Purpose Release of inhibitory coregulatory proteins into the circulation may represent one mechanism by which tumors thwart immune responses. Our objective was to determine whether sB7-H1 levels in patients with clear cell renal cell carcinoma (ccRCC) are associated with pathologic features and patient outcome. Experimental Design We developed an ELISA for quantification of sB7-H1 in biologic fluids. Biochemical confirmation of the measured analyte as sB7-H1 was done by protein micro-sequencing using supernates from tumor cell lines. Biological activity of sB7-H1 was assessed in vitro utilizing T cell apoptosis assays. We tested sB7-H1 levels in the sera from 172 ccRCC patients and correlated sB7-H1 levels with pathologic features and patient outcome. Results sB7-H1 was detected in the cell-supernatants of some B7-H1-positive tumor cell lines. Protein sequencing established that the measured sB7-H1 retained its receptor-binding domain and could deliver pro-apoptotic signals to T cells. Higher preoperative sB7-H1 levels were associated with larger tumors (p<0.001), tumors of advanced stage (p=0.017) and grade (p=0.044), and tumors with necrosis (p=0.003). A doubling of sB7-H1 levels was associated with a 41% increased risk of death (p=0.010). Conclusion Our observations suggest that sB7-H1 may be detected in the sera of ccRCC patients and that sB7-H1 may systemically impair host immunity, thereby fostering cancer progression and subsequent poor clinical outcome.
B7 coregulatory ligands can be aberrantly expressed in human disease. In the context of cancer, these ligands may act as antigen-specific inhibitors of T-cell-mediated antitumoral immunity. We recently reported that B7-H1 expression by carcinomas of the kidney and bladder portends aggressive disease and diminished survival. The expression of these proteins in prostate cancer, however, has not been investigated. We evaluated B7-H3 and B7-H1 protein expression in the pathologic specimens of 338 men treated for clinically localized prostate cancer between 1995 and 1998 with radical retropubic prostatectomy. Expression levels of B7-H3 in prostate cancer were correlated with pathologic indicators of aggressive cancer as well as clinical outcome. We report that B7-H3 is uniformly and aberrantly expressed by adenocarcinomas of the prostate, high-grade prostatic intraepithelial neoplasia, and four prostate cancer cell lines, whereas B7-H1 is rarely expressed. B7-H3 is expressed by benign prostatic epithelia, although at a more reduced level relative to neoplastic tissue. Increasing levels of B7-H3 intensity correlate with worsening clinicopathologic features of prostate cancer. Marked B7-H3 intensity, present in 67 (19.8%) specimens, confers a >4-fold increased risk of cancer progression after surgery (risk ratio, 4.42; P < 0.001). A survey of normal tissues revealed that B7-H3 is expressed within the liver, urothelium, and fetal kidney. In summary, B7-H3 is aberrantly expressed in all prostate cancers and represents an independent predictor of cancer progression following surgery. Moreover, B7-H3 encompasses a novel diagnostic and potential therapeutic target for the clinical management of prostate cancer and, perhaps, other malignancies as well. [Cancer Res 2007;67(16):7893-900]
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