CTLA4 and head and neck squamous cell carcinoma: Therefore, using the human monocyte leukemia cell line THP-1 (Tohoku Hospital Pediatrics-1) [27] as a model, we investigated the influence of plasma-derived exosomes from HNSCC patients and healthy donors on the M1/M2 differentiation of human macrophages and the expression patterns of checkpoint molecules PD-L1 and CTLA-4 (cytotoxic T-lymphocyte-associated protein 4; CD152).