Mucosal Application of a Low-Energy Electron Inactivated Respiratory Syncytial Virus Vaccine Shows Protective Efficacy in an Animal Model

Abstract

Respiratory syncytial virus (RSV) is a leading cause of acute lower respiratory tract infections in the elderly and in children, associated with pediatric hospitalizations. Recently, first vaccines have been approved for people over 60 years of age applied by intramuscular injection. However, a vaccination route via mucosal application holds great potential in the protection against respiratory pathogens like RSV. Mucosal vaccines induce local immune responses, resulting in a fast and efficient elimination of respiratory viruses after natural infection. Therefore, a low-energy electron irradiated RSV (LEEI-RSV) formulated with phosphatidylcholine-liposomes (PC-LEEI-RSV) was tested ex vivo in precision cut lung slices (PCLSs) for adverse effects. The immunogenicity and protective efficacy in vivo were analyzed in an RSV challenge model after intranasal vaccination using a homologous prime-boost immunization regimen. No side effects of PC-LEEI-RSV in PCLS and an efficient antibody induction in vivo could be observed. In contrast to unformulated LEEI-RSV, the mucosal vaccination of mice with PC formulated LEEI-RSV showed a statistically significant reduction in viral load after challenge. These results are a proof-of-principle for the use of LEEI-inactivated viruses formulated with liposomes to be administered intranasally to induce a mucosal immunity that could also be adapted for other respiratory viruses.

Mucosal immunization with a low-energy electron inactivated respiratory syncytial virus vaccine protects mice without Th2 immune bias

“…To examine the conservation of RSV antigenicity, dot blot analysis and enzyme-linked immunosorbent assays (ELISAs) were performed. ELISAs were performed as described with the same antibodies as dot blots (19)(20)(21). For dot blot, 2 µL of each inactivated RSV sample, with respective untreated controls, were put on a nitrocellulose membrane (GE Healthcare Life Sciences, Germany).…”

“…Phosphatidylcholine (PC, LIPOID GmbH, Germany) liposome formulations were prepared as previously described (19). LEEI-RSV was mixed in a ratio of 1:5 (PC : LEEI-RSV) with the liposome formulation and vortexed for 15 s. This material was kept at 4°C.…”

“…The analysis of RSV-A-binding antibodies was modified based on our previously published protocol (19). Serum dilution was 1:1,000 for IgG and 1:250 for IgA.…”

“…We have previously shown that a low-energy electrone irradiation (LEEI) RSV (LEEI-RSV) in a suitable formulation induced protective immune responses against RSV after mucosal application (19). Packaging with a phosphatidylcholine (PC) formulation of LEEI-RSV was crucial for protective efficacy, reducing the viral load in the lung of challenged mice by 170-fold (19). LEEI was used as a non-toxic and non-probe-harming inactivation method with improved safety compared to chemical inactivation or other radiation methods.…”

“…LEEI was used as a non-toxic and non-probe-harming inactivation method with improved safety compared to chemical inactivation or other radiation methods. It has been used successfully for the generation of several viral, bacterial, and parasitic vaccine candidates (19)(20)(21)(22)(23)(24)(25).…”