Targeting CD47 and CD19 with a bispecific antibody, triggers effective M1 and M2-mediated phagocytosis of malignant B cells by inducing Fc-mediated effector functions and blocking the CD47 “do not eat signal”
Eric Hatterer1, Françoise Richard1, Leticia Barba1, Anne Papaioannou1, Simon Legallou2, Karin Tarte2, Thierry Fest2, Nicolas Fischer1, Krzysztof Masternak1, Marie Kosco-Vilbois1, Walter Ferlin1, Vanessa Buatois1 & Limin Shang1
1Novimmune S.A., Geneva, Switzerland, 2Rennes University, INSERM Unit 917, Rennes, France
Many cancers up-regulate the “don’t eat me” signal of phagocytosis, CD47, to escape immune surveillance. Monoclonal antibodies (mAbs) that interfere with CD47-SIRPα axis release the brakes on this innate immune checkpoint and promote tumor removal by infiltrating phagocytes. The ubiquitous expression of CD47, however, hinders the use of mAbs as therapeutic agents. Here, we describe a fully human IgG1 bispecific antibody (BsAb), targeting CD47 and CD19. This approach affords the selective targeting of CD47 to CD19+ B cells. Using in vitro differentiated macrophages, we assessed the ability of the BsAb to trigger phagocytosis by M1, M2a and M2c macrophage subtypes. Effective phagocytosis of the Burkitt's lymphoma-derived cell line, Raji, was induced by all subtypes. Using specific blocking mAbs to FcgR I, -II and -III, respectively, the obligate role for FcgR interaction in driving antibody dependent cellular phagocytosis (ADCP) was demonstrated. Interestingly, while the three FcgRs were implicated in the BsAb-mediated ADCP, the relative contribution of each FcgR was conditional on the macrophage subtype used in the experiment. Additionally, the ADCP-index (determined by the number of phagocytosed malignant B cells per macrophage) was significantly higher when the BsAb was used as compared to traditional CD19 or CD20 mAbs. Finally, the use of CD47-silenced Raji cells confirmed the enhanced phagocytic potential unleashed by macrophages upon ablation of the CD47-SIRPα axis. Collectively, these data propose the use of a BsAb approach to effectively harness the phagocytic potential of macrophages to kill malignant B cells by both Fc-mediated effector function and CD47 blockade.