Intranasal Delivery of Inactivated Influenza Virus and Poly(I:C) Adsorbed Corn-Based Nanoparticle Vaccine Elicited Robust Antigen-Specific Cell-Mediated Immune Responses in Maternal Antibody Positive Nursery Pigs

We designed the killed swine influenza A virus (SwIAV) H1N2 antigen (KAg) with polyriboinosinic:polyribocytidylic acid [(Poly(I:C)] adsorbed corn-derived Nano-11 particle based nanovaccine called Nano-11-KAg+Poly(I:C), and evaluated its immune correlates in maternally derived antibody (MDA)-positive pigs against a heterologous H1N1 SwIAV infection. Immunologically, in tracheobronchial lymph nodes (TBLN) detected enhanced H1N2-specific cytotoxic T-lymphocytes (CTLs) in Nano-11-KAg+Poly(I:C) vaccinates, and in commercial vaccinates detected CTLs with mainly IL-17A+ and early effector phenotypes specific to both H1N2 and H1N1 SwAIV. In commercial vaccinates, activated H1N2- and H1N1-specific IFNγ+&TNFα+, IL-17A+ and central memory T-helper/Memory cells, and in Nano-11-KAg+Poly(I:C) vaccinates H1N2-specific central memory, IFNγ+ and IFNγ+&TNFα+, and H1N1-specific IL-17A+ T-helper/Memory cells were observed. Systemically, Nano-11-KAg+Poly(I:C) vaccine augmented H1N2-specific IFNγ+ CTLs and H1N1-specific IFNγ+ T-helper/Memory cells, and commercial vaccine boosted H1N2- specific early effector CTLs and H1N1-specific IFNγ+&TNFα+ CTLs, as well as H1N2- and H1N1-specific T-helper/Memory cells with central memory, IFNγ+&TNFα+, and IL-17A+ phenotypes. Remarkably, commercial vaccine induced an increase in H1N1-specific T-helper cells in TBLN and naive T-helper cells in both TBLN and peripheral blood mononuclear cells (PBMCs), while H1N1- and H1N2-specific only T-helper cells were augmented in Nano-11-KAg+Poly(I:C) vaccinates in both TBLN and PBMCs. Furthermore, the Nano-11-KAg+Poly(I:C) vaccine stimulated robust cross-reactive IgG and secretory IgA (SIgA) responses in lungs, while the commercial vaccine elicited high levels of serum and lung IgG and serum hemagglutination inhibition (HI) titers. In conclusion, despite vast genetic difference (77% in HA gene identity) between the vaccine H1N2 and H1N1 challenge viruses in Nano-11-KAg+Poly(I:C) vaccinates, compared to over 95% identity between H1N1 of commercial vaccine and challenge viruses, the virus load and macroscopic lesions in the lungs of both types of vaccinates were comparable, but the Nano-11-KAg+Poly(I:C) vaccine cleared the virus from the nasal passage better. These data suggested the important role played by Nano-11 and Poly(I:C) in the induction of polyfunctional, cross-protective cell-mediated immunity against SwIAV in MDA-positive pigs.


INTRODUCTION
Swine influenza A virus (SwIAV) constitutes a significant economic and health risk to both animals and humans throughout the world. Pigs by virtue of their susceptibility to both avian and mammalian influenza A viruses, represent an intermediate animal reservoir facilitating genetic reassortment and interspecies dissemination. Currently, three circulating SwIAV subtypes (H1N1, H1N2 and H3N2) have been identified in both swine herds and human populations. Hence, the reduction of the rate of SwIAV infections in domestic pigs is crucial (1). This objective can be realized by use of efficacious vaccines, which confer broadly cross-protective and long-lasting immunity against evolving strains and subtypes even in the presence of MDA in finisher pigs. The persistence and levels of MDA in finisher pigs are highly variable resulting in variations in the response to SwIAV vaccines and high risk of seasonal SwIAV outbreaks. Current injectable SwIAV vaccines are plagued by several deficiencies such as the lack of cross-protective immunity, inability to elicit mucosal secretory IgA (SIgA) responses, and susceptibility to interference by MDA (2). Efforts are being made to overcome the problem of interference of MDA with mucosal vaccines (3,4). In these studies, vaccines are delivered intranasally to target the nasal/nasopharynx-associated lymphoid tissues (NALT) leading to the induction of strong cognate immune responses (5)(6)(7). Intranasal administration of vaccines against respiratory pathogens is performed to simulate natural infection leading to a robust induction of antigen-specific IgA and cell-mediated immune responses. This is attributed to the induction of antigen-specific mucosal immune responses in the NALT (6,8). However, the induction of effective immune responses following intranasal vaccination is challenging because of the tolerogenic mucosal environment. Furthermore, since the SwIAV KAg lacks adequate antigenicity, potent adjuvants such as Poly(I:C) can boost the antigen-specific antiviral responses (9,10). Hence, there is an urgent unmet demand for novel intranasal vaccines that counter the current threat of SwIAV more effectively even in the presence of MDA.
Nanoparticles (NPs)-based vaccines [nanovaccines] are revolutionizing the field of vaccinology. Nanovaccines are advantageous over oil adjuvant-based inactivated virus and subunit vaccines. Nanovaccines can protect vaccine antigens from degradation leading to amplification of the bioavailability via slow release of antigens and targeting antigens to antigenpresenting cells such as dendritic cells (11). Furthermore, inactivated virus and subunit antigens can be fortified with adjuvants such as synthetic double-stranded RNA, toll-like receptor-3 (TLR-3) ligand, Poly(I:C) to elicit robust antigenspecific immune responses (12,13). The KAg adjuvanted with Poly(I:C) upon intranasal delivery elicited a strong heterologous mucosal antibody response in pigs (14). Previously, our lab designed and characterized corn-based cationic alpha-D-glucan nanoparticles (Nano-11) and confirmed its potential as a reliable nanovaccine platform in pigs (15)(16)(17)(18). Nano-11 has inherent immunostimulatory properties and acts as an adjuvant (15,16). Hence, the present study was launched with an objective of developing a novel vaccine composed of KAg with Poly(I:C) coadsorbed together on Nano-11 [Nano-11-KAg+Poly(I:C)] for use in MDA-positive pigs. We hypothesized that this vaccine offers protection even in the presence of MDA.
Influenza-specific cell-mediated immune responses play an important role in host defense mechanisms. Accumulating body of scientific data in humans, mice and pigs corroborate the critical protective role of antigen-specific cell-mediated immune responses. The protective role of cross-reactive CD8 + T-cells targeting conserved viral epitopes was reported by earlier pioneering studies (19). Likewise, the presence of antigenspecific T-cells led to the amelioration of symptoms and reduced shedding in case of 2009 influenza pandemic in humans (20,21). In mice, influenza virus infection elicits antigen-specific T-cell responses leading to protection in the absence of neutralizing antibodies (22). Administration of signal minus Flu (S-FLU) universal influenza vaccine led to alleviation of lung pathology and virus burden in nasal passages and lungs following homologous and moderately matched virus challenge devoid of neutralizing antibodies in pigs (23). In addition, intranasal delivery of poly D,L-lactic-co-glycolic acid (PLGA) nanoparticles entrapped with H1N1 influenza virus derived conserved peptides elicited a robust antigen-specific T-cell response but not neutralizing antibody response leading to reduced lung pathology following a heterologous virus challenge in pigs (24). Furthermore, in pigs, the kinetics of SwIAV H1N2-specific cell-mediated immune responses were analyzed. In the lung draining TBLN at 4 days post-infection (DPI), proliferating CD4 + T-cells were identified (25). In addition, at 9 and 12 DPI, maximum frequencies of polyfunctional IFNg + IL-2 + TNFa + CD4 + T-cells were detected in both PBMCs and TBLN mononuclear cells (MNCs). In SwIAV infected pigs at 44 DPI, IFNg + &TNFa + , IFNg + &IL-2 + , and TNFa + &IL-2 + CD4 + T-cells were present in the lungs, TBLN, and PBMC. The predominant frequencies of CD4 + Tcells, CD4 + CD8 + T-cells in SwIAV infected pig bronchoalveolar lavage (BAL) has also been reported. However, H1N2-specific proliferating IFNg + or IFNg + &TNFa + double positive Perforin + CD27 + CD8 + T-cells reached peak frequencies at 6 DPI and persisted up to 44 DPI in lungs (25). Following the H1N1 challenge, CD8 + T-cells translocated to lungs and BAL at 6 DPI (26). These findings emphasize the significance of antigenspecific polyfunctional cell-mediated immune responses. Therefore, in this study we characterized the array of SwIAVspecific cell-mediated immune responses in MDA-positive pigs, which received intranasal Nano-11-KAg+Poly(I:C) and compared vaccine efficacy with intramuscular commercial SwIAV vaccine.

Animal Studies
Three-week old influenza MDA positive weaned pigs born to sows vaccinated with FluSure XP ® twice during pregnancy as per the manufacturer guidelines were procured and vaccinated intranasal through both the nostrils twice with Nano-11-KAg +Poly(I:C) or as a control Mock saline, KAg+Poly(I:C), Nano-11-KAg by using a spray mist delivery device (Prima Tech USA, NC) (30). The commercial vaccine was administered intramuscular as per manufacturer's guidelines. Pigs were boosted with the same dose of vaccine and route after three weeks of prime vaccination. Blood was collected on day 34 postprime vaccination (Prechallenge; PC) for the isolation of PBMCs in restimulation assays in vitro. Two weeks after the second dose of vaccination (Day 35), pigs were challenged with a virulent SwIAV SW/OH/24366/2007 (H1N1-OH7), 6 × 10 6 TCID 50 /ml per pig 50% amount by intranasal and other 50% by intratracheal route (30). Pigs were kept under observation for clinical disease and euthanized at post-challenge day 6 (DPC6), examined the lungs, and collected nasal swabs, BAL fluid, lung, TBLN, and blood for immune and viral analyses (Supplementary Figure 2). Each of the above-mentioned experimental groups comprised of 4-6 pigs, and the number of animals that were used in the experimental analyses has been mentioned in the respective figure legends.

Analysis of T Cell Populations
PBMCs isolated at day 34 post-prime vaccination (prechallenge) and DPC6 and TBLN mononuclear cells (MNCs) isolated at DPC6 were restimulated with H1N2-OH10 and H1N1-OH7 SwIAV KAg [10 ug/ml] for 72 hours (hr) in vitro. The cells were labeled and analyzed by flow cytometry for frequencies of , a n d n a ï v e T -h e l p e r c e l l s [CD3 + CD4 + CD8ab -CD27 + ] as described previously (17,30).

Surface and Intracellular Cytokine Staining for Flow Cytometry
Approximately 10 million PBMCs or TBLN MNCs isolated at indicated time points as described previously (30) and were seeded in a 24-well flat bottom plate in 2-ml total volume of culture medium (RPMI 1640, 10% FBS). The cells were restimulated with H1N2-OH10 SwIAV at 0.1 multiplicity of infection (MOI) and H1N1-OH7 SwIAV KAg at 10 ug/ml for 72 h in vitro. Protein transport inhibitors Brefeldin A (GolgiPlug) and Monensin (GolgiStop) (BD Biosciences, San Jose, CA) were added for the last 6 h of the incubation period. Cells were harvested, washed, blocked with 1% normal rabbit serum, and split into appropriate number of wells in a 96-well round bottom plate for the surface and intracellular cytokine immunostaining. Appropriate isotype control antibodies staining was included as negative controls for the flow cytometry. The panels of antibodies and their corresponding isotype controls used in flow cytometry were described (Figures 1A-C; Supplementary Tables 1-3). Cells were transferred to a 96-well round bottom plate, washed twice in 200 µl of PBS/well, and subjected to surface staining using fluorochrome conjugated monoclonal antibodies (mAbs) against indicated markers and their corresponding isotype controls at previously titrated and optimized dilutions in 50 µl total volume for 30 min at 4°C. Cells were fixed using 1% paraformaldehyde at 4°C for 30 min and resuspended in FACS buffer. Cells were washed once with PBS and permeabilized with 10% Saponin for 45 min at room temperature. Subsequently, cells were washed with Saponin wash (0.1% saponin) and incubated with fluorochrome conjugated mAb against indicated markers and their corresponding isotype controls at previously titrated and optimized dilutions in 50 µl final volume for 45 min at 4°C. Cells were washed once in Saponin wash and stained with indicated secondary antibodies for 45 min at 4°C. Cells were washed once and resuspended in 200 µl FACS buffer and transferred to FACS tubes and acquired using a lymphocyte gate by using BD FACS Aria II machine. For each sample, 100,000 events were acquired. The data were analyzed using FlowJo software (FlowJo V10, Becton, Dickinson& Company; BD) and plotted using GraphPad Prism (GraphPad Prism 5, CA).

Enzyme-Linked Immunosorbent Assay
IAV specific isotype IgG and SIgA antibodies titers were analyzed by enzyme-linked immunosorbent assay (ELISA) as described previously (30,31). Briefly, 96-well flat bottom high binding affinity plates were coated with pre-titrated (10 mg/mL) killed virus antigens of IAV H1N1-OH7, H1N2-OH10, or H3N2-OH4 and incubated overnight at 4°C. Plates were washed with PBS-Tween20 (0.05%) and blocked for 2 h with 5% dry milk in PBS-Tween20. Test samples were serially diluted in 2.5% dry milk powder in PBS-Tween20 at a starting dilution of 1:2 for nasal swab and 1:100 for serum, BAL, and lung lysate samples, and 50 ml/well were added to plates and incubated overnight at 4°C. Plates were washed and incubated at RT for 2 h with 50 ml/well of goat anti-pig IgA conjugated with HRP (Bethyl Laboratories Inc., TX) at pre-titrated 1:2,000 dilution or peroxidase labeled AffiniPure Goat Anti-Swine IgG (H+L) (Jackson ImmunoResearch Laboratories Inc., PA) 1:8,000 dilution in 2.5% dry milk in PBS-Tween20. After washing plates were added with a 1:1 mixture of peroxidase substrate solution B and TMB (KPL, MD) (50 ml/well) and incubated for 20 min. The reaction was stopped by adding 1 M phosphoric acid (50 ml/well), and the optical density (OD) was measured by Spectramax microplate reader at 450 nm. The corrected OD values were obtained by subtracting the average value of blank from the test samples.

Virus Titration
Virus titers were determined as previously described (30,31). Briefly, 96-well tissue culture plates were seeded with 100 ml/well of MDCK cells (2 × 10 4 cells/well) in DMEM enriched media and incubated in a 37°C humidified 5% CO 2 incubator overnight. In another set of sterile 96-well round-bottom plates, a ten-fold serial dilution of nasal swab, BAL fluid, and lung lysate samples were prepared using serum-free DMEM. Plates containing confluent monolayer of MDCK cells were washed three times with sterile 1X PBS and inoculated with 100 ml/well of serially diluted test samples for 1.5 h at 37°C in a 5% CO 2 incubator followed by 100 ml/well of DMEM serum-free medium containing 2 µg/ml of TPCK-trypsin (Sigma, St. Louis, USA) were added. Plates were incubated for 36 h and fixed with 80% acetone (10 min) for immunostaining. Cells were incubated with (50 ml/well) an Influenza A virus (IAV) nucleoprotein specific mAb (#M058, CalBioreagents, CA) diluted 1:5,000 for 2 h at incubator. Cells were washed and incubated for 1.5 h with (50 ml/well) the secondary antibody Alexa Fluor 488 conjugated goat anti-mouse IgG (H+L) antibody (Life Technologies, OR) at incubator. Mounting media (Glycerol: PBS, pH = 8 at 6:4 proportion) 50 ml/well was added to the immunostained cell plates. Infection was recorded using an Olympus, NY fluorescent microscope, and infectious titer was determined by Reed and Muench method.

Determination and Scoring of Gross Lung Lesions
Gross lung lesions were assigned a score on the basis of purplered consolidation of virus affected lesions in each lung lobe. The final lung lesions score was determined by calculating the average of dorsal and ventral lung lobe scores as described previously (32).

Hemagglutination Inhibition Assay
The virus specific HI titers were determined as described previously (30,31). Briefly, heat-inactivated test serum samples were 2-fold serially diluted in sterile 1X PBS and incubated for 30 min with 8 HAU (Hemagglutination Units) (25 ml/ml) of H1N2-OH10 or H1N1-OH7 SwIAV. The serum/virus mixture was incubated for 30 min with 1% turkey red blood cells. HI titer in serum is the reciprocal of the last well with complete hemagglutination inhibition.

Statistical Analysis
Statistical analysis of immune cells data was carried out by using one-way ANOVA followed by Tukey's post-test. Analysis of titers of IgG and SIgA antibody responses were carried out using two-way ANOVA followed by the Bonferroni test. Data represent the mean value for four to six pigs ± SEM. A p < 0.05 was considered statistically significant.

Commercial Vaccine Elicited Strong Systemic HI Antibody Response in MDA Positive Pigs
Consistent with the augmented systemic IgG response in commercial SwIAV vaccinates, a significantly higher H1N2and H1N1-SwIAV-specific serum HI antibody titers at both DPV35 and DPC6 compared to their counterparts from Nano-11 based SwIAV vaccine groups was observed ( Figures 9A-D).
An increase in H1N2-specific HI titers was also detected in KAg+ Poly(I:C) vaccinates at DPV35 and DPC6 respectively ( Figures  9A, C). It is evident that parenterally administered commercial vaccine induces significantly higher SwIAV-specific serum HI antibody response in MDA-positive pigs.

DISCUSSION
The holy grail in modern vaccinology is the "Rational Vaccine Design" wherein we strive to improve the vaccine efficacy by adding different components including adjuvants. Statistical analysis was carried out using two-way ANOVA followed by the Bonferroni test. Each letter indicates the significant difference between the groups at the indicated dilution. The letters a, b, c, d, and e indicate the difference between the mock group compared to Mock+Ch, Commercial SwIAV vaccine+Ch, Nano-11-KAg+Ch, Nano-11-KAg+Poly(I:C)+Ch, and KAg+Poly(I:C)+Ch, respectively. The letters f, g, h, and i indicate the difference between Mock+Ch group compared to Commercial SwIAV vaccine+Ch, Nano-11-KAg+Ch, Nano-11-KAg+Poly(I:C)+Ch and KAg+Poly(I:C)+Ch, respectively. The letters j, k, and l indicate the difference between Commercial SwIAV vaccine+Ch compared to Nano-11-KAg+Ch, Nano-11-KAg+Poly(I:C)+Ch and KAg+Poly(I:C)+Ch, respectively. The letter m indicates the difference between Nano-11-KAg+Ch and Nano-11-KAg+Poly(I:C)+Ch. The letter n and o indicates the difference between KAg+Poly(I:C)+Ch group compared to Nano-11-KAg+Ch and Nano-11-KAg+Poly(I:C)+Ch groups, respectively.
complement, and inflammasomes identical to that of a live attenuated yellow fever vaccine in humans (9) In the lung draining TBLN, Nano-11-KAg+Poly(I:C) vaccine induced increased frequencies of H1N2-specific total CTLs with enhanced generation of T-helper/Memory cells having central memory phenotypes, and polyfunctional activity (IFNg + , IFNg + &TNFa + ). Furthermore, it also elicited H1N1-specific IL-17A + T-helper/Memory cell frequencies. These results indicated the induction of a robust and cross-reactive cellmediated immune response by Nano-11-KAg+Poly(I:C) vaccine in the TBLN. In contrast, in commercial vaccinates, the H1N2-specific response was characterized by augmented early effector CTLs and CTLs expressing IL-17A and central memory phenotypes, and T-helper/Memory cells expressing IFNg &TNFa. In addition, observed H1N1-specific increased early effector and polyfunctional (IL-17A + and IFNg + &TNFa + ) CTLs and activated central memory, IFNg + &TNFa + , and IL-17A + T-helper/Memory cells, with excess accumulation of naive T-helper cell populations. Taken together, these data suggested that the commercial vaccine elicits much slower kinetics and inefficient cell-mediated immune responses compared to Nano-11-KAg+Poly(I:C) vaccine at both the systemic and mucosal compartments in MDA-positive pigs.
In intranasal Nano-11-KAg+Poly(I:C) vaccinates, robust SwIAV-specific cell-mediated immune responses were mediated likely through efficient induction of innate immune pathways involved in antigen recognition/presentation/ activation such as apoptosis-associated speck-like protein containing a CARD (ASC)/Caspase-1 inflammasomes, dendritic cell (DC) maturation, nuclear factor-kB (NF-kB) signaling needed for mounting protective cognate adaptive immune responses (9,12,35). This leads to enhanced differentiation of naïve T-helper cells into effector T-helper/ Memory cells [CD3 + CD4 + CD8a + CD8b -CD27 -], which are capable of secreting high amounts of effector cytokines leading to efficient clearance of heterologous challenge virus at the site of infection. Unlike the commercial vaccine, the cytokine and cellular signatures in Nano-11-KAg+Poly(I:C) vaccinates were dominated by IFNg single positive and central memory T-helper/ Memory cells and polyfunctional T-helper/Memory cells (IFNg + &TNFa + and IL-17A + ) leading to induction of strong cell-mediated immune responses. In contrast, the commercial vaccine elicited predominant IL-17A, IFNg + &TNFa + production from CTLs, early effector CTLs, and predominantly central memory, T-helper/Memory cells expressing similar cytokines. It is possible that the adjuvant Poly(I:C) used in Nano-11-KAg delivered intranasal vs Amphigen a stable oil-in-water emulsion used in parenteral delivered commercial vaccine are playing critical role/s in these outcomes. Even though there is a predominance of IL-17A secreting cells in commercial vaccinates, it is possible that Th17 cells are transdifferentiating to Th1 cells generating IFNg (36,37), Alternatively, it is possible that IL-17A could be playing a dual role in commercial vaccine administered animals.
The in vitro generated IL-17A producing CTLs showed their ability to display memory phenotype and serve as a source of Type 1 CTLs secreting IFNg and possess potent cytotoxic ability in mice (38). In this study, we characterized IL-17A production from both antigen specific CTLs and T-helper/Memory cells. There are several reports documenting an increased population of IL-17A producing T cells and secretion of IL-17A in pigs, such as the presence of Actinobacillus pleuropneumoniae specific Th17 cells [CD4 + CD8a dim IL-17A + ] in the blood and lungs of porcine contagious pleuropneumonia infected pigs (39). IL-17 is a proinflammatory cytokine, likely associated with inflammation in the lungs of pigs infected with Porcine Reproductive and Respiratory Syndrome Virus (PRRSV), because in the serum and BAL fluid of highly pathogenic PRRSV infected pigs IL-17A was detected, and in PRRSV infected alveolar macrophages in vitro high levels of IL-17A gene expression was observed (40). The presence of enhanced IL-17A producing cells in PBMCs was detected following PMA and ionomycin activation in vitro (41).
Furthermore, there was a report on switching of systemic Th1 to tissue-resident Th17 protective response upon mucosal administration of adjuvanted tuberculosis vaccine in mice and this protection was independent of TNFa and IL-17 receptors (42). Likewise, HIVgp140 adjuvanted with glucopyranosyl lipid adjuvant [a synthetic TLR-4 agonist] administered intranasally induced protective Th17 responses in mice (43). However, the administration of a detergent split influenza antigen adjuvanted with a TLR4 ligand CRX-601 intranasally led to the induction of harmful antigen specific CD4 + TNFa + Th17 + cells in mice (44). Another group of researchers (45) reported the negative regulation of Th17 responses by IL-10 during influenza infection in mice and this effect correlates with defective protection in high dose primary but not secondary challenge infection. These results highlight the complex regulatory roles of IL-17A during infection. Further investigations are needed to elucidate the mechanisms governing the protective, inhibitory and pathological roles mediated by IL-17A during influenza infection so that better vaccine designs can be engineered to offer potent cross-protection against evolving field strains.
Our results are consistent with the published literature highlighting the critical role of antigen specific CTLs and Thelper/Memory cell responses against SwIAV (25,33,46). Furthermore, there are several reports that underline the pivotal roles of cell-mediated immune responses in a variety of settings. In pigs, the significant roles of CD4 + T-cells, CTLs and gd T-cells have been demonstrated in PRRSV infection in pigs (47); CD8 + T-cells and T-helper/memory cells following pseudorabies live attenuated vaccination (48); CD3 + CD4 -CD8a hi CTLs in classical swine fever live attenuated vaccine and virulent challenge infection (49); and CD4 + CD8a hi ab Tcells during melanoma tumor regression in swine model (50). Furthermore, Dengue virus-specific T-cell response in humans in response to live attenuated vaccination and challenge infection was detected (51). These findings emphasize the significance of cross-protective cell-mediated immune responses against conserved epitopes.
The commercial inactivated SwIAV vaccine is multivalent and consists of H1N1, H1N2, and H3N2 SwIAVs. The HA gene of our challenge virus H1N1-OH7 shares 95.2% and 77.9% identity with the corresponding H1N1 and H1N2, respectively, of the commercial vaccine. However, our monovalent Nano-11-KAg vaccine comprises of H1N2-OH10, which has 77% HA identity with the challenge H1N1-OH7 IAV. Hence, it is plausible that the commercial vaccine stimulated immune responses against the homologous virus H1N1; in contrast, the Nano-11-KAg+Poly(I:C) vaccine elicited cross-reactive cognate cell-mediated immune responses, associated with robust mucosal humoral and cytokine responses in MDA-positive pigs (Supplementary Figure 3). The control KAg+Poly(I:C) group exhibited significant antibody responses, which are consistent with a previous study in pigs (14), which can be attributed to the adjuvant Poly(I:C). In this study, we used KAg with Poly(I:C) coadsorbed on Nano-11 to target the dendritic cells to ensure efficient induction of cognate cell-mediated immune responses conferring protection in the presence of MDA.
Designing nanovaccines coupled with a potent inducer of nonspecific effector responses of innate immune cells (trained immunity) (52), which elicit broad-spectrum protective immune responses targeting conserved internal T-cell and B-cell epitopes of viruses is an efficient strategy to combat constantly evolving and emerging IAV strains. Furthermore, unbiased systems-wide characterization of novel innate and adaptive correlates of protection are essential. Studies are underway to further improve the efficacy of the Nano-11-KAg vaccine by incorporation of multivalent SwIAV and split virus antigens coupled with potent adjuvant/s to further enhance the breadth of immunity, which is long-lasting against constantly emerging field strains of SwIAVs.

CONCLUSIONS
The three IAV subtypes (H1N1, H1N2, and H3N2) circulating in the swine population are also prevalent among human seasonal flu viruses. The flu vaccines capable of eliciting broadly reactive humoral and cell-mediated immune responses in the respiratory tract are essential to mitigate both swine herds and human populations. Furthermore, to protect finisher pigs from SwIAV infections, a potent intranasal vaccine, which overcomes the interference caused by highly variable levels of MDA is required. Commercial multivalent SwIAV vaccine is capable of eliciting robust cellular immune responses but appears to be of a strong inflammatory nature, associated with the accumulation of naïve Thelper cells in both the mucosal lymph nodes and systemic compartment suggesting its possible inefficient antigen presentation nature in MDA-positive pigs. In contrast, the monovalent Nano-11-KAg+Poly(I:C) vaccine stimulated robust cross-reactive IgG and SIgA antibodies in the lungs and broadly protective polyfunctional cell-mediated immune responses to highly variant SwIAV, associated with a reduction in viral load in the airways and amelioration of lung pathology comparable to a multivalent commercial vaccine (Supplementary Figure 3). Thus, our study suggests the promise of intranasal delivery of Nano-11 and Poly(I:C) based inactivated SwIAVs vaccine in enhancing the breadth of cross-protective immunity against constantly emerging field strains of viruses in MDA-positive pigs, which will reduce economic losses from flu outbreaks.

DATA AVAILABILITY STATEMENT
The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

ETHICS STATEMENT
The animal study was reviewed and approved by Institutional Animal Care and Use Committee at The Ohio State University.

AUTHOR CONTRIBUTIONS
VP, SR, and GR conceived and developed the research, and VP and GR wrote the manuscript. SR formulated and characterized the vaccines. VP, SR, and NF-R did the experiments and analyzed the data. VP, SR, NF-R, JS, YH, and AR helped in vaccination and challenge trials in pigs, including sample collection and processing. VP performed flow cytometry analyses. HH analyzed the data and edited the manuscript. SD grew the vaccine and challenge viruses. All authors contributed to the article and approved the submitted version.

FUNDING
This work was partially supported by the National Pork Checkoff. Salaries and research support were provided by state and federal funds appropriated to OARDC, The Ohio State University.

ACKNOWLEDGMENTS
We would like to thank Dr. Juliette Hanson, Sara Tallmadge and Megan Strother for their help in animal studies.