CD20 Monoclonal Antibodies Drugs: There is an Explosion of New mAbs Against CD20!

1. What is CD20?

CD20 is a non-glycosylated phosphoprotein located on B cells and is mainly expressed at the pre-B cell to mature B cell stage. The CD20 molecule is a hydrophobic, 4-transmembrane protein consisting of 297 amino acid residues with a relative molecular mass of approximately 33 x 10³. The expression of CD20 is highly variable between different B cell malignancies ^[2-3]. The molecular function of CD20 is related to the signaling propensity of the B cell receptor (BCR). CD20 has been shown to be associated with a variety of other surface proteins on B cells (e.g. CD40, CD53, CD81 and CD82). It has been shown that some epigenetic factors (EZH2, HDAC1/2, HDAC6, Sin3A-HDAC1 complex) and transcription factors (USF, OCT1/2, PU.1, ELK1, PiP, ETS1, and SP1, NFκB, FOXO1, and SMAD2/3) can also regulate CD20 expression ^[4-6].

It is widely recognized that CD20 is a surface-specific molecular marker of human B-lymphocytes, which mediates in the proliferation and differentiation of B-lymphocytes. CD20 is expressed in a vast majority of mature B-cell neoplasms. The CD20 protein has no known natural ligand to interfere with its binding to antibodies, and there is no significant internalization and shedding of CD20 after binding to antibodies or antigenic modulation due to binding to antibodies, making it an ideal target for the treatment of B-cell lymphoma. Currently, anti-CD20 monoclonal antibody drug is an important strategy for the treatment of B-cell non-Hodgkin's lymphoma (Figure 1) ^[4]!

Figure 1. Anti-CD20 monoclonal antibody drugs for BCL treatment ^[4]

2. What is the Function of CD20?

2.1 CD20 and B Cell Antigen Receptor (BCR)

CD20 exists as an oligomer on the surface of B lymphocytes. It has been demonstrated that CD20 forms tetramers on the surface of B cells. B cell antigen receptor (BCR) signaling initiates sustained cellular calcium influx necessary for the development, differentiation, and activation of B lymphocytes. The interaction of CD20 with the membrane type IgM (sIgM) of the B cell antigen receptor (BCR) has been identified. Furthermore, after activation, BCR-CD20 complexes dissociated, phosphoproteins and calmodulin-binding proteins were transiently recruited to CD20, which provide new evidence of the involvement of CD20 in signaling downstream of the BCR ^[2-4].

2.2 CD20 and Calcium Signaling

Calcium ions (Ca²⁺) movement contributes to signal transduction by affecting local electrostatic fields and interacting with proteins to alter their conformations. In many cases, the mobilization of Ca²⁺ is controlled by intracellular store activation and calcium influx, which is characterized by sustained calcium entry into the cell via plasma membrane-associated “store-operated” calcium entry (SOCE) channels. Calcium-release-activated calcium (CRAC) channel is a primary player in SOCE to increase intracellular calcium concentration in lymphocytes. Accumulating evidence indicated that CD20 is involved in SOCE, responsible for intracellular calcium ion concentration. The intensity and duration of calcium ion movement induced by SOCE will affect the function of the cell after receptor-antigen binding ^[6-8].

3. How do Anti-CD20 Monoclonal Antibodies Work?

How do anti-CD20 drugs work? Currently, CD20 widely used in cancer treatment is CD20-targeting mAbs. How do anti-CD20 monoclonal antibodies work? A large body of evidence suggests that anti-CD20 monoclonal antibodies can induce tumor killing via various mechanisms are mainly associated with three regulation mechanisms, namely antibody-dependent cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), and directly induction of apoptosis by antibody binding to CD20 molecules.

ADCC is also known as antibody-dependent cellular cytotoxicity. ADCC is an immune response where Fc receptor-bearing effector cells recognize and kill antibody-coated target cells that express tumor or pathogen-specific antigens on their surface. CDC is another molecular mechanism for anti-CD20 antibodies, which is an immunological process in which pathogens are killed by damaging their plasma membranes without the involvement of the immune system cells or antibodies. CD20 is an effective immunotherapy target for CD20⁺ B-cell malignant cells. Besides, CD20 is commonly used in the investigation of lymphomas, leukemias, or other immune and inflammatory diseases, making the CD20 antigen a attractive target for the treatment of diseases such as lymphoma, leukemia, and certain autoimmune diseases (Figure 2) ^{[3, 9-12]}.

Figure 2. The mechanisms of anti-CD20 monoclonal antibodies in tumors ^[3]

4. CD20 Monoclonal Antibodies Treatment Research

4.1 CD20 Medication Overview?

There are three main forms for the CD20 medication: anti-CD20 monoclonal antibodies, CAR-T and bispecific antibodies. Numerous pharmaceutical companies focus on CD20 monoclonal antibodies. According to the degree of humanization and Fc fragment modification, anti-CD20 monoclonal antibodies can be divided into three generations, of which the first generation is represented by rituximab as a chimeric or mouse-derived monoclonal antibody, the second generation is represented by ovalbumin monoclonal antibody as a humanized monoclonal antibody, and the third generation of anti-CD20 monoclonal antibodies is represented by ovalbumin monoclonal antibody whose Fc fragment has been modified by glycosylation ^[13-15].

4.2 What is Anti-CD20 Immunotherapy?

CD20 has been a superb biomarker for immunotherapies targeting B-cell derived diseases. Specifically, Rituximab (RTX), a murine-human chimeric anti-CD20 mAb, was the first anti-CD20 mAb developed as a therapeutic agent. As a monoclonal antibody against CD20, Rituximab has been commonly used for lymphoma treatment. At present, Rituximab in combination with cyclophosphamide/doxorubicin/vincristine/prednisone (R-CHOP) remains the standard frontline strategy for diffuse large B-cell lymphoma. The second-generation anti-CD20 mAbs include ofatumumab, veltuzumab, and ocrelizumab, which are humanized to reduce immunogenicity. The third-generation humanized CD20 mAbs have an engineered Fc region to increase the binding affinity for the FcγRIIIa receptor on immune effector cells. Surely, the development of anti-CD20 monoclonal antibodies is ongoing. Novel agents with different regulation mechanisms are being explored like biospecific antibody, trispecific antibody, ADC, CAR-T, or others. These novel anti-CD20 mAbs may provide further improvement on immunotherapy ^[13-15].

5. The List of CD20 Monoclonal Antibodies Drugs

According to the data from Synapse, 184 novel therapeutic drugs targeting CD20 in clinical trials worldwide (Table 1), over 80% CD20 monoclonal antibodies drugs. As of now, 26 anti-CD20 monoclonal antibodies drugs have been approved by the FDA. In addition, the global manufacturers of anti-CD20 monoclonal antibodies drugs include Amgen, Roche, Novartis AG, Pfizer, Biogen, Genentech and Immunomedics, AbbVie etc. More importantly, the recent years have seen many Chinese pharmaceutical companies stepping up efforts in anti-CD20 monoclonal antibodies like Sinocelltech Group Ltd., Jiangsu Hengrui Pharmaceuticals, InnoCare Pharma, Chinese People's Liberation Army General Hospital, Zai Lab Ltd., BioRay Biopharmaceutical Co., Ltd, and others. The targeted therapies against CD20 are not limited to antibodies, more innovative drugs are being designed such as CD20 dual antibodies, ADC, CAR-T! Obviously, the competition for CD20 monoclonal antibodies drugs looms among global companies, which are estimated to gain market growth in the upcoming years!

Table 1. Data source: Synapse

To fully support researchers and pharmaceutical companies in their research on CD20 for the treatment of lymphoma, leukemia, autoimmune diseases, CUSABIO boasts CD20 active protein products (Code: CSB-MP015007HU) to assist you in your research on the mechanism of CD20 or its potential clinical value (Click to see a broad range of CD20-based products: Proteins ; Antibodies ; ELISAs).

Recombinant Human B-lymphocyte antigen CD20(MS4A1)-VLPs (Active)

High Specifity Validated
by WB

CSB-MP015007HU is detected by Mouse anti-6*His monoclonal antibody.

Bioactivity Validated
by Functional ELISA

Immobilized human CD20 at 2 μg/ml can bind Anti-CD20 recombinant antibody (CSB-RA015007A1HU), the EC⁵⁰ is 3.243-7.085 ng/mL.

Correct Structure Validated
by TEM

The presence of VLP-like structures was confirmed by TEM

LC-MS/MS Analysis

Based on the SEQUEST from database of Mammalian Cell host and target protein, the LC-MS/MS Analysis result of CSB-MP015007HU could indicate that this peptide derived from Mammalian Cell-expressed Homo sapiens (Human) CD20.

Based on the SEQUEST from database of Mammalian Cell host and target protein, the LC-MS/MS Analysis result of CSB-MP015007HU could indicate that this peptide derived from Mammalian Cell-expressed Homo sapiens (Human) CD20.

CD20 ( MS4A1) Antibodies

ELISA

MS4A1 Monoclonal Antibody
(CSB-RA015007A1HU)

ELISA

MS4A1 Monoclonal Antibody
(CSB-RA015007MA3HU)