Immunohistochemical monitoring of metastatic colorectal carcinoma in patients treated with monoclonal antibodies (MAb 17-1A).

A therapeutic trial using repeated doses of a mouse monoclonal antibody against the tumor-associated antigen (TAA) CO17-1A in metastatic colorectal carcinomas was carried out. Metastatic lesions sampled by repeated thick needle (1.2 mm) biopsies during therapy were examined immunohistochemically for the presence of various TAAs, mouse IgG, complement, and infiltrating leukocytes. The CO17-1A was consistently expressed in all cases along the basement membrane of tumor glands and could only be demonstrated on cryostat sections whereas the TAAs GICA19-9, GA73-3, and Br55-2 were also visualized in B5-fixed paraffin-embedded biopsies. The CO17-1A and GA73-3 were predominantly present at the basal region in contrast to the GICA 19-9 and Br55-2 which were predominant at the luminal and the apical region of the tumor glands. Antigenic modulation was not seen either after 24-72 h or during prolonged treatment. In all cases the infused mouse IgG was detected, from 24 h after infusion up to 6-8 weeks, mainly along the basal region of tumor glands. In 13/14 posttreatment biopsies, complement factor C3 was found at the same sites as mouse IgG. In 6 out of 9 posttreatment biopsies an increase in mononuclear cells (monocytes, natural killer (NK) cells and/or T cells) was observed. Monocytes were close to the tumor cells whereas NK cells and T cells were predominantly scattered in the stroma.