100PBalancing the efficacy and toxicity of anti-CD47 antibodies by direct screening in humanized mouse models

Background: CD47 is a transmembrane protein found on the surface of many cells in the body. Its expression is often up-regulated in many cancer cells. The receptor of CD47 was identified as SIRPa, which is expressed on phagocytic cells. Engagement of SIRPa by CD47 serves as "do not eat me" signal, thus inhibiting the phagocytic activity of macrophages. Cancer cells often hijack this pathway by boosting CD47 expression on their surface, in order to prevent innate cell-mediated phagocytosis. Molecules blocking the CD47-SIRPa interaction will unleash such inhibition and promote tumor destruction. Accordingly, anti-CD47 antibodies offer new hope to successful cancer treatment. Despite people are enthusiastic about CD47 as a potential target, the side effects associated with CD47 blockade have emerged as a major concern. For example, treatment with anti-CD47 antibody greatly reduced the number of circulating red blood cells and platelets that also express CD47. Thus, the class of CD47 antibodies that stimulate tumor cell killing while sparing normal cells in vivo is desirable for the cancer patients.

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