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Published on: June 24, 2012
Oncogenic Marek's disease viruses lacking the 132 base pair repeats can still be attenuated by serial in vitro cell
1Avian Disease and Oncology Laboratory, USDA, Agricultural Research Service, 3606 E. Mount Hope Rd., E. Lansing, Michigan 48823, USA. silvar@msu.edu
Abstract:
Marek's disease virus (MDV) can be attenuated by serially passing the virus in cell culture. During cell culture passage, two copies of a 132 bp repeat are expanded to over 30 copies. We deleted the two copies of the 132 bp repeat region in a pathogenic MDV and demonstrated that the virus was still pathogenic. The pattern and frequency of tumors in the parental and mutant virus were the same. Early virus replication, and the appearance of persistent neurological disease were also similar between the parental and deleted virus. Nevertheless, wild-type MDV and the deletion virus could be attenuated by serial in vitro cell culture passages. Based upon analyzing the passage 40 viruses, attenuation of the MDV lacking the 132 bp repeats appears to occur in a manner that is analogous to the process occurring wild-type MDV attenuation. Whatever process is involved in the cell culture attenuation of MDV, the mechanism does not involve the 132 bp repeat region.
Insights
Serial cell culture passage attenuates Marek's disease virus (MDV). Deleting the 132 bp repeat region did not affect MDV pathogenicity or attenuation, indicating this region is not involved in cell culture attenuation.
Area of Science:
- Virology
- Molecular Biology
- Immunology
Background:
- Marek's disease virus (MDV) is a highly contagious oncogenic herpesvirus.
- MDV attenuation through cell culture passage is a key strategy for vaccine development.
- A specific 132 bp repeat region in MDV is known to expand during cell culture.
Purpose of the Study:
- To investigate the role of the 132 bp repeat region in MDV pathogenicity and attenuation.
- To determine if the 132 bp repeat region is essential for MDV attenuation during cell culture passage.
Main Methods:
- Pathogenic MDV was genetically modified to delete the two copies of the 132 bp repeat region.
- Parental and mutant viruses were compared for pathogenicity, tumor formation, replication, and neurological disease.
- Both wild-type and deletion mutant viruses were subjected to serial in vitro cell culture passages to assess attenuation.
Main Results:
- Deletion of the 132 bp repeat region did not alter MDV pathogenicity, tumor patterns, early replication, or neurological disease.
- Both the parental MDV and the deletion mutant virus were successfully attenuated by serial in vitro cell culture passage.
- Attenuation of the MDV lacking the 132 bp repeats occurred analogously to wild-type MDV attenuation.
Conclusions:
- The 132 bp repeat region is not essential for MDV pathogenicity or its attenuation during cell culture.
- The mechanism of MDV attenuation in cell culture does not involve the 132 bp repeat region.
- Further research is needed to elucidate the precise molecular mechanisms underlying MDV cell culture attenuation.
