Abstract 2951: NI-2901, an affinity-optimized CD47xPD-L1 bispecific antibody for dual immune checkpoint blockade

Abstract To enhance efficacy of anti-PD-1/PD-L1 antibodies, many combinations with various therapeutic agents are being investigated. Blocking the CD47/SIRPα myeloid checkpoint with monoclonal antibodies (mAbs) or decoy receptors is emerging as an effective approach to mobilize dendritic cells and macrophages to support T-cell mediated antitumor responses. The benefit of combining CD47/SIRPα and PD-1/PD-L1 blockade to improve tumor control has been convincingly demonstrated in preclinical models and is now being explored in patients. However, CD47 mAbs are hindered by ubiquitous CD47 expression, leading to pharmacokinetic (PK) and safety issues.NI-2901, an IgG4 CD47xPD-L1 bispecific antibody (bsAb), was generated using the κλ-body platform. In vitro assays were used to characterize its binding profile and checkpoint inhibition as well as its capacity to enhance T-cell activation and macrophage-mediated phagocytosis of tumor cells. PD-L1-independent CD47 antitumor activity was assessed in vivo in a PD-L1-negative xenograft model and compared to the anti-CD47 magrolimab analog. PK and tolerability of NI-2901 were evaluated in non-human primates (NHP), allowing for translational modeling to predict PK and dosing regimens in humans. Consistent with its intermediate affinity to CD47, NI-2901 shows lower binding to RBC as compared to magrolimab analog and is still able to induce CD47/SIRPα blockade on PD-L1-negative tumor cells, that is significantly enhanced once PD-L1 is expressed. As a result, the bsAb is able to enhance the phagocytosis of PD-L1-negative and -positive tumor cell lines induced by mAbs targeting tumor-associated antigens (e.g. rituximab, trastuzumab and anti-CD19) and demonstrates in vivo activity in the Raji B-cell lymphoma xenograft model. Given its high affinity for PD-L1, NI-2901 triggers an effective blockade of the PD-1/PD-L1 interaction, inducing T-cell activation in vitro to a degree similar to anti-PD-L1 benchmark antibodies atezolizumab and avelumab. In immunocompetent huCD47/huSIRPα-transgenic mice engrafted with MC38 cells engineered to express human PD-L1 and CD47, NI-2901 displayed significant anti-tumor activity. In a NHP study, NI-2901 was well-tolerated after four weekly injections at 30mg/kg, showing no signs of hemotoxicity. In contrast, the magrolimab analog induced a significant drop in RBC already after a single injection at 10mg/kg. PK modeling and simulations in humans suggest a more favorable dosing regimen as compared to CD47 targeted approaches. In conclusion, NI-2901, a dual immune checkpoint inhibitor, triggered effective T-cell activation and enhanced phagocytosis of tumor cells. Also, NI-2901 demonstrated significant antitumor activity in vivo and is therefore expected to show improved clinical efficacy over PD-1/PD-L1 blockade alone. The bsAb was well-tolerated in NHP without inducing RBC or platelet depletion. Citation Format: Xavier Chauchet, Sebastien Calloud, Pauline LLoveras, Nicolas Bosson, Margaux Legrand, Laurence Chatel, Laura Cons, Adeline Lesnier, Pauline Malinge, Guillemette Pontini, Christophe Guillamo, Dmitry Shchelokov, Oleg Demin, Ulla Ravn, Valéry Moine, Bruno Daubeuf, Giovanni Magistrelli, Yves Poitevin, Susana Salgado-Pires, Limin Shang, Nicolas Fischer, Walter Ferlin, Krzysztof Masternak. NI-2901, an affinity-optimized CD47xPD-L1 bispecific antibody for dual immune checkpoint blockade [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2951.