Vaccination with NS1-truncated H3N2 swine influenza virus primes T cells and confers cross-protection against an H1N1 heterosubtypic challenge in pigs

Abstract

The diversity of contemporary swine influenza virus (SIV) strains impedes effective immunization of swine herds. Mucosally delivered, attenuated virus vaccines are one approach with potential to provide broad crossprotection. Reverse genetics-derived H3N2 SIV virus with truncated NS1 (NS1Δ126 TX98) is attenuated and immunogenic when delivered intranasally in young pigs. We analyzed T-cell priming and cross-protective efficacy in weanling piglets after intranasal inoculation with NS1Δ126 TX98 versus wild type TX98. In vivo replication of the truncation mutant was minimal compared to the wild type virus. T-cell responses were greater in magnitude in pigs infected with the wild type virus in in vitro restimulation assays. According to the expression of activation marker CD25, peripheral T cell recall responses in NS1Δ126 TX98 infected pigs were minimal. However, intracellular IFN-γ data indicate that the attenuated virus induced virus-specific CD4 + CD8 -, CD4 + CD8 + , CD4 -CD8 + , and γδ T cells within 28 days. The IFN-γ response appeared to contract, as responses were reduced at later time points prior to challenge. CD4 + CD8 + cells isolated 5 days after heterosubtypic H1N1 challenge (day 70 overall) showed an elevated CD25 response to virus restimulation. Pigs previously infected with wild type TX98 were protected from replication of the H1N1 challenge virus. Vaccination with NS1Δ126 TX98 was associated with significantly lower levels of Th1-associated cytokines in infected lungs but provided partial cross-protection against the H1N1 challenge. These results demonstrate that NS1Δ SIV vaccines can elicit cell-mediated cross-protection against antigenically divergent strains. The diversity of contemporary swine influenza virus (SIV) strains impedes effective immunization of swine herds. Mucosally delivered, attenuated virus vaccines are one approach with potential to provide broad cross-protection. Reverse genetics-derived H3N2 SIV virus with truncated NS1 (NS1 126 TX98) is attenuated and immunogenic when delivered intranasally in young pigs. We analyzed T-cell priming and cross-protective efficacy in weanling piglets after intranasal inoculation with NS1 126 TX98 versus wild type TX98. In vivo replication of the truncation mutant was minimal compared to the wild type virus. T-cell responses were greater in magnitude in pigs infected with the wild type virus in in vitro restimulation assays. According to the expression of activation marker CD25, peripheral T cell recall responses in NS1 126 TX98 infected pigs were minimal. However, intracellular IFN-␥ data indicate that the attenuated virus induced virus-specific CD4 + CD8 -, CD4 + CD8 + , CD4 -CD8 + , and ␥␦ T cells within 28 days. The IFN-␥ response appeared to contract, as responses were reduced at later time points prior to challenge. CD4 + CD8 + cells isolated 5 days after heterosubtypic H1N1 challenge (day 70 overall) showed an elevated CD25 response to virus restimulation. Pigs previously infected with wild type TX98 were protected from replicatio...

Live Attenuated Influenza Vaccine Provides Superior Protection from Heterologous Infection in Pigs with Maternal Antibodies without Inducing Vaccine-Associated Enhanced Respiratory Disease

“…Cross-reactive T cells primed by the WIV may also have contributed to the protective effect against the heterologous CO99 infection. Consistent with this possibility, a similarly formulated H1N2 WIV vaccine was shown to prime T cells in antibody-negative young pigs (7).…”

“…This virus (identical to the LAIV in the present report) was shown to have attenuated replication in the upper respiratory tract. When the TX98 LAIV was administered as an intranasal vaccine to young seronegative pigs, it elicited a mucosal IgA response, modest titers of serum HI antibodies, and antigen-specific T cells, while conferring protection against homologous challenge and a degree of cross-protection against variant strains, with a single-or two-dose regimen (7,26). Our previous work indicated that two intranasal applications of the LAIV vaccine did not confer any benefit against homologous challenge compared to one dose (26), and one dose would be highly preferred for use in the swine population.…”

“…This pointed again to the possibility that the adjuvanted WIV in the face of MDA primed a cellular immune response that contributed to protection against homologous virus. Moderate T-cell priming has been demonstrated for pigs vaccinated with a similar formulation of inactivated H1N2 WIV (7).…”

Efficacy in Pigs of Inactivated and Live Attenuated Influenza Virus Vaccines against Infection and Transmission of an Emerging H3N2 Similar to the 2011-2012 H3N2v

“…While live attenuated influenza virus (LAIV) vaccines have been approved for use in people and horses, a LAIV for swine has yet to make it to market. This is despite a number of LAIV vaccines that have been developed and demonstrated to provide significant cross-protection in experimentally infected pigs (12)(13)(14)(15).…”

An Eight-Segment Swine Influenza Virus Harboring H1 and H3 Hemagglutinins Is Attenuated and Protective against H1N1 and H3N2 Subtypes in Pigs

“…In addition, these vaccines primarily generate antibody responses with limited or no cell-mediated immunity (CMI). In contrast, live attenuated influenza vaccines (LAIV) provide strong, long-lived cell-mediated and humoral immunity against different influenza virus subtypes with no need for perfect antigen matching (8)(9)(10)(11). Previously, it was shown that SIVs generated by genetic modifications within the hemagglutinin (HA) or nonstructural (NS) genes are attenuated in pigs (12,13).…”