IMPROVED TUMOR TARGETING BY DISULFIDE STABILIZED DIABODIES EXPRESSED IN PICHIA-PASTORIS

Diabodies are dimeric antibody fragments held together by associated h eavy and light chain variable domains present on different polypeptide chains. To improve their stability we have introduced cysteine residu es into the V-domains to promote the disulphide crosslinking of the di mer. A crosslinked bivalent diabody against carcinoembryonic antigen ( CEA) and a crosslinked bispecific diabody against CEA and the T-cell c o-receptor CD3 were expressed from Pichia pastoris and Escherichia col i by secretion. From Pichia (but not E.coli) the chains were almost qu antitatively crosslinked. Compared with the parent diabodies both cros slinked diabodies were more stable to heat (by >7 degrees C) and the c rosslinked bivalent diabody showed improved localization to CEA(+) hum an tumour xenografts in nude mice.