Indoleamine 2,3-dioxygenase 2 depletion suppresses tumor growth in a mouse model of Lewis lung carcinoma.

Tryptophan metabolism is important to induce immune tolerance in tumors. To date, 3 types of tryptophan-metabolizing enzymes have been identified: indoleamine 2,3-dioxygenase 1 and 2 (IDO1 and IDO2) and tryptophan 2,3-dioxygenase 2. Numerous studies have focused on IDO1 as its expression is enhanced in various cancers. Recently, IDO2 has been identified as a tryptophan-metabolizing enzyme that is involved in several immune functions and expressed in cancers such as pancreatic cancer. However, the biological role of IDO2 in the induction of immune tolerance in tumors has not yet been reported. In the present study, we examined the effects of Ido2 depletion on tumor growth in a mouse model of Lewis lung carcinoma by using Ido2-knockout mice. Ido2-knockout mice had reduced tumor volumes compared to WT mice. Furthermore, Ido2 depletion altered the tumor microenvironment, such as tryptophan accumulation and kynurenine reduction, leading to enhancement of immune cell invasion. Finally, enzyme-linked immunospot assay revealed that Ido2 depletion enhanced γ-interferon secretion in the tumor. In conclusion, Ido2 is an important immune regulator in the tumor microenvironment. Our data indicate that IDO2 is a potential target for cancer treatment and drug development.

Lipopolysaccharide shock reveals the immune function of indoleamine 2,3-dioxygenase 2 through the regulation of IL-6/stat3 signalling.

Indoleamine 2,3-dioxygenase 2 (Ido2) is a recently identified catalytic enzyme in the tryptophan-kynurenine pathway that is expressed primarily in monocytes and dendritic cells. To elucidate the biological role of Ido2 in immune function, we introduced lipopolysaccharide (LPS) endotoxin shock to Ido2 knockout (Ido2 KO) mice, which led to higher mortality than that in the wild type (WT) mice. LPS-treated Ido2 KO mice had increased production of inflammatory cytokines (including interleukin-6; IL-6) in serum and signal transducer and activator of transcription 3 (stat3) phosphorylation in the spleen. Moreover, the peritoneal macrophages of LPS-treated Ido2 KO mice produced more cytokines than did the WT mice. By contrast, the overexpression of Ido2 in the murine macrophage cell line (RAW) suppressed cytokine production and decreased stat3 expression. Finally, RAW cells overexpressing Ido2 did not alter nuclear factor κB (NF-κB) or stat1 expression, but IL-6 and stat3 expression decreased relative to the control cell line. These results reveal that Ido2 modulates IL-6/stat3 signalling and is induced by LPS, providing novel options for the treatment of immune disorders.

Association between increased serum GP88 (progranulin) concentrations and prognosis in patients with malignant lymphomas.

BACKGROUND: GP88 (progranulin; PGRN) is a secreted 88kDa glycosylated protein, with important functions, including inflammation and tumorigenesis. We assessed the significance of GP88 expression in survival outcomes of patients with malignant lymphoma (ML). METHODS: Serum samples from 254 previously untreated ML patients were examined to measure GP88 concentrations using a sandwich human GP88 ELISA kit. Immunohistochemical analyses were performed to examine GP88 tumor tissue expression. RESULTS: The median serum GP88 concentration of ML patients was 91.3ng/ml, and was significantly higher than that of the control group (median, 57.7ng/ml) (p<0.0001). Association between GP88 serum concentrations and overall survival (OS) was examined in patients with diffuse large B cell lymphoma (DLBCL) who had been stratified based on their serum GP88 concentrations. Kaplan Meier survival analysis showed that patients with serum GP88 concentrations of ≤116 and >116ng/ml, had 5-y OS rates of 70% and 50%, respectively (p=0.02). The immunohistochemical analyses of GP88 tumor expression revealed that DLBCL patients had lymphoma cells that were positive for GP88. CONCLUSIONS: High serum GP88 concentrations are associated with poor prognosis in patients with DLBCL.