Mixed-culture cytopathogenicity between KC and XC oncornavirus indicator lines and "virus-free" human choriocarcinoma cells.

When rat (XC) cells transformed by Rous sarcoma virus and human (KC) cells were cocultivated with appropriate infected cells, cell fusion was extensive and rapid. Many human cell lines were screened, with negative results; however, several hormone-secreting human choriocarcinoma cells fused extensively with both KC and XC cells. No evidence of a virus involvement in this interaction was found by direct examination, transmission, or immunologic tests.