Evaluation of novel aerosol formulations designed for mucosal vaccination against influenza virus
Introduction
Influenza viruses are among the most significant human pathogens due to seasonal antigenic variations combined with aerosol transmission. The control of influenza virus infection and spread is being attempted via vaccination strategies. The conventional influenza virus vaccine comprises detergent-extracted antigen from formalin-inactivated virus strains reported to be in circulation. Non-replicative vaccines are currently being delivered seasonally by parenteral route and trigger mainly antibody and T cell responses to epitopes located on virus envelope antigens such as hemagglutinin, which vary substantially due to drift and shift variants. However, the ability of the parenterally administered vaccine to induce local immunity is limited, which has been underlined as a significant drawback [1]. Based on this observation, a few studies during the last decade attempted to evaluate intranasal delivery of non-replicative influenza virus vaccine as a logical alternative. These studies comprising nasal delivery resulted in modestly encouraging results [2], [3], [4] and prompted subsequent studies with adjuvanted vaccines [5], [6], [7]. In such cases, although some adjuvants could further increase the immunogenicity of non-replicative vaccines administered to the nose [6], [7], independent safety [8] and regulatory issues associated with such immunologically active excipients negatively interfere with their development.
To circumvent to a certain extent the requirement for seasonal administration and to broaden up the range of immune effectors to include cross-reactive CTL, a new strategy based on cold adapted live influenza vector has been developed [9]. Such a vaccine is developed for nasal administration, based on the ability of influenza virus to replicate in the respiratory epithelial cells combined with the induction of immunity at the port of entry. However, drawbacks of the live virus vaccination against the influenza virus include: (a) side effects in immunodepressed and children, in particular; (b) a potential of reversion to pathogenic strains; and (c) manufacturing/regulatory issues.
Together, studies published previously indicate that mucosal vaccination is superior for non-replicative vaccines such as the conventional influenza virus vaccines, endowed with limited intrinsic immunogenicity [10], [11] which are currently administered parenterally. In addition, mucosal formulations preclude the need for complete sterility and would be associated with enhanced stability and patient compliance. We hypothesize that increased efficacy of the conventional vaccine may be achieved by a formulation strategy that allows for optimal delivery to the bronchial tree, rather than limited antigen exposure of the nasal-associated lymphoid tissue. If successful, this strategy may obviate the use of microbial-derived adjuvants with uncertain safety profiles and offer an alternative to live vaccination.
We recently developed and tested a novel strategy to encapsulate antigens using a spray-drying technology that allows their effective delivery to bronchial-associated lymphoid tissue (BALT) [12], [13]. The major excipients of these spray-dried microparticles (SDM) are biocompatible lipids present in normal lung surfactant and immunologically inert, such as 1,2-dipalmitoylphosphatidylcholine (DPPC) or distearoylphosphatidylcholine (DSPC) [12]. In the current study, we explore simple lipid/surfactant-based spray-dried formulations of whole inactivated and subunit-split influenza virus vaccines, relative to induction of local and systemic immune responses in preclinical efficacy models of pulmonary vaccination.
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Animals
BALB/c female mice and Sprague Dawley rats, purchased from Harlan Sprague Dawley (Indianapolis, IN), were maintained in the specific pathogen-free, AAALAC accredited facility of Alliance Pharmaceutical Corp. The experiments conducted in this study adhered to the “Principles of Laboratory Animal Care” and were approved by the Institutional Animal Care and Use Committee.
Antigens
The WSN strain of influenza virus (A/WSN/32 H1N1) was grown on permissive Madin–Darby bovine kidney (MDBK) carcinoma cells. The
Design of spray-dried lipid microparticles capable of delivering whole inactivated influenza virus
Previous efforts underlined the difficulties in generating lipid-based aerosols for the delivery of whole influenza virus caused by the hydrophobic nature of the envelope [15]. Influenza virus-loaded microparticles of appropriate size were generated by spray drying, using as the major excipient, biocompatible surfactant lipid (DPPC) (Fig. 1A). The high avidity interaction between the main excipient, DPPC, and the lipid envelope, precluded effective access of viral antigen to APC, unless an
Discussion
Producing dry powder formulations of complex, labile structures, such as whole virus or subunit vaccines, offers two potential advantages over saline formulations: firstly, increased stability due to reduced exposure to aqueous environment and secondly, effective delivery to the mucosal surface of the respiratory tract, thereby offering improved local bioavailability to the mucosal-associated lymphoid tissue.
We previously demonstrated that SDM composed of biocompatible and immunologically inert
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2017, Seminars in ImmunologyCitation Excerpt :A less well recognized organ involved in tolerance induction is certainly the liver, which might not only harbor gut-derived pTregs but also represent a primary site for oral tolerance induction by liver-resident APCs, such as Kupffer cells, myeloid or plasmacytoid DCs [86,87]. The respiratory tract and its associated lymphoid tissues seem to be similarly efficient in inducing mucosal tolerance and/or a shift in pathologic T cell populations in experimental animals [88–92]. In the upper airways, rodents present with a NALT that consists of paired, bell-shaped lymphoid cell accumulations at the entrance of the nasopharyngeal tract, considered to be equivalents of the pharyngeal lymphoid ring of Waldeyer in humans [93–95].
Technologies to Improve Immunization
2017, Plotkin's Vaccines
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Present address: Isis Pharmaceuticals Inc., Carlsbad, CA, USA.