Augmented humoral and cellular immune response of hepatitis B virus DNA vaccine by micro-needle vaccination using Flt3L as an adjuvant

Microarray patches: scratching the surface of vaccine delivery

INTRODUCTION

Microneedles are emerging as a promising technology for vaccine delivery, with numerous advantages over traditional needle and syringe methods. Preclinical studies have demonstrated the effectiveness of MAPs in inducing robust immune responses over traditional needle and syringe methods, with extensive studies using vaccines targeted against different pathogens in various animal models. Critically, the clinical trials have demonstrated safety, immunogenicity, and patient acceptance for MAP-based vaccines against influenza, measles, rubella, and SARS-CoV-2.

AREAS COVERED

This review provides a comprehensive overview of the different types of microarray patches (MAPs) and analyses of their applications in preclinical and clinical vaccine delivery settings. This review also covers additional considerations for microneedle-based vaccination, including adjuvants that are compatible with MAPs, patient safety and factors for global vaccination campaigns.

EXPERT OPINION

MAP vaccine delivery can potentially be a game-changer for vaccine distribution and coverage in both high-income and low- and middle-income countries. For MAPs to reach this full potential, many critical hurdles must be overcome, such as large-scale production, regulatory compliance, and adoption by global health authorities. However, given the considerable strides made in recent years by MAP developers, it may be possible to see the first MAP-based vaccines in use within the next 5 years.

Advance in strategies to build efficient vaccines against tuberculosis

Tuberculosis is a chronic consumptive infectious disease, which can cause great damage to human and animal health all over the world. The emergence of multi-drug resistant strains, the unstable protective effect of Bacillus Calmette-Guérin (BCG) vaccine on adults, and the mixed infection with HIV all warn people to exploit new approaches for conquering tuberculosis. At present, there has been significant progress in developing tuberculosis vaccines, such as improved BCG vaccine, subunit vaccine, DNA vaccine, live attenuated vaccine and inactivated vaccine. Among these candidate vaccines, there are some promising vaccines to improve or replace BCG vaccine effect. Meanwhile, the application of adjuvants, prime-boost strategy, immunoinformatic tools and targeting components have been studied concentratedly, and verified as valid means of raising the efficiency of tuberculosis vaccines as well. In this paper, the latest advance in tuberculosis vaccines in recent years is reviewed to provide reliable information for future tuberculosis prevention and treatment.

Acute effects of FLT3L treatment on T cells in intact mice

Peripheral T cells express a diverse repertoire of antigen-specific receptors, which together protect against the full range of pathogens. In this context, the total repertoire of memory T cells which are maintained by trophic signals, long after pathogen clearance, is critical. Since these trophic factors include cytokines and self-peptide-MHC, both of which are available from endogenous antigen-presenting cells (APC), we hypothesized that enhancing APC numbers in vivo can be a viable strategy to amplify the population of memory T cells. We evaluated this by acutely treating intact mice with FMS-like tyrosine kinase 3 ligand (Flt3l), which promotes expansion of APCs. Here we report that this treatment allowed for, an expansion of effector-memory CD4+ and CD8+ T cells as well as an increase in their expression of KLRG1 and CD25. In the lymph nodes and spleen, the expansion was limited to a specific CD8 (CD44-low but CD62L-) subset. Functionally, this subset is distinct from naïve T cells and could produce significant amounts of effector cytokines upon restimulation. Taken together, these data suggest that the administration of Flt3L can impact both APC turnover as well as a corresponding flux of specific subsets of CD8+ T cells in an intact peripheral immune compartment.

Microneedle systems for delivering nucleic acid drugs

Background

Nucleic acid-based gene therapy is a promising technology that has been used in various applications such as novel vaccination platforms for infectious/cancer diseases and cellular reprogramming because of its fast, specific, and effective properties. Despite its potential, the parenteral nucleic acid drug formulation exhibits instability and low efficacy due to various barriers, such as stability concerns related to its liquid state formulation, skin barriers, and endogenous nuclease degradation. As promising alternatives, many attempts have been made to perform nucleic acid delivery using a microneedle system. With its minimal invasiveness, microneedle can deliver nucleic acid drugs with enhanced efficacy and improved stability.

Area covered

This review describes nucleic acid medicines' current state and features and their delivery systems utilizing non-viral vectors and physical delivery systems. In addition, different types of microneedle delivery systems and their properties are briefly reviewed. Furthermore, recent advances of microneedle-based nucleic acid drugs, including featured vaccination applications, are described.

Expert opinion

Nucleic acid drugs have shown significant potential beyond the limitation of conventional small molecules, and the current COVID-19 pandemic highlights the importance of nucleic acid therapies as a novel vaccination platform. Microneedle-mediated nucleic acid drug delivery is a potential platform for less invasive nucleic acid drug delivery. Microneedle system can show enhanced efficacy, stability, and improved patient convenience through self-administration with less pain.

Microarray patches enable the development of skin-targeted vaccines against COVID-19

The COVID-19 pandemic is a serious threat to global health and the global economy. The ongoing race to develop a safe and efficacious vaccine to prevent infection by SARS-CoV-2, the causative agent for COVID-19, highlights the importance of vaccination to combat infectious pathogens. The highly accessible cutaneous microenvironment is an ideal target for vaccination since the skin harbors a high density of antigen-presenting cells and immune accessory cells with broad innate immune functions. Microarray patches (MAPs) are an attractive intracutaneous biocargo delivery system that enables safe, reproducible, and controlled administration of vaccine components (antigens, with or without adjuvants) to defined skin microenvironments. This review describes the structure of the SARS-CoV-2 virus and relevant antigenic targets for vaccination, summarizes key concepts of skin immunobiology in the context of prophylactic immunization, and presents an overview of MAP-mediated cutaneous vaccine delivery. Concluding remarks on MAP-based skin immunization are provided to contribute to the rational development of safe and effective MAP-delivered vaccines against emerging infectious diseases, including COVID-19.

Progress in microneedle array patch (MAP) for vaccine delivery

A microneedle array patch (MAP) has been developed as a new delivery system for vaccines. Preclinical and clinical trials with a vaccine MAP showed improved stability, safety, and immunological efficacy compared to conventional vaccine administration. Various vaccines can be delivered with a MAP. Currently, microneedle manufacturers can mass-produce pharmaceutical MAP and cosmetic MAP and this mass-production system can be adapted to produce a vaccine MAP. Clinical trials with a vaccine MAP have shown comparable efficacy with conventional administration, and discussions about regulations for a vaccine MAP are underway. However, there are concerns of reasonable cost, mass production, efficacy, and safety standards that meet FDA approval, as well as the need for feedback regarding the best method of administration. Currently, microneedles have been studied for the delivery of many kinds of vaccines, and preclinical and clinical studies of vaccine microneedles are in progress. For the foreseeable future, some vaccines will continue to be administered with syringes and needles while the use of a vaccine MAP continues to be improved because of the advantages of less pain, self-administration, improved stability, convenience, and safety.

A Recombinant Rabies Virus Expressing Fms-like Tyrosine Kinase 3 Ligand (Flt3L) Induces Enhanced Immunogenicity in Mice

Rabies is a zoonotic disease that still causes 59,000 human deaths each year, and rabies vaccine is the most effective way to control the disease. Our previous studies suggested that the maturation of DC plays an important role in enhancing the immunogenicity of rabies vaccine. Flt3L has been reported to own the ability to accelerate the DC maturation, therefore, in this study, a recombinant rabies virus expressing mouse Flt3L, designated as LBNSE-Flt3L, was constructed, and its immunogenicity was characterized. It was found that LBNSE-Flt3L could enhance the maturation of DC both in vitro and in vivo, and significantly more T_FH cells and Germinal Center B (GC B) cells were generated in mice immunized with LBNSE-Flt3L than those immunized with the parent virus LBNSE. Consequently, expressing of Flt3L could elevate the level of virus-neutralizing antibodies (VNA) in immunized mice which provides a better protection from a lethal rabies virus challenge. Taken together, our study extends the potential of Flt3L as a good adjuvant to develop novel rabies vaccine by enhancing the VNA production through activating the DC-T_FH-GC B axis in immunized mice.

Ratios of T-helper 2 Cells to T-helper 1 Cells and Cytokine Levels in Patients with Hepatitis B

BACKGROUND

Hepatitis B is an immune response-mediated disease. The aim of this study was to explore the differences of ratios of T-helper (Th) 2 cells to Th1 cells and cytokine levels in acute hepatitis B (AHB) patients and chronic hepatitis B virus (HBV)-infected patients in immune-tolerance and immune-active phases.

METHODS

Thirty chronic HBV-infected patients in the immune-tolerant phase (IT group) and 50 chronic hepatitis B patients in the immune-active (clearance) phase (IC group), 32 AHB patients (AHB group), and 13 healthy individuals (HI group) were enrolled in the study. Th cell proportions in peripheral blood, cytokine levels in plasma, and serum levels of HBV DNA, hepatitis B surface antigen, and hepatitis B e antigen were detected.

RESULTS

The Th1 cell percentage and Th2/Th1 ratio in the HBV infection group (including IT, IC, and AHB groups) were significantly different from those in HI group (24.10% ± 8.66% and 1.72 ± 0.61 vs. 15.16% ± 4.34% and 2.40 ± 0.74, respectively; all P < 0.001). However, there were no differences in the Th1 cell percentages and Th2/Th1 ratios among the IT, IC, and AHB groups. In HBV infection group, the median levels of Flt3 ligand (Flt3L), interferon (IFN)-γ, and interleukin (IL)-17A were significantly lower than those in HI group (29.26 pg/ml, 33.72 pg/ml, and 12.27 pg/ml vs. 108.54 pg/ml, 66.48 pg/ml, and 35.96 pg/ml, respectively; all P < 0.05). IFN-α2, IL-10, and transforming growth factor (TGF)-β2 median levels in hepatitis group (including patients in AHB and IC groups) were significantly higher than those in IT group (40.14 pg/ml, 13.58 pg/ml, and 557.41 pg/ml vs. 16.74 pg/ml, 6.80 pg/ml, and 419.01 pg/ml, respectively; all P < 0.05), while patients in hepatitis group had significant lower Flt3L level than IT patients (30.77 vs. 59.96 pg/ml, P = 0.021). Compared with IC group, patients in AHB group had significant higher median levels of IL-10, TGF-β1, and TGF-β2 (22.77 pg/ml, 10,447.00 pg/ml, and 782.28 pg/ml vs. 8.66 pg/ml, 3755.50 pg/ml, and 482.87 pg/ml, respectively; all P < 0.05).

CONCLUSIONS

Compared with chronic HBV-infected patients in immune-tolerance phase, chronic HBV-infected patients in immune-active phase and AHB patients had similar Th2/Th1 ratios, significantly higher levels of IFN-α2, IL-10, and TGF-β. AHB patients had significantly higher IL-10 and TGF-β levels than chronic HBV-infected patients in immune-active phase.

Effect of zymosan and poly (I:C) adjuvants on responses to microneedle immunization coated with whole inactivated influenza vaccine

Microneedles are the micrometer size devices used for the delivery of vaccines and biotherapeutics. In order to increase the vaccine efficacy and reduce the antigen dose, there is a significant need to find some adjuvants for the microneedle vaccination. In this study, zymosan, which is the cell wall preparation of Saccharomyces cerevisiae, or poly (I:C) was coated on a microneedle with inactivated influenza virus, and then immunized into BALB/c mouse to determine the immunogenicity, protection and synergetic effect between two adjuvants. As a result, the group administered with zymosan and vaccine antigen showed significantly stronger IgG response, HI titer and IgG subtypes without any adverse effects, compared to the group immunized with the vaccine antigen alone. Also, there were enhanced cellular immune responses in the group received adjuvant with vaccine antigen. In addition, they showed superior protection and lung viral reduction against lethal viral challenge. Taken together, this study confirms that zymosan can be used as an immunostimulant for microneedle vaccination.

Choice and Design of Adjuvants for Parenteral and Mucosal Vaccines

The existence of pathogens that escape recognition by specific vaccines, the need to improve existing vaccines and the increased availability of therapeutic (non-infectious disease) vaccines necessitate the rational development of novel vaccine concepts based on the induction of protective cell-mediated immune responses. For naive T-cell activation, several signals resulting from innate and adaptive interactions need to be integrated, and adjuvants may interfere with some or all of these signals. Adjuvants, for example, are used to promote the immunogenicity of antigens in vaccines, by inducing a pro-inflammatory environment that enables the recruitment and promotion of the infiltration of phagocytic cells, particularly antigen-presenting cells (APC), to the injection site. Adjuvants can enhance antigen presentation, induce cytokine expression, activate APC and modulate more downstream adaptive immune reactions (vaccine delivery systems, facilitating immune Signal 1). In addition, adjuvants can act as immunopotentiators (facilitating Signals 2 and 3) exhibiting immune stimulatory effects during antigen presentation by inducing the expression of co-stimulatory molecules on APC. Together, these signals determine the strength of activation of specific T-cells, thereby also influencing the quality of the downstream T helper cytokine profiles and the differentiation of antigen-specific T helper populations (Signal 3). New adjuvants should also target specific (innate) immune cells in order to facilitate proper activation of downstream adaptive immune responses and homing (Signal 4). It is desirable that these adjuvants should be able to exert such responses in the context of mucosal administered vaccines. This review focuses on the understanding of the potential working mechanisms of the most well-known classes of adjuvants to be used effectively in vaccines.

The enhanced immune response of hepatitis B virus DNA vaccine using SiO2@LDH nanoparticles as an adjuvant

Various approaches have been used to improve systemic immune response to infectious disease or virus, and DNA vaccination has been demonstrated to be one of these effective ways to elicit protective immunity against pathogens. Our previous studies showed that layered double hydroxides (LDH) nanoparticles could be efficiently taken up by the MDDCs and had an adjuvant activity for DC maturation. To further enhance the immune adjuvant activity of LDH, core-shell structure SiO2@LDH nanoparticles were synthesized with an average diameter of about 210 nm. And its high transfection efficiency in vitro was demonstrated by using GFP expression plasmid as model DNA. Exposing SiO2@LDH nanoparticles to macrophages caused a higher dose-dependent expression of IFN-γ, IL-6, CD86 and MHC II, compared with SiO2 and LDH respectively. Furthermore, in vivo immunization of BALB/c mice indicated that, DNA vaccine loaded-SiO2@LDH nanoparticles not only induced much higher serum antibody response than naked DNA vaccine and plain nanoparticles, but also obviously promoted T-cell proliferation and skewed T helper to Th1 polarization. Additionally, it was proved that the caveolae-mediated uptake of SiO2@LDH nanoparticles by macrophage lead to macrophages activation via NF-κB signaling pathway. Our results indicate that SiO2@LDH nanoparticles could serve as a potential non-viral gene delivery system.

Enhanced immune response and protective effects of nano-chitosan-based DNA vaccine encoding T cell epitopes of Esat-6 and FL against Mycobacterium tuberculosis infection

Development of a novel and effective vaccine against Mycobacterium tuberculosis (M.tb) is a challenging for preventing TB infection. In this study, a novel nanoparticle-based recombinant DNA vaccine was developed, which contains Esat-6 three T cell epitopes (Esat-6/3e) and fms-like tyrosine kinase 3 ligand (FL) genes (termed Esat-6/3e-FL), and was enveloped with chitosan (CS) nanoparticles (nano-chitosan). The immunologic and protective efficacy of the nano-chitosan-based DNA vaccine (termed nano-Esat-6/3e-FL) was assessed in C57BL/6 mice after intramuscular prime vaccination with the plasmids DNA and nasal boost with the Esat-6/3e peptides. The results showed that the immunized mice remarkably elicited enhanced T cell responses and protection against M.tb H37Rv challenge. These findings indicate that the nano-chitosan can significantly elevate the immunologic and protective effects of the DNA vaccine, and the nano-Esat-6/3e-FL is a useful vaccine for preventing M.tb infection in mice.

DNA vaccines and intradermal vaccination by DNA tattooing

Over the past two decades, DNA vaccination has been developed as a method for the induction of immune responses. However, in spite of high expectations based on their efficacy in preclinical models, immunogenicity of first generation DNA vaccines in clinical trials was shown to be poor, and no DNA vaccines have yet been licensed for human use. In recent years significant progress has been made in the development of second generation DNA vaccines and DNA vaccine delivery methods. Here we review the key characteristics of DNA vaccines as compared to other vaccine platforms, and recent insights into the prerequisites for induction of immune responses by DNA vaccines will be discussed. We illustrate the development of second generation DNA vaccines with the description of DNA tattooing as a novel DNA delivery method. This technique has shown great promise both in a small animal model and in non-human primates and is currently under clinical evaluation.