CD47 blockade has emerged as a promising cancer immunotherapy by promoting phagocytosis of tumor cells. However, this treatment strategy may be limited by the predominant accumulation of macrophages with pro-tumor M2 phenotype.
Therefore, reprogramming of M2-type macrophages into M1-type macrophages has been considered as a better potential therapy to boost the antitumoral effects by macrophages. The key myeloid cytokine GM-CSF is approved as an adjunctive agent in the treatment of cancer by virtue of its ability to stimulate hematopoiesis and particularly induce the differentiation of pro-inflammatory M1 macrophages. Here we report the development of a novel immunocytokine composed of a newly discovered CD47 IgG1 fused with GMCSF at the C-terminus (1F8-GMCSF). In macrophage-tumor cell co-culture, treatment with 1F8-GMCSF fusion molecule led to significantly higher levels of tumor cell phagocytosis and M1 characteristic cytokine production than that with anti-CD47 alone. 1F8-GMCSF demonstrated superior efficacy in suppression of tumor growth as well as shift of tumor associated macrophages from M2 to M1 phenotype compared to 1F8 or GM-CSF treatment alone or in combination. In vivo tracking of injected anti-CD47 antibodies by live imaging confirmed the enriched localization of antibodies in the CD47+ tumor site. Taken together, our data showed that 1F8-GMCSF fusion exhibited enhanced phagocytosis and M1 macrophage activation, leading to a superior antitumor efficacy.