CO-induced TTP improves efficacy through resetting tumor-associated macrophages toward M1 phenotype in combined CTLA-4 and PD-1 blockade immunotherapy

Abstract Combined immune checkpoint blockade (CICB) targeting CTLA-4 and PD-1 has improved the prognosis for many malignancies, but also occurred a high rate of immune-related adverse events (irAEs). The manifestation of these toxicities is an important limiting factor for the successful implementation of CICB, restraining its anti-tumor efficacy. Carbon monoxide (CO), a pivotal endogenous signaling molecule, is able to maintain cell and tissue homeostasis and could be used as a therapeutic regimen. In our previous reports, CO could be useful therapeutics for the regulation of various inflammatory diseases through the increase of tristetraprolin (TTP) that binds to the AU-rich elements in target mRNA. In this study, we observed that CO-induced TTP activation ameliorated colitis and hepatitis, and improved anti-tumor efficacy in CICB treatment. We found that the colitis and hepatitis in TTP deficient mice were further exacerbated by CICB treatment. Moreover, CO increases CICB efficacy through TAM to M1 polarization together with diminishes irAEs through TTP enhancement in several irAEs target organ. Thus, we suggest that CO might be efficiently decouples anti-tumor efficacy and toxicity of CICB through TTP enhancement.