In 2015, studies stratified the TME into four types based on PD-L1 expression (positive or negative) and the presence or absence of TIL in melanoma patients (Type 1: PD-L1+, TILs+; Type 2: PD-L1−, TILs−; Type 3: PD-L1+, TIL−; Type 4: PD-L1−, TILs+) [73,74,75]. Here, CD274 is linked to melanoma.