Opportunities and challenges for anti-CD47 antibodies in hematological malignancies

CD47 is a cell-surface ligand that is overexpressed in various malignancies and that binds to SIRPα on macrophages to promote tumor cell evasion of phagocytosis. Blocking the CD47-SIRPα axis can increase the phagocytosis of macrophages to exert antitumor effects. CD47-based immunotherapy is a current research focus. The combination of anti-CD47 antibodies with other drugs has shown encouraging response rates in patients with hematological tumors, but side effects also occur. Bispecific antibodies and SIRPα/Fc fusion proteins appear to balance the efficacy and safety of treatment. We review the latest clinical research advances and discuss the opportunities and challenges associated with CD47-based immunotherapy for hematological malignancies.

YB-1-based oncolytic virotherapy in combination with CD47 blockade enhances phagocytosis of pediatric sarcoma cells

Oncolytic viruses (OVs) selectively replicate in tumor cells resulting in lysis, spreading of new infectious units and induction of antitumor immune responses through abrogating an immunosuppressive tumor microenvironment (TME). Due to their mode of action, OVs are ideal combination partners with targeted immunotherapies. One highly attractive combination is the inhibition of the 'don't-eat-me'-signal CD47, which is known to increase the phagocytic potential of tumor-associated macrophages. In this work, we analyzed the combination approach consisting of the YB-1-based oncolytic adenovirus XVir-N-31 (XVir) and the CD47 inhibitor (CD47i) B6.H12.2 concerning its phagocytic potential. We investigate phagocytosis of XVir-, adenovirus wildtype (AdWT)-, and non-infected established pediatric sarcoma cell lines by different monocytic cells. Phagocytes (immature dendritic cells and macrophages) were derived from THP-1 cells and healthy human donors. Phagocytosis of tumor cells was assessed via FACS analysis in the presence and absence of CD47i. Additional characterization of T cell-stimulatory surface receptors as well as chemo-/cytokine analyses were performed. Furthermore, tumor cells were infected and studied for the surface expression of the 'eat-me'-signal calreticulin (CALR) and the 'don't-eat-me'-signal CD47. We herein demonstrate that (1) XVir-infected tumor cells upregulate both CALR and CD47. XVir induces higher upregulation of CD47 than AdWT. (2) XVir-infection enhances phagocytosis in general and (3) the combination of XVir and CD47i compared to controls showed by far superior enhancement of phagocytosis, tumor cell killing and innate immune activation. In conclusion, the combination of CD47i and XVir causes a significant increase in phagocytosis exceeding the monotherapies considerably accompanied by upregulation of T cell-stimulatory receptor expression and inflammatory chemo/-cytokine secretion.

Signal regulatory protein beta 2 is a novel positive regulator of innate anticancer immunity

In recent years, the therapeutic (re)activation of innate anticancer immunity has gained prominence, with therapeutic blocking of the interaction of Signal Regulatory Protein (SIRP)-α with its ligand CD47 yielding complete responses in refractory and relapsed B cell lymphoma patients. SIRP-α has as crucial inhibitory role on phagocytes, with e.g., its aberrant activation enabling the escape of cancer cells from immune surveillance. SIRP-α belongs to a family of paired receptors comprised of not only immune-inhibitory, but also putative immune-stimulatory receptors. Here, we report that an as yet uninvestigated SIRP family member, SIRP-beta 2 (SIRP-ß2), is strongly expressed under normal physiological conditions in macrophages and granulocytes at protein level. Endogenous expression of SIRP-ß2 on granulocytes correlated with trogocytosis of cancer cells. Further, ectopic expression of SIRP-ß2 stimulated macrophage adhesion, differentiation and cancer cell phagocytosis as well as potentiated macrophage-mediated activation of T cell Receptor-specific T cell activation. SIRP-ß2 recruited the immune activating adaptor protein DAP12 to positively regulate innate immunity, with the charged lysine 202 of SIRP-ß2 being responsible for interaction with DAP12. Mutation of lysine 202 to leucine lead to a complete loss of the increased adhesion and phagocytosis. In conclusion, SIRP-ß2 is a novel positive regulator of innate anticancer immunity and a potential costimulatory target for innate immunotherapy.

Regulation of CD47 expression on CD14+ monocytes by interferon-α in PBC patients

Background

Primary biliary cholangitis (PBC) is a chronic intrahepatic cholestatic autoimmune liver disease characterized by inflammatory injury of small and medium-sized bile ducts in the liver. The pathogenesis of PBC has yet to be entirely understood. CD47/signal-regulatory protein alpha (SIRPα) is closely related to developing autoimmune diseases by promoting inflammatory response. However, the effect of CD47/SIRPα on inflammatory response in PBC patients is still unclear.

Objective

We investigated the expression of CD47/SIRPα and the effect of inflammatory cytokines on the CD47 expression, analyzed potential autoantibodies against CD47 and the effect of anti-CD47 antibody on the inflammatory response in PBC, provided laboratory basis for the study of the pathogenesis and targets for non-invasive diagnosis and treatment on PBC.

Methods

The expression levels of CD47 and SIRPα on peripheral blood mononuclear cells (PBMC) were measured in 14 patients with PBC (the PBC group) and 13 healthy subjects (the Control group) by flow cytometry (FCM). The PBMC derived from healthy subjects were stimulated with healthy subjects' serum, PBC patients' serum, IFN-α or TNF-α, and the CD47 expression level on CD14+ monocytes was detected by FCM. The level of serum anti-CD47 antibody or IFN-α in PBC patients and healthy subjects was analyzed by ELISA. FCM was used to examine the TNF-α expression level in CD14+ monocytes of healthy subjects stimulated with isotype control antibody, anti-CD47 antibody, LPS or LPS combined with CD47 antibody.

Results

The CD47 expression level on the CD14+ monocytes in PBC patients was statistically higher than that in the Control group (P<0.01). Compared with the Control group (PBMC+healthy serum), the CD47 expression on CD14+ monocyte stimulated with the PBC patients' serum (PBMC+PBC patients' serum) was increased (P<0.001); the CD47 expression on CD14+ monocyte stimulated with IFN-α (PBMC + IFN-α) increased gradually with the increased concentration of IFN-α (P<0.05). However, there was no similar trend on CD14+ monocyte stimulated with the TNF-α (PBMC+TNF-α) (P>0.05). The levels of serum anti-CD47 antibody and IFN-α in the PBC patients were higher than those in healthy subjects (P<0.05). The TNF-α expression level in CD14+ monocyte stimulated with the LPS (PBMC+LPS) or anti-CD47 antibody+LPS group (PBMC+LPS+anti-CD47 antibody) was significantly increased than that in the Control group (PBMC+isotype control antibody) (P<0.01 and P<0.001, respectively). The TNF-α expression level in CD14+ monocyte stimulated with the anti-CD47 antibody + LPS was higher than that with the LPS (P< 0.05).

Conclusion

The CD47 may be related to the pathogenesis of PBC by inflammatory response. The CD47/SIRPα signal were imbalanced in PBC patients. The presence of serum anti-CD47 antibodies in PBC patients provides a laboratory basis for clinical diagnosis and treatment.

Galectin-3 Cooperates with CD47 to Suppress Phagocytosis and T-cell Immunity in Gastric Cancer Peritoneal Metastases

The peritoneal cavity is a common site of gastric adenocarcinoma (GAC) metastasis. Peritoneal carcinomatosis (PC) is resistant to current therapies and confers poor prognosis, highlighting the need to identify new therapeutic targets. CD47 conveys a "don't eat me" signal to myeloid cells upon binding its receptor signal regulatory protein alpha (SIRPα), which helps tumor cells circumvent macrophage phagocytosis and evade innate immune responses. Previous studies demonstrated that the blockade of CD47 alone results in limited clinical benefits, suggesting that other target(s) might need to be inhibited simultaneously with CD47 to elicit a strong antitumor response. Here, we found that CD47 was highly expressed on malignant PC cells, and elevated CD47 was associated with poor prognosis. Galectin-3 (Gal3) expression correlated with CD47 expression, and coexpression of Gal3 and CD47 was significantly associated with diffuse type, poor differentiation, and tumor relapse. Depletion of Gal3 reduced expression of CD47 through inhibition of c-Myc binding to the CD47 promoter. Furthermore, injection of Gal3-deficient tumor cells into either wild-type and Lgals3-/- mice led to a reduction in M2 macrophages and increased T-cell responses compared with Gal3 wild-type tumor cells, indicating that tumor cell-derived Gal3 plays a more important role in GAC progression and phagocytosis than host-derived Gal3. Dual blockade of Gal3 and CD47 collaboratively suppressed tumor growth, increased phagocytosis, repolarized macrophages, and boosted T-cell immune responses. These data uncovered that Gal3 functions together with CD47 to suppress phagocytosis and orchestrate immunosuppression in GAC with PC, which supports exploring a novel combination therapy targeting Gal3 and CD47.

SIGNIFICANCE

Dual inhibition of CD47 and Gal3 enhances tumor cell phagocytosis and reprograms macrophages to overcome the immunosuppressive microenvironment and suppress tumor growth in peritoneal metastasis of gastric adenocarcinoma.

Checkpoint inhibition in hematologic malignancies

Checkpoint inhibitor therapy has emerged as an effective therapeutic strategy for many types of malignancies, especially in solid tumors. Within the last two decades, numerous monoclonal antibody drugs targeting the CTLA-4 and PD-1/PD-L1 checkpoint pathways have seen FDA approval. Within hematologic malignancies, Hodgkin Lymphoma has seen the greatest clinical benefits thus far with more recent data showing efficacy in the front-line setting. As our understanding of checkpoint inhibition expands, using these pathways as a therapeutic target has shown some utility in the treatment of other hematologic malignancies as well, primarily in the relapsed/refractory settings. Checkpoint inhibition also appears to have a role as a synergistic agent to augment clinical responses to other forms of therapy such as hematopoietic stem cell transplant. Moreover, alternative checkpoint molecules that bypass the well-studied CTLA-4 and PD-1/PD-L1 pathways have emerged as exciting new therapeutic targets. Most excitingly is the use of anti-CD47 blockade in the treatment of high risk MDS and TP-53 mutated AML. Overall, there has been tremendous progress in understanding the benefits of checkpoint inhibition in hematologic malignancies, but further studies are needed in all areas to best utilize these agents. This is a review of the most recent developments and progress in Immune Checkpoint Inhibition in Hematologic Malignancies in the last decade.

Cuproptosis-related gene expression is associated with immune infiltration and CD47/CD24 expression in glioblastoma, and a risk score based on these genes can predict the survival and prognosis of patients

Introduction

Glioblastoma (GBM) is the most invasive type of glioma, is insensitive to radiotherapy and chemotherapy, and has high proliferation and invasive ability, with a 5-year survival rate of <5%. Cuproptosis-related genes (CRGs) have been successfully used to predict the prognosis of many types of tumors. However, the relationship between cuproptosis and GBM remains unclear.

Methods

Here, we sought to identify CRGs in GBM and elucidate their role in the tumor immune microenvironment and prognosis. To that aim, changes in CRGs in The Cancer Genome Atlas (TCGA) transcriptional and Gene Expression Omnibus (GEO) datasets (GEO4290 and GEO15824) were characterized, and the expression patterns of these genes were analyzed.

Results

A risk score based on CRG expression characteristics could predict the survival and prognosis of patients with GBM and was significantly associated with immune infiltration levels and the expression of CD47 and CD24, which are immune checkpoints of the "don't eat me "signal. Furthermore, we found that the CDKN2A gene may predict GBM sensitivity and resistance to drugs.

Discussion

Our findings suggest that CRGs play a crucial role in GBM outcomes and provide new insights into CRG-related target drugs/molecules for cancer prevention and treatment.

Combining Multikinase Tyrosine Kinase Inhibitors Targeting the Vascular Endothelial Growth Factor and Cluster of Differentiation 47 Signaling Pathways Is Predicted to Increase the Efficacy of Antiangiogenic Combination Therapies

Angiogenesis is a critical step in tumor growth, development, and invasion. Nascent tumor cells secrete vascular endothelial growth factor (VEGF) that significantly remodels the tumor microenvironment through interaction with multiple receptors on vascular endothelial cells, including type 2 VEGF receptor (VEGFR2). The complex pathways initiated by VEGF binding to VEGFR2 lead to enhanced proliferation, survival, and motility of vascular endothelial cells and formation of a new vascular network, enabling tumor growth. Antiangiogenic therapies that inhibit VEGF signaling pathways were among the first drugs that targeted stroma rather than tumor cells. Despite improvements in progression-free survival and higher response rates relative to chemotherapy in some types of solid tumors, the impact on overall survival (OS) has been limited, with the majority of tumors eventually relapsing due to resistance or activation of alternate angiogenic pathways. Here, we developed a molecularly detailed computational model of endothelial cell signaling and angiogenesis-driven tumor growth to investigate combination therapies targeting different nodes of the endothelial VEGF/VEGFR2 signaling pathway. Simulations predicted a strong threshold-like behavior in extracellular signal-regulated kinases 1/2 (ERK1/2) activation relative to phosphorylated VEGFR2 levels, as continuous inhibition of at least 95% of receptors was necessary to abrogate phosphorylated ERK1/2 (pERK1/2). Combinations with mitogen-activated protein kinase/ERK kinase (MEK) and spingosine-1-phosphate inhibitors were found to be effective in overcoming the ERK1/2 activation threshold and abolishing activation of the pathway. Modeling results also identified a mechanism of resistance whereby tumor cells could reduce pERK1/2 sensitivity to inhibitors of VEGFR2 by upregulation of Raf, MEK, and sphingosine kinase 1 (SphK1), thus highlighting the need for deeper investigation of the dynamics of the crosstalk between VEGFR2 and SphK1 pathways. Inhibition of VEGFR2 phosphorylation was found to be more effective at blocking protein kinase B, also known as AKT, activation; however, to effectively abolish AKT activation, simulations identified Axl autophosphorylation or the Src kinase domain as potent targets. Simulations also supported activating cluster of differentiation 47 (CD47) on endothelial cells as an effective combination partner with tyrosine kinase inhibitors to inhibit angiogenesis signaling and tumor growth. Virtual patient simulations supported the effectiveness of CD47 agonism in combination with inhibitors of VEGFR2 and SphK1 pathways. Overall, the rule-based system model developed here provides new insights, generates novel hypothesis, and makes predictions regarding combinations that may enhance the OS with currently approved antiangiogenic therapies.

Novel immune directed therapies in myelodysplastic syndromes and acute myeloid leukemia

PURPOSE OF REVIEW

Therapies that target the immune system are increasingly used across oncology, including in hematologic malignancies such as myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). While allogeneic transplant has been a key therapy in these cancers, new approaches that target the immune system are being explored including immune checkpoint therapies, antibody-drug conjugates, and cellular therapies.

RECENT FINDINGS

This review outlines updates in the preclinical rationale for immune directed therapies in MDS and AML, as well as recent clinical trials exploring these therapies. This manuscript summarizes the development of therapies targeting T cell immunoglobulin and mucin domain-containing protein 3 (TIM-3) and CD47, which are being evaluated in late phase studies in MDS and AML. It also reviews the landscape of other immune based therapies including antibody-drug conjugates, chimeric antigen receptor-T cells, bispecific antibodies, and tumor vaccines.

SUMMARY

The treatment landscape in MDS and AML is rapidly changing; with a goal of improving the quality and duration of responses, a number of immune based therapies are under investigation. This review outlines recent advances with these therapies as well as some of the challenges that remain to incorporate them into leukemia care.

2-Amino-1,3,4-thiadiazoles as Glutaminyl Cyclases Inhibitors Increase Phagocytosis through Modification of CD47-SIRPα Checkpoint

Glutaminyl cyclases (QC, isoQC) convert N-terminal glutamine or glutamate into pyroglutamate (pGlu) on substrates. IsoQC has recently been demonstrated to promote pGlu formation on the N-terminus of CD47, the SIRPα binding site, contributing to the "don't eat me" cancer immune signaling of CD47-SIRPα. We developed new QC inhibitors by applying a structure-based optimization approach starting from fragments identified through library screening. Screening of metal binding fragments identified 5-(1H-benzimidazol-5-yl)-1,3,4-thiadiazol-2-amine (9) as a potent fragment, and further modification provided 5-(1-(3-methoxy-4-(3-(piperidin-1-yl)propoxy)benzyl)-1H-benzo[d]imidazol-5-yl)-1,3,4-thiadiazol-2-amine (22b) as a potent QC inhibitor. Treatment with 22b in A549 and H1975 lung cancer cells decreased the CD47/αhCD47-CC2C6 interaction, indicative of the CD47/SIRPα interaction, and enhanced the increased phagocytic activity of both THP-1 and U937 macrophages.

The Differential Expression of CD47 may be Related to the Pathogenesis From Myelodysplastic Syndromes to Acute Myeloid Leukemia

Myelodysplastic syndrome (MDS) can lead to the development of peripheral blood cytopenia and abnormal cell morphology. MDS has the potential to evolve into AML and can lead to reduced survival. CD47, a member of the immunoglobulin family, is one molecule that is overexpressed in a variety of cancer cells and is associated with clinical features and poor prognosis in a variety of malignancies. In this study, we analyzed the expression and function of CD47 in MDS and AML, and further analyzed its role in other tumors. Our analysis revealed significantly low CD47 expression in MDS and significantly high expression in AML. Further analysis of the function or pathway of CD47 from different perspectives identified a relationship to the immune response, cell growth, and other related functions or pathways. The relationship between CD47 and other tumors was analyzed from four aspects: DNA methyltransferase, TMB, MSI, and tumor cell stemness. Changes in gene expression levels have a known association with aberrant DNA methylation, and this methylation is the main mechanism of tumor suppressor gene silencing and clonal variation during the evolution of MDS to AML. Taken together, our findings support the hypothesis that the differential expression of CD47 might be related to the transformation of MDS to AML.

Neutrophil expressed CD47 regulates CD11b/CD18-dependent neutrophil transepithelial migration in the intestine in vivo

Dysregulated neutrophil (PMN) transmigration across epithelial surfaces (TEpM) significantly contributes to chronic inflammatory diseases, yet mechanisms defining this process remain poorly understood. In the intestine, uncontrolled PMN TEpM is a hallmark of disease flares in ulcerative colitis. Previous in vitro studies directed at identifying molecular determinants that mediate TEpM have shown that plasma membrane proteins including CD47 and CD11b/CD18 play key roles in regulating PMN TEpM across monolayers of intestinal epithelial cells. Here, we show that CD47 modulates PMN TEpM in vivo using an ileal loop assay. Importantly, using novel tissue-specific CD47 knockout mice and in vitro approaches, we report that PMN-expressed, but not epithelial-expressed CD47 plays a major role in regulating PMN TEpM. We show that CD47 associates with CD11b/CD18 in the plasma membrane of PMN, and that loss of CD47 results in impaired CD11b/CD18 activation. In addition, in vitro and in vivo studies using function blocking antibodies support a role of CD47 in regulating CD11b-dependent PMN TEpM and chemotaxis. Taken together, these findings provide new insights for developing approaches to target dysregulated PMN infiltration in the intestine. Moreover, tissue-specific CD47 knockout mice constitute an important new tool to study contributions of cells expressing CD47 to inflammation in vivo.

THBS1/CD47 Modulates the Interaction of γ-Catenin With E-Cadherin and Participates in Epithelial-Mesenchymal Transformation in Lipid Nephrotoxicity

Hyperlipidemia, an important risk factor for cardiovascular and end-stage renal diseases, often aggravates renal injury and compromises kidney function. Here, histological analysis of human kidney samples revealed that high lipid levels induced the development of renal fibrosis. To elucidate the mechanism underlying lipid nephrotoxicity, we used two types of mouse models (Apoe^−/− and C57BL/6 mice fed a 45 and 60% high-fat diet, respectively). Histological analysis of kidney tissues revealed high-lipid-induced renal fibrosis and inflammation; this was confirmed by examining fibrotic and inflammatory marker expression using Western blotting and real-time polymerase chain reaction. Oxidized low-density lipoprotein (OX-LDL) significantly induced the fibrotic response in HK-2 tubular epithelial cells. RNA-sequencing and Gene Ontology analysis of differentially expressed mRNAs in OX-LDL-treated HK-2 tubular epithelial cells and real-time PCR validation in Apoe^−/− mice showed that the expression of thrombospondin-1 (THBS1) in the high-fat group was significantly higher than that of the other top known genes, along with significant overexpression of its receptor CD47. THBS1 knockdown cells verified its relation to OX-LDL-induced fibrosis and inflammation. Liquid chromatography tandem mass spectrometry and STRING functional protein association network analyses predicted that THBS1/CD47 modulated the interaction between γ-catenin and E-cadherin and was involved in epithelial–mesenchymal transition, which was supported by immunoprecipitation and immunohistochemistry. CD47 downregulation following transfection with small-hairpin RNA in OX-LDL-treated tubular epithelial cells and treatment with anti-CD47 antibody restored the expression of E-cadherin and attenuated renal injury, fibrosis, and inflammatory response in OX-LDL-treated cells and in type 2 diabetes mellitus. These findings indicate that CD47 may serve as a potential therapeutic target in long-term lipid-induced kidney injury.

In Vitro Macrophage-Mediated Phagocytosis Assay of Brain Tumors

Tumor-associated macrophages (TAMs) have recently emerged as potentially crucial therapeutic targets for cancer. Thus, the development of macrophage-mediated phagocytosis assays is vital for preclinical drug screening of different tumor cells. This assay can be used to evaluate the effect of anti-cancer therapy, such as immunotherapy, radiotherapy, and chemotherapy, on different tumor cells. Here, we describe the in-vitro phagocytosis assay in detail. As an example of immunotherapy treatment, we used a monoclonal antibody to block an anti-phagocytic signal (CD47) to evaluate the assay using human brain tumor cells and monocyte-derived macrophages. We also demonstrated that this assay can be used to evaluate the effect of different irradiation doses on the phagocytosis of brain tumor cells. This functional assay is fast, accurate, and highly reproducible. Furthermore, the results successfully demonstrate that anti-CD47 antibodies and irradiation can enhance the macrophage-mediated phagocytosis of brain tumors.

Fr-PPIChem: An Academic Compound Library Dedicated to Protein-Protein Interactions

Protein-protein interactions (PPIs) mediate nearly every cellular process and represent attractive targets for modulating disease states but are challenging to target with small molecules. Despite this, several PPI inhibitors (iPPIs) have entered clinical trials, and a growing number of PPIs have become validated drug targets. However, high-throughput screening efforts still endure low hit rates mainly because of the use of unsuitable screening libraries. Here, we describe the collective effort of a French consortium to build, select, and store in plates a unique chemical library dedicated to the inhibition of PPIs. Using two independent predictive models and two updated databases of experimentally confirmed PPI inhibitors developed by members of the consortium, we built models based on different training sets, molecular descriptors, and machine learning methods. Independent statistical models were used to select putative PPI inhibitors from large commercial compound collections showing great complementarity. Medicinal chemistry filters were applied to remove undesirable structures from this set (such as PAINS, frequent hitters, and toxic compounds) and to improve drug likeness. The remaining compounds were subjected to a clustering procedure to reduce the final size of the library while maintaining its chemical diversity. In practice, the library showed a 46-fold activity rate enhancement when compared to a non-iPPI-enriched diversity library in high-throughput screening against the CD47-SIRPα PPI. The Fr-PPIChem library is plated in 384-well plates and will be distributed on demand to the scientific community as a powerful tool for discovering new chemical probes and early hits for the development of potential therapeutic drugs.

Evolutionarily conserved resistance to phagocytosis observed in melanoma cells is insensitive to upregulation of pro-phagocytic signals and to CD47 blockade

Therapeutic activation of macrophage phagocytosis has the ability to restrain tumour growth through phagocytic clearance of tumour cells and activation of the adaptive immune response. Our objective for this study was to evaluate the effects of modulating pro- and anti-phagocytic pathways in malignant melanoma. In order to identify evolutionarily conserved mechanisms of resistance that may be important for melanoma cell survival, we utilized a multi-species approach and examined the phagocytosis of human, mouse, and dog melanoma cells. We observed that melanoma cells from all three species displayed unexpected resistance to phagocytosis that could not be fully mitigated by blockade of the 'don't eat me' signal CD47 or by chemotherapeutic enhancement of known 'eat me' signals. Additionally, CD47 blockade failed to promote anti-melanoma immune responses or tumour regression in vivo. This melanoma resistance to phagocytosis was not mediated by soluble factors, and it was unaffected by siRNA-mediated knockdown of 47 prospective 'don't eat me' signals or by CRISPR-Cas-mediated CD47 knockout. Unexpectedly, CD47 knockout also did not enhance phagocytosis of lymphoma cells, but it eliminated the pro-phagocytic effect of CD47 blockade, suggesting that the pro-phagocytic effects of CD47 blockade are due in part to Fc receptor engagement. From this study, we conclude that melanoma cells possess an evolutionarily conserved resistance to macrophage phagocytosis. Further investigation will be needed to overcome the mechanisms that mediate melanoma cell resistance to innate immunity.

CD47 Deficiency in Mice Exacerbates Chronic Fatty Diet-Induced Steatohepatitis Through Its Role in Regulating Hepatic Inflammation and Lipid Metabolism

Inflammation is one of the hallmarks of non-alcoholic steatohepatitis. CD47 is a widely expressed transmembrane protein that signals through inhibitory receptor signal regulatory protein α (SIRPα) to inhibit macrophage activation and phagocytosis. In this study, we sought to investigate the role of CD47 in hepatosteatosis and fibrosis induced by a chronic high-fat diet (HFD), by comparing disease development in wild-type (WT) and CD47KO mice fed HFD for 40 weeks. The HFD induced remarkably more severe hepatic steatosis and fibrosis but less body weight gain and less subcutaneous fat accumulation in CD47KO mice compared to WT mice. Liver tissues from HFD-fed CD47KO mice exhibited enhanced inflammation characterized by increased proinflammatory cytokine production and increased nuclear factor-κB (NF-κB) activation compared to similarly fed WT mice. Although higher expression of apolipoproteins was observed in CD47KO mice compared to WT mice under a low-fat diet (LFD), HFD-fed WT and CD47KO mice showed comparably prominent downregulation of these apolipoprotein genes, suggesting that the marked difference observed in lipid accumulation and hepatosteatosis between these mice cannot be explained by changes in apolipoproteins. Like apolipoproteins, sirtuin 1 (SIRT1) and peroxisome proliferator activated receptor alpha (PPARα), which are involved in regulation of both lipid metabolism and inflammation, were more highly expressed in CD47KO than WT mice under LFD but more severely suppressed in CD47KO than in WT mice under HFD. Taken together, our results indicate that CD47 plays a significant role in the pathogenesis of HFD-induced hepatosteatosis and fibrosis through its role in regulation of inflammation and lipid metabolism.

Tuftsin-based, EGFR-targeting fusion protein and its enediyne-energized analog show high antitumor efficacy associated with CD47 down-regulation

Tuftsin (TF) is an immunomodulator tetrapeptide (Thr-Lys-Pro-Arg) that binds to the receptor neuropilin-1 (Nrp1) on the surface of cells. Many reports have described anti-tumor activity of tuftsin to relate with nonspecific activation of the host immune system. Lidamycin (LDM) that displays extremely potent cytotoxicity to cancer cells is composed of an apoprotein (LDP) and an enediyne chromophore (AE). In addition, Ec is an EGFR-targeting oligopeptide. In the present study, LDP was used as protein scaffold and the specific carrier for the highly potent AE. Genetically engineered fusion proteins LDP-TF and Ec-LDP-TF were prepared; then, the enediyne-energized fusion protein Ec-LDM-TF was generated by integration of AE into Ec-LDP-TF. The tuftsin-based fusion proteins LDP-TF and Ec-LDP-TF significantly enhanced the phagocytotic activity of macrophages as compared with LDP (P < 0.05). Ec-LDP-TF effectively bound to tumor cells and macrophages; furthermore, it markedly suppressed the growth of human epidermoid carcinoma A431 xenograft in athymic mice by 84.2 % (P < 0.05) with up-regulated expression of TNF-α and IFN-γ. Ec-LDM-TF further augmented the therapeutic efficacy, inhibiting the growth of A431 xenograft by 90.9 % (P < 0.05); notably, the Ec-LDM-TF caused marked down-regulation of CD47 in A431 cells. Moreover, the best therapeutic effect was recorded in the group of animals treated with the combination of Ec-LDP-TF with Ec-LDM-TF. The results suggest that tuftsin-based, enediyne-energized, and EGFR-targeting fusion proteins exert highly antitumor efficacy with CD47 modulation. Tuftsin-based fusion proteins are potentially useful for treatment of EGFR- and CD47-overexpressing cancers.

Osteoclast fusion is based on heterogeneity between fusion partners

Bone-resorbing osteoclasts are formed through fusion of mononucleated precursors. Their choice of partners during the fusion process remains unclear. We hypothesized that osteoclasts are selective in their choice of fusion partner and that this selectivity is based on heterogeneity among the cells with respect to their maturation stage and their expression and cellular organization of fusion factors. Support for this hypothesis was found from immunofluorescence staining of the osteoclast fusion factors CD47, dendritic cell-specific transmembrane protein (DC-STAMP), and syncytin-1. These stainings revealed heterogeneous localization patterns of all three factors within a given culture of osteoclasts. CD47 was found to be localized primarily in small osteoclasts and preosteoclasts, which were also positive for DC-STAMP but negative for cathepsin K expression. A role of CD47 in the early osteoclast fusion steps was also suggested from experiments with a CD47 blocking antibody, which resulted in an inhibition of the fusion of small osteoclasts. Conversely, blocking of connexin 43 affected the fusion of larger osteoclasts with four or more nuclei. The suggestion that different fusion factors function at different stages of osteoclast fusion supports the idea of heterogeneity in the osteoclast population; our results suggest that osteoclast fusion is indeed based on heterogeneity. Considering the in vivo environment in which osteoclasts develop and fuse, our findings seem very applicable and provide novel, important insight into key issues in bone and fusion research.

Immunoenrichment microwave and magnetic proteomics for quantifying CD47 in the experimental autoimmune encephalomyelitis model of multiple sclerosis

We hypothesized that quantitative MS/MS-based proteomics at multiple time points, incorporating immunoenrichment prior to rapid microwave and magnetic (IM(2) ) sample preparation, might enable correlation of the relative expression of CD47 and other low abundance proteins to disease progression in the experimental autoimmune encephalomyelitis (EAE) animal model of multiple sclerosis. To test our hypothesis, anti-CD47 antibodies were used to enrich for low abundance CD47 prior to microwave and magnetic proteomics in EAE. Decoding protein expression at each time point, with CD47-immunoenriched samples and targeted proteomic analysis, enabled peptides from the low abundance proteins to be precisely quantified throughout disease progression, including: CD47: 86-99, corresponding to the "marker of self" overexpressed by myelin that prevents phagocytosis, or "cellular devouring," by microglia and macrophages; myelin basic protein: 223-228, corresponding to myelin basic protein; and migration inhibitory factor: 79-87, corresponding to a proinflammatory cytokine that inhibits macrophage migration. While validation in a larger cohort is underway, we conclude that IM(2) proteomics is a rapid method to precisely quantify peptides from CD47 and other low abundance proteins throughout disease progression in EAE. This is likely due to improvements in selectivity and sensitivity, necessary to partially overcome masking of low abundance proteins by high abundance proteins and improve dynamic range.

Activated CD47 regulates multiple vascular and stress responses: implications for acute kidney injury and its management

Ischemia-reperfusion injury (IRI) remains a significant source of early and delayed renal transplant failure. Therapeutic interventions have yet to resolve this ongoing clinical challenge although the reasons for this remain unclear. The cell surface receptor CD47 is widely expressed on vascular cells and in tissues. It has one known soluble ligand, the stress-released matricellular protein thrombospondin-1 (TSP1). The TSP1-CD47 ligand receptor axis controls a number of important cellular processes, inhibiting survival factors such as nitric oxide, cGMP, cAMP, and VEGF, while activating injurious pathways such as production of reactive oxygen species. A role of CD47 in renal IRI was recently revealed by the finding that the TSP1-CD47 axis is induced in renal tubular epithelial cells (RTEC) under hypoxia and following IRI. The absence of CD47 in knockout mice increases survival, mitigates RTEC damage, and prevents subsequent kidney failure. Conversely, therapeutic blockade of TSP1-CD47 signaling provides these same advantages to wild-type animals. Together, these findings suggest an important role for CD47 in renal IRI as a proximate promoter of injury and as a novel therapeutic target.

The matricellular protein thrombospondin-1 globally regulates cardiovascular function and responses to stress via CD47

Matricellular proteins play diverse roles in modulating cell behavior by engaging specific cell surface receptors and interacting with extracellular matrix proteins, secreted enzymes, and growth factors. Studies of such interactions involving thrombospondin-1 have revealed several physiological functions and roles in the pathogenesis of injury responses and cancer, but the relatively mild phenotypes of mice lacking thrombospondin-1 suggested that thrombospondin-1 would not be a central player that could be exploited therapeutically. Recent research focusing on signaling through its receptor CD47, however, has uncovered more critical roles for thrombospondin-1 in acute regulation of cardiovascular dynamics, hemostasis, immunity, and mitochondrial homeostasis. Several of these functions are mediated by potent and redundant inhibition of the canonical nitric oxide pathway. Conversely, elevated tissue thrombospondin-1 levels in major chronic diseases of aging may account for the deficient nitric oxide signaling that characterizes these diseases, and experimental therapeutics targeting CD47 show promise for treating such chronic diseases as well as acute stress conditions that are associated with elevated thrombospondin-1 expression.

Crystallization and preliminary X-ray analysis of rat SHPS-1

SHPS-1, a receptor-type transmembrane protein, is abundantly expressed in neural and myeloid tissues. The most amino-terminal immunoglobulin-like domain of SHPS-1 plays an important role in a variety of cell functions by binding its ligand CD47. Interaction between SHPS-1 and CD47 is thought to be involved in negative regulation of phagocytosis. The ligand-binding domain of rat SHPS-1 was purified and crystallized using the vapour-diffusion method with the solution-stirring technique. Preliminary X-ray diffraction data were collected from SHPS-1 crystals to 2.8 A resolution and reduced to primitive hexagonal space group P622. Unit-cell parameters are a = b = 100.5, c = 101.3 A.

A cell surface receptor complex for fibrillar beta-amyloid mediates microglial activation

Senile plaques found in the Alzheimer's disease brain are foci of local inflammatory reactions mediated by plaque-associated microglia. The interaction of microglia with compacted deposits of beta-amyloid (Abeta) fibrils results in the stimulation of intracellular Tyr kinase-based signaling cascades and cellular activation, leading to the secretion of proinflammatory molecules. This study identifies a cell surface receptor complex that mediates the binding of microglia to Abeta fibrils and the subsequent activation of intracellular signaling pathways leading to a proinflammatory response. The receptor complex includes the B-class scavenger receptor CD36, the integrin-associated protein/CD47, and the alpha(6)beta(1)-integrin. Antagonists of scavenger receptors, CD36, CD47, and alpha(6)beta(1) inhibited the adhesion of THP-1 monocytes to Abeta fibrils. In addition, peptide competitors of Abeta fibril interactions with CD36, scavenger receptors, CD47, and the alpha(6)beta(1)-integrin inhibited Abeta stimulation of Tyr kinase-based signaling cascades in both THP-1 monocytes and murine microglia as well as interleukin 1beta production. A scavenger receptor antagonist and antibodies specific for CD36 and the beta(1)-integrin subunit also inhibited the Abeta-stimulated generation of reactive oxygen species. Importantly, the principal components of this receptor complex are shared with those for other fibrillar proteins and thus represent general elements through which myeloid lineage cells recognize complex fibrillar proteins. Identification of the cell surface molecules that interact with Abeta fibrils and mediate their activation of intracellular signaling cascades represents a potential intervention point in the treatment of Alzheimer's disease.

CD47 ligation selectively downregulates human interleukin 12 production

Interleukin (IL)-12 plays a key role not only in protective innate and adaptive T helper cell type 1 (Th1) responses but also in chronic inflammatory diseases. We report here that engagement of CD47 by either monoclonal antibody, its natural ligand thrombospondin (TSP), or 4N1K (a peptide of the COOH-terminal domain of TSP selectively binding CD47) inhibits IL-12 release by monocytes. The suppression occurred after T cell-dependent or -independent stimulation of monocytes and was selective for IL-12 inasmuch as the production of tumor necrosis factor (TNF)-alpha, IL-1, IL-6, and granulocyte/macrophage colony-stimulating factor was not inhibited. CD47 ligation did not alter transforming growth factor (TGF)-beta and IL-10 production, and the suppressive effect on IL-12 was not due to autocrine secretion of TGF-beta or IL-10. The IL-12 inhibition was not mediated by Fcgamma receptor ligation, did not require extracellular Ca(2+) influx, but was reversed by two phosphoinositide 3-kinase inhibitors (wortmannin and Ly294002). Thus, engagement of CD47 on monocytes by TSP, which transiently accumulates at the inflammatory site, is a novel and unexplored pathway to selectively downregulate IL-12 response. The pathway may be relevant in limiting the duration and intensity of the inflammatory response, and in developing novel therapeutic strategies for Th1-mediated diseases.

The vitronectin receptor and its associated CD47 molecule mediates proinflammatory cytokine synthesis in human monocytes by interaction with soluble CD23

The vitronectin receptor, alphavbeta3 integrin, plays an important role in tumor cell invasion, angiogenesis, and phagocytosis of apoptotic cells. CD47, a member of the multispan transmembrane receptor family, physically and functionally associates with vitronectin receptor (VnR). Although vitronectin (Vn) is not a ligand of CD47, anti-CD47 and beta3 mAbs suppress Vn, but not fibronectin (Fn) binding and function. Here, we show that anti-CD47, anti-beta3 mAb and Vn, but not Fn, inhibit sCD23-mediated proinflammatory function (TNF-alpha, IL-12, and IFN-gamma release). Surprisingly, anti-CD47 and beta3 mAbs do not block sCD23 binding to alphav+beta3+ T cell lines, whereas Vn and an alphav mAb (clone AMF7) do inhibit sCD23 binding, suggesting the VnR complex may be a functional receptor for sCD23. sCD23 directly binds alphav+beta3+/CD47(-) cell lines, but coexpression of CD47 increases binding. Moreover, sCD23 binds purified alphav protein and a single human alphav chain CHO transfectant. We conclude that the VnR and its associated CD47 molecule may function as a novel receptor for sCD23 to mediate its proinflammatory activity and, as such, may be involved in the inflammatory process of the immune response.