MUCOSAL DELIVERY OF INFLUENZA VACCINE ANTIGENS
Park Ochsner, Susan Soo
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Most pathogens infect humans and animals at mucosal surfaces, yet few mucosal vaccines are available to provide protection at these sites. Though influenza virus initiates its infection in the respiratory mucosal epithelium, currently approved influenza vaccines are administered by parenteral routes, which do not offer effective respiratory immunity. A successful mucosal influenza vaccine should induce both local and systemic immunity, however, the respiratory epithelium is an imposing barrier that prevents vaccine antigens to effectively traverse the airway. The neonatal Fc receptor (FcRn) mediates transport of IgG across the epithelial cell monolayer lining mucosal surfaces. To exploit this antibody transfer pathway for antigen delivery, I produced a soluble fusion protein that fused the monomeric Fc portion of IgG to an influenza hemagglutinin (HA) antigen harboring the T4 fibritin trimerization domain. Intranasal innoculation of the HA-Fc protein along with CpG adjuvant induced high levels of durable mucosal and systemic adaptive immune responses and, importantly, generation of lung-resident memory T cells. FcRn-dependent antigen delivery was corroborated when substantial protection characterized by significantly increased survival and reduced pulmonary pathology was observed in the HA-Fc-immunized wild-type (wt) mice. In contrast, control groups of wt and FcRn-deficient mice immunized with HA-Fc, a mutant version of HA-Fc that lacks FcRn binding capacity, HA alone, or PBS, experienced substantial morbidity, mortality, and lung damage. As the influenza nucleoprotein (NP) is highly conserved among strains, it is an attractive vaccine target. Thus I produced soluble NP-Fc fusion proteins as potential influenza vaccines. The preliminary study demonstrated that intranasal immunization of NP-Fc with CpG resulted in FcRn-mediated delivery of NP-Fc protein across the respiratory barrier and the induction of high levels of antibody titer compared to groups of control mice. Immunization with NP-Fc may be further explored for developing a universal mucosal influenza vaccine. Taken together, for the first time, my results prove that FcRn can effectively deliver an influenza antigen across the respiratory epithelial barrier, providing substantial protection against lethal respiratory infection. This study further suggests FcRn-mediated mucosal vaccination could be used to deliver a universal influenza vaccine antigen or protective antigens from other common respiratory pathogens.