Influence of cytokine milieu on TCR-transgenic recipient lymphocytes in vitro. (A) Surface staining of human TCR150-transgenic PBLs using human CD62L Abs on pre-gated CD8⁺, CD45RA⁻ cells that were cultured over a 5-day or a 13-day period in the presence of IL-2 alone or IL-15 combined with low-dose IL-2 (IL-15). (B) Ratio of CD8⁺ to CD4⁺ T cells at day 13 after incubation with or without IL-15 (**P = .008 by Mann-Whitney test, n = 7). (C) Percentage of intracellular IFN-γ and TNF-α double-positive cells within the CD8⁺ T-cell fraction by flow cytometric analyses. Open bars represent nonstimulated PBLs; filled bars represent PBLs stimulated at an effector-to-target ratio of 20:1 with THP-1 cells for 6 hours. Mock-transfected PBLs were used as a background control compared with TCR150-transgenic PBLs cultured with or without IL-15. (D) Intracellular staining of perforin, granzyme A, and granzyme B in lymphocytes cultured in IL-2–containing medium (filled graph) or IL-2/IL-15–conditioned medium (open bold graph). Shattered line represents staining with isotype control. (E) Lytic capacity of TCR150-transgenic PBLs (top panel) or TCRT58-transgenic PBLs (bottom panel) cultured under IL-2 or IL-15–conditions using THP-1 and mel624.38 as target cells. Specific lysis was measured in a standard 4-hour chromium-release assay.