CD4 and oral cavity squamous cell carcinoma: We have confirmed that PD-1 level is significantly increased in CD4+ T cells or CD8+ T cells from peripheral blood in solid tumors such as non-small cell lung cancer,[11] oral squamous cell carcinoma,[12] and ovarian cancer.[13] Similarly, we also found that the expression levels of PD-1 on CD4+ or CD8+ T cells and PD-L1 on CD4+ T cells from peripheral blood from cHL patients are higher than those in the healthy control group.