Expression of indoleamine 2,3-dioxygenase predicts shorter survival in patients with vulvar squamous cell carcinoma (vSCC) not influencing on the recruitment of FOXP3-expressing regulatory T cells in cancer nests

ObjectiveRegulatory T cells (Tregs), and the enzyme indoleamine 2,3-dioxygenase (IDO), have potential regulatory properties for immune escape in cancer. Inhibitors of IDO are available and could potentially be used in vulvar cancer if IDO was proved to drive progression of the disease. The aim of this study was to evaluate the expression of factor forkhead boxP3 (FOXP3), a marker of Tregs, and IDO in vulvar squamous cell carcinoma (vSCC), and to verify their prognostic significance.Methods76 primary tumors and 35 lymph node metastases derived from 76 patients with full clinical history were analyzed. The intratumoral infiltration of Tregs and IDO expression within cancer were evaluated by immunohistochemistry.ResultsThe number of Tregs in primary tumor and in corresponding lymph node metastasis was significantly correlated. Intensity of Treg infiltrates in the primary and metastatic sites was not correlated to IDO expression and had no influence on the overall patient survival. High IDO expression was associated with significantly worse overall survival among vSCC patients and was found to be an independent prognostic factor similarly to the tumor grade and patient's age.ConclusionsThe degree of intratumoral Treg infiltrates is an individual feature and remains stable throughout the course of the disease without impact on the patient's survival. IDO expression predicts shorter survival of vSCC patients. If immunologic tolerance of the tumor is promoted by the overexpression of IDO it will not influence the number of intratumoral Tregs. IDO expression seems to be an independent prognostic factor in patients with vSCC.

Research highlights
► IDO and Tregs are believed to be critical in evading immune surveillance and were both evaluated by immunohistochemistry in vulvar squamous cell vSCC.
► Strong IDO expression predicts shorter survival of vSCC patients and was found to be an independent prognostic factor.
► If immunologic tolerance of the tumor is promoted by IDO it will cause no changes in the number of Tregs.