Idiotypic replica of an anti-human tumour-associated antigen monoclonal antibody. DNA sequence comparison between Ab1 and Ab3.

2G-3 is an anti-anti-idiotypic MoAb (Ab3) obtained upon immunization with a monoclonal Ab2 (A3B10), which behaves as the 'internal image' of CaMBr1, a saccharide epitope defined by MoAb MBr1 (Ab1). CaMBr1 is expressed on glycoconjugates of the human mammary carcinoma cell line MCF-7 and on normal and neoplastic mammary gland epithelial cells. Ab1 and Ab3, although exhibiting, in many respects, superimposable paratopic and idiotopic specificities, show a non-identical fine immunoreactivity, since 2G-3 has a preferential reactivity with the saccharidic epitope mounted on glycoproteins, while MBr1 reacts with both glycoproteins and glycolipids. V-region sequence analysis has shown that: (i) the VK genes employed belong to different families (VK1 and VK10); (ii) the JK2 segment is shared by the two L chains (thus a high degree of homology is observed between VK CDR3s); (iii) the VH genes employed derive from the same family VHIIB/J558 (but show CDR homology only in CDR2); (iv) different JH region genes are employed. These data, together with the comparison of deduced secondary structure parameters, give further evidence for the possible production of similar combining sites using different VH and VL germ-line genes.