CD4 and osteosarcoma: Moreover, since osteosarcoma cells express PD-L1, and since this expression positively correlates with tumor-infiltrating lymphocytes [50], the use of aprepitant in osteosarcoma therapy can possibly reduce the number of CD4+ PD-1-positive cells, leading to a decrease in the levels of osteosarcoma-infiltrating T-regulatory lymphocytes.