Characterization and distribution of an oncofetal antigen (M2A antigen) expressed on testicular germ cell tumours

M2A antigen is an oncofetal antigen associated with germ cell neoplasia, pr esent in testis on fetal gonocytes and re-expressed on carcinoma in situ (C IS) and germ cell tumours. We developed a panel of monoclonal antibodies (m Ab), M2A (IgG2a), D1-26 (IgG2b) and D2-40 (IgG1), to this antigen in order to characterize its structure and study its distribution among germ cell tu mours. M2A antigen was purified by sequential lectin and antibody affinity chromatography and characterized as a monomeric M-r 40 000 surface sialogly coprotein, extensively glycosylated with O-linked carbohydrate structures, but devoid of N-inked sugars. Terminal sialic acid residues were required f or reactivity with mAb M2A and D1-26, but not D2-40. Sections of 69 testicu lar germ cell tumours, fixed in formalin and embedded in paraffin, were sta ined with mAb D2-40 to examine the distribution of M2A antigen. Uniform mem brane staining was observed in seminomas, and focal staining in 69% of embr yonal carcinomas, 29% of teratomas and 25% of yolk sac rumours. CIS in the vicinity of all germ cell tumours also displayed uniform membrane staining. The characterization of M2A antigen, and the development of mAb which reac t with it in conventionally preserved archival specimens, provide important initiatives to study the origin and progression of germ cell neoplasia.