A binding molecule comprising at least three binding specificities, wherein (a) the first specificity is for a Hepatitis B virus surface antigen selected from HBV small surface antigen, HBV medium surface antigen and HBV large surface antigen; (b) the second and third specificity are for CD3 and CD28, respectively; and (c) each binding specificity is provided by one or more binding sites, each binding site being independently provided by a set of six complementarity determining regions (CDRs), wherein said set of six CDRs consists of a first set of three CDRs and a second set of three CDRs, wherein said first and said second set is each comprised in an immunoglobulin domain wherein said binding molecule has structure or: wherein structure is a non-covalent dimer consisting of two bispecific bivalent polypeptides, and wherein in structure the scFv αCD28 is a single chain variable fragment against CD28 fragment, the scFv αCD3 is a single chain variable fragment against CD3, the 2 scFv αHBs are two single chain variable fragments against a HBV surface antigen, Chain A and Chain B are polypeptides with distinct amino acid sequences, Chain A and Chain B are connected to the 2 scFv αHBs by an amphiphilic coiled-coil dimerization domain, Chain A is connected to the scFv αCD28 by a peptide linker, and Chain B is connected to the scFv αCD3 by a peptide linker; and wherein structure has four binding sites which each are provided by two immunoglobulin domains, said two immunoglobulin domains being located on the same polypeptide chain, and a fifth binding site which is formed by two immunoglobulin domains being located on distinct polypeptide chains, and wherein in structure the 2 scFV αHBs are two single chain variable fragments against a HBV surface antigen, the 1 Fab αHB is a Fab fragment against HBV surface antigens, the scFv αCD28 is a single chain variable fragment against CD28, the scFv αCD3 is a single chain variable fragment against CD3, and each of the four scFvs is connected to the Fab by a peptide linker. (a) the first specificity is for a Hepatitis B virus surface antigen selected from HBV small surface antigen, HBV medium surface antigen and HBV large surface antigen; (b) the second and third specificity are for CD3 and CD28, respectively; and (c) each binding specificity is provided by one or more binding sites, each binding site being independently provided by a set of six complementarity determining regions (CDRs), wherein said set of six CDRs consists of a first set of three CDRs and a second set of three CDRs, wherein said first and said second set is each comprised in an immunoglobulin domain wherein said binding molecule has structure or: wherein structure is a non-covalent dimer consisting of two bispecific bivalent polypeptides, and wherein in structure the scFv αCD28 is a single chain variable fragment against CD28 fragment, the scFv αCD3 is a single chain variable fragment against CD3, the 2 scFv αHBs are two single chain variable fragments against a HBV surface antigen, Chain A and Chain B are polypeptides with distinct amino acid sequences, Chain A and Chain B are connected to the 2 scFv αHBs by an amphiphilic coiled-coil dimerization domain, Chain A is connected to the scFv αCD28 by a peptide linker, and Chain B is connected to the scFv αCD3 by a peptide linker; and wherein structure has four binding sites which each are provided by two immunoglobulin domains, said two immunoglobulin domains being located on the same polypeptide chain, and a fifth binding site which is formed by two immunoglobulin domains being located on distinct polypeptide chains, and wherein in structure the 2 scFV αHBs are two single chain variable fragments against a HBV surface antigen, the 1 Fab αHB is a Fab fragment against HBV surface antigens, the scFv αCD28 is a single chain variable fragment against CD28, the scFv αCD3 is a single chain variable fragment against CD3, and each of the four scFvs is connected to the Fab by a peptide linker. the scFv αCD28 is a single chain variable fragment against CD28 fragment, the scFv αCD3 is a single chain variable fragment against CD3, the 2 scFv αHBs are two single chain variable fragments against a HBV surface antigen, Chain A and Chain B are polypeptides with distinct amino acid sequences, Chain A and Chain B are connected to the 2 scFv αHBs by an amphiphilic coiled-coil dimerization domain, Chain A is connected to the scFv αCD28 by a peptide linker, and Chain B is connected to the scFv αCD3 by a peptide linker; and wherein structure has four binding sites which each are provided by two immunoglobulin domains, said two immunoglobulin domains being located on the same polypeptide chain, and a fifth binding site which is formed by two immunoglobulin domains being located on distinct polypeptide chains, and wherein in structure the 2 scFV αHBs are two single chain variable fragments against a HBV surface antigen, the 1 Fab αHB is a Fab fragment against HBV surface antigens, the scFv αCD28 is a single chain variable fragment against CD28, the scFv αCD3 is a single chain variable fragment against CD3, and each of the four scFvs is connected to the Fab by a peptide linker.