CTL assay. Spleen cells (effectors) from naive and transplanted recipients were cultured for 4 days with γ-irradiated splenocytes from syngeneic, donor, or third-party strains. Lytic activity was determined by incubating decreasing doses of stimulated effectors with a constant dose of naive 51Cr-labeled targets. All effectors were stimulated with target-strain-specific naive cells. Experimental groups (E:T): (+) naive C3H:C3H, (□) naive C3H:B10, (■) naive C3H:BALB/c, (X) C3H > OLTx:C3H, (△) C3H > OLTx:B10, and (▲) C3H > OLTx:BALB/c. The results are mean % specific 51Cr release ± 1 SD of triplicate cultures.