Scorpion envenomation and serotherapy in Morocco

A clinical and biologic study was conducted in Morocco to assess the efficiency of antivenom therapy for treating victims of scorpion stings. Epidemiologic and clinical data were collected from 275 patients envenomed by Androctonus mauretanicus mauretanicus and Buthus occitanus scorpions. Patients received antivenom or other drugs. Blood samples were collected at the time of hospital admission and 1 hr and 3 hr after treatment. Serum venom levels were quantified by using an ELISA. An association was found between clinical signs of envenoming and the level of venom in serum. Patients classified as grade II (moderate envenoming) had higher serum levels of venom level than patients classified as grade I (mild envenoming). At admission to the hospital, the mean venom concentration was not significantly different between the group not treated with antivenom, the group who received 2-5 ml of antivenom, and the group who received 10 ml of antivenom. A significant decrease in serum venom levels and an improvement in the clinical conditions were observed in patients administered 10 ml of antivenom. The lower decrease in serum venom levels in patients who received 2-5 ml of antivenom was due to lower doses of antivenom. No difference in the venom concentration was observed in patients who were not treated with antivenom. The absence of administration of antivenom increased the risk of developing clinical signs at the end of the hospitalization period. However, this risk was much higher when more than 1 hr elapsed between the time of the scorpion sting and the time of hospital admission. The results demonstrate that antivenom is effective in decreasing circulating venom and morbidity. Serotherapy is more efficient when given as soon as possible after envenomation and with adequate quantities of antivenom.

Production of Fab fragments of monoclonal antibodies using polyelectrolyte complexes

A new method for the production of monovalent Fab fragments of antibodies has been developed. Traditionally Fab fragments are produced by proteolytic digestion of antibodies in solution followed by isolation of Fab fragments. In the case of monoclonal antibodies against inactivated subunits of glyceraldehyde-3-phosphate dehydrogenase, digestion with papain resulted in significant damage of the binding sites of the Fab fragments. Antigen was covalently attached to the polycation, poly(N-ethyl-4-vinylpyridinium bromide). Proteolysis of monoclonal antibodies in the presence of the antigen-polycation conjugate followed by (i) precipitation induced by addition of polyanion, poly(methacrylic) acid, and pH shift from 7.3 to 6.5 and (ii) elution at pH 3.0 resulted in 90% immunologically competent Fab fragments. Moreover, the papain concentration required for proteolysis was 10 times less in the case of antibodies bound to the antigen-polycation conjugate than that of free antibodies in solution. The digestion of antibodies bound to the antigen-polyelectrolyte complex was less damaging, suggesting that binding to the antigen-polycation conjugate not only protected binding sites of monoclonal antibodies from proteolytic damage but also facilitated the proteolysis probably by exposing antibody molecules in a way convenient for proteolytic attack by papain.

Use of thiophilic adsorption chromatography for the one-step purification of a bacterially produced antibody F(ab) fragment without the need for an affinity tag

Thiophilic adsorption chromatography (TAC) was employed for the purification of a recombinant F(ab) fragment of the antibody IN-1 from the periplasmic protein fraction of Escherichia coli. Adsorption of the F(ab) fragment to the T-gel was achieved at a high concentration of ammonium sulfate and turned out to be independent of the presence of a His(6) tag or Strep tag or of the human or murine nature of the C(H)1 and C(L) domains (subclass IgG1/kappa). Elution was effected by means of a decreasing salt gradient, yielding fractions with the correctly assembled, heterodimeric F(ab) fragment at high purity. Interestingly, the single substitution of an alanine residue with phenylalanine in the CDR-L1 of the F(ab) fragment significantly enhanced the retention on the column so that quantitative elution necessitated prolonged application of a low-salt buffer. Our findings suggest that TAC is generally suitable for the isolation of bacterially produced F(ab) fragments and support the notion that aromatic side chains play an important role in the interaction with the affinity matrix. This method should prove valuable in the production of proteins for in vivo applications as might be the case for the F(ab) fragment of the antibody IN-1, which promotes axonal regeneration in the central nervous system.

Humanization of a murine monoclonal antibody by simultaneous optimization of framework and CDR residues

Optimal protein function often depends on co-operative interactions between amino acid residues distant in the protein primary sequence yet spatially near one another following protein folding. For example, antibody affinity is influenced by interactions of framework residues with complementarity-determining region (CDR) residues. However, despite the abundance of antibody structural information and computational tools the humanization of rodent antibodies for clinical use often results in a significant loss of affinity. To date, antibody engineering efforts have focused either on optimizing CDR residues involved in antigen binding or on optimizing antibody framework residues that serve critical roles in preserving the conformation of CDRs. In the present study a new approach which permits the rapid identification of co-operatively interacting framework and CDR residues was used to simultaneously humanize and optimize a murine antibody directed against CD40. Specifically, a combinatorial library that examined eight potentially important framework positions concomitantly with focused CDR libraries consisting of variants containing random single amino acid mutations in the third CDR of the heavy and light chains was expressed. Multiple anti-CD40 Fab variants containing as few as one murine framework residue and displaying up to approximately 500-fold higher affinity than the initial chimeric Fab were identified. The higher affinity humanized variants demonstrated a co-operative interaction between light chain framework residue Y49 and heavy chain CDR3 residue R/K101 (coupling energy, DeltaGI=0.9 kcal/mol). Screening of combinatorial framework-CDR libraries permits identification of monoclonal antibodies (mAb) with structures optimized for function, including instances in which the antigen induces conformational changes in the mAb. Moreover, the enhanced humanized variants contain fewer murine framework residues and could not be identified by sequential in vitro humanization and affinity muturation strategies. This approach to identifying co-operatively interacting residues is not restricted to antibody-antigen interactions and consequently, may be used broadly to gain insight into protein structure-function relationships, including proteins that serve as catalysts.

Isolation, characterization and sequence analysis of five IgG monoclonal anti-beta 2-glycoprotein-1 and anti-prothrombin antigen-binding fragments generated by phage display

We have isolated five monoclonal IgG anti-beta 2-glycoprotein-1 (anti-beta 2G-1) and anti-prothrombin Fab from a patient with autoantibodies to oxidized low-density lipoproteins by phage display method. Analysis of their binding specificity revealed that all three beta 2GP-1-enriched mAbs (B14, B22, B27) reacted with beta 2GP-1 while both prothrombin-isolated mAbs (P11 and P13) reacted with prothrombin. Intriguingly, mAb P11 reacted with beta 2GP-1 and prothrombin and showed comparable binding affinity to both Ags, with Kd values of 1.6 x 10-6 M for beta 2GP-1 vs 3.2 x 10-6 M for prothrombin. This clone may thus, define a hitherto unknown shared epitope between beta 2GP-1 and prothrombin. Sequence analysis of all five clones showed significant mutations of the expressed genes. One rearranged V-D-J segment was repeatedly employed by three clones (mAbs B22, B27, and P13). However, all three clones used different L chains. Of note, the pairing of VH6-D-J with the L5-Vk1 L chain in mAb P13 resulted in the loss of binding to beta 2GP-1 and specific reactivity to prothrombin. Together, these data suggest that while the VH6-D-J chain may be important in the binding to beta 2GP-1, pairing with certain L chains may influence this binding. These data are the first human IgG anti-beta 2GP-1 and anti-prothrombin sequences reported; both represent the major subsets of antiphospholipid Abs present in antiphospholipid syndrome patients.

Generation of anti-p53 Fab fragments from individuals with colorectal cancer using phage display

Although many individuals with malignancy develop Abs against p53, little is currently known of the structural features, V gene usage, and degree of somatic mutation of these Abs. Such information is critical to any meaningful understanding of the nature and significance of this humoral immune response to p53. We have constructed phage display libraries from six individuals with colorectal cancer and a demonstrable serum immune response against p53. Following panning with recombinant p53, a total of 43 binding Fab were identified. Four of these Abs bound with high affinity to wild-type denatured p53 (1.19 x 10-8 - 1.57 x 10-8), as determined by BIAcore analysis, and were highly specific for both recombinant and cell line-derived p53, as determined by ELISA and immunoprecipitation. Epitope mapping showed they were reactive with the N terminus of human p53 between residues 27 and 44. Sequence analysis showed that the heavy chains were derived from the VH1 gene family, and the light chains from VL4. The pattern of replacement and silent mutations in the Fab sequence indicated that negative selection had occurred in the framework regions of all the VH genes. We show that lymphocytes from individuals with cancer represent a valuable source of high affinity human Abs against p53. This approach provides an opportunity to examine the genetic structure of these naturally occurring Abs, and to draw inferences regarding the nature of the immune response that produced them. Abs identified in this way have a number of potential therapeutic applications.

Vipera palaestinae antivenin

A review is presented of the methods developed to raise the neutralizing capacity of anti-Vipera palaestinae (Vp) venom. These include formaldehyde detoxification of the venom, immunization with carboxymethyl-cellulose-bound neurotoxin, and enzymatic fragmentation of the neutralizing antibody.

Ebola virus can be effectively neutralized by antibody produced in natural human infection

The activity of antibodies against filoviruses is poorly understood but has important consequences for vaccine design and passive prophylaxis. To investigate this activity, a panel of recombinant human monoclonal antibodies to Ebola virus antigens was isolated from phage display libraries constructed from RNA from donors who recovered from infection in the 1995 Ebola virus outbreak in Kikwit, Democratic Republic of Congo. Antibodies reactive with nucleoprotein (NP), envelope glycoprotein (GP), and secreted envelope glycoprotein (sGP) were characterized by immunofluorescence and radioimmunoprecipitation assays. Four antibodies reacting strongly with sGP and weakly with GP and two antibodies reacting with NP were not neutralizing. An antibody specific for GP neutralized Ebola virus to 50% at 0.4 microgram/ml as the recombinant Fab fragment and to 50% at 0.3 microgram/ml (90% at 2.6 microgram/ml) as the corresponding whole immunoglobulin G1 molecule. The studies indicate that neutralizing antibodies are produced in infection by Ebola virus although probably at a relatively low frequency. The neutralizing antibody may be useful in vaccine design and as a prophylactic agent against Ebola virus infection.

Bacterial expression and purification of the Fab fragment of a monoclonal antibody specific for the low-density lipoprotein receptor-binding site of human apolipoprotein E

We report the bacterial expression and the purification of a monoclonal antibody (mAb) specific for an epitope that coincides with the LDL receptor (LDLr)-binding domain of human apolipoprotein E (apoE). This antibody resembles the LDLr in its primary structure and its specificity for apoE variants. The recombinant Fab (rFab) fragment of mAb 2E8, consisting of the entire light chain and the Fd portion of the heavy chain, was expressed in Escherichia coli and purified to homogeneity. Purification was facilitated by including a five-histidine carboxyl-terminal extension on the Fd chain. A 5- to 10-fold difference in yield of the antibody was observed when the plasmid was expressed in two different strains of E. coli. Typically 2-6 mg of rFab per liter of culture medium was recovered in the periplasm of the TG1 strain and less than 1 mg was recovered in the periplasm of the XL1-Blue strain. Culture temperatures above 35 degrees C or inclusion of sucrose in the medium reduced rFab yields. The 2E8 rFab was indistinguishable from Fab prepared from 2E8 hybridoma-generated IgG with respect to its affinity and fine specificity. We are using this system to express a panel of 2E8 variant Fabs that will be used as probes to establish the structural features responsible for the binding of apoE to the LDLr.

Structure of an activity suppressing Fab fragment to cytochrome P450 aromatase: insights into the antibody-antigen interactions

The crystal structure of a Fab fragment (Fab3-2C2) of a monoclonal antibody raised against aromatase cytochrome P450 P450arom) has been determined at 3.0 A resolution. P450arom is a membrane bound enzyme responsible for the catalysis of indrogens to estrogens, the process of aromatization, and hence has been implicated in hormone-dependent breast cancer. The Fab fragment of MAb3-2C2 IgG suppresses P450arom activity in a dose dependent manner. The Fab3-2C2 molecule crystallizes n the space group P2(1)2(1)2(1) with a unit cell of a= 154.89 A, b = 73.51 A, and c= 36.90 A. The crystal structure consists of a light and a heavy chain in the asymmetric unit, each characterized by the greek-key antiparallel beta barrel folding seen in all Fab structures. The average elbow angle between the two domains is 143 degrees. Modeling of the interactions between the variable domains of the antibody and a known model of P450arom maps the epitope to a region of the enzyme that is consistent with the available biochemical data and the activity-suppressing function of the antibody. The epitope mapping result is further supported by the inability of MAb3-2C2 IgG to suppress the activity of, or to interact with placental porcine P450arom, which is 81% identical (86% similar) to human P450arom but has a few key substitutions in the putative epitope region.

Ultrasensitive immune complex transfer enzyme immunoassay of HIV-1 p24 antigen with less serum interference using 2,4-dinitrophenyl-anti-HIV-1 p24 IgG and indirectly immobilized (anti-2,4-dinitrophenyl group) Fab

In the immune complex transfer enzyme immunoassay previously reported, the immune complex consisting of 2,4-dinitrophenyl-biotinyl-bovine serum albumin-affinity-purified rabbit anti-HIV-1 p24 Fab' conjugate, HIV-1 p24 antigen and monoclonal mouse anti-HIV-1 p24 Fab'-beta-D-galactosidase conjugate was trapped on polystyrene beads coated directly with affinity-purified (anti-2,4-dinitrophenyl group) IgG and was transferred to polystyrene beads coated with biotinyl-bovine serum albumin and streptavidin. The serum volume used was limited to 10 microL due to serious serum interference, and the detection limit of HIV-1 p24 antigen was 240 fg/mL serum. In the present study, HIV-1 p24 antigen was incubated simultaneously with 2,4-dinitrophenyl-affinity-purified rabbit anti-HIV-1 p24 IgG and monoclonal mouse anti-HIV-1 p24 Fab'-beta-D-galactosidase conjugate in the presence of excess nonspecific rabbit IgG. The immune complex of the three components formed was trapped on polystyrene beads coated successively with biotinyl-bovine serum albumin, streptavidin and biotinyl-affinity-purified (anti-2,4-dinitrophenyl group) Fab'. After washing, the immune complex was eluted from the polystyrene beads with excess epsilonN-2,4-dinitrophenyl-L-lysine and transferred to polystyrene beads coated with affinity-purified goat (antirabbit IgG) IgG. The serum volume used was increased to 90 microL with only slight serum interference, and the detection limit of HIV-1 p24 antigen was lowered 9-fold to 26 fg/mL serum.

A recombinant Fab neutralizes dengue virus in vitro

A recombinant Fab that recognizes a neutralizing epitope located in the (296-400) region of protein E of dengue virus was obtained from cloned hybridoma cells secreting the mouse monoclonal antibody (mAb) 4E11. The Fd and light chain antibody genes were amplified by polymerase chain reaction, cloned into the phagemid vector pMad, expressed in bacteria to produce Fab fragments and sequenced. The mAb 4E11, in particular its light chain complementary-determining regions, shared homologies with two other anti-viral mAbs. The affinity of the parental mAb and the cloned Fab to the MalE-E(296-400) fusion protein were shown to be of the same magnitude, i.e. nanomolar. Fab 4E11 neutralization capacity was found between 8 and 4-times or less lower than that of mAb 4E11, depending on serotypes, thus the Fab could have a smaller antiviral activity than the mAb in vitro.

A molecular approach for isolating high-affinity Fab fragments that are useful in blood group serology

BACKGROUND

Multiple mouse hybridoma antibodies recognize the antigens of the MNS blood group system. The Fab fragments of several of these antibodies were expressed on bacteriophage and as soluble proteins. The parental N92 anti-N IgG monoclonal antibody (parental N92 MoAb), but not its monovalent, soluble Fab fragment (N92 Fab fragment), agglutinated antigen-positive red cells by an antiglobulin method. Light-chain shuffling was used to isolate mutant N92 Fab fragments with higher affinity that would function by agglutination.

STUDY DESIGN AND METHODS

Light-chain cDNA libraries, constructed from mice immunized with N-type glycophorin A, were inserted into a recombinant pComb3H vector containing the N92 Fd fragment. The N92 Fd fragment:light-chain libraries were panned on N-type glycophorin A or NN red cells, and antigen-binding clones were isolated. Purified parental N92 MoAb and the Fab fragments were evaluated by enzyme-linked immunosorbent assay and agglutination.

RESULTS

The novel NNA7, C1, and G11 Fab fragments all bound to N-type glycophorin A with higher affinity than did the N92 Fab fragment. The affinity of the library-derived clones was equivalent to that of the parental N92 MoAb. Although their fine specificity differed slightly from the parental N92 MoAb, the clones functioned equivalently by agglutination using an antiglobulin method.

CONCLUSIONS

Light-chain shuffling allowed the isolation of bacterially produced, high-affinity, soluble, monovalent recombinant anti-N Fab fragments that functioned well by agglutination. This approach is useful in obtaining inexpensive serologic reagents that may replace conventional MoAbs produced by tissue culture methods.

[Isolation, crystallization, and preliminary x-ray study of a Fab fragment of monoclonal antibody against human interleukin-2 and its complex with antigenic peptide]

Antigen-binding fragments (Fab) of mouse monoclonal antibodies to human interleukin-2 were obtained in preparative quantities by a modified procedure. These Fab-fragments were shown to be homogeneous according to the isoelectric focusing method. Various monocrystals of these free Fab-fragments and their complexes with the antigenic peptide corresponding to the 59-72 sequence of interleukin-2 were obtained. These were shown to be suitable for X-ray and were preliminarily studied by X-ray.

Isolation of human anti-branched chain alpha-oxo acid dehydrogenase-E2 recombinant antibodies by Ig repertoire cloning in idiopathic dilated cardiomyopathy

The generation of human monoclonal autoantibodies is critical for understanding humoral immune response in autoimmunity. In this study, Ig gene repertoire cloning was performed from a regional lymph node of a patient with idiopathic dilated cardiomyopathy (IDCM), and the resulting combinatorial IgG library was screened with bovine branched chain alpha-oxo acid dehydrogenase-E-2 (BCOADC-E2), one of the autoantigens in IDCM. After three rounds of affinity selection, we isolated three human recombinant IgG Fab molecules, named BC1, BC2 and BC3, that specifically react with BCOADC-E2 by ELISA. Interestingly, BC2 showed weak cross-reactivity to pyruvate dehydrogenase complex-E2 (PDC-E2), another mitochondrial autoantigen found in primary biliary cirrhosis (PBC), and their kappa light chain genes have 95% homology with a light chain of the human anti-DNA antibody. Although the exact pathogenic effect of anti-BCOADC-E2 autoantibodies is still unknown in IDCM, the potential binding specificity and limited light chain gene usage of our recombinant IgG molecules may shed light on the initial mechanism as to how autoantibodies start developing in IDCM.

Recombinant human monoclonal antibodies to Ebola virus

Human Fab (IgG1kappa) phage display libraries were constructed from bone marrow RNA from 2 donors who recovered from infection with Ebola (EBO) virus during the 1995 outbreak in Kikwit, Democratic Republic of the Congo. The libraries were initially panned against a radiation-inactivated EBO virus-infected Vero cell lysate, but only weak binders were identified. In contrast, panning against secreted EBO glycoprotein (SGP) resulted in Fabs showing very strong reactivity with SGP in ELISA. These Fabs also reacted with a virion membrane preparation. The Fabs were strongly positive in IFAs with cells infected with EBO (subtype Zaire) virus but negative with uninfected cells, with a characteristic punctate staining pattern in the cytoplasm. The Fabs showed weak or no reactivity with the virus cell lysate although donor serum did react. The Fabs are now being characterized in structural and functional terms. Major interest will focus on the ability of antibodies to neutralize EBO virus and, later, to protect animals against infection.

Crystallization and preliminary X-ray data for the human transthyretin-retinol-binding protein (RBP) complex bound to an anti-RBP Fab

A macromolecular complex of human transthyretin, human retinol-binding protein and an anti-retinol-binding-protein Fab was crystallized by vapour diffusion in sitting drops. Diffraction from these crystals at cryogenic temperatures was consistent with the space group C222, with cell parameters a = 159.34, b = 222.40 and c = 121.27 A. Crystals diffracted to a resolution limit of 3.36 A using synchrotron radiation. Based on a 2:2:1 stoichiometry for the Fab-retinol-binding-protein-transthyretin complex and the presence of one such complex per asymmetric unit, a reasonable Vm coefficient of 2.74 A3 Da-1 could be estimated.

Use of streptococcal protein G in obtaining crystals of an antibody Fab fragment in complex with a meningococcal antigen

Crystals have been obtained of an antibody Fab fragment grown in the presence of a single domain from streptococcal protein G and a ten amino-acid peptide corresponding to the P1.7 serosubtype antigen from the human pathogen Neisseria meningitidis. Crystal trials using the Fab fragment and peptide antigen alone were unsuccessful, but the inclusion of a protein G domain provided an additional variable that generated suitable crystals. Crystals are in space group P21 with unit-cell parameters a = 43.60, b = 63.42, c = 89.63 A, beta = 98.58 degrees and a data set has been collected to 2.9 A resolution using synchrotron radiation. The inclusion of protein G is likely to be of general utility for the crystallization of Fab-antigen complexes.

Expression of a recombinant Fab antibody fragment against cruzipain, the major cysteine proteinase of Trypanosoma cruzi

Cruzipain, the major proteinase of Trypanosoma cruzi, plays an important role in the biology of this parasite. This study reports the development of a recombinant Fab antibody, using RNA isolated from the anti-Ag163B6 hybridoma against cruzipain. This procedure involves the use of cDNAs obtained with the aid of a specific set of primers complementary to the complete light kappa chain (L kappa) and the first two domains of the IgG1 heavy chain (VH/CH1). These products were subsequently cloned in the pComb3 system, from which the gIII gene had been removed, and expressed in Escherichia coli cells. The recombinant Fab molecule recognized cruzipain by ELISA, in a fashion similar to the original mAb anti-Ag163B6. Nucleotide sequence analysis of the recombinant molecule, together with its immunological recognition by specific anti-mouse IgG (Fab)2, indicated the immunoglobulin nature of the recombinant product. Moreover, both the mAb anti-Ag163B6 and the soluble Fab fragment described here react similarly with the intact parasite surface, as observed in an indirect immunofluorescence assay. In conclusion, our recombinant Fab anti-Ag 163B6 allows the possible use of this molecule for diagnosis, antigen purification, and eventually treatment of Chagas-afflicted individuals.

The development and use of immunotherapy in Africa

The immunotherapy was recently developed due to the improvement of purification techniques of antivenoms and results of the research in toxicology and pharmacology. The utilisation of highly purified IgG fragments leads to a better tolerance and a higher efficacy. Snake envenomations constitute in Africa, as in many tropical countries, an important public health problem. The annual incidence of snakebites reaches 1 million and the annual mortality is about 20,000 deaths. Less than 25% of the antivenom needs are effectively covered and, probably in most of envenomations, used at insufficient doses. The treatment of snakebites would be improved by better knowledge on snakebite epidemiology, standardisation of treatment and training medical staff, and development of new financial procedures for antivenom supply.

Specificity improvement of a recombinant anti-testosterone Fab fragment by CDRIII mutagenesis and phage display selection

The monoclonal antibodies so far developed by hybridoma technology have not had high enough specificity or affinity to distinguish the closely related steroid hormones in routine clinical assays. We have employed random mutagenesis and phage display approaches to improve the specificity of one anti-testosterone monoclonal antibody (3-C4F5). The affinity of the antibody is 0.3 x 10(9) M(-1) and the cross-reactivities with most of the related steroids are low. However, the antibody cross-reacts about 1% with dehydroepiandrosterone sulfate (DHEAS) and owing to the high DHEAS serum concentration this is about 1000-fold too high for clinical immunoassays. The complementarity-determining regions (CDRs) of the heavy and light chains, which were predicted by molecular modelling to be in close contact with the testosterone (TES) ligand, were randomized and mutant Fab libraries were cloned into a phagemid vector. Binders were selected by a competitive panning procedure. By combining the identified light and heavy chain CDRIII mutations the TES affinity was preserved at the wild-type level but DHEAS cross-reactivity was decreased to 0.03%. An important finding was that by the competitive panning procedure the overall binding specificity of the 3-C4F5 antibody was refined, since the cross-reactivities to related steroids were also significantly decreased in the combined mutant.