E1-transduced CTL function and phenotype are unchanged. (A) Normal proliferation of modified CTLs (C-RE). The graphs illustrate the expansion rate of nontransduced and transduced CTL lines (C-RE) cultured in minimum media (Yssel + 10% FCS) alone or activated with irradiated LCLs + IL-2 (50 U/mL). The fold expansion is illustrated on the y-axis. ▪ indicates activated E1-CTLs (C-RE); ▴, nonactivated E1-CTLs (C-RE); and ♦, activated nontransduced CTLs. Cell count was evaluated by trypan blue exclusion. The rate of expansion of the stimulated transduced CTL line (C-RE) was not significantly different from the stimulated nontransduced CTL line. (B) Cytotoxic effector function is unaffected by the retrovirus transduction. EBV-specific CTLs were used in a cytotoxic assay before and after transduction with the E1 retroviral vector. We used allogeneic or autologous LCL lines as targets. The results are expressed as the percentage of lysis at multiple effector-target ratios. ♦ indicates allogeneic (Allo) LCLs and nontransduced (nt) CTLs; ▪, autologous (Auto) LCLs and nontransduced CTLs; ▴, allogeneic LCLs and E1-CTLs (C-RE); and ×, autologous LCLs and E1-CTLs (C-RE). (C) CD4 and CD8 expression of E1-transduced EBV-specific CTLs (C-RE) is unchanged. Nontransduced or transduced CTLs (C-RE) were stained with monoclonal antibodies specific for CD4 (PE labeled) and CD8 (FITC labeled). PE and FITC isotype antibodies were used for controls, and the cells were analyzed by flow cytometry. Error bars indicate mean ± SD. Upper left: percentage of CD4⁺ cells. Lower left: control. Lower right: percentage of CD8⁺ cells.