Rapid and reliable cloning of antibody variable regions and generation of recombinant single chain antibody fragments

Bispecific T cell-engager targeting oncofetal chondroitin sulfate induces complete tumor regression and protective immune memory in mice

BACKGROUND

The malaria protein VAR2CSA binds oncofetal chondroitin sulfate (ofCS), a unique chondroitin sulfate, expressed on almost all mammalian cancer cells. Previously, we produced a bispecific construct targeting ofCS and human T cells based on VAR2CSA and anti-CD3 (V-aCD3^Hu). V-aCD3^Hu showed efficacy against xenografted tumors in immunocompromised mice injected with human immune cells at the tumor site. However, the complex effects potentially exerted by the immune system as a result of the treatment cannot occur in mice without an immune system. Here we investigate the efficacy of V-aCD3^Mu as a monotherapy and combined with immune checkpoint inhibitors in mice with a fully functional immune system.

METHODS

We produced a bispecific construct consisting of a recombinant version of VAR2CSA coupled to an anti-murine CD3 single-chain variable fragment. Flow cytometry and ELISA were used to check cell binding capabilities and the therapeutic effect was evaluated in vitro in a killing assay. The in vivo efficacy of V-aCD3^Mu was then investigated in mice with a functional immune system and established or primary syngeneic tumors in the immunologically "cold" 4T1 mammary carcinoma, B16-F10 malignant melanoma, the pancreatic KPC mouse model, and in the immunologically "hot" CT26 colon carcinoma model.

RESULTS

V-aCD3^Mu had efficacy as a monotherapy, and the combined treatment of V-aCD3^Mu and an immune checkpoint inhibitor showed enhanced effects resulting in the complete elimination of solid tumors in the 4T1, B16-F10, and CT26 models. This anti-tumor effect was abscopal and accompanied by a systemic increase in memory and activated cytotoxic and helper T cells. The combined treatment also led to a higher percentage of memory T cells in the tumor without an increase in regulatory T cells. In addition, we observed partial protection against re-challenge in a melanoma model and full protection in a breast cancer model.

CONCLUSIONS

Our findings suggest that V-aCD3^Mu combined with an immune checkpoint inhibitor renders immunologically "cold" tumors "hot" and results in tumor elimination. Taken together, these data provide proof of concept for the further clinical development of V-aCD3 as a broad cancer therapy in combination with an immune checkpoint inhibitor.

Intratumoral electroporation of plasmid encoded IL-12 and membrane-anchored anti-CD3 increases systemic tumor immunity

Intratumoral delivery of plasmid IL 12 via electroporation (IT tavo EP) induces localized expression of IL 12 leading to regression of treated and distant tumors with durable responses and minimal toxicity. A key driver in amplifying this local therapy into a systemic response is the magnitude and composition of immune infiltrate in the treated tumor. While intratumoral IL 12 typically increases the density of CD3+ tumor infiltrating lymphocytes (TIL), this infiltrate is composed of a broad range of T cell subsets, including activated tumor specific T cells, less functional bystander T cells, as well as suppressive T regulatory cells. To encourage a more favorable on treatment tumor microenvironment, we explored combining this IL 12 therapy with an intratumoral polyclonal T cell stimulator membrane anchored anti CD3 to productively engage a diverse subset of lymphocytes including the non reactive and suppressive T cells. This study highlighted that combined intratumoral electroporation of IL 12 and membrane anchored anti CD3 plasmids can enhance cytokine production, T cell cytotoxicity, and proliferation while limiting the suppressive capacity within the TME. These collective anti tumor effects not only improve regression of treated tumors but drive systemic immunity with control of non treated contralateral tumors in vivo. Moreover, combination of IL 12 and anti CD3 restored the function of TIL isolated from a melanoma patient actively progressing on PD 1 checkpoint inhibitor therapy. This DNA encodable polyclonal T cell stimulator (membrane anchored anti CD3 plasmid) may represent a key addition to intratumoral IL-12 therapies in the clinic.

Anti-tau scFvs Targeted to the Cytoplasm or Secretory Pathway Variably Modify Pathology and Neurodegenerative Phenotypes

Immunotherapies designed to treat neurodegenerative tauopathies that primarily engage extracellular tau may have limited efficacy as tau is primarily intracellular. We generated tau-targeting single-chain variable fragments (scFvs) and intrabodies (iBs) from the phosphorylated tau-specific antibodies CP13 and PHF1 and the pan-tau antibody Tau5. Recombinant adeno-associated virus (rAAV) was utilized to express these antibody fragments in homozygous JNPL3 P301L tau mice. Two iBs (CP13i, PHF1i) and one scFv (PHF1s) abrogated tau pathology and delayed time to severe hindlimb paralysis. In a second tauopathy model (rTg4510), CP13i and PHF1i reduced tau pathology, but cognate scFvs did not. These data demonstrate that (1) disease-modifying efficacy does not require antibody effector functions, (2) the intracellular targeting of tau with phosphorylated tau-specific iBs is more effective than extracellular targeting with the scFvs, and (3) robust effects on tau pathology before neurodegeneration only resulted in modest disease modification as assessed by delay of severe motor phenotype.

Structural basis of NKT cell inhibition using the T-cell receptor-blocking anti-CD1d antibody 1B1

Natural killer T (NKT) cells are a subset of T lymphocytes that recognize glycolipid antigens presented by the CD1d molecule (CD1d). They rapidly respond to antigen challenge and can activate both innate and adaptive immune cells. To study the role of antigen presentation in NKT cell activation, previous studies have developed several anti-CD1d antibodies that block CD1d binding to T-cell receptors (TCRs). Antibodies that are specific to both CD1d and the presented antigen can only be used to study the function of only a limited number of antigens. In contrast, antibodies that bind CD1d and block TCR binding regardless of the presented antigen can be widely used to assess the role of TCR-mediated NKT cell activation in various disease models. Here, we report the crystal structure of the widely used anti-mouse CD1d antibody 1B1 bound to CD1d at a resolution of 2.45 Å and characterized its binding to CD1d-presented glycolipids. We observed that 1B1 uses a long hydrophobic H3 loop that is inserted deep into the binding groove of CD1d where it makes intimate nonpolar contacts with the lipid backbone of an incorporated spacer lipid. Using an NKT cell agonist that has a modified sphingosine moiety, we further demonstrate that 1B1 in its monovalent form cannot block TCR-mediated NKT cell activation, because 1B1 fails to bind with high affinity to mCD1d. Our results suggest potential limitations of using 1B1 to assess antigen recognition by NKT cells, especially when investigating antigens that do not follow the canonical two alkyl-chain rule.

Designing antibodies against LRRK2-targeted tau epitopes

Phosphorylation of the microtubule associated protein tau is an important modulator of its normal physiological functioning; however, it may also contribute to tau mis-folding and aggregation in neurodegenerative diseases, which are collectively termed tauopathies. As such, the investigations of tau phosphorylation and kinases that modify tau are important in trying to elucidate tau function and the mechanisms involved in the development of tauopathies. We have recently demonstrated that the putative tau kinase leucine-rich repeat kinase 2 is capable of phosphorylating tau at threonines 169 and 175 in vitro, and it has been previously shown that hyperphosphorylation at threonine 175 occurs in filamentous tau species from Alzheimer’s brain tissue. These prior findings suggest that further studies of phosphorylation of tau at these epitopes may shed light on the pathogenesis of tauopathies. There is, however, a lack of tools available to analyze phosphorylation of tau at these sites. This study aimed to bridge that resource gap by generating monoclonal antibodies against tau phosphorylated at either threonine 169 or 175. While we did not succeed in generating a phospho-specific antibody, we did generate an antibody, MHT2, which is specific for human tau encompassing the threonine 169/175 epitope region. Immunostaining of transgenic rTg4510 mouse tissue as well as human tauopathy cases with MHT2 indicates that this antibody selectively detects cytoplasmic tau in the form of neurofibrillary tangles, and that it may have a further specificity pertaining to severity of disease progression, either because of phosphorylation or conformational bias.

A gold nanoparticle-single-chain fragment variable antibody as an immunoprobe for rapid detection of morphine by dipstick

Gold nanoparticle (AuNP)-based optical assays are of significant interest since the molecular phenomenon can be examined easily with change in the color of AuNPs. Herein, we report the development of a dipstick using a AuNP-labeled single-chain fragment variable (scFv) antibody for the detection of morphine. The scFv antibodies for morphine were developed using phage display-based antibody library. Immunoglobulin variable regions of heavy (V H)- and light (V L)-chain genes were connected via a glycine-serine linker isolated from murine immune repertoire and cloned into the expression vector pIT2. The scFv was produced in Escherichia coli HB2151, yielding a functional protein with a molecular weight of approximately 32 kDa. The morphine scFv was labeled with gold nanoparticles and used as an optical immunoprobe in a dipstick. The competitive dipstick assay characterized the ability of the scFv antibody to recognize free morphine. The detection range was 1-1000 ng mL-1 with a limit of detection (LOD) of 5 ng mL-1 under optimal conditions, and the IC50 value was 14 ng mL-1 for morphine. The developed optical dipstick kit of scFv antibody was capable of specifically binding to free morphine and its analogs in a solution in less than 5 min and could be useful for on-site screening of a real sample in blood, urine, and saliva.

Chimeric antigen receptor T cells targeting Fc μ receptor selectively eliminate CLL cells while sparing healthy B cells

Adoptive cell therapy of chronic lymphocytic leukemia (CLL) with chimeric antigen receptor (CAR)-modified T cells targeting CD19 induced lasting remission of this refractory disease in a number of patients. However, the treatment is associated with prolonged "on-target off-tumor" toxicities due to the targeted elimination of healthy B cells demanding more selectivity in targeting CLL cells. We identified the immunoglobulin M Fc receptor (FcμR), also known as the Fas apoptotic inhibitory molecule-3 or TOSO, as a target for a more selective treatment of CLL by CAR T cells. FcμR is highly and consistently expressed by CLL cells; only minor levels are detected on healthy B cells or other hematopoietic cells. T cells with a CAR specific for FcμR efficiently responded toward CLL cells, released a panel of proinflammatory cytokines and lytic factors, like soluble FasL and granzyme B, and eliminated the leukemic cells. In contrast to CD19 CAR T cells, anti-FcμR CAR T cells did not attack healthy B cells. T cells with anti-FcμR CAR delayed outgrowth of Mec-1-induced leukemia in a xenograft mouse model. T cells from CLL patients in various stages of the disease, modified by the anti-FcμR CAR, purged their autologous CLL cells in vitro without reducing the number of healthy B cells, which is the case with anti-CD19 CAR T cells. Compared with the currently used therapies, the data strongly imply a superior therapeutic index of anti-FcμR CAR T cells for the treatment of CLL.

Checkpoint Antibodies but not T Cell-Recruiting Diabodies Effectively Synergize with TIL-Inducing γ-Irradiation

T cell-recruiting bispecific antibodies (bsAb) show promise in hematologic malignancies and are also being evaluated in solid tumors. In this study, we investigated whether T cell-recruiting bsAbs synergize with hypofractionated tumor radiotherapy (hRT) and/or blockade of the programmed death-1 (PD-1) immune checkpoint, both of which can increase tumor-infiltrating lymphocyte (TIL) numbers. Unexpectedly, large melanomas treated with hRT plus bsAb (AC133×CD3) relapsed faster than those treated with hRT alone, accompanied by massive TIL apoptosis. This fast relapse was delayed by the further addition of anti-PD-1. Mechanistic investigations revealed restimulation-induced cell death mediated by BIM and FAS as an additional cause of bsAb-mediated TIL depletion. In contrast, the double combination of hRT and anti-PD-1 strongly increased TIL numbers, and even very large tumors were completely eradicated. Our study reveals the risk that CD3-engaging bsAbs can induce apoptotic TIL depletion followed by rapid tumor regrowth, reminiscent of tolerance induction by CD3 mAb-mediated T-cell depletion, warranting caution in their use for the treatment of solid tumors. Our findings also argue that combining radiotherapy and anti-PD-1 can be quite potent, including against very large tumors. Cancer Res; 76(16); 4673-83. ©2016 AACR.

Germinal center B cell depletion diminishes CD4+ follicular T helper cells in autoimmune mice

Background

Continuous support from follicular CD4⁺ T helper (Tfh) cells drives germinal center (GC) responses, which last for several weeks to produce high affinity memory B cells and plasma cells. In autoimmune Sle1 and NZB/W F1 mice, elevated numbers of Tfh cells persist, promoting the expansion of self-reactive B cells. Expansion of circulating Tfh like cells have also been described in several autoimmune diseases. Although, the signals required for Tfh differentiation have now been well described, the mechanisms that sustain the maintenance of fully differentiated Tfh are less understood. Recent data demonstrate a role for GC B cells for Tfh maintenance after protein immunization.

Methods and Finding

Given the pathogenic role Tfh play in autoimmune disease, we explored whether B cells are required for maintenance of autoreactive Tfh. Our data suggest that the number of mature autoreactive Tfh cells is controlled by GC B cells. Depletion of B cells in Sle1 autoimmune mice leads to a dramatic reduction in Tfh cells. In NZB/W F1 autoimmune mice, similar to the SRBC immunization model, GC B cells support the maintenance of mature Tfh, which is dependent mainly on ICOS. The CD28-associated pathway is dispensable for Tfh maintenance in SRBC immunized mice, but is required in the spontaneous NZB/W F1 model.

Conclusion

These data suggest that mature Tfh cells require signals from GC B cells to sustain their optimal numbers and function in both autoimmune and immunization models. Thus, immunotherapies targeting B cells in autoimmune disease may affect pathogenic Tfh cells.

Development of anti-bovine IgA single chain variable fragment and its application in diagnosis of foot-and-mouth disease

Recombinant antibody fragments like single chain variable fragments (scFvs) represent an attractive yet powerful alternative to immunoglobulins and hold great potential in the development of clinical diagnostic/therapeutic reagents. Structurally, scFvs are the smallest antibody fragments capable of retaining the antigen-binding capacity of whole antibodies and are composed of an immunoglobulin (Ig) variable light (VL) and variable heavy (VH) chain joined by a flexible polypeptide linker. In the present study, we constructed a scFv against bovine IgA from a hybridoma cell line IL-A71 that secretes a monoclonal antibody against bovine IgA using recombinant DNA technology. The scFv was expressed in Escherichia coli and purified using immobilized metal affinity chromatography (IMAC). The binding activity and specificity of the scFv was established by its non-reactivity toward other classes of immunoglobulins as determined by enzyme-linked immunosorbent assay (ELISA) and immunoblot analysis. Kinetic measurement of the scFv indicated that the recombinant antibody fragment had an affinity in picomolar range toward purified IgA. Furthermore, the scFv was used to develop a sensitive ELISA for the detection of foot and mouth disease virus (FMDV) carrier animals.

Targeting of antigens to B lymphocytes via CD19 as a means for tumor vaccine development

Ab therapy against surface Ags on tumor cells has demonstrated significant efficacy for some cancers. However, it is costly and patients frequently develop acquired resistance over time. In cases of Ab therapy resistance, T cell responses have been shown to be essential in controlling disease progression. Thus, vaccination that generates a sustained Ab response as well as a T cell response may be more effective and economical. In this article, we have developed a vaccination strategy by targeting protein Ags to B cells via a CD19 single-chain variable fragment miniAb. Using the tumor-associated Ag her-2/neu extracellular domain, we showed that the coengagement of CD19 and BCR induced full B cell activation to produce a high titer of Abs and enhanced CD4 Th2 response and CD8 T cell activation and differentiation. These Abs competitively inhibited humanized her-2/neu Ab binding and were capable of activating the complement and inhibiting human breast cancer growth in vitro. Therapeutic efficacy was demonstrated in vivo using murine mammary carcinoma models. Furthermore, four different extracellular domains of her-2/neu could be targeted to B cells to generate Abs against particular domains with different antitumor properties. This approach may offer a new avenue for vaccine development with significantly lower cost, which may be of use not only for cancer therapy but also for infectious agents.

Cloning of a hamster anti-mouse CD79B antibody sequences and identification of a new hamster immunoglobulin lambda constant IGLC gene region

Anti-CD79 antibodies have been effective at targeting B cell lymphoma cells and depleting B cells in animal models. In order to engineer recombinant antibodies with additional effector functions in mice, we cloned and sequenced the full-length cDNAs of the heavy and light chain of a hamster anti-mouse CD79B antibody. Although hamster antibodies represent a unique source of monoclonal antibodies against mouse, rat, and human antigens, sequence information of hamster immunoglobulins (IG) is sparse. Here, we report a new hamster (Cricetulus migratorius) IG lambda constant (IGLC) gene region that is most homologous to mouse IGLC2 and IGLC3.

Recombinant antibodies and in vitro selection technologies

Over the past decade, the accumulation of detailed knowledge of antibody structure and function has enabled antibody phage display to emerge as a powerful in vitro alternative to hybridoma methods for creating antibodies. Many antibodies produced using phage display technology have unique properties that are not obtainable using traditional hybridoma technologies. In phage display, selections are performed under controlled, in vitro conditions that are tailored to suit demands of the antigen and the sequence encoding the antibody is immediately available. These features obviate many of the limitations of hybridoma methodology, and because the entire process relies on scalable molecular biology techniques, phage display is also suitable for high-throughput applications. Thus, antibody phage display technology is well suited for genome-scale biotechnology and therapeutic applications. This review describes the antibody phage display technology and highlights examples of antibodies with unique properties that cannot easily be obtained by other technologies.

Expression of anti-HVEM single-chain antibody on tumor cells induces tumor-specific immunity with long-term memory

Genetic engineering of tumor cells to express immune-stimulatory molecules, including cytokines and co-stimulatory ligands, is a promising approach to generate highly efficient cancer vaccines. The co-signaling molecule, LIGHT, is particularly well suited for use in vaccine development as it delivers a potent co-stimulatory signal through the Herpes virus entry mediator (HVEM) receptor on T cells and facilitates tumor-specific T cell immunity. However, because LIGHT binds two additional receptors, lymphotoxin β receptor and Decoy receptor 3, there are significant concerns that tumor-associated LIGHT results in both unexpected adverse events and interference with the ability of the vaccine to enhance antitumor immunity. In order to overcome these problems, we generated tumor cells expressing the single-chain variable fragment (scFv) of anti-HVEM agonistic mAb on the cell surface. Tumor cells expressing anti-HVEM scFv induce a potent proliferation and cytokine production of co-cultured T cells. Inoculation of anti-HVEM scFv-expressing tumor results in a spontaneous tumor regression in CD4+ and CD8+ T cell-dependent fashion, associated with the induction of tumor-specific long-term memory. Stimulation of HVEM and 4-1BB co-stimulatory signals by anti-HVEM scFv-expressing tumor vaccine combined with anti-4-1BB mAb shows synergistic effects which achieve regression of pre-established tumor and T cell memory specific to parental tumor. Taken in concert, our data suggest that genetic engineering of tumor cells to selectively potentiate the HVEM signaling pathway is a promising antitumor vaccine therapy.

Isolation, kinetic analysis, and structural characterization of an antibody targeting the Bacillus anthracis major spore surface protein BclA

One method of laboratory- or field-based testing for anthrax is detection of Bacillus anthracis spores by high-affinity, high specificity binding reagents. From a pool of monoclonal antibodies, we selected one such candidate (A4D11) with high affinity for tBclA, a truncated version of the B. anthracis exosporium protein BclA. Kinetic analysis utilising both standard and kinetic titration on a Biacore biosensor indicated antibody affinities in the 300 pM range for recombinant tBclA, and the A4D11 antibody was also re-formatted into scFv configuration with no loss of affinity. However, assays against B. anthracis and related Bacilli species showed limited binding of intact spores as well as significant cross-reactivity between species. These results were rationalized by determination of the three-dimensional crystallographic structure of the scFv-tBclA complex. A4D11 binds the side of the tBclA trimer, contacting a face of the antigen normally packed against adjacent trimers within the exosporium structure; this inter-spore interface is highly conserved between Bacilli species. Our results indicate the difficulty of generating a high-affinity antibody to differentiate between the highly conserved spore structures of closely related species, but suggest the possibility of future structure-based antibody design for this difficult target.

Blocking of CD27-CD70 pathway by anti-CD70 antibody ameliorates joint disease in murine collagen-induced arthritis

Rheumatoid arthritis (RA) is characterized by inflammation and cellular proliferation in the synovial lining of joints that result in cartilage and bone destruction. Although the etiology of RA is unclear, activated lymphocytes and proinflammatory molecules, in particular TNF superfamily members, have been implicated in the disease pathology. A TNF superfamily member, CD70, is found on activated lymphocytes and shown to be important in memory and effector responses of lymphocytes. CD70 is expressed at high levels on chronically activated T cells in patients with autoimmune disorders, including RA. The involvement of CD70 in the progression of RA, however, remains unknown. In this study, we report effects of targeting CD70 on disease pathogenesis by using an anti-mouse CD70 Ab in a murine model of collagen-induced arthritis (CIA). In addition to blocking CD70 binding to its receptor CD27, the anti-CD70 Ab used also engages Fc-dependent effector functions including Ab-dependent cellular cytotoxicity, phagocytosis, and complement fixation. Treatment of mice with anti-CD70 Ab both before the onset or after the established disease in CIA model resulted in marked improvements in disease severity and significant reduction in the production of autoantibodies. Histopathological analyses of the joints of mice revealed a substantial reduction of inflammation, and bone and cartilage destruction in response to the anti-CD70 Ab treatment. These results uncover a novel role for CD27-CD70 interactions in the regulation of in vivo inflammatory response leading to arthritis, and provide a molecular basis to support the rationale for anti-CD70 therapy for autoimmune and inflammatory diseases.

Transgenic expression of single-chain anti-CTLA-4 Fv on beta cells protects nonobese diabetic mice from autoimmune diabetes

T cell-mediated immunodestruction of pancreatic beta cells is the key process responsible for both the development of autoimmune diabetes and the induction of rejection during islet transplantation. In this study, we investigate the hypothesis that transgenic expression of an agonistic, membrane-bound single-chain anti-CTLA-4 Fv (anti-CTLA-4 scFv) on pancreatic beta cells can inhibit autoimmune processes by selectively targeting CTLA-4 on pathogenic T cells. Strikingly, transgenic expression of anti-CTLA-4 scFv on pancreatic beta cells significantly protected NOD mice from spontaneous autoimmune diabetes. Interestingly, local expression of this CTLA-4 agonist did not alter the diabetogenic properties of systemic lymphocytes, because splenocytes from transgenic mice or their nontransgenic littermates equally transferred diabetes in NOD/SCID recipients. By analyzing the T cell development in anti-CTLA-4 scFv/Th1/Th2 triple transgenic mice, we found that beta cell-specific expression of CTLA-4 agonist did not affect the development of Th1/Th2 or CD4(+)CD25(+) regulatory T cells. Most strikingly, islets from transgenic mice inhibited T cell response to immobilized anti-CD3 in a T cell-islet coculture system, suggesting a trans-mediated inhibition provided by transgenic islets. Finally, transgenic islets implanted in diabetic recipients survived much longer than did wild-type islets, indicating a therapeutic potential of this genetically modified islet graft in autoimmune diabetes.

CD20-directed small modular immunopharmaceutical, TRU-015, depletes normal and malignant B cells

PURPOSE

CD20-directed therapy with rituximab is effective in many patients with malignant lymphoma or follicular lymphoma. However, relapse frequently occurs within 1 year, and patients become increasingly refractory to retreatment. Our purpose was to produce a compact, single-chain CD20-targeting immunotherapeutic that could offer therapeutic advantages in the treatment of B-cell lymphoma.

EXPERIMENTAL DESIGN

Rituximab is a chimeric antibody containing two heavy chains and two light chains. Here, we describe the properties of TRU-015, a small modular immunopharmaceutical specific for CD20, encoded by a single-chain construct containing a single-chain Fv specific for CD20 linked to human IgG1 hinge, CH2, and CH3 domains but devoid of CH1 and CL domains.

RESULTS

TRU-015 mediates potent direct signaling and antibody-dependent cellular cytotoxicity but has reduced size and complement-mediated cytotoxicity activity compared with rituximab. TRU-015 is a compact dimer of 104 kDa that comigrates with albumin in size exclusion chromatography and retains a long half-life in vivo. TRU-015 induced growth arrest in multiple B lymphoma cell lines in vitro and showed effective antitumor activity against large, established subcutaneous Ramos or Daudi xenograft tumors in nude mice. TRU-015 also showed rapid, dose-dependent, and durable depletion of peripheral blood B cells following single-dose administration to nonhuman primates.

CONCLUSION

These results indicate that TRU-015 may improve CD20-directed therapy by effectively depleting embedded malignant B cells and nonmalignant pathogenic B cells and do so with reduced complement activation.

Fc-disabled anti-mouse CD40L antibodies retain efficacy in promoting transplantation tolerance

CD40L antibodies have proven to be powerful immunosuppressive agents in nonhuman primates but unfortunately perturb blood coagulation. Neither the therapeutic nor the prothrombotic mechanism of anti-CD40L is defined sufficiently to determine whether these effects can be uncoupled. Recent evidence suggests that the Fc region of anti-CD40L antibodies interacting with Fc receptors plays an important role in stabilizing platelet aggregates. An Fc-disabled, aglycosylated anti-CD40L heavy chain variant was therefore created to determine whether it might still be useful in promoting transplantation tolerance. In a number of mouse models an engineered aglycosyl anti-CD40L recapitulated the effects of the intact anti-CD40L antibody in tolerance protocols involving transplantation of allogeneic bone marrow and skin. In contrast, another anti-CD40L variant with a conventional rat gamma2b heavy chain was less effective in ensuring long-term skin graft survival, possibly associated with its faster clearance from the circulation. These results show that short pulses of anti-CD40L antibody therapy may still be useful in tolerance protocols even when the Fc region is disabled.

Engineered antibody intervention strategies for Alzheimer's disease and related dementias by targeting amyloid and toxic oligomers

Most neurodegenerative disorders, such as Alzheimer's (AD), Parkinson's, Huntington's and Creutzfeldt-Jakob disease, are characterised by the accumulation of insoluble filamentous aggregates known as amyloid. These pathologies share common pathways involving protein aggregation which can lead to fibril formation and amyloid plaques. The 4 kDa Abeta peptide (39-43 amino acids) derived from the proteolysis of the amyloid precursor protein is currently a validated target for therapy in AD. Both active and passive immunisation studies against Abeta are being trialled as potential AD therapeutic approaches. In this study, we have characterised engineered antibody fragments derived from the monoclonal antibody, WO-2 which recognises an epitope in the N-terminal region of Abeta (amino acids 2-8 of Abeta). A chimeric recombinant Fab (rFab) and single chain fragments (scFvs) of WO-2 were constructed and expressed in Escherichia coli. Rationally designed mutants to improve the stability of antibody fragments were also constructed. All antibody formats retained high affinity (K(D) approximately 8 x 10(-9) M) for the Abeta peptide, comparable with the intact parental IgG as measured by surface plasmon resonance. Likewise, all engineered fragments were able to: (i) prevent amyloid fibrillisation, (ii) disaggregate preformed Abeta(1-42) fibrils and (iii) inhibit Abeta(1-42) oligomer-mediated neurotoxicity in vitro as efficiently as the whole IgG molecule. These data indicate that the WO-2 antibody and its fragments have immunotherapeutic potential. The perceived advantages of using small Fab and scFv engineered antibody formats which lack the effector function include more efficient passage across the blood-brain barrier and minimising the risk of triggering inflammatory side reactions. Hence, these recombinant antibody fragments represent attractive candidates and safer formulations of passive immunotherapy for AD.

Antibody targeting of B-cell maturation antigen on malignant plasma cells

B-cell maturation antigen (BCMA) is expressed on normal and malignant plasma cells and represents a potential target for therapeutic intervention. BCMA binds to two ligands that promote tumor cell survival, a proliferation inducing ligand (APRIL) and B-cell activating factor. To selectively target BCMA for plasma cell malignancies, we developed antibodies with ligand blocking activity that could promote cytotoxicity of multiple myeloma (MM) cell lines as naked antibodies or as antibody-drug conjugates. We show that SG1, an inhibitory BCMA antibody, blocks APRIL-dependent activation of nuclear factor-kappaB in a dose-dependent manner in vitro. Cytotoxicity of SG1 was assessed as a naked antibody after chimerization with and without Fc mutations that enhance FcgammaRIIIA binding. The Fc mutations increased the antibody-dependent cell-mediated cytotoxicity potency of BCMA antibodies against MM lines by approximately 100-fold with a > or = 2-fold increase in maximal lysis. As an alternative therapeutic strategy, anti-BCMA antibodies were endowed with direct cytotoxic activity by conjugation to the cytotoxic drug, monomethyl auristatin F. The most potent BCMA antibody-drug conjugate displayed IC(50) values of < or = 130 pmol/L for three different MM lines. Hence, BCMA antibodies show cytotoxic activity both as naked IgG and as drug conjugates and warrant further evaluation as therapeutic candidates for plasma cell malignancies.

Design and testing of PCR primers for the construction of scFv libraries representing the immunoglobulin repertoire of rats

Rats are widely used as a model in the study of many important diseases, yet their utility in research is limited by the lack of robust technology for the production of rat recombinant antibodies. Here we have identified and compiled putative rat immunoglobulin sequences by bioinformatic analysis of recently available genomic and EST databases, and used this information to design PCR primers to amplify rat V(H) and V(L) domain coding DNA representing the expressed repertoire of the animal. These primer sets were successfully tested and used to produce a scFv phage display library from rats that had been infected by the blood fluke, Schistosoma mansoni. The library was selected for scFvs that bind to extracellular loop epitopes on either of two known immunogenic S. mansoni membrane proteins, Sm23 and SmTsp2, both of the tetraspanin protein family. Two unique scFvs were identified that bind to each tetraspanin and shown to have excellent specificity for the target, including recognition of the native tetraspanins produced by the fluke. The primers and methods developed for rat scFvs should be of use to others seeking to characterize the antibody repertoire and/or prepare recombinant antibodies from this model.

Structure of the malaria antigen AMA1 in complex with a growth-inhibitory antibody

Identifying functionally critical regions of the malaria antigen AMA1 (apical membrane antigen 1) is necessary to understand the significance of the polymorphisms within this antigen for vaccine development. The crystal structure of AMA1 in complex with the Fab fragment of inhibitory monoclonal antibody 1F9 reveals that 1F9 binds to the AMA1 solvent-exposed hydrophobic trough, confirming its importance. 1F9 uses the heavy and light chain complementarity-determining regions (CDRs) to wrap around the polymorphic loops adjacent to the trough, but uses a ridge of framework residues to bind to the hydrophobic trough. The resulting 1F9-AMA1–combined buried surface of 2,470 Ų is considerably larger than previously reported Fab–antigen interfaces. Mutations of polymorphic AMA1 residues within the 1F9 epitope disrupt 1F9 binding and dramatically reduce the binding of affinity-purified human antibodies. Moreover, 1F9 binding to AMA1 is competed by naturally acquired human antibodies, confirming that the 1F9 epitope is a frequent target of immunological attack.

Malaria caused by Plasmodium falciparum causes more than 1 million deaths annually, and the development of a vaccine against this parasite is a major public health priority. Development of a vaccine is considered feasible because infection with malaria parasites induces protective immune responses, which include antibodies to a range of proteins on the parasite surface. Antigenic diversity allows the parasite to evade protective responses, and this may make it difficult to develop a vaccine that is effective against most infections. To facilitate the design of an effective vaccine, a more detailed understanding of how antibodies interact with their target parasite antigens is required. Here, we provide a detailed structural picture of the interaction between a growth-inhibitory monoclonal antibody and the leading vaccine candidate, AMA1. The results provide important insights into why some antibodies are inhibitory and why antigenic diversity in AMA1 enables the parasite to evade protective antibody responses.

Intracranial adeno-associated virus-mediated delivery of anti-pan amyloid beta, amyloid beta40, and amyloid beta42 single-chain variable fragments attenuates plaque pathology in amyloid precursor protein mice

Accumulation of amyloid beta protein (Abeta) aggregates is hypothesized to trigger a pathological cascade that causes Alzheimer's disease (AD). Active or passive immunizations targeting Abeta are therefore of great interest as potential therapeutic strategies. We have evaluated the use of recombinant anti-Abeta single-chain variable fragments (scFvs) as a potentially safer form of anti-Abeta immunotherapy. We have generated and characterized three anti-Abeta scFvs that recognize Abeta 1-16, Abeta x-40, or Abeta x-42. To achieve widespread brain delivery, constructs expressing these anti-Abeta scFvs were packaged into adeno-associated virus (AAV) vectors and injected into the ventricles of postnatal day 0 (P0) amyloid precursor protein CRND8-transgenic mice. Intracranial delivery of AAV to neonatal mice resulted in widespread neuronal delivery. In situ expression of each of the anti-Abeta scFvs after intracerebroventricular AAV serotype 1 delivery to P0 pups decreased Abeta deposition by 25-50%. These data suggest that intracranial anti-Abeta scFv expression is an effective strategy to attenuate amyloid deposition. As opposed to transgenic approaches, these studies also establish a "somatic brain transgenic" paradigm to rapidly and cost-effectively evaluate potential modifiers of AD-like pathology in AD mouse models.

Rapid specific amplification of rat antibody cDNA from nine hybridomas in the presence of myeloma light chains

Most monoclonal antibodies to mouse antigens have been derived from rat spleen-mouse myeloma fusions. Many resultant hybridomas express one of several myeloma kappa chain transcripts, even though the parent myeloma may have been ascribed as not expressing light chain protein. Previous reports have only differentiated against one of these mouse light chains. We have found at least three different myeloma kappa transcripts in the panel of nine hybridomas that were derived from four different myeloma parents. We have designed an amplification strategy that differentiates the rearranged rat kappa chain from all mouse light chains. Moreover, this method is expedient as it requires minimal downstream manipulation.

Sheep red blood cells armed with anti-CD20 single-chain variable fragments (scFvs) fused to a glycosylphosphatidylinositol (GPI) anchor: a strategy to target CD20-positive tumor cells

Single-chain variable fragment antibodies (scFv) retain antigen specificity and offer advantages over intact antibodies as therapeutic agents. We cloned the cDNA of the V(H) and V(kappa) regions from a mouse hybridoma (HB-9645) directed against human CD20. In addition to the basic scFv construct (V(kappa)-L-V(H)), we genetically engineered a secretory signal, six histidine residues, and a 'Flu' tag to facilitate secretion, purification, and detection. A glycosyl-phosphatidylinositol (GPI) modification signal was added at the C terminus. The GPI-tagged and the non-tagged scFvs were expressed in high yields on the surface of stably transfected insect cells. The CD20-binding properties of purified non-GPI tagged scFv were examined using flow cytometry and immunocytochemistry. The non-GPI-tagged scFv selectively recognizes CD20-positive cells in a concentration-dependent manner. Double-flow cytometry analysis using fresh peripheral blood lymphocytes and WSU-FSCCL cells revealed that our scFv resolves the B-cell population better than the intact antibody. The GPI-tagged scFv was loaded onto the surface of sheep erythrocytes to form rosettes with CD20-positive cells. The genetically engineered anti-CD20 scFv and GPI-tagged derivative have binding specificity for the CD20 antigen. The scFvs described here has potential uses as an in vivo tumor-imaging agent and as a carrier vehicle for targeted delivery of cytocidal agents to CD20-positive cancer cells.

Prevention of genital herpes in a guinea pig model using a glycoprotein D-specific single chain antibody as a microbicide

Background

Genital herpes (GH) is a recurrent sexually transmitted infection (STI) that causes significant morbidity and is also the major source of herpes simplex virus (HSV) in cases of neonatal herpes. Vaccination is a current goal which has had limited success so far in preventing GH and microbicides offer an attractive alternative. Treatment of primary disease cannot prevent establishment of latent infections and thus, cannot prevent subsequent recurrent disease. Recently, many of the molecular events leading to entry of HSV into cells have been elucidated, resulting in the description of a number of herpesvirus entry mediators (HVEMs) that interact with HSV glycoprotein D (gD) on the surface of virions. Described here is a strategy for interrupting the spread of HSV based on interfering with these interactions. The hypothesis addressed in the current report was that single chain antibody variable fragments (scFv) that interrupt associations between gD and HVEMs would not only prevent infection in vitro but could also be used as microbicides to interfere with acquisition GH.

Results and Conclusions

Here we show that a scFv derived from a particular hybridoma, DL11, not only inhibits infection in vitro but also prevents development of GH in a guinea pig model when applied intravaginally in an inert vehicle. Comparison of different anti-gD single chain antibodies supported the hypothesis that the activity of DL11-scFv is based on its ability to disrupt the associations between gD and the two major receptors for HSV, nectin-1 and HveA. Further, the results predict that bacterial expression of active single chain antibodies can be optimized to manufacture inexpensively a useful microbicidal product active against HSV.

Human monoclonal antibodies produced in transgenic BABκ,λ mice recognising idiotypic immunoglobulins of human lymphoma cells

Clonal idiotypic immunoglobulins of follicular lymphomas can be isolated by somatic fusion procedures. Idiotypic IgMs (Id-IgM) were isolated from two patients and used to immunise a strain of mice, deficient in mouse antibody production and engineered with yeast artificial chromosomes (YAC) containing fragments of the human immunoglobulin (Ig) micro/delta heavy chain and kappa/lambda light chain loci. Sequence analysis showed that hybridomas prepared from spleen cells of immunised mice expressed exclusively one of the six VH genes (VH1-2) present in the YAC transgene with different D/J rearrangements, and secrete fully human monoclonal antibodies (mAb) that recognised the tumour-specific IgM proteins. Further studies of the reactivity of the monoclonal anti-human Id-IgM antibodies revealed that they are specific for the individual protein of each patient and probably react with idiotypic determinants. In one case studied, the antibody recognised specifically the lymphoma cell expressing the corresponding idiotypic IgM and lysed those cells in the presence of complement. This is the first example of a human monoclonal antibody with such characteristics and may be of further use in the therapy of patients with B cell malignancies.

Anti-4-1BB-based immunotherapy for autoimmune diabetes: lessons from a transgenic non-obese diabetic (NOD) model

Various therapeutic strategies have been developed to tolerize autoreactive T cells and prevent autoimmune pathology in type 1 diabetes. 4-1BB, a member of the tumor necrosis factor receptor (TNFR) superfamily, is a costimulatory receptor primarily expressed on activated T cells. The administration of an agonistic anti-4-1BB antibody (2A) dramatically reduced the incidence and severity of experimental autoimmune encephalomyelitis (EAE). Treatment with the same antibody in Fas-deficient MRL/lpr mice blocked lymphadenopathy and lupus-like autoimmune processes. Paradoxically, transgenic non-obese diabetic (NOD) mice overexpressing membrane-bound agonistic single-chain anti-4-1BB Fv in pancreatic beta cells developed more severe diabetes than their non-transgenic littermates, with earlier onset, faster diabetic processes, and higher mortality. Forty percent of transgenic mice developed diabetes by 4 weeks of age, compared with their control littermates, which first exhibited diabetes at 14 weeks. The frequency of diabetes in female transgenics reached 70% by 8 weeks of age. Most female transgenic mice died around 12 weeks. Consistent with this, transgenic mice developed earlier and more severe insulitis and showed stronger GAD-specific T-cell responses, compared with age-matched control littermates. Our results indicate an adverse effect of transgenic anti-4-1BB scFv in NOD mice and suggest a potential risk of this anti-4-1BB-based immunotherapy for autoimmune diseases.

Characterization of anti-cyclin E single-chain Fv antibodies and intrabodies in breast cancer cells: enhanced intracellular stability of novel sFv-F(c) intrabodies

Cyclin E is a critical cell cycle protein in the regulated progression of normal cells to replicate their DNA. Ectopic overexpression of cyclin E results in accelerated G(1) progression, chromosome instability, and a reduced requirement for growth factors. Dysregulated cyclin E expression is found in nearly all breast cancers examined. Toward the goal of developing a system to block cyclin E function in normal and breast cancer cells, we have developed anti-cyclin E single-chain antibodies (sFvs) for use as intrabodies. We have cloned the variable region genes from two hybridoma cell lines that produce anti-human cyclin E antibodies, linked them into sFvs, and showed their ability to bind cyclin E when expressed as sFv-F(c) fusion proteins. Engineering of the sFvs as sFv-F(c) intrabodies resulted in a dramatic increase in the sFv half-life as analyzed by pulse-chase and immunofluorescence, and these fusion intrabodies can be expressed in the cytosol or retargeted to the nucleus of breast cancer cell lines. Stable expression of a nuclear-targeted anti-cyclin E intrabody appears to inhibit the growth of the breast cancer cell line SKBR3. This work sets the stage for the development of intrabody-based inducible or tissue-specific cyclin E knockouts and for identifying cyclin E and its vital cell cycle functions as a potential gene therapy target in breast and other cancers.

Gene therapy for cancer using single-chain Fv fragments specific for 4-1BB

Monoclonal antibodies against the T-cell activation molecule 4-1BB have been effective in the treatment of established mouse tumors. To create a vaccine that stimulates the immune system similarly to the efficacious monoclonal anti-4-1BB antibody, 1D8, we constructed a vector encoding cell-bound single-chain Fv fragments from 1D8. We transfected the vector into cells from the K1735 melanoma, selected because of its low immunogenicity and very low expression of major histocompatibility complex class I. The transfected cells induced a strong type 1 T-helper cell response, for which CD4+ but not CD8+ T lymphocytes were necessary and that involved natural killer cells. Vaccinated mice rejected established wild-type K1735 tumors growing as subcutaneous nodules or in the lung. An analogous approach may be effective against micrometastases in human patients, including tumors whose expression of major histocompatibility complex class I is very low.

Influence of relative binding affinity on efficacy in a panel of anti-CD3 scFv immunotoxins

The in vitro cell killing potency of an immunotoxin reflects the aggregate of several independent biochemical properties. These include antigen binding affinity; internalization rate, intracellular processing and intrinsic toxin domain potency. This study examines the influence of antigen binding affinity on potency in various immunotoxin fusion proteins where target antigen binding is mediated by single chain antibody variable region fragments (scFv). Firstly, the relationship between affinity and potency was examined in a panel of four scFv immunotoxins generated from different anti-CD3 monoclonal antibodies fused to the 38 kDa fragment of Pseudomonas aeruginosa exotoxin A (PE38). Of these four scFv-PE38 immunotoxins, the one derived from the anti-CD3 monoclonal antibody UCHT1 has highest cell killing potency. Analysis of these four scFv-PE38 immunotoxins indicated a correlation between antigen binding affinity and immunotoxin potency in the cell killing assay with the exception of the scFvPE38 immunotoxin derived from the antibody BC3. However this scFv appeared to suffer a greater drop in affinity ( approximately 100x), relative to the parent Mab than did the other three scFvs used in this study (2-10x). Secondly, the scFv(UCHT1)-PE38 immunotoxin was then compared with a further panel of scFv(UCHT1)-derived immunotoxins including a divalent PE38 version and both monovalent and divalent Corynebacterium diphtheriae toxin (DT389) fusion proteins. When the scFv-UCHT1 domain was amino-terminally positioned relative to the toxin, as in the scFv(UCHT1)-PE38, an approximately 10-fold higher antigen-binding affinity was observed than with the C-terminal fusion, used in the DT389-scFv(UCHT1) molecule. Despite this lower antigen-binding activity, the DT389-scFv immunotoxin had a 60-fold higher potency in the T-cell-killing assay. Thirdly, a divalent form of the DT389-scFv construct, containing tandem scFv domains, had a 10-fold higher binding activity, which was exactly reflected in a 10-fold increase in potency. Therefore, when comparing immunotoxins in which scFvs from different antibodies are fused to the same toxin domain (DT or PE) a broad correlation appears to exist between binding affinity and immunotoxin potency. However, no correlation between affinity and potency appears to exist when different toxin domains are combined with the same scFv antibody domain.

The influence of the buried glutamine or glutamate residue in position 6 on the structure of immunoglobulin variable domains

Immunoglobulin V(H) domain frameworks can be grouped into four distinct types, depending on the main-chain conformation of framework 1. Based on the analysis of over 200 X-ray structures representing more than 100 non-redundant V(H) domain sequences, we have come to the conclusion that the marked structural variability of the V(H) framework 1 region is caused by three residues: the buried side-chain of H6, which can be either a glutamate or a glutamine residue, the residue in position H7, which may be proline only if H6 is glutamine, and by H9 (H10 according to a new consensus nomenclature), which has to be either glycine or proline if H6 is a glutamate residue. In natural antibodies, these three residues are encoded in combinations that are compatible with each other and with the rest of the structure and therefore will yield functional molecules. However, the degenerate primer mixtures commonly used for PCR cloning of antibody fragments can and frequently do introduce out-of-context mutations to combinations that can lead to severe reduction of stability, production yield and antigen affinity.

A review of molecular recognition technologies for detection of biological threat agents

The present review summarizes the state of the art in molecular recognition of biowarfare agents and other pathogens and emphasizes the advantages of using particular types of reagents for a given target (e.g. detection of bacteria using antibodies versus nucleic acid probes). It is difficult to draw firm conclusions as to type of biorecognition molecule to use for a given analyte. However, the detection method and reagents are generally target-driven and the user must decide on what level (genetic versus phenotypic) the detection should be performed. In general, nucleic acid-based detection is more specific and sensitive than immunological-based detection, while the latter is faster and more robust. This review also points out the challenges faced by military and civilian defense components in the rapid and accurate detection and identification of harmful agents in the field. Although new and improved sensors will continue to be developed, the more crucial need in any biosensor may be the molecular recognition component (e.g. antibody, aptamer, enzyme, nucleic acid, receptor, etc.). Improvements in the affinity, specificity and mass production of the molecular recognition components may ultimately dictate the success or failure of detection technologies in both a technical and commercial sense. Achieving the ultimate goal of giving the individual soldier on the battlefield or civilian responders to an urban biological attack or epidemic, a miniature, sensitive and accurate biosensor may depend as much on molecular biology and molecular engineering as on hardware engineering. Fortunately, as this review illustrates, a great deal of scientific attention has and is currently being given to the area of molecular recognition components. Highly sensitive and specific detection of pathogenic bacteria and viruses has increased with the proliferation of nucleic acid and immuno-based detection technologies. If recent scientific progress is a fair indicator, the future promises remarkable new developments in molecular recognition elements for use in biosensors with a vast array of applications.

Lack of a role for transforming growth factor-beta in cytotoxic T lymphocyte antigen-4-mediated inhibition of T cell activation

Similarities in the phenotypes of mice deficient for cytotoxic T lymphocyte antigen-4 (CTLA-4) or transforming growth factor-beta1 (TGF-beta1) and other observations have led to speculation that CTLA-4 mediates its inhibitory effect on T cell activation via costimulation of TGF-beta production. Here, we examine the role of TGF-beta in CTLA-4-mediated inhibition of T cell activation and of CTLA-4 in the regulation of TGF-beta production. Activation of AND TCR transgenic mouse T cells with costimulatory receptor-specific antigen presenting cells results in efficient costimulation of proliferation by CD28 ligation and inhibition by CTLA-4 ligation. Neutralizing antibody to TGF-beta does not reverse CTLA-4-mediated inhibition. Also, CTLA-4 ligation equally inhibits proliferation of wild-type, TGF-beta1(-/-), and Smad3(-/-) T cells. Further, CTLA-4 engagement does not result in the increased production of either latent or active TGF-beta by CD4(+) T cells. These results indicate that CTLA-4 ligation does not regulate TGF-beta production and that CTLA-4-mediated inhibition can occur independently of TGF-beta. Collectively, these data demonstrate that CTLA-4 and TGF-beta represent distinct mechanisms for regulation of T cell responses.

Blockade of T cell activation using a surface-linked single-chain antibody to CTLA-4 (CD152)

CTLA-4 (CD152) engagement can down-regulate T cell activation and promote the induction of immune tolerance. However, the strategy of attenuating T cell activation by engaging CTLA-4 has been limited by sharing of its natural ligands with the costimulatory protein CD28. In the present study, a CTLA-4-specific single-chain Ab (scFv) was developed and expressed on the cell surface to promote selective engagement of this regulatory molecule. Transfectants expressing anti-CTLA-4 scFv at their surface bound soluble CTLA-4 but not soluble CD28. Coexpression of anti-CTLA-4 scFv with anti-CD3epsilon and anti-CD28 scFvs on artificial APCs reduced the proliferation and IL-2 production by resting and preactivated bulk T cells as well as CD4+ and CD8+ T cell subsets. Importantly, expression of anti-CTLA-4 scFv on the same cell surface as the TCR ligand was essential for the inhibitory effects of CTLA-4-specific ligation. CTLA-4-mediated inhibition of tyrosine phosphorylation of components of the proximal TCR signaling apparatus was similarly dependent on coexpression of TCR and CTLA-4 ligands on the same surface. These findings support a predominant role for CTLA-4 function in the modification of the proximal TCR signal. Using T cells from DO11.10 and 2C TCR transgenic mice, negative regulatory effects of selective CTLA-4 ligation were also demonstrated during the stimulation of Ag-specific CD4+ and CD8+ T cells by MHC/peptide complexes. Together these studies demonstrate that selective ligation of CTLA-4 using a membrane-bound scFv results in attenuated T cell responses only when coengaged with the TCR during T cell/APC interaction and define an approach to harnessing the immunomodulatory potential of CTLA-4-specific ligation.

Construction and characterization of a novel recombinant single-chain variable fragment antibody against Western equine encephalitis virus

A novel recombinant single-chain fragment variable (scFv) antibody against Western equine encephalitis virus (WEE) was constructed and characterized. Using antibody phage display technology, a scFv was generated from the WEE specific hybridoma, 10B5 E7E2. The scFv was fused to a human heavy chain IgG1 constant region (CH1-CH3) and contained an intact 6 His tag and enterokinase recognition site (RS10B5huFc). The RS10B5huFc antibody was expressed in E. coli and purified by affinity chromatography as a 70-kDa protein. The RS10B5huFc antibody was functional in binding to WEE antigen in indirect enzyme-linked immunosorbent assays (ELISAs). Furthermore, the RS10B5huFc antibody was purified in proper conformation and formed multimers. The addition of the human heavy chain to the scFv replaced effector functions of the mouse antibody. The Fc domain was capable of binding to protein G and human complement. The above properties of the RS10B5huFc antibody make it an excellent candidate for immunodetection and immunotherapy studies.

Construction of a pseudoreceptor that mediates transduction by adenoviruses expressing a ligand in fiber or penton base

Modification of adenovirus to achieve tissue specific targeting for the delivery of therapeutic genes requires both the ablation of its native tropism and the introduction of specific, novel interactions. Inactivation of the native receptor interactions, however, would cripple the virus for growth in production cells. We have developed an alternative receptor, or pseudoreceptor, for the virus which might allow propagation of viruses with modified fiber proteins that no longer bind to the native adenovirus receptor (coxsackievirus/adenovirus receptor [CAR]). We have constructed a membrane-anchored single-chain antibody [m-scFv(HA)] which recognizes a linear peptide epitope (hemagglutinin [HA]). Incorporation of HA within the HI loop of the fiber protein enabled the modified virus to transduce pseudoreceptor expressing cells under conditions where fiber-CAR interaction was blocked or absent. The pseudoreceptor mediated virus transduction with an efficiency similar to that of CAR. In addition, the HA epitope mediated virus transduction through interaction with the m-scFv(HA) when it was introduced into penton base. These findings indicate that cells expressing the pseudoreceptor should support production of HA-tagged adenoviruses independent of retaining the fiber-CAR interaction. Moreover, they demonstrate that high-affinity targeting ligands may function following insertion into either penton base or fiber.

Analysis of BR96 Binding Sites for Antigen and Anti-Idiotype by Codon-Based Scanning Mutagenesis

We performed a scanning mutagenesis study of heavy chain complementarity-determining region (CDR) residues to identify how mutations affected binding of the anti-carcinoma mAb BR96 to Ag, Lewis Y, and to an anti-Id Ab (anti-Id). By ELISA, we demonstrated that the anti-Id bound close to the Ag binding site of BR96, but the anti-Id and Ag sites were not identical. Immunoblot analysis and screening of light and heavy chain CDR libraries with multiple mutations in each CDR suggested that the heavy chain had greater involvement in anti-Id binding. We then analyzed contributions of individual residues in the heavy chain CDRs to binding of Ag and anti-Id. In a filamentous phage vector containing BR96 V region sequences, mutations were introduced by codon-based mutagenesis at single positions within the three heavy chain CDRs. The resulting libraries of Fab fragments had all amino acids represented at a CDR position. We evaluated the expressed Fabs for binding to Ag and anti-Id by plaque lift assay. We identified the positions with mutations that had the greatest negative effect on binding to the anti-Id and to Ag and analyzed them on the basis of the BR96 x-ray structure. The residues most important for binding to the anti-Id were located in heavy chain CDR1 and CDR2 and were peripheral to the residues within the Lewis Y binding pocket.

Antibody engineering

The development of recombinant techniques for the rapid cloning, expression, and characterization of cDNAs encoding antibody (Ab) subunits has revolutionized the field of antibody engineering. By fusion to heterologous protein domains, chain shuffling, and inclusion of self-assembly motifs, novel molecules such as bispecific Abs can now be generated which possess the subset of functional properties designed to fit the intended application. Rapid technological developments in phage display of peptides and proteins have led to a plethora of applications directed towards immunology and antibody engineering. Many of the problems associated with the therapeutic use of Abs are being addressed by the application of these new techniques.

Costimulation by CD28 sFv expressed on the tumor cell surface or as a soluble bispecific molecule targeted to the L6 carcinoma antigen

Interaction of the CD80 (B7-1) and CD86 (B7-2) molecules on antigen presenting cells with the receptors CD28 and CTLA-4 on T cells generates signals important in the regulation of immune responses. Because this receptor system involves multiple receptor-ligand interactions, determining the function for individual receptors has been difficult. One approach is the use of antibodies and their derivatives with singular specificity as substitute ligands to explore the activities of these molecules. We have constructed recombinant mono- and bi-specific sFv molecules specific for the CD28 receptor that are capable of binding and generating costimulatory signals to activate T cells. We demonstrate that these soluble molecules are capable of higher levels of costimulation than soluble CD80Ig at equivalent concentrations. We also constructed artificial adhesion receptors on the cell surface using two different CD28-specific sFvIgs fused to the CD80 cytoplasmic and transmembrane domains. In this report, we compared costimulation by a soluble bispecific (alpha CD28-alpha L6) single chain sFvIg fusion protein to that generated by L6 antigen positive (L6+) H3347 tumor cells transduced with cell surface expressed forms of alpha CD28 sFv's. We show that the bispecific protein can target potent CD28 costimulatory activity to L6+ tumor cells in vitro. We also show that transfection of the cell surface forms of the two different CD28 sFvIgs into H3347 tumor cells allows them to generate significant costimulatory signals to activated T cells. Finally, we demonstrate that tumor cell presentation of either the soluble bispecific or transduced cell surface sFv generate similar costimulatory effects resulting in T cell activation.