Effects of gene silencing of indoleamine 2,3-dioxygenase 1 combined with rosmarinic acid on tumor immune microenvironment in H22 tumor-bearing mice

Rosmarinic acid (RA) is a natural polyphenolic compound with several pharmacological activities, including immunomodulation and anti-tumor effect. Indoleamine 2,3-dioxygenase-1 (IDO1), the rate-limiting enzyme that metabolizes tryptophan into kynurenine, is an important negative immune regulator. This study aimed to explore the effect of combined action of IDO1 gene silencing and RA on tumor immune microenvironment. H22 tumor-bearing mice were treated with combination therapy with RA and IDO1-shRNA. The percentages and apoptosis of T-cells and subsets of splenic regulatory T-cells (Tregs) were detected by flow cytometry. Levels of tumor necrosis factor (TNF-alpha), Interferon-gamma (IFN-gamma), interleukin-2 (IL-2) and interleukin-10 (IL-10) were measured by enzyme linked immunosorbent assay (ELISA). Treatment with RA + IDO1-shRNA significantly increased the percentage of CD4+ T cells, ratio of CD4+/CD8+ and the levels of IFN-gamma and IL-2, while decreased CD8+ apoptosis, the proportion of splenic Tregs and the levels of TNF-alpha and IL-10. The present study demonstrated that combination therapy with RA and IDO1-shRNA had anti-tumor effects on HCC. The mechanism might be related to regulating immune response and immunocytokines, as well as alleviating immunosuppression induced by Tregs in the tumor immune microenvironment.