Structural Characterization of Archaeal Lipid Mucosal Vaccine Adjuvant and Delivery (AMVAD) Formulations Prepared by Different Protocols and Their Efficacy Upon Intranasal Immunization of Mice

Characterization of Systemic and Mucosal Humoral Immune Responses to an Adjuvanted Intranasal SARS-CoV-2 Protein Subunit Vaccine Candidate in Mice

Continuous viral evolution of SARS-CoV-2 has resulted in variants capable of immune evasion, vaccine breakthrough infections and increased transmissibility. New vaccines that invoke mucosal immunity may provide a solution to reducing virus transmission. Here, we evaluated the immunogenicity of intranasally administered subunit protein vaccines composed of a stabilized SARS-CoV-2 spike trimer or the receptor binding domain (RBD) adjuvanted with either cholera toxin (CT) or an archaeal lipid mucosal adjuvant (AMVAD). We show robust induction of immunoglobulin (Ig) G and IgA responses in plasma, nasal wash and bronchoalveolar lavage in mice only when adjuvant is used in the vaccine formulation. While the AMVAD adjuvant was more effective at inducing systemic antibodies against the RBD antigen than CT, CT was generally more effective at inducing overall higher IgA and IgG titers against the spike antigen in both systemic and mucosal compartments. Furthermore, vaccination with adjuvanted spike led to superior mucosal IgA responses than with the RBD antigen and produced broadly targeting neutralizing plasma antibodies against ancestral, Delta and Omicron variants in vitro; whereas adjuvanted RBD elicited a narrower antibody response with neutralizing activity only against ancestral and Delta variants. Our study demonstrates that intranasal administration of an adjuvanted protein subunit vaccine in immunologically naïve mice induced both systemic and mucosal neutralizing antibody responses that were most effective at neutralizing SARS-CoV-2 variants when the trimeric spike was used as an antigen compared to RBD.

Nasal-nanotechnology: revolution for efficient therapeutics delivery

CONTEXT

In recent years, nanotechnology-based delivery systems have gained interest to overcome the problems of restricted absorption of therapeutic agents from the nasal cavity, depending upon the physicochemical properties of the drug and physiological properties of the human nose.

OBJECTIVE

The well-tolerated and non-invasive nasal drug delivery when combined with the nanotechnology-based novel formulations and carriers, opens the way for the effective systemic and brain targeting delivery of various therapeutic agents. To accomplish competent drug delivery, it is imperative to recognize the interactions among the nanomaterials and the nasal biological environment, targeting cell-surface receptors, drug release, multiple drug administration, stability of therapeutic agents and molecular mechanisms of cell signaling involved in patho-biology of the disease under consideration.

METHODS

Quite a few systems have been successfully formulated using nanomaterials for intranasal (IN) delivery. Carbon nanotubes (CNTs), chitosan, polylactic-co-glycolic acid (PLGA) and PLGA-based nanosystems have also been studied in vitro and in vivo for the delivery of several therapeutic agents which shown promising concentrations in the brain after nasal administration.

RESULTS AND CONCLUSION

The use of nanomaterials including peptide-based nanotubes and nanogels (NGs) for vaccine delivery via nasal route is a new approach to control the disease progression. In this review, the recent developments in nanotechnology utilized for nasal drug delivery have been discussed.

Intranasal immunization with an archaeal lipid mucosal vaccine adjuvant and delivery formulation protects against a respiratory pathogen challenge

Archaeal lipid mucosal vaccine adjuvant and delivery (AMVAD) is a safe mucosal adjuvant that elicits long lasting and memory boostable mucosal and systemic immune responses to model antigens such as ovalbumin. In this study, we evaluated the potential of the AMVAD system for eliciting protective immunity against mucosal bacterial infections, using a mouse model of intranasal Francisella tularensis LVS (LVS) challenge. Intranasal immunization of mice with cell free extract of LVS (LVSCE) adjuvanted with the AMVAD system (LVSCE/AMVAD) induced F. tularensis-specific antibody responses in sera and bronchoalveolar lavage fluids, as well as antigen-specific splenocyte proliferation and IL-17 production. More importantly, the AMVAD vaccine partially protected the mice against a lethal intranasal challenge with LVS. Compared to LVSCE immunized and naïve mice, the LVSCE/AMVAD immunized mice showed substantial to significant reduction in pathogen burdens in the lungs and spleens, reduced serum and pulmonary levels of proinflammatory cytokines/chemokines, and longer mean time to death as well as significantly higher survival rates (p<0.05). These results suggest that the AMVAD system is a promising mucosal adjuvant and vaccine delivery technology, and should be explored further for its applications in combating mucosal infectious diseases.

Safety Evaluation of Calcium Administered Intranasally to Mice

Calcium, a component of approved human vaccines administered via systemic routes, has a good safety profile. Recently, intranasally administered vaccines containing calcium have shown promise in generating mucosal immune responses in animal models. However, the safety of intranasally administered calcium is unknown. This study evaluates the safety of intranasally administered calcium at 2- to 13-fold higher doses than used in experimental vaccines. At a calcium dose of 22 mg/kg, 80% of the Balb/c and 20% of the C57BL/6 mice die within the first 24 hours. At 11.0 mg/kg, there is no overt toxicity in either strain, based on body weight, clinical scores, blood chemistry, and histopathology of major organs at 7 days post administration. In C57BL/6 mice, apart from acute and subacute inflammation in the lungs at up to 3 days post administration, especially at the 22-mg/kg dose, there is no overt toxicity. Doses of calcium up to 11 mg/kg appear to be safe in a mouse model.

Glycosidase-induced fusion of isoprenoid gentiobiosyl lipid membranes at acidic pH

A difficulty in explaining the mechanism whereby archaeal lipid membrane vesicles (archaeosomes) deliver entrapped protein antigens to the MHC class I cytosolic pathway from phagolysosomes of antigen-presenting cells has been the observation that they tend not to fuse. Here, we determine that archaeosomes, composed of archaeal isoprenoid mixtures of glyco and phospholipids, can be highly fusogenic when exposed to the pH and enzymes found in late phagolysosomes. Fusions were strictly dependent on acidic pH and the presence of alpha- or beta-glucosidase. Resonance energy transfer (RET) assays demonstrated that fusion conditions induced lipid mixing of archaeosome lipids with self-unlabeled archaeosomes. Because PC/PG/cholesterol liposomes by themselves did not fuse, it was possible to unequivocally show a fusion of rhodamine-labeled liposomes with archaeosomes by fluorescence microscopy and to demonstrate lipid mixing between labeled liposomes and archaeosomes by the RET assay. Radiotracer and (1)H NMR studies revealed that glycolipids in fused archaeosomes were not degraded significantly by glucosidase treatment during fusion. Rather, the glucosidases dramatically induced small archaeosomes to rapidly and visually aggregate at pH 4.8, but not 6.8, thus bringing membranes together appropriately as a first step in the fusion process. (1)H NMR was used to demonstrate that conditions causing aggregation correlated with binding of glucosidase to the archaeosomes. Binding at acidic pH occurred by the electrostatic interaction of positively charged glucosidase with the anionic phospholipids, although the interaction also occurred with the gentiobiosyl lipids. The data indicate a mechanism of membrane-membrane fusion for archaeal glycolipid membranes induced by glycosidase and illustrate the importance for inclusion of glycolipids in compositions of vesicles designed to deliver protein antigens to the cytosol for MHC class I presentation.

Safety of Intranasally Administered Archaeal Lipid Mucosal Vaccine Adjuvant and Delivery (AMVAD) Vaccine in Mice

The safety profile of a recently described novel archaeal lipid mucosal vaccine adjuvant and delivery (AMVAD) system capable of eliciting robust antigen-specific mucosal and systemic immune responses was evaluated in female Balb/c mice (10/group) using ovalbumin (OVA) antigen. Mice were intranasally immunized (0, 7, and 21 days) with a vaccine comprising 1 μg OVA (0.05 mg/kg body weight) formulated in 0.04 mg total polar lipids extract (2.17 mg/kg body weight) of Methanobrevibacter smithii constituting the AMVAD system. Control groups were similarly immunized with 10-fold higher AMVAD vaccine dose (0.54 mg OVA and 21.7 mg lipid per kg), saline, 10 μg OVA in saline, or 0.04 or 0.4 mg lipid constituting empty AMVAD (no OVA) in saline, or were naïve mice. Clinical signs, rectal temperature, and body weight were monitored once daily or as appropriate. Half the mice in each group were euthanized at 2 days after the first immunization. Blood was collected for clinical chemistry analyses. Major organs (heart, lungs, kidneys, liver, spleen, thymus, and brain) were examined macroscopically and histologically. The remaining mice were euthanized at 29 days and blood and organs collected for analyses as done at 2 days. Feces collected at 27 days, and sera, bile, and nasal lavage at 29 days, were assayed for antibody responses. Based on clinical symptoms, temperature, body weight changes, serum clinical chemistry, and tissue histopathology, there were no overt toxicities associated with OVA/AMVAD or empty AMVAD vaccines. There were no antibodies elicited against the lipids comprising the AMVAD system. These results demonstrate that at 10-fold excess dose of that required for vaccine efficacy, intranasally administered AMVAD vaccine appears to be relatively safe.