Cytotoxicity against EBV-transformed BLCL and MSCVpp65-transduced SF was mediated by CD8⁺ CTL. Bulk, CD8-enriched, or CD4-enriched CTL culture from donor ST were tested at different E:T ratios in chromium release assay. CD8-enriched CTL (B) retained the cytotoxicity displayed by the bulk CTL (A), while the CD4-enriched CTL (C) did not.