Polymeric cGAMP microparticles affect the immunogenicity of a broadly active influenza mRNA lipid nanoparticle vaccine.

Influenza outbreaks are a major burden worldwide annually. While seasonal vaccines do provide protection against infection, they are limited in that they need to be updated every year to account for the constantly mutating virus. Recently, lipid nanoparticles (LNPs) encapsulating mRNA have seen major success as a vaccine platform for SARS-CoV-2. Herein, we applied LNPs to deliver an mRNA encoding a computationally optimized broadly active (COBRA) influenza immunogen. These COBRA mRNA LNPs induced a broadly active neutralizing antibody response and protection after lethal influenza challenge. To further increase the immunogenicity of the COBRA mRNA LNPs, we combined them with acetalated dextran microparticles encapsulating a STING agonist. Contrary to recent findings, the STING agonist decreased the immunogenicity of the COBRA mRNA LNPs which was likely due to a decrease in mRNA translation as shown in vitro. Overall, this work aids in future selection of adjuvants to use with mRNA LNP vaccines.

Enhancement of subunit vaccine delivery with zinc-carnosine coordination polymer through the addition of mannan.

Vaccines represent a pivotal health advancement for preventing infection. However, because carrier systems with repeated administration can invoke carrier-targeted immune responses that diminish subsequent immune responses (e.g., PEG antibodies), there is a continual need to develop novel vaccine platforms. Zinc carnosine microparticles (ZnCar MPs), which are composed of a one-dimensional coordination polymer formed between carnosine and the metal ion zinc, have exhibited efficacy in inducing an immune response against influenza. However, ZnCar MPs' limited suspendability hinders clinical application. In this study, we address this issue by mixing mannan, a polysaccharide derived from yeast, with ZnCar MPs. We show that the addition of mannan increases the suspendability of this promising vaccine formulation. Additionally, since mannan is an adjuvant, we illustrate that the addition of mannan increases the antibody response and T cell response when mixed with ZnCar MPs. Mice vaccinated with mannan + OVA/ZnCar MPs had elevated serum IgG and IgG1 levels in comparison to vaccination without mannan. Moreover, in the mannan + OVA/ZnCar MPs vaccinated group, mucosal washes demonstrated increased IgG, IgG1, and IgG2c titers, and antigen recall assays showed enhanced IFN-γ production in response to MHC-I and MHC-II immunodominant peptide restimulation, compared to the vaccination without mannan. These findings suggest that the use of mannan mixed with ZnCar MPs holds potential for subunit vaccination and its improved suspendability further promotes clinical translation.

Immunogenicity of an adjuvanted broadly active influenza vaccine in immunocompromised and diverse populations.

Influenza virus outbreaks are a major burden worldwide each year. Current vaccination strategies are inadequate due to antigenic drift/shift of the virus and the elicitation of low immune responses. The use of computationally optimized broadly reactive antigen (COBRA) hemagglutinin (HA) immunogens subvert the constantly mutating viruses; however, they are poorly immunogenic on their own. To increase the immunogenicity of subunit vaccines such as this, adjuvants can be delivered with the vaccine. For example, agonists of the stimulator of interferon genes (STING) have proven efficacy as vaccine adjuvants. However, their use in high-risk populations most vulnerable to influenza virus infection has not been closely examined. Here, we utilize a vaccine platform consisting of acetalated dextran microparticles loaded with COBRA HA and the STING agonist cyclic GMP-AMP. We examine the immunogenicity of this platform in mouse models of obesity, aging, and chemotherapy-induced immunosuppression. Further, we examine vaccine efficacy in collaborative cross mice, a genetically diverse population that mimics human genetic heterogeneity. Overall, this vaccine platform had variable efficacy in these populations supporting work to better tailor adjuvants to specific populations.

Multi-COBRA hemagglutinin formulated with cGAMP microparticles elicit protective immune responses against influenza viruses.

Influenza viruses cause a common respiratory disease known as influenza. In humans, seasonal influenza viruses can lead to epidemics, with avian influenza viruses of particular concern because they can infect multiple species and lead to unpredictable and severe disease. Therefore, there is an urgent need for a universal influenza vaccine that provides protection against seasonal and pre-pandemic influenza virus strains. The cyclic GMP-AMP (cGAMP) is a promising adjuvant for subunit vaccines that promotes type I interferons production through the stimulator of interferon genes (STING) pathway. The encapsulation of cGAMP in acetalated dextran (Ace-DEX) microparticles (MPs) enhances its intracellular delivery. In this study, the Computationally Optimized Broadly Reactive Antigen (COBRA) methodology was used to generate H1, H3, and H5 vaccine candidates. Monovalent and multivalent COBRA HA vaccines formulated with cGAMP Ace-DEX MPs were evaluated in a mouse model for antibody responses and protection against viral challenge. Serological analysis showed that cGAMP MPs adjuvanted monovalent and multivalent COBRA vaccines elicited robust antigen-specific antibody responses after a prime-boost vaccination and antibody titers were further enhanced after second boost. Compared to COBRA vaccine groups with no adjuvant or blank MPs, the cGAMP MPs enhanced HAI antibody responses against COBRA vaccination. The HAI antibody titers were not significantly different between cGAMP MPs adjuvanted monovalent and multivalent COBRA vaccine groups for most of the viruses tested in panels. The cGAMP MPs adjuvanted COBRA vaccines groups had higher antigen-specific IgG2a binding titers than the COBRA vaccine groups with no adjuvant or blank MPs. The COBRA vaccines formulated with cGAMP MPs mitigated disease caused by influenza viral challenge and decreased pulmonary viral titers in mice. Therefore, the formulation of COBRA vaccines plus cGAMP MPs is a promising universal influenza vaccine that elicits protective immune responses against human seasonal and pre-pandemic strains.

Comparative study of acetalated-dextran microparticle fabrication methods for a clinically translatable subunit-based influenza vaccine.

The most common influenza vaccines are inactivated viruses produced in chicken eggs, which is a time-consuming production method with variable efficacy due to mismatches of the vaccine strains to the dominant circulating strains. Subunit-based vaccines provide faster production times in comparison to the traditional egg-produced vaccines but often require the use of an adjuvant to elicit a highly protective immune response. However, the current FDA approved adjuvant for influenza vaccines (MF59) elicits a primarily helper T-cell type 2 (Th2)-biased humoral immune response. Adjuvants that can stimulate a Th1 cellular response are correlated to have more robust protection against influenza. The cyclic dinucleotide cGAMP has been shown to provide a potent Th1 response but requires the use of a delivery vehicle to best initiate its signalling pathway in the cytosol. Herein, acetalated dextran (Ace-DEX) was used as the polymer to fabricate microparticles (MPs) via double-emulsion, electrospray, and spray drying methods to encapsulate cGAMP. This study compared each fabrication method's ability to encapsulate and retain the hydrophilic adjuvant cGAMP. We compared their therapeutic efficacy to Addavax, an MF59-like adjuvant, and cGAMP Ace-DEX MPs provided a stronger Th1 response in vaccinated BALB/c mice. Furthermore, we compared Ace-DEX MPs to spray dried MPs composed from a commonly used polymer for drug delivery, poly(lactic-co-glycolic acid) (PLGA). We observed that all Ace-DEX MPs elicited similar humoral and cellular responses to the PLGA MPs. Overall, the results shown here indicate Ace-DEX can perform similarly to PLGA as a polymer for drug delivery and that spray drying can provide an efficient way to produce MPs to encapsulate cGAMP and stimulate the immune system.

Zinc Carnosine Metal-Organic Coordination Polymer as a Potent Broadly Active Influenza Vaccine Platform with In Vitro Shelf-Stability.

Current seasonal influenza vaccines are limited in that they need to be reformulated every year in order to account for the constant mutation of the virus. Hemagglutinin (HA) immunogens have been developed using a computationally optimized broadly reactive antigen (COBRA) methodology, which are able to elicit an antibody response that neutralizes antigenically distinct influenza strains; however, subunit proteins are not immunogenic enough on their own to generate a substantial immune response. Due to this, different delivery strategies and adjuvants can be used to improve immunogenicity. Recently, we reported a new coordination polymer composed of the dipeptide carnosine and zinc (ZnCar) that is able to deliver protein antigens along with CpG to generate a potent immune response. In the present work, ZnCar was used to deliver the COBRA HA immunogen Y2 and the adjuvant CpG. We incorporated Y2 into ZnCar using two different methods to assess which would be the most immunogenic. Mice vaccinated with Y2 and CpG complexed with ZnCar showed an improved humoral and cellular response when compared to mice vaccinated with soluble Y2 and CpG. Further, we demonstrate in vitro that when Y2 and CpG are coordinated with ZnCar, they are protected from degradation at 40 °C for 3 months or 24 °C for 6 months. Overall, ZnCar shows promise as a delivery vehicle for subunit vaccines, given its superior immunogenicity and in vitro storage stability.

Development of a broadly active influenza intranasal vaccine adjuvanted with self-assembled particles composed of mastoparan-7 and CpG.

Currently licensed vaccine adjuvants offer limited mucosal immunity, which is needed to better combat respiratory infections such as influenza. Mast cells (MCs) are emerging as a target for a new class of mucosal vaccine adjuvants. Here, we developed and characterized a nanoparticulate adjuvant composed of an MC activator [mastoparan-7 (M7)] and a TLR ligand (CpG). This novel nanoparticle (NP) adjuvant was co-formulated with a computationally optimized broadly reactive antigen (COBRA) for hemagglutinin (HA), which is broadly reactive against influenza strains. M7 was combined at different ratios with CpG and tested for in vitro immune responses and cytotoxicity. We observed significantly higher cytokine production in dendritic cells and MCs with the lowest cytotoxicity at a charge-neutralizing ratio of nitrogen/phosphate = 1 for M7 and CpG. This combination formed spherical NPs approximately 200 nm in diameter with self-assembling capacity. Mice were vaccinated intranasally with COBRA HA and M7-CpG NPs in a prime-boost-boost schedule. Vaccinated mice had significantly higher antigen-specific antibody responses (IgG and IgA) in serum and mucosa compared with controls. Splenocytes from vaccinated mice had significantly increased cytokine production upon antigen recall and the presence of central and effector memory T cells in draining lymph nodes. Finally, co-immunization with NPs and COBRA HA induced influenza H3N2-specific HA inhibition antibody titers across multiple strains and partially protected mice from a challenge against an H3N2 virus. These results illustrate that the M7-CpG NP adjuvant combination can induce a protective immune response with a broadly reactive influenza antigen via mucosal vaccination.

Delivery of small molecule mast cell activators for West Nile Virus vaccination using acetalated dextran microparticles.

Recently, there has been increasing interest in the activation of mast cells to promote vaccine efficacy. Several mast cell activating (MCA) compounds have been reported such as M7 and Compound 48/80 (C48/80). While these MCAs have been proven to be efficacious vaccine adjuvants, their translatability is limited by batch-to-batch variability, challenging large-scale manufacturing, and poor in vivo stability for the M7 peptide. Due to this, high throughput screening was performed to identify small molecule MCAs. Several potent MCAs were identified via this screening, but the in vivo translatability of the compounds was limited due to their poor aqueous solubility. To enhance the delivery of these MCAs we encapsulated them in acetalated dextran (Ace-DEX) microparticles (MPs). We have previously utilized Ace-DEX MPs for vaccine delivery due to their passive targeting to phagocytic cells, acid sensitivity, and tunable degradation. Four different MCA loaded MPs were combined with West Nile Virus Envelope III protein (EDIII) and their vaccine adjuvant activities were compared in vivo. MPs containing the small molecule MCA ST101036 produced the highest anti-EDIII IgG titers of all the MCAs tested. Further, ST101036 MPs produced higher titers than ST101036 formulated with PEG as a cosolvent which highlights the benefit of Ace-DEX MPs over a conventional formulation technique. Finally, in a mouse model of West Nile Virus infection ST101036 MPs produced similar survival to soluble M7 (80-90%). Overall, these data show that ST101036 MPs produce a robust antibody response against EDIII and survival emphasizing the benefits of using Ace-DEX as a delivery platform for the poorly soluble ST101036.

Preclinical developments in the delivery of protein antigens for vaccination.

INTRODUCTION: Vaccine technology has constantly advanced since its origin. One of these advancements is where purified parts of a pathogen are used rather than the whole pathogen. Subunit vaccines have no chance of causing disease; however, alone these antigens are often poorly immunogenic. Therefore, they can be paired with immune stimulating adjuvants. Further, subunits can be combined with delivery strategies such as nano/microparticles to enrich their delivery to organs and cells of interest as well as protect them from in vivo degradation. Here, we seek to highlight some of the more promising delivery strategies for protein antigens. AREAS COVERED: We present a brief description of the different types of vaccines, clinically relevant examples, and their disadvantages when compared to subunit vaccines. Also, specific preclinical examples of delivery strategies for protein antigens. EXPERT OPINION: Subunit vaccines provide optimal safety given that they have no risk of causing disease; however, they are often not immunogenic enough on their own to provide protection. Advanced delivery systems are a promising avenue to increase the immunogenicity of subunit vaccines, but scalability and stability can be improved. Further, more research is warranted on systems that promote a mucosal immune response to provide better protection against infection.

Vinyl Sulfone-functionalized Acetalated Dextran Microparticles as a Subunit Broadly Acting Influenza Vaccine.

Influenza is a global health concern with millions of infections occurring yearly. Seasonal flu vaccines are one way to combat this virus; however, they are poorly protective against influenza as the virus is constantly mutating, particularly at the immunodominant hemagglutinin (HA) head group. A more broadly acting approach involves Computationally Optimized Broadly Reactive Antigen (COBRA). COBRA HA generates a broad immune response that is capable of protecting against mutating strains. Unfortunately, protein-based vaccines are often weekly immunogenic, so to help boost the immune response, we employed the use of acetalated dextran (Ace-DEX) microparticles (MPs) two ways: one to conjugate COBRA HA to the surface and a second to encapsulate cGAMP. To conjugate the COBRA HA to the surface of the Ace-DEX MPs, a poly(L-lactide)-polyethylene glycol co-polymer with a vinyl sulfone terminal group (PLLA-PEG-VS) was used. MPs encapsulating the STING agonist cGAMP were co-delivered with the antigen to form a broadly active influenza vaccine. This vaccine approach was evaluated in vivo with a prime-boost-boost vaccination schedule and illustrated generation of a humoral and cellular response that could protect against a lethal challenge of A/California/07/2009 in BALB/c mice.

ZipperCells Exhibit Enhanced Accumulation and Retention at the Site of Myocardial Infarction.

There has been extensive interest in cellular therapies for the treatment of myocardial infarction, but bottlenecks concerning cellular accumulation and retention remain. Here, a novel system of in situ crosslinking mesenchymal stem cells (MSCs) for the formation of a living depot at the infarct site is reported. Bone marrow-derived mesenchymal stem cells that are surface decorated with heterodimerizing leucine zippers, termed ZipperCells, are engineered. When delivered intravenously in sequential doses, it is demonstrated that ZipperCells can migrate to the infarct site, crosslink, and show ≈500% enhanced accumulation and ≈600% improvement in prolonged retention at 10 days after injection compared to unmodified MSCs. This study introduces an advanced approach to creating noninvasive therapeutics depots using cellular crosslinking and provides the framework for future scaffold-free delivery methods for cardiac repair.

Nano/microparticle Formulations for Universal Influenza Vaccines.

Influenza affects millions of people worldwide and can result in severe sickness and even death. The best method of prevention is vaccination; however, the seasonal influenza vaccine often suffers from low efficacy and requires yearly vaccination due to changes in strain and viral mutations. More conserved universal influenza antigens like M2 ectodomain (M2e) and the stalk region of hemagglutinin (HA stalk) have been used clinically but often suffer from low antigenicity. To increase antigenicity, universal antigens have been formulated using nano/microparticles as vaccine carriers against influenza. Utilizing polymers, liposomes, metal, and protein-based particles, indicators of immunity and protection in mouse, pig, ferrets, and chicken models of influenza have been shown. In this review, seasonal and universal influenza vaccine formulations comprised of these materials including their physiochemical properties, fabrication, characterization, and biologic responses in vivo are highlighted. The review is concluded with future perspectives for nano/microparticles as carrier systems and other considerations within the universal influenza vaccine delivery landscape. Graphical Abstract.