PDCD1 and neoplasm: Furthermore, a strong positive correlation was observed between frequencies of FoxP3+Helios+ T cells and CD4+PD-1+ T cells in NILs in CRC patients, and it was found to be stronger in early tumor stages compared to advanced stages (r = 0.818, p = 0.005 [early]; r = 0.393, p = 0.206 [advanced]) (Figure 2A).