Immune enhancing properties of the novel Matrix-M™ adjuvant leads to potentiated immune responses to an influenza vaccine in mice
Highlights
► Mice received Matrix-M™, AS03, Alum or FCA, spleen, lymph nodes, and serum were analyzed. ► Immune response compared after vaccination with adjuvanted influenza antigen. ► Matrix-M™ activates innate immune cells, not seen by other investigated adjuvants. ► Splenocyte re-stimulation shows enhanced cytokine response in Matrix-M™ treated mice. ► High antibody levels in mice injected with Matrix-M™- or AS03-adjuvanted vaccine.
Introduction
Adjuvants that activate innate immune responses are thought to increase the likelihood of achieving efficient vaccine formulations. Many types of adjuvants potentiate immune responses by activating innate immune cells leading to cytokine secretion and cell recruitment, events important for antigen uptake and presentation. Saponins from the tree Quillaja saponaria Molina have for long been used as adjuvant in veterinary vaccines [1]. Matrix-M™ is a novel saponin-based adjuvant composed of purified saponin, cholesterol and phospholipids formulated into 40 nm cage-like structures. Particulate saponin adjuvants such as Matrix-M™ and immune stimulatory complexes (ISCOMs) are known to enhance cell trafficking, activate immune cells and have antigen dose-sparing potential [2], [3]. Furthermore they are known to induce Th1 and Th2 responses, i.e. to activate cytotoxic T lymphocytes (CTLs) alongside a strong humoral response [4], [5], [6]. Other adjuvants, such as Adjuvant System 03 (AS03), composed of squalene and α-tocopherol, also enhance Th1- and Th2-responses, demonstrated by increased IFN-γ production by in vitro re-stimulation alongside high hemagglutination inhibition titers after immunization with AS03-adjuvanted influenza [7]. In contrast, aluminum containing adjuvants (Alum) and MF59, based on squalene, are thought to mainly activate Th2 responses [8], [9]. Recently, it was shown that both Alum and MF59, in presence of antigen, recruit and activate neutrophils, monocytes and dendritic cells (DCs), cells important for antigen uptake and transportation to draining lymph nodes (dLNs) [10], [11], [12]. Thus antigen transportation may be a major function induced by Alum and MF59. Another widely used adjuvant in experimental research and commercial antibody manufacturing is Freund's Complete Adjuvant (FCA). FCA is composed of mineral oil mixed with killed mycobacteria, which creates a depot effect at the injection site. FCA enables efficient Th1 and Th2 responses [8]. Characterization of adjuvants’ mechanism of action will increase the knowledge on adjuvant design and efficient vaccine formulations for activation of both arms of the immune system. Hence, herein we have compared immune stimulatory properties of Matrix-M™, AS03, Alum and FCA without antigen present. In addition, Matrix-M formulated influenza antigen, identical to a formulation recently used in a Phase 1 study in elderly, was evaluated immunologically in mice. Humoral and cellular responses were compared to those induced by AS03 and Alum formulated with the same influenza antigen.
Section snippets
Adjuvants
Four adjuvants were studied: Matrix-M™ (AbISCO®-100, Isconova AB, Sweden) composed of two 40 nm large particles, i.e. Matrix-A™ and Matrix-C™, made from separate saponin fractions, Alhydrogel (Brenntag, Denmark) 2% Al(OH)3-suspension, FCA (Brenntag) formulated by mineral oil and heat-killed mycobacteria and AS03 (Pandemrix, GlaxoSmithKline) made of squalene and α-tocopherol.
Mice and injections
Female BALB/c mice (8–12 weeks) were purchased from, and kept at, the National Veterinary Institute (SVA, Sweden). All
Increased cellularity in dLNs and spleen after Matrix-M™ administration
To study the inherent potency of different adjuvants in recruitment and activation of immune cells during the early immune response, mice were injected s.c. with Matrix-M™, Alum, FCA or AS03 alone and the responses were compared to PBS-treated mice. After 48 h, dLNs from Matrix-M™-treated mice contained significantly higher cell numbers. This was not seen for Alum, FCA or AS03 (Fig. 1A). Also in spleen, Matrix-M™ induced a significant higher total cell count, though not as pronounced as for dLNs
Discussion
Adjuvant activities of Matrix-M™ were studied and compared to the following adjuvants: Alum, widely used and known to stimulate antibody responses in a Th2 biased manner [13], AS03, oil-based adjuvant with a balanced Th1/Th2 stimulatory effect with demonstrated efficacy in a human pandemic influenza vaccine [7], [14], FCA, inducing potent antibody and cellular responses [15]. Evaluation of inherent immune stimulatory properties by the adjuvants alone demonstrated significant differences between
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2018, Current Opinion in PharmacologyCitation Excerpt :The antibody concentrations elicited by these vaccines cannot be compared to the HAI titers induced by conventional influenza vaccines, as they contain different antigens. The saponin-based Matrix-M™ adjuvant (saponin, cholesterol and phospholipids formulated into 40 nm cage-like structures) in combination with a recombinant hemagglutinin nanoparticle vaccine induces higher antibody concentrations and protection against the vaccine strain and heterologous virus strains in ferret and mouse models compared to standard or high-dose influenza vaccine [47,48]. Early clinical evaluation together with a pandemic influenza vaccine candidate showed promising results in humans [49–51] and a phase I/II clinical trial to test its immunogenicity and safety in combination with seasonal influenza antigens in older adults is currently ongoing (NCT03293498).
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Present address: Fiomi Diagnostics AB, Dag Hammarskjöldsväg 52A, SE-752 37 Uppsala, Sweden.