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The specific immune response to tumor antigen CP1 and its correlation with improved survival in colon cancer patients.

Liu FF, Dong XY, Pang XW, Xing Q, Wang HC, Zhang HG, Li Y, Yin YH, Fant M, Ye YJ, Shen DH, Zhang Y, Wang S, Chen WF

Department of Gastroenterological Surgery, Surgical Oncology Laboratory, Peking University People's Hospital, Beijing, China.

BACKGROUND & AIMS: The present study was undertaken to determine the expression of a newly identified tumor antigen cancer-placenta 1 (CP1) in colorectal carcinoma (CRC) and explore the CP1-specific immune response in CRC patients and its correlation with patient survival. METHODS: CP1 expression was determined by reverse-transcription polymerase chain reaction, immunohistochemistry, and Western blot analysis. Serum antibodies against CP1 were detected by enzyme-linked immunosorbent assay, and T-cell response was measured by interferon-gamma/granzyme-B release enzyme-linked immunospot assays. The HLA-A2-restricted epitopes in CP1 were predicted by bioinformatics and then experimentally validated by enzyme-linked immunospot assay. RESULTS: CP1 expression was detected in a significant number of CRC tissues, reaching 47.6% at the messenger RNA (mRNA) level and 28.6% at the protein level. Of patients with CP1 mRNA(+) tumors, more than 50% had CP1-responsive CD4(+) and CD8(+) T cells and 30% spontaneous-occurring antibodies against CP1. Further studies revealed 2 dominant HLA-A2-restricted epitopes in the CP1 antigen: p31-39 and p58-66. In a follow-up study up to 33 months after surgery, 9 of the 10 patients with CP1-specific CD8 T-cell response survived, whereas 6 of the 8 nonresponders died. Kaplan-Meier analysis indicated a significant correlation between T-cell response and patient survival. CONCLUSIONS: CP1 represents a new class of tumor-specific shared antigen. Its high expression in CRC tissues, prevalence of CP1-specific immune responses in CP1 mRNA(+) CRC patients, and positive correlation with survival suggest that the antigen may be a useful target for cancer immunotherapy.

Published 8 April 2008 in Gastroenterology, 134(4): 998-1006.
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