Influenza virus-like particles composed of conserved influenza proteins and GPI-anchored CCL28/GM-CSF fusion proteins enhance protective immunity against homologous and heterologous viruses

Virus-like Particle Vaccines and Platforms for Vaccine Development

Virus-like particles (VLPs) have gained a lot of interest within the past two decades. The use of VLP-based vaccines to protect against three infectious agents-hepatitis B virus, human papillomavirus, and hepatitis E virus-has been approved; they are very efficacious and offer long-lasting immune responses. Besides these, VLPs from other viral infectious agents (that infect humans, animals, plants, and bacteria) are under development. These VLPs, especially those from human and animal viruses, serve as stand-alone vaccines to protect against viruses from which the VLPs were derived. Additionally, VLPs, including those derived from plant and bacterial viruses, serve as platforms upon which to display foreign peptide antigens from other infectious agents or metabolic diseases such as cancer, i.e., they can be used to develop chimeric VLPs. The goal of chimeric VLPs is to enhance the immunogenicity of foreign peptides displayed on VLPs and not necessarily the platforms. This review provides a summary of VLP vaccines for human and veterinary use that have been approved and those that are under development. Furthermore, this review summarizes chimeric VLP vaccines that have been developed and tested in pre-clinical studies. Finally, the review concludes with a snapshot of the advantages of VLP-based vaccines such as hybrid/mosaic VLPs over conventional vaccine approaches such as live-attenuated and inactivated vaccines.

A perspective on SARS-CoV-2 virus-like particles vaccines

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) first appeared in Wuhan, China, in December 2019. The 2019 coronavirus disease (COVID-19) pandemic, caused by SARS-CoV-2, has spread to almost all corners of the world at an alarming rate. Vaccination is important for the prevention and control of the COVID-19 pandemic. Efforts are underway worldwide to develop an effective vaccine against COVID-19 using both traditional and innovative vaccine strategies. Compared to other vaccine platforms, SARS-CoV-2 virus-like particles （VLPs ）vaccines, as a new vaccine platform, have unique advantages: they have artificial nanostructures similar to natural SARS-CoV-2, which can stimulate good cellular and humoral immune responses in the organism; they have no viral nucleic acids, have good safety and thermal stability, and can be mass-produced and stored; their surfaces can be processed and modified, such as the adjuvant addition, etc.; they can be considered as an ideal platform for COVID-19 vaccine development. This review aims to shed light on the current knowledge and progress of VLPs vaccines against COVID-19, especially those undergoing clinical trials.

Supplementation of H7N9 Virus-Like Particle Vaccine With Recombinant Epitope Antigen Confers Full Protection Against Antigenically Divergent H7N9 Virus in Chickens

The continuous evolution of the H7N9 avian influenza virus suggests a potential outbreak of an H7N9 pandemic. Therefore, to prevent a potential epidemic of the H7N9 influenza virus, it is necessary to develop an effective crossprotective influenza vaccine. In this study, we developed H7N9 virus-like particles (VLPs) containing HA, NA, and M1 proteins derived from H7N9/16876 virus and a helper antigen HMN based on influenza conserved epitopes using a baculovirus expression vector system (BEVS). The results showed that the influenza VLP vaccine induced a strong HI antibody response and provided effective protection comparable with the effects of commercial inactivated H7N9 vaccines against homologous H7N9 virus challenge in chickens. Meanwhile, the H7N9 VLP vaccine induced robust crossreactive HI and neutralizing antibody titers against antigenically divergent H7N9 viruses isolated in wave 5 and conferred on chickens complete clinical protection against heterologous H7N9 virus challenge, significantly inhibiting virus shedding in chickens. Importantly, supplemented vaccination with HMN antigen can enhance Th1 immune responses; virus shedding was completely abolished in the vaccinated chickens. Our study also demonstrated that viral receptor-binding avidity should be taken into consideration in evaluating an H7N9 candidate vaccine. These studies suggested that supplementing influenza VLP vaccine with recombinant epitope antigen will be a promising strategy for the development of broad-spectrum influenza vaccines.

Influenza Neuraminidase Characteristics and Potential as a Vaccine Target

Neuraminidase of influenza A and B viruses plays a critical role in the virus life cycle and is an important target of the host immune system. Here, we highlight the current understanding of influenza neuraminidase structure, function, antigenicity, immunogenicity, and immune protective potential. Neuraminidase inhibiting antibodies have been recognized as correlates of protection against disease caused by natural or experimental influenza A virus infection in humans. In the past years, we have witnessed an increasing interest in the use of influenza neuraminidase to improve the protective potential of currently used influenza vaccines. A number of well-characterized influenza neuraminidase-specific monoclonal antibodies have been described recently, most of which can protect in experimental challenge models by inhibiting the neuraminidase activity or by Fc receptor-dependent mechanisms. The relative instability of the neuraminidase poses a challenge for protein-based antigen design. We critically review the different solutions that have been proposed to solve this problem, ranging from the inclusion of stabilizing heterologous tetramerizing zippers to the introduction of inter-protomer stabilizing mutations. Computationally engineered neuraminidase antigens have been generated that offer broad, within subtype protection in animal challenge models. We also provide an overview of modern vaccine technology platforms that are compatible with the induction of robust neuraminidase-specific immune responses. In the near future, we will likely see the implementation of influenza vaccines that confront the influenza virus with a double punch: targeting both the hemagglutinin and the neuraminidase.

Bivalent vaccination with NA1 and NA2 neuraminidase virus-like particles is protective against challenge with H1N1 and H3N2 influenza A viruses in a murine model

Neuraminidase (NA) is the second most abundant glycoprotein on the surface of influenza A viruses (IAV). Neuraminidase type 1 (NA1) based virus-like particles (VLPs) have previously been shown to protect against challenge with H1N1 and H3N2 IAV. In this study, we produced neuraminidase type 2 (NA2) VLPs derived from the sequence of the seasonal IAV A/Perth/16/2009. Intramuscular vaccination of mice with NA2 VLPs induced high anti-NA serum IgG levels capable of inhibiting NA activity. NA2 VLP vaccination protected against mortality in a lethal A/Hong Kong/1/1968 (H3N2) virus challenge model, but not against lethal challenge with A/California/04/2009 (H1N1) virus. However, bivalent vaccination with NA1 and NA2 VLPs demonstrated no antigenic competition in anti-NA IgG responses and protected against lethal challenge with H1N1 and H3N2 viruses. Here we demonstrate that vaccination with NA VLPs is protective against influenza challenge and supports focusing on anti-NA responses in the development of future vaccination strategies.

CCL19 and CCL28 Assist Herpes Simplex Virus 2 Glycoprotein D To Induce Protective Systemic Immunity against Genital Viral Challenge

An effective HSV-2 vaccine should induce antigen (Ag)-specific immune responses against viral mucosal infection. This study reveals that chemokine CCL19 or CCL28 enhanced HSV-2 glycoprotein D ectodomain (gD-306aa)-induced immune responses against vaginal virus challenge.

Potent systemic immunity is important for recalled mucosal immune responses, but in the defense against mucosal viral infections, it usually remains low at mucosal sites. Based on our previous findings that enhanced immune responses can be achieved by immunization with an immunogen in combination with a molecular adjuvant, here we designed chemokine-antigen (Ag) fusion constructs (CCL19- or CCL28-herpes simplex virus 2 glycoprotein D [HSV-2 gD]). After intramuscular (i.m.) immunization with different DNA vaccines in a prime and boost strategy, BALB/c mice were challenged with a lethal dose of HSV-2 through the genital tract. Ag-specific immune responses and chemokine receptor-specific lymphocytes were analyzed to determine the effects of CCL19 and CCL28 in strengthening humoral and cellular immunity. Both CCL19 and CCL28 were efficient in inducing long-lasting HSV-2 gD-specific systemic immunity. Compared to CCL19, less CCL28 was required to elicit HSV-2 gD-specific serum IgA responses, Th1- and Th2-like responses of immunoglobulin (Ig) subclasses and cytokines, and CCR3⁺ T cell enrichment (>8.5-fold) in spleens. These findings together demonstrate that CCL28 tends to assist an immunogen to induce more potently protective immunity than CCL19. This work provides information for the application potential of a promising vaccination strategy against mucosal infections caused by HSV-2 and other sexually transmitted viruses.

IMPORTANCE An effective HSV-2 vaccine should induce antigen (Ag)-specific immune responses against viral mucosal infection. This study reveals that chemokine CCL19 or CCL28 enhanced HSV-2 glycoprotein D ectodomain (gD-306aa)-induced immune responses against vaginal virus challenge. In addition to eliciting robust humoral immune responses, the chemokine-Ag fusion construct also induced Th1- and Th2-like immune responses characterized by the secretion of multiple Ig subclasses and cytokines that were able to be recalled after HSV-2 challenge, while CCL28 appeared to be more effective than CCL19 in promoting gD-elicited immune responses as well as the migration of T cells to secondary lymph tissues. Of importance, both CCL19 and CCL28 significantly facilitated gD to induce protective mucosal immune responses in the genital tract. The above-described findings together highlight the potential of CCL19 or CCL28 in combination with gD as a vaccination strategy to control HSV-2 infection.

Genetic engineering strategies for construction of multivalent chimeric VLPs vaccines

Introduction: Over the past two decades, virus-like particles (VLPs) have been developed as a new generation of vaccines against viral infections. Based on VLPs, chimeric VLPs (chi-VLPs) have been generated through genetic modifications or chemical couplings. For construction of multivalent chi-VLPs vaccines, multiple genetic engineering strategies are continuously being developed. Thus, it is important to provide a summary as reference for researchers in this field.Areas covered: The representative studies on the genetic engineered multivalent chi-VLPs are summarized and mainly focused on chimeric capsid VLPs and chimeric enveloped VLPs. The advantages and limitations of each strategy are also discussed at last, as well as opinions on platform choice and future directions of eVLPs vaccines.Expert opinion: The design of multivalent chi-VLPs vaccines needs to meet the following specifications: 1) the incorporated antigens are suggested to display on the exposed surface of chi-VLPs and do not have excessive adverse effects on the stability of chi-VLPs; 2) the chi-VLPs should elicit protective antibodies against the incorporated antigen as well as the source virus of VLPs. However, there is no requirement of retaining the antigenicity of VLPs when using VLPs solely as carriers for antigens display or drug delivery.

Innovative Mucosal Vaccine Formulations Against Influenza A Virus Infections

Despite efforts made to develop efficient preventive strategies, infections with influenza A viruses (IAV) continue to cause serious clinical and economic problems. Current licensed human vaccines are mainly inactivated whole virus particles or split-virion administered via the parenteral route. These vaccines provide incomplete protection against IAV in high-risk groups and are poorly/not effective against the constant antigenic drift/shift occurring in circulating strains. Advances in mucosal vaccinology and in the understanding of the protective anti-influenza immune mechanisms suggest that intranasal immunization is a promising strategy to fight against IAV. To date, human mucosal anti-influenza vaccines consist of live attenuated strains administered intranasally, which elicit higher local humoral and cellular immune responses than conventional parenteral vaccines. However, because of inconsistent protective efficacy and safety concerns regarding the use of live viral strains, new vaccine candidates are urgently needed. To prime and induce potent and long-lived protective immune responses, mucosal vaccine formulations need to ensure the immunoavailability and the immunostimulating capacity of the vaccine antigen(s) at the mucosal surfaces, while being minimally reactogenic/toxic. The purpose of this review is to compile innovative delivery/adjuvant systems tested for intranasal administration of inactivated influenza vaccines, including micro/nanosized particulate carriers such as lipid-based particles, virus-like particles and polymers associated or not with immunopotentiatory molecules including microorganism-derived toxins, Toll-like receptor ligands and cytokines. The capacity of these vaccines to trigger specific mucosal and systemic humoral and cellular responses against IAV and their (cross)-protective potential are considered.