New approaches for the detection and characterization of alpha-fetoprotein epitope variants

Alpha-fetoprotein (AFP) is an embryo-specific protein of mammalian sera that consists of a single glycosylated polypeptide chain (approximately 70 kD) with 5-6 epitope clusters located on the native molecule. We have elaborated three approaches for the separation of AFP into fractions (variants) that are different in the distinct epitope expression on the native molecule. For this, we have used three technologies largely based on immunoaffinity electrochromatography and electrophoresis/immunoblotting. The separation of these variants was facilitated using monoclonal antibodies previously characterized to the 5 epitope clusters and two individual epitopes on AFP in the ISOBM international workshop. We have shown that these approaches facilitate the identification of cryptic epitopes in AFP, and the relevance of these findings is discussed.