An antibody is provided. The antibody comprises an Fc region and a Fab region, wherein:(i) the Fc region comprises two non-identical heavy chains, wherein at least one of the two non-identical heavy chains comprises an amino acid modification so as to form complementation between the two non-identical heavy chains thereby increasing the probability of forming heterodimers of the non-identical heavy chains and decreasing the probability of forming homodimers of identical heavy chains； and(ii) the Fab region comprises a first covalent link between a first heavy chain and a first light chain of the Fab region and a second covalent link between a second heavy chain and a second light chain of said Fab region, wherein a position of the first covalent link relative to the first heavy chain is different to a position of the second covalent link relative to the second heavy chain.
