Abstract
Influenza is a major health threat, and a broadly protective influenza vaccine would be a significant advance. Signal Minus FLU (S-FLU) is a candidate broadly protective influenza vaccine that is limited to a single cycle of replication, which induces a strong cross-reactive T cell response but a minimal Ab response to hemagglutinin after intranasal or aerosol administration. We tested whether an H3N2 S-FLU can protect pigs and ferrets from heterosubtypic H1N1 influenza challenge. Aerosol administration of S-FLU to pigs induced lung tissue-resident memory T cells and reduced lung pathology but not the viral load. In contrast, in ferrets, S-FLU reduced viral replication and aerosol transmission. Our data show that S-FLU has different protective efficacy in pigs and ferrets, and that in the absence of Ab, lung T cell immunity can reduce disease severity without reducing challenge viral replication.
Highlights
Aerosol immunization was carried out using a purpose-built mask and Aerogen Solo nebulizer that allowed efficient vaccine delivery in,5 min to the sedated animals after we had established that the nebulizer did not affect the titer of the Signal Minus FLU (S-FLU) vaccines and provided a droplet size appropriate for delivery to the lower respiratory tract (Supplemental Fig. 1)
No virus was detected in the Bronchoalveolar lavage (BAL) of the Homologous inactivated vaccine group, and S-FLU reduced viral load in the BAL, with no virus in three animals, this reduction was not statistically significant (Fig. 1B)
This evidence, combined with a long history of animal studies demonstrating the protective effect of T cells induced by live influenza virus infection [24], provides the rationale for developing a safe and broadly protective influenza A vaccine (BPIV) that induces a strong T cell response in the human lung
Summary
The design and production of pdmH1N1 S-FLU [eGFP*/N1(Eng195)].H1 (Eng/195/2009) has been described previously [3, 5]. Pigs were screened for absence of influenza A infection by matrix gene real-time RT-PCR and for Ab-free status by hemagglutination inhibition using four swine influenza virus Ags. Pigs were randomly divided into three groups of six and immunized as follows: 1) control unimmunized, 2) Homologous (1353/ 09pdmH1N1) vaccine containing 2048 hemagglutination units administered i.m. in 1 ml, and 3) H3N2 S-FLU administered by aerosol delivering ∼1.5 3 108 TCID50 in 1 ml. Viral titers in nasal swabs and BAL from pigs were determined by plaque assay on MDCK cells as previously described [6]. Cryopreserved mononuclear cells from blood, TBLN, BAL, spleen, and lung were thawed and stimulated for 12 h at 37 ̊C with either 1 3 106 PFU live MDCK-grown strain 1353/09pdmH1N1 or 1 3 106 TCID50 H3N2 S-FLU or MDCK mock supernatant as control. One-way or two-way ANOVA with Dunnett posttest for multiple comparisons were used to compare immunized groups to the control group, and analysis was performed using GraphPad Prism 6
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