential Immunization with Vaccines Based on SARS-CoV-2 Virus-like Particles Induces Broadly Neutralizing Antibodies.

Although many people have been vaccinated against COVID-19, infections with SARS-CoV-2 seem hard to avoid. There is a need to develop more effective vaccines and immunization strategies against emerging variants of infectious diseases. To understand whether different immunization strategies using variants sequence-based virus-like particles (VLPs) vaccines could offer superior immunity against future SARS-CoV-2 variants, our team constructed VLPs for the original Wuhan-Hu-1 strain (prototype), Delta (δ) variant, and Omicron (ο) variant of SARS-CoV-2, using baculovirus-insect expression system. Then we used these VLPs to assess the immune responses induced by homologous prime-boost, heterologous prime-boost, and sequential immunizations strategies in a mouse model. Our results showed that the pro+δ+ο sequential strategies elicited better neutralizing antibody responses. These sequential strategies also take advantage of inducing CD4+ T and CD8+ T lymphocytes proliferation and tendency to cytokine of Th1. Currently, our data suggest that sequential immunization with VLPs of encoding spike protein derived from SARS-CoV-2 variants of concern may be a potential vaccine strategy against emerging diseases, such as "Disease X".

Gene Editing by Ferrying of CRISPR/Cas Ribonucleoprotein Complexes in Enveloped Virus-Derived Particles.

The invention of next-generation CRISPR/Cas gene editing tools, like base and prime editing, for correction of gene variants causing disease, has created hope for in vivo use in patients leading to wider clinical translation. To realize this potential, delivery vehicles that can ferry gene editing tool kits safely and effectively into specific cell populations or tissues are in great demand. In this review, we describe the development of enveloped retrovirus-derived particles as carriers of "ready-to-work" ribonucleoprotein complexes consisting of Cas9-derived editor proteins and single guide RNAs. We present arguments for adapting viruses for cell-targeted protein delivery and describe the status after a decade-long development period, which has already shown effective editing in primary cells, including T cells and hematopoietic stem cells, and in tissues targeted in vivo, including mouse retina, liver, and brain. Emerging evidence has demonstrated that engineered virus-derived nanoparticles can accommodate both base and prime editors and seems to fertilize a sprouting hope that such particles can be further developed and produced in large scale for therapeutic applications.

Diagnostic and prophylactic potential of a stabilized foot-and-mouth disease serotype Asia1 virus like particles designed through a structure guided approach.

Intact capsids of foot-and-mouth disease virus (FMDV) play a vital role in eliciting a protective immune response. Any change in the physico-chemical environment of the capsids results in dissociation and poor immunogenicity. Structural bioinfomatics studies have been carried out to predict the amino acids at the interpentameric region that resulted in the identification of mutant virus-like particles(VLPs) of FMDV serotype Asia1/IND/63/1972. The insect cell expressed VLPs were evaluated for their stability by sandwich ELISA. Among 10 mutants, S93H showed maximum retention of antigenicity at different temperatures, indicating its higher thermal stability as revealed by the in-silico analysis and retained the antigenic sites of the virus demonstrated by Sandwich ELISA. The concordant results of the liquid phase blocking ELISA for estimation of antibody titre of known sera with stable mutant VLP as antigen in place of virus antigen demonstrate its diagnostic potential. The stable mutant VLP elicited a robust immune response with 85.6 % protection in guinea pigs against virus challenge. The stabilized VLP based antigen requires minimum biosafety and cold storage for production and transit besides, complying with differentiation of infected from vaccinated animals. It can effectively replace the conventional virus handling during antigen production for prophylactic and diagnostic use.

Expression of dengue capsid-like particles in silkworm and display of envelope domain III of dengue virus serotype 2.

Dengue virus (DENV) is a considerable public health threat affecting millions of people globally. Vaccines for dengue are an important strategy to reduce the disease burden. We expressed capsid (C2) and envelope domain III of dengue virus serotype 2 (2EDIII) separately in the silkworm expression system. We conjugated them employing the monomeric streptavidin (mSA2) and biotin affinity to display the antigenic 2EDIII on the C2-forming capsid-like particle (CLP). Purified 2EDIII-displaying C2 (CLP/2EDIII) was immunogenic in BALB/c mice, eliciting neutralizing antibodies confirmed by a single-round infectious particle (SRIP) neutralization assay. Th1 cytokine levels were upregulated for the CLP/2EDIII group, and the anti-inflammatory IL-10 and pro-inflammatory IL-6 cytokine levels were also raised compared to the 2EDIII and the control groups. Elevated cytokine levels for CLP/2EDIII indicate the importance of displaying the 2EDIII as CLP/2EDIII rather than as an individual subunit. This study is the first to express the C2 protein as self-assembling CLP in vivo and 2EDIII separately in the silkworm expression system and conjugate them to form a monovalent CLP. Thus, this CLP/2EDIII display method may pave the way for an efficient tetravalent dengue vaccine candidate.

Lassa virus Z protein hijacks the autophagy machinery for efficient transportation by interrupting CCT2-mediated cytoskeleton network formation.

The Lassa virus (LASV) is a widely recognized virulent pathogen that frequently results in lethal viral hemorrhagic fever (VHF). Earlier research has indicated that macroautophagy/autophagy plays a role in LASV replication, but, the precise mechanism is unknown. In this present study, we show that LASV matrix protein (LASV-Z) is essential for blocking intracellular autophagic flux. LASV-Z hinders actin and tubulin folding by interacting with CCT2, a component of the chaperonin-containing T-complexes (TRiC). When the cytoskeleton is disrupted, lysosomal enzyme transit is hampered. In addition, cytoskeleton disruption inhibits the merge of autophagosomes with lysosomes, resulting in autophagosome accumulation that promotes the budding of LASV virus-like particles (VLPs). Inhibition of LASV-Z-induced autophagosome accumulation blocks the LASV VLP budding process. Furthermore, it is found that glutamine at position 29 and tyrosine at position 48 on LASV-Z are important in interacting with CCT2. When these two sites are mutated, LASV-mut interacts with CCT2 less efficiently and can no longer inhibit the autophagic flux. These findings demonstrate a novel strategy for LASV-Z to hijack the host autophagy machinery to accomplish effective transportation.Abbreviation: 3-MA: 3-methyladenine; ATG5: autophagy related 5; ATG7: autophagy related 7; Baf-A1: bafilomycin A1; CCT2: chaperonin containing TCP1 subunit 2; co-IP: co-immunoprecipitation; CTSD: cathepsin D; DAPI: 4',6-diamidino-2'-phenylindole; DMSO: dimethyl sulfoxide; EGFR: epidermal growth factor receptor; GFP: green fluorescent protein; hpi: hours post-infection; hpt: hours post-transfection; LAMP1: lysosomal-associated membrane protein 1; LASV: lassa virus; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; mCherry: red fluorescent protein; PM: plasma membrane; SQSTM1/p62: sequestosome 1; STX6: syntaxin 6; VLP: virus-like particle; TEM: transmission electron microscopy; TRiC: chaperonin-containing T-complex; WB: western blotting; µm: micrometer; µM: micromole.

A getah virus-like-particle vaccine provides complete protection from viremia and arthritis in wild-type mice.

Getah virus (GETV) is an emerging mosquito-borne virus with economic impact on the livestock industry in East Asia. In this study, we successfully produced GETV virus-like particles (VLPs) in insect cells using the baculovirus expression vector system. We show that the GETV envelope glycoproteins were successfully expressed at the surface of the insect cell and were glycosylated. VLPs were isolated from the culture fluid as enveloped particles of 60-80 nm in diameter. Two 1 µg vaccinations with this GETV VLP vaccine, without adjuvant, generated neutralizing antibody responses and protected wild-type C57/BL6 mice against GETV viremia and arthritic disease. The GETV VLP vaccine may find application as a horse and/or pig vaccine in the future.

Plant-Produced Chimeric Hepatitis E Virus-like Particles as Carriers for Antigen Presentation.

A wide range of virus-like particles (VLPs) is extensively employed as carriers to display various antigens for vaccine development to fight against different infections. The plant-produced truncated variant of the hepatitis E virus (HEV) coat protein is capable of forming VLPs. In this study, we demonstrated that recombinant fusion proteins comprising truncated HEV coat protein with green fluorescent protein (GFP) or four tandem copies of the extracellular domain of matrix protein 2 (M2e) of influenza A virus inserted at the Tyr485 position could be efficiently expressed in Nicotiana benthamiana plants using self-replicating vector based on the potato virus X genome. The plant-produced fusion proteins in vivo formed VLPs displaying GFP and 4M2e. Therefore, HEV coat protein can be used as a VLP carrier platform for the presentation of relatively large antigens comprising dozens to hundreds of amino acids. Furthermore, plant-produced HEV particles could be useful research tools for the development of recombinant vaccines against influenza.

Immunizing Mice with Influenza Virus-like Particles Expressing the Leishmania amazonensis Promastigote Surface Antigen Alleviates Inflammation in Footpad.

Cutaneous leishmaniasis (CL) is a tropical disease endemic in many parts of the world. Characteristic clinical manifestations of CL include the formation of ulcerative skin lesions that can inflict life-long disability if left untreated. Although drugs are available, they are unaffordable and out of reach for individuals who need them the most. Developing a highly cost-efficient CL vaccine could address this problem but such a vaccine remains unavailable. Here, we developed a chimeric influenza virus-like particle expressing the Leishmania amazonensis promastigote surface antigen (LaPSA-VLP). LaPSA-VLPs were self-assembled in Spodoptera frugiperda insect cell lines using the baculovirus expression system. After characterizing the vaccines and confirming successful VLP assembly, BALB/c mice were immunized with these vaccines for efficacy assessment. Sera acquired from mice upon subcutaneous immunization with the LaPSA-VLP specifically interacted with the L. amazonensis soluble total antigens. LaPSA-VLP-immunized mice elicited significantly greater quantities of parasite-specific IgG from the spleens, popliteal lymph nodes, and footpads than unimmunized mice. LaPSA-VLP immunization also enhanced the proliferation of B cell populations in the spleens of mice and significantly lessened the CL symptoms, notably the footpad swelling and IFN-γ-mediated inflammatory response. Overall, immunizing mice with the LaPSA-VLPs prevented mice from developing severe CL symptoms, signifying their developmental potential.

Deciphering the Thermal Stability of Bacteriophage MS2-Derived Virus-like Particle and Its Engineered Variant.

RNA bacteriophage MS2-derived virus-like particles (VLPs) have been widely used in biomedical research as model systems to study virus assembly, structure-function relationships, vaccine development, and drug delivery. Considering the diverse utility of these VLPs, a systemic engineering approach has been utilized to generate smaller particles with optimal serum stability and tissue penetrance. Additionally, it is crucial to demonstrate the overall stability of these mini MS2 VLPs, ensuring cargo protection until they reach their target cell/organ. However, no detailed analysis of the thermal stability and heat-induced disassembly of MS2 VLPs has yet been attempted. In this work, we investigated the thermal stability of both wild-type (WT) MS2 VLP and its "mini" variant containing S37P mutation (mini MS2 VLP). The mini MS2 VLP exhibits a higher capsid melting temperature (Tm) when compared to its WT MS2 VLP counterpart, possibly attributed to its smaller interdimer angle. Our study presents that the thermal unfolding of MS2 VLPs follows a sequential process involving particle destabilization, nucleic acid exposure/melting, and disassembly of VLP. This observation underscores the disruption of cooperative intersubunit interactions and protein-nucleic acid interactions, shedding light on the mechanism of heat-induced VLP disassembly.

Preclinical development of a stabilized RH5 virus-like particle vaccine that induces improved antimalarial antibodies.

Plasmodium falciparum reticulocyte-binding protein homolog 5 (RH5) is a leading blood-stage malaria vaccine antigen target, currently in a phase 2b clinical trial as a full-length soluble protein/adjuvant vaccine candidate called RH5.1/Matrix-M. We identify that disordered regions of the full-length RH5 molecule induce non-growth inhibitory antibodies in human vaccinees and that a re-engineered and stabilized immunogen (including just the alpha-helical core of RH5) induces a qualitatively superior growth inhibitory antibody response in rats vaccinated with this protein formulated in Matrix-M adjuvant. In parallel, bioconjugation of this immunogen, termed "RH5.2," to hepatitis B surface antigen virus-like particles (VLPs) using the "plug-and-display" SpyTag-SpyCatcher platform technology also enables superior quantitative antibody immunogenicity over soluble protein/adjuvant in vaccinated mice and rats. These studies identify a blood-stage malaria vaccine candidate that may improve upon the current leading soluble protein vaccine candidate RH5.1/Matrix-M. The RH5.2-VLP/Matrix-M vaccine candidate is now under evaluation in phase 1a/b clinical trials.