CD8 CTLs maintain an effector phenotype and do not proliferate after transfer into naive, syngeneic recipients. (a–d) Three and seven days after transfer of 6 × 10⁶ Thy1.1 CD8 CTLs into Thy1.2 BALB/c recipients, splenocytes were stained for CD8α, Thy1.1, CD44, CD25, and with LLO_91-99 H2-K^d tetramers. (a) Dot plots are gated on live CD8 T cells, and the percentage of cells positive for Thy1.1 (y axis) and LLO_91-99 (x axis) is shown. (b) Absolute number of cells that stained positive for Thy1.1 and LLO_91-99 on days 3 and 7 after transfer; each point represents an individual mouse. (c) LLO_91-99–specific CD8 CTLs were labeled with CFSE prior to transfer, and the percentage of CFSE⁺ Thy1.1 CD8 T cells 3 days after transfer is indicated. (d) Activation-marker expression of LLO_91-99–specific T cells was determined 72 hours after transfer. Staining for Thy1.1 is shown on the x axis, and staining with LLO_91-99 H2-K^d tetramers and for CD62L, CD25, and CD44 is shown on the y axis. Dot plots are gated on live CD8 T cells. (a, c, and d) Dot plots are representative of three to four mice per group.