RECOMBINANT VIRAL VACCINES FOR ENZOOTIC BOVINE LEUKOSIS

Recently published studies on the development and use of recombinant v accinia virus (VV) vaccines incorporating either the complete envelope (env) gene or only a fragment of the env gene consisting of the codin g sequence for the env glycoprotein 51 (gp51) and part of gp30 of the bovine leukaemia virus (BLV) are described. It has been reported that vaccination of sheep with recombinant VV vaccines containing the compl ete env gene a pears to protect sheep against challenge infection with BLV. The evidence for this protection is based on the lack of persist ence of high titres of anti-gp51 antibodies compared with unvaccinated BLV infected controls, on the enhanced CD4 proliferative responses to specific BLV gp51 synthetic peptides in the vaccinated sheep, and on the inability to detect BLV pro-virus by polymerase chain reaction in the vaccinated sheep after 4 months following challenge infection comp ared with continual detection in unvaccinated sheep over a 16 month tr ial period. It has been suggested that cell-mediated immune responses may be an important aspect of protective immunity against BLV infectio n and it has been reported that large tracts of amino acid sequences w ithin the env and pol genes are highly conserved in different isolates from different countries which is of importance in designing peptide derived vaccines.