The human NKG2D ligands (NKG2DL) MICA and MICB have been shown to be expressed on tumors of epithelial and hematopoietic origin in vivo. Recently we reported that MICA is shed from the cell surface of tumor cells and is present in sera of tumor patients (

J Immunol
169
:
4098
(
2002
)
,
Blood
102
:
1389
(
2003
)
). Since the strength of an anti-tumor response by NK cells and CD8 T cells is critically depending on NKG2DL expression levels, down-regulation of MICA-expression on tumor cells represents an immune escape mechanism that diminishes anti-tumor reactivity of NKG2D-bearing lymphocytes. However, no data are yet available regarding the correlation of soluble MICA (sMICA) levels with specific tumor entities, aggressiveness of the disease, and hence the potential implementation of sMICA as novel marker in differential diagnosis and prognosis of cancer. In this study, we determined sMICA levels in sera of 512 individuals including 296 patients with various cancers, 154 patients with benign disorders and 62 healthy individuals. Healthy individuals revealed significantly lower sMICA values (median<30pg/mL) than patients with benign diseases (84pg/mL; p=0.005) and cancer patients (161pg/mL; p<0.0001). In addition, sMICA levels differed significantly between cancer patients and patients with benign disorders (p<0.0001) that represent the most relevant control group for differential diagnosis. In cancer patients, while there was no association between sMICA levels and tumor size (p=0.456), cell differentiation (p=0.271), or lymph node involvement (p=0.674), sMICA correlated significantly with cancer stage and metastasis (p=0.015 and p=0.007, respectively). Our data indicate that release of MICA might play a role in late stages of tumor progression by overcoming the confining effect of NK cells and CD8 T cells. Thus, determination of sMICA levels provides valuable information for cancer staging, and sMICA in serum seems to be an indicator for systemic manifestation of malignancy rather than for local tumor extent.

Topics:
neoplasm metastasis, neoplasms, cancer, cancer staging, tumor cells, ligands, tumor progression, tumor size, natural killer cells, serum

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2005, The American Society of Hematology
2004
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