Late-stage colorectal cancer with liver metastasis is common and affords poor prognosis, yet there is a dearth of reliable biomarkers. Cancer is often characterized by an increase in serologic autoantibodies. Hence, we embarked on an immuno-proteomic strategy by using autoantibodies to discover antigens in tumor tissue as potential cancer markers. Matched sets of tissues from primary colon cancer, liver metastases, and adjacent benign tissues were obtained from colon cancer patients. Tissue proteins were extracted, and autoantigens were uncovered by immunoblotting with autoantibodies and sequenced by mass spectrometry. Informatics analyses identified 48 proteins that were found in tumor only but were absent in normal tissue. Five of these were reproducibly found in two independent experiments, including olfactomedin 4 (OLFM4), CD11b, integrin α2 (ITGA2), periostin, and thrombospondin-2. Further confirmation with tissue from 43 patients by Western blotting, immunohistochemistry, and tissue microarray deemed OLFM4, CD11b, and ITGA2 to be significantly overexpressed in both primary colon tumors and liver metastases. These tumor tissue autoantigens may serve as promising markers for developing differential diagnostics and immunotherapies for colorectal cancers, in particular, those with tendency to progress to liver metastases.

Biological significance: Late-stage colorectal cancer with liver metastasis is common and affords poor prognosis, yet there is a dearth of reliable biomarkers. Cancer is often characterized by an increase in serologic autoantibodies. Cancer tissue immunogens - antigens capable of inducing specific antibody production in patients - are promising targets for development of precision diagnostics and immunotherapies. In our manuscript, we describe on an immuno-proteomic strategy by using autoantibodies to discover antigens in tumor tissue as potential cancer markers. Matched sets of tissues from primary colon cancer, liver metastases, and adjacent benign tissues were analyzed. Putative autoantigens were first uncovered by immunoblotting with autoantibodies and sequenced by mass spectrometry. Informatics analyses identified 48 proteins that were found in tumor only but were absent in normal tissue. Using follow-up validation in two independent cohorts, we discovered that OLFM4, CD11b, and ITGA2 are proteins that are overexpressed in both primary colon tumors and liver metastases. We highlight the possible roles of these 3 proteins in carcinogenesis and tumor microenvironment and the implications for autoantigenic immune recognition. More generally, colon cancer biomarkers with autoantigenic properties, like the ones we describe in our manuscript, may open new opportunities for diagnosis, molecular classification, and therapy of colorectal cancer, particularly of aggressive tumors with tendency to progress to liver metastases. The autoantigenic properties of biomarkers are also expected to be of great relevance for immunotherapeutic development.