Bispecific monoclonal antibody

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A bispecific monoclonal antibody (BsAb) is an engineered protein that can bind two different targets at the same time. Ordinary antibodies usually bind just one antigen, but BsAbs are designed to grab two.

What BsAbs look like and how they’re made
- Two main formats: IgG-like BsAbs, which keep the familiar antibody structure with two Fab arms and an Fc region, and non-IgG-like BsAbs, which may be made from smaller pieces without an Fc.
- Ways to make them include hybridoma-based methods (quadromas), chemical linking, and genetic engineering. Each method creates different formats.
- Common designs include:
- IgG-like BsAbs that have two different binding sites and can still recruit immune cells through the Fc region.
- Tri- or tetra-functional antibodies (three or four binding sites) for more complex targeting.
- BiTEs (bispecific T-cell engagers) that link two single-chain variable fragments (ScFvs), usually one against CD3 on T cells and one against a tumor antigen.
- TandAbs (tetravalent antibodies) and Bi-Nanobodies (smaller, multi-specific antibodies).
- DVD-Ig and other newer platforms that aim to improve targeting and stability.

What BsAbs do
- They can recruit and activate immune cells to attack cancer cells, block or alter receptor signaling, or bring two proteins into proximity to change their activity.
- They offer potential beyond cancer, including research and therapy in other diseases.

Key examples and what they treat
- Blinatumomab: targets CD19 on B cells and CD3 on T cells (used for certain leukemias).
- Emicizumab: brings factors in the blood coagulation cascade together (used for hemophilia A).
- Amivantamab: targets EGFR and MET (used in some lung cancers).
- Tebentafusp: redirects T cells to a melanoma target (uveal melanoma).
- Faricimab: targets VEGF-A and Angiopoietin-2 (used for eye disease like age-related macular degeneration).
- Teclistamab, mosunetuzumab, epcoritamab, glofitamab: active in various B-cell cancers (different CD3/CDx targets such as BCMA, CD20, CD19, etc.).
- Catumaxomab: a trifunctional antibody that once found use in cancer but was withdrawn for commercial reasons.

Why BsAbs matter in medicine
- They can shut down cancer cell pathways while engaging the patient’s immune system, reducing the chance that tumors escape treatment.
- Smaller, non-IgG-like BsAbs can reach targets that ordinary antibodies miss, though they may need more frequent dosing because they don’t always stay in the body as long.
- BsAbs are also explored for diagnostic imaging, pre-targeting strategies, and other diseases beyond cancer.

Manufacturing challenges and safety
- A major early hurdle was getting the two different arms to pair correctly instead of making unwanted homodimers. Newer methods (like knobs-into-holes) improve correct pairing and yield.
- The Fc region in IgG-like BsAbs can trigger immune responses, so safety and immunogenicity are important considerations.
- Side effects can include infusion reactions and immune-related effects, and risks vary by target, patient, and treatment. Each BsAb must be evaluated for benefits and risks in individual patients.

What’s the current outlook
- More than 180 BsAb therapies are in clinical trials, with several already approved and many in development targeting immune cells, cancer antigens, and other disease targets.
- The most common and active strategy involves combining CD3 with a tumor target to recruit T cells to cancer. Popular target pairs include CD3 with CD19, BCMA, EGFR, and other cancer-related or immune targets.
- Researchers are working on better formats, stronger pairing techniques, and ways to reduce side effects while boosting effectiveness.

In short, bispecific monoclonal antibodies are a fast-growing class of engineered medicines designed to hit two targets at once, offering new ways to fight cancer and other diseases by coordinating immune responses and blocking disease pathways.