A significant increase of PD-1 mRNA in Jurkat T cells cultured with mixed CM of cancer cells, macrophages and T cells was observed (Bar 4, Figure 4F), while culture with CM from Rab37 silenced THP-1 macrophages (Bar 5, Figure 4F) or blockade of IL-6 by α-IL-6 (Bars 6-7, Figure 4F) markedly attenuated PD-1 expression in T cells, verifying the role of Rab37-mediated IL-6 derived from macrophages in mediating PD-1 expression in T cells. Here, RAB37 is linked to cancer.