Polymeric Pathogen-Like Particles-Based Combination Adjuvants Elicit Potent Mucosal T Cell Immunity to Influenza A Virus

Overview of Antimicrobial Biodegradable Polyester-Based Formulations

As the clinical complications induced by microbial infections are known to have life-threatening side effects, conventional anti-infective therapy is necessary, but not sufficient to overcome these issues. Some of their limitations are connected to drug-related inefficiency or resistance and pathogen-related adaptive modifications. Therefore, there is an urgent need for advanced antimicrobials and antimicrobial devices. A challenging, yet successful route has been the development of new biostatic or biocide agents and biomaterials by considering the indisputable advantages of biopolymers. Polymers are attractive materials due to their physical and chemical properties, such as compositional and structural versatility, tunable reactivity, solubility and degradability, and mechanical and chemical tunability, together with their intrinsic biocompatibility and bioactivity, thus enabling the fabrication of effective pharmacologically active antimicrobial formulations. Besides representing protective or potentiating carriers for conventional drugs, biopolymers possess an impressive ability for conjugation or functionalization. These aspects are key for avoiding malicious side effects or providing targeted and triggered drug delivery (specific and selective cellular targeting), and generally to define their pharmacological efficacy. Moreover, biopolymers can be processed in different forms (particles, fibers, films, membranes, or scaffolds), which prove excellent candidates for modern anti-infective applications. This review contains an overview of antimicrobial polyester-based formulations, centered around the effect of the dimensionality over the properties of the material and the effect of the production route or post-processing actions.

Enhancing the protection of influenza virus vaccines with BECC TLR4 adjuvant in aged mice

Influenza A virus (IAV) is a leading cause of respiratory disease worldwide often resulting in severe morbidity and mortality. We have previously shown that the Bacterial Enzymatic Combinatorial Chemistry (BECC) adjuvants, BECC438 and BECC470, formulated with an influenza virus hemagglutinin (HA) protein vaccine, offer greater protection from influenza virus challenge in mouse respiratory models using adult mice than standard HA:adjuvant combinations. In this study, we determined that immunization with HA + BECC adjuvants also significantly broadened the epitopes targeted on HA as compared with other adjuvants, resulting in increased titers of antibodies directed against the highly conserved HA stalk domain. Importantly, we demonstrate that BECC470 combined with an influenza virus HA protein antigen in a prime-only immunization regimen was able to achieve complete protection from challenge in a ~ 12-month-old mouse aged model. Together, this demonstrates the heightened protection provided by the BECC470 adjuvant in an influenza virus vaccine model and shows the enhanced immune response, as compared to other adjuvants elicited by the formulation of HA with BECC470.

Development and Evaluation of a Novel Diammonium Glycyrrhizinate Phytosome for Nasal Vaccination

The objective of the present research was to formulate diammonium glycyrrhizinate (DG) into phytosomes (DG-P) to induce nasal immune responses and enhance absorption. Plackett- Burman design was used for process optimization, incorporating specific formulation and process variables to obtain the optimal parameters. Fourier transform infrared spectroscopy (FTIR), X-ray power diffraction (P-XRD), and transmission electron microscopy (TEM) were used for characterization. The adjuvant activity of the DG-P was evaluated by using bone marrow dendritic cells. In vitro nasal mucosal permeation and in situ nasal perfusion were also investigated to evaluate nasal absorption. The DG phytosomes were in the size range of 20~30 nm and zeta-potential range of −30~−40 mV. DG-P demonstrated 4.2-fold increased solubility in n-octanol. Coculturing bone marrow dendritic cells with DG-P led to enhanced dendritic cell maturation. Apparent permeability coefficient of the phytosomal formulation was almost four times higher than that of free DG determined by ex vivo permeation studies on excised porcine mucosa. In situ nasal perfusion studies in rats demonstrated that the nasal absorption of DG-P was significantly higher than that of free DG. Conclusively, the results confirmed that DG-P have potential for use as an adjuvant for nasal vaccine.

Vaccine adjuvants to engage the cross-presentation pathway

Adjuvants are indispensable components of vaccines for stimulating optimal immune responses to non-replicating, inactivated and subunit antigens. Eliciting balanced humoral and T cell-mediated immunity is paramount to defend against diseases caused by complex intracellular pathogens, such as tuberculosis, malaria, and AIDS. However, currently used vaccines elicit strong antibody responses, but poorly stimulate CD8 cytotoxic T lymphocyte (CTL) responses. To elicit potent CTL memory, vaccines need to engage the cross-presentation pathway, and this requirement has been a crucial bottleneck in the development of subunit vaccines that engender effective T cell immunity. In this review, we focus on recent insights into DC cross-presentation and the extent to which clinically relevant vaccine adjuvants, such as aluminum-based nanoparticles, water-in oil emulsion (MF59) adjuvants, saponin-based adjuvants, and Toll-like receptor (TLR) ligands modulate DC cross-presentation efficiency. Further, we discuss the feasibility of using carbomer-based adjuvants as next generation of adjuvant platforms to elicit balanced antibody- and T-cell based immunity. Understanding of the molecular mechanism of DC cross-presentation and the mode of action of adjuvants will pave the way for rational design of vaccines for infectious diseases and cancer that require balanced antibody- and T cell-based immunity.

Nasal Nanovaccines for SARS-CoV-2 to Address COVID-19

COVID-19 is still prevalent around the globe. Although some SARS-CoV-2 vaccines have been distributed to the population, the shortcomings of vaccines and the continuous emergence of SARS-CoV-2 mutant virus strains are a cause for concern. Thus, it is vital to continue to improve vaccines and vaccine delivery methods. One option is nasal vaccination, which is more convenient than injections and does not require a syringe. Additionally, stronger mucosal immunity is produced under nasal vaccination. The easy accessibility of the intranasal route is more advantageous than injection in the context of the COVID-19 pandemic. Nanoparticles have been proven to be suitable delivery vehicles and adjuvants, and different NPs have different advantages. The shortcomings of the SARS-CoV-2 vaccine may be compensated by selecting or modifying different nanoparticles. It travels along the digestive tract to the intestine, where it is presented by GALT, tissue-resident immune cells, and gastrointestinal lymph nodes. Nasal nanovaccines are easy to use, safe, multifunctional, and can be distributed quickly, demonstrating strong prospects as a vaccination method for SARS-CoV-2, SARS-CoV-2 variants, or SARS-CoV-n.

T Cell/B Cell Interactions in the Establishment of Protective Immunity

Follicular helper T cells (Tfh) are the T cell subset providing help to B cells for the generation of high-affinity antibodies and are therefore of key interest for the development of vaccination strategies against infectious diseases. In this review, we will discuss how the generation of Tfh cells and their interaction with B cells in secondary lymphoid organs can be optimized for therapeutic purposes. We will summarize different T cell subsets including Tfh-like peripheral helper T cells (Tph) capable of providing B cell help. In particular, we will highlight the novel concept of T cell/B cell interaction in non-lymphoid tissues as an important element for the generation of protective antibodies directly at the site of pathogen invasion.

CCR2 Regulates Vaccine-Induced Mucosal T-Cell Memory to Influenza A Virus

Elicitation of lung tissue-resident memory CD8 T cells (T_RMs) is a goal of T cell-based vaccines against respiratory viral pathogens, such as influenza A virus (IAV). C-C chemokine receptor type 2 (CCR2)-dependent monocyte trafficking plays an essential role in the establishment of CD8 T_RMs in lungs of IAV-infected mice. Here, we used a combination adjuvant-based subunit vaccine strategy that evokes multifaceted (T_C1/T_C17/T_H1/T_H17) IAV nucleoprotein-specific lung T_RMs to determine whether CCR2 and monocyte infiltration are essential for vaccine-induced T_RM development and protective immunity to IAV in lungs. Following intranasal vaccination, neutrophils, monocytes, conventional dendritic cells (DCs), and monocyte-derived dendritic cells internalized and processed vaccine antigen in lungs. We found that basic leucine zipper ATF-like transcription factor 3 (BATF3)-dependent DCs were essential for eliciting T cell responses, but CCR2 deficiency enhanced the differentiation of CD127^hi, KLRG-1^lo, OX40^+ve CD62L^+ve, and mucosally imprinted CD69^+ve CD103^+ve effector and memory CD8 T cells in lungs and airways of vaccinated mice. Mechanistically, increased development of lung T_RMs induced by CCR2 deficiency was linked to dampened expression of T-bet but not altered TCF-1 levels or T cell receptor signaling in CD8 T cells. T1/T17 functional programming, parenchymal localization of CD8/CD4 effector and memory T cells, recall T cell responses, and protective immunity to a lethal IAV infection were unaffected in CCR2-deficient mice. Taken together, we identified a negative regulatory role for CCR2 and monocyte trafficking in mucosal imprinting and differentiation of vaccine-induced T_RMs. Mechanistic insights from this study may aid the development of T-cell-based vaccines against respiratory viral pathogens, including IAV and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). IMPORTANCE While antibody-based immunity to influenza A virus (IAV) is type and subtype specific, lung- and airway-resident memory T cells that recognize conserved epitopes in the internal viral proteins are known to provide heterosubtypic immunity. Hence, broadly protective IAV vaccines need to elicit robust T cell memory in the respiratory tract. We have developed a combination adjuvant-based IAV nucleoprotein vaccine that elicits strong CD4 and CD8 T cell memory in lungs and protects against H1N1 and H5N1 strains of IAV. In this study, we examined the mechanisms that control vaccine-induced protective memory T cells in the respiratory tract. We found that trafficking of monocytes into lungs might limit the development of antiviral lung-resident memory T cells following intranasal vaccination. These findings suggest that strategies that limit monocyte infiltration can potentiate vaccine-induced frontline T-cell immunity to respiratory viruses, such as IAV and SARS-CoV-2.