LILRB4 signaling in leukemia cells mediates T cell suppression and tumor infiltration

Immune checkpoint blockade therapy has been successful in treating some types of cancers but has not shown clinical benefits for treating leukemia (1). This result suggests that leukemia exploits unique escape mechanisms. Certain immune inhibitory receptors that are expressed by normal immune cells are also present on leukemia cells. It remains unknown whether these receptors can initiate immune-related primary signaling in tumor cells. Here we show that LILRB4, an ITIM-containing receptor and a monocytic leukemia marker, supports tumor cell infiltration into tissues and suppresses T cell activity via ApoE/LILRB4/SHP-2/uPAR/Arginase-1 signaling axis in acute myeloid leukemia (AML) cells. Blocking LILRB4 signaling using knockout and antagonistic antibody approaches impeded AML development. Thus, LILRB4 orchestrates tumor invasion pathways in monocytic leukemia cells by creating an immune-suppressive microenvironment. LILRB4 represents a compelling target for treatment of monocytic AML.