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

Clinical Significance of SIRPα Expression on Tumor-Associated Macrophages in Patients with Lung Squamous Cell Carcinoma

BACKGROUND

Signal-regulatory protein alpha (SIRPα) is an immune checkpoint molecule expressed on macrophages that functions to inhibit phagocytosis by binding to CD47 expressed on tumor cells. SIRPα has attracted increasing attention as a novel target for cancer immunotherapy; however, the expression and immune function of SIRPα in lung squamous cell carcinoma (LUSC) remain unclear. Therefore, this study aimed to identify the clinical importance of SIRPα expression in LUSC and to explore the factors that elevate SIRPα expression.

PATIENTS AND METHODS

Primary LUSC specimens surgically resected from 172 patients underwent immunohistochemical evaluation of the association of SIRPα expression on tumor-associated macrophages with clinicopathological features and clinical outcomes. Furthermore, we analyzed the association of SIRPα expression with tumor-infiltrating lymphocytes and the expression of programmed cell death ligand 1 (PD-L1). In vitro, monocytes were treated with cytokines, and SIRPα protein expression was assessed by flow cytometry.

RESULTS

There were no differences in SIRPα expression and clinicopathological factors. High SIRPα expression was significantly associated with PD-L1-positive expression, and high CD8, PD-1, and CD163 expression. The high SIRPα expression group showed significantly shorter recurrence-free survival (RFS) and overall survival (OS). On multivariate analysis, high SIRPα expression was an independent poor prognostic factor for RFS and OS. The expression of SIRPα protein in monocytes was upregulated by treatment with IFNγ.

CONCLUSION

Our analysis revealed that high SIRPα expression significantly predicts poor prognosis in patients with surgically resected LUSC.

Biomimetic Nano-Degrader Based CD47-SIRPα Immune Checkpoint Inhibition Promotes Macrophage Efferocytosis for Cardiac Repair

CD47-SIRPα axis is an immunotherapeutic target in tumor therapy. However, current monoclonal antibody targeting CD47-SIRPα axis is associated with on-target off-tumor and antigen sink effects, which significantly limit its potential clinical application. Herein, a biomimetic nano-degrader is developed to inhibit CD47-SIRPα axis in a site-specific manner through SIRPα degradation, and its efficacy in acute myocardial infarction (AMI) is evaluated. The nano-degrader is constructed by hybridizing liposome with red blood cell (RBC) membrane (RLP), which mimics the CD47 density of senescent RBCs and possesses a natural high-affinity binding capability to SIRPα on macrophages without signaling capacity. RLP would bind with SIRPα and induce its lysosomal degradation through receptor-mediated endocytosis. To enhance its tissue specificity, Ly6G antibody conjugation (aRLP) is applied, enabling its attachment to neutrophils and accumulation within inflammatory sites. In the myocardial infarction model, aRLP accumulated in the infarcted myocardium blocks CD47-SIRPα axis and subsequently promoted the efferocytosis of apoptotic cardiomyocytes by macrophage, improved heart repair. This nano-degrader efficiently degraded SIRPα in lysosomes, providing a new strategy for immunotherapy with great clinical transformation potential.

Disruption of CD47-SIRPα signaling restores inflammatory function in tumor-associated myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous immune population with diverse immunosuppressive functions in solid tumors. Here, we explored the role of the tumor microenvironment in regulating MDSC differentiation and immunosuppressive properties via signal-regulatory protein alpha (SIRPα)/CD47 signaling. In a murine melanoma model, we observed progressive increases in monocytic MDSCs and monocyte-derived dendritic cells that exhibited potent T cell-suppressive capabilities. These adaptations could be recapitulated in vitro by exposing hematopoietic stem cells to tumor-derived factors. Engagement of CD47 with SIRPα on myeloid cells reduced their phagocytic capability, enhanced expression of immune checkpoints, increased reactive oxygen species production, and suppressed T cell proliferation. Perturbation of SIRPα signaling restored phagocytosis and antigen presentation by MDSCs, which was accompanied by renewed T cell activity and delayed tumor growth in multiple solid cancers. These data highlight that therapeutically targeting myeloid functions in combination with immune checkpoint inhibitors could enhance anti-tumor immunity.

Transcriptional profile and immune infiltration in colorectal cancer reveal the significance of inducible T-cell costimulator as a crucial immune checkpoint molecule

BACKGROUND

Emergence of novel immuno-therapeutics has shown promising improvement in the clinical outcome of colorectal cancer (CRC).

OBJECTIVE

To identify robust immune checkpoints based on expression and immune infiltration profiles of clinical CRC samples.

METHODS

One dataset from The Cancer Genome Atlas database and two from Gene Expression Omnibus were independently employed for the analysis. Genes associated with overall survival were identified, and distribution of each immune checkpoint with respect to different clinical features was determined to explore key immune checkpoints. Multiple staining methods were used to verify the correlation between key immune checkpoint ICOS and clinical pathological features. Differentially expressed mRNA and long non-coding RNA (lncRNA) were then detected for gene set enrichment analysis and gene set variation analysis to investigate the differentially enriched biological processes between low- and high-expression groups. Significant immune-related mRNAs and lncRNA were subjected to competing endogenous RNA (ceRNA) network analysis. Correlation of inducible T-cell costimulator (ICOS) and top 10 genes in ceRNA network were further considered for validation.

RESULTS

ICOS was identified from 14 immune checkpoints as the most highly correlated gene with survival and clinical features in CRC. The expression of ICOS protein in the poorly differentiated group was lower than that in the moderately differentiated group, and the expression in different pathological stages was significant. In addition, the expressions of ICOS were negatively correlated with Ki67. A conspicuous number of immune-related pathways were enriched in differentially expressed genes in the ICOS high- and low-expression groups. Integration with immune infiltration data revealed a multitude of differentially expressed immune-related genes enriched for ceRNA network. Furthermore, expression of top 10 genes investigated from ceRNA network showed high correlation with ICOS.

CONCLUSION

ICOS might serve as a robust immune checkpoint for prognosis with several genes being potential targets of ICOS-directed immunotherapy in CRC.

Targeting HDAC6 improves anti-CD47 immunotherapy

BACKGROUND

Cancer cells can overexpress CD47, an innate immune checkpoint that prevents phagocytosis upon interaction with signal regulatory protein alpha (SIRPα) expressed in macrophages and other myeloid cells. Several clinical trials have reported that CD47 blockade reduces tumor growth in hematological malignancies. However, CD47 blockade has shown modest results in solid tumors, including melanoma. Our group has demonstrated that histone deacetylase 6 inhibitors (HDAC6is) have immunomodulatory properties, such as controlling macrophage phenotype and inflammatory properties. However, the molecular and cellular mechanisms controlling these processes are not fully understood. In this study, we evaluated the role of HDAC6 in regulating the CD47/SIRPα axis and phagocytosis in macrophages.

METHODS

We tested the role of HDAC6is, especially Nexturastat A, in regulating macrophage phenotype and phagocytic function using bone marrow-derived macrophages and macrophage cell lines. The modulation of the CD47/SIRPα axis and phagocytosis by HDAC6is was investigated using murine and human melanoma cell lines and macrophages. Phagocytosis was evaluated via coculture assays of macrophages and melanoma cells by flow cytometry and immunofluorescence. Lastly, to evaluate the antitumor activity of Nexturastat A in combination with anti-CD47 or anti-SIRPα antibodies, we performed in vivo studies using the SM1 and/or B16F10 melanoma mouse models.

RESULTS

We observed that HDAC6is enhanced the phenotype of antitumoral M1 macrophages while decreasing the protumoral M2 phenotype. In addition, HDAC6 inhibition diminished the expression of SIRPα, increased the expression of other pro-phagocytic signals in macrophages, and downregulated CD47 expression in mouse and human melanoma cells. This regulatory role on the CD47/SIRPα axis translated into enhanced antitumoral phagocytic capacity of macrophages treated with Nexturastat A and anti-CD47. We also observed that the systemic administration of HDAC6i enhanced the in vivo antitumor activity of anti-CD47 blockade in melanoma by modulating macrophage and natural killer cells in the tumor microenvironment. However, Nexturastat A did not enhance the antitumor activity of anti-SIRPα despite its modulation of macrophage populations in the SM1 tumor microenvironment.

CONCLUSIONS

Our results demonstrate the critical regulatory role of HDAC6 in phagocytosis and innate immunity for the first time, further underscoring the use of these inhibitors to potentiate CD47 immune checkpoint blockade therapeutic strategies.

Discovery and Preclinical Activity of BMS-986351, an Antibody to SIRPα That Enhances Macrophage-mediated Tumor Phagocytosis When Combined with Opsonizing Antibodies

In normal cells, binding of the transmembrane protein CD47 to signal regulatory protein-α (SIRPα) on macrophages induces an antiphagocytic signal. Tumor cells hijack this pathway and overexpress CD47 to evade immune destruction. Macrophage antitumor activity can be restored by simultaneously blocking the CD47-SIRPα signaling axis and inducing a prophagocytic signal via tumor-opsonizing antibodies. We identified a novel, fully human mAb (BMS-986351) that binds SIRPα with high affinity. BMS-986351 demonstrated broad binding coverage across SIRPα polymorphisms and potently blocked CD47-SIRPα binding at the CD47 binding site in a dose-dependent manner. In vitro, BMS-986351 increased phagocytic activity against cell lines from solid tumors and hematologic malignancies, and this effect was markedly enhanced when BMS-986351 was combined with the opsonizing antibodies cetuximab and rituximab. A phase I dose-escalation/-expansion study of BMS-986351 for the treatment of advanced solid and hematologic malignancies is underway (NCT03783403).

SIGNIFICANCE

Increasing the phagocytotic capabilities of tumor-associated macrophages by modulating macrophage-tumor cell surface signaling via the CD47-SIRPα axis is a novel strategy. Molecules targeting CD47 have potential but its ubiquitous expression necessitates higher therapeutic doses to overcome potential antigen sink effects. The restricted expression pattern of SIRPα may limit toxicities and lower doses of the SIRPα antibody BMS-986351 may overcome target mediated drug disposition while maintaining the desired pharmacology.

Clinicopathological analysis of CD47 and signal regulatory protein alpha expression in myeloid sarcoma patients: CD47 expression is a favourable prognostic factor

Myeloid sarcoma is a rare extramedullary haematopoietic malignancy. Interaction between CD47 and signal regulatory protein α (SIRPα) inhibits phagocytosis. CD47-positive tumours confer poor prognoses in various malignant tumours, including acute myeloid leukaemia. This study aimed to investigate the clinicopathological effects of CD47 and SIRPα expression in myeloid sarcoma. Immunohistochemistry (IHC) of CD47 and SIRPα was performed in 84 biopsy samples obtained from patients with myeloid sarcoma, some of which were CD47-positive. Patients were categorised into the following two groups based on IHC of SIRPα: those with SIRPα-positive neoplastic cells (nSIRPα) and, SIRPα expression on non-neoplastic stromal cells in tumour microenvironment (miSIRPα). In addition, patients with CD47 positivity had higher lymphocytic infiltration into the tumour microenvironment. Overall, these patients had significantly higher overall survival, however, no significant difference was observed in progression-free survival. No significant prognostic differences were observed between the nSIRPα and miSIRPα groups. This is the first study to demonstrate an association between CD47 expression and improved prognosis in myeloid sarcoma. Nonetheless, it will be necessary to conduct additional research on gene expression and genomic abnormalities to elucidate the corresponding pathogenesis of myeloid sarcoma.

Preclinical evaluation of the efficacy of an antibody to human SIRPα for cancer immunotherapy in humanized mouse models

Tumor-associated macrophages (TAMs) are abundant in the tumor microenvironment and are considered potential targets for cancer immunotherapy. To examine the antitumor effects of agents targeting human TAMs in vivo, we here established preclinical tumor xenograft models based on immunodeficient mice that express multiple human cytokines and have been reconstituted with a human immune system by transplantation of human CD34+ hematopoietic stem and progenitor cells (HIS-MITRG mice). HIS-MITRG mice supported the growth of both human cell line (Raji)- and patient-derived B cell lymphoma as well as the infiltration of human macrophages into their tumors. We examined the potential antitumor action of an antibody to human SIRPα (SE12C3) that inhibits the interaction of CD47 on tumor cells with SIRPα on human macrophages and thereby promotes Fcγ receptor-mediated phagocytosis of the former cells by the latter. Treatment with the combination of rituximab (antibody to human CD20) and SE12C3 inhibited Raji tumor growth in HIS-MITRG mice to a markedly greater extent than did rituximab monotherapy. This enhanced antitumor effect was dependent on human macrophages and attributable to enhanced rituximab-dependent phagocytosis of lymphoma cells by human macrophages. Treatment with rituximab and SE12C3 also induced reprogramming of human TAMs toward a proinflammatory phenotype. Furthermore, the combination treatment essentially prevented the growth of patient-derived diffuse large B cell lymphoma in HIS-MITRG mice. Our findings thus support the study of HIS-MITRG mice as a model for the preclinical evaluation in vivo of potential therapeutics, such as antibodies to human SIRPα, that target human TAMs.

The role of CD47 in non-neoplastic diseases

CD47 is a 50 kDa five-spanning membrane receptor that plays a crucial role in multiple cellular processes, including myeloid cell activation, neutrophils transmigration, vascular remodeling, leukocyte adhesion and trans-endothelial migration. Recent studies have revealed that CD47 is a highly expressed anti-phagocytic signal in several types of cancer, and therefore, blocking of CD47 has shown an effective therapeutic potential in cancer immunotherapy. In addition, CD47 has been found to be involved in a complex interplay with microglia and other types of cells, and increasing evidence indicates that CD47 can be targeted as part of immune modulatory strategies for non-neoplastic diseases as well. In this review, we focus on CD47 and its role in non-neoplastic diseases, including neurological disorders, atherosclerosis and autoimmune diseases. In addition, we discuss the major challenges and potential remedies associated with CD47-SIRPα-based immunotherapies.

SIRP-alpha-IL-6 axis induces immunosuppressive macrophages in non-small-cell lung cancer

Signal regulatory protein-alpha (SIRPα) and IL-6 participate in the induction of tumor immune suppressive environment and facilitate tumor growth. In this study, we found that SIRPα was significantly elevated in macrophages of non-small cell lung cancer (NSCLC) tissues, which was positively correlated to the expression of CD163, PD-1, IL-6, and lung cancer progression. SIRPα in peripheral blood mononuclear cells (PBMCs) of NSCLC patients was also associated with CD163, PD-1, and plasma IL-6. Blockade of SIRPα signaling in SIRPα ± and SIRPα-/- mice attenuated lung cancer growth and reduced IL-6 expression in LLC cells-transplanted murine lung cancer model. Co-targeting SIRPα and IL-6 additively suppressed the expression of IL-6 and activation of STAT3, accompanied with a reduced population of pro-tumorigenic CD206+ M2 subtype of macrophages, PD-1+ tumor-associated macrophages (TAMs), and PD-1+CD8+ T cells in tumor tissues of anti-IL-6 antibody (aIL-6)-treated mice deficient in SIRPα. Further in vitro studies showed that blockade of SIRPα signaling by anti-SIRPα effectively improved phagocytosis of human PBMCs. IL-6 treatment improved polarization of M2 subtypes and the expression of PD-1 in bone marrow-derived macrophages (BMDMs); whereas both aIL-6 and STAT3 inhibitor C188-9 suppressed the expression of PD-1 and SIRPα in BMDMs. M2 cell-biased polarization was also reduced in aIL-6 or C188-9 treated BMDMs. Thereby, SIRPα and IL-6 form a positive feedback loop and regulate each other through STAT3 signaling in macrophages. The increased SIRPα/IL-6 axis may promote immune suppressive environment and lung cancer growth, which may be a potential target for clinical treatment.

Biomimetic Systems Involving Macrophages and Their Potential for Targeted Drug Delivery

The concept of targeted drug delivery can be described in terms of the drug systems' ability to mimic the biological objects' property to localize to target cells or tissues. For example, drug delivery systems based on red blood cells or mimicking some of their useful features, such as long circulation in stealth mode, have been known for decades. On the contrary, therapeutic strategies based on macrophages have gained very limited attention until recently. Here, we review two biomimetic strategies associated with macrophages that can be used to develop new therapeutic modalities: first, the mimicry of certain types of macrophages (i.e., the use of macrophages, including tumor-associated or macrophage-derived particles as a carrier for the targeted delivery of therapeutic agents); second, the mimicry of ligands, naturally absorbed by macrophages (i.e., the use of therapeutic agents specifically targeted at macrophages). We discuss the potential applications of biomimetic systems involving macrophages for new advancements in the treatment of infections, inflammatory diseases, and cancer.

Atezolizumab plus Magrolimab, Niraparib, or Tocilizumab versus Atezolizumab Monotherapy in Platinum-Refractory Metastatic Urothelial Carcinoma: A Phase Ib/II Open-Label, Multicenter, Randomized Umbrella Study (MORPHEUS Urothelial Carcinoma)

PURPOSE

The MORPHEUS platform was designed to identify early efficacy signals and evaluate the safety of novel immunotherapy combinations across cancer types. The phase Ib/II MORPHEUS-UC trial (NCT03869190) is evaluating atezolizumab plus magrolimab, niraparib, or tocilizumab in platinum-refractory locally advanced or metastatic urothelial carcinoma (mUC). Additional treatment combinations were evaluated and will be reported separately.

PATIENTS AND METHODS

Patients had locally advanced or mUC that progressed during or following treatment with a platinum-containing regimen. The primary efficacy endpoint was investigator-assessed objective response rate (ORR). Key secondary endpoints included investigator-assessed progression-free survival (PFS) and overall survival (OS). Safety and exploratory biomarker analyses were also conducted.

RESULTS

Seventy-six patients were randomized to receive either atezolizumab plus magrolimab (n = 16), atezolizumab plus niraparib (n = 15), atezolizumab plus tocilizumab (n = 15), or atezolizumab monotherapy (control; n = 30). No additive benefit in ORR, PFS, or OS was seen in the treatment arms versus the control. The best confirmed ORR was 26.7% with atezolizumab plus magrolimab, 6.7% with atezolizumab plus niraparib, 20.0% with atezolizumab plus tocilizumab, and 27.6% with atezolizumab monotherapy. Overall, the treatment combinations were tolerable, and adverse events were consistent with each agent's known safety profile. Trends were observed for shrinkage of programmed death-ligand 1-positive tumors (atezolizumab, atezolizumab plus magrolimab, atezolizumab plus tocilizumab), inflamed tumors, or tumors with high mutational burden (atezolizumab), and immune excluded tumors (atezolizumab plus magrolimab).

CONCLUSIONS

The evaluated regimens in MORPHEUS-UC were tolerable. However, response rates for the combinations did not meet the criteria for further development in platinum-experienced locally advanced or mUC.

SIRPA enhances osteosarcoma metastasis by stabilizing SP1 and promoting SLC7A3-mediated arginine uptake

The function of signal regulatory protein alpha (SIRPA) has been well studied in macrophages and dendritic cells, but relatively less in tumors. Notably, SIRPA is upregulated in osteosarcoma tissues, particularly in metastatic tissues, and is associated with unfavorable clinical outcomes. Knockdown of SIRPA impaired OS cell migration by decreasing specificity protein 1 (SP1) stability and arginine uptake. Importantly, SIRPA phosphorylated SP1 at threonine 278 (Thr278) through extracellular signal-regulated kinase (ERK) activation to protect SP1 from proteasomal degradation. In addition, SP1 increased solute carrier family 7 member 3 (SLC7A3) expression by binding to the SLC7A3 promoter and increased the capability of arginine uptake, thereby facilitating OS cell migration. More interestingly, arginine promoted the stability of SP1 in an ERK-independent manner and thus formed the "SP1 stabilization circle". Combined treatment with the anti-SIRPA antibody and arginase, which blocked the circle, impaired tumor metastasis in mice bearing xenografts formed from SIRPA-overexpressing cells. In summary, our study demonstrates that the upregulation of SIRPA promotes OS metastasis via the "SP1 stabilization circle" and SLC7A3-mediated arginine uptake, which might serve as a target for OS treatment.

A Biomimetic Nanogel System Restores Macrophage Phagocytosis for Magnetic Resonance Imaging-Guided Synergistic Chemoimmunotherapy of Breast Cancer

Novel strategies to facilitate tumor-specific drug delivery and restore immune attacks remain to be developed to overcome the current limitations of chemotherapy. Herein, a cancer cell membrane (CM)-camouflaged and ultrasmall iron oxide nanoparticles (USIO NPs)-loaded polyethylenimine nanogel (NG) system is reported to co-deliver docetaxel (DTX) and CD47 siRNA (siCD47). The prepared co-delivery system exhibits good colloidal stability, biocompatibility, and r1 relaxivity (1.35 mM-1 s-1 ) and enables redox-responsive release of the loaded DTX in the tumor microenvironment. The NG system realizes homologous targeting delivery of DTX and siCD47 to murine breast cancer cells (4T1 cells) for efficient chemotherapy and gene silencing; thus, inducing immunogenic cell death (ICD) and restoring macrophage phagocytic effect through downregulation of "don't eat me" signals on cancer cells. Likewise, the co-delivery system can also act on macrophages to promote their M1 polarization, which can be combined with DTX-mediated ICD and antibody-mediated immune checkpoint blockade to generate effector T cells for robust chemoimmunotherapy. Further, the USIO NPs-incorporated NG system also allows for magnetic resonance imaging of tumors. The developed biomimetic NG system acting on both cancer cells and macrophages holds a promising potential for macrophage phagocytosis-restored chemoimmunotherapy.

Cooperative phagocytosis of solid tumours by macrophages triggers durable anti-tumour responses

In solid tumours, the abundance of macrophages is typically associated with a poor prognosis. However, macrophage clusters in tumour-cell nests have been associated with survival in some tumour types. Here, by using tumour organoids comprising macrophages and cancer cells opsonized via a monoclonal antibody, we show that highly ordered clusters of macrophages cooperatively phagocytose cancer cells to suppress tumour growth. In mice with poorly immunogenic tumours, the systemic delivery of macrophages with signal-regulatory protein alpha (SIRPα) genetically knocked out or else with blockade of the CD47-SIRPα macrophage checkpoint was combined with the monoclonal antibody and subsequently triggered the production of endogenous tumour-opsonizing immunoglobulin G, substantially increased the survival of the animals and helped confer durable protection from tumour re-challenge and metastasis. Maximizing phagocytic potency by increasing macrophage numbers, by tumour-cell opsonization and by disrupting the phagocytic checkpoint CD47-SIRPα may lead to durable anti-tumour responses in solid cancers.

Immunobiology of cholangiocarcinoma

Recent literature has significantly advanced our knowledge and understanding of the tumour immune microenvironment of cholangiocarcinoma. Detailed characterisation of the immune landscape has defined new patient subtypes. While not utilised in clinical practice yet, these novel classifications will help inform decisions regarding immunotherapeutic approaches. Suppressive immune cells, such as tumour-associated macrophages and myeloid-derived suppressor cells, form a barrier that shields tumour cells from immune surveillance. The presence of this immunosuppressive barrier in combination with a variety of immune escape mechanisms employed by tumour cells leads to poor tumour immunogenicity. Broad strategies to re-equip the immune system include blockade of suppressive immune cell recruitment to priming cytotoxic effector cells against tumour antigens. While immunotherapeutic strategies are gaining traction for the treatment of cholangiocarcinoma, there is a long road of discovery ahead in order to make meaningful contributions to patient therapy and survival.

Emerging advances in nanobiomaterials-assisted chimeric antigen receptor (CAR)-macrophages for tumor immunotherapy

Adoptive cell immunotherapy, especially chimeric antigen receptor (CAR)-T-cells therapy, has made great progress in the clinical treatment of hematological malignancies. However, restricted by the complex tumor microenvironment, the potential efficiency of T-cell infiltration and activated immune cells are limited, thus failure prevented the progression of the solid tumor. Alternatively, tumor-associated macrophages (TAMs), one sustentacular and heterogeneous cellular population within the tumor microenvironment, are regarded as potential therapeutic targets. Recently, CARs have shown tremendous promise in treating malignancies by equipping macrophages. This novel therapeutic strategy circumvents the tumor microenvironment's limitations and provides a safer therapeutic approach. Meanwhile, nanobiomaterials as gene delivery carriers not only substantially reduce the treatment cost of this novel therapeutic strategy, but also set the foundation for in vivo CAR-M therapy. Here, we highlight the major strategies prepared for CAR-M, emphasizing the challenges and opportunities of these approaches. First, the common therapeutic strategies for macrophages are summarized in clinical and preclinical trials. Namely, TAM-targeted therapeutic strategies: 1) Inhibit monocyte or macrophage recruitment into tumors, 2) deplete TAMs, and 3) reprogramme TAMs to antitumor M1 phenotype. Second, the current development and progress of CAR-M therapy are reviewed, including the researchers' attempts in CAR structure design, cell origin, and gene delivery vectors, especially nanobiomaterials as an alternative to viral vectors, as well as some challenges faced by current CAR-M therapy are also summarized and discussed. Finally, the field of genetically engineered macrophages integration with nanotechnology for the future in oncology has been prospected.

The CD47-SIRPα axis is a promising target for cancer immunotherapies

Cluster of differentiation 47(CD47) is a transmembrane protein that is ubiquitously found on the surface of many cells in the body and uniquely overexpressed by both solid and hematologic malignant cells. CD47 interacts with signal-regulatory protein α (SIRPα), to trigger a "don't eat me" signal and thereby achieve cancer immune escape by inhibiting macrophage-mediated phagocytosis. Thus, blocking the CD47-SIRPα phagocytosis checkpoint, for release of the innate immune system, is a current research focus. Indeed, targeting the CD47-SIRPα axis as a cancer immunotherapy has shown promising efficacies in pre-clinical outcomes. Here, we first reviewed the origin, structure, and function of the CD47-SIRPα axis. Then, we reviewed its role as a target for cancer immunotherapies, as well as the factors regulating CD47-SIRPα axis-based immunotherapies. We specifically focused on the mechanism and progress of CD47-SIRPα axis-based immunotherapies and their combination with other treatment strategies. Finally, we discussed the challenges and directions for future research and identified potential CD47-SIRPα axis-based therapies that are suitable for clinical application.

Emerging advances in engineered macrophages for tumor immunotherapy

Macrophages are versatile antigen-presenting cells. Recent studies suggest that engineered modifications of macrophages may confer better tumor therapy. Genetic engineering of macrophages with specific chimeric antigen receptors offers new possibilities for treatment of solid tumors and has received significant attention. In vitro gene editing of macrophages and infusion into the body can inhibit the immunosuppressive effect of the tumor microenvironment in solid tumors. This strategy is flexible and can be applied to all stages of cancer treatment. In contrast, nongenetic engineering tools are used to block relevant signaling pathways in immunosuppressive responses. In addition, macrophages can be loaded with drugs and engineered into cellular drug delivery systems. Here, we analyze the effect of the chimeric antigen receptor platform on macrophages and other existing engineering modifications of macrophages, highlighting their status, challenges and future perspectives. Indeed, our analyses show that new approaches in the treatment of solid tumors will likely exploit macrophages, an innate immune cell.

CD47-Dependent Regulation of Immune Checkpoint Gene Expression and MYCN mRNA Splicing in Murine CD8 and Jurkat T Cells

Elevated expression of CD47 in some cancers is associated with poor survival related to its function as an innate immune checkpoint when expressed on tumor cells. In contrast, elevated CD47 expression in cutaneous melanomas is associated with improved survival. Previous studies implicated protective functions of CD47 expressed by immune cells in the melanoma tumor microenvironment. RNA sequencing analysis of responses induced by CD3 and CD28 engagement on wild type and CD47-deficient Jurkat T lymphoblast cells identified additional regulators of T cell function that were also CD47-dependent in mouse CD8 T cells. MYCN mRNA expression was upregulated in CD47-deficient cells but downregulated in CD47-deficient cells following activation. CD47 also regulated alternative splicing that produces two N-MYC isoforms. The CD47 ligand thrombospondin-1 inhibited expression of these MYCN mRNA isoforms, as well as induction of the oncogenic decoy MYCN opposite strand (MYCNOS) RNA during T cell activation. Analysis of mRNA expression data for melanomas in The Cancer Genome Atlas identified a significant coexpression of MYCN with CD47 and known regulators of CD8 T cell function. Thrombospondin-1 inhibited the induction of TIGIT, CD40LG, and MCL1 mRNAs following T cell activation in vitro. Increased mRNA expression of these T cell transcripts and MYCN in melanomas was associated with improved overall survival.

Organogermanium THGP Induces Differentiation into M1 Macrophages and Suppresses the Proliferation of Melanoma Cells via Phagocytosis

M1 macrophages are an important cell type related to tumor immunology and are known to phagocytose cancer cells. In previous studies, the organogermanium compound poly-trans-[(2-carboxyethyl)germasesquioxane] (Ge-132) and its hydrolysate, 3-(trihydroxygermyl) propanoic acid (THGP), have been reported to exert antitumor effects by activating NK cells and macrophages through the induction of IFN-γ activity in vivo. However, the detailed molecular mechanism has not been clarified. In this study, we found that macrophages differentiate into the M1 phenotype via NF-κB activation under long-term culture in the presence of THGP in vitro and in vivo. Furthermore, long-term culture with THGP increases the ability of RAW 264.7 cells to suppress B16 4A5 melanoma cell proliferation. These mechanisms indicate that THGP promotes the M1 polarization of macrophages and suppresses the expression of signal-regulatory protein alpha (SIRP-α) in macrophages and CD47 in cancers. Based on these results, THGP may be considered a new regulatory reagent that suppresses tumor immunity.

Prognostic role of the innate immune signature CD163 and "eat me" signal calreticulin in clear cell renal cell carcinoma

The effects of the innate immune status on patients with clear cell renal cell carcinoma (ccRCC) currently remain unknown. We herein provided more extensive information about the inner landscape of immunobiology of ccRCC. In total, 260 ccRCC samples from three different cohorts consisting of 213 primary tumors and 47 metastases were obtained. We focused on five representative innate immune signatures, CD68, CD163, the "eat me" signal calreticulin, the "don't eat me" signal CD47, and signal regulatory protein α, and examined the role of each signature by quantitative immunohistochemistry. We then conducted an integrated genome mutation analysis by next-generation sequencing. Among the five markers, high CD163 and low calreticulin expression levels were prognostic in ccRCC. The application of a new risk model based on CD163 and calreticulin levels, named the innate immune risk group (high risk: high-CD163/low calreticulin, intermediate risk: high-CD163/high calreticulin or low CD163/low calreticulin, low risk: low-CD163/high calreticulin), enabled the sequential stratification of patient prognosis and malignancy. Although organ-specific differences were observed, metastases appeared to have a higher innate immune risk, particularly in the lungs, with 50% of ccRCC metastases being classified into the high-risk group according to our risk score. An analysis of genomic alterations based on the innate immune risk group revealed that alterations in the TP53/Cell cycle pathway were highly prevalent in high-risk ccRCC patients according to two innate immune signatures CD163 and calreticulin. The present results provide insights into the immune-genomic biology of ccRCC tumors for innate immunity and will contribute to future therapies focused on the innate immune system in solid cancers.

Clinical Significance of Signal Regulatory Protein Alpha (SIRPα) Expression in Hepatocellular Carcinoma

BACKGROUND

Signal regulatory protein alpha (SIRPα), expressed in the macrophage membrane, inhibits phagocytosis of tumor cells via CD47/SIRPα interaction, which acts as an immune checkpoint factor in cancers. This study aimed to clarify the clinical significance of SIRPα expression in hepatocellular carcinoma (HCC).

METHODS

This study analyzed SIRPα expression using RNA sequencing data of 372 HCC tissues from The Cancer Genome Atlas (TCGA) and immunohistochemical staining of our 189 HCC patient cohort. The correlation between SIRPα expression and clinicopathologic factors, patient survival, and intratumor infiltration of immune cells was investigated.

RESULTS

Overall survival (OS) was significantly poorer with high SIRPα expression than with low expression in both TCGA and our cohort. High SIRPα expression correlated with lower recurrence-free survival (RFS) in our cohort. High SIRPα expression was associated with higher rates of microvascular invasion and lower serum albumin levels and correlated with greater intratumor infiltration of CD68-positive macrophages and myeloid-derived suppressor cells (MDSCs). Multivariate analysis showed that SIRPα expression and high infiltration of CD8-positive T cells and MDSCs were predictive factors for both RFS and OS. Patients with high SIRPα expression and infiltration of CD8-positive T cells and MDSCs had significantly lower RFS and OS rates. In spatial transcriptomics sequencing, SIRPα expression was significantly correlated with CD163 expression.

CONCLUSIONS

High SIRPα expression in HCC indicates poor prognosis, possibly by inhibiting macrophage phagocytosis of tumor cells, promoting MDSC infiltration and inducing antitumor immunity. Treatment alternatives using SIRPα blockage should be considered in HCC as inhibiting macrophage antitumor immunity and MDSCs.

Neutrophil phenotypes implicated in the pathophysiology of post-traumatic sepsis

Background

The disruption of immune homeostasis after trauma is a major cause of post-traumatic organ dysfunction and/or sepsis. Recently, a variety of neutrophil phenotypes with distinct functions have been identified and suggested as involved in various clinical conditions. The association between neutrophil phenotypes and post-traumatic immunodeficiency has also been reported, yet the specific neutrophil phenotypes and their functional significance in post-traumatic sepsis have not been fully clarified. Therefore, we sought to investigate neutrophil phenotypic changes in a murine model, as these may hold prognostic value in post-traumatic sepsis.

Materials and methods

Third-degree burns affecting 25% of the body surface area were used to establish trauma model, and sepsis was induced 24 h later through cecal ligation and puncture (CLP). The Burn/CLP post-traumatic sepsis model and the Sham/CLP control model were established to assess the immunological status after trauma. Histopathological evaluation was performed on the spleen, liver, kidneys, and lung tissues. Immunological evaluation included the assessment of neutrophil markers using mass cytometry as well as cytokine measurements in serum and ascitic fluid through multiplex analysis using LUMINEX®.

Results

The Burn/CLP group had a lower survival rate than the Sham/CLP group. Histopathological examination revealed an impaired immune response and more advanced organ damage in the Burn/CLP group. Furthermore, the Burn/CLP group exhibited higher levels of transforming growth factor-beta 1 in the blood and generally lower levels of cytokines than the Sham/CLP group. CD11b, which is involved in neutrophil adhesion and migration, was highly expressed on neutrophils in the Burn/CLP group. The expression of CD172a, which is related to the inhibition of phagocytosis, was also upregulated on neutrophils in the Burn/CLP group. The expression of sialic acid-binding lg-like lectin F and CD68 also differed between the two groups.

Conclusion

Different neutrophil phenotypes were observed between Burn/CLP and Sham/CLP groups, suggesting that neutrophils are implicated in the immune imbalance following trauma. However, further studies are needed to prove the causal relationships between neutrophil phenotypes and outcomes, including survival rate and organ dysfunction.

CD47-SIRPα axis blockade in NASH promotes necroptotic hepatocyte clearance by liver macrophages and decreases hepatic fibrosis

Necroptosis contributes to hepatocyte death in nonalcoholic steatohepatitis (NASH), but the fate and roles of necroptotic hepatocytes (necHCs) in NASH remain unknown. We show here that the accumulation of necHCs in human and mouse NASH liver is associated with an up-regulation of the "don't-eat-me" ligand CD47 on necHCs, but not on apoptotic hepatocytes, and an increase in the CD47 receptor SIRPα on liver macrophages, consistent with impaired macrophage-mediated clearance of necHCs. In vitro, necHC clearance by primary liver macrophages was enhanced by treatment with either anti-CD47 or anti-SIRPα. In a proof-of-concept mouse model of inducible hepatocyte necroptosis, anti-CD47 antibody treatment increased necHC uptake by liver macrophages and inhibited markers of hepatic stellate cell (HSC) activation, which is responsible for liver fibrogenesis. Treatment of two mouse models of diet-induced NASH with anti-CD47, anti-SIRPα, or AAV8-H1-shCD47 to silence CD47 in hepatocytes increased the uptake of necHC by liver macrophages and decreased markers of HSC activation and liver fibrosis. Anti-SIRPα treatment avoided the adverse effect of anemia found in anti-CD47-treated mice. These findings provide evidence that impaired clearance of necHCs by liver macrophages due to CD47-SIRPα up-regulation contributes to fibrotic NASH, and suggest therapeutic blockade of the CD47-SIRPα axis as a strategy to decrease the accumulation of necHCs in NASH liver and dampen the progression of hepatic fibrosis.

Suppressing or Enhancing Macrophage Engulfment through the Use of CD47 and Related Peptides

Foreign particles and microbes are rapidly cleared by macrophages in vivo, although many key aspects of uptake mechanisms remain unclear. "Self" cells express CD47 which functions as an anti-phagocytic ligand for SIRPα on macrophages, particularly when pro-phagocytic ligands such as antibodies are displayed in parallel. Here, we review CD47 and related "Self" peptides as modulators of macrophage uptake. Nanoparticles conjugated with either CD47 or peptides derived from its SIRPα binding site can suppress phagocytic uptake by macrophages in vitro and in vivo, with similar findings for CD47-displaying viruses. Drugs, dyes, and genes as payloads thus show increased delivery to targeted cells. On the other hand, CD47 expression by cancer cells enables such cells to evade macrophages and immune surveillance. This has motivated development of soluble antagonists to CD47-SIRPα, ranging from blocking antibodies in the clinic to synthetic peptides in preclinical models. CD47 and peptides are thus emerging as dual-use phagocytosis modulators against diseases.

Tumor-intrinsic SIRPA promotes sensitivity to checkpoint inhibition immunotherapy in melanoma

Checkpoint inhibition immunotherapy has revolutionized cancer treatment, but many patients show resistance. Here we perform integrative transcriptomic and proteomic analyses on emerging immuno-oncology targets across multiple clinical cohorts of melanoma under anti-PD-1 treatment, on both bulk and single-cell levels. We reveal a surprising role of tumor-intrinsic SIRPA in enhancing antitumor immunity, in contrast to its well-established role as a major inhibitory immune modulator in macrophages. The loss of SIRPA expression is a marker of melanoma dedifferentiation, a key phenotype linked to immunotherapy efficacy. Inhibition of SIRPA in melanoma cells abrogates tumor killing by activated CD8+ T cells in a co-culture system. Mice bearing SIRPA-deficient melanoma tumors show no response to anti-PD-L1 treatment, whereas melanoma-specific SIRPA overexpression significantly enhances immunotherapy response. Mechanistically, SIRPA is regulated by its pseudogene, SIRPAP1. Our results suggest a complicated role of SIRPA in the tumor ecosystem, highlighting cell-type-dependent antagonistic effects of the same target on immunotherapy.

SIRPα antibody combined with oncolytic virus OH2 protects against tumours by activating innate immunity and reprogramming the tumour immune microenvironment

BACKGROUND

The combination of oncolytic viruses (OVs) with immune checkpoint blockades is a research hotspot and has shown good efficacy. Here, we present the first attempt to combine oncolytic herpes simplex virus 2 (OH2) with an anti-SIRPα antibody as an antitumour treatment. Our results provide unique insight into the combination of innate immunity with OV.

METHODS

We verified the polarization and activation of OH2 in RAW264.7 cells in vitro. Subsequently, we evaluated the antitumour ability of OH2 and anti-SIRPα combined therapy in a tumour-bearing mouse model. RNA-seq and Single-cell RNA-seq were used to characterize the changes in the tumour microenvironment.

RESULTS

The OH2 lysates effectively stimulated RAW264.7 cells to polarize towards the M1 but not the M2 phenotype and activated the function of the M1 phenotype in vitro. In the macrophage clearance experiment, OH2 therapy induced polarization of M1 macrophages and participated in the antitumour immune response in a tumour-bearing mouse model. Treatment with a combination of OH2 and anti-SIRPα effectively inhibited tumour growth and significantly prolonged the survival time of the mice, and this result was more obvious in the mouse model with a larger tumour volume at the beginning of the treatment. These results suggest that combination therapy can more profoundly reshape the TME and activate stronger innate and adaptive immune responses.

CONCLUSIONS

Our data support the feasibility of oncolytic virus therapy in combination with anti-SIRPα antibodies and suggest a new strategy for oncolytic virus therapy.

Targeting the CD47-SIRPα Innate Immune Checkpoint to Potentiate Antibody Therapy in Cancer by Neutrophils

Simple Summary

Immunotherapy aims to engage various immune cells in the elimination of cancer cells. Neutrophils are the most abundant leukocytes in the circulation and have unique mechanisms by which they can kill cancer cells opsonized by antibodies. However, neutrophil effector functions are limited by the inhibitory receptor SIRPα, when it interacts with CD47. The CD47 protein is expressed on all cells in the body and acts as a ‘don’t eat me’ signal to prevent tissue damage. Cancer cells can express high levels of CD47 to circumvent tumor elimination. Thus, blocking the interaction between CD47 and SIRPα may enhance anti-tumor effects by neutrophils in the presence of tumor-targeting monoclonal antibodies. In this review, we discuss CD47-SIRPα as an innate immune checkpoint on neutrophils and explore the preliminary results of clinical trials using CD47-SIRPα blocking agents.

Abstract

In the past 25 years, a considerable number of therapeutic monoclonal antibodies (mAb) against a variety of tumor-associated antigens (TAA) have become available for the targeted treatment of hematologic and solid cancers. Such antibodies opsonize cancer cells and can trigger cytotoxic responses mediated by Fc-receptor expressing immune cells in the tumor microenvironment (TME). Although frequently ignored, neutrophils, which are abundantly present in the circulation and many cancers, have demonstrated to constitute bona fide effector cells for antibody-mediated tumor elimination in vivo. It has now also been established that neutrophils exert a unique mechanism of cytotoxicity towards antibody-opsonized tumor cells, known as trogoptosis, which involves Fc-receptor (FcR)-mediated trogocytosis of cancer cell plasma membrane leading to a lytic/necrotic type of cell death. However, neutrophils prominently express the myeloid inhibitory receptor SIRPα, which upon interaction with the ‘don’t eat me’ signal CD47 on cancer cells, limits cytotoxicity, forming a mechanism of resistance towards anti-cancer antibody therapeutics. In fact, tumor cells often overexpress CD47, thereby even more strongly restricting neutrophil-mediated tumor killing. Blocking the CD47-SIRPα interaction may therefore potentiate neutrophil-mediated antibody-dependent cellular cytotoxicity (ADCC) towards cancer cells, and various inhibitors of the CD47-SIRPα axis are now in clinical studies. Here, we review the role of neutrophils in antibody therapy in cancer and their regulation by the CD47-SIRPα innate immune checkpoint. Moreover, initial results of CD47-SIRPα blockade in clinical trials are discussed.

Targeting Myeloid Checkpoint Molecules in Combination With Antibody Therapy: A Novel Anti-Cancer Strategy With IgA Antibodies?

Immunotherapy with therapeutic antibodies has shown a lack of durable responses in some patients due to resistance mechanisms. Checkpoint molecules expressed by tumor cells have a deleterious impact on clinical responses to therapeutic antibodies. Myeloid checkpoints, which negatively regulate macrophage and neutrophil anti-tumor responses, are a novel type of checkpoint molecule. Myeloid checkpoint inhibition is currently being studied in combination with IgG-based immunotherapy. In contrast, the combination with IgA-based treatment has received minimal attention. IgA antibodies have been demonstrated to more effectively attract and activate neutrophils than their IgG counterparts. Therefore, myeloid checkpoint inhibition could be an interesting addition to IgA treatment and has the potential to significantly enhance IgA therapy.

CD47/SIRPα axis: bridging innate and adaptive immunity

Myeloid immune cells are frequently present in the tumor environment, and although they can positively contribute to tumor control they often negatively impact anticancer immune responses. One way of inhibiting the positive contributions of myeloid cells is by signaling through the cluster of differentiation 47 (CD47)/signal regulatory protein alpha (SIRPα) axis. The SIRPα receptor is expressed on myeloid cells and is an inhibitory immune receptor that, upon binding to CD47 protein, delivers a ‘don’t eat me’ signal. As CD47 is often overexpressed on cancer cells, treatments targeting CD47/SIRPα have been under active investigation and are currently being tested in clinical settings. Interestingly, the CD47/SIRPα axis is also involved in T cell-mediated antitumor responses. In this perspective we provide an overview of recent studies showing how therapeutic blockade of the CD47/SIRPα axis improves the adaptive immune response. Furthermore, we discuss the interconnection between the myeloid CD47/SIRPα axis and adaptive T cell responses as well as the potential therapeutic role of the CD47/SIRPα axis in tumors with acquired resistance to the classic immunotherapy through major histocompatibility complex downregulation. Altogether this review provides a profound insight for the optimal exploitation of CD47/SIRPα immune checkpoint therapy.

Clinical significance of signal regulatory protein alpha and T cell immunoreceptor with immunoglobulin and immunoreceptor tyrosine-based inhibition motif domain expression in undifferentiated pleomorphic sarcoma

PURPOSE

Undifferentiated pleomorphic sarcoma (UPS) is associated with poor prognosis. Recently, signal regulatory protein alpha (SIRPα), which is the immune checkpoint of macrophages, and T cell immunoreceptor with immunoglobulin and immunoreceptor tyrosine-based inhibition motif domains (TIGIT), which is the immune checkpoint of T cells and natural killer cells, have been considered as potential targets for cancer immunotherapy. This study aimed to assess the value of SIRPα and TIGIT as prognostic factors of UPS.

MATERIALS AND METHODS

The cBio Cancer Genomics Portal was used to analyze mRNA expression data of 50 UPS cases in the Cancer Genome Atlas. We retrieved 49 UPS cases and performed immunohistochemistry (IHC) to detect programmed death ligand 1 (PD-L1), SIRPα, CD68, CD163, TIGIT, CD155, and CD8.

RESULTS

SIRPα was positively associated with CD163 (Pearson's r = 0.51, p = 0.0002) as per open access data and IHC of the cohort (p = 0.002), which revealed that SIRPα-positive macrophage infiltration was higher in UPS cells with ≥ 1% PD-L1 expression than that in UPS cells with < 1% PD-L1 expression (p = 0.047). TIGIT was positively correlated with PD-L1 (r = 0.54, p < 0.0001) and CD8A (r = 0.98, p < 0.0001). In 35 of 49 cases, IHC revealed high levels of TIGIT expression on tumor cells. Furthermore, TIGIT expression on tumor cells was negatively correlated with CD155-positive (p = 0.0144) and CD8-positive (p = 0.0487) cell infiltration. Survival analysis showed that the high degree of SIRPα-positive macrophage infiltration was associated with poor overall survival and metastasis (p < 0.0001, p = 0.0006, respectively).

CONCLUSION

SIRPα-positive macrophages infiltrated UPS cells, which predicted poor prognosis. High TIGIT expression on tumor cells was associated with decreased levels of tumor-infiltrating macrophages in UPS.

Imaging and therapeutic targeting of the tumor immune microenvironment with biologics

The important role of tumor microenvironmental elements in determining tumor progression and metastasis has been firmly established. In particular, the presence and activity profile of tumor-infiltrating immune cells may be associated with the outcome of the disease and may predict responsiveness to (immuno)therapy. Indeed, while some immune cell types, such as macrophages, support cancer cell outgrowth and mediate therapy resistance, the presence of activated CD8⁺ T cells is usually indicative of a better prognosis. It is therefore of the utmost interest to obtain a full picture of the immune infiltrate in tumors, either as a prognostic test, as a way to stratify patients to maximize therapeutic success, or as therapy follow-up. Hence, the non-invasive imaging of these cells is highly warranted, with biologics being prime candidates to achieve this goal.

Bispecific antibodies for immune cell retargeting against cancer

INTRODUCTION

Following the approval of the T-cell engaging bispecific antibody blinatumomab, immune cell retargeting with bispecific or multispecific antibodies has emerged as a promising cancer immunotherapy strategy, offering alternative mechanisms compared to immune checkpoint blockade. As we gain more understanding of the complex tumor microenvironment, rules and design principles have started to take shape on how to best harness the immune system to achieve optimal anti-tumor activities.

AREAS COVERED

In the present review, we aim to summarize the most recent advances and challenges in using bispecific antibodies for immune cell retargeting and to provide insights into various aspects of antibody engineering. Discussed herein are studies that highlight the importance of considering antibody engineering parameters, such as binding epitope, affinity, valency, and geometry to maximize the potency and mitigate the toxicity of T cell engagers. Beyond T cell engaging bispecifics, other bispecifics designed to recruit the innate immune system are also covered.

EXPERT OPINION

Diverse and innovative molecular designs of bispecific/multispecific antibodies have the potential to enhance the efficacy and safety of immune cell retargeting for the treatment of cancer. Whether or not clinical data support these different hypotheses, especially in solid tumor settings, remains to be seen.

Role of CD47-SIRPα Checkpoint in Nanomedicine-Based Anti-Cancer Treatment

Many cancers have evolved various mechanisms to evade immunological surveillance, such as the inhibitory immune checkpoint of the CD47-SIRPα signaling pathway. By targeting this signaling pathway, researchers have developed diverse nanovehicles with different loaded drugs and modifications in anticancer treatment. In this review, we present a brief overview of CD47-SIRPα interaction and nanomedicine. Then, we delve into recent applications of the CD47-SIRPα interaction as a target for nanomedicine-based antitumor treatment and its combination with other targeting pathway drugs and/or therapeutic approaches.

The Role of Type-2 Conventional Dendritic Cells in the Regulation of Tumor Immunity

Simple Summary

Recent studies revealed that type-2 conventional dendritic cells (cDC2s) play an important role in antitumor immunity by promoting cytotoxic T-cell responses and helper T-cell differentiation. This review outlines the role of cDC2s in tumor immunity and summarizes the latest progress regarding their potential in cancer vaccination and cDC2-targeted cancer immunotherapy.

Abstract

Conventional dendritic cells (cDCs) orchestrate immune responses to cancer and comprise two major subsets: type-1 cDCs (cDC1s) and type-2 cDCs (cDC2s). Compared with cDC1s, which are dedicated to the activation of CD8⁺ T cells, cDC2s are ontogenically and functionally heterogeneous, with their main function being the presentation of exogenous antigens to CD4⁺ T cells for the initiation of T helper cell differentiation. cDC1s play an important role in tumor-specific immune responses through cross-presentation of tumor-derived antigens for the priming of CD8⁺ T cells, whereas little is known of the role of cDC2s in tumor immunity. Recent studies have indicated that human cDC2s can be divided into at least two subsets and have implicated these cells in both anti- and pro-tumoral immune responses. Furthermore, the efficacy of cDC2-based vaccines as well as cDC2-targeted therapeutics has been demonstrated in both mouse models and human patients. Here we summarize current knowledge about the role of cDC2s in tumor immunity and address whether these cells are beneficial in the context of antitumor immune responses.

Expression of CD47 and SIRPα Macrophage Immune-Checkpoint Pathway in Non-Small-Cell Lung Cancer

Simple Summary

Cancer cells escape macrophage phagocytosis by exploiting the CD47/SIRPα axis. We found that extensive membranous CD47 expression by cancer cells characterized 29/98 cases. SIRPα and CD68 were expressed by tumor-associated macrophages (Μφ, TAMs). A high CD68Mφ-score was linked with improved overall survival. High expression, however, of SIRPα by CD68+ TAMs was linked with CD47 expression by cancer cells, low TIL-score, and poor prognosis. A direct association of CD47 expression by cancer cells and the % FOXP3+ TILs was also noted. The CD47/SIRPα axis is a sound target for adjuvant immunotherapy policies, aiming to improve the cure rates in operable NSCLC.

Abstract

Background: Cancer cells escape macrophage phagocytosis by expressing the CD47 integrin-associated protein that binds to the SIRPα ligand (signal regulatory protein alpha) expressed by macrophages. Immunotherapy targeting this pathway is under clinical development. Methods: We investigated the expression of CD47/SIRPα molecules in a series of 98 NSCLCs, in parallel with the infiltration of tumor stroma by CD68+ macrophages, tumor-infiltrating lymphocytes (TILs), and PD-L1/PD-1 molecules. Results: Extensive membranous CD47 expression by cancer cells characterized 29/98 cases. SIRPα and CD68 were expressed, to a varying extent, by tumor-associated macrophages (Μφ, TAMs). A high CD68Mφ-score in inner tumor areas was linked with improved overall survival (p = 0.005); and this was independent of the stage (p = 0.02, hazard ratio 0.4). In contrast, high SIRPα expression by CD68+ TAMs (SIRPα/CD68-ratio) was linked with CD47 expression by cancer cells, low TIL-score, and poor prognosis (p = 0.02). A direct association of CD47 expression by cancer cells and the % FOXP3+ TILs (p = 0.01, r = 0.25) was also noted. Conclusions: TAMs play an important role in the prognosis of operable NSCLC. As SIRPα+ macrophages adversely affect prognosis, it is suggested that the CD47/SIRPα axis is a sound target for adjuvant immunotherapy policies, aiming to improve the cure rates in operable NSCLC.

Preclinical characterization of the novel anti-SIRPα antibody BR105 that targets the myeloid immune checkpoint

BACKGROUND

The CD47-SIRPα pathway acts as an important myeloid cell immune checkpoint and targeting the CD47/SIRPα axis represents a promising strategy to promote antitumor immunity. Several CD47-targeting agents show encouraging early activity in clinical trials. However, due to ubiquitous expression of CD47, the antigen sink and hematologic toxicity, such as anemia and thrombocytopenia, are main problems for developing CD47-targeting therapies. Considering the limited expression of SIRPα, targeting SIRPα is an alternative approach to block the CD47-SIRPα pathway, which may result in differential efficacy and safety profiles.

METHODS

SIRPα-targeting antibody BR105 was generated by hybridoma fusion and following humanization. BR105 was characterized for binding to human SIRPα alleles and blockade of the interaction with CD47. The functional activity was determined in in vitro phagocytosis assays by using human macrophages. The effect of BR105 on human T cell activation was studied using an OKT3-induced T-cell proliferation assay and an allogeneic mixed lymphocyte reaction. Human SIRPα-humanized immunodeficient mice were used in cancer models for evaluating the in vivo antitumor efficacy of BR105. Safety was addressed in a repeat-dose toxicity study in cynomolgus monkeys, and toxicokinetic analysis was further evaluated.

RESULTS

BR105 shows broad binding activity across various SIRPα variants, and potently blocks the interaction of SIRPα and CD47. In vitro functional assays demonstrated that BR105 synergizes with therapeutic antibodies to promote phagocytosis of tumor cells. Moreover, the combination of BR105 and therapeutic antibody significantly inhibits tumor growth in a xenograft tumor model. Although BR105 may slightly bind to SIRPγ, it does not inhibit T cell activation, unlike other non-selective SIRPα-targeting antibody and CD47-targeting agents. Toxicity studies in non-human primates show that BR105 is well tolerated with no treatment-related adverse effects noted.

CONCLUSIONS

The novel and differentiated SIRPα-targeting antibody, BR105, was discovered and displays promising antitumor efficacy in vitro and in vivo. BR105 has a favorable safety profile and shows no adverse effects on T cell functionality. These data support further clinical development of BR105, especially as a therapeutic agent to enhance efficacy when used in combination with tumor-targeting antibodies or antibodies that target other immune checkpoints.

Concerted BAG3 and SIRPα blockade impairs pancreatic tumor growth

The BAG3- and SIRPα- mediated pathways trigger distinct cellular targets and signaling mechanisms in pancreatic cancer microenvironment. To explore their functional connection, we investigated the effects of their combined blockade on cancer growth in orthotopic allografts of pancreatic cancer mt4–2D cells in immunocompetent mice. The anti-BAG3 + anti-SIRPα mAbs treatment inhibited (p = 0.007) tumor growth by about the 70%; also the number of metastatic lesions was decreased, mostly by the effect of the anti-BAG3 mAb. Fibrosis and the expression of the CAF activation marker α-SMA were reduced by about the 30% in animals treated with anti-BAG3 mAb compared to untreated animals, and appeared unaffected by treatment with the anti-SIRPα mAb alone; however, the addition of anti-SIRPα to anti-BAG3 mAb in the combined treatment resulted in a > 60% (p < 0.0001) reduction of the fibrotic area and a 70% (p < 0.0001) inhibition of CAF α-SMA positivity. Dendritic cells (DCs) and CD8+ lymphocytes, hardly detectable in the tumors of untreated animals, were modestly increased by single treatments, while were much more clearly observable (p < 0.0001) in the tumors of the animals subjected to the combined treatment. The effects of BAG3 and SIRPα blockade do not simply reflect the sum of the effects of the single blockades, indicating that the two pathways are connected by regulatory interactions and suggesting, as a proof of principle, the potential therapeutic efficacy of a combined BAG3 and SIRPα blockade in pancreatic cancer.

High SIRPA Expression Predicts Poor Prognosis and Correlates with Immune Infiltrates in Patients with Esophageal Carcinoma

BACKGROUND

Signal regulatory protein alpha (SIRPA) is an inhibitory receptor expressed in macrophages and a potential therapeutic target in cancers. This study aims to investigate the functional role of SIRPA in esophageal carcinoma (ESCA).

METHODS

Based on the Oncomine and The Cancer Genome Atlas (TCGA) database, SIRPA expression and clinical value were determined. Gene set enrichment analysis (GSEA) was performed to predict the mechanism underlying the oncogene role of SIRPA. Spearman's correlation analysis was used to analyze the effects of SIRPA on the molecular relationship and immune landscape.

RESULTS

SIRPA was highly expressed across Oncomine and TCGA databases and correlated with poor overall survival and disease-specific survival. There was an expression difference among clinical characteristics. Functional annotation showed that cancer-related biological function and pathways were enriched in the high SIRPA expression group. Besides, SIRPA strongly and extensively affected the immune infiltrates.

CONCLUSION

SIRPA might be an oncogene and a target of immunotherapy in ESCA.

Anticancer efficacy of monotherapy with antibodies to SIRPα/SIRPβ1 mediated by induction of antitumorigenic macrophages

The interaction of signal regulatory protein α (SIRPα) on macrophages with CD47 on cancer cells is thought to prevent antibody (Ab)-dependent cellular phagocytosis (ADCP) of the latter cells by the former. Blockade of the CD47-SIRPα interaction by Abs to CD47 or to SIRPα, in combination with tumor-targeting Abs such as rituximab, thus inhibits tumor formation by promoting macrophage-mediated ADCP of cancer cells. Here we show that monotherapy with a monoclonal Ab (mAb) to SIRPα that also recognizes SIRPβ1 inhibited tumor formation by bladder and mammary cancer cells in mice, with this inhibitory effect being largely dependent on macrophages. The mAb to SIRPα promoted polarization of tumor-infiltrating macrophages toward an antitumorigenic phenotype, resulting in the killing and phagocytosis of cancer cells by the macrophages. Ablation of SIRPα in mice did not prevent the inhibitory effect of the anti-SIRPα mAb on tumor formation or its promotion of the cancer cell-killing activity of macrophages, however. Moreover, knockdown of SIRPβ1 in macrophages attenuated the stimulatory effect of the anti-SIRPα mAb on the killing of cancer cells, whereas an mAb specific for SIRPβ1 mimicked the effect of the anti-SIRPα mAb. Our results thus suggest that monotherapy with Abs to SIRPα/SIRPβ1 induces antitumorigenic macrophages and thereby inhibits tumor growth and that SIRPβ1 is a potential target for cancer immunotherapy.

Barriers to Immunotherapy in Ovarian Cancer: Metabolic, Genomic, and Immune Perturbations in the Tumour Microenvironment

A lack of explicit early clinical signs and effective screening measures mean that ovarian cancer (OC) often presents as advanced, incurable disease. While conventional treatment combines maximal cytoreductive surgery and platinum-based chemotherapy, patients frequently develop chemoresistance and disease recurrence. The clinical application of immune checkpoint blockade (ICB) aims to restore anti-cancer T-cell function in the tumour microenvironment (TME). Disappointingly, even though tumour infiltrating lymphocytes are associated with superior survival in OC, ICB has offered limited therapeutic benefits. Herein, we discuss specific TME features that prevent ICB from reaching its full potential, focussing in particular on the challenges created by immune, genomic and metabolic alterations. We explore both recent and current therapeutic strategies aiming to overcome these hurdles, including the synergistic effect of combination treatments with immune-based strategies and review the status quo of current clinical trials aiming to maximise the success of immunotherapy in OC.

Progress of CD47 immune checkpoint blockade agents in anticancer therapy: a hematotoxic perspective

CD47, a transmembrane protein, acts as a "do not eat me" signal that is overexpressed in many tumor cell types, thereby forming a signaling axis with its ligand signal regulatory protein alpha (SIRPα) and enabling the tumor cells to escape from macrophage-mediated phagocytosis. Several clinical trials with CD47 targeting agents are underway and have achieved impressive results preliminarily. However, hematotoxicity (particularly anemia) has emerged as the most common side effect that cannot be neglected. In the development of CD47 targeting agents, various methods have been used to mitigate this toxicity. In this review, we summarized five strategies used to alleviate CD47 blockade-induced hematotoxicity, as follows: change in the mode of administration; dual targeting bispecific antibodies of CD47; CD47 antibodies/SIRPα fusion proteins with negligible red blood cell binding; anti-SIRPα antibodies; and glutaminyl-peptide cyclotransferase like inhibitors. With these strategies, the development of CD47 targeting agents can be improved.

CD47/SIRPα pathway mediates cancer immune escape and immunotherapy

The adaptive immune checkpoints such as PD-1(programmed death-1)/PD-L1 (programmed death-ligand 1) play an important role in cancer immunotherapy, whereas increasing evidence suggests that cancer cell evades immune surveillance by innate immune checkpoints such as SIRPα (signal-regulatory protein α)/CD47 (cluster of differentiation 47). In multiple types of cancer cells and solid tumor tissues, highly expressed CD47 protein level has been observed, which is triggered by some transcription factors including NFκB, Myc, and HIF. As a transmembrane protein, the binding of CD47 to SIRPα ligand on phagocytes results in phagocytosis resistance and cancer cell immune escape. In contrast, CD47-SIRPα interaction blockade enhances cancer cell clearance by phagocytes such as macrophages and dendritic cells (DCs) to activate an innate immune response, whereas this process could promote antigen cross-presentation by antigen present cells (APCs) leading to T cell priming, consequently, activates an adaptive antitumor immune response. In this review, we discussed the current SIRPα-CD47 axis-mediated cancer cell immune escape and immunotherapy, which could provide an effective antitumor strategy by the innate and adaptive immune response.

The pivotal role of cytotoxic NK cells in mediating the therapeutic effect of anti-CD47 therapy in mycosis fungoides

CD47 is frequently overexpressed on tumor cells and is an attractive therapeutic target. The mechanism by which anti-CD47 immunotherapy eliminates cutaneous lymphoma has not been explored. We utilized CRISPR/Cas-9 CD47 knock-out, depletion of NK cells, and mice genetically deficient in IFN-γ to elucidate the mechanism of anti-CD47 therapy in a murine model of cutaneous T cell lymphoma (CTCL). CD47 was found to be a crucial factor for tumor progression since CD47 KO CTCL exhibited a delay in tumor growth. The treatment of CD47 WT murine CTCL with anti-CD47 antibodies led to a significant reduction in tumor burden as early as four days after the first treatment and accompanied by an increased percentage of cytotoxic NK cells at the tumor site. The depletion of NK cells resulted in marked attenuation of the anti-tumor effect of anti-CD47. Notably, the treatment of CD47 WT tumors in IFN-γ KO mice with anti-CD47 antibodies was efficient, demonstrating that IFN-γ was not required to mediate anti-CD47 therapy. We were able to potentiate the therapeutic effect of anti-CD47 therapy by IFN-α. That combination resulted in an increased number of cytotoxic CD107a + IFN-γ-NK1.1 cells and intermediate CD62L + NKG2a-NK1.1. Correlative data from a clinical trial (clinicaltrials.gov, NCT02890368) in patients with CTCL utilizing SIRPαFc to block CD47 confirmed our in vivo observations.

Role of autophagy on cancer immune escape

Autophagy is catabolic process by degradation of intracellular components in lysosome including proteins, lipids, and mitochondria in response to nutrient deficiency or stress such as hypoxia or chemotherapy. Increasing evidence suggests that autophagy could induce immune checkpoint proteins (PD-L1, MHC-I/II) degradation of cancer cells, which play an important role in regulating cancer cell immune escape. In addition to autophagic degradation of immune checkpoint proteins, autophagy induction in immune cells (macrophages, dendritic cells) manipulates antigen presentation and T cell activity. These reports suggest that autophagy could negatively or positively regulate cancer cell immune escape by immune checkpoint protein and antigens degradation, cytokines release, antigens generation. These controversial phenomenon of autophagy on cancer cell immune evasion may be derived from different experimental context or models. In addition, autophagy maybe exhibit a role in regulating host excessive immune response. So rational combination with autophagy could enhance the efficacy of cancer immunotherapy. In this review, the current progress of autophagy on cancer immune escape is discussed.

PD-1/PD-L1 inhibitors-based treatment for advanced renal cell carcinoma: Mechanisms affecting efficacy and combination therapies

With the widespread use of PD-1/PD-L1 monoclonal antibodies (mAbs) in the treatment of multiple malignant tumors, they were also gradually applied to advanced renal cell carcinoma (aRCC). Nowadays, multiple PD-1/PD-L1 mAbs, such as nivolumab, avelumab, and pembrolizumab, have achieved considerable efficacy in clinical trials. However, due to the primary, adaptive, and acquired resistance to these mAbs, the efficacy of this immunotherapy is not satisfactory. Theories also vary as to why the difference in efficacy occurs. The alterations of PD-L1 expression and the interference of cellular immunity may affect the efficacy. These mechanisms demand to be revealed to achieve a sustained and complete objective response in patients with aRCC. Tyrosine kinase inhibitors have been proven to have synergistic mechanisms with PD-1/PD-L1 mAb in the treatment of aRCC, and CTLA-4 mAb has been shown to have a non-redundant effect with PD-1/PD-L1 mAb to enhance efficacy. Although combinations with targeted agents or other checkpoint mAbs have yielded enhanced clinical outcomes in multiple clinical trials nowadays, the potential of PD-1/PD-L1 mAbs still has a large development space. More potential mechanisms that affect the efficacy demand to be developed and transformed into the clinical treatment of aRCC to search for possible combination regimens. We elucidate these mechanisms in RCC and present existing combination therapies applied in clinical trials. This may help physicians' select treatment options for patients with refractory kidney cancer.

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.