Cell substrate and risk in killed poliomyelitis vaccine.

By using 3H-T labeled HeLa cell DNA it was possible to evaluate the quantity and the state of substrate DNA present in crude and purified killed poliovaccine. The results showed that 1.7 x 10(5) pg/ml of DNA is present in crude vaccine while in purified vaccine this product can not be detected (the limit of the detection method was 1.1 x 10(2) pg/ml). The theoretical problems of the risk of the formation of poliovirus pseudotypes and the potential contamination of the vaccine with a type C retrovirus are examined.