PDCD1LG2 and head and neck carcinoma: Upregulation of PD-L2 was detected using flow cytometry in cell lines of different cancer cell types that underwent TIS (U2O2, and human head and neck carcinoma UT-SCC-2 and UT-SCC-42B) (Fig. 1j) and occurred gradually during the development of TIS over 7 days (Extended Data Fig. 2d).