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Title: ONCOGENIC MDV'S LACKING THE 132 BP REPEATS CAN BE ATTENUATED BY REPEATEDLY PASSING THE VIRUS IN CELL CULTURE

Author
item Silva, Robert
item Gimeno, Isabel

Submitted to: International Marek's Disease Symposium Abstracts and Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 7/14/2004
Publication Date: 7/14/2004
Citation: Silva, R.F., Gimeno, I.M. 2004. Oncogenic MDVs lacking the 132 bp repeats can be attenuated by repeatedly passing the virus in cell culture [abstract]. International Marek's Disease Symposium Abstracts and Proceedings. Paper No. P.1.

Interpretive Summary:

Technical Abstract: Marek's disease virus (MDV) can be attenuated by serially passing the virus in cell culture. Concurrently with attenuation, the number of copies of the 132 bp repeats increases from two to over 20 copies. By deleting the 132 bp repeats, we previously demonstrated that the expansion of the 132 bp is not sufficient to induce attenuation. To confirm this finding, we investigated whether oncogenic MDV that lack the 132 bp repeats can be attenuated by serially passing the mutant MDV in cell culture. To do this, we serially passed wild-type MDV, rMd5 (recombinant MDV derived from an overlapping cosmid clone library), and a recombinant MDV lacking the 132 bp repeats, rMd5('132bp), in duck embryo fibroblasts for 40 passages (high-pass). After four cell-culture passages (low pass), all three viruses induced persistent neurological disease in susceptible chickens, observable from day 17 through day 50 post-inoculation. No neurological disease was observed in any chicken infected with high-pass virus. All three low-pass viruses induced a variety of gross lesions, whereas, in the high-pass inoculated group, only four of 17 birds inoculated with the high-pass rMd5 had minor lesions. We were able to reactivate MDV at termination (60 days PI) from all the low-pass inoculated birds. Very little virus could be reactivated from the high-pass inoculated birds. In conclusion, oncogenic MDV, lacking the 132 bp repeats, can be attenuated by serial cell culture passages and the kinetics of attenuation appears to be similar to cell culture attenuation of wild-type MDV. These findings suggest that the 132 bp repeats play no role in the attenuation process.