Abstract 2440: CD47 is a prognostic factor and an antibody target that synergizes with rituximab to eradicate non-Hodgkin lymphoma

Abstract

Abstract Monoclonal antibodies are standard therapeutics for several cancers including the anti-CD20 antibody rituximab for B cell non-Hodgkin lymphoma (NHL). Rituximab and other antibodies are not curative, and must be combined with cytotoxic chemotherapy for clinical benefit. Here we identify CD47 as an attractive monoclonal antibody target in NHL. A major function of CD47 is to inhibit phagocytosis, through binding its receptor, SIRP-alpha, on phagocytes. We hypothesize that NHL cells over-express CD47 to evade immune phagocytosis and that blockade of CD47 signaling by a monoclonal antibody can eliminate NHL cells by enabling phagocytic engulfment. Here we investigate the therapeutic potential of an anti-CD47 antibody alone and in combination with rituximab for the treatment of NHL. We predict that the combination of anti-CD47 antibody and rituximab through utilization of two independent antibody mechanisms will result in synergistic phagocytosis and elimination of NHL cells. We found that CD47 protein is highly expressed on primary human NHL cells compared to normal B cell counterparts. Higher CD47 gene expression predicted an inferior outcome in several cohorts of NHL patients, providing independent prognostic value. Blocking anti-CD47 antibodies preferentially enabled phagocytosis of NHL cells but not normal cell counterparts in vitro while the combination of anti-CD47 antibody and rituximab resulted in synergistic phagocytosis of NHL cells. In vivo, anti-CD47 antibody treatment of human NHL-engrafted mice reduced lymphoma burden and prolonged survival compared to IgG control treatment. Furthermore, anti-CD47 antibody treatment in combination with rituximab led to elimination of lymphoma and cure of NHL-engrafted mice compared to either antibody treatment as a single agent. The above in vivo results were observed in both a disseminated and localized human NHL cell line mouse model as well as in primary human lymphoma xenotransplants. These antibodies synergized through a novel mechanism combining Fc receptor (FcR)-dependent and FcR-independent stimulation of phagocytosis that might be applicable to many other cancers. Together, these data provide the rationale for utilizing an anti-CD47 antibody either alone or in combination with rituximab in treating human NHL. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2440.