Serum cytokine profiles associated with specific adjuvants used in a DNA prime-protein boost vaccination strategy

A Glycolipidated-liposomal peptide vaccine confers long-term mucosal protection against Streptococcus pyogenes via IL-17, macrophages and neutrophils

Mucosally active subunit vaccines are an unmet clinical need due to lack of licensed immunostimulants suitable for vaccine antigens. Here, we show that intranasal administration of liposomes incorporating: the Streptococcus pyogenes peptide antigen, J8; diphtheria toxoid as a source of T cell help; and the immunostimulatory glycolipid, 3D(6-acyl) PHAD (PHAD), is able to induce long-lived humoral and cellular immunity. Mice genetically deficient in either mucosal antibodies or total antibodies are protected against S. pyogenes respiratory tract infection. Utilizing IL-17-deficient mice or depleting cellular subsets using antibodies, shows that the cellular responses encompassing, CD4+ T cells, IL-17, macrophages and neutrophils have important functions in vaccine-mediated mucosal immunity. Overall, these data demonstrate the utility of a mucosal vaccine platform to deliver multi-pronged protective responses against a highly virulent pathogen.

A microarray patch SARS-CoV-2 vaccine induces sustained antibody responses and polyfunctional cellular immunity

Sustainable global immunization campaigns against COVID-19 and other emerging infectious diseases require effective, broadly deployable vaccines. Here, we report a dissolvable microarray patch (MAP) SARS-CoV-2 vaccine that targets the immunoresponsive skin microenvironment, enabling efficacious needle-free immunization. Multicomponent MAPs delivering both SARS-CoV-2 S1 subunit antigen and the TLR3 agonist Poly(I:C) induce robust antibody and cellular immune responses systemically and in the respiratory mucosa. MAP vaccine-induced antibodies bind S1 and the SARS-CoV-2 receptor-binding domain, efficiently neutralize the virus, and persist at high levels for more than a year. The MAP platform reduces systemic toxicity of the delivered adjuvant and maintains vaccine stability without refrigeration. When applied to human skin, MAP vaccines activate skin-derived migratory antigen-presenting cells, supporting the feasibility of human translation. Ultimately, this shelf-stable MAP vaccine improves immunogenicity and safety compared to traditional intramuscular vaccines and offers an attractive alternative for global immunization efforts against a range of infectious pathogens.

Synthetic Biology-derived triterpenes as efficacious immunomodulating adjuvants

The triterpene oil squalene is an essential component of nanoemulsion vaccine adjuvants. It is most notably in the MF59 adjuvant, a component in some seasonal influenza vaccines, in stockpiled, emulsion-based adjuvanted pandemic influenza vaccines, and with demonstrated efficacy for vaccines to other pandemic viruses, such as SARS-CoV-2. Squalene has historically been harvested from shark liver oil, which is undesirable for a variety of reasons. In this study, we have demonstrated the use of a Synthetic Biology (yeast) production platform to generate squalene and novel triterpene oils, all of which are equally as efficacious as vaccine adjuvants based on physiochemical properties and immunomodulating activities in a mouse model. These Synthetic Biology adjuvants also elicited similar IgG1, IgG2a, and total IgG levels compared to marine and commercial controls when formulated with common quadrivalent influenza antigens. Injection site morphology and serum cytokine levels did not suggest any reactogenic effects of the yeast-derived squalene or novel triterpenes, suggesting their safety in adjuvant formulations. These results support the advantages of yeast produced triterpene oils to include completely controlled growth conditions, just-in-time and scalable production, and the capacity to produce novel triterpenes beyond squalene.

Rational Design and In Vivo Characterization of Vaccine Adjuvants

Many different adjuvants are currently being developed for subunit vaccines against a number of pathogens and diseases. Rational design is increasingly used to develop novel vaccine adjuvants, which requires extensive knowledge of, for example, the desired immune responses, target antigen-presenting cell subsets, their localization, and expression of relevant pattern-recognition receptors. The adjuvant mechanism of action and efficacy are usually evaluated in animal models, where mice are by far the most used. In this review, we present methods for assessing adjuvant efficacy and function in animal models: (1) whole-body biodistribution evaluated by using fluorescently and radioactively labeled vaccine components; (2) association and activation of immune cell subsets at the injection site, in the draining lymph node, and the spleen; (4) adaptive immune responses, such as cytotoxic T-lymphocytes, various T-helper cell subsets, and antibody responses, which may be quantitatively evaluated using ELISA, ELISPOT, and immunoplex assays and qualitatively evaluated using flow cytometric and single cell sequencing assays; and (5) effector responses, for example, antigen-specific cytotoxic potential of CD8+ T cells and antibody neutralization assays. While the vaccine-induced immune responses in mice often correlate with the responses induced in humans, there are instances where immune responses detected in mice are not translated to the human situation. We discuss some examples of correlation and discrepancy between mouse and human immune responses and how to understand them.

Mannosylation of LNP Results in Improved Potency for Self-Amplifying RNA (SAM) Vaccines

Mannosylation of Lipid Nanoparticles (LNP) can potentially enhance uptake by Antigen Presenting Cells, which are highly abundant in dermal tissues, to improve the potency of Self Amplifying mRNA (SAM) vaccines in comparison to the established unmodified LNP delivery system. In the current studies, we evaluated mannosylated LNP (MLNP), which were obtained by incorporation of a stable Mannose-cholesterol amine conjugate, for the delivery of an influenza (hemagglutinin) encoded SAM vaccine in mice, by both intramuscular and intradermal routes of administration. SAM MLNP exhibited in vitro enhanced uptake in comparison to unglycosylated LNP from bone marrow-derived dendritic cells, and in vivo more rapid onset of the antibody response, independent of the route. The increased binding antibody levels also translated into higher functional hemagglutinin inhibition titers, particularly following intradermal administration. T cell assay on splenocytes from immunized mice also showed an increase in antigen specific CD8⁺ T responses, following intradermal administration of MLNP SAM vaccines. Induction of enhanced antigen specific CD4⁺ T cells, correlating with higher IgG2a antibody responses, was also observed. Hence, the present work illustrates the benefit of mannosylation of LNPs to achieve a faster immune response with SAM vaccines and these observations could contribute to the development of novel skin delivery systems for SAM vaccines.

Saponins from Quillaja saponaria and Quillaja brasiliensis: Particular Chemical Characteristics and Biological Activities

Quillaja saponaria Molina represents the main source of saponins for industrial applications. Q. saponaria triterpenoids have been studied for more than four decades and their relevance is due to their biological activities, especially as a vaccine adjuvant and immunostimulant, which have led to important research in the field of vaccine development. These saponins, alone or incorporated into immunostimulating complexes (ISCOMs), are able to modulate immunity by increasing antigen uptake, stimulating cytotoxic T lymphocyte production (Th1) and cytokines (Th2) in response to different antigens. Furthermore, antiviral, antifungal, antibacterial, antiparasitic, and antitumor activities are also reported as important biological properties of Quillaja triterpenoids. Recently, other saponins from Q. brasiliensis (A. St.-Hill. & Tul.) Mart. were successfully tested and showed similar chemical and biological properties to those of Q. saponaria barks. The aim of this manuscript is to summarize the current advances in phytochemical and pharmacological knowledge of saponins from Quillaja plants, including the particular chemical characteristics of these triterpenoids. The potential applications of Quillaja saponins to stimulate further drug discovery research will be provided.

Evaluation of the safety and adjuvant effect of a detoxified listeriolysin O mutant on the humoral response to dengue virus antigens

Listeriolysin O (LLO) has been proposed as a potential carrier or adjuvant molecule in the vaccination field. However, the cytotoxic and pro-apoptotic effects of LLO are the major limitations for this purpose. Here, we have performed a preclinical safety evaluation and characterized a new potential adjuvant application for a non-cytolytic LLO mutant (dtLLO) to enhance and modulate the immune response against the envelope (E) protein from dengue virus. In addition, we have studied the adjuvant effects of dtLLO on human immune cells and the role of membrane cholesterol for the binding and proinflammatory property of the toxoid. Our in-vivo results in the murine model confirmed that dtLLO is a safer molecule than wild-type LLO (wtLLO), with a significantly increased survival rate for mice challenged with dtLLO compared with mice challenged with wtLLO (P < 0·001). Histopathological analysis showed non-toxic effects in key target organs such as brain, heart, liver, spleen, kidney and lung after challenge with dtLLO. In vitro, dtLLO retained the capacity of binding to plasma membrane cholesterol on the surface of murine and human immune cells. Immunization of 6-8-week-old female BALB/c mice with a combination of dtLLO mixed with E protein elicited a robust specific humoral response with isotype diversification of immunoglobulin (Ig)G antibodies (IgG1 and IgG2a). Finally, we demonstrated that cholesterol and lipid raft integrity are required to induce a proinflammatory response by human cells. Taken together, these findings support a potential use of the dtLLO mutant as a safe and effective adjuvant molecule in vaccination.

Identification of QS-21 as an Inflammasome-activating Molecular Component of Saponin Adjuvants

Many immunostimulants act as vaccine adjuvants via activation of the innate immune system, although in many cases it is unclear which specific molecules contribute to the stimulatory activity. QS-21 is a defined, highly purified, and soluble saponin adjuvant currently used in licensed and exploratory vaccines, including vaccines against malaria, cancer, and HIV-1. However, little is known about the mechanisms of cellular activation induced by QS-21. We observed QS-21 to elicit caspase-1-dependent IL-1β and IL-18 release in antigen-presenting cells such as macrophages and dendritic cells when co-stimulated with the TLR4-agonist adjuvant monophosphoryl lipid A. Furthermore, our data suggest that the ASC-NLRP3 inflammasome is responsible for QS-21-induced IL-1β/IL-18 release. At higher concentrations, QS-21 induced macrophage and dendritic cell death in a caspase-1-, ASC-, and NLRP3-independent manner, whereas the presence of cholesterol rescued cell viability. A nanoparticulate adjuvant that contains QS-21 as part of a heterogeneous mixture of saponins also induced IL-1β in an NLRP3-dependent manner. Interestingly, despite the role NLRP3 plays for cellular activation in vitro, NLRP3-deficient mice immunized with HIV-1 gp120 and QS-21 showed significantly higher levels of Th1 and Th2 antigen-specific T cell responses and increased IgG1 and IgG2c compared with wild type controls. Thus, we have identified QS-21 as a nonparticulate single molecular saponin that activates the NLRP3 inflammasome, but this signaling pathway may contribute to decreased antigen-specific responses in vivo.

A Novel Prime and Boost Regimen of HIV Virus-Like Particles with TLR4 Adjuvant MPLA Induces Th1 Oriented Immune Responses against HIV

HIV virus-like particles (VLPs) present the HIV envelope protein in its native conformation, providing an ideal vaccine antigen. To enhance the immunogenicity of the VLP vaccine, we sought to improve upon two components; the route of administration and the additional adjuvant. Using HIV VLPs, we evaluated sub-cheek as a novel route of vaccine administration when combined with other conventional routes of immunization. Of five combinations of distinct prime and boost sequences, which included sub-cheek, intranasal, and intradermal routes of administration, intranasal prime and sub-cheek boost (IN+SC) resulted in the highest HIV-specific IgG titers among the groups tested. Using the IN+SC regimen we tested the adjuvant VesiVax Conjugatable Adjuvant Lipid Vesicles (CALV) + monophosphoryl lipid A (MPLA) at MPLA concentrations of 0, 7.5, 12.5, and 25 μg/dose in combination with our VLPs. Mice that received 12.5 or 25 μg/dose MPLA had the highest concentrations of Env-specific IgG2c (20.7 and 18.4 μg/ml respectively), which represents a Th1 type of immune response in C57BL/6 mice. This was in sharp contrast to mice which received 0 or 7.5 μg MPLA adjuvant (6.05 and 5.68 μg/ml of IgG2c respectively). In contrast to IgG2c, MPLA had minor effects on Env-specific IgG1; therefore, 12.5 and 25 μg/dose of MPLA induced the optimal IgG1/IgG2c ratio of 1.3. Additionally, the percentage of germinal center B cells increased significantly from 15.4% in the control group to 31.9% in the CALV + 25 μg MPLA group. These mice also had significantly more IL-2 and less IL-4 Env-specific CD8⁺ T cells than controls, correlating with an increased percentage of Env-specific central memory CD4⁺ and CD8⁺ T cells. Our study shows the strong potential of IN+SC as an efficacious route of administration and the effectiveness of VLPs combined with MPLA adjuvant to induce Env specific Th1-oriented HIV-specific immune responses.

Contribution of TLR4 and MyD88 for adjuvant monophosphoryl lipid A (MPLA) activity in a DNA prime-protein boost HIV-1 vaccine

Recombinant protein vaccines are commonly formulated with an immune-stimulatory compound, or adjuvant, to boost immune responses to a particular antigen. Recent studies have shown that, through recognition of molecular motifs, receptors of the innate immune system are involved in the functions of adjuvants to generate and direct adaptive immune responses. However, it is not clear to which degree those receptors are also important when the adjuvant is used as part of a novel heterologous prime-boost immunization process in which the priming and boosting components are not the same type of vaccines. In the current study, we compared the immune responses elicited by a pentavalent HIV-1 DNA prime-protein boost vaccine in mice deficient in either Toll-like receptor 4 (TLR4) or myeloid differentiation primary response gene 88 (MyD88) to wildtype mice. HIV gp120 protein administered in the boost phase was formulated with either monophosphoryl lipid A (MPLA), QS-21, or Al(OH)3. Endpoint antibody titer, serum cytokine response and T-cell memory response were assessed. Neither TLR4 nor MyD88 deficiency had a significant effect on the immune response of mice given vaccine formulated with QS-21 or Al(OH)3. However, TLR4- and MyD88-deficiency decreased both the antibody and T-cell responses in mice administered HIV gp120 formulated with MPLA. These results further our understanding of the activation of TLR4 and MyD88 by MPLA in the context of a DNA prime/protein boost immunization strategy.

The HIV-1 gp120 V1V2 loop: structure, function and importance for vaccine development

Although the second variable loop (V2) of the HIV-1 gp120 envelope glycoprotein shows substantial sequence diversity between strains, its functional importance imposes critical conservation of structure, and within particular microdomains, of sequence. V2 influences HIV-1 viral entry by contributing to trimer stabilization and co-receptor binding. It is one of 4 key domains targeted by the broadly neutralizing antibodies that arise during HIV-1 infection. HIV-1 uses V1V2 sequence variation and glycosylation to escape neutralizing antibody. In the Thai Phase III HIV-1 vaccine trial, RV144, vaccine-induced IgG against V1V2 inversely correlated with the risk of HIV-1 acquisition, and HIV-1 strains infecting RV144 vaccine recipients differed from those infecting placebo recipients in the V2 domain. Similarly, non-human primate challenge studies demonstrated an inverse correlation between vaccine-induced anti-V2 responses and simian immunodeficiency virus acquisition. We hypothesize that increased magnitude, frequency and duration of vaccine-induced anti-V2 antibody responses should improve efficacy afforded by pox-protein prime-boost HIV vaccine strategies.

Nonneutralizing functional antibodies: a new "old" paradigm for HIV vaccines

Animal and human data from various viral infections and vaccine studies suggest that nonneutralizing antibodies (nNAb) without neutralizing activity in vitro may play an important role in protection against viral infection in vivo. This was illustrated by the recent human immunodeficiency virus (HIV) RV144 vaccine efficacy trial, which demonstrated that HIV-specific IgG-mediated nNAb directed against the V2 loop of HIV type 1 envelope (Env) were inversely correlated with risk for HIV acquisition, while Env-specific plasma IgA-mediated antibodies were directly correlated with risk. However, tier 1 NAb in the subset of responders with a low level of plasma Env-specific IgA correlated with decreased risk. Nonhuman primate simian immunodeficiency virus (SIV) and simian-human immunodeficiency virus (SHIV) challenge studies suggest that Env-mediated antibodies are essential and sufficient for protection. A comparison of immune responses generated in human efficacy trials reveals subtle differences in the fine specificities of the antibody responses, in particular in HIV-specific IgG subclasses. The underlying mechanisms that may have contributed to protection against HIV acquisition in humans, although not fully understood, are possibly mediated by antibody-dependent cell-mediated cytotoxicity (ADCC) and/or other nonneutralizing humoral effector functions, such as antibody-mediated phagocytosis. The presence of such functional nNAb in mucosal tissues and cervico-vaginal and rectal secretions challenges the paradigm that NAb are the predominant immune response conferring protection, although this does not negate the desirability of evoking neutralizing antibodies through vaccination. Instead, NAb and nNAb should be looked upon as complementary or synergistic humoral effector functions. Several HIV vaccine clinical trials to study these antibody responses in various prime-boost modalities in the systemic and mucosal compartments are ongoing. The induction of high-frequency HIV-specific functional nNAb at high titers may represent an attractive hypothesis-testing strategy in future HIV vaccine efficacy trials.

A novel vaccine against Porcine circovirus type 2 (PCV2) and Streptococcus equi ssp. zooepidemicus (SEZ) co-infection

To develop a vaccine against Porcine circovirus type 2 (PCV2) and Streptococcus equi ssp. zooepidemicus (SEZ) co-infection, the genes of porcine IL-18, capsid protein (Cap) of PCV2 and M-like protein (SzP) of SEZ were inserted into the swinepox virus (SPV) genome by homologous recombination. The recombinant swinepox virus rSPV-ICS was verified by PCR and indirect immunofluorescence assays. To evaluate the immunogenicity of rSPV-ICS, 28 PCV2 and SEZ seronegative Bama minipigs were immunized with rSPV-ICS (n=8), commercial PCV2 vaccine and SEZ vaccine (n=8) or wild type SPV (n=8). The results showed that SzP-specific antibody and PCV2 neutralizing antibody of the rSPV-ICS immunized group increased significantly compared to the wild type SPV treated group after vaccination and increased continuously over time. The levels of IL-4 and IFN-γ in the rSPV-ICS immunized group were significantly higher than the other three groups, respectively. After been co-challenged with PCV2 and SEZ, 87.5% piglets in rSPV-ICS immunized group were survived. Significant reductions in gross lung lesion score, histopathological lung lesion score, and lymph node lesion score were noticed in the rSPV-ICS immunized group compared with the wtSPV treated group. The results suggested that the recombinant rSPV-ICS provided piglets with significant protection against PCV2-SEZ co-infection; thus, it offers proof-of-principle for the development of a vaccine for the prevention of these swine diseases.

DNA Immunization for HIV Vaccine Development

DNA vaccination has been studied in the last 20 years for HIV vaccine research. Significant experience has been accumulated in vector design, antigen optimization, delivery approaches and the use of DNA immunization as part of a prime-boost HIV vaccination strategy. Key historical data and future outlook are presented. With better understanding on the potential of DNA immunization and recent progress in HIV vaccine research, it is anticipated that DNA immunization will play a more significant role in the future of HIV vaccine development.

Comparison of multiple adjuvants on the stability and immunogenicity of a clade C HIV-1 gp140 trimer

Immunogens based on the human immunodeficiency virus type-1 (HIV-1) Envelope (Env) glycoprotein have to date failed to elicit potent and broadly neutralizing antibodies against diverse HIV-1 strains. An understudied area in the development of HIV-1 Env-based vaccines is the impact of various adjuvants on the stability of the Env immunogen and the magnitude of the induced humoral immune response. We hypothesize that optimal adjuvants for HIV-1 gp140 Env trimers will be those with high potency but also those that preserve structural integrity of the immunogen and those that have a straightforward path to clinical testing. In this report, we systematically evaluate the impact of 12 adjuvants on the stability and immunogenicity of a clade C (CZA97.012) HIV-1 gp140 trimer in guinea pigs and a subset in non-human primates. Oil-in-water emulsions (GLA-emulsion, Ribi, Emulsigen) resulted in partial aggregation and loss of structural integrity of the gp140 trimer. In contrast, alum (GLA-alum, Adju-Phos, Alhydrogel), TLR (GLA-aqueous, CpG, MPLA), ISCOM (Matrix M) and liposomal (GLA-liposomes, virosomes) adjuvants appeared to preserve trimer integrity as measured by size exclusion chromatography. However, multiple classes of adjuvants similarly augmented Env-specific binding and neutralizing antibody responses in guinea pigs and non-human primates.

Reduced MyD88 dependency of ISCOMATRIX™ adjuvant in a DNA prime-protein boost HIV vaccine

ISCOMATRIX™ adjuvant is an integrated adjuvant system due to its ability to both facilitate antigen delivery and immunomodulate the innate and adaptive immune responses to vaccination. ISCOMATRIX™ adjuvant strongly induces both humoral and cell-mediated immunity in formulation with a range of antigens in pre-clinical and clinical evaluations. In this study, we describe the adaptive and innate immune responses associated with ISCOMATRIX™ adjuvant in the context of a previously described HIV-1 vaccine, DP6-001. The DP6-001 vaccine consists of a unique pentavalent HIV-1 Env DNA prime-protein boost regimen. This study demonstrates the potent induction of vaccine-specific antibodies in a mouse model, as well as broadly neutralizing antibodies in immunized rabbits. In addition, we identify a potentially critical role for DNA priming in the induction of the vaccine-specific immune response as well as the serum cytokine profiles associated with ISCOMATRIX™ adjuvant. Most interestingly, DNA prime immunizations made ISCOMATRIX™ adjuvant less dependent on the central innate immune adaptor MyD88, revealing a previously unknown mechanism that may expand our knowledge on the use of adjuvants.