Highly efficient destruction of squamous carcinoma cells of the head and neck by photochemical internalization of Ranpirnase

INTRODUCTION

Photochemical Internalization is a novel drug delivery technology for cancer treatment based on the principle of Photodynamic Treatment. Using a photosensitizer that locates in endocytic vesicles membranes of tumor cells, Photochemical internalization enables cytosolic release of endocytosed antitumor agents in a site-specific manner. The purpose of the present in-vitro study was to explore whether Photochemical Internalization is able to enhance the efficacy of Ranpirnase, a cytotoxic amphibian ribonuclease, for eradication of squamous cell carcinoma of the head and neck.

METHODS

Cell viability was measured in 8 primary human cell lines of squamous cell carcinoma of the head and neck after treatment with Ranpirnase and Photochemical Internalization. For Photochemical Internalization the photosensitizer disulfonated tetraphenyl porphine was incubated with tumor cells followed by exposure to blue light (435 nm).

RESULTS

Our study demonstrates significant enhancement of antitumor activity of Ranpirnase by Photochemical Internalization. Treatment responses were heterogeneous between the primary cancer cell lines. Combining Photochemical Internalization with Ranpirnase resulted in 4.6 to 1,940-fold increased cytotoxicity when compared with the ribonuclease alone (P < 0.05).

CONCLUSION

Cytotoxicity of Ranpirnase can be markedly enhanced by Photochemical Internalization in squamous cell carcinoma of the head and neck.

Photodynamic therapy of bladder cancer - a phase I study using hexaminolevulinate (HAL)

OBJECTIVES

To assess the safety and feasibility of hexaminolevulinate (HAL) based photodynamic therapy (PDT) as adjuvant treatment after transurethral resection of the bladder (TURB) in patients with intermediate or high-risk urothelial cell carcinoma (UCC) of the bladder.

MATERIALS AND METHODS

Seventeen patients received 50 ml of either a 16 mM (4 patients) or 8 mM HAL (13 patients) solution instilled intravesically. Bladder wall irradiation was performed using an incoherent white light source coupled via a quartz fiber assembled into a flexible transurethral irrigation catheter. Each patient received 3 treatments with HAL-PDT 6 weeks apart. After PDT, patients were followed by regular cystoscopy for up to 21 months to assess time to recurrence. Reported adverse events (AEs) were coded according the World Health Organization Adverse Reaction Terminology (WHO-ART). Efficacy was assessed by cystoscopy, cytology, and histology, and was defined as the number of patients who were tumor-free at 6 or 21 months after initial PDT treatment. Transient bladder irritability was reported by 15 of the 17 patients and resolved completely in all patients. No evidence of a cumulative effect of treatment on the incidence of AEs could be detected. PDT treatment was performed without any technical complications. Furthermore preliminary assessment of efficacy showed that of the 17 patients included, 9 (52.9%; 95% CI: 27.8-77.0) were tumor-free at 6 months, 4 (23.5%; 95% CI: 6.8-49.9) were tumor-free at 9 months, and 2 (11.8%, 95% CI: 1.5-36.4) were tumor-free after 21 months.

CONCLUSIONS

PDT using hexaminolevulinate and an incoherent white light system with the special flexible irradiation catheter system is technically feasible and safe and may offer an alternative in the treatment of non-muscle-invasive intermediate and high-risk bladder cancer.

Kindling-induced overexpression of Homer 1A and its functional implications for epileptogenesis

Despite an extensive research on the molecular basis of epilepsy, the essential players in the epileptogenic process leading to epilepsy are not known. Gene expression analysis is one strategy to enhance our understanding of the genes contributing to the functional neuronal changes underlying epileptogenesis. In the present study, we used the novel MPSS (massively parallel signature sequencing) method for analysis of gene expression in the rat kindling model of temporal lobe epilepsy. Kindling by repeated electrical stimulation of the amygdala resulted in the differential expression of 264 genes in the hippocampus compared to sham controls. The most strongly induced gene was Homer 1A, an immediate early gene involved in the modulation of glutamate receptor function. The overexpression of Homer 1A in the hippocampus of kindled rats was confirmed by RT-PCR. In order to evaluate the functional implications of Homer 1A overexpression for kindling, we used transgenic mice that permanently overexpress Homer 1A. Immunohistochemical characterization of these mice showed a marked Homer 1A overexpression in glutamatergic neurons of the hippocampus. Kindling of Homer 1A overexpressing mice resulted in a retardation of seizure generalization compared to wild-type controls. The data demonstrate that kindling-induced epileptogenesis leads to a striking overexpression of Homer 1A in the hippocampus, which may represent an intrinsic antiepileptogenic and anticonvulsant mechanism in the course of epileptogenesis that counteracts progression of the disease.

Tolerance-Inducing dose of 3-nitropropionic acid modulates bcl-2 and bax balance in the rat brain: a potential mechanism of chemical preconditioning

Many studies have reported ischemia protection using various preconditioning techniques, including single dose 3-nitropropionic acid (3-NPA), a mitochondrial toxin. However, the cellular signal transduction cascades resulting in ischemic tolerance and the mechanisms involved in neuronal survival in the tolerant state still remain unclear. The current study investigated the mRNA and protein expression of the antiapoptotic bcl-2 and the proapoptotic bax. two antagonistic members of the bcl-2 gene family, in response to a single dose of 3-NPA, to global cerebral ischemia-reperfusion. and to the combination of both 3-NPA-pretreatment and subsequent global cerebral ischemia-reperfusion. Brain homogenates of adult Wistar rats (n = 25) were analyzed for bcl-2 and bax mRNA expression using a new highly sensitive and quantitative polymerase chain reaction (PCR) technique that allows real-time fluorescence measurements of the PCR product (LightCycler; Roche Diagnostics, Mannheim, Germany). Animals for mRNA analysis received 3-NPA (20 mg/kg, intraperitoneal; "chemical preconditioning") or vehicle (normal saline), and were either observed for 24 plus 3 hours or were subjected to 15 minutes of global cerebral ischemia 24 hours after the pretreatment and observed for 3 hours of reperfusion. Immunohistochemistry was applied to serial brain sections of additional rats (n = 68) to determine amount and localization of the respective Bcl-2 and Bax protein expression in various brain areas. One set of animals was injected with 3-NPA and observed for 3, 12, 24, and 96 hours; a second set was exposed to 15 minutes global cerebral ischemia, 3, 12, and 24 hours reperfusion; and a third set was pretreated with 3-NPA or saline 24 hours before the ischemic brain insult and observed for 96 hours of reperfusion. The authors found single dose 3-NPA treatment to be associated with an elevated bcl-2:bax ratio (increased bcl-2 expression, decreased bax expression), both on the transcriptional (mRNA) and the translational (protein) level. The differential influence of 3-NPA was maintained during early recovery from global cerebral ischemia (3 hours), when 3-NPA pretreated animals showed higher bcl-2 and lower bax mRNA levels compared with rats with saline treatment. Respective changes in protein expression were localized predominately in neurons vulnerable to ischemic damage. Compared with baseline, Bcl-2 protein was significantly higher in surviving neurons at 96 hours after the insult, whereas Bax protein remained unchanged. However, at this late time of postischemic recovery (96 hours), the protein expression pattern of surviving neurons was not different between animals with and without 3-NPA pretreatment. To the authors' knowledge, the current study is the first report on the differential expression of pro- and antiapoptotic genes after a single, nonlethal dose of 3-NPA. The current results suggest alterations in the balance between pro- and antiapoptotic proteins as a potential explanation for the reported protection provided by chemical preconditioning using 3-NPA in rats.

One-step single-chain Fv recombinant antibody-based purification of gp96 for vaccine development

Heat shock proteins such as gp96 (grp94) isolated from tumor or infected cells are able to induce specific cytotoxic T-cell responses and protective immunity. To facilitate rapid and efficient isolation, we generated gp96-specific recombinant single-chain Fv (scFv) antibodies from a semisynthetic phage display library. When immobilized on Sepharose beads, these antibodies allow a high-yield, one-step purification of native gp96 molecules from both mouse and human tumor cell lysates. gp96 molecules eluted from these affinity columns under mild conditions are still capable of generating antigen-specific CTL responses in mice. Thus, scFv-purified gp96 is still associated with peptides; however, in contrast to conventionally purified gp96, scFv-isolated gp96 is free of contaminating material such as mitogenic concanavalin A and proteolytic cathepsins. With the help of these high-yield antibody columns, it is now possible to rapidly isolate immunogenic gp96-peptide complexes from small amounts of tumor material to a purity that allows their use in cancer immunotherapy protocols.

Generation of a large complex antibody library from multiple donors

We have generated a large complex library of single chain antibodies based on four individual libraries from each of 50 donors. DNA coding for the heavy and light chain variable domains of the IgM and IgG repertoires was amplified by PCR using two different sets of primers. Each individual library was composed of approximately 1-5x10(7) independent clones giving a final combined library of 4x10(9) members. Screening this library by phage display of single chain antibodies with small haptens, peptides and proteins yielded specific antibodies for each class of antigen.

The antigen binding domain of non-idiotypic human anti-F(ab')2 autoantibodies: study of their interaction with IgG hinge region epitopes

In previous studies we described a natural human IgG-anti-F(ab')2 autoantibody family with immunoregulatory properties. Genes coding for the variable regions of the heavy and light chains of the Abs were isolated from a natural Ig gene library and scFv Abs were expressed in E. coli. The scFv Abs bound to F(ab')2 but not to Fab fragments. This points to an epitope located in the hinge region since Fab fragments are lacking most of the hinge. In order to verify our hypothesis, double chain peptides comprising the lower-, middle-, and part of the upper hinge subregion of IgG1-IgG4 were synthesized on cellulose membranes and tested for binding to the Abs. The results show binding of Abs to IgG1 and IgG4 hinge region peptides. In order to identify the key residues of the discontinuous epitopes we carried out complete substitutional analyses in which each amino acid of the wt peptides was substituted by all other amino acids except cysteine. The exchange of proline in the IgG1 or IgG4 middle hinge region abrogated the binding, revealing the importance of this subregion for epitope expression. No binding to the IgG2 or IgG3 hinge was detected. These results indicate that scFv anti-F(ab')2 Abs recognize the hinge region of IgG1 and IgG4 and that the expression of the epitope depends on an intact middle hinge subregion.

Monitoring of scFv selected by phage display using detection of scFv-pIII fusion proteins in a microtiter scale assay

We describe here a method for the efficient and rapid analysis of antigen binding characteristics of recombinant antibodies (ab) selected by phage display. This novel approach combines the bacterial production of soluble single chain ab (scFv)-pIII fusion proteins on a microtiter scale with the detection of these fusion proteins via a pIII-specific ab. It facilitates the parallel analysis of large numbers of clones and is more efficient than current analysis protocols. Applying this technique, we analysed phage display selection of tetanus toxoid (TTX) specific scFv with respect to: (i) the productive expression of fusion proteins; (ii) the enrichment of specific scFv in subsequent rounds of phage display selection on a polyclonal level; (iii) the antigen specificity of individual scFv clones; (iv) the antigen binding affinity of a selected scFv. A TTX-specific scFv (clone 4.3) was further examined in a mono- and bivalent form by surface plasmon resonance analysis. ScFv 4.3 possesses a subnanomolar affinity and a low off rate constant.

Recognition of HLA-DR1/DRB1*0101 molecules presenting HLA-A2 derived peptides by a human recombinant antibody, Fab-5 A1

MHC molecules present peptides in their binding groove to T-cell receptors inducing proliferation or cytotoxicity of alloreactive T cells. A previously generated human monoclonal antibody (mAb) UL-5 A1, recognizing a conformational epitope formed by HLA DR1/DRB1*0101 molecules and HLA-A2 derived peptides, demonstrates T-cell-like recognition of the peptide/MHC complex (PMC). To study the genes of the antigen binding region, the nucleotide sequences of the rearranged genes in the variable regions of UL-5 A1 were determined and the V-gene usage (VH3, V lambda 2) was identified by comparison with published germlines. The genes encoding heavy (Fd) and light (L) chains of UL-5 A1 were linked and expressed in a bacterial system. Specificity of the recombinant Fab-5 A1 was determined with HLA-typed LCLs by flow cytometric analysis. As demonstrated in competitive inhibition assays, UL-5 A1 and Fab-5 A1 recognize the same PMC epitope on HLA-A2+, -DR1/DRB1*0101+ typed LCLs. Additionally, mAb UL-5 A1 and Fab-5 A1 both recognize HLA-A2-, -DR1/DRB1*0101+ LCLs exogenously loaded with HLA-A2 peptides (105-117, 103-117). UL-5 A1-like antibodies against peptide/MHC complexes could prove valuable tools for research on T-cell recognition and MHC function.

Production of a Human Antibody Library in the Phage-Display Vector pSEX81

Human monoclonal antibodies (MAbs) are more suitable than MAbs of animal origin for clinical applications because of lower hypersensitivity reactions, less formation of circulating immune complexes and lower anti-immunoglobulin responses The classical production of human MAbs via the hybridoma technique or Epstein-Barr virus (EBV) transformation is limited by the instability of cell lines, low antibody production, and the problems of imununizing humans with certain antigens (1,2). A promising alternative 1s the production of human recombinant antibodies (3). Recombinant DNA technology has made it possible to clone human antibody genes in vectors and to generate antibody expression libraries (4-7). One approach has been to amplify and recombine the IgG repertoire of an "immunized" donor. This has been used to isolate several antibodies related to diseases (8,9). In order to obtain more universal antibody libraries the naive IgM repertoire of several "unimmunized" donors were pooled (10,12). The complexity of the combinatorial libraries has been further increased by creating the so-called "semisynthetic" antibody libraries (22-14).

Screening of phage-displayed antibody libraries

The problem of amplifying a specific antibody in a population of millions of other antibodies has been solved by the immune system using the process of clonal selection Binding of an antigen to an IgM receptor on the surface of B-lymphocytes stimulates the proliferation and differentiation of the lymphocyte until it matures to an IgG-producing plasma cell. To mimic the first step of this process in bacteria, vectors have been constructed for the expression of antibodies on the surface of bacteria and phages (for review see Chapter 32 ).

Antibodies to steroids from a small human naive IgM library

Human antibodies specific for digoxigenin, estradiol, testosterone and progesterone have been isolated from a small combinatorial IgM repertoire (4 x 10(7)) of single chain antibodies (scFv). The affinities of both the anti-estradiol and antiprogesterone scFv were approximately 10(8) M(-1). Naive IgM genes appeared to be highly represented, since only the heavy chain variable domain of the anti estradiol antibody contained differences to corresponding germline sequences. The light chain variable domain of the progesterone receptor was also identical to a germline sequence, showing that it is possible for completely naive antibodies to bind steroids with affinities comparable to those obtained after a secondary immune response.

Idiotypic vaccine for treatment of human B-cell lymphoma. Construction of IgG variable regions from single malignant B cells

Immunoglobulin idiotypes (Id) of malignant B cells represent highly specific markers which can be used for vaccination. PCR-amplification of immunoglobulin genes enables the rapid production of large amounts of Id vaccines. However, the separate amplification and subsequent recombination of heavy and light chains can lead to a loss of the relevant Id. To preserve the original chain pairs, we used single malignant B cells derived from an immunocytoma patient. Cytoplasm was extracted and the mRNA transcribed into cDNA. The VH and VL genes were then amplified by PCR and cloned into a vector for expression in E. coli. Id production was checked using an anti-Id mouse monoclonal Ab raised against the patient's tumor-specific IgG. One out of 3 constructs expressed the relevant Id. Analysis of the first 31 light chain residues revealed an identical sequence for the malignant B cells' IgG and the recombinant Id construct. Exchange of either the heavy or light chain with an unrelated chain resulted in loss of the Id. An unrelated sequence derived from the c-myc protein is coupled to the Id vaccine. The lymphoma patient was shown to have Abs to the c-myc sequence. This sequence therefore, increases the Id+ Ab's antigenicity. CD spectroscopy showed an alpha-helical structure for the c-myc epitope. In conclusion, a B-cell lymphoma autovaccine was produced containing immunogenic sequences that do not alter the steric conformation of the tumor-specific Id.

Cloning and cytotoxicity of a human pancreatic RNase immunofusion

BACKGROUND

Immunotoxins based on plant and bacterial proteins are usually very immunogenic. Human ribonucleases could provide an alternative basis for the construction of less immunogenic reagents. Two members of the human RNase family, angiogenin and eosinophil-derived neurotoxin (EDN), have been fused to a single chain antibody against the transferrin receptor, which is known to be internalised by endocytosis. The fusion proteins proved to be very efficient inhibitors of protein synthesis using various cell lines. It is not yet known whether the side effects of angiogenin and EDN will compromise their potential use as immunotoxins.

OBJECTIVES

The goal of this work was to construct a human immunotoxin with no harmful side effects. Bovine pancreatic ribonuclease has been shown to be as potent as ricin at abolishing protein synthesis on injection into oocytes. We therefore decided to clone its human analogue, which is fairly ubiquitous and per se non-toxic. An immunofusion of human pancreatic RNase with a single chain antibody against the transferrin receptor was tested for its ability to inhibit protein synthesis in three different human tumor cell lines.

STUDY DESIGN

DNA coding for the human pancreatic RNase was cloned partially from a human fetal brain cDNA library and then completed by PCR using a human placental cDNA library as a template. The RNase gene was then fused with a DNA coding for an single chain antibody against the transferrin receptor (CD71). After expressing the fusion protein in E. coli, the gene product was isolated from inclusion bodies and tested for cytotoxicity.

RESULTS

This fusion protein inhibited the protein synthesis of three human tumor cell lines derived from a melanoma, a renal carcinoma and a breast carcinoma, with IC50s of 8, 5 and 10 nM, respectively. These values were comparable with those using a similar fusion protein constructed with eosinophil derived neurotoxin (EDN) as the toxic moiety (IC50s of 8, 1.2 and 3 nM, respectively). The slightly lower activities of the human pancreatic RNase-scFv (pancRNase-scFv) with two of the cell lines suggests that fewer molecules are reaching the cytoplasmic compartment, since it was twice as active as EDN-scFv in inhibiting the protein synthesis of a rabbit reticulocyte lysate.

CONCLUSION

These results demonstrate that the human pancreatic RNase, which is expected to have a very low immunogenic potential in humans with no inherent toxicity, may be a potent cytotoxin for tumor cells after antibody targeting.

Inverse correlation between IgG-antihinge region and antierythrocyte autoantibody in chronic benign and malignant cold agglutination

Previous reports provided evidence of an immunosuppressive role of natural anti-F(ab')2 antibodies. If suppressive anti-F(ab')2 antibodies also regulated the autoantibody production in cold agglutination, one would expect high titers of anti-F(ab')2 to be associated with low titers of cold agglutinins. Indeed, our previous studies revealed an inverse correlation between IgG-anti-F(ab')2 and cold agglutinins. Many previous experiments focused on anti-F(ab')2 of an antiidiotypic nature. Recent epitope mapping showed that anti-F(ab')2 of healthy persons is not an antiidiotype but recognizes a hinge region sequence. We attempted to answer the question whether this IgG-antihinge antibody is responsible for the previously described association between anti-F(ab')2 and cold agglutinins. IgG-antihinge and IgG-anti-F(ab')2 antibody was determined and statistically analyzed in the serum of 334 patients with cold agglutination. Our experiments revealed a strong correlation between the concentrations of antihinge and the previously described anti-F(ab')2 antibody. The anti-F(ab')2 activity was competitively inhibited by a synthetic hinge peptide. Moreover, patients with high antihinge titers had low cold agglutinin titers, and vice versa. A stratification according to cold agglutinin specificity and disease etiology showed that the inverse correlation is present only in anti-I and anti-i patients suffering from monoclonal B-lymphocyte proliferation. In conclusion, our results confirm the correlation previously described for anti-F(ab')2 antibody and antierythrocyte autoantibody and define for the first time an association between an idiotype-independent anti-IgG autoantibody and cold agglutinin.

The antigen-binding domain of a human IgG-anti-F(ab')2 autoantibody

Recent studies revealed an immunoregulatory role of natural IgG-anti-F(ab')2 antibodies in both healthy individuals and patients with certain diseases. The implication of anti-F(ab')2 antibodies in the pathogenesis of diseases prompted us to study the gene segment structure of their antigen-binding domains and their binding characteristics. cDNA was prepared from the lymphocytes of a patient with a high IgG-anti-F(ab')2 serum titer. Variable heavy and light gene segments were amplified by PCR and inserted into a phagemid surface expression vector. Single-chain antibodies displayed on the phage surface were screened for binding to F(ab')2 fragments. The subsequent analysis of 95 single clones demonstrated that they all bound specifically to F(ab')2. Sequence analyses of 12 clones showed that 11 were identical and 1 contained a silent point mutation in the heavy chain and three amino acid exchanges in the light chain. The heavy chains belonged to the V(H)3 and the light chains to the V(kappa)2 gene family. The 11 identical light-chain genes were completely homologous to a germ-line sequence (DPK-15). Binding assays showed that the single-chain antibodies bind to F(ab')2, but not to Fab, Fc, or intact IgG. This binding pattern was confirmed by surface plasmon resonance studies, which revealed a relatively high affinity (Ka = 2.8 x 10(7) M(-1)). The strong binding capacity was further demonstrated by competitive inhibition of the serum anti-IgG antibody's interaction with antigen. The present study defines for the first time to our knowledge the gene segment structure of the antigen-binding domain of two human IgG-anti-F(ab')2 autoantibody clones and describes the binding kinetics of the purified monomeric fragments.

A natural IgA-anti-F(ab')2gamma autoantibody occurring in healthy individuals and kidney graft recipients recognizes an IgG1 hinge region epitope

Natural anti-IgG autoantibodies are found both in healthy individuals and in patients with certain diseases. One group of these Abs recognizes epitopes located in the F(ab')2 region of the IgG molecule. The immunoregulatory role of these Abs in healthy individuals, graft rejection, and disease was previously studied, usually with a focus on the characterization of anti-idiotypic Abs. In the present study, we characterize the epitope recognized by an anti-F(ab')2gamma autoantibody of the IgA isotype, which occurs in the serum of healthy individuals and kidney transplant recipients. The autoantibody described herein reacts strongly with F(ab')2gamma but only poorly with Fab(gamma) fragments, a binding pattern pointing to an epitope located in the hinge region. Using synthetic peptides, we identified a conformational epitope that overlaps the middle and part of the lower hinge region. Structural analyses of peptide constructs showed that a defined conformation of the first three residues of the lower hinge is required for a full expression of the epitope. Binding of IgA to the hinge region of IgG1 covers part of the physiologically active Fc domain, immobilizes the Fab arms, and thereby can be expected to exert immunoregulatory functions.

A natural IgA-anti-F(ab')2gamma autoantibody occurring in healthy individuals and kidney graft recipients recognizes an IgG1 hinge region epitope

Natural anti-IgG autoantibodies are found both in healthy individuals and in patients with certain diseases. One group of these Abs recognizes epitopes located in the F(ab')2 region of the IgG molecule. The immunoregulatory role of these Abs in healthy individuals, graft rejection, and disease was previously studied, usually with a focus on the characterization of anti-idiotypic Abs. In the present study, we characterize the epitope recognized by an anti-F(ab')2gamma autoantibody of the IgA isotype, which occurs in the serum of healthy individuals and kidney transplant recipients. The autoantibody described herein reacts strongly with F(ab')2gamma but only poorly with Fab(gamma) fragments, a binding pattern pointing to an epitope located in the hinge region. Using synthetic peptides, we identified a conformational epitope that overlaps the middle and part of the lower hinge region. Structural analyses of peptide constructs showed that a defined conformation of the first three residues of the lower hinge is required for a full expression of the epitope. Binding of IgA to the hinge region of IgG1 covers part of the physiologically active Fc domain, immobilizes the Fab arms, and thereby can be expected to exert immunoregulatory functions.

A single expression system for the display, purification and conjugation of single-chain antibodies

To facilitate the purification and conjugation of single-chain antibodies (scFv) selected from a phage display library, we have incorporated His6, an amber stop codon and a C-terminal Cys into a surface expression vector. The vector also contains a lacIq gene for improving the efficiency of regulation and a sequence coding for a marker peptide.

The natural human IgG anti-F(ab')2 antibody recognizes a conformational IgG1 hinge epitope

Natural IgG anti-F(ab')2 Abs are part of the physiologic immune repertoire and have important immunoregulatory functions. Although previous work suggested that some of these Abs recognize epitopes located in the constant region of the F(ab')2 molecule, an exact epitope mapping has not been performed. We found that the anti-F(ab')2 Ab binds strongly to F(ab')2 but only weakly to Fab fragments. Fab fragments are lacking the core and lower hinge region. In our experiments, we show that the IgG anti-F(ab')2 Ab binds strongly to a synthetic double chain peptide (225-237/225'-237') comprising the core and lower hinge region of the human IgG1 molecule. In contrast, it binds only weakly to the same peptide in monomeric form (225-237) or to a short double chain hinge peptide (225-232/225'-232'). The double chain peptides comprise a cyclic region between the two cystine bridges and an exocyclic region. Previous nuclear magnetic resonance analyses showed that the cyclic portion of the short double chain hinge peptide adopts the same conformation as that found in the intact IgG1 molecule. The dichroic properties of the short and long double chain hinge peptides indicate that they have identical conformations in their cyclic regions, but have different conformations in their exocyclic regions. The conformational differences in the exocyclic regions explain the binding of the Ab to the long double chain hinge peptide and the lack of binding to the short one. The circular dichroism spectrum of the monomeric hinge peptide, which is not recognized by the Ab, is consistent with the absence of an ordered peptide structure. These findings lead us to conclude that the IgG anti-F(ab')2 Ab recognizes a conformational IgG1 hinge epitope.

The natural human IgG anti-F(ab')2 antibody recognizes a conformational IgG1 hinge epitope

Natural IgG anti-F(ab')2 Abs are part of the physiologic immune repertoire and have important immunoregulatory functions. Although previous work suggested that some of these Abs recognize epitopes located in the constant region of the F(ab')2 molecule, an exact epitope mapping has not been performed. We found that the anti-F(ab')2 Ab binds strongly to F(ab')2 but only weakly to Fab fragments. Fab fragments are lacking the core and lower hinge region. In our experiments, we show that the IgG anti-F(ab')2 Ab binds strongly to a synthetic double chain peptide (225-237/225'-237') comprising the core and lower hinge region of the human IgG1 molecule. In contrast, it binds only weakly to the same peptide in monomeric form (225-237) or to a short double chain hinge peptide (225-232/225'-232'). The double chain peptides comprise a cyclic region between the two cystine bridges and an exocyclic region. Previous nuclear magnetic resonance analyses showed that the cyclic portion of the short double chain hinge peptide adopts the same conformation as that found in the intact IgG1 molecule. The dichroic properties of the short and long double chain hinge peptides indicate that they have identical conformations in their cyclic regions, but have different conformations in their exocyclic regions. The conformational differences in the exocyclic regions explain the binding of the Ab to the long double chain hinge peptide and the lack of binding to the short one. The circular dichroism spectrum of the monomeric hinge peptide, which is not recognized by the Ab, is consistent with the absence of an ordered peptide structure. These findings lead us to conclude that the IgG anti-F(ab')2 Ab recognizes a conformational IgG1 hinge epitope.

The cAMP response element binding protein is involved in hydra regeneration

Hydra provides an interesting developmental model system where pattern formation processes are easily accessible to experimentation during regeneration. Previous studies have shown that the neuropeptide head activator affects cellular growth and head-specific cellular differentiation during head regeneration and budding. In order to investigate the signal transduction pathway and the regulatory genes involved in these processes, we measured cAMP levels after head activator treatment and found that head activator leads to an increase in cAMP levels at concentrations where effects on nerve cell determination and differentiation are observed (10(−11) to 10(−9) M). Moreover, exposure of intact hydra to a permeable form of cAMP stimulates nerve-cell differentiation and thus mimicks the effect of endogenous head activator. Band-shift assays were performed to detect changes in hydra nuclear protein binding activity during regeneration or after head activator treatment. We found that the cAMP response element (CRE) promotes a specific and strong DNA-binding activity which is dramatically enhanced and modified during early regeneration or after HA treatment. We also identified a surprisingly highly conserved hydra gene encoding the cAMP Response Element Binding protein, which is involved in this CRE-binding activity. Initiation of regeneration upon wounding provokes an endogenous release of HA which leads to the final differentiation of determined nerve cells. We propose that the nerve-cell differentiation observed within the first 4–8 hours of regeneration relies on the agonist effect of head activator on the cAMP pathway, which would in turn modulate the CRE-binding activity of the hydra CREB protein and thus regulate the transcriptional activity of genes involved in regeneration processes.

Amino acid sequence based PCR primers for amplification of rearranged human heavy and light chain immunoglobulin variable region genes

Previously described primers for PCR amplification of variable immunoglobulin (Ig) genes were based on gene sequences. To include the large number of amino acid sequences of antibodies whose DNA has not been sequenced and to ensure a maximal fit to rearranged human Ig variable region genes, we have made a comprehensive comparison of both protein and nucleotide sequences. The resulting set of 15 primers was able to amplify a wide range of rearranged antibody variable region genes. Restriction sites included in the primers facilitate cloning of the PCR products into various expression vectors. Sequence analyses of PCR-amplified cDNA derived from a polyclonal B cell population showed that maximal enrichment is obtained for highly represented variable Ig gene subgroups. Rarely occurring V kappa 4 and V lambda 5 subgroups were not detected. Rearranged Ig variable region genes from each of 19 human B cell lines were also amplified. Comparisons to germline sequences allowed the allocation of rearranged genes to the original Ig genes. This primer set should be very useful for generating large repertoires of rearranged V genes and for amplifying genes of individual B cell clones.

Isolation of IgG antibody Fv-DNA from various mouse and rat hybridoma cell lines using the polymerase chain reaction with a simple set of primers

To facilitate the isolation of IgG antibody Fv-DNA sequences from hybridoma cell lines, we have established a polymerase chain reaction (PCR) procedure requiring only a small number of primers. The sense primers homologous to DNA coding for the first framework sequences were designed to hybridize to all the known antibody sequences under conditions that permit a high number of mismatches. The antisense primers were homologous to DNA coding for the beginning of the constant regions of the gamma and kappa chains. Restriction sites introduced by the primers enable the DNA to be cloned into bacterial expression vectors. Only three sense VH primers and two sense VL primers paired with one backward primer for the heavy and light chains, respectively, were necessary for the amplification of Fv-DNA from a total of 17 rodent cell lines that we have so far worked with. These consisted of 12 mouse cell lines and five rat cell lines. This procedure will therefore probably be sufficient to isolate the Fv-DNA from most mouse cell lines and possibly also from most rat cell lines.

Simultaneous mutagenesis of antibody CDR regions by overlap extension and PCR

A method for the facile simultaneous mutagenesis of complementary-determining regions (CDRs) in a single chain antibody (scFv) is described. Overlapping sets of oligonucleotides containing random sequences within the CDRs corresponding to the heavy chain variable region (VH) jointed to a linker peptide (J) and the light chain variable region (VL) were extended under PCR conditions to full-length genes. These gene products were then further amplified using short PCR primers containing complementary overlaps between the 3' and 5' ends of the VH-J and VL genes respectively. In a final step, the VH-J and VL gene products were mixed and assembled into scFv DNA products by overlap extension under standard PCR conditions. Sequence analyses indicated that the method is basically successful. However, some deletions were observed, which probably reflects difficulties in the automatic synthesis of long degenerate oligonucleotides.

Suppression of anti-erythrocyte autoantibody-producing B cells by a physiological IgG-anti-F(ab')2 antibody and escape from suppression by tumour transformation; a model relevant for the pathogenesis of autoimmune haemolytic anaemia

We showed previously that broadly reactive IgG anti-immunoglobulin autoantibodies produced by rats during the immune response suppress the B cell response. We report here on the effect of a similar human antibody on self-reactive human B cells. IgG anti-F(ab')2 was added to cultures of anti-erythrocyte autoantibody-producing B cells derived from healthy donors. A dose-dependent suppression of the antibody response was obtained (maximum at 1.3 ng IgG/10(6) cells). This effect was competitively inhibited by F(ab')2 gamma. Autoimmune haemolytic anaemia can be caused by chronic monoclonal B cell proliferation. To reproduce this condition in vitro we immortalized B cells with Epstein-Barr virus (EBV) and raised a B cell population with anti-erythrocyte autoantibody activity. These cells were electrically fused with CB-F7 tumour cells and an IgG1 cold-reactive anti-erythrocyte autoantibody-producing B cell line was established. Surprisingly, the tumour cells were not suppressed by IgG anti-F(ab')2. It is known that anti-immunoglobulins selectively suppress antigen-receptor (AgR)-occupied B cells by a Fc gamma-receptor (Fc gamma R)-mediated mechanism. To occupy their AgR, we preincubated the tumour cells with anti-AgR antibody. In spite of this, their susceptibility to suppression was not restored. As shown by rabbit IgG-sensitized ox erythrocyte (EA)-rosetting, this refractoriness was not due to a loss of Fc gamma R. Our experiments delineate a mechanism of peripheral B cell suppression to autoantigens, and show a way of escape from control relevant for the pathogenesis of autoimmune haemolytic anaemia.