Effects of Cdk5 gene deletion on GVL activity. Lethally irradiated B6D2F1 mice received HCT from either syngeneic (B6D2F1) or allogeneic Cdk5^+/+C (Allo Cdk5 WT) or Cdk5^−/−C (Allo Cdk5 KO) donors as described in Figure 4. Consistent with previous experiments, animals receiving HCT from Cdk5^−/−C donors have significantly reduced mortality from GVHD (A). In subsequent experiments, groups of HCT recipients received 250 or 500 P815 tumor cells at time of transplant. Recipients of BM and T cells from Cdk5 KO donors effectively eliminate low-dose tumor challenge and show improved leukemia-free survival (B). At higher tumor dose, significant GVL activity remains, but some Cdk5 KO HCT recipients succumb to tumor (C). The expression of Cdk5 and p35 was determined on P815 and EL4 tumor cell lysate using western blot analysis (D). Tumor cells (10⁴ cells per well) were incubated with ³H-Thy for 24 hours in the presence or absence of roscovitine or CIP and cell proliferation was determined (E-F). In parallel experiments, tumor cells incubated with roscovitine or CIP for 24 hours were stained with Annexin V and 7AAD and the percentage of early apoptotic cells was determined (G). Data are from at least 2 combined experiments: n = 8 to 12 per group (A-C), or 1 of at least 2 comparable experiments (E-F). *P < .01.