In vivo, Ccr5-/- CTLs that were co-transferred with WT CTLs showed impaired homing into CCL3/CCL4-secreting tumours (Figure 5—figure supplement 2A,B) and, in contrast to WT CTLs, did not bind fluorescent CCL3 (Figure 5—figure supplement 2C,D). Here, CCL3 is linked to neoplasm.