Immunogenicity and Protective Capacity of a Virus-like Particle Vaccine against Chlamydia trachomatis Type 3 Secretion System Tip Protein, CT584

An effective vaccine against Chlamydia trachomatis is urgently needed as infection rates continue to rise and C. trachomatis causes reproductive morbidity. An obligate intracellular pathogen, C. trachomatis employs a type 3 secretion system (T3SS) for host cell entry. The tip of the injectosome is composed of the protein CT584, which represents a potential target for neutralization with vaccine-induced antibody. Here, we investigate the immunogenicity and efficacy of a vaccine made of CT584 epitopes coupled to a bacteriophage virus-like particle (VLP), a novel platform for Chlamydia vaccines modeled on the success of HPV vaccines. Female mice were immunized intramuscularly, challenged transcervically with C. trachomatis, and assessed for systemic and local antibody responses and bacterial burden in the upper genital tract. Immunization resulted in a 3-log increase in epitope-specific IgG in serum and uterine homogenates and in the detection of epitope-specific IgG in uterine lavage at low levels. By contrast, sera from women infected with C. trachomatis and virgin controls had similarly low titers to CT584 epitopes, suggesting these epitopes are not systemically immunogenic during natural infection but can be rendered immunogenic by the VLP platform. C. trachomatis burden in the upper genital tract of mice varied after active immunization, yet passive protection was achieved when immune sera were pre-incubated with C. trachomatis prior to inoculation into the genital tract. These data demonstrate the potential for antibody against the T3SS to contribute to protection against C. trachomatis and the value of VLPs as a novel platform for C. trachomatis vaccines.

Safety, immunogenicity, and protection provided by unadjuvanted and adjuvanted formulations of a recombinant plant-derived virus-like particle vaccine candidate for COVID-19 in nonhuman primates

Although antivirals are important tools to control severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, effective vaccines are essential to control the current coronavirus disease 2019 (COVID-19) pandemic. Plant-derived virus-like particle (VLP) vaccine candidates have previously demonstrated immunogenicity and efficacy against influenza. Here, we report the immunogenicity and protection induced in rhesus macaques by intramuscular injections of a VLP bearing a SARS-CoV-2 spike protein (CoVLP) vaccine candidate formulated with or without Adjuvant System 03 (AS03) or cytidine-phospho-guanosine (CpG) 1018. Although a single dose of the unadjuvanted CoVLP vaccine candidate stimulated humoral and cell-mediated immune responses, booster immunization (at 28 days after priming) and adjuvant administration significantly improved both responses, with higher immunogenicity and protection provided by the AS03-adjuvanted CoVLP. Fifteen micrograms of CoVLP adjuvanted with AS03 induced a polyfunctional interleukin-2 (IL-2)-driven response and IL-4 expression in CD4 T cells. Animals were challenged by multiple routes (i.e., intratracheal, intranasal, and ocular) with a total viral dose of 106 plaque-forming units of SARS-CoV-2. Lower viral replication in nasal swabs and bronchoalveolar lavage fluid (BALF) as well as fewer SARS-CoV-2-infected cells and immune cell infiltrates in the lungs concomitant with reduced levels of proinflammatory cytokines and chemotactic factors in the BALF were observed in animals immunized with the CoVLP adjuvanted with AS03. No clinical, pathologic, or virologic evidence of vaccine-associated enhanced disease was observed in vaccinated animals. The CoVLP adjuvanted with AS03 was therefore selected for vaccine development and clinical trials.

RG203KR mutations in SARS-CoV-2 Nucleocapsid: Assessing the impact using Virus-like particle model system

The emergence and evolution of SARS-CoV-2 is characterized by the occurrence of diverse sets of mutations that affect virus characteristics, including transmissibility and antigenicity. Recent studies have focused mostly on Spike protein mutations; however, SARS-CoV-2 variants of interest (VoI) or concern (VoC) contain significant mutations in the nucleocapsid protein as well. To study the relevance of the mutations at the virion level, recombinant baculovirus expression system based VLPs were generated for the prototype Wuhan sequence along with Spike mutants like D614G, G1124V and the significant RG203KR mutation in Nucleocapsid. All the four structural proteins assembled in a particle wherein the morphology and size of the particle confirmed by TEM closely resembles the native virion. The VLP harbouring RG203KR mutations in nucleocapsid exhibited augmentation of humoral immune responses and enhanced neutralization by the immunized mice sera. Results demonstrate a non-infectious platform to quickly assess the implication of mutations in structural proteins of the emerging variant.

New Generation Vaccines for COVID-19 Based on Peptide, Viral Vector, Artificial Antigen Presenting Cell, DNA or mRNA

At present, effective vaccines have been developed as the most successful approaches for preventing widespread infectious disease. The global efforts are focusing with the aim of eliminating and overcoming the Coronavirus Disease 2019 (COVID-19) and are developing vaccines from the date it was announced as a pandemic disease. In this study, PubMed, Embase, Cochrane Library, Clinicaltrial.gov, WHO reports, Science Direct, Scopus, Google Scholar, and Springer databases were searched for finding the relevant studies about the COVID-19 vaccines. This article provides an overview of multiple vaccines that have been manufactured from December 2020 up to April 2021 and also offers a perspective on their efficacy, safety, advantages, and limitations. Currently, there are several categories of COVID-19 vaccines based on Protein Subunit (PS), Inactivated Virus (IV), Virus Like Particle (VLP), Live Attenuated Virus (LAV), Viral Vector (replicating) (VVr) and Viral Vector (non-replicating) (VVnr) in progress or finalized as indicated by the WHO reporting of April 1, 2020.

COVID-19 vaccine and immune response

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2; βCoV), the causative agent of coronavirus disease 2019 (COVID-19), causes severe lower respiratory tract infections and acute respiratory failure syndrome (ARDS). Deaths due to the ongoing COVID-19 pandemic for more than a year are still seen worldwide. Therefore, vaccine trials have gained importance. The discovery of the genome and protein structure of SARS-CoV-2 in a short time allowed the development of nucleic acid-based vaccines (mRNA and DNA vaccines), vector vaccines, inactivated virus vaccines, protein-based vaccines, virus-like particle vaccines, and live attenuated virus vaccines. Many companies, universities, and institutes around the world continue to develop effective vaccines against SARS-CoV-2. In this review, the structural features, classification, genome, and intracellular entry of SARS-CoV-2 coronaviruses, stimulation of the immune system and immunity, COVID-19 vaccine types, and the latest status of clinical trials of these vaccines have been reviewed.

Effectiveness of Coronavirus Vaccines against Syndrome Coronavirus 2 (SARS-CoV-2) and Its New Variants

The widespread outbreak of coronavirus disease 2019 in late 2019 caused many people worldwide to die or suffer from certain clinical complications even after the recovery. The virus has many social and economic adverse effects. Studies on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have specified that spike, surface glycoprotein antigen, is considered as a major target to stimulate the immune system. This glycoprotein binds to the angiotensin-converting enzyme 2 on the surface of human cells especially lung epithelial cells and facilitates the virus entry. Therefore, the immune response stimulated by vaccination targeting this antigen may cause immunity against the whole virus. Currently, many companies are working on SARS-CoV-2 vaccines. They include ‘traditional’ vaccines like attenuated or inactivated virus platforms as well as the brand-new generations of vaccines such as viral vector-based, subunit, nucleic acid-based, and virus-like particle vaccines. Certainly, each vaccine platform presents several advantages and disadvantages affecting its efficacy and safety which is the main topic of this paper.

Dendritic cell targeting virus-like particle delivers mRNA for in vivo immunization

mRNA vaccine was approved clinically in 2020. Future development includes delivering mRNA to dendritic cells (DCs) specifically to improve effectiveness and avoid off-target cytotoxicity. Here, we developed virus-like particles (VLPs) as a DC tropic mRNA vaccine vector and showed the prophylactic effects in both SARS-CoV-2 and HSV-1 infection models. The VLP mRNA vaccine elicited strong cytotoxic T cell immunity and durable antibody response with the spike-specific antibodies that lasted for more than 9 months. Importantly, we were able to target mRNA to DCs by pseudotyping VLP with engineered Sindbis virus glycoprotein and found the DC-targeting mRNA vaccine significantly enhanced the titer of antigen-specific IgG, protecting the hACE-2 mice from SARS-CoV-2 infection. Additionally, we showed DC-targeted mRNA vaccine also protected mice from HSV-1 infection when co-delivering the gB and gD mRNA. Thus, the VLP may serve as an in situ DC vaccine and accelerate the further development of mRNA vaccines.

Transdermal Vaccination with the Matrix-2 Protein Virus-like Particle (M2e VLP) Induces Immunity in Mice against Influenza A Virus

In this study, our goal was to utilize the extracellular domain matrix-2 protein virus-like particle (M2e VLP) that has been found to be highly conserved amongst all strains of influenza and could serve as a potential vaccine candidate against influenza. Previous studies have demonstrated that the VLP of the M2e showed increased activation of innate and adaptive immune responses. Therefore, to further explore its level of efficacy and protection, this vaccine was administered transdermally and tested in a pre-clinical mouse model. The M2e VLP was encapsulated into a polymeric matrix with the addition of Alhydrogel® and Monophosphoryl Lipid-A (MPL-A®), together referred to as AS04. The M2e VLP formulations induced IgG titers, with increased levels of IgG1 in the M2e VLP MP groups and further elevated levels of IgG2a were found specifically in the M2e VLP MP Adjuvant group. This trend in humoral immunity was also observed from a cell-mediated standpoint, where M2e VLP MP groups showed increased expression in CD4+ T cells in the spleen and the lymph node and high levels of CD8+ T cells in the lymph node. Taken together, the results illustrate the immunogenic potential of the matrix-2 protein virus-like particle (M2e VLP) vaccine.