The dynamics of the replication activity of mesogenic strains was determined for all tumor cell lines and for the Vero cell line as a positive control (Fig. 4). Titration of VCL of NDV/Altai/pigeon/770/2011 collected after 3, 6, 24, 48 and 72 h showed the dynamics of viral titer growth. The highest titer on day 3 was observed for Vero cells; the lowest titer, for the HCT116 cell line. Similar **data** were obtained for the NDV/Altai/ pigeon/777/2010 strain. The lowest titer was obtained on the HCT116 and MCF 7 cell lines.