GVL effect is maintained in the presence of Tr_VIPs. (A) Balb/c mice (H-2^d) were given transplants of T cell-depleted BM cells (1.5 × 10⁷) supplemented with different numbers (1.5 × 10⁶ cells, left panels; 5 × 10⁵ cells, middle panels; 1 × 10⁵ cells, right panels) of spleen mononuclear cells from B6 (H-2^b) mice. GVL effect was induced by injecting A20 leukemic cells (H-2^d) into recipients at time of BMS transplantation. Recipients were treated at time of transplantation with different numbers of CD4Tr_controls (○) or CD4Tr_VIPs (▾) (H-2^b) (1.5 × 10⁶ cells, left panels; 5 × 10⁵ cells, middle panels; 1 × 10⁵ cells, right panels) generated in the presence of DC_controls or DC_VIPs (H-2^d). Mice that received injections of A20 cells alone were used as controls (none, •). Survival was monitored and tumor growth/elimination was assessed by the presence of A20 cells in blood detected by coexpression of B220 and H-2K^d and by size (6-10 animals/group). P < .01 untreated recipients versus any Tr_VIPs group. (B) GVHD was induced in recipient Balb/c (H-2^d) mice by allogeneic transplantation of BMS from B6 (H-2^b) mice. GVT effect was induced by injecting A20 leukemic (H-2^d) cells into recipients mice at time of BMS transplantation. At time of transplantation, recipients were treated with CD8Tr_controls (○) or CD8Tr_VIPs (▾) generated by coculture with DC_controls or DC_VIPs. Mice that received injections of A20 cells alone were used as controls (untreated, •). Recipients were monitored for survival and leukemia growth/elimination (5-10 mice/group). ^*P < .01 versus untreated recipients. (C) Tr_VIPs suppress CD4 and CD8 T-cell expansion but not cytotoxicity activity of CD8 T cells against leukemic cells. T cells (10⁵) isolated from B6 (H-2^b) mice were cultured with allogeneic mDCs (10⁴) from Balb/c (H-2^d) mice in the absence (none) or presence of CD4Tr_controls or CD4Tr_VIPs (H-2^b) (3 × 10⁴) generated in the presence of DC_controls or DC_VIPs from Balb/c mice. After 5 days, the proliferative response and absolute cell number of CD4 and CD8 T cells in cultures were determined by flow cytometry. CD4 and CD8 T-cell numbers were the same in all the treatment groups at initiation of culture (dashed lines). CD8 T cells (5 × 10⁴) were reisolated by flow cytometry from the cultures and tested for A20 tumor cytolysis at an E/T ratio of 10:1. Each result is the mean ± SD of 4 experiments performed in duplicate. ^*P < .01 versus untreated recipients.