Types and Applications of Bispecific Antibodies

At present, bispecific antibodies are widely used in the field of tumor therapy. For example, by combining anti-CD3 antibodies with tumor-targeting antibodies, the constructed bispecific antibodies can recruit T cells to approach tumor cells and mediate T cells to kill tumor cells. In addition, bispecific antibodies are also used in the treatment of osteoporosis, hemophilia, autoimmune diseases and other fields.

Compared with monoclonal antibodies, the advantages of bispecific antibodies include:

(1) Bispecific antibodies target effector cells directly to tumor cells and enhance their cytotoxicity.

(2) Bispecific antibodies can recognize two molecules at the same time, which improves the selectivity and functional affinity of the antibody, and improves the safety and effectiveness of the drug.

(3) Compared with the combination therapy of two monoclonal antibody drugs, bispecific antibody drugs reduce development and clinical trial costs.

Preparation method of bispecific antibody

(1) Chemical conjugation method: This method was first used in 1985. Its principle is to couple two complete monoclonal antibodies or Fab2 fragments into a bispecific antibody through a chemical conjugation agent.

(2) Two-hybridoma fusion method: Two hybridoma cell lines are synthesized by the cell fusion method of two hybridoma cells, and stable target cell lines with two antibody functions are screened out.

(3) Genetic engineering method: The antibody is modified by genetic engineering technology to form various forms of bispecific antibodies.

So far, only two bispecific antibodies have been approved for use, one is Blinatumomab, and the other is Catumaxomab. Currently, 60 types of bispecific antibodies are in preclinical research, and 30 types of bispecific antibodies are in clinical trials.

Blinatumomab was approved by the US FDA at the end of 2014 for the treatment of Fischer-negative precursor B-cell acute lymphoblastic leukemia. It was registered in the European Union in 2015.

Blinatumomab is a bispecific antibody based on BITE technology. It is composed of two scFvs containing only variable regions connected by polypeptides, one targeting the CD19 antigen on the surface of tumor cells and the other targeting CD3 on the surface of cytotoxic T lymphocytes. Clinical trials have proved that Blinatumomab can still recruit T cells to kill tumor cells at very low concentrations (~10-100pg/mL), but due to the single-chain structure of Blinatumomab, it lacks Fc Due to the fact that the half-life of the drug in the body is very short, the actual use requires an additional continuous infusion device.

Clinical trials have shown that adult patients with recurrent acute lymphoblastic leukemia can obtain 72% complete positive results after Blinatumomab treatment, and the average life expectancy after treatment is more than nine months; in the treatment of non-Hodgkin’s lymphoma, Blinatumomab is more simple Clonal antibody therapy has also shown good curative effects. In the case of achieving the same therapeutic effect, the concentration of Blinatumomab in plasma is much lower than that of monoclonal antibodies; however, it is used in the treatment of lymphatic surface CD19 loss and recurrence of extramedullary hematopoiesis. In acute lymphocytic leukemia, Blinatumomab treatment is ineffective.

Catumaxomab was approved by the European Drug Administration in 2009 for the treatment of malignant ascites. It is the world's first bispecific antibody to be marketed.

Catumaxomab is a bispecific antibody based on quadroma (hybrid-hybridoma) technology that combines the expression of rat antibody (IgG2b) targeting tumor EpCAM and mouse antibody (IgG2a) targeting CD3 in a bispecific molecule. Catumaxomab also contains the Fc fragment. Catumaxomab recognizes the EpCAM antigen on the tumor surface and recruits T cells. At the same time, Catumaxomab can bind to the receptor on the surface of the killer cell through the Fc fragment to mediate the direct killing of the killer cell. The target cell can realize the "three-function" antibody activity and improve the patient's immune activity against tumor cells.

Clinical trials show that low-dose therapeutic concentrations (10-100mg) are administered intraperitoneally 4-5 times with an interval of 10-14 days. The results show that Catumaxomab has a high therapeutic potential and its safety is within an acceptable range. Catumaxomab is currently undergoing clinical trials for ovarian cancer, gastric cancer, and epithelial cancer in addition to being approved for the treatment of malignant ascites. In ovarian cancer trials, it has shown that it can reduce the formation of ascites.

Like other treatments for tumors, bispecific antibodies can also cause different side effects during treatment, the most common of which are nausea, vomiting, abdominal pain, leukopenia and neutropenia.

Many bispecific antibodies are currently undergoing clinical trials for the treatment of tumors, most of which are combinations similar to Catumaxomab and Blinatumomab, containing an anti-CD3 antigen binding site to recruit T cells to the vicinity of tumor cells. Another binding site targets tumor surface antigens such as CD19, CD20, CD33, HER1, HER2, etc. In addition, there are other combinations of bispecific antibodies, such as HER2+HER3, IL1α+IL1β, IL13+IL17, etc.

Application of bispecific antibodies

(1) Immunotherapy of tumor

In order to develop new anti-tumor drugs, improve therapeutic effects and reduce side effects, it is necessary to find bispecific antibodies that target new targets in the future. At the same time, bispecific antibodies can also be used in combination with other drugs, such as drugs that control the cell cycle. Indoleamine dioxygenase inhibitors, etc., help improve the efficacy.

The design of the new bispecific antibody aims to increase the targeting specificity to reduce the killing effect on non-tumor cells. In addition, during the production process of bispecific antibodies, their random combination will reduce the yield, so it is necessary to optimize the design to improve the binding of the target bispecific antibody, increase the recovery rate, and reduce the cost of medicine.

(2) Clinical diagnosis

Due to the high sensitivity and specificity of bispecific antibodies, they can be used for clinical diagnosis. For the detection of bispecific antibody drugs, one of the binding domains binds to the detected pathogen, virus or tumor cell, and the other binding domain binds to root peroxidase or alkaline phosphatase. Bispecific antibodies simplify detection methods and are therefore very promising in diagnostic tools.

(3) Medical imaging

Tumor imaging with bispecific antibodies can be completed in two steps, using bispecific antibodies to pre-label tumor cells, and then inject radioisotopes for imaging. Compared with radioisotope-labeled antibody imaging, this method has better specificity, sensitivity, and low background signal, because unbound radioisotopes can be quickly eliminated.

(4) Bispecific antibodies are currently also used to develop simple, fast and highly sensitive bacterial virus infections and cancer diagnosis.

Summary

Clinical studies have found that bispecific antibody drugs block several biological pathways at the same time, showing a synergistic effect that cannot be achieved by the combination of monoclonal antibodies. At the same time, bispecific antibodies can also be developed into "next generation" diagnostic equipment. The ability to detect a collection of several antigens or to connect the antigen binding site with the assay marker makes bispecific antibodies an important object for further research in biomedicine, pharmacology and diagnostics.