Abstract
The CO17-1A/GA733 antigen is associated with human carcinomas and some normal epithelial tissues. This antigen has shown promise as a target in approaches to passive and active immunotherapy of colorectal cancer. The relevance of animal models for studies of immunotherapy targeting this antigen in patients is dependent on the expression of the antigen on normal animal tissues. Immunohistoperoxidase staining with polyclonal rabbit antibodies to the human antigen revealed the human homologue on normal small intestine, colon and liver of mice, rats and non-human primates, whereas mouse monoclonal antibodies to the CO17-1A or GA733 epitopes on the human antigen did not detect the antigen. Polyclonal rabbit antibodies, elicited by the murine antigen homologue derived from recombinant baculovirus-infected insect cells, immunoprecipitated the antigen from mouse small intestine, colon, stomach, kidney and lung. The isolated recombinant murine protein bound polyclonal, but not monoclonal, antibodies to the human CO17-1A/GA733 antigen, and recombinant human antigen bound polyclonal antibodies elicited by the murine antigen homologue. Thus, the antigen homologue expressed by animal tissues is similar, but not identical, to the human antigen. These results have important implications for experimental active and passive immunotherapy targeting the CO17-1A/GA733 antigen.
Highlights
Reactivities of tissues from experimental animals with polyclonal rabbit antibodies to the GA733 antigen in immunohistoperoxidase assay
The intestinal mucosa was stained in mice, rats and nonhuman primates but not in rabbits
The relevance of preclinical studies of targeting this antigen in passive and active immunotherapy for clinical trials in patients has been difficult to determine in the absence of information on normal tissue expression of the antigen homologue in animals
Summary
Three-month-old female BALB/c and CBA mice, 6-monthold female Sprague-Dawley rats (Harlan-Sprague-Dawley, Indianapolis, IN, USA), 6-month-old female New Zealand White rabbits (Hare Marland, Hewitt, NJ, USA) and two adult male baboons (Papio cynomolgus) raised at the Southwest Foundation for Biomedical Research (San Antonio, TX, USA) were used as sources of tissues. The human colorectal carcinoma cell line SWI 116 and the gastric carcinoma cell line Kato III were obtained from the American Type Culture Collection (Rockville, MD, USA). MAbs CO 17-lA and GA733 (Herlyn et al, 1979, 1984; Gottlinger et al, 1986) were purified from ascites on protein A-agarose columns. For production of rabbit polyclonal antibodies to GA733 antigen, rabbits were immunized with the antigen purified from
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