Abstract B54: Antagonizing CD47-SIRP alpha interaction with a bispecific antibody: A novel cancer immunotherapy approach

CD47 is a ubiquitous cell surface glycoprotein that serves as a negative regulator of numerous innate immune functions such as phagocytosis, neutrophil inflammatory responses or dendritic cell maturation and activation. In particular, the interaction of CD47 with Signal Regulatory Protein Alpha (SIRP alpha) on myeloid cells is a mechanism of self-recognition, a ‘don9t eat me’ signal used by healthy cells to impede their elimination by phagocytes. Cancer cells often up-regulate CD47 expression, which helps them to evade immune surveillance and killing. What is more, increased CD47 levels are generally predictive of poor clinical outcome. Inhibiting CD47-SIRP alpha interaction represents therefore an attractive, generally applicable therapeutic strategy. Yet, achieving that goal with an anti-CD47 monoclonal antibody (Mab) may be challenging in practice, given the ubiquitous expression of the target. The “drug sink” represented by erythrocytes, platelets and other CD47-expressing cells may lead to a rapid elimination of an anti-CD47 Mab through target-mediated drug disposition; another likely consequence of ubiquitous CD47 expression are on-target toxicities like, e.g., anemia. To overcome these limitations, we have developed dual-targeting bispecific antibodies to CD47 and different Tumor-Associated Antigens (TAAs). Dual targeting CD47/TAA bispecific antibodies bind preferentially to TAA-expressing cancer cells and enable selective CD47 neutralization at the same time sparing healthy TAA-negative cells. Various TAAs are currently being pursued at Novimmune (e.g., CD19, mesothelin, or glypican 3). Such dual targeting CD47/TAA bispecific antibodies have the kappa/lambda body format i.e., they are fully human bispecific IgGs composed of a high-affinity anti-TAA arm, a CD47-neutralizing arm, and an unmodified IgG1 Fc. So far, only CD47/CD19 kappa/lambda bodies have been thoroughly characterized in vitro and in vivo. Various human B cell leukemia and lymphoma lines were used to demonstrate selective, CD19-dependent binding of these CD47/CD19 kappa/lambda bodies. As anticipated, the neutralization of the CD47-SIRP alpha interaction was also CD19-dependent, and led to the enhancement of Fc-mediated cancer cell killing through ADCP (antibody mediated cellular phagocytosis) or ADCC (antibody mediated cellular cytotoxicity). Efficient killing of CD19-positive cancer cells was also observed in vivo using a localized tumor xenograft model with NOD/SCID mice implanted with Raji Burkitt lymphoma cells. A dose dependent inhibition of tumor growth or tumor regression was observed, depending on the potency of the CD47-neutralizing arm used to generate the kappa/lambda body. In parallel, a single dose PK study in cynomolgus demonstrated favorable elimination kinetics, comparable to human IgG Mab. Moreover, no effects on hematological parameters were apparent at either of the doses tested (0.5 and 10 mg/kg). The example of CD47/CD19 kappa/lambda bodies illustrates the power of the dual-targeting approach: A favorable safety profile and pharmacokinetics could be achieved in parallel to potent inhibition of the CD47-SIRP alpha interaction and effective cancer cell killing. Antagonizing CD47-SIRP alpha interaction with bispecific antibodies is therefore an attractive immune-potentiating strategy. Because of its distinct mechanism of action and the ability to that harnesses the innate immunity to fight cancer, CD47/TAA bispecific antibodies would be good candidates for combination therapies with immune checkpoint inhibitors or other immunotherapeutics. Citation Format: Krzysztof Masternak, Zoe Johnson, Vanessa Buatois, Francois Rousseau, Giovanni Magistrelli, Valery Moine, Ulla Ravn, Franck Gueneau, Lucile Broyer, Susana Salgado Pires, Maureen Deehan, Nicolas Fischer, Walter Ferlin, Marie Kosco-Vilbois. Antagonizing CD47-SIRP alpha interaction with a bispecific antibody: A novel cancer immunotherapy approach. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy: A New Chapter; December 1-4, 2014; Orlando, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2015;3(10 Suppl):Abstract nr B54.