Transfection studies in vitro and in vivo with isolated Marek's disease virus DNA

For tranfection studies in vitro and in vivo, infectious Marek's disease virus (MDV) DNA was isolated from purified virus particles. Its sedimentation coefficient in neutral sucrose gradients was found to be 53 +/- 2S and the buoyant density in caesium chloride corresponded to 1.707 g/cm3. The virus DNA was also analysed by using the restriction endonucleases EcoRI and HindIII. High molecular-weight MDV DNA precipitated by the calcium phosphate technique was shown to be infectious in cultivated chicken embryo fibroblasts and newly hatched antibody-free chickens. Three out of eight chickens which each received between 0.5 and 2 micrograms MDV DNA by the intraabdominal route produced precipitating A-antigens in the feather follicles and/or lymphoroliferative tumours in the visceral organs. Infectious MDV was also detected in spleen and blood lymphocytes. Transformation experiemnts in vitro performed with isolated thymus cells, however, have so far produced negative results. The induction of Marek's disease and tumours by purified MDV DNA also indicates that the presence of contaminating avian oncornaviruses in the inoculum is not a necessary condition for the initiation of an MDV infection.