Cell division rate of CIK cells in vivo compared with naive splenocytes. Lethally irradiated Balb/c recipient mice were injected with 5 × 10⁶ C57BL/6 (H-2^b, Thy1.2) wild-type BM cells with either CFSE-labeled 10 × 10⁶ CIK cells or splenocytes generated from congenic C57BL/6 (H-2^b, Thy1.1). (A) On day 3, the cell division rate from splenocytes (top row) and CIK cells (bottom row) in the spleen was analyzed by a CFSE-based cell proliferation assay. Similar results were obtained in 3 allogeneic and 3 syngeneic receipient mice. (B) Proliferation index of CD4 and CD8 T cells of splenocytes and CIK cells. Error bars represent SD. *P < .05; **P < .01.