PDCD1 and neoplasm: LAG3 is highly associated and synergistic with PD-1 as it is co-expressed with this immune checkpoint on CD4 and CD8 T cells: one study found that more macrophages, CD3, CD4, and CD8 T cells were present in murine tumours when LAG3 and PD-1 were both knocked out, which suggests that the combined deletion of these two factors alters regulator T cell homeostasis while enhancing tumour immunity [22].