A human monoclonal antibody recognizing a surface antigen on stomach cancer cells

Monoclonal antibody against the fusion junction of a deletion-mutant epidermal growth factor receptor

A mouse monoclonal antibody (IgG2b), 3C10, was produced against the truncated epidermal growth factor receptor (EGFR), encoded by the (type III) in-frame deletion mutation of 801 nucleotides of EGFR affecting the external domain, known to be expressed in some human glioblastoma. As this mutation newly generates a glycine residue at the fusion point, a 14 amino acid peptide around the fusion junction including this glycine was chemically synthesised and used for immunisation of (B6 x DBA/2) F1 mice. Flow cytometric analysis showed 3C10 antibody staining of a mouse NIH/3T3 transfectant (ERM5) with the type III EGFR deletion-mutant gene, but not one with wild-type EGFR. The antibody immunoprecipitated the truncated EGFR protein with a molecular mass of approximately 140 kDa from ERM5 cells. Immunostaining of glioblastomas revealed binding in the case with the type III EGFR mutation, the five other specimens without the mutation being negative despite overexpression of EGFR in some cases.

Tumor-associated antigens recognized by human monoclonal antibodies

BACKGROUND

Nonhuman monoclonal antibodies (MoAbs) of desired specificities have been studied in cancer treatment and tumor targeting with minimal success. Attempts of using humanized chimeric antibodies have not improved significantly their clinical applications. We have engaged in the development of human MoAbs by incorporating the in vitro immunization protocols to the nodal lymphocytes of cancer patients. Three human MoAbs thus generated were found to be strongly reactive with various human malignancies. The antigens recognized by the three antibodies were selected for immunochemical and biochemical characterizations.

METHODS

The antigens investigated were AgSK1, PA 1-2 and PA 3-1. The patterns of each antigen expression in various human cancer cell lines were studied by the immunocytochemical staining technique. The expression of AgSK1 in association with cellular proliferation was examined by the flow cytometry analysis. In studying the biochemical natures of these antigens, their sensitivities toward various chemical and physical treatments were determined. The antigens that were shown to be proteins were subjected to SDS-PAGE and Western blot for estimations of molecular weights.

RESULTS

The AgSK1 was detected in 10 human carcinoma cell lines but in none of the melanoma cell lines. This suggests that SK1 may be an epithelial or carcinoma marker. The phenotypic expressions of AgSK1 were shown to be associated with proliferation of carcinoma cells. Biochemically AgSK1 was a sialophycoprotein with an estimated molecular weight of 42-44 kilodaltons (kDa). HuMAb PA1-2 demonstrated a unique staining pattern at both the cytoplasmic and intercellular interface. The stained filamentlike structures extending from cell to cell indicated that Ag PA1-2 might play a role in cellular interactions. Biochemically, Ag PA1-2 appeared to be an asialocarbohydrate. The Ag PA3-1 was a cytoplasmic glycoprotein expressed by all 13 cell lines. The estimated molecular weights of PA3-1 were 164, 104, and 40 kDa.

CONCLUSIONS

Tumor-associated antigens recognized by the human MoAbs may be more relevant clinically than those recognized by the mouse immune system. Carcinoma-specific human MoAbs are desirable for cancer treatment and tumor localization.

Production of a human monoclonal antibody to normal basal and squamous cell carcinoma-associated antigen

A human monoclonal antibody, BM2, was produced by a hybridoma line generated by fusion of lymph node cells from a patient with squamous cell carcinoma (SCC) of the tongue with human B-lymphoblastoid cell line HO-323. BM2, an IgM class antibody, was reactive with all of the SCC cell lines tested. Frozen sections of normal and malignant tumor specimens were investigated to examine the reactivity of BM2 towards them. All 35 oral SCC specimens reacted with BM2. Normal stratified squamous epithelium showed positive staining in basal cells, but no staining was seen in other layers of the stratified epithelium, simple epithelium, and tissues of nonepithelial origin. Ductal basal cells of normal salivary gland also showed positive staining. Western blotting and immunoprecipitation analysis revealed that BM2 recognized 52 kDa membrane-associated protein. BM2 may therefore be a useful tool for biological and clinical studies of SCC.