To investigate Gzm-B-mediated killing of M6PR-expressing effector T cells within an in vivo Treg-enriched tumor environment, Treg-replete tumor-bearing mice were intratumorally injected with IL-2(CD45.1) or IL-7(CD45.1) effectors together with GranToxiLux, a cell-permeable fluorogenic substrate of Gzm-B. Here, IL2 is linked to neoplasm.