Expression of indoleamine 2,3-dioxygenase in tumor endothelial cells correlates with long-term survival of patients with renal cell carcinoma.
OBJECTIVE
The inflammatory enzyme indoleamine 2,3-dioxygenase (IDO) participates in immune tolerance and tumor immune escape processes by degradation of the essential amino acid tryptophan and formation of toxic catabolites. Here, we analyzed the role of IDO in tumor growth and disease progression in patients with clear cell renal cell carcinoma (RCC).


METHODS
Expression of IDO mRNA was analyzed by quantitative reverse transcription-PCR in 55 primary and 52 metastatic RCC, along with 32 normal kidneys. Western blot and immunohistochemistry analyses were used to semiquantitatively determine IDO proteins in a subset of tumor samples, in RCC cell lines, and microvessel endothelial cells. IDO expression was correlated with expression of the proliferation marker Ki67 in tumor cells and survival of patients with tumor.


RESULTS
More than 75% of the clear cell RCC in comparison to normal kidney contained elevated levels of IDO mRNA, which correlated with their IDO protein content. Low IDO mRNA levels in primary tumors represented an unfavorable independent prognostic factor (hazard ratio, 3.8; P = 0.016). Unexpectedly, immunohistochemical analyses revealed that IDO is nearly exclusively expressed in endothelial cells of newly formed blood vessels and is virtually absent from tumor cells, although RCC cells could principally synthesize IDO as shown by in vitro stimulation with IFN-gamma. A highly significant inverse correlation between the density of IDO-positive microvessels and the content of proliferating Ki67-positive tumor cells in primary and metastatic clear cell RCC was found (P = 0.004).


CONCLUSIONS
IDO in endothelial cells might limit the influx of tryptophan from the blood to the tumor or generate tumor-toxic metabolites, thus restricting tumor growth and contributing to survival.
Tumor Immunology Laboratory, LIFE Center, Department of Urology, University Clinic Grosshadern, Institute of Pathology, Ludwig-Maximilians-University Munich, Munich, Germany.
Rainer
R
Riesenberg
Christoph
C
Weiler
Oliver
O
Spring
Martin
M
Eder
Alexander
A
Buchner
Tanja
T
Popp
Mirna
M
Castro
Robert
R
Kammerer
Osamu
O
Takikawa
Rudolf A
RA
Hatz
Christian G
CG
Stief
Alfons
A
Hofstetter
Wolfgang
W
Zimmermann
D000368:Aged; D002292:Carcinoma, Renal Cell / Q000098:blood supply* / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D045744:Cell Line, Tumor; D018450:Disease Progression; D042783:Endothelial Cells / Q000201:enzymology* / Q000473:pathology; D005260:Female; D006801:Humans; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D007371:Interferon-gamma / Q000494:pharmacology; D007680:Kidney Neoplasms / Q000098:blood supply* / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D008297:Male; D008875:Middle Aged; D009362:Neoplasm Metastasis; D009389:Neovascularization, Pathologic / Q000201:enzymology / Q000473:pathology; D011379:Prognosis; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D012189:Retrospective Studies; D014364:Tryptophan / Q000378:metabolism
D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; D012333:RNA, Messenger; D007371:Interferon-gamma; D014364:Tryptophan