CD40 Enhances Type I Interferon Responses Downstream of CD47 Blockade, Bridging Innate and Adaptive Immunity

Disrupting the binding of CD47 to SIRPa has emerged as a promising immunotherapeutic strategy for advanced cancers by potentiating antibody-dependent cellular phagocytosis (ADCP) of targeted antibodies. Preclinically, CD47/SIRPa blockade induces antitumor activity by increasing the phagocytosis of tumor cells by macrophages and enhancing the cross-presentation of tumor antigens to CD8(+) T cells by dendritic cells; both of these processes are potentiated by CD40 signaling. Here we generated a novel, two-sided fusion protein incorporating the extracellular domains of SIRPa and CD40L, adjoined by a central Fc domain, termed SIRP alpha-Fc-CD40L. SIRP alpha-Fc-CD40L bound CD47 and CD40 with high affinity and activated CD40 signaling in the absence of Fc receptor cross-linking. No evidence of hemolysis, hemagglutination, or thrombocytopenia was observed in vitro or in cynomolgus macaques. Murine SIRP alpha-Fc-CD40L outperformed CD47 blocking and CD40 agonist antibodies in murine CT26 tumor models and synergized with immune checkpoint blockade of PD-1 and CTLA4. SIRP alpha-Fc-CD40L activated a type I interferon response in macrophages and potentiated the activity of ADCP-competent targeted antibodies both in vitro and in vivo. These data illustrated that whereas CD47/SIRP alpha inhibition could potentiate tumor cell phagocytosis, CD40-mediated activation of a type I interferon response provided a bridge between macrophage- and T-cell-mediated immunity that significantly enhanced durable tumor control and rejection.