Indoleamine 2,3-dioxygenase activity and expression in patients with chronic lymphocytic leukemia

Indoleamine 2,3-dioxygenase (IDO) activity and expression is increased in many hematological malignancies, but has not been previously studied in chronic lymphocytic leukemia (CLL). We determined IDO activity and expression in 49 patients with CLL. We found that IDO activity is increased in CLL. This may have some influence on CLL progression.

Indoleamine 2,3-dioxygenase (IDO) is an enzyme involved in the catabolism of tryptophan, suppressing T-cell activity. IDO activity and expression are increased in many malignant diseases, including hematological malignancies. IDO expression can mediate immunotolerance to tumors. IDO activity and expression have not previously been studied in chronic lymphocytic leukemia (CLL).

We measured IDO activity by calculating the kynurenine-tryptophan (kyn-trp) ratio. IDO and IDO2 gene expression was determined by using real-time polymerase chain reaction (PCR).

In patients with CLL, the serum kyn-trp ratio--reflecting increased IDO activity--was significantly higher compared with controls, but in peripheral blood mononuclear cells (PBMCs)--mainly representing malignant B cells--the expression of genes encoding IDO and IDO2 enzymes was reduced.

Increased IDO activity in patients with CLL may affect disease progression, although it originates from cells other than malignant B cells.