Abstract 1495: Neutralization of CD47 in cancer cells with bispecific antibodies harnesses the phagocytic potential of tumor-infiltrating macrophages
Authors: Masternak Krzysztof , Moine Valéry , Broyer Lucile , Chauchet Xavier , Buatois Vanessa , Dheilly Elie , Majocchi Stefano , Magistrelli Giovanni , Poitevin Yves , Ravn Ulla , Hatterer Eric , Salgado Pires Susana , Shang Limin , Johnson Zoë , Ferlin Walter , Kosco-Vilbois Marie , Fischer Nicolas 
Published: July 2016

Abstract
The inhibitory “don't eat me” signal of phagocytosis, CD47, is commonly overexpressed in cancer cells, a feature generally associated with poor prognosis. CD47 overexpression in cancer is believed to promote immune evasion by allowing tumor cells to “hide” from innate immune phagocytes like macrophages or dendritic cells. CD47 is therefore a new type of immune checkpoint and an attractive target for cancer immunotherapy. However, as CD47 is also universally expressed on healthy cells, clinical development of anti-CD47 monoclonal antibodies is inevitably limited by toxicity and/or pharmacokinetic issues. To overcome these liabilities, we engineered dual-targeting bispecific antibodies (biAbs) for selective blockade of CD47 in malignant cells. By tethering the biAbs strongly to cells expressing a tumor-associated antigen (TAA), such as CD19 or mesothelin, CD47 is blocked selectively on the target cell. In contrast, as these biAbs will lose the avidity effect with TAA-negative cells, they will bind with very low affinity to healthy cells which express CD47. In this manner, dual-targeting should help to sidestep safety and pharmacokinetic “sink” problems resulting from ubiquitous CD47 expression. Studies in non-human primates performed with the CD47/CD19 therapeutic candidate NI-1701 confirmed this prediction, demonstrating normal IgG1 pharmacokinetics and absence of toxicity, even at high antibody doses (100 mg/kg per week).
Hence, the mechanism of action of CD47/TAA dual-targeting antibodies is heavily contingent upon target co-engagement. In vitro, CD19-positive or mesothelin-positive cancer cells are efficiently killed through antibody dependent cellular phagocytosis (ADCP) and/or antibody-dependent cell-mediated cytotoxicity (ADCC) in the presence of effector cells, such as macrophages or natural killer cells, and the corresponding dual-targeting CD47/TAA antibodies. Their enhanced ability to induce tumor cell phagocytosis was also demonstrated in vivo, in xenograft models: Mice implanted with subcutaneous human B cell lymphoma xenografts controlled tumor growth following therapy with NI-1701, contrary to mice treated with an anti-CD19 mAb. Importantly, tumor microenvironment (TME) studies revealed that mouse macrophages infiltrating human tumors engulfed tumor cells more frequently—and at a significantly higher rate—in animals treated with NI-1701 as compared to controls. Moreover, the observed superior phagocytic activity of tumor-infiltrating macrophages was associated with a reduction of granulocytic myeloid-derived suppressor cell infiltrates, suggesting that NI-1701 may favor the establishment of a tumor-hostile, immunostimulatory TME. We conclude that dual-targeting CD47/TAA bispecific antibodies may open the way to the safe and efficacious therapeutic neutralization of CD47, the universal ‘don't eat me’ signal hijacked by cancer cells.
Citation Format: Krzysztof Masternak, Valéry Moine, Lucile Broyer, Xavier Chauchet, Vanessa Buatois, Elie Dheilly, Stefano Majocchi, Giovanni Magistrelli, Yves Poitevin, Ulla Ravn, Eric Hatterer, Susana Salgado Pires, Limin Shang, Zoë Johnson, Walter Ferlin, Marie Kosco-Vilbois, Nicolas Fischer. Neutralization of CD47 in cancer cells with bispecific antibodies harnesses the phagocytic potential of tumor-infiltrating macrophages. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1495.