A herpesvirus of turkeys (HVT) recombinant containing a 3.9 kbp fragment of Marek's disease virus (MDV) DNA encoding MDV glycoprotein B (gB), stably integrated into the thymidine kinase (TK) gene of HVT, has been constructed. The replication of the recombinant in chick embryo fibroblasts (CEF) was comparable to that of wild-type HVT. The recombinant expressed authentic MDV gB and its processed forms (ll0K, 65K and 48K) in CEF as shown by immunoblotting using an MDV-specific anti-peptide serum. Northern blot analysis showed that MDV gB mRNA was transcribed from MDV promoter sequences flanking the MDV gB open reading frame and also from the HVT TK promoter. However, the level of replication of the recombinant in vivo appeared to be lower than wild-type HVT as shown by the titres of HVT antibodies, determined by ELISA. Pathogenicity tests showed that the recombinant was safe and did not cause microscopic or gross Marek's disease lesions or other abnormalities. The results suggest that HVT has potential as a vector for recombinant vaccines.
In the process of generating an insertional mutant of herpesvirus of turkeys (HVT) expressing lacZ at the protein kinase (PK) locus, we isolated a recombinant which contained an intact PK gene but the short unique regions US1, US10 and SORF3 had been deleted and replaced by the lacZ cassette. Moreover, the virus contained duplicate copies of gD, gI and gE in an opposite orientation flanking lacZ, US2 and PK which were contiguous. These results are of interest in relation to the flexibility of the short unique segment (U~) and of the inverted repeats flanking Us of the alphaherpesviruses.The recombinant expressed flgalactosidase and was genetically stable in vitro and in vivo. Chickens inoculated with the virus developed antibodies to HVT antigens and to fl-galactosidase but the replication of the recombinant in vivo was impaired in comparison to parental HVT as shown by a reduction in the proportion of infected lymphocytes.
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