Introduction: We investigated a novel immunotherapy that targets CD47, a cell surface marker that binds SIRPa on the surface of macrophages and prevents phagocytosis. Recent experiments by our collaborators demonstrated that blocking CD47 in leukemia and several non-CNS solid tumors can lead to tumor destruction. We tested the effect of anti-human CD47 treatment in GBM.
Methods: Expression Analysis: Publically available gene expression array data of glioma patients was analyzed for the level of CD47 expression and correlated to outcomes. Primary GBM cells were dissociated, stained with florescent conjugated anti-human CD47 (anti-CD47) and analyzed by FACS.
In Vitro: Primary GBM cells were cultured, CSFE labeled, incubated with either mouse or human macrophages, and exposed to either anti-human CD47 antibody or isotype control. Phagocytic index was then assayed by fluorescence microscopy.
In Vivo: Primary GBM cells were cultured and transduced with lenti-virus expressing green fluorescent protein (GFP) and luciferase. Transduced cells are then injected into the brains of 6-week old immunocompromised mice. After two weeks, tumor growth was confirmed by bioluminescence imaging, and mice were then treated by interperitoneal injections of either anti-CD47 or isotype controls. Tumor growth was assessed at weekly intervals to 8 weeks by bioluminescence.
Results: Our expression analysis indicated that CD47 was highly expressed on GBM tumors and was an adverse prognostic factor of patient outcomes. In vitro phagocytosis assay of tumor cells by both mouse macrophages and human macrophages showed significant higher phagocytic index in CD47 group than IgG group. Anti-CD47 Ab may eliminate tumor cells in GBM xenograft mouse model.
Conclusions: GBM CD47 expression inversely correlates with patient survival. The targeting of CD47 clears tumors in vitro and in vivo. We are currently conducting more preclinical studies in order to advance this therapy into clinical trials.
Patient Care: Our research is an integral part of developing a new immunotherapy for GBM.
Learning Objectives: By the conclusion of this session, the participants should be able to understand the role of CD47 in GBM and the potential therapeutic benefit of an immunotherapy blocking CD47 to activate tumor clearing by the innate immune response.