CFP and neoplasm: Here, the activity and cytotoxicity of CTLs against target tumor cells were demonstrated in vitro by flow cytometry of B16 tumor cells that stably express mutants of the cyan fluorescent protein mCerulean (CFP-B16 tumor cells, Figure 1—figure supplement 1), which is minimally immunogenic in C57BL/6 mice (Skelton et al., 2001; Yang et al., 2016).