A New Strategy for Efficient Screening and Identification of Monoclonal Antibodies against Oncogenic Avian Herpesvirus Utilizing CRISPR/Cas9-Based Gene-Editing Technology

Herpesvirus Diseases in Humans and Animals: Recent Developments, Challenges, and Charting Future Paths

Herpesviruses, a family of enveloped DNA viruses, pose significant threats to both humans and animals [...].

Emerging Hypervirulent Marek's Disease Virus Variants Significantly Overcome Protection Conferred by Commercial Vaccines

As one of the most important avian immunosuppressive and neoplastic diseases, Marek's disease (MD), caused by oncogenic Marek's disease virus (MDV), has caused huge economic losses worldwide over the past five decades. In recent years, MD outbreaks have occurred frequently in MD-vaccinated chicken flocks, but the key pathogenic determinants and influencing factors remain unclear. Herein, we analyzed the pathogenicity of seven newly isolated MDV strains from tumor-bearing chickens in China and found that all of them were pathogenic to chicken hosts, among which four MDV isolates, SDCW01, HNXZ05, HNSQ05 and HNSQ01, were considered to be hypervirulent MDV (HV-MDV) strains. At 73 days of the virus infection experiment, the cumulative incidences of MD were 100%, 93.3%, 90% and 100%, with mortalities of 83.3%, 73.3%, 60% and 86.7%, respectively, for the four viruses. The gross occurrences of tumors were 50%, 33.3%, 30% and 63.3%, respectively, accompanied by significant hepatosplenomegaly and serious atrophy of the immune organs. Furthermore, the immune protection effects of four commercial MD vaccines against SDCW01, CVI988, HVT, CVI988+HVT, and 814 were explored. Unexpectedly, during the 67 days of post-virus challenge, the protection indices (PIs) of these four MD vaccines were only 46.2%, 38.5%, 50%, and 28%, respectively, and the birds that received the monovalent CVI988 or HVT still developed tumors with cumulative incidences of 7.7% and 11.5%, respectively. To our knowledge, this is the first demonstration of the simultaneous comparison of the immune protection efficacy of multiple commercial MD vaccines with different vaccine strains. Our study revealed that the HV-MDV variants circulating in China could significantly break through the immune protection of the classical MD vaccines currently widely used. For future work, there is an urgent need to develop novel, more effective MD vaccines for tackling the new challenge of emerging HV-MDV strains or variants for the sustainable control of MD.

Efficient Cross-Screening and Characterization of Monoclonal Antibodies against Marek's Disease Specific Meq Oncoprotein Using CRISPR/Cas9-Gene-Edited Viruses

Marek's disease (MD) caused by pathogenic Marek's disease virus type 1 (MDV-1) is one of the most important neoplastic diseases of poultry. MDV-1-encoded unique Meq protein is the major oncoprotein and the availability of Meq-specific monoclonal antibodies (mAbs) is crucial for revealing MDV pathogenesis/oncogenesis. Using synthesized polypeptides from conserved hydrophilic regions of the Meq protein as immunogens, together with hybridoma technology and primary screening by cross immunofluorescence assay (IFA) on Meq-deleted MDV-1 viruses generated by CRISPR/Cas9-gene editing, a total of five positive hybridomas were generated. Four of these hybridomas, namely 2A9, 5A7, 7F9 and 8G11, were further confirmed to secrete specific antibodies against Meq as confirmed by the IFA staining of 293T cells overexpressing Meq. Confocal microscopic analysis of cells stained with these antibodies confirmed the nuclear localization of Meq in MDV-infected CEF cells and MDV-transformed MSB-1 cells. Furthermore, two mAb hybridoma clones, 2A9-B12 and 8G11-B2 derived from 2A9 and 8G11, respectively, displayed high specificity for Meq proteins of MDV-1 strains with diverse virulence. Our data presented here, using synthesized polypeptide immunization combined with cross IFA staining on CRISPR/Cas9 gene-edited viruses, has provided a new efficient approach for future generation of specific mAbs against viral proteins.

Critical roles of non-coding RNAs in lifecycle and biology of Marek's disease herpesvirus

Over the past two decades, numerous non-coding RNAs (ncRNAs) have been identified in different biological systems including virology, especially in large DNA viruses such as herpesviruses. As a representative oncogenic alphaherpesvirus, Marek's disease virus (MDV) causes an important immunosuppressive and rapid-onset neoplastic disease of poultry, namely Marek's disease (MD). Vaccinations can efficiently prevent the onset of MD lymphomas and other clinical disease, often heralded as the first successful example of vaccination-based control of cancer. MDV infection is also an excellent model for research into virally-induced tumorigenesis. Recently, great progress has been made in understanding the functions of ncRNAs in MD biology. Herein, we give a review of the discovery and identification of MDV-encoded viral miRNAs, focusing on the genomics, expression profiles, and emerging critical roles of MDV-1 miRNAs as oncogenic miRNAs (oncomiRs) or tumor suppressor genes involved in the induction of MD lymphomas. We also described the involvements of host cellular miRNAs, lincRNAs, and circRNAs participating in MDV life cycle, pathogenesis, and/or tumorigenesis. The prospects, strategies, and new techniques such as the CRISPR/Cas9-based gene editing applicable for further investigation into the ncRNA-mediated regulatory mechanisms in MDV pathogenesis/oncogenesis were also discussed, together with the possibilities of future studies on antiviral therapy and the development of new efficient MD vaccines.