Plaque development by vaccinia-viruses on the chicken chorio-allantois under the influence of cyclophosphamide

The development of Vaccinia-virus plaques on the chorioallantois of embryonated eggs was studied under the influence of active cyclophosphamide metabolites. The viruses were inoculated on the 9th or the 13th incubation day. Cyclophosphamide was injected in doses of 62.5--500 mug in 0.2 ml NaCl into the yolk sac either 7 hrs after the virus inoculation or 3, 6, or 9 hrs in advance. The plaque development was not influenced when cyclophosphamide was given after the virus inoculation. But in treating the embryos before the infection a decrease dependent on the dose in the number of embryos with recognizable plaques occurred. This decrease was more marked with cyclophosphamide treatment 6 or 9 hrs, than with cyclophosphamide treatment 3 hrs before the virus inoculation. When the embryos were inoculated on the 13th day and treated with cyclophosphamide 9 hrs in advance, the mean effective dose was 316 mug/egg. The range of effective doses corresponds with that of the inhibitory effective doses of cyclophosphamide on transplantation tumors grown on the chorio-allantois of embryonated eggs.