ANTIIDIOTYPIC MONOCLONAL-ANTIBODY AB3, REACTING WITH THE PRIMARY ANTIGEN (CEA), CAN LOCALIZE IN HUMAN COLON-CARCINOMA XENOGRAFTS AS EFFICIENTLY AS AB1

BALB/c mice were immunized with anti-idiotypic monoclonal (MAb) antibo dy (anti-Id or Ab2) directed against an AB1 MAb anti-carcinoembryonic (CEA) in order to obtain AB3 MAbs (anti-anti-Id). AB3 MAbs were shown to recognise the primary antigen (CEA) and one of them was tested exte nsively in vitro and in vivo. This AB3 MAb was shown to bind specifica lly to CEA on frozen sections of a human colon carcinoma by immuoperox idase. Scatchard plot analyses showed that the affinity of this AB3 wa s of the same order of magnitude as the AB1. In vivo experiments, in n ude mice bearing CEA-producing human colon-carcinoma xenografts showed that up to 30% of the intravenously injected dose of I-125-labelled A B3 were localized per gram of tumour tissue. Furthermore, calculation of the ratios of AB3 concentration in the tumour over those in normal organs such as lung, liver, kidney, spleen and bone gave relatively hi gh values similar to results obtained with AB1. All together our resul ts show that AB3 can localize as efficiently and specifically in the t umour as AB1, despite the fact that the mice from which it was derived were immunized with a mouse MAb (AB2) and had never been exposed to C EA. (C) 1994 Wiley-Liss, Inc.