Abstract 3429: NI-2601, an Fc-active CD47xPD-L1 bispecific antibody that selectively targets CD47 on PD-L1-positive tumors

Abstract PD-1/PD-L1 blockade has improved survival across many types of cancer, but only in a minority of patients. Co-targeting PD-1/PD-L1 and the CD47/SIRPα myeloid checkpoint with monoclonal antibody (mAb) combinations showed increased antitumor responses in preclinical studies. However, CD47 mAbs are hindered by ubiquitous CD47 expression leading to rapid target-mediated clearance and safety concerns, including anemia and thrombocytopenia. Consequently, dual-targeting CD47xPD-L1 bispecific antibodies (bsAbs) enabling selective inhibition of CD47 on PD-L1-positive tumors offer an alternative approach. A fully human bsAb pairing a high affinity PD-L1 arm to a low affinity CD47 arm was generated using the κλ-body platform. The latter is also used in our CD47xCD19 bispecific antibody NI-1701/TG-1801, currently in phase I clinical trials (NCT03804996, NCT04806035). The resulting CD47xPD-L1 bsAb of human IgG1 isotype (NI-2601) was evaluated in various binding and receptor-blocking assays, and then tested for its capacity to enhance T-cell activation in vitro and induce Fc-mediated killing of tumor cells through phagocytosis (ADCP) and antibody-dependent cell cytotoxicity (ADCC). A surrogate bsAb was also evaluated in vivo in a syngeneic mouse model. NI-2601 demonstrated effective blockade of PD-1/PD-L1 interaction, and T-cell activation in vitro, similar to the anti-PD-L1 clinical benchmarks atezolizumab and avelumab. Consistent with its low-affinity CD47 arm, the bsAb did not bind to red blood cells (RBC) and CD47 blockade was driven by PD-L1 co-engagement. Using a panel of tumor cell lines, expressing various PD-L1 levels, NI-2601 showed superior activity in ADCP and ADCC as compared to the anti-PD-L1 IgG1 mAb, avelumab. The anti-tumor activity of this approach using surrogate CD47xPD-L1 bsAb was confirmed in a syngeneic MC38 colon carcinoma model. Thus, NI-2601 is able to harness Fc-effector function to eliminate PD-L1-positive tumor cells while sparing PD-L1-negative cells, such as RBC or platelets. Pharmacokinetic and tolerability studies in non-human primate are planned for 2022. Citation Format: Xavier Chauchet, Nicolas Bosson, Margaux Legrand, Laura Cons, Sébastien Calloud, Alizée Viandier, Françoise Richard, Pauline Malinge, Tereza Bautzova, Jérémie Bourguignon, Guillemette Pontini, Elise Penarrieta, Mengzhu Sun, Ulla Ravn, Valéry Moine, Giovanni Magistrelli, Yves Poitevin, Stéphanie Hugues, Limin Shang, Walter Ferlin, Krzysztof Masternak. NI-2601, an Fc-active CD47xPD-L1 bispecific antibody that selectively targets CD47 on PD-L1-positive tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3429.