CIK cells retain tumor killing activity and home to tumor site in vivo. (A) NKG2D ligands were expressed on A20 tumor cells, (B) but not on GVHD target tissues such as small (SB) and large bowel (LB), skin, and liver on day 3 after irradiation. (C) Cytolysis against A20 cells. Effectors (allogeneic CIK cells) were combined with targets at indicated ratio either alone or in the presence of isotype control antibodies or NKG2D antibodies. *P < .05. (D) A20 luc⁺ leukemia/lymphoma cells (10⁶; H-2^d) were injected into Balb/c (H-2^d) hosts in the right flank subcutaneously after lethal irradiation, followed by injection of 5 × 10⁶ FVB wild-type (H-2^q) TCD-BM with or without 10 × 10⁶ CIK cells generated from FVB wild-type animals. Tumor regression was observed in CIK cell–receiving mice. (E) Emitted photons from luc⁺ tumor cells over time. (F) A20 cells (10⁶) were injected into the right flank of Balb/c hosts subcutaneously after lethal irradiation, followed by injection of 5 × 10⁶ FVB wild-type TCD-BM with 10 × 10⁶ CIK cells generated from luc⁺ L2G85 animals. Accumulation of luc⁺ CIK cells was observed in the tumor site. (G) CIK cells were collected on day 7 after BMT and compared with expanded CIK cells prior to injection. Lethally irradiated Balb/c (H-2^d) mice were given 5 × 10⁶ C57BL/6 BM plus 10 × 10⁶ CIK cells generated from GFP⁺C57BL/6 splenocytes. On day 7, GFP⁺ cells were recovered from the host spleen by FACS sorting and then used in a ⁵¹Cr release cytotoxicity assay against A20 cells. Error bars represent SD. (H) Activation status of allogeneic CIK cells from the host spleen in vivo was analyzed on day 7 after BMT.