Evaluation of two strains of Marek's disease virus serotype 1 for the development of recombinant vaccines against very virulent infectious bursal disease virus

Development of a recombinant VP2 vaccine for the prevention of novel variant strains of infectious bursal disease virus

Since 2017, novel variant strains of infectious bursal disease virus (nvIBDV) have been detected in China, while the current vaccines on the market against very virulent IBDV have limited protection against this subtype virus. In this context, a strain of the virus has been isolated, and sequencing alignment and bird regression experiments showed that the virus was IBDV, belonging to the nvIBDV subtype (and named IBDV FJ-1812). Furthermore, the Escherichia coli expression system was used to successfully express soluble nvIBDV rVP2, which is specifically recognized by an anti-IBDV standard serum and anti-nvIBDV positive serum, and could be assembled into 14 - 17 nm virus-like particles. Based on the purified nvIBDV rVP2, we developed an IBDV FJ-1812 VP2 VLP vaccine at a laboratory scale to evaluate protection by this vaccine; in addition, we also prepared an IBDV JZ 3/02 VP2 subunit vaccine targeting very virulent IBDV and evaluated its cross-protection against nvIBDV. Results of bird experiments showed that the nvIBDV rVP2 vaccine could induce high titres of specific antibodies, completely protect the bursa of Fabricius from viral infection, and provide 100% immune protection to SPF and Ross 308 broiler chickens. Furthermore, the IBDV JZ 3/02 VP2 subunit vaccine targeting very virulent IBDV could provide 60% protection for SPF chickens and 80% protection for Ross 308 broiler chickens. This report provides important technical supports for the prevention and control of nvIBDV in the future.

Prevention of Avian Retrovirus Infection in Chickens Using CRISPR-Cas9 Delivered by Marek's Disease Virus

Reticuloendotheliosis virus (REV) is an avian retrovirus that causes an oncogenic, immunosuppressive, and runting-stunting syndrome in avian hosts. The co-infection of REV and Marek’s disease virus (MDV), an oncogenic herpesvirus in chickens, further increases disease severity and reduces MDV vaccine efficacy. The clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 system has successfully been used against pathogens in mammalian cells. However, the large size of the CRISPR-Cas9 coding sequences makes its in vivo delivery challenging. Here, following the design of a panel of single-guided RNAs targeting REV, we demonstrate that CRISPR/Cas9 can efficiently mediate the editing of the long terminal repeats of REV, resulting in the inhibition of viral protein expression. The CRISPR-Cas9 system disrupts the integrated proviral genome and provides defense against new viral infection and replication in chicken cells. Moreover, by constructing recombinant MDV carrying CRISPR-Cas9 components using an attenuated MDV vaccine strain as the vector, we efficiently delivered the CRISPR-Cas9 system into chickens, and the MDV-delivered CRISPR-Cas9 drastically reduced REV viral load and significantly diminished REV-associated symptoms. To our knowledge, this is the first study establishing avian retrovirus resistance in chickens utilizing herpesvirus-delivered CRISPR-Cas9, which provides a novel and effective strategy against viral infections.

Neutralizing-antibody-mediated protection of chickens against infectious bursal disease via one-time vaccination with inactivated recombinant Lactococcus lactis expressing a fusion protein constructed from the RCK protein of Salmonella enterica and VP2 of infectious bursal disease virus

Background

Infectious bursal disease (IBD) is an acute contagious immunosuppressive disease which lead to acute bursal injury and immune dysfunction in poultry. It has caused heavy economic losses in the commercial poultry industry for many years in worldwide. Attenuated live vaccine has widely used in poultry showing some promising signs against IBDV infection. But it has defects such as generating enhanced virulence and immunosuppression prohibits. Therefore, the development of mucosal vaccines using the food-grade lactic acid bacterium is necessary. Here, we construct a recombinant Lactococcus co-expressing the major IBDV antigens VP2 and RCK protein of Salmonella enterica to prevent IBD.

Results

The recombinant fusion protein VP2-RCK was expressed in a soluble and stable form in the cytoplasm of the recombinant Lactococcus lactis. Animal experiments showed that: (1) the survival rates of the injected immunization inactivated recombinant LAB group and oral immunization live recombinant LAB group were 100% and 80%, respectively; (2) ELISA titers of all serum samples from all experimental groups were negative, but high amounts of specific neutralizing antibodies were detected (1:2¹⁰ to 1:2¹²); and (3) the bursas of the injected immunization inactivated recombinant LAB group did not suffer damage, as confirmed by clinical observation and bursal histopathological examination. Our results indicate that r-L. lactis-OptiVP2-RCK induces a specific neutralizing-antibody-mediated immune response that confers full protection against very-virulent IBDV (vvIBDV) challenge.

Conclusion

Lactococcus lactis NZ3900 strain and its matching plasmid pNZ8149 could express the recombinant fusion protein VP2-RCK in a soluble form in the cytoplasm. The protective efficacy of r-L. lactis-OptiVP2-RCK (100%) was better than r-L. lactis-OptiVP2 (0%) which prove RCK protein played its unique role. The neutralizing antibodies titers against infectious bursal disease virus via one-time vaccination with inactivated r-L. lactis-OptiVP2-RCK could reach 1:2¹⁰ to 1:2¹², but ELISA titers of all serum samples were negative. For this phenomenon, perhaps because of the change of delivery pathway or the spatial structure of fusion protein. We need further study to test these hypotheses.