Chimeric SV40 virus-like particles induce specific cytotoxicity and protective immunity against influenza A virus without the need of adjuvants

A comparative assessment of reference genes in mouse brown adipocyte differentiation and thermogenesis in vitro

Adipogenic differentiation and thermogenesis in brown adipose tissue (BAT) undergo dynamic processes, altering phenotypes and gene expressions. Proper reference genes in gene expression analysis are crucial to mitigate experimental variances and ensure PCR efficacy. Unreliable reference genes can lead to erroneous gene expression quantification, resulting in data misinterpretation. This study focused on identifying suitable reference genes for mouse brown adipocyte research, utilizing brown adipocytes from the Ucp1-luciferase ThermoMouse model. Comparative analysis of gene expression data under adipogenesis and thermogenesis conditions was conducted, validating 13 housekeeping genes through various algorithms, including DeltaCq, BestKeeper, geNorm, Normfinder, and RefFinder. Tbp and Rer1 emerged as optimal references for Ucp1 and Pparg expression in brown adipogenesis, while Tbp and Ubc were ideal for the expression analysis of these target genes in thermogenesis. Conversely, certain conventional references, including Actb, Tubb5, and Gapdh, proved unstable as reference genes under both conditions. These findings stress the critical consideration of reference gene selection in gene expression analysis within specific biological systems to ensure accurate conclusions.

Immunogenicity of novel vB_EcoS_NBD2 bacteriophage-originated nanotubes as a carrier for peptide-based vaccines

Non-infectious virus-like nanoparticles mimic native virus structures and can be modified by inserting foreign protein fragments, making them immunogenic tools for antigen presentation. This study investigated, for the first time, the immunogenicity of long and flexible polytubes formed by yeast-expressed tail tube protein gp39 of bacteriophage vB_EcoS_NBD2 and evaluated their ability to elicit an immune response against the inserted protein fragments. Protein gp39-based polytubes induced humoral immune response in mice, even without the use of adjuvant. Bioinformatics analysis guided the selection of protein fragments from Acinetobacter baumannii for insertion into the C-terminus of gp39. Chimeric polytubes, displaying 28-amino acid long OmpA protein fragment, induced IgG response against OmpA protein fragment in immunized mice. These polytubes demonstrated their effectiveness both as antigen carrier and an adjuvant, when the OmpA fragments were either displayed on chimeric polytubes or used alongside with the unmodified polytubes. Our findings expand the potential applications of long and flexible polytubes, contributing to the development of novel antigen carriers with improved immunogenicity and antigen presentation capabilities.

Simultaneous CD8+ T-Cell Immune Response against SARS-Cov-2 S, M, and N Induced by Endogenously Engineered Extracellular Vesicles in Both Spleen and Lungs

Most advanced vaccines against severe acute respiratory syndrome coronavirus (SARS-CoV)-2 are designed to induce antibodies against spike (S) protein. Differently, we developed an original strategy to induce CD8+ T cytotoxic lymphocyte (CTL) immunity based on in vivo engineering of extracellular vesicles (EVs). This is a new vaccination approach based on intramuscular injection of DNA expression vectors coding for a biologically inactive HIV-1 Nef protein (Nefmut) with an unusually high efficiency of incorporation into EVs, even when foreign polypeptides are fused to its C-terminus. Nanovesicles containing Nefmut-fused antigens released by muscle cells can freely circulate into the body and are internalized by antigen-presenting cells. Therefore, EV-associated antigens can be cross-presented to prime antigen-specific CD8+ T-cells. To apply this technology to a strategy of anti-SARS-CoV-2 vaccine, we designed DNA vectors expressing the products of fusion between Nefmut and different viral antigens, namely N- and C-terminal moieties of S (referred to as S1 and S2), M, and N. We provided evidence that all fusion products are efficiently uploaded in EVs. When the respective DNA vectors were injected in mice, a strong antigen-specific CD8+ T cell immunity became detectable in spleens and, most important, in lung airways. Co-injection of DNA vectors expressing the diverse SARS-CoV-2 antigens resulted in additive immune responses in both spleen and lungs. Hence, DNA vectors expressing Nefmut-based fusion proteins can be proposed for new anti-SARS-CoV-2 vaccine strategies.

Chimeric Virus-Like Particles and Capsomeres Induce Similar CD8+ T Cell Responses but Differ in Capacity to Induce CD4+ T Cell Responses and Antibody Responses

Despite extensive research, the development of an effective malaria vaccine remains elusive. The induction of robust and sustained T cell and antibody response by vaccination is an urgent unmet need. Chimeric virus-like particles (VLPs) are a promising vaccine platform. VLPs are composed of multiple subunit capsomeres which can be rapidly produced in a cost-effective manner, but the ability of capsomeres to induce antigen-specific cellular immune responses has not been thoroughly investigated. Accordingly, we have compared chimeric VLPs and their sub-unit capsomeres for capacity to induce CD8⁺ and CD4⁺ T cell and antibody responses. We produced chimeric murine polyomavirus VLPs and capsomeres each incorporating defined CD8⁺ T cell, CD4⁺ T cell or B cell repeat epitopes derived from Plasmodium yoelii CSP. VLPs and capsomeres were evaluated using both homologous or heterologous DNA prime/boost immunization regimens for T cell and antibody immunogenicity. Chimeric VLP and capsomere vaccine platforms induced robust CD8⁺ T cell responses at similar levels which was enhanced by a heterologous DNA prime. The capsomere platform was, however, more efficient at inducing CD4⁺ T cell responses and less efficient at inducing antigen-specific antibody responses. Our data suggest that capsomeres, which have significant manufacturing advantages over VLPs, should be considered for diseases where a T cell response is the desired outcome.

Induction of adaptive immune responses against antigens incorporated within the capsid of simian virus 40

Simian virus 40 (SV40) is a monkey polyomavirus. The capsid structure is icosahedral and comprises VP1 units that measure 45 nm in diameter. Five SV40 VP1 molecules form one pentamer subunit, and a single icosahedral subunit comprises 72 pentamers; a single SV40 VP1 capsid comprises 360 SV40 VP1 molecules. In a previous study, we showed that an influenza A virus matrix protein 1 (M1) CTL epitope inserted within SV40 virus-like particles (VLPs) induced cytotoxic T lymphocytes (CTLs) without the need for an adjuvant. Here, to address whether SV40 VLPs induce adaptive immune responses against VLP-incorporated antigens, we prepared SV40 VLPs containing M1 or chicken ovalbumin (OVA). This was done by fusing M1 or OVA with the carboxyl terminus of SV40 VP2 and co-expressing them with SV40 VP1 in insect cells using a baculovirus vector. Intraperitoneal (i.p.) or intranasal administration of SV40 VLPs incorporating M1 induced the production of CTLs specific for the M1 epitope without the requirement for adjuvant. The production of antibodies against SV40 VLPs was also induced by i.p. administration of SV40 VLPs in the absence of adjuvant. Finally, the administration of SV40 VLPs incorporating OVA induced anti-OVA antibodies in the absence of adjuvant; in addition, the level of antibody production was comparable with that after i.p. administration of OVA plus alum adjuvant. These results suggest that the SV40 capsid incorporating foreign antigens can be used as a vaccine platform to induce adaptive immune responses without the need for adjuvant.

The biomedical and bioengineering potential of protein nanocompartments

Protein nanocompartments (PNCs) are self-assembling biological nanocages that can be harnessed as platforms for a wide range of nanobiotechnology applications. The most widely studied examples of PNCs include virus-like particles, bacterial microcompartments, encapsulin nanocompartments, enzyme-derived nanocages (such as lumazine synthase and the E2 component of the pyruvate dehydrogenase complex), ferritins and ferritin homologues, small heat shock proteins, and vault ribonucleoproteins. Structural PNC shell proteins are stable, biocompatible, and tolerant of both interior and exterior chemical or genetic functionalization for use as vaccines, therapeutic delivery vehicles, medical imaging aids, bioreactors, biological control agents, emulsion stabilizers, or scaffolds for biomimetic materials synthesis. This review provides an overview of the recent biomedical and bioengineering advances achieved with PNCs with a particular focus on recombinant PNC derivatives.

Revealing in real-time a multistep assembly mechanism for SV40 virus-like particles

Many viruses use their genome as template for self-assembly into an infectious particle. However, this reaction remains elusive because of the transient nature of intermediate structures. To elucidate this process, optical tweezers and acoustic force spectroscopy are used to follow viral assembly in real time. Using Simian virus 40 (SV40) virus-like particles as model system, we reveal a multistep assembly mechanism. Initially, binding of VP1 pentamers to DNA leads to a significantly decreased persistence length. Moreover, the pentamers seem able to stabilize DNA loops. Next, formation of interpentamer interactions results in intermediate structures with reduced contour length. These structures stabilize into objects that permanently decrease the contour length to a degree consistent with DNA compaction in wild-type SV40. These data indicate that a multistep mechanism leads to fully assembled cross-linked SV40 particles. SV40 is studied as drug delivery system. Our insights can help optimize packaging of therapeutic agents in these particles.

Chimeric Murine Polyomavirus Virus-Like Particles Induce Plasmodium Antigen-Specific CD8+ T Cell and Antibody Responses

An effective vaccine against the Plasmodium parasite is likely to require the induction of robust antibody and T cell responses. Chimeric virus-like particles are an effective vaccine platform for induction of antibody responses, but their capacity to induce robust cellular responses and cell-mediated protection against pathogen challenge has not been established. To evaluate this, we produced chimeric constructs using the murine polyomavirus structural protein with surface-exposed CD8+ or CD4+ T cell or B cell repeat epitopes derived from the Plasmodium yoelii circumsporozoite protein, and assessed immunogenicity and protective capacity in a murine model. Robust CD8+ T cell responses were induced by immunization with the chimeric CD8+ T cell epitope virus-like particles, however CD4+ T cell responses were very low. The B cell chimeric construct induced robust antibody responses but there was no apparent synergy when T cell and B cell constructs were administered as a pool. A heterologous prime/boost regimen using plasmid DNA priming followed by a VLP boost was more effective than homologous VLP immunization for cellular immunity and protection. These data show that chimeric murine polyomavirus virus-like particles are a good platform for induction of CD8+ T cell responses as well as antibody responses.

Effect of dsDNA on the Assembly Pathway and Mechanical Strength of SV40 VP1 Virus-like Particles

Simian virus 40 (SV40) is a possible vehicle for targeted drug delivery systems because of its low immunogenicity, high infectivity, and high transfection efficiency. To use SV40 for biotechnology applications, more information is needed on its assembly process to efficiently incorporate foreign materials and to tune the mechanical properties of the structure. We use atomic force microscopy to determine the effect of double-stranded DNA packaging, buffer conditions, and incubation time on the morphology and strength of virus-like particles (VLPs) composed of SV40 VP1 pentamers. DNA-induced assembly results in a homogeneous population of native-like, ∼45 nm VLPs. In contrast, under high-ionic-strength conditions, the VP1 pentamers do not seem to interact consistently, resulting in a heterogeneous population of empty VLPs. The stiffness of both in-vitro-assembled empty and DNA-filled VLPs is comparable. Yet, the DNA increases the VLPs' resistance to large deformation forces by acting as a scaffold, holding the VP1 pentamers together. Both disulfide bridges and Ca²⁺, important in-vitro-assembly factors, affect the mechanical stability of the VLPs: the reducing agent DTT makes the VLPs less resistant to mechanical stress and prone to damage, whereas Ca²⁺-chelating EDTA induces a marked softening of the VLP. These results show that negatively charged polymers such as DNA can be used to generate homogeneous particles, thereby optimizing VLPs as vessels for drug delivery. Moreover, the storage buffer should be chosen such that VP1 interpentamer interactions are preserved.

Virus-Like Particle Engineering: From Rational Design to Versatile Applications

As mimicking natural virus structures, virus-like particles (VLPs) have evolved to become a widely accepted technology used for humans which are safe, highly efficacious, and profitable. Several remarkable advantages have been achieved to revolutionize the molecule delivery for diverse applications in nanotechnology, biotechnology, and medicine. Here, the rational structure design, manufacturing process, functionalization strategy, and emerging applications of VLPs is reviewed. The situation and challenges in the VLP engineering, the key development orientation, and future applications have been discussed. To develop a good VLP design concept, the virus/VLP-host interactions need to be examined and the screening methods of the VLP stabilization factors need to be established. The functionalization toolbox can be expanded to fabricate smart, robust, and multifunctional VLPs. Novel robust VLP manufacturing platforms are required to deliver vaccines in resource-poor regions with a significant reduction in the production time and cost. The future applications of VLPs are always driven by the development of emerging technologies and new requirements of modern life.

Nanoassembly routes stimulate conflicting antibody quantity and quality for transmission-blocking malaria vaccines

Vaccine development efforts have recently focused on enabling strong immune responses to poorly immunogenic antigens, via display on multimerisation scaffolds or virus like particles (VLPs). Typically such studies demonstrate improved antibody titer comparing monomeric and nano-arrayed antigen. There are many such studies and scaffold technologies, but minimal side-by-side evaluation of platforms for both the amount and efficacy of antibodies induced. Here we present direct comparison of three leading platforms displaying the promising malaria transmission-blocking vaccine (TBV) target Pfs25. These platforms encompass the three important routes to antigen-scaffold linkage: genetic fusion, chemical cross-linking and plug-and-display SpyTag/SpyCatcher conjugation. We demonstrate that chemically-conjugated Qβ VLPs elicited the highest quantity of antibodies, while SpyCatcher-AP205-VLPs elicited the highest quality anti-Pfs25 antibodies for transmission blocking upon mosquito feeding. These quantative and qualitative features will guide future nanoassembly optimisation, as well as the development of the new generation of malaria vaccines targeting transmission.

Nontoxic outer membrane vesicles efficiently increase the efficacy of an influenza vaccine in mice and ferrets

In this study, we developed a further-modified outer membrane vesicle (fmOMV) from the ΔmsbB/ΔpagP mutant of Escherichia coli transformed with the plasmid, pLpxF, in order to use it as an adjuvant for pandemic H1N1 (pH1N1) influenza vaccine. We evaluated the efficacy of the pH1N1 influenza vaccine containing the fmOMV in animal models as compared to the commercial adjuvants, alum or AddaVax^TM. The fmOMV-adjuvanted pH1N1 influenza vaccine induced a significant increase in the humoral immunity; however, this effect was less than that of the AddaVax^TM. The fmOMV-adjuvanted vaccine displayed pronounced an enhanced protective efficacy with increased T cell immune response and reduced the viral load in the lungs of the infected mice after challenging them with a lethal dose of the homologous virus. Moreover, it resulted in a significantly higher cross-protection against heterologous virus challenge than that of the pH1N1 vaccine with alum or with no adjuvants. In ferrets, the fmOMV-adjuvanted vaccine elicited a superior antibody response based on the HI titer and efficiently protected the animals from the lethal viral challenges. Taken together, the nontoxic fmOMV could be a promising adjuvant for inducing robust T cell priming into the pH1N1 vaccine and might be broadly applicable to the development of preventive measures against influenza virus infection.

Virus-based nanoparticles as platform technologies for modern vaccines

Nanoscale engineering is revolutionizing the development of vaccines and immunotherapies. Viruses have played a key role in this field because they can function as prefabricated nanoscaffolds with unique properties that are easy to modify. Viruses are immunogenic via multiple pathways, and antigens displayed naturally or by engineering on the surface can be used to create vaccines against the cognate virus, other pathogens, specific molecules or cellular targets such as tumors. This review focuses on the development of virus-based nanoparticle systems as vaccines indicated for the prevention or treatment of infectious diseases, chronic diseases, cancer, and addiction. WIREs Nanomed Nanobiotechnol 2016, 8:554-578. doi: 10.1002/wnan.1383 For further resources related to this article, please visit the WIREs website.

Immunogenicity of Virus Like Particle Forming Baculoviral DNA Vaccine against Pandemic Influenza H1N1

An outbreak of influenza H1N1 in 2009, representing the first influenza pandemic of the 21st century, was transmitted to over a million individuals and claimed 18,449 lives. The current status in many countries is to prepare influenza vaccine using cell-based or egg-based killed vaccine. However, traditional influenza vaccine platforms have several limitations. To overcome these limitations, many researchers have tried various approaches to develop alternative production platforms. One of the alternative approach, we reported the efficacy of influenza HA vaccination using a baculoviral DNA vaccine (AcHERV-HA). However, the immune response elicited by the AcHERV-HA vaccine, which only targets the HA antigen, was lower than that of the commercial killed vaccine. To overcome the limitations of this previous vaccine, we constructed a human endogenous retrovirus (HERV) envelope-coated, baculovirus-based, virus-like-particle (VLP)–forming DNA vaccine (termed AcHERV-VLP) against pandemic influenza A/California/04/2009 (pH1N1). BALB/c mice immunized with AcHERV-VLP (1×10⁷ FFU AcHERV-VLP, i.m.) and compared with mice immunized with the killed vaccine or mice immunized with AcHERV-HA. As a result, AcHERV-VLP immunization produced a greater humoral immune response and exhibited neutralizing activity with an intrasubgroup H1 strain (PR8), elicited neutralizing antibody production, a high level of interferon-γ secretion in splenocytes, and diminished virus shedding in the lung after challenge with a lethal dose of influenza virus. In conclusion, VLP-forming baculovirus DNA vaccine could be a potential vaccine candidate capable of efficiently delivering DNA to the vaccinee and VLP forming DNA eliciting stronger immunogenicity than egg-based killed vaccines.

The application of virus-like particles as vaccines and biological vehicles

Virus-like particles (VLPs) can be spontaneously self-assembled by viral structural proteins under appropriate conditions in vitro while excluding the genetic material and potential replication probability. In addition, VLPs possess several features including can be rapidly produced in large quantities through existing expression systems, highly resembling native viruses in terms of conformation and appearance, and displaying repeated cluster of epitopes. Their capsids can be modified via genetic insertion or chemical conjugation which facilitating the multivalent display of a homologous or heterogeneous epitope antigen. Therefore, VLPs are considered as a safe and effective candidate of prophylactic and therapeutic vaccines. VLPs, with a diameter of approximately 20 to 150 nm, also have the characteristics of nanometer materials, such as large surface area, surface-accessible amino acids with reactive moieties (e.g., lysine and glutamic acid residues), inerratic spatial structure, and good biocompatibility. Therefore, assembled VLPs have great potential as a delivery system for specifically carrying a variety of materials. This review summarized recent researches on VLP development as vaccines and biological vehicles, which demonstrated the advantages and potential of VLPs in disease control and prevention and diagnosis. Then, the prospect of VLP biology application in the future is discussed as well.

Evaluation of Trichodysplasia Spinulosa-Associated Polyomavirus Capsid Protein as a New Carrier for Construction of Chimeric Virus-Like Particles Harboring Foreign Epitopes

Recombinant virus-like particles (VLPs) represent a promising tool for protein engineering. Recently, trichodysplasia spinulosa-associated polyomavirus (TSPyV) viral protein 1 (VP1) was efficiently produced in yeast expression system and shown to self-assemble to VLPs. In the current study, TSPyV VP1 protein was exploited as a carrier for construction of chimeric VLPs harboring selected B and T cell-specific epitopes and evaluated in comparison to hamster polyomavirus VP1 protein. Chimeric VLPs with inserted either hepatitis B virus preS1 epitope DPAFR or a universal T cell-specific epitope AKFVAAWTLKAAA were produced in yeast Saccharomyces cerevisiae. Target epitopes were incorporated either at the HI or BC loop of the VP1 protein. The insertion sites were selected based on molecular models of TSPyV VP1 protein. The surface exposure of the insert positions was confirmed using a collection of monoclonal antibodies raised against the intact TSPyV VP1 protein. All generated chimeric proteins were capable to self-assemble to VLPs, which induced a strong immune response in mice. The chimeric VLPs also activated dendritic cells and T cells as demonstrated by analysis of cell surface markers and cytokine production profiles in spleen cell cultures. In conclusion, TSPyV VP1 protein represents a new potential carrier for construction of chimeric VLPs harboring target epitopes.

Transgenic mouse models of gastric cancer: Pathological characteristic and applications

Transgenic animal models of gastric cancer have high specificity and similar tumor characteristics to human gastric cancer. Current research and application of transgenic animal models of gastric cancer are wide, and several models have been developed. In transgenic animal models of gastric cancer, primary gastric carcinoma can develop spontaneously. These transgenic animal models have been widely used to study the mechanism of gastric cancer development, and have great significance for clinical diagnosis and treatment of gastric cancer. This paper systematically summarizes several different kinds of transgenic animal models and describes the molecular pathogenic mechanisms and pathological characteristics of gastric mucosal lesions in these models as well as their applications.

SV40 VP1 major capsid protein in its self-assembled form allows VP1 pentamers to coat various types of artificial beads in vitro regardless of their sizes and shapes

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Monomeric VP1 pentamers of simian virus 40 coat artificial beads larger than natural capsids.

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Polystyrene beads (100, 200, and 500 nm in diameter) can be covered by VP1 pentamers.

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Silica beads can also be covered by VP1 pentamers.

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VP1 pentamers can also coat angular-shaped magnetite-particle and rough-shaped liposomes.

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The self-reassembly property of VP1 may allow it to coat various artificial beads, regardless of their sizes or shapes.

The icosahedral capsid structure of simian virus 40 (diameter, 45 nm) consists of 72 pentameric subunits, with each subunit formed by five VP1 molecules. Electron microscopy, immuno-gold labeling, and ζ-potential analysis showed that purified recombinant VP1 pentamers covered polystyrene beads measuring 100, 200, and 500 nm in diameter, as well as silica beads. In addition to covering spherical beads, VP1 pentamers covered cubic magnetite beads, as well as the distorted surface structures of liposomes. These findings indicate that VP1 pentamers could coat artificial beads of various shapes and sizes larger than the natural capsid. Technology based on VP1 pentamers may be useful in providing a capsid-like surface for enclosed materials, enhancing their stability and cellular uptake for drug delivery systems.

Structural basis for the development of avian virus capsids that display influenza virus proteins and induce protective immunity

Bioengineering of viruses and virus-like particles (VLPs) is a well-established approach in the development of new and improved vaccines against viral and bacterial pathogens. We report here that the capsid of a major avian pathogen, infectious bursal disease virus (IBDV), can accommodate heterologous proteins to induce protective immunity. The structural units of the ~70-nm-diameter T=13 IBDV capsid are trimers of VP2, which is made as a precursor (pVP2). The pVP2 C-terminal domain has an amphipathic α helix that controls VP2 polymorphism. In the absence of the VP3 scaffolding protein, 466-residue pVP2 intermediates bearing this α helix assemble into genuine VLPs only when expressed with an N-terminal His6 tag (the HT-VP2-466 protein). HT-VP2-466 capsids are optimal for protein insertion, as they are large enough (cargo space, ~78,000 nm(3)) and are assembled from a single protein. We explored HT-VP2-466-based chimeric capsids initially using enhanced green fluorescent protein (EGFP). The VLP assembly yield was efficient when we coexpressed EGFP-HT-VP2-466 and HT-VP2-466 from two recombinant baculoviruses. The native EGFP structure (~240 copies/virion) was successfully inserted in a functional form, as VLPs were fluorescent, and three-dimensional cryo-electron microscopy showed that the EGFP molecules incorporated at the inner capsid surface. Immunization of mice with purified EGFP-VLPs elicited anti-EGFP antibodies. We also inserted hemagglutinin (HA) and matrix (M2) protein epitopes derived from the mouse-adapted A/PR/8/34 influenza virus and engineered several HA- and M2-derived chimeric capsids. Mice immunized with VLPs containing the HA stalk, an M2 fragment, or both antigens developed full protection against viral challenge.

IMPORTANCE

Virus-like particles (VLPs) are multimeric protein cages that mimic the infectious virus capsid and are potential candidates as nonliving vaccines that induce long-lasting protection. Chimeric VLPs can display or include foreign antigens, which could be a conserved epitope to elicit broadly neutralizing antibodies or several variable epitopes effective against a large number of viral strains. We report the biochemical, structural, and immunological characterization of chimeric VLPs derived from infectious bursal disease virus (IBDV), an important poultry pathogen. To test the potential of IBDV VLPs as a vaccine vehicle, we used the enhanced green fluorescent protein and two fragments derived from the hemagglutinin and the M2 matrix protein of the human murine-adapted influenza virus. The IBDV capsid protein fused to influenza virus peptides formed assemblies able to protect mice against viral challenge. Our studies establish the basis for a new generation of multivalent IBDV-based vaccines.

Introduction of a point mutation into an HLA class I single-chain trimer induces enhancement of CTL priming and antitumor immunity

We previously discovered one particular HLA-A*02:01 mutant that enhanced peptide-specific cytotoxic T lymphocyte (CTL) recognition in vitro compared to wild-type HLA-A*02:01. This mutant contains a single amino acid substitution from histidine to leucine at position 74 (H74L) that is located in the peptide-binding groove. To investigate the effect of the H74L mutation on the in vivo CTL priming, we took advantage of the technology of the HLA class I single-chain trimer (SCT) in which three components involving a peptide, β2 microglobulin and the HLA class I heavy chain are joined together via flexible linkers. We generated recombinant adenovirus expressing SCT comprised influenza A matrix protein (FMP)-derived peptide, β2 microglobulin and the H74L heavy chain. HLA-A*02:01 transgenic mice were immunized with the adenovirus, and the induction of peptide-specific CTLs and antitumor immunity was investigated. It was clearly shown that the H74L mutation enabled the HLA-A*02:01 SCT molecule to dramatically enhance both in vivo priming of FMP-specific CTLs and protection against a lethal challenge of tumor cells expressing FMP. These data present the first evidence that a simple point mutation in the HLA class I heavy chain of SCT is beneficial for improving CTL-based immunotherapy and prophylaxis to control tumors.

Subviral particle as vaccine and vaccine platform

Recombinant subvirual particles retain similar antigenic features of their authentic viral capsids and thus have been applied as nonreplicating subunit vaccines against viral infection and illness. Additionally, the self-assembled, polyvalent subviral particles are excellent platforms to display foreign antigens for immune enhancement for vaccine development. These subviral particle-based vaccines are noninfectious and thus safer than the conventional live attenuated and inactivated vaccines. While several VLP vaccines are available in the markets, numerous others, including dual vaccines against more than one pathogen, are under clinical or preclinical development. This article provides an update of these efforts.