Human FL cells can be killed by allogeneic T cells, but not freshly isolated or IL-2–activated T-TIL. (A) Chromium release assay of allogeneic T cells stimulated three times with CD40-FL cells and cytotoxicity assessed at day 28 after initiation of culture. Results shown are from patient FL4. A total of 2 × 10⁴ FL cells (▪), CD40-FL cells (•), or control targets including FL6 (○), CD40-FL cells from FL6 (▵) were placed in 96-well round-bottom plates and T cells added at E:T ratios of 3:1, 10:1, and 30:1 in a final volume of 0.2 mL. A TCL from one of three healthy donors is depicted. (B) The same TCL was examined at the same time for cytotoxicity against FL4 tumor cells by JAM test. Target cells included FL cells (▪), CD40-FL cells (•), or control targets including CD40-FL cells from FL6 (▵), unstimulated FL6 cells (○), normal B cells (□), or CD40-activated normal B cells (⋄). (C) Blockade of MHC class I (⋄) and MHC class II (□) by MoAbs decreases anti-FL–directed T-cell cytotoxicity, and the combination of both (○) almost abrogates cytotoxicity. T-TILs were isolated from FL4 and analyzed for cytotoxicity against FL4 (D) immediately after isolation, or (E) after culture in IL-2 for 7 days (FL cells [▪], CD40-FL cells [•], or normal CD40-activated B cells [□]). Comparable results were obtained with FL cells from three additional patients.