not-yet-known not-yet-known not-yet-known unknown 2.7 CD47 CD47, also known as integrin-associated protein (IAP), is a cell surface protein belonging to the immunoglobulin superfamily, that plays a critical role in immune evasion, particularly in cancer. It comprises an extracellular N-terminal IgV domain, five transmembrane domains, and a short C-terminal cytoplasmic tail [187]. CD47 is recognized as a marker on red blood cells, where it functions as a ”don’t eat me” signal to prevent their phagocytosis. As red blood cells age, they lose this CD47 signal, resulting in their removal from circulation by macrophages in the spleen [188, 189]. Platelets, and lymphocytes also utilize this marker, to avoid rapid elimination by splenic macrophages [190]. When CD47 binds to signal regulatory protein alpha (SIRPα), it triggers a signaling cascade that inhibits phagocytosis. The ”don’t eat me” signal is conveyed through the phosphorylation of immunoreceptor tyrosine-based inhibition motifs on the cytoplasmic tail of SIRPα. This phosphorylation leads to the binding and activation of SHP-1 and SHP-2 (src homology-2 (SH2)-domain containing protein tyrosine phosphatases), which subsequently inhibit phagocytosis, possibly by preventing myosin-IIA from accumulating at the phagocytic synapse [191]. CD47 can bind to other proteins, like integrin and thrombospondin-1 (TSP-1). CD47 ligands are expressed on various innate immune cells, including macrophages, dendritic cells, granulocytes, monocytes, as well as neurons [192]. CD47 is universally expressed in both normal and malignant tissues [187]. CD47 was initially recognized as a tumor antigen in human ovarian cancer during the 1980s [193]. Since then, increased expression of CD47 has been observed in various cancers, including colorectal cancer, gastric cancer, bladder cancer, and lung squamous carcinoma, among others. Up regulation of CD47, helps tumors evade immune surveillance and clearance. Further, it is involved in numerous cellular functions, playing a crucial role in processes such as proliferation, apoptosis, adhesion, and migration [194, 195]. As described above, the interaction between CD47 on cancer cells and SIRPα on macrophages triggers a signaling cascade that inhibits phagocytosis. This signaling includes the activation of pathways that suppress macrophage activation and phagocytic function, thereby allowing cancer cells to persist and proliferate unchecked within the body[187, 194, 195]. In recent years, targeting the CD47-SIRPα pathway has emerged as a promising strategy in cancer immunotherapy. Preclinical studies have shown that blocking CD47 using monoclonal antibodies or possibly with a recombinant SIRPα protein that can bind and block CD47  can reverse this ”don’t eat me” signal, enabling macrophages to recognize and engulf cancer cells effectively [196]. Anti-CD47 antibodies can facilitate the elimination of tumor cells through several mechanisms, including phagocytes, Fc-dependent mechanisms such as antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC), as well as direct induction of apoptosis [196]. Studies on mouse models have shown that administering a blocking anti-human CD47 antibody, resulted in the elimination of AML and ALL cells in both the peripheral blood and bone marrow. This treatment led to long-term remissions in some cases [196, 197]. In an in-vivo myeloma model, a bivalent single-chain antibody fragment (scFv) targeting CD47 demonstrated cell death through the ligation of CD47 [198]. In a research work by Chan et al., it was noted that, blocking CD47 with a monoclonal antibody (mAb) resulted in macrophage engulfment of bladder cancer cells in vitro [199]. A study by Chao et al. reported that the anti-CD47 antibody synergizes with rituximab to promote phagocytosis and eradicate non-Hodgkin lymphoma cells, in human NHL-engrafted mice [200]. Antagonistic antibodies against SIRPα significantly enhances the in vitro killing of trastuzumab-opsonized Her2/Neu-positive breast cancer cells by phagocytes [201]. Combination approaches that target the CD47-SIRPα pathway hold significant therapeutic promise. This includes incorporating antibodies against CD47-SIRPα into combination therapies with other therapeutic antibodies, chemo-radiation therapy, agents that enhance macrophage activity, adjuvant therapy to prevent metastasis or standard cancer treatments [196]. One of the most advanced CD47 inhibitors in clinical development is magrolimab, a humanized 5F9 antibody (also known as Hu5F9-G4). Hu5F9-G4 induced robust macrophage-mediated phagocytosis of primary human AML cells in vitro and achieved complete eradication of human AML in vivo, resulting in long-term disease-free survival of patient-derived xenografts [202]. Clinical trials investigating magrolimab (Hu5F9-G4) have demonstrated encouraging results across various hematologic malignancies, including acute myeloid leukemia (AML), myelodysplastic syndrome (MDS), non-Hodgkin lymphoma and multiple myeloma  (NCT02641002) (NCT02367196) [203, 204, 205]. TTI-622, a bispecific antibody targeting both CD47 and CD19, is currently undergoing phase I clinical trials for patients with relapsed or refractory B-cell lymphoma and chronic lymphocytic leukemia (CLL) [206]. Moreover, CD47 blockade is also being evaluated in solid tumors, where it has shown potential in enhancing anti-tumor immunity and improving responses to other therapies, such as chemotherapy and ICIs. ALX148, a fusion protein targeting CD47, is currently under evaluation in multiple clinical trials, including a phase I/II trial for patients with advanced solid tumors [187]. KSI-3716, a monoclonal antibody targeting CD47, is currently undergoing phase I/II trials for patients with advanced solid tumors [207].