The frequency of PD1Hi cells among CD8+ T cells showed a similar trend: tumor tissues harbored a significantly higher frequency of PD1Hi CD8+ T cells (median = 26.60, 9.60–58.55%) than that of peri-tumor CD8+ T cells (median = 13.47, 6.35–27.05%; P = 0.0006), while blood contained minimal PD1Hi CD8+ T cells (Fig. 1c). Here, CD8A is linked to neoplasm.