Monoclonal Antibody (mAb)

Key facts

Regulatory type

Biologic, licensed through a BLA under PHS Act Section 351(a)

FDA review center

Center for Drug Evaluation and Research (CDER)

First U.S. approval

Muromonab-CD3 (Orthoclone OKT3), 1986

Traditional name stem

-mab, as in adalimumab or pembrolizumab

Follow-on versions

Biosimilars under PHS Act Section 351(k)

What is a monoclonal antibody?

Antibodies are Y-shaped proteins the immune system uses to recognize specific molecules. A monoclonal antibody is made by cells descended from a single clone, so every copy recognizes the same site (epitope) on the same target.

Therapeutic mAbs work in several ways: neutralizing a signaling molecule, as adalimumab does with tumor necrosis factor; blocking a receptor or immune checkpoint, as pembrolizumab does with PD-1; or marking cells for destruction by the immune system.

Because they are large proteins, most mAbs are given by intravenous infusion or subcutaneous injection rather than as pills.

Types of monoclonal antibody products

Older names often signal origin with an infix before -mab: -ximab (chimeric), -zumab (humanized) and -umab (human). In 2021 the World Health Organization adopted a new naming scheme that replaces -mab for newly named antibodies with four stems: -tug, -bart, -mig and -ment. Common product formats include:

• Naked antibodies: unmodified antibodies that act on their own, such as trastuzumab.
• Antibody-drug conjugates (ADCs): antibodies linked to a cytotoxic payload, such as ado-trastuzumab emtansine.
• Bispecific antibodies: engineered to bind two different targets, such as blinatumomab or emicizumab.
• Radiolabeled antibodies: antibodies that carry a radioactive isotope to targeted cells.
• Antibody fragments: smaller antigen-binding pieces, such as the Fab fragment ranibizumab.

Why monoclonal antibodies matter

Monoclonal antibodies concentrate spending and shape specialty markets:

• Forecasting: many of the highest-revenue drugs are mAbs, so their patent and exclusivity dates drive biosimilar forecasts.
• Site of care: infused mAbs are commonly billed under Medicare Part B with HCPCS codes, so their use shows up in medical claims and provider-level Part B data rather than Part D prescription data.
• Targeting: prescribers of a given mAb cluster in specialties such as oncology, rheumatology, dermatology and gastroenterology, which guides field teams and key opinion leader mapping.
• Class analysis: grouping mAbs by target, such as PD-1, HER2 or IL-23, is often more useful for competitive intelligence than grouping by indication.