Immune response in domestic ducks following intradermal delivery of inactivated vaccine against H5N1 highly pathogenic avian influenza virus adjuvanted with oligodeoxynucleotides containing CpG motifs

Duck CD8+ T Cell Response to H5N1 Highly Pathogenic Avian Influenza Virus Infection In Vivo and In Vitro

Domestic ducks are the important host for H5N1 highly pathogenic avian influenza virus (HPAIV) infection and epidemiology, but little is known about the duck T cell response to H5N1 AIV infection. In infection experiments of mallard ducks, we detected significantly increased CD8+ cells and augmented expression of cytotoxicity-associated genes, including granzyme A and IFN-γ, in PBMCs from 5 to 9 d postinfection when the virus shedding was clearly decreased, which suggested the importance of the duck cytotoxic T cell response in eliminating H5N1 infection in vivo. Intriguingly, we found that a CD8high+ population of PBMCs was clearly upregulated in infected ducks from 7 to 9 d postinfection compared with uninfected ducks. Next, we used Smart-Seq2 technology to investigate the heterogeneity and transcriptional differences of the duck CD8+ cells. Thus, CD8high+ cells were likely to be more responsive to H5N1 AIV infection, based on the high level of expression of genes involved in T cell responses, activation, and proliferation, including MALT1, ITK, LCK, CD3E, CD247, CFLAR, IL-18R1, and IL-18RAP. More importantly, we have also successfully cultured H5N1 AIV-specific duck T cells in vitro, to our knowledge, for the first time, and demonstrated that the CD8high+ population was increased with the duck T cell activation and response in vitro, which was consistent with results in vivo. Thus, the duck CD8high+ cells represent a potentially effective immune response to H5N1 AIV infection in vivo and in vitro. These findings provide novel insights and direction for developing effective H5N1 AIV vaccines.

The Immunomodulatory Functions of Various CpG Oligodeoxynucleotideson CEF Cells and H9N2 Subtype Avian Influenza Virus Vaccination

CpG oligodeoxynucleotides (CpG ODN) present adjuvant activities for antigen proteins, which can induce humoral and cellular immune responses to antigens. However, the immunomodulatory functions of CpG ODNs with different sequences are very different. In this paper, six CpG ODNs with different sequences were designed based on CpG2007 as a template. Through the screening of CEF cells in vitro, the stimulating activity of CpG ODNs was determined. Then, two selected CpG ODN sequence backbones were modified by substituting the oxygen with sulfur (S-CpG) and verifying the immune activity. Next, to prove the feasibility of S-CpG as an immune potentiator, two immune models with or without white oil adjuvant were prepared in 20-day-old chicken vaccinations. The screening experiment in vitro showed that the inducing roles of CpG ODN 4 and 5 could strongly stimulate various immune-related molecular expressions. Additionally, CpG ODN 4 and 5 with sulfation modification significantly induced various cytokines’ expressions. Furthermore, CpG ODN 4 and 5 induced the strongly humoral and cellular immune responses during vaccination, in which white oil, as an adjuvant, could significantly improve the immune effect of CpG ODN. These results provide an important experimental basis for exploring the structural characteristics and vaccine immunity of CpG ODN.

Toll-Like Receptor 21 of Chicken and Duck Recognize a Broad Array of Immunostimulatory CpG-oligodeoxynucleotide Sequences

CpG-oligodeoxynucleotides (CpG-ODNs) mimicking the function of microbial CpG-dideoxynucleotides containing DNA (CpG-DNA) are potent immune stimuli. The immunostimulatory activity and the species-specific activities of a CpG-ODN depend on its nucleotide sequence properties, including CpG-hexamer motif types, spacing between motifs, nucleotide sequence, and length. Toll-like receptor (TLR) 9 is the cellular receptor for CpG-ODNs in mammalian species, while TLR21 is the receptor in avian species. Mammalian cells lack TLR21, and avian cells lack TLR9; however, both TLRs are expressed in fish cells. While nucleotide sequence properties required for a CpG-ODN to strongly activate mammalian TLR9 and its species-specific activities to different mammalian TLR9s are better studied, CpG-ODN activation of TLR21 is not yet well investigated. Here we characterized chicken and duck TLR21s and investigated their activation by CpG-ODNs. Chicken and duck TLR21s contain 972 and 976 amino acid residues, respectively, and differ from TLR9s as they do not have an undefined region in their ectodomain. Cell-based TLR21 activation assays were established to investigate TLR21 activation by different CpG-ODNs. Unlike grouper TLR21, which was preferentially activated by CpG-ODN with a GTCGTT hexamer motif, chicken and duck TLR21s do not distinguish among different CpG-hexamer motifs. Additionally, these two poultry TLR21s were activated by CpG-ODNs with lengths ranging from 15 to 31 nucleotides and with different spacing between CpG-hexamer motifs. These suggested that compared to mammalian TLR9 and grouper TLR21, chicken and duck TLR21s have a broad CpG-ODN sequence recognition profile. Thus, they could also recognize a wide array of DNA-associated molecular patterns from microbes. Moreover, CpG-ODNs are being investigated as antimicrobial agents and as vaccine adjuvants for different species. This study revealed that there are more optimized CpG-ODNs that can be used in poultry farming as anti-infection agents compared to CpG-ODN choices available for other species.

Experimental infection of dogs with highly pathogenic avian influenza virus (H5N8)

During the highly pathogenic avian influenza (HPAI) H5N8 virus outbreak in Korea, a dog in layer farm contaminated by H5N8 was reported seropositive for HPAI H5N8. To investigate the possibility of adaptation and transmission of HPAI H5N8 to dogs, we experimentally inoculated dogs with H5N8. Viral genes were weakly detected in nasal swabs and seroconversions in inoculated and contact dogs. Although the H5N8 virus did not induced severe clinical signs to dogs, the results suggest that surveillance of farm dogs should continue as a species in which the avian influenza virus may acquire infectivity to mammals through frequent contact with the virus.

Topical CpG Oligodeoxynucleotide Adjuvant Enhances the Adaptive Immune Response against Influenza A Infections

Current influenza vaccines generate humoral immunity, targeting highly variable epitopes and thus fail to achieve long-term protection. T cells recognize and respond to several highly conserved epitopes across influenza serotypes. A strategy of raising strong cytotoxic T cell memory responses to epitopes conserved across serotypes would provide cross serotype protection, eliminating the need for annual vaccination. We explored the adjuvant potential of epicutaneous (ec) and subcutaneous (sc) delivery of CpG oligodeoxynucleotide in conjunction with sc protein immunization to improve protection against influenza A virus (IAV) infections using a mouse model. We found enhanced long-term protection with epicutaneous CpG ODN (ecCpG) compared to subcutaneous CpG ODN (scCpG) as demonstrated by reduced viral titers in the lungs. This correlated with increased antigen-specific CD8 T cells in the airways and the lungs. The memory T cell response after immunization with ecCpG adjuvant was comparable to memory response by priming with IAV infection in the lungs. In addition, ecCpG was more efficient than scCpG in inducing the generation of IFN-γ producing CD4 T cells. The adjuvant effect of ecCpG was accompanied with its ability to modulate tissue-homing molecules on T cells that may direct them to the site of infection. Together, this work provides evidence for using ecCpG to induce strong antibody and memory T cell responses to confer protection against IAV infection.