CD4 and thyroid cancer: Subsequently, the role of PDL1-PD1 interaction in thyroid cancer has only been investigated in a handful of in vitro experiments and through staining of patient tissue samples; Cunha et al demonstrated higher levels of PD-L1 in papillary thyroid cancer tissue samples compared to normal and benign lesions and showed a positive correlation between PD-L1 levels and infiltration of CD8+, CD4+, FoxP3+ lymphocytes and tumor associated macrophages [19, 20].