Enhancement of humoral and cellular immunity in chickens against reticuloendotheliosis virus by DNA prime-protein boost vaccination

An optimized secretory expression system and immunogenicity evaluation for glycosylated gp90 of avian reticuloendotheliosis virus

Reticuloendotheliosis is an important immunosuppressive disease, associated with avian reticuloendotheliosis virus (REV) infection, and causes notable economic losses worldwide. Glycoprotein gp90 is an important structural protein of REV, and considered to be the most important immunogenic antigen, which can induce neutralizing antibodies against REV. In this study, an optimized suspension culture system was developed and applied to secretory express the immunogenic surface antigen gp90. To achieve an optimal glycosylation, the gp90 was designed to secretory expressed into the supernatant of the cell culture, which also occurs in the natural protein maturation procedure of REV. Serum-free culture medium was introduced to simplify the purification process and reduce the production costs. Based on the purified glycosylated gp90, an oil-emulsion subunit REV vaccine candidate was developed and evaluated in chickens. The subunit gp90-based vaccine induced fast immune responses, high levels of antibodies (REV-specific antibody, gp90-specific antibody, and neutralizing antibody against REV), and preferential T helper 2 (Th2) (interleukin-4 secretion) not Th1 (interferon-γ secretion) response. Furthermore, the viremia induced by REV infection was significantly reduced in chickens immunized with the glycosylated gp90. Overall, an optimized secretory expression system for glycosylated gp90 was developed, and the glycosylated gp90 obtained in this study retained good immunogenicity and could be an attractive vaccine candidate to protect chickens against REV horizonal infection.

A DNA priming and protein boosting immunization scheme to augment immune responses against parvovirus in ducks

AIMS

To evaluate the effect of a DNA priming and protein boosting immunization scheme in ducks.

METHODS AND RESULTS

Pekin ducks were immunized with pTCY/VP2 DNA vaccine; on day 14 (D14) after primary immunization, the ducks were boosted with either the same vaccine (DNA + DNA) or the rVP2 vaccine (DNA + rVP2). CpG oligodeoxynucleotides containing three copies of GACGTT motifs were used as the adjuvant in the vaccines. Compared with unimmunized controls, both immunization schemes significantly increased the titre of antigen-specific antibodies, lymphocyte proliferation index, percentage of CD4⁺ and CD8⁺ cells in peripheral blood mononuclear cells (PBMCs) and mRNA expression of interferon (IFN)-α, IFN-γ, interleukin (IL)-6 and IL-12 in antigen-stimulated PBMCs. Furthermore, compared with the DNA + DNA homologous scheme, the DNA + rVP2 heterologous scheme significantly increased lymphocyte proliferation, percentage of CD4⁺ and CD8⁺ cells in PBMCs and upregulation of mRNA expression of cytokines 2 weeks after the boost (D28).

CONCLUSIONS

The DNA + rVP2 immunization scheme enhanced immune responses, mainly Th1 type, against parvovirus in ducks.

SIGNIFICANCE AND IMPACT OF THE STUDY

The DNA priming and protein boosting heterologous immunization strategy can be applied to develop vaccines against viral infections in ducks. It can potentially be used in breeding ducks because of long-term immunity may confer protection for ducklings.

Preparation of the Secretory Recombinant ALV-J gp85 Protein Using Pichia pastoris and Its Immunoprotection as Vaccine Antigen Combining with CpG-ODN Adjuvant

This study focuses on preparing the secretory recombinant J subgroup of avian leukosis virus (ALV-J) gp85 protein using Pichia pastoris and evaluating its immunoprotection as vaccine antigen combining with CpG-ODN adjuvant. The secretory recombinant plasmid pPIC9-gp85 containing ALV-J gp85 gene was designed and was transfected into the genome of P. pastoris (GS115) cells. The recombinant plasmid was expressed under the induction of methanol. The expressed products in the medium of the cells were purified and identified with endoglycosidase digestion assay and western blot mediated with monoclonal antibody (MAb) JE9. The purified product combining with CpG-ODN adjuvant was inoculated intramuscularly into 7-day-old chickens and three booster inoculations were performed on 21 days post first inoculation (dpfi), 42, and 56 dpfi. The antibody responses and cellular immune responses were detected, and the protective effects were analyzed after challenge with ALV-J. The results showed that the secretory pPIC9-gp85 plasmid was successfully constructed and could be stably expressed in GS115 cells. The expressed products were N-acetylglucosylated and could specifically combine with MAb (JE9). The secreted gp85 protein combining with CpG-ODN adjuvant could induce higher antibody response and spleen lymphocyte proliferation response and IFN-γ-inducing response, and could protect all the inoculated chickens against the viremia and the immunosuppressive lesions caused by ALV-J challenge. The results of neutralizing test in vitro suggested that the antisera with some ALV-J antibody titers could neutralize ALV-J strain and inhibit the growth of virus in vitro. The result of IFA showed that IgG antibody in the antisera could specifically combine with ALV-J strain in cells. It can be concluded that the secretory recombinant gp85 protein, as a new acetylglucosylated gp85 protein, was successfully prepared and combining with CpG-ODN adjuvant could protect the inoculated chickens against ALV-J infection. This study first reported the methods on preparing the secretory recombinant ALV-J gp85 protein using P. pastoris and evaluated its immunoprotection.

An Inactivated Novel Genotype Fowl Adenovirus 4 Protects Chickens against the Hydropericardium Syndrome That Recently Emerged in China

Since 2015, China has experienced outbreaks of severe hydropericardium syndrome (HPS), associated with a novel genotype and hypervirulent fowl adenovirus serotype 4 (FAdV-4) infection, with a prevalence in various provinces of the country. This has resulted in huge economic losses in the poultry industry. The novel FAdV-4 showed new genome characters, such as the natural deletion of open reading frame (ORF) 19 and ORF 27 (1966 bp), and high pathogenicity toward chickens. These are coupled with severe hydropericardium, inclusion body hepatitis, and mortality rates ranging from 30% to 90%. Although several inactivated and subunit vaccines against the traditional FAdV-4 have been developed, no commercial vaccine against the emerged disease caused by the novel strain has been available until now. The potential risks of infection with this novel hypervirulent FAdV-4 urgently require an effective vaccine. Thus, an inactivated oil-emulsion FAdV-4 vaccine formulated with the novel genotype virus was developed in this study. The vaccine provided a high level of antibody, preferential T helper 2 (Th2) (interleukin-4 secretion) not Th1 (interferon-γ secretion) response, and full protection against a lethal dose of the novel hypervirulent FAdV-4. Therefore, the novel genotype FAdV-4 vaccine is proposed as an attractive candidate to prevent and reduce the spread of HPS in the poultry industry of China.

Immunoprotection induced by CpG-ODN/Poly(I:C) combined with recombinant gp90 protein in chickens against reticuloendotheliosis virus infection

The present study is focused on investigating the immunoprotective effects of CpG-ODN/Poly(I:C) combined with the viral glycoprotein gp90 protein against reticuloendotheliosis virus (REV) infection in chickens. REV's gp90 gene was amplified from the REV-infected cells and expressed in Escherichia coli (E.coli). The expressed products, upon purification, were inoculated into 7-day-old chickens with PBS, CpG-ODN or Poly(I:C) adjuvant; Two booster inoculations were then conducted, and then each chicken was challenged. The presence of REV-antibodies in serum was determined weekly after the first vaccination. The viremia and immunosuppressive effects of REV infection were also monitored after the challenge. The neutralizing effects of the antisera were tested in vitro. The results showed that the recombinant gene containing REV gp90 gene was expressed into the recombinant protein with a size of 51 Kilo Dalton (KD), which could be recognized by a monoclonal antibody (MAb) against the gp90 protein. The viremia and immunosuppressive effects of avian influenza virus (AIV) vaccine caused by REV challenge in CpG-ODN group and in Poly(I:C) group were dramatically decreased. REV antibody with low titers was induced in gp90 group and the inoculated chickens were partly protected. Compared with those in gp90 group, the titers and the positive ratios of REV antibody in CpG+gp90 group were significantly increased, whereas the viremia and immunosuppressive effects of AIV vaccine caused by REV infection were significantly decreased. In the Poly(I:C) +gp90 group, the viremia and immunosuppressive effects caused by REV infection were also dramatically decreased, although REV antibody responses were softly increased. The diluted antisera from the vaccinated chickens in both groups could completely inhibit the replication of REV in chick fibroblast cells (CEF). Hence, it can be concluded that CpG-ODN or the Poly(I:C) adjuvant can enhance the antiviral effects of the REV subunit vaccine against REV infection, which may result from different mechanisms.

A prime/boost vaccination with HA DNA and Pichia-produced HA protein elicits a strong humoral response in chickens against H5N1

Highly pathogenic avian influenza viruses cause severe disease and huge economic losses in domestic poultry and might pose a serious threat to people because of the high mortality rates in case of an accidental transmission to humans. The main goal of this work was to evaluate the immune responses and hemagglutination inhibition potential elicited by a combined DNA/recombinant protein prime/boost vaccination compared to DNA/DNA and protein/protein regimens in chickens. A plasmid encoding hemagglutinin (HA) from the A/swan/Poland/305-135V08/2006 (H5N1) virus, or the recombinant HA protein produced in Pichia pastoris system, both induced H5 HA-specific humoral immune responses in chickens. In two independent experiments, anti-HA antibodies were detected in sera collected two weeks after the first dose and the response was enhanced by the second dose of a vaccine, regardless of the type of subunit vaccine (DNA or recombinant protein) administered. The serum collected from chickens two weeks after the second dose was characterized by three types of assays: indirect ELISA, hemagglutination inhibition (HI) and a diagnostic test based on H5 antibody competition. Although the indirect ELISA failed to detect superiority of any of the three vaccine regimens, the other two tests clearly indicated that priming of chickens with the DNA vaccine significantly enhanced the protective potential of the recombinant protein vaccine produced in P. pastoris.

An enhanced immune response against G250, induced by a heterologous DNA prime‑protein boost vaccination, using polyethyleneimine as a DNA vaccine adjuvant

The heterologous DNA prime‑protein boost vaccination approach has been widely applied as an immune treatment for carcinoma. However, inefficient delivery of DNA remains a major issue. In the present study, polyethyleneimine (PEI) was used as a DNA vector carrier to improve the transfection efficiency of the DNA vaccine and stimulate the humoral and cellular immunity against the renal carcinoma‑associated antigen G250. A protein vaccine was included in the immunization strategy in order to produce a prime‑boost effect. A DNA plasmid encoding an antigen G250 fragment was constructed and complexed with PEI. A protein vaccine against G250 was expressed in BL21 (DE3) Escherichia coli cells, by transformation with a pET28a(+)/C‑G250 plasmid. The protein was purified using a nickel‑nitriloacetic acid purification system. The in vitro transfection efficiency of the DNA vaccine was analyzed in HEK293 human endothelial kidney cells. The in vitro transfection efficiency in HEK293 cells was highest 48 h after transfection. Furthermore, mice were primed with 200 µg pVAX1/C‑250 plasmid complexed with PEI, and boosted using 50 µg of purified C‑G250 protein. In order to evaluate the immune response the antibody titer, splenocyte response, and interferon‑γ levels from CD8+ T‑cell splenocytes were analyzed using ELISA, lymphocyte proliferation or enzyme‑linked immunosorbent spot assays. Firstly, the pVAX1/C‑G250 plasmid was shown to be constructed successfully. As compared with the DNA group, the antibody titer, lymphocyte proliferation percentage, and cytokine production level induced by the DNA‑PEI and DNA‑PEI+C‑G250 groups were significantly higher. Furthermore, the DNA‑PEI+C‑G250 group exhibited the strongest humoral and cellular response. Owing to the adjuvant effect of PEI, the pVAX1/C‑G250‑PEI prime plus C‑G250 protein boost regimen could induce a strong immune response, and has been proved to be a potent vaccine candidate against renal cell carcinoma.