Determination of the Rituximab Binding Site to the CD20 Epitope Using SPOT Synthesis and Surface Plasmon Resonance Analyses

Peptide-based CE-SELEX enables convenient isolation of aptamers specifically recognizing CD20-expressing cells

The CD20 antigen is a key target for several diseases including lymphoma and autoimmune diseases. For over 20 years, several monoclonal antibodies were developed to treat CD20-related disorders. As many therapeutic proteins, their clinical use is however limited due to their nature with a costly biotechnological procedure and side effects such as the production of anti-drug neutralizing antibodies. Nucleic acid aptamers have some advantages over mAbs and are currently investigated for clinical use. We herein report the selection of DNA aptamer by using a peptide-based CE-SELEX (Capillary Electrophoresis-Systematic Evolution of Ligands by Exponential Enrichment) method. It was demonstrated that these aptamers bind specifically a CD20-expressing human cell line, with Kd estimated from isothermal titration calorimetry experiments in the micromolar range. This study demonstrates that the CE-SELEX is suitable as alternative method to the conventional Cell-SELEX to discover new cell-targeting compounds.

Mechanisms of Action and Limitations of Monoclonal Antibodies and Single Chain Fragment Variable (scFv) in the Treatment of Cancer

Monoclonal antibodies are among the most effective tools for detecting tumor-associated antigens. The U.S. Food and Drug Administration (FDA) has approved more than 36 therapeutic antibodies for developing novel alternative therapies that have significant success rates in fighting cancer. However, some functional limitations have been described, such as their access to solid tumors and low interaction with the immune system. Single-chain variable fragments (scFv) are versatile and easy to produce, and being an attractive tool for use in immunotherapy models. The small size of scFv can be advantageous for treatment due to its short half-life and other characteristics related to the structural and functional aspects of the antibodies. Therefore, the main objective of this review was to describe the current situation regarding the mechanisms of action, applications, and limitations of monoclonal antibodies and scFv in the treatment of cancer.

Loop CD20/CD19 CAR-T cells eradicate B-cell malignancies efficiently

CD19 chimeric antigen receptor (CAR) T cells have shown robust efficacy in relapsed and refractory acute lymphoblastic leukemia (R/R ALL), but compromising result in chronic lymphoblastic leukemia (CLL) and non-Hodgkin's lymphoma (NHL). CD19 relapse and the lack of CAR-T cell persistence which result in treatment failure are considerable obstacles to overcome. CAR-T targeting CD20 is an option for salvaging CD19 CAR-T failure. Previous studies have established variant structures of bispecific CAR-T which could avoid antigen-loss and immune escape. Here, we constructed tandem and loop CAR structures targeting both CD19 and CD20 antigen. Bispecific CAR-T cells could eliminate either CD19 or CD20 negative lymphoma cells, suggesting they exhibited dual antigen targeting of CD19 and CD20. By comparing the efficiency of four bispecific CAR modified T cells, it was found that loop2019 CAR was the best structure among them to eradicate lymphoma cell lines and patients' primary lymphoma or CLL cells in a very low dose in vitro and prolong the survival time dramatically in lymphoma xenograft mice model. These data highlighted the potential of loop2019 CAR-T in clinical treatment.

Resemblance-Ranking Peptide Library to Screen for Binders to Antibodies on a Peptidomic Scale

A novel resemblance-ranking peptide library with 160,000 10-meric peptides was designed to search for selective binders to antibodies. The resemblance-ranking principle enabled the selection of sequences that are most similar to the human peptidome. The library was synthesized with ultra-high-density peptide arrays. As proof of principle, screens for selective binders were performed for the therapeutic anti-CD20 antibody rituximab. Several features in the amino acid composition of antibody-binding peptides were identified. The selective affinity of rituximab increased with an increase in the number of hydrophobic amino acids in a peptide, mainly tryptophan and phenylalanine, while a total charge of the peptide remained relatively small. Peptides with a higher affinity exhibited a lower sum helix propensity. For the 30 strongest peptide binders, a substitutional analysis was performed to determine dissociation constants and the invariant amino acids for binding to rituximab. The strongest selective peptides had a dissociation constant in the hundreds of the nano-molar range. The substitutional analysis revealed a specific hydrophobic epitope for rituximab. To show that conformational binders can, in principle, be detected in array format, cyclic peptide substitutions that are similar to the target of rituximab were investigated. Since the specific binders selected via the resemblance-ranking peptide library were based on the hydrophobic interactions that are widespread in the world of biomolecules, the library can be used to screen for potential linear epitopes that may provide information about the cross-reactivity of antibodies.

Quantification of chromogranin A using a surface plasmon resonance-based biosensor

The chromogranin A (CgA) level in the blood is an important biomarker for neuroendocrine tumors and other diseases. Traditional methods for detecting CgA are expensive and time-consuming with low reproducibility. In this study, surface plasmon resonance (SPR), a simple and label-free technique, was validated for quantifying CgA. CgA antibody (CgA-Ab) was immobilized on the CM5 sensor chip (CgA-Ab-CM5) at optimal conditions (pH 5.0, 10 μg mL^-1). Next, different concentrations of CgA were measured by CgA-Ab-CM5. The binding and regeneration conditions were optimized and used in each measurement. A binding time of 240 s, and flow rate of 30 μL min^-1 were chosen as the optimal binding conditions. A pH of 1.75 was the optimal regeneration condition. Compared to the detection range of 23.4-187 ng mL^-1 for enzyme-linked immunosorbent assay (ELISA), a linear range of 0.2-187 ng mL^-1 was detected based on the response unit (RU), showing high sensitivity and reliability of SPR. Finally, the reproducibility of the CgA-Ab-CM5 chip was accessed by consecutive binding-regeneration cycles for 300 times. In conclusion, the SPR-based CgA-Ab-CM5 chip is a sensitive and reproducible method for quantifying CgA levels in a real-time manner.