Biotech Values

[DonShimoda]

Since CD47 is also expressed on healthy cells, a concern is that anti-CD47 will also block healthy cells from expressing CD47 and consequently they will be "eaten" by mistake. The hope is that the lack of calreticulin expression in healthy cells will allow the anti-CD47 drugs being developed by Stanford and SCTPF to safely initiate phagocytosis in cancer cells. Calreticulin is a pro-phagocytic molecule that is highly expressed on the surface of several types of human cancer cells, including acute myeloid and lymphoblastic leukemias. Importantly, calreticulin is not expressed on healthy cells. If CD47 is the "don't eat me" signal then think of calreticulin as the "eat me" signal. It appears that in order for phagocytosis to occur requires both the CD47 "don't eat me" signal be turned off and a calreticulin "eat me" signal to be turned on. The hope is that turning off the "don't eat me" signal in healthy cells alone won't be sufficient to initiate phagocytosis because healthy cells don't express the calreticulin "eat me" signal.