Generation of recombinant parapoxviruses: non-essential genes suitable forinsertion and expression of foreign genes

Orf virus (OV) is an epitheliotropic poxvirus and belongs to the genus Para poxvirus (PPV). PPV, especially OV, is regarded as a promising candidate fo r an expression vector. Among available live vaccines only strain D1701 rep resents a highly attenuated OV strain with clearly reduced pathogenicity. T herefore, we started to identify potentially non-essential genes or regions of D1701, which might be suitable for insertion and expression of foreign genes. The present contribution reviews some of the progress using the vegf -e (homologue of the mammalian vascular endothelial growth factor) gene loc us for the generation of recombinant D1701. The vegf-e gene of D1701 is dis pensable for virus growth in vitro and in vivo, and represents a major viru lence determinant of OV. It is shown that foreign genes can be inserted and functionally expressed in the vegf-e locus, also leading to the induction of a specific immune response in the non-permissive host. Furthermore, it i s reported that adaptation to VERO cells led to the deletion of three furth er regions of the OV D1701 genome, which seems to be combined with addition al virus attenuation in sheep. Molecular analysis of this OV D1701 variant allows the identification of new, potentially non-essential sites in the vi ral genome. (C) 2000 Elsevier Science B.V. All rights reserved.