PDCD1 and melanoma: While an increase in circulating exosomal PD-L1 in the blood before anti-PD-1antibody treatment was associated with poor response in patients with melanoma [38], increased PD-1 and CD28 expression in exosomes, which may be derived from T cells, was associated with improved progression-free survival (PFS) in anti-CTLA4-treated patients [40].