Imaging, Diagnosis, Prognosis NKG2D Ligand Expression in Human Colorectal Cancer Reveals Associations with Prognosis and Evidence for Immunoediting

Purpose: NKG2D (natural killer group 2, member D) binds to cellular ligands of the MIC and ULBP/RAET family. These ligands have restricted expression in normal tissue, but are frequently expressed on primary tumors. The role of NKG2D ligands is thought to be important in carcinogenesis but its prognostic effect has not been investigated in such a large cohort. Experimental Design: In our study, 462 primary colorectal tumors were screened for the expression of all MIC/ULBP/RAET proteins and NK cell infiltration. Tumor microarray technology was used for the purpose of this investigation. Results: NKG2D ligands were expressed by the majority of colorectal tumors; however, the level of expression varied considerably. High expression of MIC (68 versus 56 months) or RAET1G (74 versus 62 months) showed improved patient survival. Tumors expressing high levels of MIC and RAET1G showed improved survival of 77 months over tumors that expressed high levels of one ligand or low levels of both. High-level expression of all ligands was frequent in tumor-node-metastasis stage I tumors, but became progressively less frequent in stages II, III, and IV tumors. Expression of MIC was correlated with NK cellular infiltration. Conclusion: The observations presented are consistent with an immunoediting mechanism that selects tumor cells that have lost or reduced their expression of NKG2D ligands. The combination of MIC and tumor-node-metastasis stage was found to be the strongest predictor of survival, splitting patients into eight groups and suggesting prognostic value in clinical assessment. Of particular interest were stage I patients with low expression of MIC who had a similar survival to stage III patients, and may be candidates for adjuvant therapy. (Clin Cancer Res 2009;15(22):6993–7002) NKG2D (natural killer group 2, member D) is a stimulatory receptor expressed on the surface of NK cells and subsets of T cells (1). It is unusual among activating receptors in binding to a diverse array of cellular ligands (2). Human NKG2D ligands comprise two members of the MIC (MHC class I–related chain) family and six members of the ULBP/RAET (UL16 binding protein, or retinoic acid early transcript) family (3–7). In mice, they include five members of the Rae1 (retinoic acid early inducible) family, the minor histocompatibility antigen H60, and Mult1 (murine ULBP-like transcript; refs. 8–10). NKG2D ligand expression is generally absent from healthy tissues but can be induced on infection, and by cell stress stimuli. NKG2D ligands are also widely expressed on a variety of cancer cell lines, as well as primary solid tumors and leukemia (4, 11–14). The mechanisms regulating NKG2D ligand expression in cancer are not well understood, although activation of DNA damage response pathways have been implicated, as has the expression of the BCR/ABL oncogene (15–17). In mouse models, it has been shown that tumor cell lines transfected with Rae1 are rejected in vivo via NKG2D-mediated immunity (18, 19). The recent generation of an NKG2D knockout mouse has provided the most convincing evidence to date for NKG2D involvement in antitumor immune responses (20). Using the knockout mice in conjunction with several different cancer models it became clear NKG2D interactions are variable between different types of cancer. For example, there was no increase in the incidence of methylcolanthrene-induced tumors in the knockout compared with wild-type; however, NKG2D deficiency was associated with increased incidence of Authors' Affiliations: Academic Division of Clinical Oncology, University of Nottingham, City Hospital Campus, Section of Gastrointestinal Surgery, Queen's Medical Centre, John Van Geest Research Centre, Nottingham Trent University, Clifton Campus, Nottingham, United Kingdom, and Cambridge Institute for Medical Research, Wellcome Trust/MRC Building, Addenbrookes Hospital, Cambridge, United Kingdom Received 4/18/09; revised 7/29/09; accepted 8/18/09; published OnlineFirst 10/27/09. Grant support: Lewis Trust (L.G. Durrant) and Cancer Research UK (R.A Eagle and J. Trowsdale). The costs of publication of this article were defrayed in part by the payment of page charges. This articlemust therefore be herebymarked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Note: R.W. McGilvray and R.A Eagle contributed equally to this work. Requests for reprints: Lindy Durrant, Academic Division of Clinical Oncology, University of Nottingham, City Hospital Campus, Nottingham, NG5 1PB, United Kingdom. Phone/Fax: 44-115-823-1863; E-mail: lindy.durrant@ nottingham.ac.uk. F 2009 American Association for Cancer Research. doi:10.1158/1078-0432.CCR-09-0991 6993 Clin Cancer Res 2009;15(22) November 15, 2009 www.aacrjournals.org Research. on May 28, 2017. © 2009 American Association for Cancer clincancerres.aacrjournals.org Downloaded from Published OnlineFirst October 27, 2009; DOI: 10.1158/1078-0432.CCR-09-0991