Production of functionally active murine and murine::human chimeric F(ab')2 fragments in COS-1 cells

CD3 x CD28 cross-interacting bispecific antibodies improve tumor cell dependent T-cell activation

Bispecific antibodies (Bs-Abs) containing an anti-CD3 and an anti-TAA specificity can recruit T cells to the tumor for cancer immunotherapy. To be effective, efficient activation at the tumor site is a prerequisite. This can be achieved by triggering both the T-cell receptor and the co-stimulatory molecule CD28. We engineered two recombinant cross-interacting Bs-Abs (CriBs-Abs) by incorporating a peptide tag and its cognate single-chain variable fragment (scFv), respectively, into a pair of (tumor x CD3) and (tumor x CD28) binding Bs-Abs. A 30-fold lower concentration of the activating CriBs-Ab as compared to non interacting Bs-Ab was sufficient for strong T-cell activation in the presence of tumor cells. One thousand-fold higher concentrations of both CriBs-Abs were required for marginal T-cell activation (70-fold below maximal response) in the absence of tumor cells. An optimized stoichiometry (1 : 1000) of activating versus co-stimulating CriBs-Ab thus allowed low doses of activating CriBs-Ab to induce tumor-cell dependent T-cell activation when used in combination with high concentrations of the pre-targeted co-stimulating CriBs-Ab in vitro. This indicates a large window of operation in which only tumor cell dependent T-cell activation is induced and systemic tumor cell independent T-cell activation is avoided, while ensuring optimal activation with a low concentration of the activating CriBs-Ab, which has the highest potential to induce toxic effects in vivo.

Optimizing expression and purification from cell culture medium of trispecific recombinant antibody derivatives

Antibody fragments offer the possibility to build multifunctional manifolds tailored to meet a large variety of needs. We optimized the production of a manifold consisting of one (bibody) or two (tribody) single-chain variable fragments coupled to the C-terminus of Fab chains. Different strong mammalian promoters were compared and the influence of expression media on production and recovery was investigated. Since the physical and chemical nature of these molecules largely depends on the nature of the antibody building blocks incorporated, a generally applicable process for the purification of recombinant antibody derivatives from serum containing mammalian cell culture medium was designed. To this end we compared protein L, hydroxyapatite, immobilized metal affinity chromatography, cation-exchange chromatography and hydrophobic charge induction chromatography.

A new model for intermediate molecular weight recombinant bispecific and trispecific antibodies by efficient heterodimerization of single chain variable domains through fusion to a Fab-chain

Due to their specificity and versatility in use, bispecific antibodies (BsAbs) are promising therapeutic tools in tomorrow's medicine, provided sufficient BsAb can be produced. Expression systems favoring efficient heterodimerization of intermediate-sized bispecific antibodies will significantly improve existing production methods. Recombinant BsAb can be made by fusing single chain variable fragments (scFv) to a heterodimerization domain. We compare the efficiency of the isolated CL and CH1 constant domains with complete Fab chains to drive heterodimerization of BsAbs in mammalian cells. We found that the isolated CL:CH1 domain interaction was inefficient for secretion of heterodimers. However, when the complete Fab chains were used, secretion of a heterodimerized bispecific antibody was successful. Since the Fab chain encodes a binding specificity on its own, bispecific (BsAb) or trispecific (TsAb) antibodies can be made by C-terminal fusion of scFv molecules to the L or Fd Fab chains. This gave rise to disulphide stabilized Fab-scFv BsAb (Bibody)or Fab-(scFv)2 TsAb (Tribody) of intermediate molecular size. Heterodimerization of the L and Fd-containing fusion proteins was very efficient, and up to 90% of all secreted antibody fragments was in the desired heterodimerized format. All building blocks remained functional in the fusion product, and the bispecific character of the molecules as well as the immunological functionality was demonstrated.

Fab chains as an efficient heterodimerization scaffold for the production of recombinant bispecific and trispecific antibody derivatives

Due to their multispecificity and versatility, bispecific Abs (BsAbs) are promising therapeutic tools in tomorrow's medicine. Especially intermediate-sized BsAbs that combine body retention with tissue penetration are valuable for therapy but necessitate expression systems that favor heterodimerization of the binding sites for large-scale application. To identify heterodimerization domains to which single-chain variable fragments (scFv) can be fused, we compared the efficiency of heterodimerization of CL and CH1 constant domains with complete L and Fd chains in mammalian cells. We found that the isolated CL:CH1 domain interaction was inefficient for secretion of heterodimers. However, when the complete L and Fd chains were used, secretion of L:Fd heterodimers was highly successful. Because these Fab chains contribute a binding moiety, C-terminal fusion of a scFv molecule to the L and/or Fd chains generated BsAbs or trispecific Abs (TsAbs) of intermediate size (75-100 kDa). These disulfide-stabilized bispecific Fab-scFv ("bibody") and trispecific Fab-(scFv)(2) ("tribody") heterodimers represent up to 90% of all secreted Ab fragments in the mammalian expression system and possess fully functional binding moieties. Furthermore, both molecules recruit and activate T cells in a tumor cell-dependent way, whereby the trispecific derivative can exert this activity to two different tumor cells. Thus we propose the use of the disulfide-stabilized L:Fd heterodimer as an efficient platform for production of intermediate-sized BsAbs and TsAbs in mammalian expression systems.

A COS-cell-based system for rapid production and quantification of scFv::IgC kappa antibody fragments

Single-chain Fv (scFv) antibody (Ab) fragments were transiently produced in COS-1 cells utilizing a mammalian expression vector featuring a murine immunoglobulin (Ig) light-chain leader sequence for efficient secretion and a murine Ig kappa constant domain (IgC kappa) for detection. Several hundred milliliters of supernatants from large-scale COS cell transfections were sufficient to purify the scFv::IgC kappa fusion proteins by one-step affinity chromatography utilizing an immobilized rat anti-mouse IgC kappa monoclonal Ab. Furthermore, the murine IgC kappa domain allowed for accurate quantification of the scFv::IgC kappa fusion protein secreted into the COS cell supernatant by a sandwich enzyme-linked immunosorbent assay (S-ELISA).

Production in Escherichia coli of a functional murine and murine::human chimeric F(ab')2 fragment and mature antibody directed against human placental alkaline phosphatase

We report the production in Escherichia coli of a murine antibody IgG2b, a murine::human chimeric antibody IgG3 and the corresponding F(ab')2 fragments, all directed against human placental alkaline phosphatase, a tumor marker. The cDNA of the heavy chain of the mature antibodies and their fragments were linked up to the bacterial alkaline phosphatase signal sequence and were placed under control of the inducible tac promoter. Coexpression with the murine kappa light chain resulted in production of functional dimeric, trimeric and tetrameric, mature antibodies and F(ab')2 fragments in the periplasm of E. coli in a yield of 200-300 micrograms l-1. High amounts of light and heavy chains were present also in the insoluble fraction.

A bifunctional murine::human chimeric antibody with one antigen-binding arm replaced by bacterial beta-lactamase

We here report the genetic engineering of a murine::human chimeric antibody--directed against the tumor marker human placental alkaline phosphatase--in which one antigen-binding arm (Fab) has been replaced by Escherichia coli beta-lactamase (Bla). A mutated Bla gene in which the termination codon had been replaced by GAG, was fused in-phase to the cDNA sequence encoding the hinge region, CH2 and CH3 of the human IgG3 heavy chain. The resulting BlaHG3f fusion gene was placed under control of the Simian Virus 40 late promoter, and transiently expressed in COS-1 cells together with the genes encoding the murine light and murine::human chimeric heavy chains. Approximately 200 ng/ml of correctly assembled bifunctional antibody-Bla immunoconjugates were detected in the culture supernatant. This observation indicates that Bla (with its own leader peptide) can efficiently direct secretion into the culture medium of adventitious sequences fused at its C-terminus. Furthermore, the assembly in the Fc region was not affected by steric hindrance due to a Bla moiety and an Fab arm in close proximity. The antibody-Bla immunoconjugate could be of therapeutic value for the activation of cephalosporin-based anti-cancer prodrugs at the tumor site. Moreover, the expression strategy adopted here is particularly suitable for a quick and convenient analysis of newly designed gene products in which the Bla moiety has been replaced by other enzymes or by antigen-binding fragments in order to engineer bispecific antibodies.

Assembly of an antibody and its derived antibody fragment in Nicotiana and Arabidopsis

The yield and assembly of an IgG1 antibody and its derived F(ab) fragment were compared in Nicotiana and Arabidopsis. The results obtained showed a lot of interclonal variability. For 45% of the primary transgenic calluses, antigen-binding entities represented less than 0.1% of the total soluble protein (TSP). Only two of the 103 analysed transformants contained more than 1% of antigen-binding protein, with 1.26% being the highest yield. Analogous amounts of complete antibody and F(ab) accumulated in primary callus tissue. Moreover, yields were in the same range for both species as far as primary callus tissue is concerned. However, the accumulation of the F(ab) fragment in leaf tissue of regenerated plants differed significantly between Nicotiana and Arabidopsis. The F(ab) fragment accumulated to only 0.044% of TSP in Nicotiana leaves but up to 1.3% in Arabidopsis leaves. Furthermore, both species showed differences in the assembly pattern of the complete antibody. Whereas Arabidopsis contained primarily fully assembled antibodies of 150 kDa, Nicotiana showed an abundance of fragments in the 50 kDa range.

Disulphide bridge formation in the periplasm of Escherichia coli: beta-lactamase:: human IgG3 hinge fusions as a model system

We report the construction and the expression in Escherichia coli of three different fusion genes encoding the extended human IgG3 hinge region (Hi) fused in-phase to the C-terminal end of bacterial TEM1 beta-lactamase (Bla). In the first fusion gene blahi, TEM1 beta-lactamase (Bla). In the first fusion gene blahi, the hinge sequence was directly coupled to the 3' end of the beta-lactamase gene, whereas in the two other constructs, blal1hi and blal2hi, a linker encoding 14 and 10 amino acids, respectively, was inserted between the two subunits. After expression (24 h, 20 degrees C) under control of the constitutive kanamycin phosphoribosyl transferase promoter, the fusion proteins, BlaHi, BlaL1Hi and BlaL2Hi, respectively, were almost exclusively detected in the periplasmic fraction, and they conferred carbenicillin-resistance to the cells. These results indicate that beta-lactamase can efficiently direct the export of proteins fused to its C-terminus, and moreover, at least some of the exported fusion proteins must carry the beta-lactamase moiety in a properly folded form. Analysis of their assembly, however, revealed that only a minor fraction was recovered as the expected F(ab')2-like dimer. The presence in the periplasm of 'oxidized' monomers (with intrachain disulphide bonds) as well as of several high-molecular-mass proteins, probably resulting from the association between monomers and other cysteine-rich proteins, strongly suggests that the conditions in the bacterial periplasm are insufficient to allow proper assembly of multimeric proteins with several interchain disulphide bonds.