Red blood cells-heme-exposure and tumor-associated macrophage identity

To study TAM phenotypes in hemorrhagic tumor tissues, we treated GFP-MC3 tumor-bearing mice with a single injection of immunotherapeutic anti-CD40 antibody on day 7 after tumor cell injection. Three days later, the tumors were collected for histology and genome-wide spatial analysis of mRNA expression. In both tumor samples, H&E histology visualized extensive tumor necrosis with RBCs extravasated into the necrotic areas of the tumors. Spatial gene-expression analysis allowed us to perform more detailed phenotyping, clearly discriminating zones of remaining viable cancer surrounded by hemorrhagic necrosis as evidenced by the enrichment of RBC-derived RNA (Hbb-bs). In these hemorrhagic regions, we found a Cd68 signal, confirming macrophage infiltration, superimposed by a strong signal for Hmox1 and Arg1. Like CD163 and Spp1 in human cancers, Arg1 is the archetypal marker gene for pro-cancerous and immunosuppressive TAMs in the mouse. Two GFP-MC3 tumor-bearing mice were treated with a single injection of immunotherapeutic anti-CD40 antibody on day 7 after tumor cell injection. Three days later, the tumors were collected for histology and genome-wide spatial analysis of mRNA expression.