Protective effect of a 7-day GCV treatment on the occurrence of GVHD in mice receiving (A) EpTK or (B) EpΔTK transgenic T cells. Irradiation control group (○): Ungrafted irradiated B6 mice (n = 15 in both [A] and [B]). Reconstitution control group (•): Irradiated B6 mice engrafted with FVB BM (n = 15 [A] and 11 [B]). GVHD control group (□): Irradiated B6 mice engrafted with FVB BM plus either FVB nontransgenic T cells and GCV administration or transgenic T cells and PBS administration (n = 25 [A] and 23 [B]). Experimental group (▪): Irradiated B6 mice engrafted with FVB BM plus (A) EpTK or (B) EpΔTK T cells and treated with GCV (n = 13 [A] and 19 [B]). Results are presented as Kaplan-Meier survival curves of cumulative data for each set of 3 independent experiments in both (A) and (B).