Targeting of functional antibody-CD59 fusion proteins to a cell surface

Complement is involved in the pathogenesis of many diseases, and there is great interest in developing inhibitors of complement for therapeutic application. CD59 is a natural membrane-bound inhibitor of the cytolytic complement membrane attack complex (MAC). In this study, the preparation and characterization of antibody-CD59 (IgG-CD59) chimeric fusion proteins are described. Constructs were composed of soluble CD59 fused to an antibody-combining site at the end of CH1, after the hinge (H), and after CH3 Ig regions. The antigen specificity of each construct was for the hapten 5-dimethylamino-naphthalene-1-sulfonyl (dansyl). Correct folding of each IgG-CD59 fusion partner was indicated by recognition with anti-CD59 antibodies specific for conformational determinants and by IgG-CD59 binding to dansyl. The IgG-CD59 fusion proteins all bound specifically to dansyl-labeled Chinese hamster ovary cells and provided targeted cells, but not untargeted cells, with effective protection from complement-mediated lysis. Data indicate that CD59 must be positioned in close proximity to the site of MAC formation for effective function, and that modes of membrane attachment other than glycophosphatidylinositol linkage can affect CD59 functional activity.

The specificity of synovial IgM rheumatoid factors (RF) for genetically engineered IgG antibodies is not affected by the method used to immortalize RF-producing B cells

Previously, we have shown that some rheumatoid factors (RFs) produced by Epstein-Barr virus (EBV)-transformed B cells from patients with rheumatoid arthritis (EBV-RA-RF) appear to be disease-specific autoantibodies that bind differently to defined epitopes on genetically engineered IgG antibodies, compared with RFs expressed by patients with Waldenstrom's macroglobulinaemia (Wmac-RFs) and healthy immunized donors (HID-RFs). To exclude the possibility that EBV transformation is responsible for these differences, we have now studied 15 other monoclonal IgM RFs from patients with RA that were produced by heterohybridoma-B-cell fusion (HRA-RFs). These HRA-RFs show the same gross specificity profiles for IgG as do their EBV-RA-RF counterparts. However, when the specificities of the HRA-RF and EBV-RA-RF panels were combined and compared with those RFs from patients with Wmac or HID, significant differences in binding specificity were again observed. Hybrid IgG3/4 antibodies made by exon shuffles between the IgG3 and IgG4 wild-type genes, and families of IgG variant antibodies made by site-directed mutagenesis, were used to map the fine specificity of HRA-RFs. The fine specificity of HRA-RFs were also similar to those of EBV-RA-RFs. These studies demonstrate that the method used for immortalizing IgM, RF-producing B cells from RA patients does not influence the specificity of the RFs obtained. Furthermore, some RFs expressed in RA have distinct and unique specificities, and may therefore represent disease-specific autoantibodies.

Homogeneous immunoconjugates for boron neutron-capture therapy: design, synthesis, and preliminary characterization

The application of immunoprotein-based targeting strategies to the boron neutron-capture therapy of cancer poses an exceptional challenge, because viable boron neutron-capture therapy by this method will require the efficient delivery of 10(3) boron-10 atoms by each antigen-binding protein. Our recent investigations in this area have been focused on the development of efficient methods for the assembly of homogeneous immunoprotein conjugates containing the requisite boron load. In this regard, engineered immunoproteins fitted with unique, exposed cysteine residues provide attractive vehicles for site-specific modification. Additionally, homogeneous oligomeric boron-rich phosphodiesters (oligophosphates) have been identified as promising conjugation reagents. The coupling of two such boron-rich oligophosphates to sulfhydryls introduced to the CH2 domain of a chimeric IgG3 has been demonstrated. The resulting boron-rich immunoconjugates are formed efficiently, are readily purified, and have promising in vitro and in vivo characteristics. Encouragingly, these studies showed subtle differences in the properties of the conjugates derived from the two oligophosphate molecules studied, providing a basis for the application of rational design to future work. Such subtle details would not have been as readily discernible in heterogeneous conjugates, thus validating the rigorous experimental design employed here.

A RANTES-antibody fusion protein retains antigen specificity and chemokine function

The successful eradication of cancer cells in the setting of minimal residual disease may require targeting of metastatic tumor deposits that evade the immune system. We combined the targeting flexibility and specificity of mAbs with the immune effector function of the chemokine RANTES to target established tumor deposits. We describe the construction of an Ab fusion molecule with variable domains directed against the tumor-associated Ag HER2/neu, linked to sequences encoding the chemokine RANTES (RANTES.her2.IgG3). RANTES is a potent chemoattractant of T cells, NK cells, monocytes, and dendritic cells, and expression of RANTES has been shown to enhance immune responses against tumors in murine models. RANTES.her2.IgG3 fusion protein bound specifically to HER2/neu Ag expressed on EL4 cells and on SKBR3 breast cancer cells as assayed by flow cytometry. RANTES.her2.IgG3 could elicit actin polymerization of THP-1 cells and transendothelial migration of primary T lymphocytes. RANTES.her2.IgG3 prebound to SKBR3 cells also facilitated migration of T cells. RANTES.her2.IgG3 bound specifically to the CCR5 chemokine receptor, as demonstrated by flow cytometry, and inhibited HIV-1 infection via the CCR5 coreceptor. RANTES.her2.IgG3, alone or in combination with other chemokine or cytokine fusion Abs, may be a suitable reagent for recruitment and activation of an expanded repertoire of effector cells to tumor deposits.

A RANTES-Antibody Fusion Protein Retains Antigen Specificity and Chemokine Function

The successful eradication of cancer cells in the setting of minimal residual disease may require targeting of metastatic tumor deposits that evade the immune system. We combined the targeting flexibility and specificity of mAbs with the immune effector function of the chemokine RANTES to target established tumor deposits. We describe the construction of an Ab fusion molecule with variable domains directed against the tumor-associated Ag HER2/neu, linked to sequences encoding the chemokine RANTES (RANTES.her2.IgG3). RANTES is a potent chemoattractant of T cells, NK cells, monocytes, and dendritic cells, and expression of RANTES has been shown to enhance immune responses against tumors in murine models. RANTES.her2.IgG3 fusion protein bound specifically to HER2/neu Ag expressed on EL4 cells and on SKBR3 breast cancer cells as assayed by flow cytometry. RANTES.her2.IgG3 could elicit actin polymerization of THP-1 cells and transendothelial migration of primary T lymphocytes. RANTES.her2.IgG3 prebound to SKBR3 cells also facilitated migration of T cells. RANTES.her2.IgG3 bound specifically to the CCR5 chemokine receptor, as demonstrated by flow cytometry, and inhibited HIV-1 infection via the CCR5 coreceptor. RANTES.her2.IgG3, alone or in combination with other chemokine or cytokine fusion Abs, may be a suitable reagent for recruitment and activation of an expanded repertoire of effector cells to tumor deposits.

Chimeric human-mouse IgG antibodies with shuffled constant region exons demonstrate that multiple domains contribute to in vivo half-life

Structural features that determine the differing rates of immunoglobulin catabolism are of great relevance to the engineering of immunologically active reagents. Sequences in the CH2 and CH3 region of IgG have been shown to regulate the rate of clearance through their interaction with FcRn. In an attempt to probe additional structural features that regulate antibody half-life, we have investigated two families of chimeric antibodies, composed of identical murine heavy and light antidansyl variable regions joined to human kappa light-chains and wild-type or shuffled human IgG heavy-chain constant regions. These antibodies were iodinated, and their clearance was studied in severe combined immunodeficient mice hosts by whole-body radioactivity measurements. Clearances of the wild-type and recombinant antibodies were biphasic. In a panel of immunoglobulins derived from IgG2 and IgG3, as successive domains were varied from gamma2 to gamma3, beta-phase half-life gradually decreased from 337.0 h to 70.6 h. Statistical analysis suggested that the composition of each of the three domains affected half-life, and no single region of the molecule by itself determined the rate of clearance. In the second panel of immunoglobulins derived from IgG1 and IgG4, the construct with the amino terminus portion of the molecule derived from IgG4, joined within the CH2 domain to the COOH terminus portion of IgG1, had a half-life paradoxically greater than either IgG1, or IgG4 (P < 0.012). All four IgG1/IgG4 constructs demonstrated presence of the concentration catabolism phenomenon, which is a unique hallmark of immunoglobulin catabolism. The contribution of all three constant region domains to immunoglobulin half-life may be due to distant conformational effects in addition to direct binding to protective receptors, and emphasizes the importance of distant sequences on the rate of immunoglobulin catabolism. Interesting possibilities regarding mechanisms controlling immunoglobulin metabolism are raised by the hybrid gamma4/gamma1 molecule with a half-life greater than either parental immunoglobulin. Understanding the relationships between the structure of these molecules and their clearance rate will further our ability to produce immunoglobulins with improved pharmacokinetic properties.

An IgG3-IL-2 fusion protein recognizing a murine B cell lymphoma exhibits effective tumor imaging and antitumor activity

Antibody (Ab)-based tumor therapeutics use the tumor-binding specificity of the Ab to target Fc functions or associated molecules to the site of the tumor. We have used an Ab-interleukin-2 (IL-2) fusion protein to deliver IL-2 to a murine B cell lymphoma (38C13). This anti-Id IgG3-CH3-IL-2, which recognizes the idiotype present on the surface of the lymphoma has a half-life in mice approximately 17-fold longer than the half-life reported for IL-2. Gamma camera studies showed that anti-Id IgG3-CH3-IL-2 localizes at the site of a subcutaneous tumor in mice. The anti-Id IgG3-CH3-IL-2 also shows enhanced antitumor activity compared with the combination of Ab and IL-2 administered together. However, the mechanism of antitumor activity appears to depend on the dose and the treatment schedule used. A single dose of fusion protein prevented tumor in only 50% of the animals, although all the survivors showed some evidence of immunologic memory. Although multiple doses are more effective in preventing tumor growth (87% survivors), they are ineffective in generating protective immunologic memory. Our results suggest that Ab-IL-2 fusion proteins will be useful in the diagnosis and treatment of human B cell lymphomas and other related malignancies.

Effectiveness of topical non-steroidal anti-inflammatory drugs in the management of breast pain

A prospective study of the effectiveness of the topical application of non-steroidal anti-inflammatory drugs (NSAIDs) as a gel preparation was carried out in 26 women with severe breast pain. The results showed a satisfactory relief of pain in 81% of the women: 11 of 13 with cyclical pain, eight of 11 with non-cyclical pain, and in two women with severe scar pain after lumpectomy and radiotherapy. Topical NSAID gel was applied as required; the relief of severe pain was rapid and no side effects were reported. These factors compare favourably with established recommended treatments which usually involve months of continuous treatment, tailoring of drug dosages and a significant incidence of intolerable side effects. This study has shown that topical NSAID application is an effective, safe, acceptable and easily administered treatment for severe cyclical and non-cyclical breast pain.

Effect of C2-associated carbohydrate structure on Ig effector function: studies with chimeric mouse-human IgG1 antibodies in glycosylation mutants of Chinese hamster ovary cells

The complex biantennary oligosaccharide at Asn297 of IgG is essential for some effector functions. To investigate the effect of carbohydrate structure on Ab function, we have now expressed mouse-human chimeric IgG1 Abs in Chinese hamster ovary (CHO) cells with defined defects in carbohydrate biosynthesis. We had previously shown that IgG1 Abs produced in the cell line Lec 1, which attaches a high-mannose intermediate carbohydrate, were severely deficient in complement activation, showed a slightly reduced affinity for Fc gammaRI, and had a reduced in vivo half-life. We have extended these studies by producing the same dansyl-specific IgG1 in cell lines deficient in attachment of sialic acid (Lec 2) and galactose (Lec 8). IgG1-Lec 1, IgG1-Lec 2, and IgG1-Lec 8 all showed varying reactivity with a mAb specific for an epitope in the amino terminal region of C(H)2, suggesting that the conformations of these proteins were altered by the different carbohydrate structures. Functionally, IgG1-Lec 2 and IgG1-Lec 8 were comparable to wild type with respect to in vivo half-life, affinity for Fc gammaRI, and capacity for complement-mediated hemolysis. While IgG1-Lec 2 was essentially identical to wild type in its capacity to interact with individual components of the classical complement activation pathway, IgG1-Lec 8 demonstrated equivalent maximal binding at lower concentrations and was preferentially bound by mannose-binding protein. Although IgG1-Lec 1 was deficient in activation of the classical pathway, it had a superior capacity to activate the alternative pathway. These studies demonstrate that Abs bearing C(H)2-linked carbohydrate of differing structures have different functional properties.

A B7.1-antibody fusion protein retains antibody specificity and ability to activate via the T cell costimulatory pathway

We describe the construction and characterization of an Ab fusion protein specific for the tumor-associated Ag HER2/neu linked to sequences encoding the extracellular domain of the B7.1 T cell costimulatory ligand. The Ab domain of the fusion molecule will specifically target HER2/neu-expressing tumor cells, while the B7.1 domain is designed to activate a specific immune response. We show that the B7.1 fusion Ab retained ability to selectively bind to the HER2/neu Ag and to the CTLA4/CD28 counter-receptors for B7.1. Specific T cell activation was observed when the B7.1 Ab fusion protein was bound to HER2/neu-expressing cells. The use of the B7.1 Ab fusion protein may overcome limitations of gene transfer and/or standard Ab therapy and represents a novel approach to the eradication of minimal residual disease.

A B7.1-Antibody Fusion Protein Retains Antibody Specificity and Ability to Activate Via the T Cell Costimulatory Pathway

We describe the construction and characterization of an Ab fusion protein specific for the tumor-associated Ag HER2/neu linked to sequences encoding the extracellular domain of the B7.1 T cell costimulatory ligand. The Ab domain of the fusion molecule will specifically target HER2/neu-expressing tumor cells, while the B7.1 domain is designed to activate a specific immune response. We show that the B7.1 fusion Ab retained ability to selectively bind to the HER2/neu Ag and to the CTLA4/CD28 counter-receptors for B7.1. Specific T cell activation was observed when the B7.1 Ab fusion protein was bound to HER2/neu-expressing cells. The use of the B7.1 Ab fusion protein may overcome limitations of gene transfer and/or standard Ab therapy and represents a novel approach to the eradication of minimal residual disease.

Effect of C2-Associated Carbohydrate Structure on Ig Effector Function: Studies with Chimeric Mouse-Human IgG1 Antibodies in Glycosylation Mutants of Chinese Hamster Ovary Cells

The complex biantennary oligosaccharide at Asn297 of IgG is essential for some effector functions. To investigate the effect of carbohydrate structure on Ab function, we have now expressed mouse-human chimeric IgG1 Abs in Chinese hamster ovary (CHO) cells with defined defects in carbohydrate biosynthesis. We had previously shown that IgG1 Abs produced in the cell line Lec 1, which attaches a high-mannose intermediate carbohydrate, were severely deficient in complement activation, showed a slightly reduced affinity for FcγRI, and had a reduced in vivo half-life. We have extended these studies by producing the same dansyl-specific IgG1 in cell lines deficient in attachment of sialic acid (Lec 2) and galactose (Lec 8). IgG1-Lec 1, IgG1-Lec 2, and IgG1-Lec 8 all showed varying reactivity with a mAb specific for an epitope in the amino terminal region of CH2, suggesting that the conformations of these proteins were altered by the different carbohydrate structures. Functionally, IgG1-Lec 2 and IgG1-Lec 8 were comparable to wild type with respect to in vivo half-life, affinity for FcγRI, and capacity for complement-mediated hemolysis. While IgG1-Lec 2 was essentially identical to wild type in its capacity to interact with individual components of the classical complement activation pathway, IgG1-Lec 8 demonstrated equivalent maximal binding at lower concentrations and was preferentially bound by mannose-binding protein. Although IgG1-Lec 1 was deficient in activation of the classical pathway, it had a superior capacity to activate the alternative pathway. These studies demonstrate that Abs bearing CH2-linked carbohydrate of differing structures have different functional properties.

Variable Region Domain Exchange Influences the Functional Properties of IgG

In the present study we have characterized a family of anti-dansyl Abs with the variable region of the heavy chain on human Cκ and the variable region of the light chain on different human γ constant regions (creating inside-out molecules). Although fully assembled molecules were secreted, this variable region exchange slowed the kinetics of Ab assembly. Although the variable region exchange does not lead to a detectable change in the microenvironment of the combining site, it did alter the kinetic parameters of binding to immobilized Ag, slowing both the on and off rates. When effector functions were evaluated, inside-out IgG1 and IgG3 were more effective in complement-mediated cytolysis than their wild-type counterparts. Variable region domain exchange may be one approach to obtaining Abs of identical specificity with altered binding characteristics.

Variable region domain exchange influences the functional properties of IgG

In the present study we have characterized a family of anti-dansyl Abs with the variable region of the heavy chain on human Ckappa and the variable region of the light chain on different human gamma constant regions (creating inside-out molecules). Although fully assembled molecules were secreted, this variable region exchange slowed the kinetics of Ab assembly. Although the variable region exchange does not lead to a detectable change in the microenvironment of the combining site, it did alter the kinetic parameters of binding to immobilized Ag, slowing both the on and off rates. When effector functions were evaluated, inside-out IgG1 and IgG3 were more effective in complement-mediated cytolysis than their wild-type counterparts. Variable region domain exchange may be one approach to obtaining Abs of identical specificity with altered binding characteristics.

Mapping IgG Epitopes Bound by Rheumatoid Factors from Immunized Controls Identifies Disease-Specific Rheumatoid Factors Produced by Patients with Rheumatoid Arthritis

We have mapped the specificity of 28 monoclonal IgM rheumatoid factors (RFs) produced by heterohybridomas derived from five healthy blood donors immunized with mismatched human red blood cells (HID). The HID-RFs did not differ in their binding specificity for IgG epitopes from RFs that we previously analyzed from patients with Waldenström’s macroglobulinemia. However, IgM RFs produced by HID differed in their specificity for IgG compared with RFs expressed by patients with rheumatoid arthritis (RA-RFs). Only 1 of 28 HID-RFs bound all IgG subclasses (pan binding pattern) compared with 7 of 19 RA-RFs (p = 0.006). Three HID-RFs bound IgG3 compared with 9 RA-RFs (p = 0.007). Fine specificity differences were also identified between HID- and RA-RFs. Therefore, some RA-RFs show novel specificities for IgG not found among RFs from HID or individuals with Waldenström’s macroglobulinemia who do not have joint disease. These Abs with unique specificities may represent disease-specific autoantibodies in patients with RA. Nine of the HID-RFs from the same individual were clonally related, and several contained somatic mutations. Even when the clonally related HID-RFs were considered as one RF for comparison, the reactivity of the HID-RFs differed significantly from RA-RFs in their inability to recognize all IgG subclasses (p = 0.044) and recognize IgG3 (p = 0.041). Interestingly, among the clonally related RFs, considerable differences in the specificity for IgG were also observed, with the RF containing the most somatic mutations in VH and VL showing the most distinctive specificity changes. Therefore, these studies also demonstrate a correlation between somatic mutation and binding specificity.

Mapping IgG epitopes bound by rheumatoid factors from immunized controls identifies disease-specific rheumatoid factors produced by patients with rheumatoid arthritis

We have mapped the specificity of 28 monoclonal IgM rheumatoid factors (RFs) produced by heterohybridomas derived from five healthy blood donors immunized with mismatched human red blood cells (HID). The HID-RFs did not differ in their binding specificity for IgG epitopes from RFs that we previously analyzed from patients with Waldenström's macroglobulinemia. However, IgM RFs produced by HID differed in their specificity for IgG compared with RFs expressed by patients with rheumatoid arthritis (RA-RFs). Only 1 of 28 HID-RFs bound all IgG subclasses (pan binding pattern) compared with 7 of 19 RA-RFs (p = 0.006). Three HID-RFs bound IgG3 compared with 9 RA-RFs (p = 0.007). Fine specificity differences were also identified between HID- and RA-RFs. Therefore, some RA-RFs show novel specificities for IgG not found among RFs from HID or individuals with Waldenström's macroglobulinemia who do not have joint disease. These Abs with unique specificities may represent disease-specific autoantibodies in patients with RA. Nine of the HID-RFs from the same individual were clonally related, and several contained somatic mutations. Even when the clonally related HID-RFs were considered as one RF for comparison, the reactivity of the HID-RFs differed significantly from RA-RFs in their inability to recognize all IgG subclasses (p = 0.044) and recognize IgG3 (p = 0.041). Interestingly, among the clonally related RFs, considerable differences in the specificity for IgG were also observed, with the RF containing the most somatic mutations in VH and VL showing the most distinctive specificity changes. Therefore, these studies also demonstrate a correlation between somatic mutation and binding specificity.

Antibody-IL-2 fusion proteins: a novel strategy for immune protection

Advances in genetic engineering and expression systems have led to a rapid progress in the development of immunoglobulins fused to other proteins. These 'antibody fusion proteins' have novel properties and include antibodies fused to the cytokine interleukin-2. In the present review we describe strategies for construction of these antibody-interleukin-2 fusion proteins and discuss their in vitro and in vivo properties. Antibody-interleukin-2 fusion proteins retain both antibody associated functions such as antigen binding, complement activation and Fc gamma receptor binding as well as interleukin-2 associated functions such as the stimulation of proliferation of CTLL2 cells. In vivo, they produce strong potentiation of the host immune response against any associated antigen. In addition, these novel molecules are able to target tumor cells and produce a specific and effective T cell response capable of eliminating the tumor. These properties suggest that antibody-interleukin-2 fusion proteins will be useful in the diagnosis and/or treatment of human cancer as well as in the potentiation of human response against any associated antigen.

Amino acid differences in the N-terminus of C(H)2 influence the relative abilities of IgG2 and IgG3 to activate complement

The four human IgG isotypes are highly conserved in amino acid sequence, but show differential ability to activate complement (C'): IgG3 and IgG1 are very active, IgG2 is active under certain conditions, and IgG4 is inactive. Although the second constant domain [C(H)2] is critical for C' activation, the individual amino acids that confer isotype-specific activity have not been identified. We have generated a series of mutants between IgG2 and IgG3, resulting in the exchange of the four N-terminal and six C-terminal polymorphic residues within C(H)2. Mutants containing the N-terminus of the C(H)2 of IgG3 were as effective as wildtype IgG3 in C1q binding, C1 activation and terminal complex (MAC) formation, but had reduced ability to effect C'-mediated lysis. IgG2 and mutants containing the N-terminal portion of the C(H)2 of IgG2 were reduced compared to IgG3 in activating C1, binding C1q and inducing assembly of the MAC, and were inactive in mediating lysis of target cells. Thus, the amino acid sequence differences in the N-terminus of C(H)2 play a critical role in determining the relative abilities of IgG2 and IgG3 to bind C1q and activate the C' cascade although additional residues of C(H)2 must be involved in mediating optimal target cells lysis. The sequence of the N-terminus of C(H)2 was less critical in determining C4 and C3 binding. Characterization of domain exchange mutants suggests that intermediate steps may be partly dependent on domains other than C(H)2. IgGs that do not direct target cell lysis nevertheless activate intermediate steps in the pathway, which may contribute to immune complex-associated disorders.

Production of secretory immunoglobulin A by a single mammalian cell

Secretory IgA (sIgA) plays a critical role in providing protection against infection at the mucosal surfaces. Normally, sIgA is the product of two different cell types with heavy, light, and J chains produced by the plasma cells, whereas secretory component (SC), a cleavage product of the polymeric immunoglobulin receptor (pIgR), is added during the transit of dimeric IgA through the epithelial cell layer. In the current study, by introducing a gene for the processed form of SC into a cell line that produces dimeric IgA, we have succeeded in creating a single cell that is able to produce and secrete covalently joined sIgA. To our knowledge, this is the first time it has been possible to efficiently produce large quantities of sIgA of defined specificity in mammalian cells. The sIgA made using this approach has great potential as an immunotherapeutic.

Functional and pharmacokinetic properties of antibody-avidin fusion proteins

In an attempt to produce broadly useful targeting agents, genetic engineering and expression techniques have been used to produce Ab-avidin fusion proteins. Chicken avidin has been fused to mouse-human chimeric IgG3 at the end of C(H)1 (C(H)1-Av), immediately after the hinge (H-Av), and at the end of C(H)3 (C(H)3-Av). Fusion heavy chains of the expected molecular mass were expressed, assembled with a co-expressed light chain, and secreted. The resulting molecules continued to bind Ag. They also bound biotinylated human serum albumin; C(H)3-Av had reduced affinity (K(A) = 5.13 x 10(9) M(-1)) compared with the tetrameric avidin (K(A) = 1 x 10(15) M(-1)), but greater affinity than monomeric avidin (K(A) = 1 x 10(7) M(-1)). Importantly, the avidin-IgG fusion proteins had a longer serum t1/2 in rats than avidin. The favorable pharmacokinetic parameters suggest that these avidin fusion proteins can be used effectively to deliver biotinylated ligands such as drugs and peptides to locales expressing any Ag recognized by the associated Ab.

Functional and pharmacokinetic properties of antibody-avidin fusion proteins

In an attempt to produce broadly useful targeting agents, genetic engineering and expression techniques have been used to produce Ab-avidin fusion proteins. Chicken avidin has been fused to mouse-human chimeric IgG3 at the end of C(H)1 (C(H)1-Av), immediately after the hinge (H-Av), and at the end of C(H)3 (C(H)3-Av). Fusion heavy chains of the expected molecular mass were expressed, assembled with a co-expressed light chain, and secreted. The resulting molecules continued to bind Ag. They also bound biotinylated human serum albumin; C(H)3-Av had reduced affinity (K(A) = 5.13 x 10(9) M(-1)) compared with the tetrameric avidin (K(A) = 1 x 10(15) M(-1)), but greater affinity than monomeric avidin (K(A) = 1 x 10(7) M(-1)). Importantly, the avidin-IgG fusion proteins had a longer serum t1/2 in rats than avidin. The favorable pharmacokinetic parameters suggest that these avidin fusion proteins can be used effectively to deliver biotinylated ligands such as drugs and peptides to locales expressing any Ag recognized by the associated Ab.

Design and production of novel tetravalent bispecific antibodies

We have produced novel bispecific antibodies by fusing the DNA encoding a single chain antibody (ScFv) after the C terminus (CH3-ScFv) or after the hinge (Hinge-ScFv) with an antibody of a different specificity. The fusion protein is expressed by gene transfection in the context of a murine variable region. Transfectomas secrete a homogeneous population of the recombinant antibody with two different specificities, one at the N terminus (anti-dextran) and one at the C terminus (anti-dansyl). The CH3-ScFv antibody, which maintains the constant region of human IgG3, has some of the associated effector functions such as long half-life and Fc receptor binding. The Hinge-ScFv antibody which lacks the CH2 and CH3 domains has no known effector functions.

Elimination of N-linked glycosylation sites from the human IgA1 constant region: effects on structure and function

IgA1 Abs possess conserved N-linked glycosylation sites in the second C region and secreted tailpiece domains. To understand the role of these carbohydrates in the structure and function of human IgA1, site-directed mutants that produce human IgA1 lacking either one or both of the N-linked carbohydrate sites have been produced. When the mutant heavy chains are expressed in myeloma lines producing the relevant kappa-light chain, efficient secretion of the monomer and dimer forms of IgA1 is seen. In addition, higher polymer forms of the IgA molecules lacking the third domain carbohydrate, either singly or in the double mutant, are present. Functional analysis of the IgA1 proteins has shown significant differences between the various mutants and wild-type IgA. The carbohydrate mutants show a reduced affinity for their target Ag, dansyl. All of the IgA1 molecules retained the ability to bind to the polymeric Ig receptor. C3 binding was observed for all of the IgA molecules, with the IgA mutants lacking the third domain carbohydrate showing a reduced ability to bind C3; however, IgA did not effectively activate the alternative pathway, as determined by factor B cleavage and terminal complex binding. These studies demonstrate that N-linked glycosylation in the constant domain of human IgA1 plays an important role in the biologic properties of IgA1.

Bifunctional fusion between nerve growth factor and a transferrin receptor antibody

The cDNAs encoding the variable regions of the heavy and light chains of a murine antibody specific for the human TfR were cloned and a human chimera (gamma1, kappa) was produced. A gene fusion was created by joining the 3' end of the coding region of the human nerve growth factor (NGF) precursor to the 5' end of the heavy chain variable region of the chimeric antibody. When expressed with the unmodified light chain in mammalian cells, the protein fusion is properly processed, assembled, and secreted. Subsequent purification and characterization established the uncompromised bifunctional activities of the protein, relative to the unmodified components, as demonstrated by its ability to both bind to the human TfR and induce neurite outgrowth in primary sympathetic or spinal ganglia and in trkA-transfected pheochromocytoma cells. The ability to generate biologically active NGF fused to a TfR targeting antibody, which was previously shown to cross the blood-brain barrier, may offer a novel way to deliver NGF and other neurotrophic factors to the central nervous system.

The hinge as a spacer contributes to covalent assembly and is required for function of IgG

Chimeric IgG3 lacking a genetic hinge but with Cys residues in CH2 between position 231 and 232 (IgG3 deltaH+Cys) and position 279 (IgG3 deltaH+2Cys) produced by site-directed mutagenesis have been found to be deficient in their intermolecular assembly. Although some H2L2 molecules are formed, significant quantities of assembly intermediates, in particular HL, are found in the secretions. Both IgG3 deltaH+Cys and IgG3 deltaH+2Cys were greatly reduced in their ability to bind Fc gammaRI. They also failed to bind C1q and activate the complement cascade. Addition of the tailpiece from IgM (microtp) to IgG3 deltaH+Cys (yielding IgG3 deltaH+Cys microtp) failed to lead to efficient oligomerization. IgG3 deltaH+Cys microtp failed to bind Fc gammaRII. However, at high concentrations it was able to bind C1q and effect complement-dependent cytolysis. It consumed complement in the absence of added Ag, indicating that removing the flexible hinge was not sufficient to yield polymeric IgG that resembled IgM in its dependence on added Ag for complement activation.