Therapeutic Antibody Targeting of CD47 Synergizes with Rituximab to Completely Eradicate Human B-Cell Lymphoma Xenografts.

Abstract 2716

Poster Board II-692

The anti-CD20 antibody, rituximab, is standard therapy for many CD20 positive B-cell lymphomas, significantly improving long-term survival in combination with chemotherapy. However, rituximab alone is not curative in many non-Hodgkin lymphoma (NHL) patients with observation of primary and acquired resistance, arguing for a need for additional targeted therapies. We identified the cell surface protein CD47 as a potential therapeutic antibody target in human NHL. A major function of CD47 is to inhibit phagocytosis through binding its receptor SIRPα, on phagocytes. We hypothesize that NHL cells over-express CD47 to evade immune phagocytosis and that blockade of CD47 signaling with a monoclonal antibody can eliminate NHL cells by enabling phagocytic engulfment. We have previously shown that an anti-CD47 antibody enables phagocytosis of acute myeloid leukemia (AML) stem cells and eliminates AML in vivo. 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 will result in synergistic elimination of NHL cells by both blocking an inhibitory signal and delivering a positive signal for phagocytosis.

We found that CD47 protein is highly expressed on primary human B-cell NHL cells compared to normal peripheral blood B-cells. Higher CD47 gene expression independently predicted a worse clinical outcome in several cohorts of NHL patients including diffuse large B-cell lymphoma (DLBCL), mantle cell lymphoma, and chronic lymphocytic leukemia. Blocking anti-CD47 antibodies preferentially enabled phagocytosis of NHL cells but not normal cell counterparts in vitro. Using isobologram analyses, the combination of anti-CD47 antibody and rituximab resulted in synergistic phagocytosis of NHL cells at higher levels compared to either anti-CD47 antibody or rituximab alone. In addition, anti-CD47 antibody and rituximab mediated their therapeutic effects through Fc-receptor-independent and Fc-receptor-dependent effector mechanisms, respectively. In vivo, anti-CD47 antibody treatment of NHL-engrafted mice reduced lymphoma burden and prolonged survival compared to IgG control. Furthermore, combination treatment with anti-CD47 antibody and rituximab led to elimination of lymphoma and cure of NHL-engrafted mice. These in vivo results were observed in both a disseminated and localized human NHL cell line mouse model as well as in primary human DLBCL mouse xenotransplants. Together, these data provide the rationale for utilizing an anti-CD47 antibody either alone or in combination with rituximab in treating human NHL.