Anti-leukemia effect associated with down-regulated CD47 and up-regulated calreticulin by stimulated macrophages in co-culture.

CD47 is over-expressed in Acute Myeloid Leukemia (AML) and functions as an inhibitory signal, suppressing phagocytosis by binding to signal regulatory protein α (SIRPα) on the surface of macrophages. Inhibition of CD47 restores the immune surveillance of AML cells. However, the inhibition of CD47 in AML by activated macrophages and the subsequent effects on different immune response parameters are not fully understood. Here, we demonstrate the use of a distinct co-culture method to inhibit CD47 and therefore eliminate AML cells by macrophages in vitro. Human chemically induced THP-1 macrophages were activated using different concentrations of lipopolysaccharide (LPS) and co-culturing with three AML cancer cell lines (HL-60, NB4, and THP-1), respectively, as well as normal human peripheral blood mononuclear cells (PBMC). CD47 inhibition was observed in and selective to AML but not observed in normal PBMC. Additionally, calreticulin (CRT) levels were elevated in the same cell lines simultaneously, after co-culturing with activated human macrophages, but not elevated in normal cells. We also show that the activated macrophages secreted high levels of cytokines, including IL-12p70, IL-6, and TNF-α, consistent with the elimination of AML by macrophages. Our study reveals the potential of this model for screening new drugs against AML and the possibility of using human macrophages in AML treatment in the future.