Targeted inhibition of CD47-SIRPα requires Fc-FcγR interactions to maximize activity in T-cell lymphomas

KLRG1 Cell Depletion as a Novel Therapeutic Strategy in Patients with Mature T-Cell Lymphoma Subtypes

PURPOSE

Develop a novel therapeutic strategy for patients with subtypes of mature T-cell and NK-cell neoplasms.

EXPERIMENTAL DESIGN

Primary specimens, cell lines, patient-derived xenograft models, commercially available, and proprietary anti-KLRG1 antibodies were used for screening, target, and functional validation.

RESULTS

Here we demonstrate that surface KLRG1 is highly expressed on tumor cells in subsets of patients with extranodal NK/T-cell lymphoma (ENKTCL), T-prolymphocytic leukemia (T-PLL), and gamma/delta T-cell lymphoma (G/D TCL). The majority of the CD8+/CD57+ or CD3-/CD56+ leukemic cells derived from patients with T- and NK-large granular lymphocytic leukemia (T-LGLL and NK-LGLL), respectively, expressed surface KLRG1. The humanized afucosylated anti-KLRG1 monoclonal antibody (mAb208) optimized for mouse in vivo use depleted KLRG1+ TCL cells by mechanisms of ADCC, ADCP, and CDC rather than apoptosis. mAb208 induced ADCC and ADCP of T-LGLL patient-derived CD8+/CD57+ cells ex vivo. mAb208 effected ADCC of subsets of healthy donor-derived KLRG1+ NK, CD4+, CD8+ Tem, and TemRA cells while sparing KLRG1- naïve and CD8+ Tcm cells. Treatment of cell line and TCL patient-derived xenografts with mAb208 or anti-CD47 mAb alone and in combination with the PI3K-δ/γ inhibitor duvelisib extended survival. The depletion of macrophages in vivo antagonized mAb208 efficacy.

CONCLUSIONS

Our findings suggest the potential benefit of a broader treatment strategy combining therapeutic antibodies with PI3Ki for the treatment of patients with mature T-cell and NK-cell neoplasms. See related commentary by Varma and Diefenbach, p. 2300.

Aggressive T-cell lymphomas: 2024: Updates on diagnosis, risk stratification, and management

INTRODUCTION

Aggressive T-cell lymphomas continue to have a poor prognosis. There are over 30 different subtypes of peripheral T-cell lymphoma (PTCL), and we are now beginning to understand the differences between the various subtypes beyond histologic variations.

MOLECULAR PATHOGENESIS OF VARIOUS SUBTYPES OF PTCL

Gene expression profiling and other molecular techniques have enabled deeper understanding of differences in various subtypes as reflected in the latest 5th WHO classification of PTCL. It is becoming increasingly clear that therapeutic approaches that target specific cellular pathways are needed to improve the clinical outcomes of PTCL.

TARGETED THERAPIES

There are many targeted agents currently in various stages of clinical trials for PTCL that take advantage of the differential expression of specific proteins or receptors in PTCL tumors. This includes the CD30 directed antibody drug conjugate brentuximab vedotin. Other notable targets are phosphatidylinositol 3-kinase inhibitors, histone deacetylase inhibitors, CD25, and chemokine receptor 4. Anaplastic lymphoma kinase (ALK) inhibitors are promising for ALK expressing tumors.

IMMUNOTHERAPIES

Allogeneic stem cell transplant continues to be the curative therapy for most aggressive subtypes of PTCL. The use of checkpoint inhibitors in the treatment of PTCL is still controversial, with best results seen in cases of extranodal natural killer cell/T-cell lymphoma. Bispecific antibody-based treatments and chimeric antigen receptor cell-based therapies are in clinical trials.

Enhanced potency of immunotherapy against B-cell precursor acute lymphoblastic leukemia by combination of an Fc-engineered CD19 antibody and CD47 blockade

CD19-directed immunotherapy has become a cornerstone in the therapy of B-cell precursor acute lymphoblastic leukemia (BCP-ALL). CD19-directed cellular and antibody-based therapeutics have entered therapy of primary and relapsed disease and contributed to improved outcomes in relapsed disease and lower therapy toxicity. However, efficacy remains limited in many cases due to a lack of therapy response, short remission phases, or antigen escape. Here, BCP-ALL cell lines, patient-derived xenograft (PDX) samples, human macrophages, and an in vivo transplantation model in NOD.Cg-PrkdcscidIl2rgtm1Wjl/SzJ (NSG) mice were used to examine the therapeutic potency of a CD19 antibody Fc-engineered for improved effector cell recruitment (CD19-DE) and antibody-dependent cellular phagocytosis (ADCP), in combination with a novel modified CD47 antibody (Hu5F9-IgG2σ). For the in vivo model, only samples refractory to CD19-DE monotherapy were chosen. Hu5F9-IgG2σ enhanced ADCP by CD19-DE in various BCP-ALL cell line models with varying CD19 surface expression and cytogenetic backgrounds, two of which contained the KMT2A-AFF1 fusion. Also, the antibody combination was efficient in inducing ADCP by human macrophages in pediatric PDX samples with and adult samples with and without KMT2A-rearrangement in vitro. In a randomized phase 2-like PDX trial using seven KMT2A-rearranged BCP-ALL samples in NSG mice, the CD19/CD47 antibody combination proved highly efficient. Our findings support that the efficacy of Fc-engineered CD19 antibodies may be substantially enhanced by a combination with CD47 blockade. This suggests that the combination may be a promising therapy option for BCP-ALL, especially in relapsed patients and/or patients refractory to CD19-directed therapy.

Targeting CD47-SIRPα axis for Hodgkin and non-Hodgkin lymphoma immunotherapy

The interaction between cluster of differentiation 47 (CD47) and signal regulatory protein α (SIRPα) protects healthy cells from macrophage attack, which is crucial for maintaining immune homeostasis. Overexpression of CD47 occurs widely across various tumor cell types and transmits the "don't eat me" signal to macrophages to avoid phagocytosis through binding to SIRPα. Blockade of the CD47-SIRPα axis is therefore a promising approach for cancer treatment. Lymphoma is the most common hematological malignancy and is an area of unmet clinical need. This review mainly described the current strategies targeting the CD47-SIRPα axis, including antibodies, SIRPα Fc fusion proteins, small molecule inhibitors, and peptides both in preclinical studies and clinical trials with Hodgkin lymphoma and non-Hodgkin lymphoma.

The antitumor activities of anti-CD47 antibodies require Fc-FcγR interactions

While anti-CD47 antibodies hold promise for cancer immunotherapy, early-phase clinical trials have shown limited clinical benefit, suggesting that CD47 blockade alone might be insufficient for effective tumor control. Here, we investigate the contributions of the Fc domain of anti-CD47 antibodies required for optimal in vivo antitumor activity across multiple species-matched models, providing insights into the mechanisms behind the efficacy of this emerging class of therapeutic antibodies. Using a mouse model humanized for CD47, SIRPα, and FcγRs, we demonstrate that local administration of Fc-engineered anti-CD47 antibodies with enhanced binding to activating FcγRs promotes tumor infiltration of macrophages and antigen-specific T cells, while depleting regulatory T cells. These effects result in improved long-term systemic antitumor immunity and minimal on-target off-tumor toxicity. Our results highlight the importance of Fc optimization in the development of effective anti-CD47 therapies and provide an attractive strategy to enhance the activity of this promising immunotherapy.

slan+ Monocytes Kill Cancer Cells Coated in Therapeutic Antibody by Trogoptosis

Monocytes positive for 6-Sulfo LacNAc (slan) are a major subset of nonclassical CD14dimCD16+ monocytes in humans. We have shown that slan+ cells infiltrate lymphomas and elicit an antibody-dependent cellular cytotoxicity (ADCC) of neoplastic B cells mediated by the anti-CD20 therapeutic rituximab. Herein, by performing blocking experiments and flow cytometry analyses, as well as confocal microscopy and live-cell imaging assays, we extended the findings to other humanized antibodies and deciphered the underlying effector mechanism(s). Specifically, we show that, after coculture with target cells coated with anti-CD20 or anti-CD38, slan+ monocytes mediate trogocytosis, a cell-cell contact dependent, antibody-mediated process that triggers an active, mechanic disruption of target cell membranes. Trogocytosis by slan+ monocytes leads to a necrotic type of target cell death known as trogoptosis, which, once initiated, was partially sustained by endogenous TNFα. We also found that slan+ monocytes, unlike natural killer (NK) cells, mediate a direct ADCC with all types of anti-CD47 analyzed, and this was independent of their IgG isotype. The latter findings unveil a potentially relevant contribution by slan+ monocytes in mediating the therapeutic efficacy of anti-CD47 in clinical practice, which could be particularly important when NK cells are exhausted or deficient in number. Overall, our observations shed new light on the cytotoxic mechanisms exerted by slan+ monocytes in antibody-dependent tumor cell targeting and advance our knowledge on how to expand our therapeutic arsenal for cancer therapy.

CD47 blockade ameliorates autoimmune vasculitis via efferocytosis of neutrophil extracellular traps

Neutrophil extracellular trap (NET) formation contributes to immune defense and is a distinct form of cell death. Excessive NET formation is found in patients with anti-neutrophil cytoplasmic antibody-associated (ANCA-associated) vasculitis (AAV), contributing to disease progression. The clearance of dead cells by macrophages, a process known as efferocytosis, is regulated by the CD47-mediated "don't eat me" signal. Hence, we hypothesized that pathogenic NETs in AAV escape from efferocytosis via the CD47 signaling pathway, resulting in the development of necrotizing vasculitis. Immunostaining for CD47 in human renal tissues revealed high CD47 expression in crescentic glomerular lesions of patients with AAV. In ex vivo studies, ANCA-induced netting neutrophils increased the expression of CD47 with the reduction of efferocytosis. After efferocytosis, macrophages displayed proinflammatory phenotypes. The blockade of CD47 in spontaneous crescentic glomerulonephritis-forming/Kinjoh (SCG/Kj) mice ameliorated renal disease and reduced myeloperoxidase-ANCA (MPO-ANCA) titers with a reduction in NET formation. Thus, CD47 blockade would protect against developing glomerulonephritis in AAV via restored efferocytosis of ANCA-induced NETs.

SOHO State of the Art Updates and Next Questions | New Pathways and New Targets in PTCL: Staying on Target

While the peripheral T-cell lymphomas (PTCL) remain a therapeutic challenge, and increasingly account for a disproportionate number of lymphoma-related deaths, improved understanding of disease pathogenesis and classification, and the development of novel therapeutic agents over the past decade, all provide reasons for a more optimistic outlook in the next. Despite their genetic and molecular heterogeneity, many PTCL are dependent upon signaling input provided by antigen, costimulatory, and cytokine receptors. While gain-of-function alterations effecting these pathways are recurrently observed in many PTCL, more often than not, signaling remains ligand-and tumor microenvironment (TME)-dependent. Consequently, the TME and its constituents are increasingly recognized as "on target". Utilizing a "3 signal" model, we will review new-and old-therapeutic targets that are relevant for the more common nodal PTCL subtypes.

Nodal peripheral T-cell lymphoma: Chemotherapy-free management, are we there yet?

Peripheral T-cell lymphomas (PTCLs) are a diverse and uncommon type of lymphoid malignancies with a dismal prognosis. Recent advances in genomic studies have shown recurring mutations that are changing our knowledge of the disease's molecular genetics and pathogenesis. As such, new targeted therapies and treatments to improve disease outcomes are currently being explored. In this review, we discussed the current understanding of the nodal PTCL biology with potential therapeutic implications and gave our insights on the promising novel therapies that are currently under study such as immunotherapy, chimeric antigen receptor T-cell therapy, and oncolytic virotherapy.

The Antitumor Activities of Anti-CD47 Antibodies Require Fc-FcγR interactions

While anti-CD47 antibodies hold promise for cancer immunotherapy, early phase clinical trials have shown limited signs of clinical benefit, suggesting that blockade of CD47 alone may not be sufficient for effective tumor control. Here, we investigate the contributions of the Fc domain of anti-CD47 antibodies required for optimal in vivo antitumor activity across multiple species-matched models, providing new insights into the mechanisms underlying the efficacy of this emerging class of therapeutic antibodies. Using a novel mouse model humanized for CD47, SIRPα and FcγRs, we demonstrate that local administration of an Fc-engineered anti-CD47 antibody with enhanced binding to activating FcγRs modulates myeloid and T-cell subsets in the tumor microenvironment, resulting in improved long-term systemic antitumor immunity and minimal on-target off-tumor toxicity. Our results highlight the importance of Fc optimization in the development of effective anti-CD47 therapies and provide a novel approach for enhancing the antitumor activity of this promising immunotherapy.

Emerging phagocytosis checkpoints in cancer immunotherapy

Cancer immunotherapy, mainly including immune checkpoints-targeted therapy and the adoptive transfer of engineered immune cells, has revolutionized the oncology landscape as it utilizes patients' own immune systems in combating the cancer cells. Cancer cells escape immune surveillance by hijacking the corresponding inhibitory pathways via overexpressing checkpoint genes. Phagocytosis checkpoints, such as CD47, CD24, MHC-I, PD-L1, STC-1 and GD2, have emerged as essential checkpoints for cancer immunotherapy by functioning as "don't eat me" signals or interacting with "eat me" signals to suppress immune responses. Phagocytosis checkpoints link innate immunity and adaptive immunity in cancer immunotherapy. Genetic ablation of these phagocytosis checkpoints, as well as blockade of their signaling pathways, robustly augments phagocytosis and reduces tumor size. Among all phagocytosis checkpoints, CD47 is the most thoroughly studied and has emerged as a rising star among targets for cancer treatment. CD47-targeting antibodies and inhibitors have been investigated in various preclinical and clinical trials. However, anemia and thrombocytopenia appear to be formidable challenges since CD47 is ubiquitously expressed on erythrocytes. Here, we review the reported phagocytosis checkpoints by discussing their mechanisms and functions in cancer immunotherapy, highlight clinical progress in targeting these checkpoints and discuss challenges and potential solutions to smooth the way for combination immunotherapeutic strategies that involve both innate and adaptive immune responses.

Inhibitory effects of circulating natural autoantibodies to CD47-derived peptides on OSCC cells

OBJECTIVES

Natural autoantibodies serve as an important anti-tumorigenic component in the body. This study was thus designed to investigate whether circulating natural IgG autoantibodies against a cluster of differentiation 47 (CD47) could exert inhibitory effects on oral squamous cell carcinoma (OSCC).

SUBJECTS AND METHODS

The expression levels of 13 tumor-targeted genes in three OSCC cell lines were analyzed by qPCR, and CD47 expression in OSCC tissues was also verified with IHC staining. An in-house ELISA was performed to analyze circulating anti-CD47 IgG levels in control subjects, oral benign tumor, and OSCC patients, and to detect anti-CD47 IgG-abundant plasma. Three OSCC cell lines were treated with anti-CD47 IgG-abundant and -deficient plasma, respectively, followed by the analysis of cell proliferation, apoptosis, and invasion/metastasis.

RESULTS

The CD47 gene showed the highest expression among 13 genes detected in three OSCC cell lines; its expression was significantly higher in OSCC tissues than adjacent tissues. Plasma anti-CD47 IgG levels showed the differences between control subjects, oral benign tumor, and OSCC patients. Anti-CD47 IgG-abundant plasma could evidently reduce cell viability via suppressing p-AKT expression and inducing cell apoptosis and inhibit the invasion of all three OSCC cell lines.

CONCLUSIONS

Natural autoantibodies against CD47 may be a potential agent for OSCC immunotherapy.

Integrating novel agents into the treatment of advanced mycosis fungoides and Sézary syndrome

Agents targeting the unique biology of mycosis fungoides and Sézary syndrome are quickly being incorporated into clinical management. With these new therapies, we are now capable of inducing more durable responses and even complete remissions in advanced disease, outcomes which were exceedingly rare with prior therapies. Yet, even this new generation of therapies typically produce objective responses in only a minority of patients. As our therapeutic options increase, we are now challenged with selecting treatments from a growing list of options. To gain the full benefit of these novel agents, we must develop strategies to match treatments for the patients most likely to benefit from them. Here, we consider both the current approaches to treatment selection based on clinical features and the future of molecular biomarker-guided therapy for patients with this heterogeneous disease.

A pH-dependent anti-CD47 antibody that selectively targets solid tumors and improves therapeutic efficacy and safety

BACKGROUND

The antiphagocytic molecule CD47 is overexpressed in a wide variety of cancer cells, and antibodies targeting CD47 for cancer therapies are currently under intensive investigation. However, owing to the ubiquitous expression of CD47 on healthy cells, anti-CD47 therapies often achieve only weak therapeutic benefits and can induce severe side effects. Here, we report the generation of a pH-dependent anti-CD47 antibody (BC31M4) which selectively binds to tumors under the acidic solid tumor microenvironment.

METHODS

BC31M4 was generated using antibody phage display and a pH-dependent selection strategy. The pH-dependent binding and blocking activities of BC31M4 were verified using in vitro assays, and the structural basis of the pH-dependent binding property was characterized. BC31M4's antitumor effect was confirmed by both phagocytosis assays and studies in xenograft models. The tumor selectivity, mechanism of action, PK properties, side effects, and therapeutic efficacy were further evaluated in humanized (hCD47 and its receptor hSIRPα) immunocompetent syngeneic mouse models.

RESULTS

The crystal structure reveals that two histidines locate within the CDRs of the light chain directly contribute to the pH-dependent binding of BC31M4. BC31M4 promotes macrophage phagocytosis of tumor cells more potently at acidic-pH than at physiological-pH. Our hCD47/hSIRPα humanized syngeneic mouse model results demonstrated that BC31M4 selectively accumulates in tumors but not in normal tissues. BC31M4 causes minimal side effects and exhibits superior PK properties as compared to the other examined anti-CD47 antibodies. When combined with adoptive T cell transfer, BC31M4 efficiently promotes adaptive immune responses against tumors and also induces immune memory. Moreover, we show that BC31M4's antitumor effects rely on an Fc that mediates strong effector functions.

CONCLUSIONS

Our study illustrates that the development of a tumor-selective, pH-dependent anti-CD47 antibody safely confers strong therapeutic effects against solid tumors, thus providing a promising therapeutic strategy to overcome the challenges of anti-CD47 therapy.

Targeting Lymphoma-associated Macrophage Expansion via CSF1R/JAK Inhibition is a Therapeutic Vulnerability in Peripheral T-cell Lymphomas

The reciprocal relationship between malignant T cells and lymphoma-associated macrophages (LAM) within the tumor microenvironment (TME) is unique, as LAMs are well poised to provide ligands for antigen, costimulatory, and cytokine receptors that promote T-cell lymphoma growth. Conversely, malignant T cells promote the functional polarization and homeostatic survival of LAM. Therefore, we sought to determine the extent to which LAMs are a therapeutic vulnerability in these lymphomas, and to identify effective therapeutic strategies for their depletion. We utilized complementary genetically engineered mouse models and primary peripheral T-cell lymphoma (PTCL) specimens to quantify LAM expansion and proliferation. A high-throughput screen was performed to identify targeted agents that effectively deplete LAM within the context of PTCL. We observed that LAMs are dominant constituents of the TME in PTCL. Furthermore, their dominance was explained, at least in part, by their proliferation and expansion in response to PTCL-derived cytokines. Importantly, LAMs are a true dependency in these lymphomas, as their depletion significantly impaired PTCL progression. These findings were extrapolated to a large cohort of human PTCL specimens where LAM proliferation was observed. A high-throughput screen demonstrated that PTCL-derived cytokines led to relative resistance to CSF1R selective inhibitors, and culminated in the identification of dual CSF1R/JAK inhibition as a novel therapeutic strategy to deplete LAM in these aggressive lymphomas. Malignant T cells promote the expansion and proliferation of LAM, which are a bone fide dependency in these lymphomas, and are effectively depleted with a dual CSF1R/JAK inhibitor.

Significance

LAMs are a therapeutic vulnerability, as their depletion impairs T-cell lymphoma disease progression. Pacritinib, a dual CSF1R/JAK inhibitor, effectively impaired LAM viability and expansion, prolonged survival in preclinical T-cell lymphoma models, and is currently being investigated as a novel therapeutic approach in these lymphomas.

CD47 blockade improves the therapeutic effect of osimertinib in non-small cell lung cancer

The third-generation epidermal growth factor receptor (EGFR) inhibitor osimertinib (OSI) has been approved as the first-line treatment for EGFR-mutant non-small cell lung cancer (NSCLC). This study aims to explore a rational combination strategy for enhancing the OSI efficacy. In this study, OSI induced higher CD47 expression, an important anti-phagocytic immune checkpoint, via the NF-κB pathway in EGFR-mutant NSCLC HCC827 and NCI-H1975 cells. The combination treatment of OSI and the anti-CD47 antibody exhibited dramatically increasing phagocytosis in HCC827 and NCI-H1975 cells, which highly relied on the antibody-dependent cellular phagocytosis effect. Consistently, the enhanced phagocytosis index from combination treatment was reversed in CD47 knockout HCC827 cells. Meanwhile, combining the anti-CD47 antibody significantly augmented the anticancer effect of OSI in HCC827 xenograft mice model. Notably, OSI induced the surface exposure of "eat me" signal calreticulin and reduced the expression of immune-inhibitory receptor PD-L1 in cancer cells, which might contribute to the increased phagocytosis on cancer cells pretreated with OSI. In summary, these findings suggest the multidimensional regulation by OSI and encourage the further exploration of combining anti-CD47 antibody with OSI as a new strategy to enhance the anticancer efficacy in EGFR-mutant NSCLC with CD47 activation induced by OSI.

Targeting macrophages in hematological malignancies: recent advances and future directions

Emerging evidence indicates that the detection and clearance of cancer cells via phagocytosis induced by innate immune checkpoints play significant roles in tumor-mediated immune escape. The most well-described innate immune checkpoints are the "don't eat me" signals, including the CD47/signal regulatory protein α axis (SIRPα), PD-1/PD-L1 axis, CD24/SIGLEC-10 axis, and MHC-I/LILRB1 axis. Molecules have been developed to block these pathways and enhance the phagocytic activity against tumors. Several clinical studies have investigated the safety and efficacy of CD47 blockades, either alone or in combination with existing therapy in hematological malignancies, including myelodysplastic syndrome (MDS), acute myeloid leukemia (AML), and lymphoma. However, only a minority of patients have significant responses to these treatments alone. Combining CD47 blockades with other treatment modalities are in clinical studies, with early results suggesting a synergistic therapeutic effect. Targeting macrophages with bispecific antibodies are being explored in blood cancer therapy. Furthermore, reprogramming of pro-tumor macrophages to anti-tumor macrophages, and CAR macrophages (CAR-M) demonstrate anti-tumor activities. In this review, we elucidated distinct types of macrophage-targeted strategies in hematological malignancies, from preclinical experiments to clinical trials, and outlined potential therapeutic approaches being developed.

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.

Recent Advances in the Management of Relapsed and Refractory Peripheral T-Cell Lymphomas

Peripheral T-cell lymphomas (PTCLs) are a group of heterogeneous lymphomas with poor overall prognosis, particularly in the setting of relapsed/refractory PTCL. Given the limited efficacy of current therapies, several different novel therapies encompassing multiple different mechanisms of action have been evaluated for relapsed and refractory PTCLs. In this review, we explore the current standard of care for relapsed/refractory PTCL, and evaluate in depth novel and emerging therapies, their scientific basis, and current trials for relapsed/refractory PTCL.

Targeting macrophages for enhancing CD47 blockade-elicited lymphoma clearance and overcoming tumor-induced immunosuppression

Tumor-associated macrophages (TAMs) are often the most abundant immune cells in the tumor microenvironment (TME). Strategies targeting TAMs to enable tumor cell killing through cellular phagocytosis have emerged as promising cancer immunotherapy. Although several phagocytosis checkpoints have been identified, the desired efficacy has not yet been achieved by blocking such checkpoints in preclinical models or clinical trials. Here, we showed that late-stage non-Hodgkin lymphoma (NHL) was resistant to therapy targeting phagocytosis checkpoint CD47 due to the compromised capacity of TAMs to phagocytose lymphoma cells. Via a high-throughput screening of the US Food and Drug Administration-approved anticancer small molecule compounds, we identified paclitaxel as a potentiator that promoted the clearance of lymphoma by directly evoking phagocytic capability of macrophages, independently of paclitaxel's chemotherapeutic cytotoxicity toward NHL cells. A combination with paclitaxel dramatically enhanced the anticancer efficacy of CD47-targeted therapy toward late-stage NHL. Analysis of TME by single-cell RNA sequencing identified paclitaxel-induced TAM populations with an upregulation of genes for tyrosine kinase signaling. The activation of Src family tyrosine kinases signaling in macrophages by paclitaxel promoted phagocytosis against NHL cells. In addition, we identified a role of paclitaxel in modifying the TME by preventing the accumulation of a TAM subpopulation that was only present in late-stage lymphoma resistant to CD47-targeted therapy. Our findings identify a novel and effective strategy for NHL treatment by remodeling TME to enable the tumoricidal roles of TAMs. Furthermore, we characterize TAM subgroups that determine the efficiency of lymphoma phagocytosis in the TME and can be potential therapeutic targets to unleash the antitumor activities of macrophages.

Targeting CD47/SIRPα as a therapeutic strategy, where we are and where we are headed

Immunotherapy using PD-1 and CTLA4 inhibitors to stimulate T cell immunity has achieved significant clinical success. However, only a portion of patients benefit from T cell-based immunotherapy. Macrophages, the most abundant type of innate immune cells in the body, play an important role in eliminating tumor cells and infectious microbes. The phagocytic check point protein CD47 inhibits the phagocytic activity of macrophages through binding to SIRPα expressed on macrophages. Blockade of the interaction between CD47 and SIRPα could restore phagocytic activity and eliminate tumor cells in vitro and in vivo. In this manuscript, we review the mechanism of action and development status of agents (antibodies targeting CD47 and SIRPα, SIRPα-Fc fusion proteins, and bi-specific antibodies) that block CD47/SIRPα interaction in preclinical studies and in the clinical setting. In addition, small molecules, mRNA, and CAR-T/M that target the CD47/SIRPα axis are also reviewed in this article.

Macrophage-Based Combination Therapies as a New Strategy for Cancer Immunotherapy

BACKGROUND

Cells of the immune system can inhibit tumor growth and progression; however, immune cells can also promote tumor cell growth, survival, and angiogenesis as a result of the immunosuppressive microenvironments. In the last decade, a growing number of new therapeutic strategies focused on reversing the immunosuppressive status of tumor microenvironments (TMEs), to reprogram the TME to be normal, and to further activate the antitumor functions of immune cells. Most of the "hot tumors" are encompassed with M2 macrophages promoting tumor growth, and the accumulation of M2 macrophages into tumor islets leads to poor prognosis in a wide variety of tumors.

SUMMARY

Therefore, how to uncover more immunosuppressive signals and to reverse the M2 tumor-associated macrophages (TAMs) to M1-type macrophages is essential for reversing the immunosuppressive state. Except for reeducation of TAMs in the cancer immunotherapy, macrophages as central effectors and regulators of the innate immune system have the capacity of phagocytosis and immune modulation in macrophage-based cell therapies.

KEY MESSAGES

We review the current macrophage-based cell therapies that use genetic engineering to augment macrophage functionalities with antitumor activity for the application of novel genetically engineered immune cell therapeutics. A combination of TAM reeducation and macrophage-based cell strategy may bring us closer to achieving the original goals of curing cancer. In this review, we describe the characteristics, immune status, and tumor immunotherapy strategies of macrophages to provide clues and evidences for future macrophage-based immune cell therapies.

Emerging Therapeutic Landscape of Peripheral T-Cell Lymphomas Based on Advances in Biology: Current Status and Future Directions

Simple Summary

Peripheral T-cell lymphoma is a rare but aggressive tumor. Due to its rarity, the disease has not been completely understood. In our review, we look at this lymphoma at the molecular level based on available literature. We highlight the mechanism behind the progression and resistance of this tumor. In doing so, we bring forth possible mechanism that could be exploited through novel chemotherapy drugs. In addition, we also look at the current available drugs used in treating this disease, as well as highlight other new drugs, describing their potential in treating this lymphoma. We comprehensively have collected and present the available biology behind peripheral T-cell lymphoma and discuss the available treatment options.

Abstract

T-cell lymphomas are a relatively rare group of malignancies with a diverse range of pathologic features and clinical behaviors. Recent molecular studies have revealed a wide array of different mechanisms that drive the development of these malignancies and may be associated with resistance to therapies. Although widely accepted chemotherapeutic agents and combinations, including stem cell transplantation, obtain responses as initial therapy for these diseases, most patients will develop a relapse, and the median survival is only 5 years. Most patients with relapsed disease succumb within 2 to 3 years. Since 2006, the USFDA has approved five medications for treatment of these diseases, and only anti-CD30-therapy has made a change in these statistics. Clearly, newer agents are needed for treatment of these disorders, and investigators have proposed studies that evaluate agents that target these malignancies and the microenvironment depending upon the molecular mechanisms thought to underlie their pathogenesis. In this review, we discuss the currently known molecular mechanisms driving the development and persistence of these cancers and discuss novel targets for therapy of these diseases and agents that may improve outcomes for these patients.

Structural analysis and binding sites of inhibitors targeting the CD47/SIRPα interaction in anticancer therapy

Cluster of differentiation 47 (CD47)/signal regulatory protein alpha (SIRPα) is a negative innate immune checkpoint signaling pathway that restrains immunosurveillance and immune clearance, and thus has aroused wide interest in cancer immunotherapy. Blockade of the CD47/SIRPα signaling pathway shows remarkable antitumor effects in clinical trials. Currently, all inhibitors targeting CD47/SIRPα in clinical trials are biomacromolecules. The poor permeability and undesirable oral bioavailability of biomacromolecules have caused researchers to develop small-molecule CD47/SIRPα pathway inhibitors. This review will summarize the recent advances in CD47/SIRPα interactions, including crystal structures, peptides and small molecule inhibitors. In particular, we have employed computer-aided drug discovery (CADD) approaches to analyze all the published crystal structures and docking results of small molecule inhibitors of CD47/SIRPα, providing insight into the key interaction information to facilitate future development of small molecule CD47/SIRPα inhibitors.

SIRPα-αCD123 fusion antibodies targeting CD123 in conjunction with CD47 blockade enhance the clearance of AML-initiating cells

Background

Acute myeloid leukaemia (AML) stem cells (LSCs) cause disease relapse. The CD47 “don’t eat me signal” is upregulated on LSCs and contributes to immune evasion by inhibiting phagocytosis through interacting with myeloid-specific signal regulatory protein alpha (SIRPα). Activation of macrophages by blocking CD47 has been successful, but the ubiquitous expression of CD47 on healthy cells poses potential limitations for such therapies. In contrast, CD123 is a well-known LSC-specific surface marker utilized as a therapeutic target. Here, we report the development of SIRPα-αCD123 fusion antibodies that localize the disruption of CD47/SIRPα signalling to AML while specifically enhancing LSC clearance.

Methods

SIRPα-αCD123 antibodies were generated by fusing the extracellular domain of SIRPα to an αCD123 antibody. The binding properties of the antibodies were analysed by flow cytometry and surface plasmon resonance. The functional characteristics of the fusion antibodies were determined by antibody-dependent cellular phagocytosis and antibody-dependent cellular cytotoxicity assays using primary AML patient cells. Finally, an in vivo engraftment assay was utilized to assess LSC targeting.

Results

SIRPα-αCD123 fusion antibodies exhibited increased binding and preferential targeting of CD123⁺ CD47⁺ AML cells even in the presence of CD47⁺ healthy cells. Furthermore, SIRPα-αCD123 fusion antibodies confined disruption of the CD47-SIRPα axis locally to AML cells. In vitro experiments demonstrated that SIRPα-αCD123 antibodies greatly enhanced AML cell phagocytosis mediated by allogeneic and autologous macrophages. Moreover, SIRPα-αCD123 fusion antibodies efficiently targeted LSCs with in vivo engraftment potential.

Conclusions

SIRPα-αCD123 antibodies combine local CD47 blockade with specific LSC targeting in a single molecule, minimize the risk of targeting healthy cells and efficiently eliminate AML LSCs. These results validate SIRPα-αCD123 antibodies as promising therapeutic interventions for AML.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13045-021-01163-6.

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.

Novel therapies targeting cutaneous T cell lymphomas and their microenvironment

Cutaneous T-cell lymphomas (CTCL) are rare non-Hodgkin lymphomas with a generally indolent course managed with topical, skin-directed therapies. A small subset, however, will progress to advanced stage disease necessitating systemic therapy for disease control. Currently approved therapies have low response rates and generally short durations of response. Novel therapies, therefore, are urgently needed to address this unmet need. In this review, the mechanisms of CTCL pathogenesis and progression, including the role of the tumor microenvironment and molecular alterations, are summarized. Based on these biologic insights, novel therapies currently under investigation and those with a strong preclinical biologic rationale including T cell and macrophage checkpoint inhibitors, epigenetic regulators, targeted antibodies, tyrosine kinase inhibitors, and apoptosis modulating therapies are discussed.

Warburg Effect Is a Cancer Immune Evasion Mechanism Against Macrophage Immunosurveillance

Evasion of immunosurveillance is critical for cancer initiation and development. The expression of “don’t eat me” signals protects cancer cells from being phagocytosed by macrophages, and the blockade of such signals demonstrates therapeutic potential by restoring the susceptibility of cancer cells to macrophage-mediated phagocytosis. However, whether additional self-protective mechanisms play a role against macrophage surveillance remains unexplored. Here, we derived a macrophage-resistant cancer model from cells deficient in the expression of CD47, a major “don’t eat me” signal, via a macrophage selection assay. Comparative studies performed between the parental and resistant cells identified self-protective traits independent of CD47, which were examined with both pharmacological or genetic approaches in in vitro phagocytosis assays and in vivo tumor models for their roles in protecting against macrophage surveillance. Here we demonstrated that extracellular acidification resulting from glycolysis in cancer cells protected them against macrophage-mediated phagocytosis. The acidic tumor microenvironment resulted in direct inhibition of macrophage phagocytic ability and recruitment of weakly phagocytic macrophages. Targeting V-ATPase which transports excessive protons in cancer cells to acidify extracellular medium elicited a pro-phagocytic microenvironment with an increased ratio of M1-/M2-like macrophage populations, therefore inhibiting tumor development and metastasis. In addition, blockade of extracellular acidification enhanced cell surface exposure of CD71, targeting which by antibodies promoted cancer cell phagocytosis. Our results reveal that extracellular acidification due to the Warburg effect confers immune evasion ability on cancer cells. This previously unrecognized role highlights the components mediating the Warburg effect as potential targets for new immunotherapy harnessing the tumoricidal capabilities of macrophages.

Tumor-associated macrophages: potential therapeutic strategies and future prospects in cancer

Macrophages are the most important phagocytes in vivo. However, the tumor microenvironment can affect the function and polarization of macrophages and form tumor-associated macrophages (TAMs). Usually, the abundance of TAMs in tumors is closely associated with poor prognosis. Preclinical studies have identified important pathways regulating the infiltration and polarization of TAMs during tumor progression. Furthermore, potential therapeutic strategies targeting TAMs in tumors have been studied, including inhibition of macrophage recruitment to tumors, functional repolarization of TAMs toward an antitumor phenotype, and other therapeutic strategies that elicit macrophage-mediated extracellular phagocytosis and intracellular destruction of cancer cells. Therefore, with the increasing impact of tumor immunotherapy, new antitumor strategies to target TAMs are now being discussed.

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.

CD47/SIRPα blocking peptide identification and synergistic effect with irradiation for cancer immunotherapy

Background

Immunotherapy has achieved remarkable advances via a variety of strategies against tumor cells that evade immune surveillance. As important innate immune cells, macrophages play important roles in maintaining homeostasis, preventing pathogen invasion, resisting tumor cells and promoting adaptive immune response. CD47 is found to be overexpressed on tumor cells and act as a don’t eat me’ signal, which contributes to immune evasion. Macrophages mediated phagocytosis via blockade CD47/SIRPα (signal regulatory protein alpha) interaction was proved to induce effective antitumor immune response.

Methods

A novel peptide pep-20, specifically targeting CD47 and blocking CD47/SIRPα interaction, was identified via high-throughput phage display library bio-panning. The capability to enhance the macrophage-mediated phagocytosis activities and antitumor effects of pep-20 were investigated. The mechanism of pep-20 to induce T-cell response was explored by ex vivo analysis and confirmed via macrophage depleting strategy. The structure-activity relationship and D-amino acid substitution of pep-20 were also studied. The antitumor effects and mechanism of a proteolysis resistant D-amino acid derivate pep-20-D12 combined with irradiation (IR) were also investigated.

Results

Pep-20 showed remarkable enhancement of macrophage-mediated phagocytosis to both solid and hematologic tumor cells in vitro, and inhibited tumor growth in immune-competent tumor-bearing mice. Furthermore, pep-20 promoted macrophages to mobilize the antitumor T-cell response with minimal toxicity. Furthermore, systemic administration of the derivate pep-20-D12 showed robust synergistic antitumor efficacy in combination with IR.

Conclusion

In summary, these results demonstrated that CD47/SIRPα blocking peptides, pep-20 and its derivate, could serve as promising candidates to promote macrophages-mediated phagocytosis and immune response in 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.

Peripheral T cell lymphomas: from the bench to the clinic

Peripheral T cell lymphomas (PTCLs) are a heterogeneous group of orphan neoplasms. Despite the introduction of anthracycline-based chemotherapy protocols, with or without autologous haematopoietic transplantation and a plethora of new agents, the progression-free survival of patients with PTCLs needs to be improved. The rarity of these neoplasms, the limited knowledge of their driving defects and the lack of experimental models have impaired clinical successes. This scenario is now rapidly changing with the discovery of a spectrum of genomic defects that hijack essential signalling pathways and foster T cell transformation. This knowledge has led to new genomic-based stratifications, which are being used to establish objective diagnostic criteria, more effective risk assessment and target-based interventions. The integration of genomic and functional data has provided the basis for targeted therapies and immunological approaches that underlie individual tumour vulnerabilities. Fortunately, novel therapeutic strategies can now be rapidly tested in preclinical models and effectively translated to the clinic by means of well-designed clinical trials. We believe that by combining new targeted agents with immune regulators and chimeric antigen receptor-expressing natural killer and T cells, the overall survival of patients with PTCLs will dramatically increase.

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.

Checkpoint CD47 Function On Tumor Metastasis And Immune Therapy

The success of cancer immunotherapy on recognition checkpoints for killing cancer cells has raised a great interest of scientists in understanding new and old methods of immunotherapeutic. CD47 (cluster of differentiation 47) is a cell surface glycoprotein and widely expressed on cells, which belongs to the immunoglobulin (Ig) superfamily as a cell membrane receptor which serves in immune therapy. CD47 is an inhibitory receptor expressed on tumor cell surface and interacts with signal receptor protein-alpha (SIPR-α, also named CD172a or SHPS-1) which may escape from immune cells such as macrophage and T cells. Meanwhile, tumor cells express high CD47 protein which may secrete exosomes with high CD47 expression. The high CD47 expression-exosomes could serve the tumor metastasis process and provide transfer convenience for tumors on the microenvironment. CD47 on cancer cells can also affect the migration and invasion of cells. The high CD47 expression on tumor or CTC (circulating tumor cell) surface means the stronger migration and invasion and makes them escape from immune cells for phagocytosis such as T cells, NK (natural killer) cells and macrophage, which could be used for diagnosis and prognosis on cancer patients. Meanwhile, targeting CD47 combined with other biomarkers such as EpCAM (epithelial cell adhesion molecule), CD44, etc on cancer surface could be used to isolate CTCs from patients' blood. In terms of treatment, anti-CD47 antibody combined with another antibody such as anti-PD-L1 (programmed death-ligand 1) antibody or drugs such as rituximab, DOX or oxaliplatin also has better therapeutic effects and antitumor function to tumors. Using nanomaterials as an intermediary for CD47-related immune therapy could greatly increase the therapeutic effect and overcome multiple biological barriers for anti-CD47 antibody in vivo. In this review, we discuss the important role and the function of CD47 in tumor metastasis and also provide a reference for related research.