Patent ID: 8053562

Claim:
An antibody fragment having a heavy chain constant region (C H 1) and a light chain constant region (C L ), one or more effector molecules being attached to said fragment, said fragment characterized in that the native interchain disulphide bond between native interchain cysteines in the heavy (C H 1) and light (C L ) chain constant regions is absent and the heavy chain (C H 1) and light chain (C L ) constant regions are linked by an interehain disulphide bond between a pair of engineered cysteines, one in the light chain constant (C L )region and the other in the heavy chain constant (C H 1) region, wherein the position of the pair of engineered cysteines is selected form position 116 of the light chain and 138 of the heavy chain, position 119 of the light chain and 128 of the heavy chain or position 210 of the light chain and 129 of the heavy chain, said positions as defined by the Kabat numbering system for IgG1.