IDO1 Expression in Ovarian Cancer Induces PD-1 in T Cells via Aryl Hydrocarbon Receptor Activation

Area of Science:

• Immunology
• Cancer Biology
• Metabolic Pathways

Background:

• The indoleamine 2,3-dioxygenase (IDO1) enzyme and PD-1/PD-L1 axis are key inhibitors of anti-tumor immunity in ovarian cancer.
• The specific role of the IDO pathway in regulating PD-1 expression on T cells remains unclear.

Purpose of the Study:

• To investigate the impact of tumoral IDO1 expression on the tumor microenvironment and T cell phenotype.
• To elucidate the mechanism by which the IDO pathway influences PD-1 expression in ovarian cancer.

Main Methods:

• Analysis of metabolic pathway changes in the ovarian tumor microenvironment.
• Flow cytometry to quantify PD-1 expression on CD8+ T cells.
• Assessment of aryl hydrocarbon receptor (AHR) activation and inhibition using kynurenine and CH223191.
• Chromatin accessibility assays and AHR binding site analysis in the PD-1 promoter region.

Main Results:

• Tumoral IDO1 expression significantly altered tryptophan, nicotinate/nicotinamide, and purine metabolism.
• IDO1 expression correlated with an increased frequency of PD-1+CD8+ tumor-infiltrating T cells.
• Kynurenine-induced AHR activation was identified as a driver of PD-1 expression, an effect blocked by the AHR antagonist CH223191.
• Kynurenine alters chromatin accessibility, facilitating AHR binding to the PD-1 promoter.

Conclusions:

• IDO1 pathway activation, via kynurenine and AHR, directly upregulates PD-1 expression on T cells in ovarian cancer.
• Targeting the IDO1 and AHR pathways presents a promising therapeutic strategy for enhancing anti-tumor immunity in ovarian cancer.