Anti-GD2 synergizes with CD47 blockade to mediate tumor eradication

The disialoganglioside GD2 is overexpressed on several solid tumors, and monoclonal antibodies targeting GD2 have substantially improved outcomes for children with high-risk neuroblastoma. However, approximately 40% of patients with neuroblastoma still relapse, and anti-GD2 has not mediated significant clinical activity in any other GD2+ malignancy. Macrophages are important mediators of anti-tumor immunity, but tumors resist macrophage phagocytosis through expression of the checkpoint molecule CD47, a so-called 'Don't eat me' signal. In this study, we establish potent synergy for the combination of anti-GD2 and anti-CD47 in syngeneic and xenograft mouse models of neuroblastoma, where the combination eradicates tumors, as well as osteosarcoma and small-cell lung cancer, where the combination significantly reduces tumor burden and extends survival. This synergy is driven by two GD2-specific factors that reorient the balance of macrophage activity. Ligation of GD2 on tumor cells (a) causes upregulation of surface calreticulin, a pro-phagocytic 'Eat me' signal that primes cells for removal and (b) interrupts the interaction of GD2 with its newly identified ligand, the inhibitory immunoreceptor Siglec-7. This work credentials the combination of anti-GD2 and anti-CD47 for clinical translation and suggests that CD47 blockade will be most efficacious in combination with monoclonal antibodies that alter additional pro- and anti-phagocytic signals within the tumor microenvironment.

261 A functional genetic screen uncovers regulators of intratumoral macrophage function and reveals CD24 as a novel target for cancer immunotherapy by macrophages

Background

Cancer cells are capable of evading clearance by macrophages through the overexpression of anti-phagocytic, innate immune checkpoint molecules called ‘don’t eat me’ signals, including CD47,1 PD-L1,2 and MHC class I.3 Monoclonal antibodies that antagonize the interaction of ‘don’t eat me’ signals with their macrophage-expressed receptors have demonstrated therapeutic potential in several cancers. However, variability in the magnitude and durability of the responses to these agents has suggested the presence of additional, as yet unknown innate immune checkpoints. Here, we present a functional screening platform which identifies tumor-specific regulators of intratumoral macrophage function. We show that CD24 is a dominant innate immune checkpoint in many solid tumors, including ovarian cancer and breast cancer.4

Methods

By applying our screening method, we uncovered the novel innate immune checkpoint molecule, CD24. To characterize the role of CD24 as a macrophage checkpoint, we leveraged the MCF-7 human xenograft tumor model and the ID8 syngeneic ovarian cancer tumor model. We evaluated the anti-tumor effect of CD24 antagonism through genetic ablation experiments in addition to therapeutic CD24 monoclonal antibody (mAb) blockade. We also utilized primary human immune cells and tumor specimens to assess the effect of CD24 blockade either alone or in combination with additional tumor-targeting antibodies.

Results

We demonstrate that CD24 promotes immune evasion through its interaction with the inhibitory macrophage receptor Siglec-10. Genetic ablation of either CD24 or Siglec-10, as well as blockade of the CD24–Siglec-10 interaction using monoclonal antibodies, robustly augmented the phagocytosis of all CD24-expressing human tumors that we tested. Therapeutic blockade of CD24 resulted in a macrophage-dependent reduction of tumor growth in vivo and an increase in survival time. The therapeutic efficacy of anti-CD24 mAbs was enhanced when combined with a second anti-tumor antibody. In particular, dual treatment of HER2-positive breast cancers with anti-CD24 mAb and trastuzumab, augmented phagocytosis relative to either treatment alone, even among cancers with inherent trastuzumab resistance (figure 1).

Abstract 261 Figure 1

Macrophage checkpoints are therapeutic targets. (A) There are four defined innate immune checkpoint signaling axes which exist between macrophages and cancer cells, which all rely on ITIM or ITSM signaling on the cytoplasmic side of the macrophage. (B) Phagocytosis of BT-474 (n = 8 donors) in the presence of anti-CD24 mAb, anti-HER2 mAb or dual treatment, compared with IgG control.

Conclusions

These data reveal CD24 as a highly expressed, anti-phagocytic signal in several cancers, and demonstrate the therapeutic potential for CD24 blockade in cancer immunotherapy, either alone or in combination with existing anticancer treatments. Collectively, this work suggests a new paradigm that innate immune checkpoints are redundant and employed in a tissue-specific and even tumor-specific manner, and makes clear the need to measure the collective expression of these ‘don’t eat me’ signals in order to optimize patient responses to both innate and adaptive immunotherapies.

References

Majeti R, et al. CD47 is an adverse prognostic factor and therapeutic antibody target on human acute myeloid leukemia stem cells. Cell 2009;138: 286–299.

Gordon SR, et al. PD-1 expression by tumour-associated macrophages inhibits phagocytosis and tumour immunity. Nature 2017;545:495–499.

Barkal AA, et al. Engagement of MHC class I by the inhibitory receptor LILRB1 suppresses macrophages and is a target of cancer immunotherapy. Nat Immunol 2018;19:76–84.

Barkal AA, Brewer RE, Markovic M, Kowarsky MA, Barkal SA, Zaro BW, Krishnan V, Hatakeyama J, Dorigo O, Barkal LJ, Weissman IL. CD24 signaling through macrophage siglec-10 is a new target for cancer immunotherapy. Nature 2019;572:392–396.

Ethics Approval

The Human Immune Monitoring Center Biobank and the Stanford Tissue Bank all received IRB approval from the Stanford University Administrative Panels on Human Subjects Research and complied with all ethical guidelines for human subjects research to obtain samples from patients with ovarian cancer and breast cancer, and received informed consent from all patients.

Eradication of Canine Diffuse Large B-Cell Lymphoma in a Murine Xenograft Model with CD47 Blockade and Anti-CD20

Cancer immunotherapies hold much promise, but their potential in veterinary settings has not yet been fully appreciated. Canine lymphomas are among the most common tumors of dogs and bear remarkable similarity to human disease. In this study, we examined the combination of CD47 blockade with anti-CD20 passive immunotherapy for canine lymphoma. The CD47/SIRPα axis is an immune checkpoint that regulates macrophage activation. In humans, CD47 is expressed on cancer cells and enables evasion from phagocytosis. CD47-blocking therapies are now under investigation in clinical trials for a variety of human cancers. We found the canine CD47/SIRPα axis to be conserved biochemically and functionally. We identified high-affinity SIRPα variants that antagonize canine CD47 and stimulate phagocytosis of canine cancer cells in vitro When tested as Fc fusion proteins, these therapeutic agents exhibited single-agent efficacy in a mouse xenograft model of canine lymphoma. As robust synergy between CD47 blockade and tumor-specific antibodies has been demonstrated for human cancer, we evaluated the combination of CD47 blockade with 1E4-cIgGB, a canine-specific antibody to CD20. 1E4-cIgGB could elicit a therapeutic response against canine lymphoma in vivo as a single agent. However, augmented responses were observed when combined with CD47-blocking therapies, resulting in synergy in vitro and in vivo and eliciting cures in 100% of mice bearing canine lymphoma. Our findings support further testing of CD47-blocking therapies alone and in combination with CD20 antibodies in the veterinary setting. Cancer Immunol Res; 4(12); 1072-87. ©2016 AACR.

CD47-blocking immunotherapies stimulate macrophage-mediated destruction of small-cell lung cancer

Small-cell lung cancer (SCLC) is a highly aggressive subtype of lung cancer with limited treatment options. CD47 is a cell-surface molecule that promotes immune evasion by engaging signal-regulatory protein alpha (SIRPα), which serves as an inhibitory receptor on macrophages. Here, we found that CD47 is highly expressed on the surface of human SCLC cells; therefore, we investigated CD47-blocking immunotherapies as a potential approach for SCLC treatment. Disruption of the interaction of CD47 with SIRPα using anti-CD47 antibodies induced macrophage-mediated phagocytosis of human SCLC patient cells in culture. In a murine model, administration of CD47-blocking antibodies or targeted inactivation of the Cd47 gene markedly inhibited SCLC tumor growth. Furthermore, using comprehensive antibody arrays, we identified several possible therapeutic targets on the surface of SCLC cells. Antibodies to these targets, including CD56/neural cell adhesion molecule (NCAM), promoted phagocytosis in human SCLC cell lines that was enhanced when combined with CD47-blocking therapies. In light of recent clinical trials for CD47-blocking therapies in cancer treatment, these findings identify disruption of the CD47/SIRPα axis as a potential immunotherapeutic strategy for SCLC. This approach could enable personalized immunotherapeutic regimens in patients with SCLC and other cancers.

Influence of sialic acid groups on the retention of glycosphingolipids in blood plasma

The removal of several glycosphingolipids from the circulation and their disposal in different tissue and fluid compartments was studied in adult rats. 3H-labeled dihydro analogs of several glycosphingolipids were injected intravenously and radioactivity was measured in arterial blood samples at subsequent time intervals, to obtain half life values for the labeled compound in the plasma. Half life values of less than 1 min were obtained for neutral glycosphingolipids whereas the half lives of labeled gangliosides were much longer and ranged from 3.8 to 21 h. The prompt removal of labeled neutral glycosphingolipids but not of the gangliosides indicates that sialic acid groups play a significant role in the retention of glycosphingolipids in the circulation. The results suggest that neutral glycosphingolipids are rapidly exchanged with their counterparts in a large extraplasma pool and that a major portion of this exchange could occur between plasma and liver. The detection of only a minute fraction of the injected glycosphingolipids in the cerebrospinal fluid indicates that a blood-cerebrospinal fluid barrier exists for these compounds in the rat.