Immunological characterization of a novel human colon‐associated antigen (CAA) by a monoclonal antibody

Abstract

We have generated a monoclonal antibody (MAb), designated anti-CAA (colon-associated antigen), using as immunogen a membrane-enriched fraction of a biopsy from a moderately-differentiated human colonic adenocarcinoma. The molecular weight of this reactive antigen was determined by Western blotting to be greater than 200 kDa. When immunohistochemical techniques were used, MAb anti-CAA reacted with epithelium in the majority of normal, dysplastic and malignant colon specimens tested (greater reactivity was observed in normal colon than in benign or malignant lesions). Cell sorter analyses demonstrated a heterogeneous distribution of CAA on the cell surface of the well-differentiated LS-174T cell line. Antigen positive and antigen-negative cells were separated by means of flow cytometric techniques. These two subpopulations were then inoculated into immunosuppressed rats, resulting in xenograft tumors which differed significantly in their degree of histologic differentiation. Antigen-positive cells developed into well-differentiated adenocarcinomas, while antigen-negative cells developed into poorly differentiated adenocarcinomas. These results, along with immunohistochemical studies, indicate that the antigen detected by MAb anti-CAA has characteristics of a colon-associated antigen whose expression correlates with cellular differentiation. Moreover, differences in molecular weight as well as tissue distribution indicate that CAA may be a novel antigen different from those previously described.

Characterization of the Colorectal Antigen IOR-C2

“…However, I0R-C2 seems to be different from the CAA antigen regarding to its molecular weight, lack of correlation with degree of tumor differentiation (data not shown) and the absence of CAA in breast and lung carcinomas studied (40). Also the recently described colorectal antigen NCC-CO-450 differs from I0R-C2 with regard to its absence in some I0R-C2 positive tumors such as breast and lung cancers (41).…”

“…The I0R-C2 antigen has some similarities in expression to the CAA and NCC-CO-450 (40,41) antigens that are more expressed in the differentiated normal colon cells compared to corresponding cancer cells.…”

A metastatic nude-mouse model of human pancreatic cancer constructed orthotopically with histologically intact patient specimens.

“…The generation, characterization, and purification of murine mAbs CC49 and COL-1 to the human TAA tumor-associated glycoprotein 72 (TAG-72) and carcinoembryonic antigen (CEA), respectively, have been well described (33,34). The murine IgG1, MOPC-21 (Litton Bionetics), was used as a negative control.…”

Characterization, isolation and amino terminal sequencing of a rat colon carcinoma‐associated antigen

“…A large number of MAbs has been raised against colon tumor cell lines or normal components of colon, which recognized glycoproteins related to mucins characterized by their high molecular weight under denaturing conditions. Thus, the antigens recognized on malignant colonic tissues by MAbs named B72.3 (Stramignoni et al, 1983), 1D3 (Gangopadhyay et al, 1985, anti-CAA (Muraro et al, 1987), SPanl (Ho et al, 1988), G9 (Gold et al, 1989), AM3 (Hanski et al, 1990) are high-MW proteins and are therefore different from pE4. However, proteins related to mucins with molecular weight close to that of pE4 have also been found Griffiths et al, 1987), but these proteins were also detected in the cytoplasm of the cell, which is not the case for Several other colon-tumor-associated antigens have been recently defined by MAbs.…”