Abstract B37: NI-1701, a bispecific antibody for selective neutralization of CD47 in B cell malignancies
Authors: Masternak Krzysztof , Chauchet Xavier , Buatois Vanessa , Salgado-Pires Susana , Shang Limin , Johnson Zoë , Dheilly Elie , Moine Valéry , Ferlin Walter G. , Kosco-Vilbois Marie H. , Fischer Nicolas 
Published: March 2017

Abstract
Upregulation of the immune checkpoint receptor, CD47, on cancer cells promotes immune evasion and is correlated with poor clinical outcome. CD47 is therefore an attractive immuno-oncology target but also a challenging one, given its ubiquitous distribution in healthy tissues. Bispecific antibodies (biAbs) offer superior selectivity as compared to mAbs, as they combine two antigen specificities in one molecule allowing the simultaneous targeting of two cell surface receptors. We used such a dual targeting design to create NI-1701, a biAb that pairs an anti CD47 arm with a high-affinity arm specific for CD19, a clinically validated target expressed by B leukemias and lymphomas. The target cell selectivity of NI-1701 relies principally on the binding affinity of the biAbs anti-CD19 arm. Thus, NI-1701 binds weakly to CD19-negative healthy cells expressing physiological levels of CD47, such as erythrocytes, platelets or T cells. In contrast, NI-1701 binds strongly to CD19-positive cells and blocks CD47 upon concurrent engagement of the two targets at the cell surface. As shown by numerous experiments involving CD19-positive human cancer cell lines and patients cells, NI-1701 effectively kills B cell tumors through antibody-dependent cellular phagocytosis (ADCP) and antibody-dependent cell-mediated cytotoxicity (ADCC). Furthermore, NI-1701 controls the growth of sub-cutaneous Raji cell tumors, in a way that was dependent on the co-ligation of both CD19 and CD47 antigens. Examination of the excised tumors revealed that NI-1701 actively reshaped the tumors microenvironment by enhancing the phagocytic activity of macrophages and by reducing the proportion of CD11b+Gr1+myeloid-derived suppressor cells (MDSCs) infiltrating the xenograft tumors. In disseminated mouse models of B-ALL, using both leukemia cell lines and patient-derived xenografts (PDX), NI-1701 was able to reduce tumor burden in peripheral blood and to block the spread of tumor cells to the bone marrow. The therapeutic potential of NI-1701 was also expanded to Diffuse Large B-Cell Lymphoma (DLBCL) using a PDX model, in which the tumor burden was abrogated with significantly higher efficacy than the BTK inhibitor, ibrutinib. In vitro and in vivo studies demonstrated a favorable pharmacokinetic (PK) and tolerability profile of NI-1701. Single and multiple dose studies in non-human primates showed typical IgG PK and no effects on hematological parameters (e.g., red blood cell and platelet counts) up to 100mg/kg, the highest dose tested. Accordingly, in vitro safety testing with human blood showed no evidence of platelet activation or aggregation, hemagglutination or hemolysis event at high antibody concentrations. We also show that NI-1701 target cell selectivity is important for the preservation of tumor cell killing efficacy in the presence of CD47 antigen sink. ADCP and ADCC experiments performed with an excess of bystander CD47-positive cells demonstrate that NI-1701-induced tumor cell killing is not affected by the presence of such antigen sink, in contrast to anti-CD47 mAbs, which loose potency in this situation. We conclude that the dual targeting biAb approach allows a safe yet effective blockade of CD47 due to selectivity for a B cell associated antigen, resulting in impressive tumor cell killing in a range of preclinical models. Thus, dual-targeting biAb open the way to the safe and efficacious therapeutic neutralization of CD47, an immune checkpoint receptor hijacked by cancer cells. NI-1701 is in preclinical enabling studies in preparation for a Phase I clinical study in patients with B cell malignancies, planned for 2017.
Citation Format: Krzysztof Masternak, Xavier Chauchet, Vanessa Buatois, Susana Salgado-Pires, Limin Shang, Zoë Johnson, Elie Dheilly, Valéry Moine, Walter G. Ferlin, Marie H. Kosco-Vilbois, Nicolas Fischer. NI-1701, a bispecific antibody for selective neutralization of CD47 in B cell malignancies. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2016 Oct 20-23; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2017;5(3 Suppl):Abstract nr B37.