Anti-SIRP antibodies as a potential new tool for cancer immunotherapy

Antibody:CD47 ratio regulates macrophage phagocytosis through competitive receptor phosphorylation

Cancer immunotherapies often modulate macrophage effector function by introducing either targeting antibodies that activate Fcγ receptors (FcγRs) or blocking antibodies that disrupt inhibitory SIRPα-CD47 engagement. However, how these competing signals are integrated is poorly understood, raising questions about how to effectively titrate immune responses. Here, we find that macrophage phagocytic decisions are regulated by the ratio of activating ligand to inhibitory ligand over a broad range of absolute molecular densities. Using both endogenous and chimeric receptors, we show that activating:inhibitory ligand ratios of at least 10:1 are required to promote phagocytosis of model antibody-opsonized CD47-inhibited targets and that lowering that ratio reduces FcγR phosphorylation because of inhibitory phosphatases recruited to CD47-bound SIRPα. We demonstrate that ratiometric signaling is critical for phagocytosis of tumor cells and can be modified by blocking SIRPα, indicating that balancing targeting and blocking antibodies may be important for controlling macrophage phagocytosis in cancer immunotherapy.

The Fully human anti-CD47 antibody SRF231 exerts dual-mechanism antitumor activity via engagement of the activating receptor CD32a

Background

CD47 is a broadly expressed cell surface glycoprotein associated with immune evasion. Interaction with the inhibitory receptor signal regulatory protein alpha (SIRPα), primarily expressed on myeloid cells, normally serves to restrict effector function (eg, phagocytosis and immune cell homeostasis). CD47/SIRPα antagonists, commonly referred to as ‘macrophage checkpoint’ inhibitors, are being developed as cancer interventions. SRF231 is an investigational fully human IgG₄ anti-CD47 antibody that is currently under evaluation in a phase 1 clinical trial. The development and preclinical characterization of SRF231 are reported here.

Methods

SRF231 was characterized in assays designed to probe CD47/SIRPα blocking potential and effects on red blood cell (RBC) phagocytosis and agglutination. Additionally, SRF231-mediated phagocytosis and cell death were assessed in macrophage:tumor cell in vitro coculture systems. Further mechanistic studies were conducted within these coculture systems to ascertain the dependency of SRF231-mediated antitumor activity on Fc receptor engagement vs CD47/SIRPα blockade. In vivo, SRF231 was evaluated in a variety of hematologic xenograft models, and the mechanism of antitumor activity was assessed using cytokine and macrophage infiltration analyses following SRF231 treatment.

Results

SRF231 binds CD47 and disrupts the CD47/SIRPα interaction without causing hemagglutination or RBC phagocytosis. SRF231 exerts antitumor activity in vitro through both phagocytosis and cell death in a manner dependent on the activating Fc-gamma receptor (FcγR), CD32a. Through its Fc domain, SRF231 engagement with macrophage-derived CD32a serves dual purposes by eliciting FcγR-mediated phagocytosis of cancer cells and acting as a scaffold to drive CD47-mediated death signaling into tumor cells. Robust antitumor activity occurs across multiple hematologic xenograft models either as a single agent or in combination with rituximab. In tumor-bearing mice, SRF231 increases tumor macrophage infiltration and induction of the macrophage cytokines, mouse chemoattractant protein 1 and macrophage inflammatory protein 1 alpha. Macrophage depletion results in diminished SRF231 antitumor activity, underscoring a mechanistic role for macrophage engagement by SRF231.

Conclusion

SRF231 elicits antitumor activity via apoptosis and phagocytosis involving macrophage engagement in a manner dependent on the FcγR, CD32a.

Tumor microenvironment in giant cell tumor of bone: evaluation of PD-L1 expression and SIRPα infiltration after denosumab treatment

Giant cell tumor of bone (GCTB) is an intermediate malignant bone tumor that is locally aggressive and rarely metastasizes. Denosumab, which is a receptor activator of nuclear factor kappa B ligand (RANKL) inhibitor, can be used to treat GCTB. We focused on potential immunotherapy for GCTB and investigated the tumor microenvironment of GCTB. Programmed death-ligand 1 (PD-L1) and indoleamine 2,3-dioxygenase 1 (IDO1) expression and signal-regulatory protein alpha (SIRPα), forkhead box P3 (FOXP3), and cluster of differentiation 8 (CD8) infiltration were assessed by immunohistochemical studies of 137 tumor tissues from 96 patients. Of the naive primary specimens, 28% exhibited PD-L1 expression and 39% exhibited IDO1 expression. There was significantly more SIRPα⁺, FOXP3⁺, and CD8⁺ cell infiltration in PD-L1- and IDO1-positive tumors than in PD-L1- and IDO1-negative tumors. The frequency of PD-L1 expression and SIRPα⁺ cell infiltration in recurrent lesions treated with denosumab was significantly higher than in primary lesions and recurrent lesions not treated with denosumab. PD-L1 expression and higher SIRPα⁺ cell infiltration were significantly correlated with shorter recurrence-free survival. PD-L1 and SIRPα immune checkpoint inhibitors may provide clinical benefit in GCTB patients with recurrent lesions after denosumab therapy.

Turning enemies into allies-reprogramming tumor-associated macrophages for cancer therapy

Checkpoint blockade therapies that target inhibitory receptors on T cells have revolutionized clinical oncology. Antibodies targeting CTLA-4 or the PD-1/PD-L1 axis are now successfully used alone or in combination with chemotherapy for numerous tumor types. Despite the clinical success of checkpoint blockade therapies, tumors exploit multiple mechanisms to escape or subvert the anti-tumor T cell response. Within the tumor microenvironment, tumor-associated macrophages (TAM) can suppress T cell responses and facilitate tumor growth in various ways, ultimately debilitating clinical responses to T cell checkpoint inhibitors. There is therefore significant interest in identifying biologicals and drugs that target immunosuppressive TAM within the tumor microenvironment and can be combined with immune checkpoint inhibitors. Here we review approaches that are currently being evaluated to convert immunosuppressive TAM into immunostimulatory macrophages that promote T cell responses and tumor elimination. Tumor-associated macrophages (TAMs) are a major component of the tumor microenvironment that impact anti-tumor immune responses and susceptibility to checkpoint blockade. TAMs are very heterogeneous and can be either immunosuppressive or immunostimulatory. Here, Molgora and Colonna review current strategies that aim to reprogram TAMs to enhance rather than inhibit immune responses.

Clinical significance of signal regulatory protein alpha (SIRPα) expression in esophageal squamous cell carcinoma

Signal regulatory protein alpha (SIRPα) is a type I transmembrane protein that inhibits macrophage phagocytosis of tumor cells upon interaction with CD47, and the CD47‐SIRPα pathway acts as an immune checkpoint factor in cancers. This study aims to clarify the clinical significance of SIRPα expression in esophageal squamous cell carcinoma (ESCC). First, we assessed SIRPα expression using RNA sequencing data of 95 ESCC tissues from The Cancer Genome Atlas (TCGA) and immunohistochemical analytic data from our cohort of 131 patients with ESCC. Next, we investigated the correlation of SIRPα expression with clinicopathological factors, patient survival, infiltration of tumor immune cells, and expression of programmed cell death‐ligand 1 (PD‐L1). Overall survival was significantly poorer with high SIRPα expression than with low expression in both TCGA and our patient cohort (P < .001 and P = .027, respectively). High SIRPα expression was associated with greater depth of tumor invasion (P = .0017). Expression of SIRPα was also significantly correlated with the tumor infiltration of M1 macrophages, M2 macrophages, CD8⁺ T cells, and PD‐L1 expression (P < .001, P < .001, P = .03, and P < .001, respectively). Moreover, patients with SIRPα/PD‐L1 coexpression tended to have a worse prognosis than patients with expression of either protein alone or neither. Taken together, SIRPα indicates poor prognosis in ESCC, possibly through inhibiting macrophage phagocytosis of tumor cells and inducing suppression of antitumor immunity. Signal regulatory protein alpha should be considered as a potential therapeutic target in ESCC, especially if combined with PD‐1‐PD‐L1 blockade.

SIRPα-specific monoclonal antibody enables antibody-dependent phagocytosis of neuroblastoma cells

Immunotherapy with anti-G_D2 monoclonal antibodies (mAbs) provides some benefits for patients with neuroblastoma (NB). However, the therapeutic efficacy remains limited, and treatment is associated with significant neuropathic pain. Targeting O-acetylated G_D2 (OAcG_D2) by 8B6 mAb has been proposed to avoid pain by more selective tumor cell targeting. Thorough understanding of its mode of action is necessary to optimize this treatment strategy. Here, we found that 8B6-mediated antibody-dependent cellular phagocytosis (ADCP) performed by macrophages is a key effector mechanism. But efficacy is limited by upregulation of CD47 expression on neuroblastoma cells in response to OAcG_D2 mAb targeting, inhibiting 8B6-mediated ADCP. Antibody specific for the CD47 receptor SIRPα on macrophages restored 8B6-induced ADCP of CD47-expressing NB cells and improved the antitumor activity of 8B6 mAb therapy. These results identify ADCP as a critical mechanism for tumor cytolysis by anti-disialoganglioside mAb and support a combination with SIRPα blocking agents for effective neuroblastoma therapy.

Tumor-associated macrophages in cholangiocarcinoma: complex interplay and potential therapeutic target

Cholangiocarcinoma (CCA) is an aggressive and multifactorial malignancy of the biliary tract. The carcinogenesis of CCA is associated with genomic and epigenetic abnormalities, as well as environmental effects. However, early clinical diagnosis and reliable treatment strategies of CCA remain unsatisfactory. Multiple compartments of the tumor microenvironment significantly affect the progression of CCA. Tumor-associated macrophages (TAMs) are a type of plastic immune cells that are recruited and activated in the CCA microenvironment, especially at the tumor invasive front and perivascular sites. TAMs create a favorable environment that benefits CCA growth by closely interacting with CCA cells and other stromal cells via releasing multiple protumor factors. In addition, TAMs exert immunosuppressive and antichemotherapeutic effects, thus intensifying the malignancy. Targeting TAMs may provide an improved understanding of, and novel therapeutic approaches for, CCA. This review focuses on revealing the interplay between TAMs and CCA.

Quantitative Proteomics Identifies Secreted Diagnostic Biomarkers as well as Tumor-Dependent Prognostic Targets for Clear Cell Renal Cell Carcinoma

Clear cell renal cell carcinoma (ccRCC) is the third most common and most malignant urological cancer, with a 5-year survival rate of 10% for patients with advanced tumors. Here, we identified 10,160 unique proteins by in-depth quantitative proteomics, of which 955 proteins were significantly regulated between tumor and normal adjacent tissues. We verified four putatively secreted biomarker candidates, namely, PLOD2, FERMT3, SPARC, and SIRPα, as highly expressed proteins that are not affected by intratumor and intertumor heterogeneity. Moreover, SPARC displayed a significant increase in urine samples of patients with ccRCC, making it a promising marker for the detection of the disease in body fluids. Furthermore, based on molecular expression profiles, we propose a biomarker panel for the robust classification of ccRCC tumors into two main clusters, which significantly differed in patient outcome with an almost three times higher risk of death for cluster 1 tumors compared with cluster 2 tumors. Moreover, among the most significant clustering proteins, 13 were targets of repurposed inhibitory FDA-approved drugs. Our rigorous proteomics approach identified promising diagnostic and tumor-discriminative biomarker candidates which can serve as therapeutic targets for the treatment of ccRCC. IMPLICATIONS: Our in-depth quantitative proteomics analysis of ccRCC tissues identifies the putatively secreted protein SPARC as a promising urine biomarker and reveals two molecular tumor phenotypes.

Functions of Thrombospondin-1 in the Tumor Microenvironment

The identification of thrombospondin-1 as an angiogenesis inhibitor in 1990 prompted interest in its role in cancer biology and potential as a therapeutic target. Decreased thrombospondin-1 mRNA and protein expression are associated with progression in several cancers, while expression by nonmalignant cells in the tumor microenvironment and circulating levels in cancer patients can be elevated. THBS1 is not a tumor suppressor gene, but the regulation of its expression in malignant cells by oncogenes and tumor suppressor genes mediates some of their effects on carcinogenesis, tumor progression, and metastasis. In addition to regulating angiogenesis and perfusion of the tumor vasculature, thrombospondin-1 limits antitumor immunity by CD47-dependent regulation of innate and adaptive immune cells. Conversely, thrombospondin-1 is a component of particles released by immune cells that mediate tumor cell killing. Thrombospondin-1 differentially regulates the sensitivity of malignant and nonmalignant cells to genotoxic stress caused by radiotherapy and chemotherapy. The diverse activities of thrombospondin-1 to regulate autophagy, senescence, stem cell maintenance, extracellular vesicle function, and metabolic responses to ischemic and genotoxic stress are mediated by several cell surface receptors and by regulating the functions of several secreted proteins. This review highlights progress in understanding thrombospondin-1 functions in cancer and the challenges that remain in harnessing its therapeutic potential.

Function of Macrophages in Disease: Current Understanding on Molecular Mechanisms

Tissue-resident macrophages (TRMs) are heterogeneous populations originating either from monocytes or embryonic progenitors, and distribute in lymphoid and non-lymphoid tissues. TRMs play diverse roles in many physiological processes, including metabolic function, clearance of cellular debris, and tissue remodeling and defense. Macrophages can be polarized to different functional phenotypes depending on their origin and tissue microenvironment. Specific macrophage subpopulations are associated with disease progression. In studies of fate-mapping and single-cell RNA sequencing methodologies, several critical molecules have been identified to induce the change of macrophage function. These molecules are potential markers for diagnosis and selective targets for novel macrophage-mediated treatment. In this review, we discuss some of the recent findings regarding less-known molecules and new functions of well-known molecules. Understanding the mechanisms of these molecules in macrophages has the potential to yield new macrophage-mediated treatments or diagnostic approaches to disease.

Single-cell map of diverse immune phenotypes in the acute myeloid leukemia microenvironment

BACKGROUND

Knowledge of immune cell phenotypes, function, and developmental trajectory in acute myeloid leukemia (AML) microenvironment is essential for understanding mechanisms of evading immune surveillance and immunotherapy response of targeting special microenvironment components.

METHODS

Using a single-cell RNA sequencing (scRNA-seq) dataset, we analyzed the immune cell phenotypes, function, and developmental trajectory of bone marrow (BM) samples from 16 AML patients and 4 healthy donors, but not AML blasts.

RESULTS

We observed a significant difference between normal and AML BM immune cells. Here, we defined the diversity of dendritic cells (DC) and macrophages in different AML patients. We also identified several unique immune cell types including T helper cell 17 (TH17)-like intermediate population, cytotoxic CD4+ T subset, T cell: erythrocyte complexes, activated regulatory T cells (Treg), and CD8+ memory-like subset. Emerging AML cells remodels the BM immune microenvironment powerfully, leads to immunosuppression by accumulating exhausted/dysfunctional immune effectors, expending immune-activated types, and promoting the formation of suppressive subsets.

CONCLUSION

Our results provide a comprehensive AML BM immune cell census, which can help to select pinpoint targeted drug and predict efficacy of immunotherapy.

The role of CD47-SIRPα immune checkpoint in tumor immune evasion and innate immunotherapy

As a transmembrane protein, CD47 plays an important role in mediating cell proliferation, migration, phagocytosis, apoptosis, immune homeostasis, inhibition of NO signal transduction and other related reactions. Upon the interaction of innate immune checkpoint CD47-SIRPα occurrence, they send a "don't eat me" signal to the macrophages. This signal ultimately helps tumors achieve immune escape by inhibiting macrophage contraction to prevent tumor cells from phagocytosis. Therefore, the importance of CD47-SIRPα immune checkpoint inhibitors in tumor immunotherapy has attracted more attention in recent years. Based on the cognitive improvement of the effect with CD47 in tumor microenvironment and tumor characteristics, the pace of tumor treatment strategies for CD47-SIRPα immune checkpoint inhibitors has gradually accelerated. In this review, we introduced the high expression of CD47 in cancer cells to avoid phagocytosis by immune cells and the importance of CD47 in the structure of cancer microenvironment and the maintenance of cancer cell characteristics. Given the role of the innate immune system in tumorigenesis and development, an improved understanding of the anti-tumor process of innate immune checkpoint inhibitors can lay the foundation for more effective combinations with other anti-tumor treatment strategies.

Selective SIRPα blockade reverses tumor T cell exclusion and overcomes cancer immunotherapy resistance

T cell exclusion causes resistance to cancer immunotherapies via immune checkpoint blockade (ICB). Myeloid cells contribute to resistance by expressing signal regulatory protein-α (SIRPα), an inhibitory membrane receptor that interacts with ubiquitous receptor CD47 to control macrophage phagocytosis in the tumor microenvironment. Although CD47/SIRPα-targeting drugs have been assessed in preclinical models, the therapeutic benefit of selectively blocking SIRPα, and not SIRPγ/CD47, in humans remains unknown. We report a potent synergy between selective SIRPα blockade and ICB in increasing memory T cell responses and reverting exclusion in syngeneic and orthotopic tumor models. Selective SIRPα blockade stimulated tumor nest T cell recruitment by restoring murine and human macrophage chemokine secretion and increased anti-tumor T cell responses by promoting tumor-antigen crosspresentation by dendritic cells. However, nonselective SIRPα/SIRPγ blockade targeting CD47 impaired human T cell activation, proliferation, and endothelial transmigration. Selective SIRPα inhibition opens an attractive avenue to overcoming ICB resistance in patients with elevated myeloid cell infiltration in solid tumors.

Novel SIRPα Antibodies That Induce Single-Agent Phagocytosis of Tumor Cells while Preserving T Cells

The signal regulatory protein α (SIRPα)/CD47 axis has emerged as an important innate immune checkpoint that enables cancer cell escape from macrophage phagocytosis. SIRPα expression is limited to macrophages, dendritic cells, and neutrophils-cells enriched in the tumor microenvironment. In this study, we present novel anti-SIRP Abs, SIRP-1 and SIRP-2, as an approach to targeting the SIRPα/CD47 axis. Both SIRP-1 and SIRP-2 bind human macrophage SIRPα variants 1 and 2, the most common variants in the human population. SIRP-1 and SIRP-2 are differentiated among reported anti-SIRP Abs in that they induce phagocytosis of solid and hematologic tumor cell lines by human monocyte-derived macrophages as single agents. We demonstrate that SIRP-1 and SIRP-2 disrupt SIRPα/CD47 interaction by two distinct mechanisms: SIRP-1 directly blocks SIRPα/CD47 and induces internalization of SIRPα/Ab complexes that reduce macrophage SIRPα surface levels and SIRP-2 acts via disruption of higher-order SIRPα structures on macrophages. Both SIRP-1 and SIRP-2 engage FcγRII, which is required for single-agent phagocytic activity. Although SIRP-1 and SIRP-2 bind SIRPγ with varying affinity, they show no adverse effects on T cell proliferation. Finally, both Abs also enhance phagocytosis when combined with tumor-opsonizing Abs, including a highly differentiated anti-CD47 Ab, AO-176, currently being evaluated in phase 1 clinical trials, NCT03834948 and NCT04445701 SIRP-1 and SIRP-2 are novel, differentiated SIRP Abs that induce in vitro single-agent and combination phagocytosis and show no adverse effects on T cell functionality. These data support their future development, both as single agents and in combination with other anticancer drugs.

Targeting tumor-associated macrophages as an antitumor strategy

Tumor-associated macrophages (TAMs) are the most widely infiltrating immune cells in the tumor microenvironment (TME). Clinically, the number of TAMs is closely correlated with poor outcomes in multiple cancers. The biological actions of TAMs are complex and diverse, including mediating angiogenesis, promoting tumor invasion and metastasis, and building an immunosuppressive microenvironment. Given these pivotal roles of TAMs in tumor development, TAM-based strategies are attractive and used in certain tumor therapies, including inhibition of angiogenic signalling, blockade of the immune checkpoint, and macrophage enhancement phagocytosis. Several attempts to develop TAM-targeted agents have been made to deplete TAMs or reprogram the behaviour of TAMs. Some have shown a favourable curative effect in monotherapy, combination with chemotherapy or immunotherapy in clinical trials. Additionally, a new macrophage-based cell therapeutic technology was recently developed by equipping macrophages with CAR molecules. It is expected to break through barriers to solid tumor treatment. Although TAM-related studies have yielded positive antitumor outcomes, further investigations are needed to better characterize TAMs, which will benefit further establishment of novel strategies for tumor therapy. Here, we concisely summarize the functions of TAMs in the TME and comprehensively introduce the latest TAM-based regimens in cancer treatment.

Targeting the myeloid checkpoint receptor SIRPα potentiates innate and adaptive immune responses to promote anti-tumor activity

Background

Signal regulatory protein α (SIRPα) is a myeloid-lineage inhibitory receptor that restricts innate immunity through engagement of its cell surface ligand CD47. Blockade of the CD47–SIRPα interaction synergizes with tumor-specific antibodies and T-cell checkpoint inhibitors by promoting myeloid-mediated antitumor functions leading to the induction of adaptive immunity. Inhibition of the CD47–SIRPα interaction has focused predominantly on targeting CD47, which is expressed ubiquitously and contributes to the accelerated blood clearance of anti-CD47 therapeutics. Targeting SIRPα, which is myeloid-restricted, may provide a differential pharmacokinetic, safety, and efficacy profile; however, SIRPα polymorphisms and lack of pan-allelic and species cross-reactive agents have limited the clinical translation of antibodies against SIRPα. Here, we report the development of humanized AB21 (hAB21), a pan-allelic anti-SIRPα antibody that binds human, cynomolgus monkey, and mouse SIRPα alleles with high affinity and blocks the interaction with CD47.

Methods

Human macrophages derived from donors with various SIRPα v1 and v2 allelic status were used to assess the ability of hAB21 to enhance phagocytosis. HAB21_IgG subclasses were evaluated for targeted depletion of peripheral blood mononuclear cells, phagocytosis and in vivo efficacy in xenograft models. Combination therapy with anti-PD1/anti-PD-L1 in several syngeneic models was performed. Immunophenotyping of tissues from MC38 tumor-bearing mice treated with AB21 and anti-PD-1 was evaluated. PK, PD and tolerability of hAB21 were evaluated in cynomolgus monkeys.

Results

SIRPα blockade with hAB21 promoted macrophage-mediated antibody-dependent phagocytosis of tumor cells in vitro and improved responses to rituximab in the Raji human tumor xenograft mouse model. Combined with PD-1/PD-L1 blockade, AB21 improved response rates by facilitating monocyte activation, dendritic cell activation, and T cell effector functions resulting in long term, durable antitumor immunity. In cynomolgus monkeys, hAB21 has a half-life of 5.3 days at 10 mg/kg and complete target occupancy with no hematological toxicity or adverse findings at doses up to 30 mg/kg.

Conclusions

The in vitro and in vivo antitumor activity of hAB21 broadly recapitulates that of CD47 targeted therapies despite differences in ligand expression, binding partners, and function, validating the CD47–SIRPα axis as a fundamental myeloid checkpoint pathway and its blockade as promising therapeutic intervention for treatment of human malignancies.

Potential New Cancer Immunotherapy: Anti-CD47-SIRPα Antibodies

CD47 belongs to immunoglobulin superfamily and is widely expressed on the surface of cell membrane, while another transmembrane protein SIRPα is restricted to the surface of macrophages, dendritic cells, and nerve cells. As a cell surface receptor and ligand, respectively, CD47 and SIRPα interact to regulate cell migration and phagocytic activity, and maintain immune homeostasis. In recent years, studies have found that immunoglobulin superfamily CD47 is overexpressed widely across tumor types, and CD47 plays an important role in suppressing phagocytes activity through binding to the transmembrane protein SIRPα in phagocytic cells. Therefore, targeting CD47 may be a novel strategy for cancer immunotherapy, and a variety of anti-CD47 antibodies have appeared, such as humanized 5F9 antibody, B6H12 antibody, ZF1 antibody, and so on. This review mainly describes the research history of CD47-SIRPα and focuses on macrophage-mediated CD47-SIRPα immunotherapy of tumors.

Stroma-derived ANGPTL2 establishes an anti-tumor microenvironment during intestinal tumorigenesis

Previous studies show that tumor cell-derived angiopoietin-like protein 2 (ANGPTL2) functions as a tumor promoter in some cancer contexts. However, we recently reported that host ANGPTL2 also shows tumor suppressive activity by enhancing dendritic cell-mediated CD8⁺ T cell anti-tumor immune responses in mouse kidney cancer and murine syngeneic models. However, mechanisms underlying ANGPTL2-mediated tumor suppression are complex and not well known. Here, we investigated ANGPTL2 tumor suppressive function in chemically-induced intestinal tumorigenesis. ANGPTL2 deficiency enhanced intestinal tumor growth in an experimental mouse colitis-associated colon cancer (CAC) model. Angptl2-deficient mice also showed a decrease not only in CD8⁺ T cell responses but in CD4⁺ T cell responses during intestinal tumorigenesis. Furthermore, we show that stroma-derived ANGPTL2 can activate the myeloid immune response. Notably, ANGPTL2 drove generation of immunostimulatory macrophages via the NF-κB pathway, accelerating CD4⁺ T helper 1 (Th1) cell activation. These findings overall provide novel insight into the complex mechanisms underlying ANGPTL2 anti-tumor function in cancer pathology.

Engineering Macrophages for Cancer Immunotherapy and Drug Delivery

Macrophages play an important role in cancer development and metastasis. Proinflammatory M1 macrophages can phagocytose tumor cells, while anti-inflammatory M2 macrophages such as tumor-associated macrophages (TAMs) promote tumor growth and invasion. Modulating the tumor immune microenvironment through engineering macrophages is efficacious in tumor therapy. M1 macrophages target cancerous cells and, therefore, can be used as drug carriers for tumor therapy. Herein, the strategies to engineer macrophages for cancer immunotherapy, such as inhibition of macrophage recruitment, depletion of TAMs, reprograming of TAMs, and blocking of the CD47-SIRPα pathway, are discussed. Further, the recent advances in drug delivery using M1 macrophages, macrophage-derived exosomes, and macrophage-membrane-coated nanoparticles are elaborated. Overall, there is still significant room for development in macrophage-mediated immune modulation and macrophage-mediated drug delivery, which will further enhance current tumor therapies against various malignant solid tumors, including drug-resistant tumors and metastatic tumors.

Targeting tumor-associated macrophages for cancer immunotherapy

Macrophages are important effector cells of the innate immune system and are also major components of the tumor microenvironment (TME). Macrophages that are abundant in the TME are called tumor-associated macrophages (TAMs). As TAMs promote strong tumor angiogenesis and support tumor cell survival, they are closely related to tumor growth. Several studies have demonstrated that reducing the density or effects of TAMs can inhibit the growth of tumors, making them targets for cancer immunotherapy, which has become a research hot spot. Several clinical and preclinical trials have studied drugs that inhibit the effects of and reduce the population of phagocytes that target TAMs achieve cancer immunotherapy. In this paper, we summarize the various methods of targeting TAMs for tumor immunotherapy, focusing on TAM mechanisms, sources, and polarization.

miR-148a Affects Polarization of THP-1-Derived Macrophages and Reduces Recruitment of Tumor-Associated Macrophages via Targeting SIRPα

Purpose

The objective of this study was to investigate the effect of miR-148a on the polarization and recruitment of tumor-associated macrophages (TAMs).

Methods

In human monocyte THP-1 cells, M1 or M2 differentiation was induced by phorbol 12-myristate 13-acetate (PMA) with specific induction supplements and identified using flow cytometry and ELISA. To alter cellular miR-148a expression level, THP-1 cells were transfected with miR-148a mimics or inhibitors. A dual-luciferase assay was used to determine whether miR-148a could directly regulate the expression of signal regulatory protein α (SIRPα). Expression of miR-148a and SIRPα was detected with RT-PCR or Western blot. A co-culture system of THP-1 cells and colorectal cancer SW480 cells was used for TAM induction. The recruitment of macrophage to SW480 cells was measured using chemotaxis assay. In SW480 cells, apoptosis induced by macrophages was detected using flow cytometry and a xenograft assay. Macrophage infiltration was detected by immunofluorescence assay in tumor tissues.

Results

miR-148a over-expression increased M1-related CD86 expression in THP-1 cells and promoted differentiation to M1-like macrophages. Inhibition of miR-148a increased M2-related CD206 expression and promoted differentiation to M2-like macrophages. In the co-culture system, THP-1 cells were induced to the M2-like state by SW480 cells. The level of miR-148a negatively correlated with the levels of M2-related cytokines. Additionally, miR-148a expression level was negatively associated with macrophage recruitment by colorectal cancer cells. Furthermore, in miR-148a over-expression, the number of macrophages recruited by SW480 cells was reduced. Meanwhile, cancer cell apoptosis induced by macrophages was enhanced. Thus, miR-148a expression was beneficial for the transformation of macrophages, from an immune-suppressive status to an immune-promoting status. These anti-cancer effects of miR-148a were related to the down-regulation of SIRPα in macrophages, directly targeted by miR-148a. A xenograft assay showed that the co-inoculation of macrophages over-expressing miR-148a reduced subcutaneous tumorigenesis and M2 macrophage infiltration.

Conclusion

miR-148a promoted the differentiation of M0 macrophages into anti-tumor classical activation type M1, and reduced TAM recruitment by targeting SIRPα to inhibit colorectal cancer cell viability.

Blockade of CD47 or SIRPα: a new cancer immunotherapy

The CD47-Signal regulatory protein α (SIRPα) singling axis acts as a crucial regulator that limits the phagocytic activity of professional phagocytes such as macrophages. Recent studies have demonstrated that the interaction between CD47 on tumor cells and SIRPα on macrophages is implicated in the ability of tumors to evade immunosurveillance. Targeting the CD47-SIRPα interaction is therefore considered to be a promising approach for cancer therapy. Herein, we review some of studies displaying the potential clinical application of antibodies and other modalities that target the CD47-SIRPα interaction. Current limitations of the CD47-SIRPα-targeted immunotherapeutic approaches are also discussed as well as other avenues for future study to improve the current strategies in targeting the CD47-SIRPα signaling axis for cancer immunotherapy.

Clinicopathological analysis of immunohistochemical expression of CD47 and SIRPα in adult T-cell leukemia/lymphoma

The interaction of CD47 and signal-regulatory protein alpha (SIRPα) induces "don't eat me signal", leading suppression of phagocytosis. This signal can affect the clinical course of malignant disease. Although CD47 and SIRPα expression are associated with clinicopathological features in several neoplasms, the investigation for adult T-cell leukemia/lymphoma (ATLL) has not been well-documented. This study aimed to declare the association between CD47 and SIRPα expression and clinicopathological features in ATLL. We performed immunostaining on 73 biopsy samples and found that CD47 is primarily expressed in tumor cells, while SIRPα is expressed in non-neoplastic stromal cells. CD47 positive cases showed significantly higher FoxP3 (P = .0232) and lower CCR4 (P = .0214). SIRPα positive cases presented significantly better overall survival than SIRPα negative cases (P = .0132). SIRPα positive cases showed significantly HLA class I (P = .0062), HLA class II (P = .0133), microenvironment PD-L1 (miPD-L1) (P = .0032), and FoxP3 (P = .0229) positivity. In univariate analysis, SIRPα expression was significantly related to prognosis (Hazard ratio [HR] 0.470; 95% confidence interval [CI] 0.253-0.870; P = .0167], although multivariate analysis did not show SIPRα as an independent prognostic factor. The expression of SIRPα on stromal cells reflects activated immune surveillance mechanism in tumor microenvironment and induce good prognosis in ATLL. More detailed studies for gene expression or genomic abnormalities will disclose clinical and biological significance of the CD47 and SIRPα in ATLL.

Role of CD47 in Hematological Malignancies

CD47, or integrin-associated protein, is a cell surface ligand expressed in low levels by nearly all cells of the body. It plays an integral role in various immune responses as well as autoimmunity, by sending a potent "don't eat me" signal to prevent phagocytosis. A growing body of evidence demonstrates that CD47 is overexpressed in various hematological malignancies and its interaction with SIRPα on the phagocytic cells prevents phagocytosis of cancer cells. Additionally, it is expressed by different cell types in the tumor microenvironment and is required for establishing tumor metastasis. Overexpression of CD47 is thus often associated with poor clinical outcomes. CD47 has emerged as a potential therapeutic target and is being investigated in various preclinical studies as well as clinical trials to prove its safety and efficacy in treating hematological neoplasms. This review focuses on different therapeutic mechanisms to target CD47, either alone or in combination with other cell surface markers, and its pivotal role in impairing tumor growth and metastatic spread of various types of hematological malignancies.

Macrocyclic Peptide-Mediated Blockade of the CD47-SIRPα Interaction as a Potential Cancer Immunotherapy

Medium-sized macrocyclic peptides are an alternative to small compounds and large biomolecules as a class of pharmaceutics. The CD47-SIRPα signaling axis functions as an innate immune checkpoint that inhibits phagocytosis in phagocytes and has been implicated as a promising target for cancer immunotherapy. The potential of macrocyclic peptides that target this signaling axis as immunotherapeutic agents has remained unknown, however. Here we have developed a macrocyclic peptide consisting of 15 amino acids that binds to the ectodomain of mouse SIRPα and efficiently blocks its interaction with CD47 in an allosteric manner. The peptide markedly promoted the phagocytosis of antibody-opsonized tumor cells by macrophages in vitro as well as enhanced the inhibitory effect of anti-CD20 or anti-gp75 antibodies on tumor formation or metastasis in vivo. Our results suggest that allosteric inhibition of the CD47-SIRPα interaction by macrocyclic peptides is a potential approach to cancer immunotherapy.

Preclinical and Clinical Development of Therapeutic Antibodies Targeting Functions of CD47 in the Tumor Microenvironment

CD47 is a ubiquitously expressed cell surface glycoprotein that functions as a signaling receptor for thrombospondin-1 and as the counter-receptor for signal regulatory protein-α (SIRPα). Engaging SIRPα on macrophages inhibits phagocytosis, and CD47 thereby serves as a physiological marker of self. However, elevated CD47 expression on some cancer cells also protects tumors from innate immune surveillance and limits adaptive antitumor immunity via inhibitory SIRPα signaling in antigen presenting cells. CD47 also mediates inhibitory thrombospondin-1 signaling in vascular cells, T cells, and NK cells, and blocking inhibitory CD47 signaling on cytotoxic T cells directly increases tumor cell killing. Therefore, CD47 functions as an innate and adaptive immune checkpoint. These findings have led to the development of antibodies and other therapeutic approaches to block CD47 functions in the tumor microenvironment. Preclinical studies in mice demonstrated that blocking CD47 can limit the growth of hematologic malignancies and solid tumors and enhance the efficacy of conventional chemotherapy, radiation therapy, and some targeted cancer therapies. Humanized CD47 antibodies are showing promise in early clinical trials, but side effects related to enhanced phagocytic clearance of circulating blood cells remain a concern. Approaches to circumvent these include antibody preloading strategies, development of antibodies that recognize tumor-specific epitopes of CD47, SIRPα antibodies, and bivalent antibodies that restrict CD47 blockade to specific tumor cells. Preclinical and clinical development of antibodies and related biologics that inhibit CD47/SIRPα signaling are reviewed, including strategies to combine these agents with various conventional and targeted therapeutics to improve patient outcome for various cancers.

SIRPα on CD11c+ cells induces Th17 cell differentiation and subsequent inflammation in the CNS in experimental autoimmune encephalomyelitis

Signal regulatory protein α (SIRPα) is expressed predominantly on type 2 conventional dendritic cells (cDC2s) and macrophages. We previously showed that mice systemically lacking SIRPα were resistant to experimental autoimmune encephalomyelitis (EAE). Here, we showed that deletion of SIRPα in CD11c⁺ cells of mice (Sirpa^ΔDC mice) also markedly ameliorated the development of EAE. The frequency of cDCs and migratory DCs (mDCs), as well as that of Th17 cells, were significantly reduced in draining lymph nodes of Sirpa^ΔDC mice at the onset of EAE. In addition, we found the marked reduction in the number of Th17 cells and DCs in the CNS of Sirpa^ΔDC mice at the peak of EAE. Whereas inducible systemic ablation of SIRPα before the induction of EAE prevented disease development, that after EAE onset did not ameliorate the clinical signs of disease. We also found that EAE development was partially attenuated in mice with CD11c⁺ cell-specific ablation of CD47, a ligand of SIRPα. Collectively, our results suggest that SIRPα expressed on CD11c⁺ cells, such as cDC2s and mDCs, is indispensable for the development of EAE, being required for the priming of self-reactive Th17 cells in the periphery as well as for the inflammation in the CNS.

Therapeutic modulation of the CD47-SIRPα axis in the pediatric tumor microenvironment: working up an appetite

Evasion of immune surveillance is one of the hallmarks of cancer. Although the adaptive immune system has been targeted via checkpoint inhibition, many patients do not sustain durable remissions due to the heterogeneity of the tumor microenvironment, so additional strategies are needed. The innate immune system has its own set of checkpoints, and tumors have co-opted this system by expressing surface receptors that inhibit phagocytosis. One of these receptors, CD47, also known as the "don't eat me" signal, has been found to be overexpressed by most cancer histologies and has been successfully targeted by antibodies blocking the receptor or its ligand, signal regulatory protein α (SIRPα). By enabling phagocytosis via antigen-presenting cells, interruption of CD47-SIRPα binding leads to earlier downstream activation of the adaptive immune system. Recent and ongoing clinical trials are demonstrating the safety and efficacy of CD47 blockade in combination with monoclonal antibodies, chemotherapy, or checkpoint inhibitors for adult cancer histologies. The aim of this review is to highlight the current literature and research on CD47, provide an impetus for investigation of its blockade in pediatric cancer histologies, and provide a rationale for new combination therapies in these patients.

Tumor-associated macrophages and macrophage-related immune checkpoint expression in sarcomas

Early trials for immune checkpoint inhibitors in sarcomas have delivered mixed results, and efforts to improve outcomes now look to combinatorial strategies with novel immunotherapeutics, including some that target macrophages. To enhance our understanding of the sarcoma immune landscape, we quantified and characterized tumor-associated macrophage infiltration and expression of the targetable macrophage-related immune checkpoint CD47/SIRPα across sarcoma types. We surveyed immunohistochemical expression of CD68, CD163, CD47, and SIRPα in tissue microarrays of 1242 sarcoma specimens (spanning 24 types). Non-translocation sarcomas, particularly undifferentiated pleomorphic sarcoma and dedifferentiated liposarcoma, had significantly higher counts of both CD68+ and CD163+ macrophages than translocation-associated sarcomas. Across nearly all sarcoma types, macrophages outnumbered tumor-infiltrating lymphocytes and CD163+ (M2-like) macrophages outnumbered CD68+ (M1-like) macrophages. These findings were supported by data from The Cancer Genome Atlas, which showed a correlation between increasing macrophage contributions to immune infiltration and several measures of DNA damage. CD47 expression was bimodal, with most cases showing either 0% or >90% tumor cell staining, and the highest CD47 scores were observed in chordoma, angiosarcoma, and pleomorphic liposarcoma. SIRPα scores correlated well with CD47 expression. Given the predominance of macrophage infiltrates over tumor-infiltrating lymphocytes, the bias toward M2-like (immunosuppressive) macrophage polarization, and the generally high scores for CD47 and SIRPα, macrophage-focused immunomodulatory agents, such as CD47 or IDO-1 inhibitors, may be particularly worthwhile to pursue in sarcoma patients, alone or in combination with lymphocyte-focused agents.

Targeting an adenosine-mediated "don't eat me signal" augments anti-lymphoma immunity by anti-CD20 monoclonal antibody

A growing body of evidence suggests that macrophage immune checkpoint molecules are potential targets in the era of cancer immunotherapy. Here we showed that extracellular adenosine, an abundant metabolite in the tumor microenvironment, critically impedes the therapeutic efficacy of anti-CD20 monoclonal antibodies (mAbs) against B-cell lymphoma. Using a syngeneic B-cell lymphoma model, we showed that host deficiency of adenosine 2A receptor (A2AR), but not A2BR, remarkably improved lymphoma control by anti-CD20 mAb therapy. Conditional deletion of A2AR in myeloid cells, and to a lesser extent in NK cells, augmented therapeutic efficacy of anti-CD20 mAb. Indeed, adenosine signaling impaired antibody-mediated cellular phagocytosis (ADCP) by macrophages and limited the generation of anti-lymphoma CD8⁺ T cells. Pharmacological inhibition of A2AR overcame the adenosine-mediated negative regulation of ADCP by rituximab in a xeno-transplanted lymphoma model. Moreover, aberrant overexpression of CD39, an apical ecto-enzyme for adenosine generation, showed a negative impact on prognosis in patients with diffuse large B-cell lymphoma, as well as on preclinical efficacy of rituximab. Together, adenosine acts as a "don't eat me signal", and may be a potential target to harness anti-lymphoma immunity.

Macrophage checkpoint blockade: results from initial clinical trials, binding analyses, and CD47-SIRPα structure-function

The macrophage checkpoint is an anti-phagocytic interaction between signal regulatory protein alpha (SIRPα) on a macrophage and CD47 on all types of cells - ranging from blood cells to cancer cells. This interaction has emerged over the last decade as a potential co-target in cancer when combined with other anti-cancer agents, with antibodies against CD47 and SIRPα currently in preclinical and clinical development for a variety of hematological and solid malignancies. Monotherapy with CD47 blockade is ineffective in human clinical trials against many tumor types tested to date, except for rare cutaneous and peripheral lymphomas. In contrast, pre-clinical results show efficacy in multiple syngeneic mouse models of cancer, suggesting that many of these tumor models are more immunogenic and likely artificial compared to human tumors. However, combination therapies in humans of anti-CD47 with agents such as the anti-tumor antibody rituximab do show efficacy against liquid tumors (lymphoma) and are promising. Here, we review such trials as well as key interaction and structural features of CD47-SIRPα.

NK Cell-Based Immune Checkpoint Inhibition

Immunotherapy, with an increasing number of therapeutic dimensions, is becoming an important mode of treatment for cancer patients. The inhibition of immune checkpoints, which are the source of immune escape for various cancers, is one such immunotherapeutic dimension. It has mainly been aimed at T cells in the past, but NK cells are a newly emerging target. Simultaneously, the number of checkpoints identified has been increasing in recent times. In addition to the classical NK cell receptors KIRs, LIRs, and NKG2A, several other immune checkpoints have also been shown to cause dysfunction of NK cells in various cancers and chronic infections. These checkpoints include the revolutionized CTLA-4, PD-1, and recently identified B7-H3, as well as LAG-3, TIGIT & CD96, TIM-3, and the most recently acknowledged checkpoint-members of the Siglecs family (Siglec-7/9), CD200 and CD47. An interesting dimension of immune checkpoints is their candidacy for dual-checkpoint inhibition, resulting in therapeutic synergism. Furthermore, the combination of immune checkpoint inhibition with other NK cell cytotoxicity restoration strategies could also strengthen its efficacy as an antitumor therapy. Here, we have undertaken a comprehensive review of the literature to date regarding NK cell-based immune checkpoints.

NK Cell-Based Immunotherapy in Renal Cell Carcinoma

Natural killer (NK) cells are cytotoxic lymphocytes that are able to kill tumor cells without prior sensitization. It has been shown that NK cells play a pivotal role in a variety of cancers, highlighting their relevance in tumor immunosurveillance. NK cell infiltration has been reported in renal cell carcinoma (RCC), the most frequent kidney cancer in adults, and their presence has been associated with patients’ survival. However, the role of NK cells in this disease is not yet fully understood. In this review, we summarize the biology of NK cells and the mechanisms through which they are able to recognize and kill tumor cells. Furthermore, we discuss the role that NK cells play in renal cell carcinoma, and review current strategies that are being used to boost and exploit their cytotoxic capabilities.

Advances in Anti-Tumor Treatments Targeting the CD47/SIRPα Axis

CD47 is an immunoglobulin that is overexpressed on the surface of many types of cancer cells. CD47 forms a signaling complex with signal-regulatory protein α (SIRPα), enabling the escape of these cancer cells from macrophage-mediated phagocytosis. In recent years, CD47 has been shown to be highly expressed by various types of solid tumors and to be associated with poor patient prognosis in various types of cancer. A growing number of studies have since demonstrated that inhibiting the CD47-SIRPα signaling pathway promotes the adaptive immune response and enhances the phagocytosis of tumor cells by macrophages. Improved understanding in this field of research could lead to the development of novel and effective anti-tumor treatments that act through the inhibition of CD47 signaling in cancer cells. In this review, we describe the structure and function of CD47, provide an overview of studies that have aimed to inhibit CD47-dependent avoidance of macrophage-mediated phagocytosis by tumor cells, and assess the potential and challenges for targeting the CD47-SIRPα signaling pathway in anti-cancer therapy.

Lipid-based phagocytosis nanoenhancer for macrophage immunotherapy

Tumor associated macrophages (TAMs) play an important role in initiating the immunosuppressive environment that negatively impacts the immunotherapy efficacy and has long been linked with cancer progression. On the other hand, activated macrophages display immense phagocytic potential and can be used as an effector cell for cancer therapy. But, activating TAMs to effectively phagocytose cancer cells is challenging. Cancer cells upregulate CD47, a "don't eat me" receptor that ligates with SIRPα present on macrophages to downregulate the phagocytosis. Since phagocytosis is a physical phenomenon based on engulfment of aberrant cells, we hypothesized that the phagocytic function of macrophages can be enhanced by blocking both CD47 and SIRPα in tandem and at the same time, engaging both macrophages and cancer cells can favor increased macrophage-cancer cellular interactions. Here, we demonstrate that a simple approach of anti-CD47 and anti-SIRPα antibodies conjugated lipid-based phagocytosis nanoenhancer (LPN) can perform both of these functions. The LPNs were stable in both physiological and biologically relevant conditions, bound to both macrophages and cancer cells and significantly enhanced phagocytosis of cancer cells as compared to combination of free antibodies. LPN treatment showed significant tumor growth inhibition and increased survival in B16F10 melanoma tumor bearing mice with no systemic toxicity. Mechanistic analysis of efficacy revealed an increase in intra-tumoral infiltration of effector T cells and NK cells. Cytokine analysis revealed increased secretion of intracellular iNOS, a hallmark of activated macrophages. This study shows that LPN can simultaneously block both CD47 and SIRPα and can effectively engage macrophage and cancer cell in close proximity. Combining these facets provide a simple approach to enhance phagocytosis and improve anti-cancer macrophage immunotherapy.

[Next generation of anti-immune checkpoints antibodies]

Immune checkpoints balance initial antigen-driven T cell stimulation by enhancing or dampening activation, allowing co-existence of efficient immune responses and maintenance of self-tolerance. In oncology, checkpoints currently targeted by inhibitors to amplify activity of T cell, NK cells or myeloid cells responses comprise CTLA-4 (cytolytic T-lymphocyte-associated antigen 4 or CD152), PD-1 (programmed cell death 1, or CD279), PD-L1 ( programmed cell death-ligand 1, or CD274), LAG-3 (Lymphocyte-activation gene 3, or CD223), TIM3 (T-cell immunoglobulin and mucin-domain containing-3), TIGIT (T cell immunoreceptor with Ig and ITIM domains ), VISTA (V-domain Ig suppressor of T cell activation), B7/H3 (or CD276), KIR (killer-cell immunoglobulin-like receptor), NKG2A, CD39, CD73, CSF1R (colony-stimulating factor 1 receptor), CD47 or CD172a. Other "checkpoints" are being pharmacologically triggered in order to directly amplify T cell co-stimulation. Among these molecules, CD28, CD137 (also called 4-1BB), OX40 [also called tumor necrosis factor receptor superfamily, member 4 (TNFRSF4)], GITR (Glucocorticoid-induced tumor necrosis factor receptor family-related protein) or CD40 are also tested in oncology, most often in combination with an inhibitory checkpoint inhibitor. In autoimmune and inflammatory diseases, checkpoint inhibitors or activators (LAG-3, CD28, CD40L) are also being tested. In this review, we focus on some modulators of immune checkpoints for which the mechanism of action has been particularly studied. As this description cannot be exhaustive, we have grouped in Table I all monoclonal antibodies (MAbs) or recombinant proteins in clinical use (to our knowledge), modulating the action of a control point of the immune system.

Functional characterization of the selective pan-allele anti-SIRPα antibody ADU-1805 that blocks the SIRPα-CD47 innate immune checkpoint

Background

Accumulating preclinical data indicate that targeting the SIRPα/CD47 axis alone or in combination with existing targeted therapies or immune checkpoint inhibitors enhances tumor rejection. Although several CD47-targeting agents are currently in phase I clinical trials and demonstrate activity in combination therapy, high and frequent dosing was required and safety signals (acute anemia, thrombocytopenia) were recorded frequently as adverse events. Based on the restricted expression pattern of SIRPα we hypothesized that antibodies targeting SIRPα might avoid some of the concerns noted for CD47-targeting agents.

Methods

SIRPα-targeting antibodies were generated and characterized for binding to human SIRPα alleles and blockade of the interaction with CD47. Functional activity was established in vitro using human macrophages or neutrophils co-cultured with human Burkitt’s lymphoma cell lines. The effect of SIRPα versus CD47 targeting on human T-cell activation was studied using an allogeneic mixed lymphocyte reaction and a Staphylococcus enterotoxin B-induced T-cell proliferation assay. Potential safety concerns of the selected SIRPα-targeting antibody were addressed in vitro using a hemagglutination assay and a whole blood cytokine release assay, and in vivo in a single-dose toxicity study in cynomolgus monkeys.

Results

The humanized monoclonal IgG2 antibody ADU-1805 binds to all known human SIRPα alleles, showing minimal binding to SIRPβ1, while cross-reacting with SIRPγ, and potently blocking the interaction of SIRPα with CD47. Reduced FcγR binding proved critical to retaining its function towards phagocyte activation. In vitro characterization demonstrated that ADU-1805 promotes macrophage phagocytosis, with similar potency to anti-CD47 antibodies, and enhances neutrophil trogocytosis. Unlike CD47-targeting agents, ADU-1805 does not interfere with T-cell activation and is not expected to require frequent and extensive dosing due to the restricted expression of SIRPα to cells of the myeloid lineage. ADU-1805 is cross-reactive to cynomolgus monkey SIRPα and upon single-dose intravenous administration in these non-human primates (NHPs) did not show any signs of anemia, thrombocytopenia or other toxicities.

Conclusions

Blocking the SIRPα-CD47 interaction via SIRPα, while similarly efficacious in vitro, differentiates ADU-1805 from CD47-targeting agents with respect to safety and absence of inhibition of T-cell activation. The data presented herein support further advancement of ADU-1805 towards clinical development.

CSF1R- and SHP2-Inhibitor-Loaded Nanoparticles Enhance Cytotoxic Activity and Phagocytosis in Tumor-Associated Macrophages

Immune modulation of macrophages has emerged as an attractive approach for anti-cancer therapy. However, there are two main challenges in successfully utilizing macrophages for immunotherapy. First, macrophage colony stimulating factor (MCSF) secreted by cancer cells binds to colony stimulating factor 1 receptor (CSF1-R) on macrophages and in turn activates the downstream signaling pathway responsible for polarization of tumor-associated macrophages (TAMs) to immunosuppressive M2 phenotype. Second, ligation of signal regulatory protein α (SIRPα) expressed on myeloid cells to CD47, a transmembrane protein overexpressed on cancer cells, activates the Src homology region 2 (SH2) domain -phosphatases SHP-1 and SHP-2 in macrophages. This results in activation of "eat-me-not" signaling pathway and inhibition of phagocytosis. Here, it is reported that self-assembled dual-inhibitor-loaded nanoparticles (DNTs) target M2 macrophages and simultaneously inhibit CSF1R and SHP2 pathways. This results in efficient repolarization of M2 macrophages to an active M1 phenotype, and superior phagocytic capabilities as compared to individual drug treatments. Furthermore, suboptimal dose administration of DNTs in highly aggressive breast cancer and melanoma mouse models show enhanced anti-tumor efficacy without any toxicity. These studies demonstrate that the concurrent inhibition of CSF1-R and SHP2 signaling pathways for macrophage activation and phagocytosis enhancement could be an effective strategy for macrophage-based immunotherapy.

IgA-Mediated Killing of Tumor Cells by Neutrophils Is Enhanced by CD47-SIRPα Checkpoint Inhibition

Therapeutic monoclonal antibodies (mAb), directed toward either tumor antigens or inhibitory checkpoints on immune cells, are effective in cancer therapy. Increasing evidence suggests that the therapeutic efficacy of these tumor antigen-targeting mAbs is mediated-at least partially-by myeloid effector cells, which are controlled by the innate immune-checkpoint interaction between CD47 and SIRPα. We and others have previously demonstrated that inhibiting CD47-SIRPα interactions can substantially potentiate antibody-dependent cellular phagocytosis and cytotoxicity of tumor cells by IgG antibodies both in vivo and in vitro IgA antibodies are superior in killing cancer cells by neutrophils compared with IgG antibodies with the same variable regions, but the impact of CD47-SIRPα on IgA-mediated killing has not been investigated. Here, we show that checkpoint inhibition of CD47-SIRPα interactions further enhances destruction of IgA antibody-opsonized cancer cells by human neutrophils. This was shown for multiple tumor types and IgA antibodies against different antigens, i.e., HER2/neu and EGFR. Consequently, combining IgA antibodies against HER2/neu or EGFR with SIRPα inhibition proved to be effective in eradicating cancer cells in vivo In a syngeneic in vivo model, the eradication of cancer cells was predominantly mediated by granulocytes, which were actively recruited to the tumor site by SIRPα blockade. We conclude that IgA-mediated tumor cell destruction can be further enhanced by CD47-SIRPα checkpoint inhibition. These findings provide a basis for targeting CD47-SIRPα interactions in combination with IgA therapeutic antibodies to improve their potential clinical efficacy in tumor patients.

Myeloid immunosuppression and immune checkpoints in the tumor microenvironment

Tumor-promoting inflammation and the avoidance of immune destruction are hallmarks of cancer. While innate immune cells, such as neutrophils, monocytes, and macrophages, are critical mediators for sterile and nonsterile inflammation, persistent inflammation, such as that which occurs in cancer, is known to disturb normal myelopoiesis. This disturbance leads to the generation of immunosuppressive myeloid cells, such as myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs). Due to their potent suppressive activities against effector lymphocytes and their abundance in the tumor microenvironment, immunosuppressive myeloid cells act as a major barrier to cancer immunotherapy. Indeed, various therapeutic approaches directed toward immunosuppressive myeloid cells are actively being tested in preclinical and clinical studies. These include anti-inflammatory agents, therapeutic blockade of the mobilization and survival of myeloid cells, and immunostimulatory adjuvants. More recently, immune checkpoint molecules expressed on tumor-infiltrating myeloid cells have emerged as potential therapeutic targets to redirect these cells to eliminate tumor cells. In this review, we discuss the complex crosstalk between cancer-related inflammation and immunosuppressive myeloid cells and possible therapeutic strategies to harness antitumor immune responses.

SIRPα expression delineates subsets of intratumoral monocyte/macrophages with different functional and prognostic impact in follicular lymphoma

Signal regulatory protein-α (SIRPα) is a key member of the “do-not-eat-me” signaling pathway, but its biological role and clinical relevance in B-cell NHL is relatively unknown. Using biopsy specimens from follicular lymphoma (FL), we identified three subsets (CD14⁺SIRPα^hi, CD14⁻SIRPα^low, and CD14⁻SIRPα^neg) of monocyte/macrophages (Mo/MΦ) based on CD14 and SIRPα expression. CD14⁺SIRPα^hi cells expressed common Mo/MΦ markers; exhibited characteristic differentiation, migration, and phagocytosis; and suppressed T-cell function. CD14⁻SIRPα^low cells expressed fewer typical Mo/MΦ markers; migrated less and phagocytosed tumor cells less efficiently; and stimulated rather than suppressed T-cell function. Interestingly, the CD14⁻SIRPα^neg subset expressed distinct Mo/MΦ markers compared to the other two subsets; had limited ability to migrate and phagocytose; but stimulated T-cell function. When using SIRPα-Fc to block the interaction between SIRPα and CD47, alone or in combination with rituximab, phagocytosis of tumor cells was differentially increased in the three Mo/MΦ subsets. Clinically, increased numbers of CD14⁺SIRPα^hi cells were associated with an inferior survival in FL. In contrast, increased numbers of the CD14⁻SIRPα^low subset appeared to correlate with a better survival. Taken together, our results show that SIRPα expression delineates unique subsets of intratumoral Mo/MΦs with differing prognostic importance.

Current Perspectives in Cancer Immunotherapy

Different immunotherapeutic approaches have proved to be of significant clinical value to many patients with different types of advanced cancer. However, we need more precise immunotherapies and predictive biomarkers to increase the successful response rates. The advent of next generation sequencing technologies and their applications in immuno-oncology has helped us tremendously towards this aim. We are now moving towards the realization of personalized medicine, thus, significantly increasing our expectations for a more successful management of the disease. Here, we discuss the current immunotherapeutic approaches against cancer, including immune checkpoint blockade with an emphasis on anti-PD-L1 and anti-CTLA-4 monoclonal antibodies. We also analyze a growing list of other co-inhibitory and co-stimulatory markers and emphasize the mechanism of action of the principal pathway for each of these, as well as on drugs that either have been FDA-approved or are under clinical investigation. We further discuss recent advances in other immunotherapies, including cytokine therapy, adoptive cell transfer therapy and therapeutic vaccines. We finally discuss the modulation of gut microbiota composition and response to immunotherapy, as well as how tumor-intrinsic factors and immunological processes influence the mutational and epigenetic landscape of progressing tumors and response to immunotherapy but also how immunotherapeutic intervention influences the landscape of cancer neoepitopes and tumor immunoediting.

Natural Killer Cell Recruitment and Activation Are Regulated by CD47 Expression in the Tumor Microenvironment

Elevated CD47 expression in some cancers is associated with decreased survival and limited clearance by phagocytes expressing the CD47 counterreceptor SIRPα. In contrast, elevated CD47 mRNA expression in human melanomas was associated with improved survival. Gene-expression data were analyzed to determine a potential mechanism for this apparent protective function and suggested that high CD47 expression increases recruitment of natural killer (NK) cells into the tumor microenvironment. The CD47 ligand thrombospondin-1 inhibited NK cell proliferation and CD69 expression in vitro Cd47 ^-/- NK cells correspondingly displayed augmented effector phenotypes, indicating an inhibitory function of CD47 on NK cells. Treating human NK cells with a CD47 antibody that blocks thrombospondin-1 binding abrogated its inhibitory effect on NK cell proliferation. Similarly, treating wild-type mice with a CD47 antibody that blocks thrombospondin-1 binding delayed B16 melanoma growth, associating with increased NK cell recruitment and increased granzyme B and interferon-γ levels in intratumoral NK but not CD8⁺ T cells. However, B16 melanomas grew faster in Cd47 ^-/- than in wild-type mice. Melanoma-bearing Cd47 ^-/- mice exhibited decreased splenic NK cell numbers, with impaired effector protein expression and elevated exhaustion markers. Proapoptotic gene expression in Cd47^-/- NK cells was associated with stress-mediated increases in mitochondrial proton leak, reactive oxygen species, and apoptosis. Global gene-expression profiling in NK cells from tumor-bearing mice identified CD47-dependent transcriptional responses that regulate systemic NK activation and exhaustion. Therefore, CD47 positively and negatively regulates NK cell function, and therapeutic antibodies that block inhibitory CD47 signaling can enhance NK immune surveillance of melanomas.

Dual role of macrophage in tumor immunity

Macrophages are significant in immune responses, assuming a defensive role. In contrast, macrophages often cause undesirable changes. These reactions are processes by which macrophages express different functional programs in response to microenvironmental signals, defined as M1/M2 polarization. Tumor immunity has been acknowledged for contributing to the elucidation of the mechanism and clinical application in cancer therapy. One of the mechanisms for the refractoriness to cancer immunotherapy is the production of inhibitory cytokines by tumor cells or macrophages. Therefore, therapeutic strategy targeting macrophage or macrophage-derived cytokines may be effective and attractive. This review aims to investigate macrophage-associated pathophysiology and biological behavior in cancers, especially related to microenvironment, such as hypoxia, and current topics regarding some therapies involving macrophages.

Engineering macrophages to phagocytose cancer cells by blocking the CD47/SIRPɑ axis

The use of immunotherapy has achieved great advances in the treatment of cancer. Macrophages play a pivotal role in the immune defense system, serving both as phagocytes (removal of pathogens and cancer cells) and as antigen‐presenting cells (activation of T cells). However, research regarding tumor immunotherapy is mainly focused on the adaptive immune system. The usefulness of innate immune cells (eg, macrophages) in the treatment of cancer has not been extensively investigated. Recent advances in synthetic biology and the increasing understanding of the cluster of differentiation 47/signal regulatory protein alpha (CD47/SIRPɑ) axis may provide new opportunities for the clinical application of engineered macrophages. The CD47/SIRPɑ axis is a major known pathway, repressing phagocytosis and activation of macrophages. In this article, we summarize the currently available evidence regarding the CD47/SIRPɑ axis, and immunotherapies based on blockage. In addition, we propose cell therapy strategies based on macrophage engineering.

OMIC signatures to understand cancer immunosurveillance and immunoediting: Melanoma and immune cells interplay in immunotherapy

Melanoma is the deadliest form of skin cancer. Cutaneous melanomas usually originate from exposure to the mutagenic effects of ultraviolet radiation, and as such they exhibit the highest rate of somatic mutations than any other human cancer, and an extensive expression of neoantigens concurrently with a dense infiltrate of immune cells. The coexistence of high immunogenicity and high immune cell infiltration may sound contradictory for cancers carrying a gloomy outcome. However, recent studies have unveiled a variety of immunosuppressive mechanisms that often permeate the tumor microenvironment and that are responsible for tumor escaping from immunosurveillance mechanisms. Nonetheless, this particular immune profile has opened a new window of treatments based on immunotherapy that have significantly improved the clinical outcome of melanoma patients. Still, positive and complete therapy responses have been limited, and this particular cancer continues to be a major clinical challenge. The transcriptomic signatures of those patients with clinical benefit and those with progressive disease have provided a more complete picture of the universe of interactions between the tumor and the immune system. In this review, we integrate the results of the immunotherapy clinical trials to discuss a novel understanding of the mechanisms guiding cancer immunosurveillance and immunoediting. A clear notion of the cellular and molecular processes shaping how the immune system and the tumor are continuously coevolving would result in the rational design of combinatory therapies aiming to counteract the signaling pathways and cellular processes responsible for immunoescape mechanisms and provide clinical benefit to immunotherapy nonresponsive patients.

Adverse Events Following Cancer Immunotherapy: Obstacles and Opportunities

Oncology has recently undergone a revolutionary change with widespread adoption of immunotherapy for many cancers. Immunotherapy using monoclonal antibodies against checkpoint molecules, including programmed death (PD)-1, PD ligand (PD-L)1, and cytotoxic T lymphocyte-associated antigen (CTLA)-4, is effective in a significant subset of patients. However, immune-related adverse events (irAEs) have emerged as frequent complications of checkpoint blockade, likely due to the physiological role of checkpoint pathways in regulating adaptive immunity and preventing autoimmunity. As immunotherapy becomes more common, a better understanding of the etiology of irAEs and ways to limit these events is needed. At the same time, studying these new therapy-related disorders provides an opportunity to better understand naturally occurring human autoimmune and inflammatory disorders, with the potential to improve therapies for cancer and autoimmune diseases.

Effect of Serum Deprivation Stress on Signal Induction Regulatory Protein-Alpha (SIRP-Alpha)-Mediated Erythrophagocytosis by Macrophages

BACKGROUND Hemophagocytic lymphohistiocytosis (HLH) is a rare syndrome that involves loss of macrophages' self-cells recognition resulting in auto-phagocytosis of erythrocytes, leukocytes, and platelets and leading to multi-system effects. The pathogenesis of HLH is unclear but can be explained by malfunction of the physiologic inhibitory pathway through interaction between macrophage SIRP-alpha and erythrocyte CD 47. The goal of the present study was to evaluate if erythrocytes phagocytosis occurs as a result of altered macrophage SIRP-alpha expression during inflammatory/stressful conditions as seen in HLH. MATERIAL AND METHODS RAW264.7 macrophages were cultured in serum-free media (SFM) and complete media (CM) to simulate stressful and physiologic conditions, respectively. CD47+ mouse erythrocytes were used to test interactions with macrophages at different stages. SIRP-alpha expressions and phagocytosis assays were measured and analyzed at different steps. The study was in vitro and used murine cells to simulate in vivo human interactions. RESULTS SIRP-alpha expressions and phagocytosis rates were higher in SFM compared to CM. Interestingly, after adding SIRP-alpha blocking antibodies (Ab), phagocytosis rates significantly decreased. CONCLUSIONS Serum deprivation and LPS/INF-Gamma induction resulted in increased SIRP-alpha expression and erythrophagocytosis. Using SIRP-alpha Ab during this condition decreased the rate of erythrophagocytosis, which indicates that SIRP-alpha receptor can have pro-phagocytic activity.

Eutopic endometrium from patients with endometriosis modulates the expression of CD36 and SIRP-α in peritoneal macrophages

Aim

This study aimed to investigate the in vitro alterations of the expression of signal regulatory protein‐α (SIRP‐α) and CD36 in macrophages in the endometriosis condition.

Methods

The expression of SIRP‐α and CD36 was measured in peritoneal macrophages and peripheral blood mononuclear cells of endometriosis patients and control participants. The expressions of SIRP‐α and CD36 were measured in human acute monocytic leukemia (THP‐1) cell‐derived macrophages that were treated with interleukin‐6 (IL‐6)‐induced conditioned medium, eutopic versus normal endometrial homogenate, or lipopolysaccharide in the presence or absence of nuclear factor kappa‐B (NF‐κB) or transforming growth factor (TGF‐β) inhibitors, respectively.

Results

Peritoneal macrophages that were isolated from women with endometriosis exhibited an enhanced expression of SIRP‐α and a decreased expression of CD36 compared to control participants. Women with endometriosis had significantly higher levels of SIRP‐α and CD36 in peripheral circulating mononuclear cells than in control participants. SIRP‐α expression was significantly increased, whereas the CD36 expression was decreased in THP‐1 cell‐derived macrophages after treatment with eutopic endometrial homogenate. Intervention with IL‐6‐induced conditioned medium resulted in the downregulation of SIRP‐α but the upregulation of CD36 in THP‐1 cells. Incubation with the NF‐κBp50 inhibitor decreased the expression of CD36 and SIRP‐α in macrophages that were treated with normal endometrial homogenate, whereas the TGF‐β inhibitor enhanced the CD36 expression of THP‐1 cell‐derived macrophages treated with eutopic endometrial homogenate.

Conclusion

The eutopic endometrium could reduce the phagocytic ability of peritoneal macrophages in women with endometriosis through the modulation of SIRP‐α and CD36 expression. Inhibition of the TGF‐β signal pathway may be a potential therapeutic target for the treatment of endometriosis.

Attenuation of CD47-SIRPα Signal in Cholangiocarcinoma Potentiates Tumor-Associated Macrophage-Mediated Phagocytosis and Suppresses Intrahepatic Metastasis

The involvement of chronic inflammation in cholangiocarcinoma (CCA) progression is well established. Cluster of differentiation 47 (CD47) is mutually expressed in various cancers and serves as a protective signal for phagocytic elimination. CD47 signaling blockage is a recent treatment strategy; however, little is known regarding CD47 in CCA. Therefore, the potential use of CD47 targeting in CCA was focused. CD47 was highly expressed in CCA compared to hepatocellular carcinoma (HCC). Disturbance of CD47-signal regulatory protein-α (SIRPα) interaction by blocking antibodies promoted the macrophage phagocytosis. The therapeutic potential of anti-CD47 therapy was demonstrated in liver metastatic model; alleviation of cancer colonization together with dense macrophage infiltrations was observed. The usefulness of anti-CD47 was emphasized by its universal facilitating macrophage activities. Moreover, increased production of inflammatory cytokines, such as IL-6 and IL-10, in macrophage exposed to CCA-conditioned media suggested that CCA alters macrophages toward cancer promotion. Taken together, interfering of CD47-SIRPα interaction promotes macrophage phagocytosis in all macrophage subtypes and consequently suppresses CCA growth and metastasis. The unique overexpression of CD47 in CCA but not HCC offers an exceptional opportunity for a targeted therapy. CD47 is therefore a novel target for CCA treatment.