Rate of apoptosis of transferred T cells. Lethally irradiated host mice (Balb/c, H-2^d) were injected with 5 × 10⁶ C57BL/6 (H-2^b, Thy1.2) wild-type BM cells with either 10 × 10⁶ CIK cells generated from congeneic C57BL/6 (H-2^b, Thy1.1) or 10 × 10⁶ splenocytes. (A) Early apoptotic cells from CIK cells (n = 3) and GVHD effector cells (n = 3) from the spleen were analyzed on day 7 after BMT separately in CD8⁺ and CD4⁺ lymphocytes by FACS using annexin V and PI staining. Error bars represent SD. **P < .01. (B) Comparison of Fas and FasL expression between GVHD controls and CIK cell–receiving mice on day 7 after BMT. One representative result of 3 similar experiments is shown.