Cricket paralysis virus internal ribosome entry site-derived RNA promotes conventional vaccine efficacy by enhancing a balanced Th1/Th2 response

Ally, adversary, or arbitrator? The context-dependent role of eosinophils in vaccination for respiratory viruses and subsequent breakthrough infections

Eosinophils are a critical type of immune cell and central players in type 2 immunity. Existing literature suggests that eosinophils also can play a role in host antiviral responses, typically type 1 immune events, against multiple respiratory viruses, both directly through release of antiviral mediators and indirectly through activation of other effector cell types. One way to prime host immune responses toward effective antiviral responses is through vaccination, where typically a type 1-skewed immunity is desirable in the context of intracellular pathogens like respiratory viruses. In the realm of breakthrough respiratory viral infection in vaccinated hosts, an event in which virus can still establish productive infection despite preexisting immunity, eosinophils are most prominently known for their link to vaccine-associated enhanced respiratory disease upon natural respiratory syncytial virus infection. This was observed in a pediatric cohort during the 1960s following vaccination with formalin-inactivated respiratory syncytial virus. More recent research has unveiled additional roles of the eosinophil in respiratory viral infection and breakthrough infection. The specific contribution of eosinophils to the quality of vaccine responses, vaccine efficacy, and antiviral responses to infection in vaccinated hosts remains largely unexplored, especially regarding their potential roles in protection. On the basis of current findings, we will speculate upon the suggested function of eosinophils and consider the many potential ways by which eosinophils may exert protective and pathological effects in breakthrough infections. We will also discuss how to balance vaccine efficacy with eosinophil-related risks, as well as the use of eosinophils and their products as potential biomarkers of vaccine efficacy or adverse events.

Influenza breakthrough infection in vaccinated mice is characterized by non-pathological lung eosinophilia

Eosinophils are important mediators of mucosal tissue homeostasis, anti-helminth responses, and allergy. Lung eosinophilia has previously been linked to aberrant Type 2-skewed T cell responses to respiratory viral infection and may also be a consequence of vaccine-associated enhanced respiratory disease (VAERD), particularly in the case of respiratory syncytial virus (RSV) and the formalin-inactivated RSV vaccine. We previously reported a dose-dependent recruitment of eosinophils to the lungs of mice vaccinated with alum-adjuvanted trivalent inactivated influenza vaccine (TIV) following a sublethal, vaccine-matched H1N1 (A/New Caledonia/20/1999; NC99) influenza challenge. Given the differential role of eosinophil subset on immune function, we conducted the investigations herein to phenotype the lung eosinophils observed in our model of influenza breakthrough infection. Here, we demonstrate that eosinophil influx into the lungs of vaccinated mice is adjuvant- and sex-independent, and only present after vaccine-matched sublethal influenza challenge but not in mock-challenged mice. Furthermore, vaccinated and challenged mice had a compositional shift towards more inflammatory eosinophils (iEos) compared to resident eosinophils (rEos), resembling the shift observed in ovalbumin (OVA)-sensitized allergic control mice, however without any evidence of enhanced morbidity or aberrant inflammation in lung cytokine/chemokine signatures. Furthermore, we saw a lung eosinophil influx in the context of a vaccine-mismatched challenge. Additional layers of heterogeneity in the eosinophil compartment were observed via unsupervised clustering analysis of flow cytometry data. Our collective findings are a starting point for more in-depth phenotypic and functional characterization of lung eosinophil subsets in the context of vaccine- and infection-induced immunity.

Heterologous vaccination utilizing viral vector and protein platforms confers complete protection against SFTSV

Severe fever with thrombocytopenia syndrome virus was first discovered in 2009 as the causative agent of severe fever with thrombocytopenia syndrome. Despite its potential threat to public health, no prophylactic vaccine is yet available. This study developed a heterologous prime-boost strategy comprising priming with recombinant replication-deficient human adenovirus type 5 (rAd5) expressing the surface glycoprotein, Gn, and boosting with Gn protein. This vaccination regimen induced balanced Th1/Th2 immune responses and resulted in potent humoral and T cell-mediated responses in mice. It elicited high neutralizing antibody titers in both mice and non-human primates. Transcriptome analysis revealed that rAd5 and Gn proteins induced adaptive and innate immune pathways, respectively. This study provides immunological and mechanistic insight into this heterologous regimen and paves the way for future strategies against emerging infectious diseases.

Adjuvant effect of IRES-based single-stranded RNA on melanoma immunotherapy

Background

Adjuvant therapies such as radiation therapy, chemotherapy, and immunotherapy are usually given after cancer surgery to improve the survival of cancer patients. However, despite advances in several adjuvant therapies, they are still limited in the prevention of recurrences.

Methods

We evaluated the immunological effects of RNA-based adjuvants in a murine melanoma model. Single-stranded RNA (ssRNA) were constructed based on the cricket paralysis virus (CrPV) internal ribosome entry site (IRES). Populations of immune cells in bone marrow cells and lymph node cells following immunization with CrPV^IRES-ssRNA were determined using flow cytometry. Activated cytokine levels were measured using ELISA and ELISpot. The tumor protection efficacy of CrPV^IRES-ssRNA was analyzed based on any reduction in tumor size or weight, and overall survival.

Results

CrPV^IRES-ssRNA treatment stimulated antigen-presenting cells in the drain lymph nodes associated with activated antigen-specific dendritic cells. Next, we evaluated the expression of CD40, CD86, and XCR1, showing that immunization with CrPV^IRES-ssRNA enhanced antigen presentation by CD8a⁺ conventional dendritic cell 1 (cDC1), as well as activated antigen-specific CD8 T cells. In addition, CrPV^IRES-ssRNA treatment markedly increased the frequency of antigen-specific CD8 T cells and interferon-gamma (IFN-γ) producing cells, which promoted immune responses and reduced tumor burden in melanoma-bearing mice.

Conclusions

This study provides evidence that the CrPV^IRES-ssRNA adjuvant has potential for use in therapeutic cancer vaccines. Moreover, CrPV^IRES-ssRNA possesses protective effects on various cancer cell models.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-10140-2.

Single-stranded RNA adjuvant enhances the efficacy of 10-valent human papilloma virus-like particle vaccine

Following the development of various types of vaccines, the use of adjuvants to boost vaccine efficacy has become a focus of research. Aluminum hydroxide (alum), the most commonly used adjuvant, induces a certain immune response and ensures safety in human trials. However, alum mainly induces only a Th2 response; its Th1 response is weak. Thus, we previously developed a single-stranded ribose nucleic acid (ssRNA) adjuvant that induces a Th1 response through toll-like receptors. Here, we explored whether 10-valent human papilloma virus (HPV)-like particle (VLP) vaccine formulated with ssRNA adjuvant and alum helped enhance immune response and maintained memory response. The mice were immunized intramuscularly twice at 2-week intervals and were inoculated 4 days after the second boost (after about 1 year). Antibody response and T cell activation were measured by Elispot, ELISA using harvested serum and splenocytes. 10-valent HPV VLP vaccine formulated with ssRNA adjuvant and alum increased antigen-specific immune response than alum used alone. It increased each type-specific IgG1/IgG2c titers, and antigen-specific IFN-γ cells. Furthermore, the ssRNA adjuvant with alum induced memory response. In memory response, each type-specific IgG1/IgG2c, IFN-γ, and IL-6 cytokines, and neutralizing antibodies were increased by the ssRNA adjuvant with alum. Overall, the ssRNA adjuvant with alum induced memory responses and balanced Th1/Th2 responses. The ssRNA adjuvant and alum may help to enhanced prophylactic vaccine efficacy. This article is protected by copyright. All rights reserved.

In vivo observation of multi-phase spatiotemporal cellular dynamics of transplanted HSPCs during early engraftment

Hematopoietic stem cell transplantation (HSCT) is commonly used to treat patients with various blood disorders, genetic and immunological diseases, and solid tumors. Several systemic complications following HSCT are critical limiting factors for achieving a successful outcome. These systemic complications are mainly due to the lack of initial engraftment after transplantation. However, the detailed underlying cellular dynamics of early engraftment have not been fully characterized yet. We performed in vivo longitudinal visualization of early engraftment characteristics of transplanted hematopoietic stem and progenitor cells (HSPCs) in the mouse calvarial bone marrow (BM). To achieve this, we utilized an in vivo laser-scanning confocal microscopy imaging system with a cranial BM imaging window and stereotaxic device. We observed two distinct cellular behaviors of HSPCs in vivo, cluster formation and cluster dissociation, early after transplantation. Furthermore, we successfully identified three cellular phases of engraftment with distinct cellular distances which are coordinated with cell proliferation and cell migration dynamics during initial engraftment.

Effective inactivated influenza vaccine for the elderly using a single-stranded RNA-based adjuvant

There is an unmet need for new influenza vaccine strategies that compensate for impaired vaccine responses in elderly individuals. Here, we evaluated the effectiveness of a single-stranded RNA (ssRNA) as an adjuvant to enhance the efficacy of inactivated influenza vaccine (IIV) in mouse models. Immunization with the ssRNA along with IIV reduced viral titers as well as pathological and inflammatory scores in the lungs after influenza challenge in aged mice. ssRNA induced balanced Th1/Th2 responses with an increase in IgA titers. Moreover, the ssRNA adjuvant markedly increased the frequency of influenza HA-specific T cells and IFN-γ production along with the expression of genes related to innate and adaptive immune systems that could overcome immunosenescence in aged mice. Our findings indicate that ssRNA is an efficient vaccine adjuvant that boosts cellular and humoral immunity in aged mice, demonstrating its potential as a novel adjuvant for currently available influenza virus vaccines for elderly individuals.

Cell-Penetrating Peptides-Based Liposomal Delivery System Enhanced Immunogenicity of Peptide-Based Vaccine against Group A Streptococcus

Peptide-based vaccine development represents a highly promising strategy for preventing Group A Streptococcus (GAS) infection. However, these vaccines need to be administered with the help of a delivery system and/or immune adjuvant. Cell-penetrating peptides (CPPs) have been used as a powerful tool for delivering various therapeutic agents, including peptides, as they can overcome the permeability barrier of cell membranes. Here, we used CPPs to deliver our lead lipopeptide-based vaccine (LCP-1). CPPs were anchored through a spacer to LCP-1-bearing multilamellar and unilamellar liposomes and administered to Swiss outbred mice. Tat47-57 conjugated to two palmitic acids via a (Gly)6 spacer (to form a liposome-anchoring moiety) was the most efficient system for triggering immune responses when combined with multilamellar liposomes bearing LCP-1. The immunostimulatory potential of a variety of other CPPs was examined following intranasal administration in mice. Among them, LCP-1/liposomes/Tat47-57 and LCP-1/liposomes/KALA induced the highest antibody titers. The antibodies produced showed high opsonic activity against clinically isolated GAS strains D3840 and GC2 203. The use of the CPP-liposome delivery system is a promising strategy for liposome-based GAS vaccine development.

Adjuvants for Coronavirus Vaccines

Vaccine development utilizing various platforms is one of the strategies that has been proposed to address the coronavirus disease 2019 (COVID-19) pandemic. Adjuvants are critical components of both subunit and certain inactivated vaccines because they induce specific immune responses that are more robust and long-lasting. A review of the history of coronavirus vaccine development demonstrates that only a few adjuvants, including aluminum salts, emulsions, and TLR agonists, have been formulated for the severe acute respiratory syndrome-associated coronavirus (SARS-CoV), Middle East respiratory syndrome-related coronavirus (MERS-CoV), and currently the SARS-CoV-2 vaccines in experimental and pre-clinical studies. However, there is still a lack of evidence regarding the effects of the adjuvants tested in coronavirus vaccines. This paper presents an overview of adjuvants that have been formulated in reported coronavirus vaccine studies, which should assist with the design and selection of adjuvants with optimal efficacy and safety profiles for COVID-19 vaccines.

MERS-CoV Spike Protein Vaccine and Inactivated Influenza Vaccine Formulated with Single Strand RNA Adjuvant Induce T-Cell Activation through Intranasal Immunization in Mice

The effectiveness of vaccines is enhanced by adding adjuvants. Furthermore, the selection of an inoculation route depends on the type of adjuvant used and is important for achieving optimum vaccine efficacy. We investigated the immunological differences between two types of vaccines—spike protein from the Middle East respiratory syndrome virus and inactivated influenza virus vaccine, in combination with a single-stranded RNA adjuvant—administered through various routes (intramuscular, intradermal, and intranasal) to BALB/c mice. Intramuscular immunization with the RNA adjuvant-formulated spike protein elicited the highest humoral immune response, characterized by IgG1 and neutralizing antibody production. Although intranasal immunization did not elicit a humoral response, it showed extensive T-cell activation through large-scale induction of interferon-γ- and interleukin-2-secreting cells, as well as CD4+ T-cell activation in mouse splenocytes. Moreover, only intranasal immunization induced IgA production. When immunized with the inactivated influenza vaccine, administration of the RNA adjuvant via all routes led to protection after viral challenge, regardless of the presence of a vaccine-specific antibody. Therefore, the inoculation route should depend on the type of immune response needed; i.e., the intramuscular route is suitable for eliciting a humoral immune response, whereas the intranasal route is useful for T-cell activation and IgA induction.

Nanoformulated Single-Stranded RNA-Based Adjuvant with a Coordinative Amphiphile as an Effective Stabilizer: Inducing Humoral Immune Response by Activation of Antigen-Presenting Cells

As agonists of TLR7/8, single-stranded RNAs (ssRNAs) are safe and promising adjuvants that do not cause off-target effects or innate immune overactivation. However, low stability prevents them from mounting sufficient immune responses. This study evaluates the adjuvant effects of ssRNA derived from the cricket paralysis virus intergenic region internal ribosome entry site, formulated as nanoparticles with a coordinative amphiphile, containing a zinc/dipicolylamine complex moiety as a coordinative phosphate binder, as a stabilizer for RNA-based adjuvants. The nanoformulated ssRNA adjuvant was resistant to enzymatic degradation in vitro and in vivo, and that with a coordinative amphiphile bearing an oleyl group (CA-O) was approximately 100 nm, promoted effective recognition, and improved activation of antigen-presenting cells, leading to better induction of neutralizing antibodies following single immunization. Hence, CA-O may increase the efficacy of ssRNA-based adjuvants, proving useful to meet the urgent need for vaccines during pathogen outbreaks.

Evaluation of glycoprotein E subunit and live attenuated varicella-zoster virus vaccines formulated with a single-strand RNA-based adjuvant

Introduction

Varicella‐zoster virus (VZV), a human alphaherpesvirus 3, elicits both chickenpox and shingles and/or postherpetic neuralgia. A live attenuated vaccine (LAV) and glycoprotein E (gE) subunit vaccine were developed to prevent VZV‐induced diseases. We recently reported that single‐strand RNA (ssRNA) based on the intergenic region of the internal ribosome entry site of cricket paralysis virus (CrPV) is an effective adjuvant for protein‐based and virus‐like particle‐based vaccines. Here, Chinese hamster ovary expression system and an LAV from Oka/SK strains.

Methods

We appraised the adjuvant effect of the same CrPV ssRNA encoding the gE gene formulated in the two vaccines using VZV‐primed C57BL/6 mice and guinea pigs. Humoral immunity and cell‐mediated immunity were assessed by enzyme‐linked immunosorbent assay (ELISA) and ELISPOT in gE subunit vaccine and by ELISA and fluorescent antibody to membrane antigen in LAV.

Results

The gE subunit vaccine‐induced gE‐specific antibodies and CD4⁺ T‐cell responses (indicated by interferon‐γ [IFN‐γ] and interleukin‐2 secretion) in the ssRNA‐based adjuvant containing the VZV gE gene. Therefore, an ssRNA adjuvant combined with gE antigen can trigger the innate immune response and induce an adaptive immune response to ultimately activate humoral and cell‐mediated responses. VZV LAV could also induce VZV‐specific antibodies and IFN‐γ stimulated by LAV, whereas the effect of ssRNA as a vaccine adjuvant could not be confirmed. However, the ssRNA adjuvant increased VZV‐specific neutralizing antibody response.

Conclusions

Taken together, these results highlight that the gE subunit vaccine and LAV developed in this study can be functional VZV vaccines, and ssRNAs appear to function better as adjuvants in a subunit vaccine than in an LAV.

Comprehensive Analysis of the Safety Profile of a Single-Stranded RNA Nano-Structure Adjuvant

Adjuvants enhance the efficacy of vaccines by stimulating immune response-related gene expression and pathways. Although some adjuvants have been approved for commercial use in human vaccines (e.g., Alum, MF59, and AS03), they might elicit adverse side effects, such as autoimmune diseases. Recently, we developed a novel single-stranded RNA (ssRNA) nano-structure adjuvant, which can stimulate both Th1 and Th2 responses. In this study, we evaluated the safety and toxicological profiles of this ssRNA nano-structure adjuvant in vitro and in vivo. Mice were intramuscularly immunized with the ssRNA nano-structure adjuvant three times, once every 2 weeks. The results indicate no significant differences in hematological and serum biochemistry parameters between the ssRNA-treated groups and the control group. From a histopathological perspective, no evidence of tissue damage was found in any group. The levels of IgE and anti-nuclear antibodies, which are markers of autoimmune disease, were not different between the ssRNA-treated groups and the control group. The findings of this study suggest that the ssRNA nano-structure can be used as a safe adjuvant to increase vaccine efficacies.