Presentation description

LILRB4 is a known inhibitor of macrophage phagocytosis of tumor cells, and its expression is downregulated in cord blood-derived macrophages compared to adult-derived macrophages. Anti-CD47 is a potent activator of antibody-dependent cancer cell phagocytosis (ADCCP) by macrophages, as it blocks the "don't eat me" signal delivered when CD47, expressed on tumor cells, binds to SIRPα expressed on macrophages. Our research demonstrates that macrophages derived from the cord blood of newborn donors could phagocytize medulloblastoma cancer cells much better than macrophages derived from adult donors in response to anti-CD47 treatment. We then conducted RNA-seq analysis of each of these macrophage populations. We identified several mediators that stimulate and inhibit ADCCP, which are upregulated and downregulated, respectively, in cord blood macrophages compared to adult macrophages. LILRB4 was one of the most differentially expressed inhibitors of ADCCP that was downregulated in cord blood macrophages. Thus, we began a mechanistic approach to understanding the role of LILRB4 in regulating anti-CD47-mediated ADCCP by constructing LILRB4 shRNA-expressing lentivirus, which could transduce adult macrophages and downregulate LILRB4 expression. Upon lentiviral transduction, we assessed the macrophage expression levels of cell surface LILRB4 by flow cytometry. Our initial experiment did not show reduced expression of LILRB4 on macrophages; however, a subsequent modification of our lentivirus, to co-express RFP and LILRB4, was able to transduce macrophages. We are awaiting the results of the LILRB4 expression on these cells. If the LILRB4 protein expression is significantly reduced, we will determine whether adult-derived macrophages with reduced LILRB4 expression will phagocytize tumor cells better in response to anti-CD47.