Monoclonal Antibody Therapeutics

## Nomenclature

Monoclonal antibody (mAb) names follow a systematic convention (updated by WHO in 2022):

- **-mab** suffix indicates a monoclonal antibody.
- **-ximab** -- Chimeric (mouse variable + human constant regions). Example: infliximab.
- **-zumab** -- Humanized (CDR-grafted onto human framework). Example: trastuzumab.
- **-mumab** -- Fully human. Example: adalimumab.

Newer naming conventions simplify to just the -mab suffix with a random prefix, but legacy names remain in widespread use.

## Mechanisms of Action

Monoclonal antibodies achieve therapeutic effects through several distinct mechanisms:

- **Target neutralization** -- Binding and blocking a soluble ligand or receptor. Example: adalimumab neutralizes TNF-alpha.
- **Receptor downregulation** -- Antibody binding triggers receptor internalization. Example: trastuzumab against HER2.
- **Antibody-dependent cellular cytotoxicity (ADCC)** -- The Fc region recruits natural killer cells to destroy antibody-coated target cells. Example: rituximab against CD20+ B cells.
- **Complement-dependent cytotoxicity (CDC)** -- Fc region activates the classical complement cascade on target cell surfaces.
- **Antibody-drug conjugates (ADCs)** -- mAb linked to a cytotoxic payload, delivering chemotherapy specifically to tumor cells. Example: trastuzumab deruxtecan (T-DXd).
- **Bispecific antibodies** -- Engineered to bind two different targets simultaneously. Example: blinatumomab (CD19 x CD3, redirecting T cells to kill leukemia cells).
- **Immune checkpoint inhibition** -- Blocking inhibitory receptors (PD-1, PD-L1, CTLA-4) to unleash anti-tumor immunity.

## Key Therapeutic Areas

**Oncology:** Trastuzumab (HER2+ breast cancer), rituximab (B-cell lymphomas), pembrolizumab and nivolumab (PD-1 checkpoint inhibitors for multiple cancers), bevacizumab (VEGF inhibitor for anti-angiogenesis).

**Autoimmune:** Adalimumab and infliximab (TNF-alpha in RA, Crohn's, psoriasis), ustekinumab (IL-12/23 in psoriasis and IBD), secukinumab (IL-17A in psoriatic arthritis), dupilumab (IL-4/13 in atopic dermatitis and asthma).

**Other:** Omalizumab (anti-IgE for severe asthma), eculizumab (anti-C5 complement for PNH), denosumab (RANKL inhibitor for osteoporosis), evolocumab (PCSK9 for hyperlipidemia).

## Adverse Effects

**Infusion reactions** -- Range from mild (flushing, fever, chills) to severe anaphylaxis. More common with chimeric antibodies. Premedication with acetaminophen, diphenhydramine, and corticosteroids reduces risk.

**Immunogenicity** -- Patients can develop anti-drug antibodies (ADAs) that neutralize the therapeutic effect or cause allergic reactions. Fully human mAbs have lower immunogenicity than chimeric ones. Concurrent methotrexate or other immunosuppressants reduce ADA formation.

**Immune-related adverse events (irAEs)** -- Unique to checkpoint inhibitors. Autoimmune-like inflammation of any organ: colitis, hepatitis, pneumonitis, thyroiditis, hypophysitis, dermatitis. Management involves corticosteroids and sometimes additional immunosuppression. Can be fatal if not recognized early.

**Infections** -- TNF inhibitors increase risk of TB reactivation, hepatitis B reactivation, and serious bacterial infections. Screen for latent TB before initiating anti-TNF therapy.

## Biosimilars

As patents expire, biosimilar versions offer significant cost savings. Biosimilars are not generics -- they are highly similar biological products with no clinically meaningful differences from the reference product. Rigorous analytical, preclinical, and clinical comparability studies are required for approval.

## Key Takeaways

- Monoclonal antibodies are highly specific but not free of systemic side effects.
- Checkpoint inhibitors can cause immune-related adverse events affecting any organ.
- Screen for latent TB and hepatitis B before starting TNF inhibitors.
- Biosimilars provide equivalent efficacy at lower cost and are transforming biologic access.