To evaluate whether the targeted split Neo-2/15 proteins could trans-activate immune cells when bound to target tumor cells, we first targeted the Neo2A and Neo2B split fragments to the double-positive HER2+/EGFR+ K562 cell line, described above, in the presence of an IL-2-responsive human natural killer (NK) cell line31 (YT-1) and assessed STAT5 phosphorylation as a readout for IL-2 signaling (Fig. 2c). Here, IL2 is linked to neoplasm.