SPECIFIC ANTIBODY FRAGMENTS FOR THE HUMAN CARCINOEMBRYONIC ANTIGEN (CEA)

摘要

The invention relates to mono- and bivalent (diabody) single-chain Fv-type (scFv) antibody fragments which are obtained using recombinant DNA techniques from the carcinoembryonic anti-antigen (CEA) monoclonal antibody (McA) CB/ior-CEA.1. The aforementioned McA has a high affinity for the CEA and is used in the diagnosis and monitoring of colorectal tumours in humans. As with the original McA, diabody and monovalent scFv fragments exhibit high affinities for the human CEA and recognise an epitope that is dependent on carbohydrate conservation. The diabody and monovalent scFv fragments have affinity constants for the CEA of (5.0 +/- 0.4) x 10<9> L mol<-1> and (2.8 +/- 0.3) x 10<10> L mol<-1> respectively. The two aforementioned fragments do not display cross-reactivity with normal human tissues and cells, except for the normal colonic mucosa where the CEA is occasionally present. Said fragments can be produced through expression in recombinant micro-organisms from the cloning of nucleic acid sequences that code for variable regions obtained from the hybridoma that is produced by the CB/ior-CEA.1 McA. As with the original McA, the diabody and the monovalent scFv have a capacity for the in vivo identification in rats of human CEA-producing cells which grow forming tumours. The monovalent scFv and diabody do not posses Fc domains and the molecular sizes of said monovalent scFv and diabody are 5 and 2.5 times, respectively, less than the rat McA. As a result, the aforementioned monovalent scFv and diabody can better penetrate tissues in vivo and are less immunogenic in humans.