Rabbit monoclonal antibodies: generating a fusion partner to produce rabbit-rabbit hybridomas.

During the last 15 years several laboratories have attempted to generate rabbit monoclonal antibodies, mainly because rabbits recognize antigens and epitopes that are not immunogenic in mice or rats, two species from which monoclonal antibodies are usually generated. Monoclonal antibodies from rabbits could not be generated, however, because a plasmacytoma fusion partner was not available. To obtain a rabbit plasmacytoma cell line that could be used as a fusion partner we generated transgenic rabbits carrying two transgenes, c-myc and v-abl. These rabbits developed plasmacytomas, and we obtained several plasmacytoma cell lines from which we isolated hypoxanthine/aminopterin/thymidine-sensitive clones. One of these clones, when fused with spleen cells of immunized rabbits, produced stable hybridomas that secreted antibodies specific for the immunogen. The hybridomas can be cloned and propagated in nude mice, and they can be frozen without change in their ability to secrete specific monoclonal antibodies. These rabbit-rabbit hybridomas will be useful not only for production of monoclonal antibodies but also for studies of immunoglobulin gene rearrangements and isotype switching.

Inhibition of nuclear vesicle fusion by antibodies that block activation of inositol 1,4,5-trisphosphate receptors.

Inositol 1,4,5-trisphosphate (IP3) receptors are ligand-gated channels that release intracellular Ca2+ stores in response to the second messenger, IP3. We investigated the potential role of IP3 receptors during nuclear envelope assembly in vitro, using Xenopus egg extracts. Previous work suggested that Ca2+ mobilization is required for nuclear vesicle fusion and implicated IP3 receptor activity. To test the involvement of IP3 receptors using selective reagents, we obtained three distinct polyclonal antibodies to the type 1 IP3 receptor. Pretreatment of membranes with two of the antibodies inhibited IP3-stimulated CA2+ release in vitro and also inhibited nuclear vesicle fusion. One inhibitory serum was directed against 420 residues within the "coupling" domain, which includes several potential regulatory sites. The other inhibitory serum was directed against 95 residues near the C terminus and identifies an inhibitory epitope(s) in this region. The antibodies had no effect on receptor affinity for IP3. Because nuclear vesicle fusion was inhibited by antibodies that block Ca2+ flux, but not by control and preimmune antibodies, we concluded that the activation of IP3 receptors is required for fusion. The signal that activates the channel during fusion is unknown.

Identification and localization of huntingtin in brain and human lymphoblastoid cell lines with anti-fusion protein antibodies.

The Huntington disease (HD) phenotype is associated with expansion of a trinucleotide repeat in the IT15 gene, which is predicted to encode a 348-kDa protein named huntington. We used polyclonal and monoclonal anti-fusion protein antibodies to identify native huntingtin in rat, monkey, and human. Western blots revealed a protein with the expected molecular weight which is present in the soluble fraction of rat and monkey brain tissues and lymphoblastoid cells from control cases. In lymphoblastoid cell lines from juvenile-onset heterozygote HD cases, both normal and mutant huntingtin are expressed, and increasing repeat expansion leads to lower levels of the mutant protein. Immunocytochemistry indicates that huntingtin is located in neurons throughout the brain, with the highest levels evident in larger neurons. In the human striatum, huntingtin is enriched in a patch-like distribution, potentially corresponding to the first areas affected in HD. Subcellular localization of huntingtin is consistent with a cytosolic protein primarily found in somatodendritic regions. Huntingtin appears to particularly associate with microtubules, although some is also associated with synaptic vesicles. On the basis of the localization of huntingtin in association with microtubules, we speculate that the mutation impairs the cytoskeletal anchoring or transport of mitochondria, vesicles, or other organelles or molecules.

Anti-C5 monoclonal antibody therapy prevents collagen-induced arthritis and ameliorates established disease.

Activated components of the complement system are potent mediators of inflammation that may play an important role in numerous disease states. For example, they have been implicated in the pathogenesis of inflammatory joint diseases including rheumatoid arthritis (RA). To target complement activation in immune-mediated joint inflammation, we have utilized monoclonal antibodies (mAbs) that inhibit the complement cascade at C5, blocking the generation of the major chemotactic and proinflammatory factors C5a and C5b-9. In this study, we demonstrate the efficacy of a mAb specific for murine C5 in the treatment of collagen-induced arthritis, an animal model for RA. We show that systemic administration of the anti-C5 mAb effectively inhibits terminal complement activation in vivo and prevents the onset of arthritis in immunized animals. Most important, anti-C5 mAb treatment is also highly effective in ameliorating established disease. These results demonstrate a critical role for activated terminal complement components not only in the induction but also in the progression of collagen-induced arthritis and suggest that C5 may be an attractive therapeutic target in RA.

Daidzin suppresses ethanol consumption by Syrian golden hamsters without blocking acetaldehyde metabolism.

Daidzin is a potent, selective, and reversible inhibitor of human mitochondrial aldehyde dehydrogenase (ALDH) that suppresses free-choice ethanol intake by Syrian golden hamsters. Other ALDH inhibitors, such as disulfiram (Antabuse) and calcium citrate carbimide (Temposil), have also been shown to suppress ethanol intake of laboratory animals and are thought to act by inhibiting the metabolism of acetaldehyde produced from ingested ethanol. To determine whether or not daidzin inhibits acetaldehyde metabolism in vivo, plasma acetaldehyde in daidzin-treated hamsters was measured after the administration of a test dose of ethanol. Daidzin treatment (150 mg/kg per day i.p. for 6 days) significantly suppresses (> 70%) hamster ethanol intake but does not affect overall acetaldehyde metabolism. In contrast, after administration of the same ethanol dose, plasma acetaldehyde concentration in disulfiram-treated hamsters reaches 0.9 mM, 70 times higher than that of the control. In vitro, daidzin suppresses hamster liver mitochondria-catalyzed acetaldehyde oxidation very potently with an IC50 value of 0.4 microM, which is substantially lower than the daidzin concentration (70 microM) found in the liver mitochondria of daidzin-treated hamsters. These results indicate that (i) the action of daidzin differs from that proposed for the classic, broad-acting ALDH inhibitors (e.g., disulfiram), and (ii) the daidzin-sensitive mitochondrial ALDH is not the one and only enzyme that is essential for acetaldehyde metabolism in golden hamsters.

Targeting cancer micrometastases with monoclonal antibodies: a binding-site barrier.

Monoclonal antibodies penetrate bulky tumors poorly after intravenous administration, in part because of specific binding to the target antigen. Experiments presented here demonstrate an analogous phenomenon in micrometastases; poor antibody penetration, attributable to a "binding-site barrier" phenomenon, can be seen in guinea pig micrometastases as small as 300 microns in diameter. Increasing the dose of antibody can partially overcome this limitation, but at a cost in specificity.

Preparation and properties of nido-carborane-specific monoclonal antibodies for potential use in boron neutron capture therapy for cancer.

As the first step of a research program aimed at developing a bispecific monoclonal antibody system for the delivery of boron-rich molecules to tumor cells for boron neutron capture therapy, monoclonal antibodies (mAbs) were produced against an anionic nido-carborane derivative, 4-[7,8-dicarbadodecahydroundecaborat(-1)-7-yl]butanoic acid. Two IgG subclass mAbs, designated HAW101 and HAW102, were identified that specifically bound the anionic nido-carborane hapten, as well as a variety of other anionic nido-carborane cage derivatives. By using surface plasmon resonance technology, the affinity constants of HAW101 and HAW102 were determined to be 1.9 x 10(9) and 6.8 x 10(8) M-1, respectively. A diverse array of 7-substituted and 7,8-disubstituted anionic nido-carborane derivatives reacted with the mAb HAW101 in competition ELISA, whereas anionic closo-polyhedral boranes showed negligible binding, suggesting a role for the open nido-carborane cage structure. These results suggest that mAbs such as HAW101, which bind anionic nido-carboranes, are useful in the development of bispecific mAbs for specific targeting and enhanced boron delivery to tumor sites.

Directed selection of recombinant human monoclonal antibodies to herpes simplex virus glycoproteins from phage display libraries.

Human monoclonal antibodies have considerable potential in the prophylaxis and treatment of viral disease. However, only a few such antibodies suitable for clinical use have been produced to date. We have previously shown that large panels of human recombinant monoclonal antibodies against a plethora of infectious agents, including herpes simplex virus types 1 and 2, can be established from phage display libraries. Here we demonstrate that facile cloning of recombinant Fab fragments against specific viral proteins in their native conformation can be accomplished by panning phage display libraries against viral glycoproteins "captured" from infected cell extracts by specific monoclonal antibodies immobilized on ELISA plates. We have tested this strategy by isolating six neutralizing recombinant antibodies specific for herpes simplex glycoprotein gD or gB, some of which are against conformationally sensitive epitopes. By using defined monoclonal antibodies for the antigen-capture step, this method can be used for the isolation of antibodies to specific regions and epitopes within the target viral protein. For instance, monoclonal antibodies to a nonneutralizing epitope can be used in the capture step to clone antibodies to neutralizing epitopes, or antibodies to a neutralizing epitope can be used to clone antibodies to a different neutralizing epitope. Furthermore, by using capturing antibodies to more immunodominant epitopes, one can direct the cloning to less immunogenic ones. This method should be of value in generating antibodies to be used both in the prophylaxis and treatment of viral infections and in the characterization of the mechanisms of antibody protective actions at the molecular level.

Anti-melanoma antibodies from melanoma patients immunized with genetically modified autologous tumor cells: selection of specific antibodies from single-chain Fv fusion phage libraries.

Fusion phage libraries expressing single-chain Fv antibodies were constructed from the peripheral blood lymphocytes of two melanoma patients who had been immunized with autologous melanoma cells transduced the gamma-interferon gene to enhance immunogenicity, in a trial conducted at another institution. Anti-melanoma antibodies were selected from each library by panning the phage against live cultures of the autologous tumor. After two or three rounds of panning, clones of the phage were tested by ELISA for binding to the autologous tumor cells; > 90% of the clones tested showed a strong ELISA reaction, demonstrating the effectiveness of the panning procedure for selecting antimelanoma antibodies. The panned phage population was extensively absorbed against normal melanocytes to enrich for antibodies that react with melanoma cells but not with melanocytes. The unabsorbed phage were cloned, and the specificities of the expressed antibodies were individually tested by ELISA with a panel of cultured human cells. The first tests were done with normal endothelial and fibroblast cells to identify antibodies that do not react, or react weakly, with two normal cell types, indicating some degree of specificity for melanoma cells. The proportion of phage clones expressing such antibodies was approximately 1%. Those phage were further tested by ELISA with melanocytes, several melanoma lines, and eight other tumor lines, including a glioma line derived from glial cells that share a common lineage with melanocytes. The ELISA tests identified three classes of anti-melanoma antibodies, as follows: (i) a melanoma-specific class that reacts almost exclusively with the melanoma lines; (ii) a tumor-specific class that reacts with melanoma and other tumor lines but does not react with the normal melanocyte, endothelial and fibroblast cells; and (iii) a lineage-specific class that reacts with the melanoma lines, melanocytes, and the glioma line but does not react with the other lines. These are rare classes from the immunized patients' repertoires of anti-melanoma antibodies, most of which are relatively nonspecific anti-self antibodies. The melanoma-specific class was isolated from one patient, and the lineage-specific class was isolated from the other patient, indicating that different patients can have markedly different responses to the same immunization protocol. The procedures described here can be used to screen the antibody repertoire of any person with cancer, providing access to an enormous untapped pool of human monoclonal anti-tumor antibodies with clinical and research potential.

Interferon gamma signals via a high-affinity multisubunit receptor complex that contains two types of polypeptide chain.

Signaling by interferon gamma (IFN-gamma) requires two structurally related cell surface proteins: a ligand-binding polypeptide, known as the IFN-gamma receptor (IFN-gamma R), and an accessory factor. However, it is not known whether IFN-gamma forms a ternary complex with the IFN-gamma R and accessory factor to initiate signaling. Here we demonstrate complex formation between IFN-gamma and the two proteins, both in solution and at the cell surface. We observe complexes containing ligand, two molecules of IFN-gamma R (designated the IFN-gamma R alpha chain), and one or two molecules of accessory factor (designated the IFN-gamma R beta chain). Transfected cells expressing both IFN-gamma R chains bind IFN-gamma with higher affinity than do cells expressing alpha chain alone. Anti-beta-chain antibodies prevent the beta chain from participating in the ligand-receptor complex, reduce the affinity for IFN-gamma, and block signaling. Soluble alpha- or beta-chain extracellular domains also inhibit function. These results demonstrate that IFN-gamma signals via a high-affinity multisubunit complex that contains two types of receptor chain and suggest a potential approach to inhibiting specific actions of IFN-gamma by blocking the association of receptor subunits.

Human anti-idiotypic antibodies induced a humoral and cellular immune response against a colorectal carcinoma-associated antigen in patients.

Induction of immunity against antigens expressed on tumor cells might prevent or delay recurrence of the disease. Six patients operated on for colorectal carcinoma were immunized with human monoclonal anti-idiotypic antibodies (h-Ab2) against the mouse 17-1A anti-colon carcinoma antibody, mimicking a nominal antigen (GA733-2). All patients developed a long-lasting T-cell immunity against the extracellular domain of GA733-2 (GA733-2E) (produced in a baculovirus system) and h-Ab2. This was shown in vitro by specific cell proliferation (DNA-synthesis) assay as well as by interleukin 2 and interferon gamma production and in vivo by the delayed-type hypersensitivity reaction. Five patients mounted a specific humoral response (IgG) against the tumor antigen GA733-2E (ELISA) and tumor cells expressing GA733-2. Epitope mapping using 23 overlapping peptides of GA733-2E revealed that the B-cell epitope was localized close to the N terminus of GA733-2. Binding of the antibodies to the tumor antigen and to one 18-aa peptide was inhibited by h-Ab2, indicating that the antibodies were able to bind to the antigen as well as to h-Ab2. The results suggest that our h-Ab2 might be able to induce an anti-tumor immunity which may control the growth of tumor cells in vivo.

Basis for selection of improved carbohydrate-binding single-chain antibodies from synthetic gene libraries.

A technique is described for the simultaneous and controlled random mutation of all three heavy or light chain complementarity-determining regions (CDRs) in a single-chain Fv specific for the O polysaccharide of Salmonella serogroup B. Sense oligonucleotides were synthesized such that the central bases encoding a CDR were randomized by equimolar spiking with A, G, C, and T at a level of 10% while the antisense strands contained inosine in the spiked regions. Phage display of libraries assembled from the spiked oligonucleotides by a synthetic ligase chain reaction demonstrated a bias for selection of mutants that formed dimers and higher oligomers. Kinetic analyses showed that oligomerization increased association rates in addition to slowing dissociation rates. In combination with some contribution from reduced steric clashes with residues in heavy-chain CDR2, oligomerization resulted in functional affinities that were much higher than that of the monomeric form of the wild-type single-chain Fv.

Presence of antibodies to different subunits of replication protein A in autoimmune sera.

A human cDNA expression library was used to investigate the nature of molecules recognized by serum from a patient with Sjögren syndrome that exhibits a mixed immunofluorescence pattern and reacts with multiple components on an immunoblot. The data demonstrated that this serum contains IgG antibodies specific for the 70- and 32-kDa subunits of replication protein A (RPA; RPA-70 and RPA-32, respectively), a highly conserved multisubunit DNA binding protein. Affinity purification of serum autoantibodies demonstrated a complete lack of cross-reactivity between RPA-70 and RPA-32, suggesting a direct participation of the native protein complex in the autoimmune response in this patient. Purified anti-RPA-70 and anti-RPA-32 antibodies labeled nuclear and cytoplasmic components in an immunofluorescence assay, suggesting that RPA is present in both cellular compartments. Additional sera from 55 patients with different autoimmune conditions were screened against purified RPA-70 and RPA-32 recombinant proteins. One of these 55 sera was positive and reacted with only RPA-32. Twenty sera from healthy control individuals did not react with RPA. These results show that RPA is a target for autoantibodies in human autoimmune diseases, although its precise frequency, occurrence in other autoimmune diseases, and pathological significance remain to be fully elucidated.

Rapid selection of cell subpopulation-specific human monoclonal antibodies from a synthetic phage antibody library.

Peripheral blood leukocytes incubated with a semisynthetic phage antibody library and fluorochrome-labeled CD3 and CD20 antibodies were used to isolate human single-chain Fv antibodies specific for subsets of blood leukocytes by flow cytometry. Isolated phage antibodies showed exclusive binding to the subpopulation used for selection or displayed additional binding to a restricted population of other cells in the mixture. At least two phage antibodies appeared to display hitherto-unknown staining patterns of B-lineage cells. This approach provides a subtractive procedure to rapidly obtain human antibodies against known and novel surface antigens in their native configuration, expressed on phenotypically defined subpopulations of cells. This approach does not depend on immunization procedures or the necessity to repeatedly construct phage antibody libraries.

Transendothelial migration of neutrophils involves integrin-associated protein (CD47).

Inflammation is a primary pathological process. The development of an inflammatory reaction involves the movement of white blood cells through the endothelial lining of blood vessels into tissues. This process of transendothelial cell migration of neutrophils has been shown to involve neutrophil beta 2 integrins (CD18) and endothelial cell platelet-endothelium cell adhesion molecules (PECAM-1; CD31). We now show that F(ab')2 fragments of the monoclonal antibody B6H12 against integrin-associated protein (IAP) blocks the transendothelial migration of neutrophils stimulated by an exogenous gradient of the chemokine interleukin 8 (IL-8; 60% inhibition), by the chemotactic peptide N-formyl-methionylleucylphenylalanine (FMLP; 76% inhibition), or by the activation of the endothelium by the cytokine tumor necrosis factor alpha (98% inhibition). The antibody has two mechanisms of action: on neutrophils it prevents the chemotactic response to IL-8 and FMLP, and on endothelium it prevents an unknown but IL-8-independent process. Blocking antibodies to IAP do not alter the expression of adhesion proteins or production of IL-8 by endothelial cells, and thus the inhibition of neutrophil transendothelial migration is selective. These data implicate IAP as the third molecule essential for neutrophil migration through endothelium into sites of inflammation.