HIF activation enhances FcγRIIb expression on mononuclear phagocytes impeding tumor targeting antibody immunotherapy

Background: Hypoxia is a hallmark of the tumor microenvironment (TME) and in addition to altering metabolism in cancer cells, it transforms tumor-associated stromal cells. Within the tumor stromal cell compartment, tumor-associated macrophages (TAMs) provide potent pro-tumoral support. However, TAMs can also be harnessed to destroy tumor cells by monoclonal antibody (mAb) immunotherapy, through antibody dependent cellular phagocytosis (ADCP). This is mediated via antibody-binding activating Fc gamma receptors (Fc gamma R) and impaired by the single inhibitory Fc gamma R, Fc gamma RIIb. Methods: We applied a multi-OMIC approach coupled with in vitro functional assays and murine tumor models to assess the effects of hypoxia inducible factor (HIF) activation on mAb mediated depletion of human and murine cancer cells. For mechanistic assessments, siRNA-mediated gene silencing, Western blotting and chromatin immune precipitation were utilized to assess the impact of identified regulators on FCGR2B gene transcription. Results: We report that TAMs are Fc gamma RIIb(bright) relative to healthy tissue counterparts and under hypoxic conditions, mononuclear phagocytes markedly upregulate Fc gamma RIIb. This enhanced Fc gamma RIIb expression is transcriptionally driven through HIFs and Activator protein 1 (AP-1). Importantly, this phenotype reduces the ability of macrophages to eliminate anti-CD20 monoclonal antibody (mAb) opsonized human chronic lymphocytic leukemia cells in vitro and EL4 lymphoma cells in vivo in human Fc gamma RIIb(+/+) transgenic mice. Furthermore, post-HIF activation, mAb mediated blockade of Fc gamma RIIb can partially restore phagocytic function in human monocytes. Conclusion: Our findings provide a detailed molecular and cellular basis for hypoxia driven resistance to antitumor mAb immunotherapy, unveiling a hitherto unexplored aspect of the TME. These findings provide a mechanistic rationale for the modulation of Fc gamma RIIb expression or its blockade as a promising strategy to enhance approved and novel mAb immunotherapies.

Automated summary

Hypoxia in the tumor microenvironment can upregulate the expression of Fc gamma RIIb receptors on tumor-associated macrophages (TAMs), which leads to reduced antibody dependent cellular phagocytosis (ADCP) and decreased efficacy of monoclonal antibody (mAb) immunotherapy. This finding provides a mechanistic basis for targeting Fc gamma RIIb expression or blocking it as a promising strategy for enhancing mAb immunotherapies.