Myeloid-derived suppressor cells mitochondrial fitness governs chemotherapeutic efficacy in hematologic malignancies

Myeloid derived suppressor cells (MDSCs) are key regulators of immune responses and correlated with poor outcomes in hematologic malignancies. Here, we identify the mitochondrial fitness in MDSCs controlling the efficacy of doxorubicin chemotherapy for lymphoma. Mechanistically, we show that triggering STAT3 signaling via β2-adrenergic receptor (β2-AR) activation leads to metabolic reprograming of MDSCs, marked by sustained mitochondrial respiration (OX/PHOS) and higher ATP generation which reduces the AMPK signaling. Furthermore, induced STAT3 signaling in MDSCs enhanced glutamine consumption via the tricarboxylic acid (TCA) cycle. Metabolized glutamine generates itaconate which downregulates mitochondrial reactive oxygen species (mROS) via regulation of nuclear factor erythroid 2-related factor 2 (Nrf2) and the antioxidant machinery. We found that targeting the STAT3 pathway or ATP/Itaconate metabolites by blocking β2-AR signaling, the electron transport chain and ATP generation, or itaconate generation, results in disrupted MDSC mitochondrial fitness. This disruption increases the in vivo response to doxorubicin, delaying lymphoma progression.