SIRPA and neoplasm: Crosslinking between tumor cell-associated CD47 and myeloid cell-specific checkpoint receptor signal regulatory protein-α (SIRPα) triggers negative signaling through immunotyrosine based inhibitory motif (ITIM), via recruitment of tyrosine phosphatases SHP-1 and SHP-2, and ultimately results in their phagocytic activity exhaustion (Figure 3) 15, 67, 68.