CTLs are induced to survive and proliferate when targeted. (A) Effect of targeting on CTL viability. H-2^d/b (F1) CTLs or H-2^s CTLs were placed in culture with 2C CD8⁺ T cells at a CTL-to-2C ratio of 1:1 or 1:10, or were incubated without 2C cells. In parallel, CTLs were placed alone in untraversable transwells and cultured in the surrounding media of respective CTLs interacting with 2C cells at both 1:1 and 1:10 CTL-to-2C ratios. After 72 hours of incubation, viable CTL counts were obtained by enumerating the number of 7AAD-excluding CTLs as determined by FACS. Values are presented as the number of viable CTLs per 10⁵ CTLs cultured at time zero. (B) Effect of targeting on CTL proliferation. F1 CTLS were loaded with CFSE and placed in culture or in untraversable transwells as described in panel A. After 72 hours of incubation the percentage of divided CTLs was determined by CFSE dilution. (C) Specific TCR recognition and integrin-mediated adhesion are required to induce CTL survival. F1 CTLs were incubated as described in A with either 2C CD8⁺, 2C CD8⁻, OT-I CD8⁺, or wild-type C57B/6 CD8⁺ cells. Only the recognizing 2C CD8⁺ cells induced significant CTL survival and proliferation. The observed CTL response was inhibited on addition of 20ug/mL anti–LFA-1 antibody. Data in panels A-C are from a single experiment representative of 3 independent experiments. Error bars represent SD from triplicate wells. **P < .01, ***P < .001.