Prognostic significance of tryptophan catabolism in adult T-cell leukemia/lymphoma

PURPOSE: Indoleamine 2,3-dioxygenase 1 (IDO1: IDO) is an enzyme catabolizing tryptophan (Trp) into the kynurenine (Kyn) pathway, and is an important micro-environmental factor suppressing antitumor immune responses. We investigated the prognostic significance of Trp catabolism in adult T-cell leukemia/lymphoma (ATL).

EXPERIMENTAL DESIGN: We quantified serum Trp and Kyn in 96 ATL patients, 38 human T-cell lymphotropic virus type-1 asymptomatic carriers (HTLV-1 ACs), and 40 healthy adult volunteers. The relationships between various clinical parameters were analyzed. IDO expression was evaluated in the affected lymph nodes of ATL patients.

RESULTS: Serum Kyn concentrations and Kyn/Trp ratios were significantly higher in HTLV-1 ACs than in healthy controls. Both increased significantly with progression from HTLV-1 AC to ATL. There were no significant differences in serum Trp concentrations between ATL patients, HTLV-1 ACs and controls. IDO was possibly produced by ATL and/or cells in the microenvironment. Multivariate analyses demonstrated a high serum Kyn/Trp ratio and high Kyn level, but not a high Trp level, to be significant independent detrimental prognostic factors in ATL and aggressive variant ATL.

CONCLUSIONS: Quantification of serum Kyn and Trp is prognostically useful for individual ATL patients. Furthermore, ATL is an appropriate disease for testing novel cancer immunotherapies targeting IDO.