Purification and characterization of a new 85-kDa glycoprotein antigen from human breast tumor

A new breast-tumor-associated antigen (BTAA) was purified and partially characterized from human breast tumor. By DEAE-cellulose discontinuous NaCl-gradient chromatography of a crude extract of human malignant breast tumor, 3 major protein peaks were obtained. Circulating antibodies against one of the protein peaks, HF1, was observed in breast-cancer patients. The antibodies were absent in patients with carcinoma of the uterine cervix, lung, stomach and liver or with benign breast diseases and in healthy women. Absorption of the sera of breast-cancer patients with normal human breast tissue pellet did not remove the HF1-reactive circulating antibodies. The BTAA was partially purified from HF1 by subjecting the fraction to SDS-PAGE and eluting the band 3 (HF1-3). Western-blot analysis confirmed the presence of the BTAA in HF1-3. Using an affinity column of protein-A-Sepharose-bound IgG, purified from breast-cancer patients' sera, the BTAA was also recovered from HF1. Purification of the BTAA was achieved by subjecting HF1 to size-exclusion high-performance liquid chromatography (SE-HPLC). The antigen was characterized as a glycoprotein with MW of approximately 85 kDa and appeared not to be related either to murine mammary-tumor virus (MuMTV) structural antigens or to human fetal antigens. The BTAA-reactive circulating antibodies in the breast-cancer patients were of IgG, sub-type, and the level of these antibodies significantly decreased in patients following surgical removal of the breast tumors.