Harnessing the Tumor Microenvironment for the Treatment of Double Hit Lymphoma

Abstract

Since their inception into clinical practice, antibodies have become a mainstay in the treatment of cancer and other diseases. Antibodies eliminate tumor cells through several mechanisms, including inducing tumor cell death upon binding or immune-mediated killing. Cancer resistance to antibody therapy remains an important therapeutic challenge. Herein we utilized patient-derived xenograft (PDXs) of Double Hit Lymphoma (DHL), which is frequently resistant or refractory to antibody containing chemotherapy regimens, to study mechanisms of acquired lymphoma antibody resistance and ways to overcome them. We demonstrate progressive loss of the ability of alemtuzumab, a monoclonal antibody targeting the CD52 antigen, to clear bone marrow disease in DHL engrafted mice and identify the lymphoma to macrophage ratio as a driver of acquired antibody resistance. Alemtuzumab resistance was successfully overcome by high-doses therapy with alkylating agents like cyclophosphamide (CTX), which demonstrated >80-fold synergy with alemtuzumab to clear bone marrow disease. CTX administration induced a pro-phagocytic phenotypic of DHL cells by decreasing surface expression of CD47, thereby promoting their uptake by macrophages. CTX also induced paracrine secretion of VEGF-A, IL-16 and TNF-a that promoted bone marrow macrophage influx and increased macrophage phagocytosis. Many of these DHL phenotypic changes were caused by CTX-mediated induction of ER stress. Macrophages from lymphoma engrafted CTX-treated mice displayed an increased ability to phagocytose lymphoma cells, including a subset defined by surface CD36/FcgR4 that were “super-phagocytic.” Together, these findings demonstrate a unique mechanism of macrophage dependent tumor clearance by high-dose alkylating agents.