Finally, in both lymphopenic hosts (after lethal irradiation) with the TRP-1 TCR transgenic model and B16 melanoma, the OT-II TCR and B16-OVA melanoma, and immunocompetent hosts implanted with MCA205 sarcoma, the anti-tumor function of GZMB+ CD4+ T cells is enhanced by anti-CTLA-4 in a mechanism that involves competition with Treg cells for IL-2 binding (Śledzińska et al., 2020). Here, CD4 is linked to sarcoma.