Polyomavirus DNA is damaged in target cells during cytotoxic T-lymphocyte-mediated killing.

Target cell DNA damage is an early event in cytotoxic T-lymphocyte (CTL)-mediated killing. It has been hypothesized that this DNA damage may serve as one mechanism of destroying viral genetic material inside infected cells. We directly examined the fate of viral DNA in target cells during CTL-mediated lysis. Polyomavirus DNA in transfected murine P815 mastocytoma targets was digested along with cellular DNA into oligonucleosome-sized fragments, although intact forms, possibly virion-associated DNA, were also present. In infected BALB/3T3 murine fibroblasts, which normally undergo single-stranded nicks when killed by CTL, polyomavirus DNA was converted to relaxed forms in the presence of CTL. These results suggest that the fate of the viral DNA depends on the stage of the viral life cycle and corresponds to the fate of the host cell DNA. Cleavage of the viral genome prior to assembly may thus be an important mechanism in specific antiviral immunity.