Expression of a bispecific dsFv-dsFv' antibody fragment in Escherichia coli

Antibody-Incorporated Nanomedicines for Cancer Therapy

Antibody-based cancer therapy, one of the most significant therapeutic strategies, has achieved considerable success and progress over the past decades. Nevertheless, obstacles including limited tumor penetration, short circulation half-lives, undesired immunogenicity, and off-target side effects remain to be overcome for the antibody-based cancer treatment. Owing to the rapid development of nanotechnology, antibody-containing nanomedicines that have been extensively explored to overcome these obstacles have already demonstrated enhanced anticancer efficacy and clinical translation potential. This review intends to offer an overview of the advancements of antibody-incorporated nanoparticulate systems in cancer treatment, together with the nontrivial challenges faced by these next-generation nanomedicines. Diverse strategies of antibody immobilization, formats of antibodies, types of cancer-associated antigens, and anticancer mechanisms of antibody-containing nanomedicines are provided and discussed in this review, with an emphasis on the latest applications. The current limitations and future research directions on antibody-containing nanomedicines are also discussed from different perspectives to provide new insights into the construction of anticancer nanomedicines.

Generation and functional analysis of single chain variable fragments (scFvs) targeting the nucleocapsid protein of Porcine epidemic diarrhea virus

Abstract

Porcine epidemic diarrhea virus (PEDV) is the causative agent of porcine epidemic diarrhea, which can cause death in suckling piglets. Vaccines confer only partial protection against new mutant strains, whereas antibodies targeting virus-encoded proteins may be effective prophylactics. In this study, we constructed a recombinant single chain variable fragment (scFv) library from the spleens of two pigs immunized with a recombinant PEDV nucleocapsid (N) protein. Among the positive clones directed against PEDV N protein isolated from the library, four scFvs that showed higher affinity for N were functionally analyzed. These scFvs specifically bound to the PEDV N protein, but not to the transmissible gastroenteritis virus (TGEV) N protein. Their framework regions were highly conserved, whereas their complementarity-determining regions displayed clear diversity. An immunofluorescence assay showed the co-localization of the four scFvs with PEDV N protein in cells. They significantly suppressed PEDV replication, detected with reverse transcription (RT)-quantitative PCR (qPCR; P < 0.01). Two of them significantly reduced the viral titer at 48 hpi and 72 hpi (P < 0.05). In addition, they observably suppressed the production of viral protein at 72 hpi. The expression of interferons, interferon regulatory factor 3 (IRF3), and IRF7 was assessed with RT-qPCR, which indicated that PEDV dramatically suppressed the transcription of interferon-λ1 and IRF7 and that the scFvs significantly upregulated their expression (P < 0.05). These findings facilitated the investigation of the mechanism by which PEDV evaded the host immune response and suggested that these porcine scFvs were potential candidate agents for the prevention and treatment of porcine diarrhea caused by PEDV.

Key points

• Four scFvs targeting PEDV N protein were generated from porcine spleens

• These scFvs co-localized with PEDV N protein and suppressed PEDV replication

• These scFvs significantly upregulated IFN-λ1 expression

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-021-11722-z.

Single-Chain Fragment Variables Targeting Leukocidin ED Can Alleviate the Inflammation of Staphylococcus aureus-Induced Mastitis in Mice

Staphylococcus aureus is a vital bovine mastitis pathogen causing huge economic losses to the dairy industry worldwide. In our previous studies, leukotoxin ED (LukED) was detected in most S. aureus strains isolated from bovine mastitis. Here, four single-chain fragment variables (scFvs) (ZL8 and ZL42 targeting LukE, ZL22 and ZL23 targeting LukD) were obtained using purified LukE and LukD proteins as the antigens after five rounds of bio-panning. The complementarity-determining region 3 (CDR3) of the VH domain of these scFvs exhibited significant diversities. In vitro, the scFvs significantly decreased LukED-induced cell killing by inhibiting the binding of LukED to chemokine receptors (CCR5 and CXCR2) and reduced the death rates of bovine neutrophils and MAC-T cells caused by LukED and S. aureus (p < 0.05). In an S. aureus-induced mouse mastitis model, histopathology and MPO results revealed that scFvs ameliorated the histopathological damages and reduced the infiltration of inflammatory cells (p < 0.05). The ELISA and qPCR assays showed that scFvs reduced the transcription and expression levels of Tumor Necrosis Factor-alpha (TNF-α), interleukin-1β (IL-1β), IL-6, IL-8 and IL-18 (p < 0.05). The overall results demonstrated the protective anti-inflammatory effect of scFvs in vitro and in vivo, enlightening the potential role of scFvs in the prevention and treatment of S. aureus-induced mastitis.

Shelf-Life Extension of Fc-Fused Single Chain Fragment Variable Antibodies by Lyophilization

Generation of sequence defined antibodies from universal libraries by phage display has been established over the past three decades as a robust method to cope with the increasing market demand in therapy, diagnostics and research. For applications requiring the bivalent antigen binding and an Fc part for detection, phage display generated single chain Fv (scFv) antibody fragments can rapidly be genetically fused to the Fc moiety of an IgG for the production in eukaryotic cells of antibodies with IgG-like properties. In contrast to conversion of scFv into IgG format, the conversion to scFv-Fc requires only a single cloning step, and provides significantly higher yields in transient cell culture production than IgG. ScFv-Fcs can be effective as neutralizing antibodies in vivo against a panel of pathogens and toxins. However, different scFv fragments are more heterologous in respect of stability than Fab fragments. While some scFv fragments can be made extremely stable, this may change due to few mutations, and is not predictable from the sequence of a newly selected antibody. To mitigate the necessity to assess the stability for every scFv-Fc antibody, we developed a generic lyophilization protocol to improve their shelf life. We compared long-term stability and binding activity of phage display-derived antibodies in the scFv-Fc and IgG format, either stored in liquid or lyophilized state. Conversion of scFv-Fcs into the full IgG format reduced protein degradation and aggregation, but in some cases compromised binding activity. Comparably to IgG conversion, lyophilization of scFv-Fc resulted in the preservation of the antibodies' initial properties after storage, without any drop in affinity for any of the tested antibody clones.

Anti-Staphylococcus aureus Single-Chain Fragment Variables Play a Protective Anti-Inflammatory Role In Vitro and In Vivo

Staphylococcus aureus is a causative agent of bovine mastitis, capable of causing significant economic losses to the dairy industry worldwide. This study focuses on obtaining single-chain fragment variables (scFvs) against the virulence factors of S. aureus and evaluates the protective effect of scFvs on bovine mammary epithelial (MAC-T) cells and mice mammary gland tissues infected by S. aureus. After five rounds of bio-panning, four scFvs targeting four virulence factors of S. aureus were obtained. The complementarity-determining regions (CDRs) of these scFvs exhibited significant diversities, especially CDR3 of the VH domain. In vitro, each of scFvs was capable of inhibiting S. aureus growth and reducing the damage of MAC-T cells infected by S. aureus. Preincubation of MAC-T cells with scFvs could significantly attenuate the effect of apoptosis and necrosis compared with the negative control group. In vivo, the qPCR and ELISA results demonstrated that scFvs reduced the transcription and expression of Tumor Necrosis Factor alpha (TNF-α), interleukin-1β (IL-1β), IL-6, IL-8, and IL-18. Histopathology and myeloperoxidase (MPO) results showed that scFvs ameliorated the histopathological damages and reduced the inflammatory cells infiltration. The overall results demonstrated the positive anti-inflammatory effect of scFvs, revealing the potential role of scFvs in the prevention and treatment of S. aureus infections.

Selection for Anti-transferrin Receptor Bispecific T-cell Engager in Different Molecular Formats

Selecting an ideal molecular format from diverse structures is a major challenge in developing a bispecific antibody (BsAb). To choose an ideal format of anti-CD3 × anti-transferrin receptor (TfR) bispecific antibodies for clinical application, we constructed TfR bispecific T-cell engager (BiTE) in two extensively applied formats, including single-chain tandem single-chain variable fragments (scFvs) and double-chain diabodies, and evaluated their functional characterizations in vitro. Results demonstrated that TfR-BiTE in both formats directed potent killing of TfR⁺ HepG2 cells. However, compared to two-chain diabodies, scFvs were more efficient in antigen binding and TfR⁺ target killing. Furthermore, different domain orders in scFvs would also be evaluated because single-TfR-CD3-His was preferable to single-CD3-TfR-His in immunotherapeutic strategies. Thus, the single-chain tandem TfR-CD3 format was favored for further investigation in cancer therapy.

Characterization and analysis of scFv-IgG bispecific antibody size variants

Bispecific antibodies are an emergent class of biologics that is of increasing interest for therapeutic applications. In one bispecific antibody format, single-chain variable fragments (scFv) are linked to or inserted in different locations of an intact immunoglobulin G (IgG) molecule to confer dual epitope binding. To improve biochemical stability, cysteine residues are often engineered on the heavy- and light-chain regions of the scFv to form an intrachain disulfide bond. Although this disulfide bond often improves stability, it can also introduce unexpected challenges to manufacturing or development. We report size variants that were observed for an appended scFv-IgG bispecific antibody. Structural characterization studies showed that the size variants resulted from the engineered disulfide bond on the scFv, whereby the engineered disulfide was found to be either open or unable to form an intrachain disulfide bond due to cysteinylation or glutathionylation of the cysteines. Furthermore, the scFv engineered cysteines also formed intermolecular disulfide bonds, leading to the formation of highly stable dimers and aggregates. Because both the monomer variants and dimers showed lower bioactivity, they were considered to be product-related impurities that must be monitored and controlled. To this end, we developed and optimized a robust, precise, and accurate high-resolution size-exclusion chromatographic method, using a statistical design-of-experiments methodology.

The making of bispecific antibodies

During the past two decades we have seen a phenomenal evolution of bispecific antibodies for therapeutic applications. The 'zoo' of bispecific antibodies is populated by many different species, comprising around 100 different formats, including small molecules composed solely of the antigen-binding sites of two antibodies, molecules with an IgG structure, and large complex molecules composed of different antigen-binding moieties often combined with dimerization modules. The application of sophisticated molecular design and genetic engineering has solved many of the technical problems associated with the formation of bispecific antibodies such as stability, solubility and other parameters that confer drug properties. These parameters may be summarized under the term 'developability'. In addition, different 'target product profiles', i.e., desired features of the bispecific antibody to be generated, mandates the need for access to a diverse panel of formats. These may vary in size, arrangement, valencies, flexibility and geometry of their binding modules, as well as in their distribution and pharmacokinetic properties. There is not 'one best format' for generating bispecific antibodies, and no single format is suitable for all, or even most of, the desired applications. Instead, the bispecific formats collectively serve as a valuable source of diversity that can be applied to the development of therapeutics for various indications. Here, a comprehensive overview of the different bispecific antibody formats is provided.

Functional comparison of single-chain and two-chain anti-CD3-based bispecific antibodies in gene immunotherapy applications

Gene therapy to achieve in vivo secretion of recombinant anti-CD3 x anti-tumor bispecific antibodies in cancer patients is being explored as a strategy to counterbalance rapid renal elimination, thereby sustaining levels of bispecific antibodies in the therapeutic range. Here, we performed a comparative analysis between single- and two-chain configurations for anti-CD3 x anti-CEA (carcinoembryonic antigen) bispecific antibodies secreted by genetically-modified human cells. We demonstrate that tandem single-chain variable fragment (scFv) antibodies and two-chain diabodies are expressed as soluble secreted proteins with similar yields. However, we found significant differences in their biological functionality (i.e., antigen binding) and in their ability to induce non-specific T cell activation. Whereas single-chain tandem scFvs induced human T cell activation and proliferation in an antigen-independent manner, secreted two-chain diabodies exerted almost no proliferative stimulus when human T cells were cultured alone or in co-cultures with CEA negative cells. Thus, our data suggest that two-chain diabodies are preferable to single-chain tandem scFvs for immunotherapeutic strategies comprising in vivo secretion of bispecific antibodies aiming to recruit and activate anticancer specific lymphocytic effector T cells.

Bispecific antibody derivatives with restricted binding functionalities that are activated by proteolytic processing

We have designed bispecific antibodies that bind one target (anti-Her3) in a bivalent IgG-like manner and contain one additional binding entity (anti-cMet) composed of one V(H) and one V(L) domain connected by a disulfide bond. The molecules are assembled by fusing a V(H,Cys44) domain via flexible connector peptides to the C-terminus of one H-chain (heavy chain), and a V(L,Cys100) to another H-chain. To ensure heterodimerization during expression in mammalian cells, we introduced complementary knobs-into-holes mutations into the different H-chains. The IgG-shaped trivalent molecules carry as third binding entity one disulfide-stabilized Fv (dsFv) without a linker between V(H) and V(L). Tethering the V(H) and V(L) domains at the C-terminus of the C(H)3 domain decreases the on-rates of the dsFv to target antigens without affecting off-rates. Steric hindrance resolves upon removal of one side of the double connection by proteolysis: this improves flexibility and accessibility of the dsFv and fully restores antigen access and affinity. This technology has multiple applications: (i) in cases where single-chain linkers are not desired, dsFvs without linkers can be generated by addition of furin site(s) in the connector that are processed during expression within mammalian cells; (ii) highly active (toxic) entities which affect expression can be produced as inactive dsFvs and subsequently be activated (e.g. via PreScission cleavage) during purification; (iii) entities can be generated which are targeted by the unrestricted binding entity and can be activated by proteases in target tissues. For example, Her3-binding molecules containing linkers with recognition sequences for matrix metalloproteases or urokinase, whose inactivated cMet binding site is activated by proteolytic processing.

The P25 pathogenicity factor of Beet necrotic yellow vein virus targets the sugar beet 26S proteasome involved in the induction of a hypersensitive resistance response via interaction with an F-box protein

P25, a Beet necrotic yellow vein virus (BNYVV) pathogenicity factor, interacts with a sugar beet protein with high homology to Arabidopsis thaliana kelch repeat containing F-box family proteins (FBK) of unknown function in yeast. FBK are members of the Skp1-Cullin-F-box (SCF) complex that mediate protein degradation. Here, we confirm this sugar beet FBK-P25 interaction in vivo and in vitro and provide evidence for in planta interaction and similar subcellular distribution in Nicotiana tabacum leaf cells. P25 even interacts with an FBK from A. thaliana, a BNYVV nonhost. FBK functional classification was possible by demonstrating the interaction with A. thaliana orthologs of Skp1-like (ASK) genes, a member of the SCF E3 ligase. By means of a yeast two-hybrid bridging assay, a direct effect of P25 on SCF-complex formation involving ASK1 protein was demonstrated. FBK transient Agrobacterium tumefaciens-mediated expression in N. benthamiana leaves induced a hypersensitive response. The full-length F-box protein consists of one F-box domain followed by two kelch repeats, which alone were unable to interact with P25 in yeast and did not lead to cell-death induction. The results support the idea that P25 is involved in virus pathogenicity in sugar beet and suggest suppression of resistance response.

Towards a universal disulphide stabilised single chain Fv format: importance of interchain disulphide bond location and vL-vH orientation

Engineered introduction of interface interchain disulphide bonds is perceived to be a simple method to increase the stability of single chain Fv (scFv). Six disulphide bond locations have been cited within the literature but the potential for the broad use of each has not been examined. Five of these disulphide bond locations were introduced into one scFv in order to compare their relative effects on expression, thermal stability, percent monomer formation and retention of antigen binding. The disulphide bond position vH44-vL100 was observed to enable the most favourable balance of biophysical properties. The vH44-vL100 disulphide bond was introduced into five additional scFv in both vL-vH and vH-vL orientations in order to investigate its general applicability. Data are presented to show the relative influence of scFv sequence, v-region organisation and interchain disulphide bond on expression yield, thermal stability and percent monomer. Introduction of the vH44-vL100 disulphide bond typically resulted in no or little increase in thermal stability and no change in percent monomer but did confer the benefit of permanently fixing monomer:dimer ratios during purification and analysis.

Functional knockdown of VCAM-1 at the posttranslational level with ER retained antibodies

Vascular cell adhesion molecule 1 (VCAM-1) is involved in the recruitment of leukocytes to inflammatory sites. In this study we present the first functional knockdown of VCAM-1 using an ER retained antibody construct. We generated a knockdown construct encoding the VCAM-1 specific single chain variable fragment scFv6C7.1 fused to the C-terminal ER retention sequence KDEL. HEK-293:VCAM-YFP cells stably expressing a VCAM-YFP fusion protein were transiently transfected with the knockdown construct and showed down-regulation of surface VCAM-1. Knockdown efficiency of the system is time-dependent due to used transient transfection of the intrabody construct. Furthermore, intrabody mediated knockdown of HEK-293:VCAM-YFP cells also impaired cell-cell interaction with Jurkat cells that are endogenously expressing VLA-4, the physiological partner of VCAM-1. Posttranslational knockdown with ER retained antibodies seems to be a promising technique, as shown here for VCAM-1.

Multivalency: the hallmark of antibodies used for optimization of tumor targeting by design

High-precision tumor targeting with conventional therapeutics is based on the concept of the ideal drug as a "magic bullet"; this became possible after techniques were developed for production of monoclonal antibodies (mAbs). Innovative DNA technologies have revolutionized this area and enhanced clinical efficiency of mAbs. The experience of applying small-size recombinant antibodies (monovalent binding fragments and their derivatives) to cancer targeting showed that even high-affinity monovalent interactions provide fast blood clearance but only modest retention time on the target antigen. Conversion of recombinant antibodies into multivalent format increases their functional affinity, decreases dissociation rates for cell-surface and optimizes biodistribution. In addition, it allows the creation of bispecific antibody molecules that can target two different antigens simultaneously and do not exist in nature. Different multimerization strategies used now in antibody engineering make it possible to optimize biodistribution and tumor targeting of recombinant antibody constructs for cancer diagnostics and therapy.

Production of single chain Fab (scFab) fragments in Bacillus megaterium

Background

The demand on antigen binding reagents in research, diagnostics and therapy raises questions for novel antibody formats as well as appropriate production systems. Recently, the novel single chain Fab (scFab) antibody format combining properties of single chain Fv (scFv) and Fab fragments was produced in the Gram-negative bacterium Escherichia coli. In this study we evaluated the Gram-positive bacterium Bacillus megaterium for the recombinant production of scFab and scFvs in comparison to E. coli.

Results

The lysozyme specific D1.3 scFab was produced in B. megaterium and E. coli. The total yield of the scFab after purification obtained from the periplasmic fraction and culture supernatant of E. coli was slightly higher than that obtained from culture supernatant of B. megaterium. However, the yield of functional scFab determined by analyzing the antigen binding activity was equally in both production systems. Furthermore, a scFv fragment with specificity for the human C reactive protein was produced in B. megaterium. The total yield of the anti-CRP scFv produced in B. megaterium was slightly lower compared to E. coli, whereas the specific activity of the purified scFvs produced in B. megaterium was higher compared to E. coli.

Conclusion

B. megaterium allows the secretory production of antibody fragments including the novel scFab antibody format. The yield and quality of functional antibody fragment is comparable to the periplasmic production in E. coli.

Single chain Fab (scFab) fragment

Background

The connection of the variable part of the heavy chain (VH) and and the variable part of the light chain (VL) by a peptide linker to form a consecutive polypeptide chain (single chain antibody, scFv) was a breakthrough for the functional production of antibody fragments in Escherichia coli. Being double the size of fragment variable (Fv) fragments and requiring assembly of two independent polypeptide chains, functional Fab fragments are usually produced with significantly lower yields in E. coli. An antibody design combining stability and assay compatibility of the fragment antigen binding (Fab) with high level bacterial expression of single chain Fv fragments would be desirable. The desired antibody fragment should be both suitable for expression as soluble antibody in E. coli and antibody phage display.

Results

Here, we demonstrate that the introduction of a polypeptide linker between the fragment difficult (Fd) and the light chain (LC), resulting in the formation of a single chain Fab fragment (scFab), can lead to improved production of functional molecules. We tested the impact of various linker designs and modifications of the constant regions on both phage display efficiency and the yield of soluble antibody fragments. A scFab variant without cysteins (scFabΔC) connecting the constant part 1 of the heavy chain (CH1) and the constant part of the light chain (CL) were best suited for phage display and production of soluble antibody fragments. Beside the expression system E. coli, the new antibody format was also expressed in Pichia pastoris. Monovalent and divalent fragments (DiFabodies) as well as multimers were characterised.

Conclusion

A new antibody design offers the generation of bivalent Fab derivates for antibody phage display and production of soluble antibody fragments. This antibody format is of particular value for high throughput proteome binder generation projects, due to the avidity effect and the possible use of common standard sera for detection.

The design, construction and function of a new chimeric anti-CD20 antibody

A novel murine IgM-type anti-human CD20 monoclonal antibody (mAb) 1-28 was prepared in our Lab, which can induce apoptosis and inhibit proliferation of Daudi and Raji cells. However, the efficacy of 1-28mAb in human cancer therapy is likely to be limited by human anti-mouse antibody responses. A chimeric antibody, C1-28, containing 1-28mAb variable region genes fused to human constant region genes (gamma 1, kappa) was constructed. However, C1-28 lost the antigen-binding activity. Here, using sequence similarity and known 3D structure of antibody variable regions as template, the spatial conformations of 1-28 variable regions (i.e. V(H) and V(L)) were analyzed with computer-guided homology modeling methods. According to the surface electrostatic distribution and interaction free energy analysis, the relationship between structure and stability of 1-28 variable regions was studied theoretically and a new chimeric anti-CD20 antibody scFv-Ig named 5S was designed. Expression level of 5S in the culture supernatant was determined to be around 50mug/mL using sandwich ELISA method with chimeric antibody Rituxan as reference. 5S retained its murine counterpart's binding activity by fluorescence-activated cell-sorting analysis. Furthermore, it could kill CD20 positive Daudi and Raji cells by complement-dependent cytotoxicity. For binding affinity often decreased even lost when IgM antibody was constructed into chimeric IgG1 form, our success give a hint about how to construct a IgG1-type chimeric antibody from IgM-type murine antibody to preserve its binding activity.

Production of recombinant antibody fragments in Bacillus megaterium

BACKGROUND

Recombinant antibodies are essential reagents for research, diagnostics and therapy. The well established production host Escherichia coli relies on the secretion into the periplasmic space for antibody synthesis. Due to the outer membrane of gram-negative bacteria, only a fraction of this material reaches the medium. Recently, the gram-positive bacterium Bacillus megaterium was shown to efficiently secrete recombinant proteins into the growth medium. Here we evaluated B. megaterium for the recombinant production of antibody fragments.

RESULTS

The lysozyme specific single chain Fv (scFv) fragment D1.3 was successfully produced using B. megaterium. The impact of culture medium composition, gene expression time and culture temperatures on the production of functional scFv protein was systematically analyzed. A production and secretion at 41 degrees C for 24 h using TB medium was optimal for this individual scFv. Interestingly, these parameters were very different to the optimal conditions for the expression of other proteins in B. megaterium. Per L culture supernatant, more than 400 microg of recombinant His6-tagged antibody fragment were purified by one step affinity chromatography. The material produced by B. megaterium showed an increased specific activity compared to material produced in E. coli.

CONCLUSION

High yields of functional scFv antibody fragments can be produced and secreted into the culture medium by B. megaterium, making this production system a reasonable alternative to E. coli.

Dimerisation strategies for shark IgNAR single domain antibody fragments

Immunoglobulin new antigen receptors (IgNARs) are unique single domain antibodies found in the serum of sharks. The individual variable (VNAR) domains bind antigen independently and are candidates for the smallest antibody-based immune recognition units (approximately 13 kDa). Here, we first isolated and sequenced the cDNA of a mature IgNAR antibody from the spotted wobbegong shark (Orectolobus maculatus) and confirmed the independent nature of the VNAR domains by dynamic light scattering. Second, we asked which of the reported antibody fragment dimerisation strategies could be applied to VNAR domains to produce small bivalent proteins with high functional affinity (avidity). In contrast to single chain Fv (scFv) fragments, separate IgNARs could not be linked into a tandem single chain format, with the resulting proteins exhibited only monovalent binding due solely to interaction of the N-terminal domain with antigen. Similarly, incorporation of C-terminal helix-turn-helix (dhlx) motifs, while resulting in efficiently dimerised protein, resulted in only a modest enhancement of affinity, probably due to an insufficiently long hinge region linking the antibody to the dhlx motif. Finally, generation of mutants containing half-cystine residues at the VNAR C-terminus produced dimeric recombinant proteins exhibiting high functional affinity for the target antigens, but at the cost of 50-fold decreased protein expression levels. This study demonstrates the potential for construction of bivalent or bispecific IgNAR-based binding reagents of relatively small size (approximately 26 kDa), equivalent to a monovalent antibody Fv fragment, for formulation into future diagnostic and therapeutic formats.

Stably tethered multifunctional structures of defined composition made by the dock and lock method for use in cancer targeting

We describe a platform technology, termed the dock and lock method, which uses a natural binding between the regulatory subunits of cAMP-dependent protein kinase and the anchoring domains of A kinase anchor proteins for general application in constructing bioactive conjugates of different protein and nonprotein molecules from modular subunits on demand. This approach could allow quantitative and site-specific coupling of many different biological substances for diverse medical applications. The dock and lock method is validated herein by producing bispecific, trivalent-binding complexes composed of three stably linked Fab fragments capable of selective delivery of radiotracers to human cancer xenografts, resulting in rapid, significantly improved cancer targeting and imaging, providing tumor/blood ratios from 66 +/- 5 at 1 h to 395 +/- 26 at 24 h.

Prolonged in vivo residence times of llama single-domain antibody fragments in pigs by binding to porcine immunoglobulins

The therapeutic parenteral application of llama single-domain antibody fragments (VHHs) is hampered by their small size, resulting in a fast elimination from the body. Here we describe a method to increase the serum half-life of VHHs in pigs by fusion to another VHH binding to porcine immunoglobulin G (pIgG). We isolated 19 pIgG-binding VHHs from an immunized llama using phage display. Six VHHs were genetically fused to model VHH K 609 that binds to Escherichia coli F4 fimbriae. All six yeast-produced genetic fusions of two VHH domains (VHH2s) were functional in ELISA and bound to pIgG with high affinity (1-33 nM). Four pIgG-binding VHH2s were administered to pigs and showed a 100-fold extended in vivo residence times as compared to a control VHH2 that does not bind to pIgG. This could provide the basis for therapeutic application of VHHs in pigs.

Parameters affecting the display of antibodies on phage

Despite the fact that a multitude of antibody phage display libraries has been built, systematic comparisons of critical design parameters are rare. Here we analysed the impact of various factors on the performance of the phage display system. First, we compared several vector designs for the display of Fab fragments of antibodies. Bicistronic as well as monocistronic expression of the antibody/pIII operon and vectors using fd-pIII as well as LC-pIII fusions were tested. Further, we evaluated the influence of glucose on the promoter induction. We compared monovalent versus oligovalent display of the antibody fragments and we used antibody fragments with different folding efficiency to assess the influence of the individual antibody sequences on the performance of the system. Finally, both phage display efficiency and yield of soluble Fab fragments were analysed. The significant differences found for phage yield, display of Fabs on the phage and expression of soluble Fabs suggest to use a bicistronic vector with an fd-fragment-pIII fusion for the construction of future Fab phage display libraries.

Design and assembly of anti-CD16 ScFv antibody with two different linker peptides

Several studies have focused on the effect of different lengths of linker peptides on the properties of single-chain Fv (ScFv). The expressing level and stability of anti-CD16 ScFv with common linker peptide (Gly(4)Ser)(3) were very poor. Considering 3-D structures of heavy and light chain variable region gene of anti-CD16 antibody, a novel linker peptide PT7 (i.e. Gly(3)SerAla(3)) was designed. As a comparison, the linker PT5 (Gly(4)Ser) was chosen to construct anti-CD16 ScFv. A molecular modeling of anti-CD16 ScFv antibody with the two different linker peptides was designed using computer-assisted modeling techniques and molecular dynamics method. Based on the crystal structure of human IgG1 Fc fragment-Fc gamma receptor III (Fc gamma RIII) complex, putative interactions between anti-CD16 ScFv antibody with two different linker peptide and Fc gamma receptor III fragment were predicted with Docking method. Using molecular graphic techniques, the structure-function relationship of anti-CD16 ScFv antibody with two different linker peptides was analyzed and the combining ability was predicted. The binding activity to Daudi cells by FACS showed that anti-CD16 ScFv antibody with two different linker peptides possessed similar ability and the experimental result was consistent with the theoretical prediction.

Construction and characterization of affibody-Fc chimeras produced in Escherichia coli

Affibody-Fc chimeras were constructed by genetic fusion between different affibody affinity proteins with prescribed specificities and an Fc fragment derived from human IgG. Using affibody ligands previously selected for binding to respiratory syncytial virus (RSV) surface protein G and Thermus aquaticus (Taq) DNA polymerase, respectively, affibody-Fc fusion proteins showing spontaneous Fc fragment-mediated homodimerization via disulfide bridges were produced in Escherichia coli and affinity purified on protein A Sepharose from bacterial periplasms at yields ranging between 1 and 6 mg/l culture. Further characterization of the chimeras using biosensor technology showed that the affibody moieties have retained high selectivities for their respective targets after fusion to the Fc fragment. Avidity effects in the target binding were observed for the affibody-Fc chimeras compared to monovalent affibody fusion proteins, indicating that both affibody moieties in the chimeras were accessible and contributed in the binding. Fusion of a head-to-tail dimeric affibody moiety to the Fc fragment resulted in tetravalent affibody constructs which showed even more pronounced avidity effects. In addition, the Fc moiety of the chimeras was demonstrated to be specifically recognized by anti-human IgG antibody enzyme conjugates. One application for this class of "artificial antibodies" was demonstrated in a western blotting experiment in which one of the anti-RSV surface protein G affibody-Fc chimeras was demonstrated to be useful for specific detection of the target protein in a complex background consisting of a total E. coli lysate. The results show that through the replacement of the Fab portion of an antibody for an alternative binding domain based on a less complicated structure, chimeric proteins compatible with bacterial production routes containing both antigen recognition domains and Fc domains can be constructed. Such "artificial antibodies" should be interesting alternatives to, for example, whole antibodies or scFv-Fc fusions as detection devices and in diagnostic or therapeutic applications.