Taken together, the demonstration of perforin and granzyme B in PIT (Supplementary Figure 2), a predominant effector-memory differentiation state (Supplementary Figure 4), and the ease with which cytotoxic effector function and effector cytokines are generated in vitro (Figure 5F), indicates that the immediate precursors of anti-tumor effector T cells are numerous but suppressed in MPE. Here, PRF1 is linked to neoplasm.