TIL from digested tumor samples analyzed by flow cytometry displayed relatively high levels of PD-1, as over 30 % of CD4+ TIL (38.2 ± 22.1 %) and 40 % of CD8+ TIL (45.7 ± 26.8 %) were positive for surface PD-1 (Fig. 2a). Here, CD4 is linked to neoplasm.