Cytolytic activity of cells from CMV seropositive autograft recipients with detectable CMV-specific HLA class I-restricted CD8⁺ CTL responses. Class I-restricted CTL specific for CMV were demonstrable in 8 patients pretransplantation and in 12 patients during the first 3 months after transplantation. Cytotoxicity was assayed at an E:T ratio of 15:1 against autologous CMV-infected (A) and mock-infected (B) fibroblast targets as well as against HLA-mismatched CMV-infected (C) and mock-infected (D) fibroblast targets. Lysis of the autologous CMV-infected targets was significantly higher than lysis of each of the other three targets before transplantation (P = .008) and at 1 month (P = .04), 2 months (P = .04), and 3 months (P = .005) after transplantation. The median is indicated by the horizontal bar.