Hybrid hybridomas producing bispecific antibodies to CEA and peroxidase isolated by a combination of HAT medium selection and fluorescence activated cell sorting

Bispecific T-Cell Redirection versus Chimeric Antigen Receptor (CAR)-T Cells as Approaches to Kill Cancer Cells

The concepts for T-cell redirecting bispecific antibodies (TRBAs) and chimeric antigen receptor (CAR)-T cells are both at least 30 years old but both platforms are just now coming into age. Two TRBAs and two CAR-T cell products have been approved by major regulatory agencies within the last ten years for the treatment of hematological cancers and an additional 53 TRBAs and 246 CAR cell constructs are in clinical trials today. Two major groups of TRBAs include small, short-half-life bispecific antibodies that include bispecific T-cell engagers (BiTE®s) which require continuous dosing and larger, mostly IgG-like bispecific antibodies with extended pharmacokinetics that can be dosed infrequently. Most CAR-T cells today are autologous, although significant strides are being made to develop off-the-shelf, allogeneic CAR-based products. CAR-Ts form a cytolytic synapse with target cells that is very different from the classical immune synapse both physically and mechanistically, whereas the TRBA-induced synapse is similar to the classic immune synapse. Both TRBAs and CAR-T cells are highly efficacious in clinical trials but both also present safety concerns, particularly with cytokine release syndrome and neurotoxicity. New formats and dosing paradigms for TRBAs and CAR-T cells are being developed in efforts to maximize efficacy and minimize toxicity, as well as to optimize use with both solid and hematologic tumors, both of which present significant challenges such as target heterogeneity and the immunosuppressive tumor microenvironment.

Use of Human Hybridoma Technology To Isolate Human Monoclonal Antibodies

The human hybridoma technique offers an important approach for isolation of human monoclonal antibodies. A diversity of approaches can be used with varying success. Recent technical advances in expanding the starting number of human antigen-specific B cells, improving fusion efficiency, and isolating new myeloma partners and new cell cloning methods have enabled the development of protocols that make the isolation of human monoclonal antibodies from blood samples feasible. Undoubtedly, additional innovations that could improve efficiency are possible.

Using protein microarray technology to screen anti-ERCC1 monoclonal antibodies for specificity and applications in pathology

Background

An antibody with cross-reactivity can create unexpected side effects or false diagnostic reports if used for clinical purposes. ERCC1 is being explored as a predictive diagnostic biomarker for cisplatin-based chemotherapy. High ERCC1 expression is linked to drug resistance on cisplatin-based chemotherapy. 8F1 is one of the most commonly used monoclonal antibodies for evaluating ERCC1 expression levels in lung cancer patient tissues, but it has been noted that this antibody cross-reacts with an unknown protein.

Results

By using a high density protein microarray chip technology, we discovered that 8F1 not only reacts with its authentic target, ERCC1, but also cross-reacts with an unrelated nuclear membrane protein, PCYT1A. The cross-reactivity is due to a common epitope presented on these two unrelated proteins. Similar to the subcellular localization of ERCC1, IHC tests demonstrated that PCYT1A is localized mainly on nuclear membrane. In this study, we also discovered that the PCYT1A gene expression level is significantly higher than the ERCC1 gene expression level in a certain population of lung cancer patient tissue samples. To develop the best monoclonal antibody for ERCC1 IHC analysis, 18 monoclonal antibodies were generated and 6 of them were screened against our protein microarray chip. Two clones showed high mono-specificity on the protein microarray chip test and both worked for the IHC application.

Conclusion

In summary, the 8F1 clone is not suitable for ERCC1 IHC assay due to its cross-reactivity with PCYT1A protein. Two newly generated monoclonal antibodies, 4F9 and 2E12, demonstrated ultra-specificity against ERCC1 protein and superior performance for IHC analyses.

Performance characteristics of monoclonal antibodies as recyclable binders to cardiac troponin I

Acute myocardial infarction is a typical disorder that requires continuous monitoring for early detection of potential life-threatening situations. To this end, we used different methods to screen for rapidly reversible antibodies, among 22 hybridoma clones, against cardiac troponin I (cTnI), which is a specific marker indicating the disease. The dissociation rates of antibodies were underestimated by up to a factor of 1000 because of bivalent binding when tested with the antigen immobilized on solid surfaces. This effect was also observed in a sandwich immunoassay, in which the detection antibody cross-linked with various antigen molecules already bound to the capture antibody. Although multiple binding events contributed to enhanced detection capability, it was difficult to recycle the immunosensor. We then devised a screening system by arranging the test antibody for the capture binder immobilized on a label-free sensor. This enabled us to select fast reactive antibodies of which one (clone 24) was shown to be recyclable, even in serum-containing medium. Using this antibody, repetitive detection of cTnI with a rapid response time (half-life of dissociation: about 4min on average) and high detection capability (0.1ng/ml) was achieved, which is very important for detection in a clinical setting.

Premature antibodies with rapid reaction kinetics and their characterization for diagnostic applications

In this study, rapidly reversible antibodies were produced and the binding kinetics, stability, and utility as an analytical binder were evaluated. The number of times the animals were immunized with the antigen (myoglobin as marker for acute myocardial infarction [AMI]) was limited to two, increasing the chances of producing premature antibodies that rapidly reacted with the binding partner in both association and dissociation. The rate constants were higher than 1×10(6)M(-1)s(-1) and 1×10(-3)s(-1), respectively, and the affinity exceeded 10(8)M(-1). They responded to an abrupt environmental change (acidic pH in this study) where the reaction kinetics was changed to slow binding, particularly for dissociation, resulting in a 10-fold increase in affinity. The binding characteristic before and after the transition were stable at 37°C for longer than 1 month, suggesting that the rapidly reversible antibody was the intermediate of the slow binder. The rapid kinetic antibody was used as the primary binder in the conventional competitive immunoassay, which displayed a lower sensitivity than the transformed antibody due to its lower affinity. We further demonstrated that, on combination with a microfluidic label-free sensor, the reaction could be continuously monitored in serum medium by recycling the same antibody without employing the regeneration step.

Production of rapidly reversible antibody and its performance characterization as binder for continuous glucose monitoring

To effectively control diabetes, a method to reliably measure glucose fluctuations in the body over given time periods needs to be developed. Current glucose monitoring systems depend on the substrate decomposition by an enzyme to detect the product; however, the enzyme activity significantly decays over time, which complicates analysis. In this study, we investigated an alternative method of glucose analysis based on antigen-antibody binding, which may be active over an extended period of time. To produce monoclonal antibodies, mice were immunized with molecular weight (M(W)) 10K dextran chemically conjugated with keyhole limpet hemocyanin. Since dextran contains glucose molecules polymerized via a 1,6-linkage, the produced antibodies had a binding selectivity that could discriminate biological glucose compounds with a 1,4-linkage. Three antibody clones with different affinities were screened using the M(W) 1K dextran-bovine serum albumin conjugates as the capture ligand. Among the antibodies tested, the antibody clone Glu 26 had the lowest affinity (K(A) = 3.56 × 10(6) M(-1)) and the most rapid dissociation (k(d) = 1.17 × 10(-2) s(-1)) with the polysaccharide immobilized on the solid surfaces. When glucose was added to the medium, the sensor signal was inversely proportional to the glucose concentration in a range between 10 and 1000 mg dL(-1), which covered the clinical range. Under the optimal conditions, the response time was about 3 min for association and 8 min for dissociation based on a 95% recovery of the final equilibrium.

Site-directed biotinylation of antibodies for controlled immobilization on solid surfaces

Site-directed biotinylation of antibodies at the hinge region was developed to immobilize antibodies in an oriented manner via biotin-streptavidin linkage. When intact antibody was biotinylated with maleimide-activated biotin after reduction, the reaction preferentially occurred at the sulfhydryl groups between the C(H1) and the C(L) domains and, provided that the reagent concentration exceeded a certain level, at those between the C(H2) and the C(H2) domains at the hinge. Based on this result, we devised an approach in which free maleimide was added to compete with the activated biotin for the preferential sites between the C(H1) and the C(L) domains. Since the smaller molecular size of free maleimide made it more accessible for the reaction than biotin, maleimide bound to the groups between the C(H1) and the C(L) domains first and thus conceded the groups between the C(H2) and the C(H2) domains to biotin under optimal conditions. In an alternative approach, selective biotinylation at the hinge was also achieved by reacting activated biotin with F(ab')(2) fragment prepared by enzymatic cleavage. This result indicated that, when free of Fc, the hinge structure, which contains the functional groups, of the fragment was open, allowing easy access to the biotin derivative from the aqueous medium. Both site-directed biotinylation preparations were tested as capture antibodies in sandwich-type immunoassays and compared to whole antibody randomly biotinylated at amino groups on the molecule. Preparations of both the intact antibody and the F(ab')(2) showed consistently enhanced detection capabilities that were 2.6 and 20 times that of the control, respectively.

Plastic enzyme-linked immunosorbent assays (ELISA)-on-a-chip biosensor for botulinum neurotoxin A

A plastic ELISA-on-a-chip (EOC) employing the concept of cross-flow immuno-chromatographic analysis was applied to the measurement of botulinum neurotoxin A (BoNT/A) as agent for bio-terrorism. Two monoclonal antibodies specific to the heavy chain of the toxin were raised and identified to form sandwich binding complexes as the pair with the analyte. For the construction of an immuno-strip, one was utilized as the capture antibody immobilized onto nitrocellulose membrane and the other as the detection coupled to an enzyme, horseradish peroxidase. The two plates of EOC used in this study were fabricated by injection molding of polycarbonate to improve the reproducibility of manufacture and, after inclusion of the immuno-strip, bonded using a UV-sensitive adhesive. Under optimal conditions of analysis, the chip produced a color signal in proportion to the analyte dose and the signal was quantified using a detector equipped with a digital camera. From the dose-response curve, the detection limit of BoNT/A was 2.0 ng mL(-1), approximately five times more sensitive than a commercial-version detection kit employing colloidal gold tracer.

Plastic ELISA-on-a-Chip Based on Sequential Cross-Flow Chromatography

A plastic chip that can perform immunoassays using an enzyme as signal generator, i.e., ELISA-on-a-chip, was developed by incorporating an immunostrip into channels etched on the surfaces of the chip. To utilize an analytical concept of cross-flow chromatography, the chip consisted of two cross-flow channels in the horizontal and vertical directions. In the vertical channel, we placed a 2-mm-wide immunostrip for cardiac troponin I (cTnI), which was identical to a conventional rapid test kit except for the utilization of an enzyme, horseradish peroxidase (HRP), as tracer. An enzyme substrate supply channel and a horizontal flow absorption pad compartment were transversely arranged on each lateral side of the signal generation pad of the strip, respectively. Upon application of a sample containing cTnI, it migrated vertically through the membrane strip by capillary action, and antigen-antibody binding occurred. After 15 min, the horizontal flow was initiated by the addition of a chromogenic substrate solution for HRP into the supply channel and by partial superimposition of the horizontal flow absorption pad onto the signal generation pad. A color signal proportional to the analyte concentration was produced on this pad, measured after 5 min as optical densities using a digital camera-based detector, and quantified by integration of the densities under the peak after normalization. Its calibration curve indicated that the detection limit of the chip was approximately 0.1 ng/mL and its quantification limit was 0.25 ng/mL. In measuring blindly prepared samples, the chip performance correlated with that of a reference system, Beckman Coulter Access, within 2.5-fold discrepancy at the detection limit.

The selection of high-producing cell lines using flow cytometry and cell sorting

The selection of high-producing cell lines is usually time-consuming and labour-intensive. Following transfection, high-producing cells are selected using limiting dilution cloning to prevent non- and low-producing cells from outgrowing high-producing cells, a process that normally takes > 3 months. During this time, the cells have to be screened occasionally to ensure stability of the selected clone. Several new methods for selecting and screening cells using flow cytometry and cell sorting have recently been developed; these include gel microdrop technology, which encapsulates the cells in gelatine beads, and matrix-based secretion assays. This paper reviews these techniques for selecting high-producing cell lines and isolating rare cells.

Improved cell line development by a high throughput affinity capture surface display technique to select for high secretors

A novel process is described which permits rapid and objective selection of rare cells from a heterogeneous population based on quantity of secreted target protein. The process involves construction of an immobilised affinity surface display matrix that specifically binds secreted target product which is then detected using a fluorescent labelled ligand. Cells with the highest fluorescence can then be sorted using conventional flow cytometric technology. Overall, the whole process can be completed in less than 4 h during which time in the region of five million cells can be analysed. Cells are rapidly selected for in a quantitative manner compared to traditional methods which can take several months and have a reduced probability of finding low abundance high secretors due to practical limitations imposed on the number of cells which can be screened.

Bispecific antibodies as novel bioconjugates

Bispecific antibodies are unique macromolecular heterobifunctional cross-linkers with two different binding specificities within a single molecule. As ideal bioconjugates, they can specifically glue any two different molecules together without the need for chemical conjugation. With this unique feature, they have immense potential in biological and immunological fields. Their applications range from immunohistochemistry, immunoassays, radioimmunodiagnosis, radioimmunotherapy, and immunotherapy. Recently, a new second generation of bispecific molecules, bispecific single chain Fv and diabodies, has been produced by DNA recombinant technology. They can be considered as the ultimate magic bullets for in vivo applications. They may theoretically improve tumor or pathogen targeting and minimize side effects, eventually replacing the full-length bispecific antibodies. Emphasizing on developmental methodology and clinical applications of bispecific antibodies, this review gives a bird's-eye view of these unique bioconjugates.

Secretion capture and report web: use of affinity derivatized agarose microdroplets for the selection of hybridoma cells

A novel assay is described which allows the entrapment and detection of the immunoglobulin secreted from individual viable hybridoma cells using a secretion capture and reporter web (SCRW). By encapsulating the cells in agarose microdroplets which have been derivatized to create a fluorescent antigen-specific sandwich assay, flow cytometry can be used to identify and sort productive cells from a heterogeneous population. Using agarase, the cells can be recovered from the microdroplets and clonally expanded after selection. The assay has been used to reclone rare secretors from hybridoma cultures and to enhance the production of cultures with poor producers. The assay is easily generalized for the detection of any secreted protein for which specific antibodies or other ligands are available.