How targeted therapies act
You will be able to: Explain the recognition system and killing mechanism of antibody, engager, ADC (antibody-drug conjugate), radioligand and cellular therapies.
A binder determines what a molecule recognizes. The rest of the therapeutic product determines delivery, signaling, payload release, persistence and safety. Changing the format can change the binder's behavior as well as the killing mechanism.
Before starting: HLA and the modality map.
Recognition and action
| Format | Recognition | How it can act |
|---|---|---|
| Monoclonal antibody | A defined accessible target | Blocks signaling or engages immune effectors, depending on target and antibody design |
| Surface-target T-cell engager | A surface target plus CD3 on T cells | Brings T cells and target-bearing cells together and activates cytotoxic functions |
| Peptide–HLA (human leukocyte antigen) T-cell engager | A particular peptide–HLA complex plus CD3 | Redirects T cells while retaining the HLA requirement of its target arm |
| Antibody–drug conjugate (ADC) | An accessible target recognized by an antibody | Delivers a chemical payload through product-specific binding, trafficking and release |
| Radioligand or radioimmunotherapy | A target recognized by a small molecule, peptide or antibody | Delivers radiation; distribution and dosimetry determine exposure |
| CAR (chimeric antigen receptor)-T | Usually an intact surface target recognized by a synthetic receptor | Engineered T cells activate and kill after recognition |
| TCR (T-cell receptor)-T | A peptide displayed on a particular HLA molecule | Engineered T cells use a selected TCR to recognize and attack target-bearing cells |
Antibodies and engagers
An antibody may block a growth signal, flag a cell for immune attack or block an immune checkpoint. These are distinct mechanisms. Anti-PD-1 antibodies primarily modify immune interactions; a tumor-only drug-sensitivity score does not validate a switch from one anti-PD-1 drug to another.
A surface-target engager can recruit T cells without their native TCR recognizing the tumor peptide. It still needs functional, accessible effector cells. Exhaustion, low cell numbers, trafficking barriers and a suppressive environment can limit activity. Peptide–HLA engagers remain HLA-dependent: tebentafusp is a concrete example.
Engager size, half-life and dosing depend on the product. Some require continuous infusion; others use intermittent dosing. Cytokine release syndrome (CRS) and neurotoxicity can occur with both engagers and cell therapies. There is no universal toxicity ordering between formats.
ADCs: target, linker and payload
An ADC combines an antibody, linker and cytotoxic drug. Binding and internalization often lead to intracellular payload release; some linkers also permit extracellular release. A membrane-permeable payload can affect neighboring cells, called a bystander effect.
Resistance can involve target changes, altered trafficking, payload targets or efflux. Keeping the target while changing payload is a plausible strategy, not a guarantee. Two different payloads can share a mechanism and potentially share resistance. An assay showing target expression is only one part of the evidence.
Radioligands: distribution and dose
A radioligand carries a radionuclide to sites where its binder accumulates. Therapeutic beta or alpha emissions damage cells; their ranges and energy deposition differ. Alpha particles have short tissue ranges, so “deeper penetration” is not the explanation for their action.
Imaging a related tracer may help map distribution, but imaging and therapy can differ in molecule, dose and kinetics. Uptake does not itself establish a safe therapeutic dose. Marrow, kidney and other organ exposures require product-specific evaluation. Antibodies can also carry radionuclides; they are not categorically excluded by size.
Radiation may alter immune biology, but systemic immune benefit and synergy with checkpoint blockade need clinical evidence. A single patient's response after multiple treatments cannot isolate that effect.
Living cell products
A CAR provides an engineered recognition and signaling system. A TCR recognizes peptide–HLA; this opens intracellular antigen targets but creates an HLA-specific requirement. Engineering a receptor into peripheral T cells is different from expanding naturally tumor-infiltrating lymphocytes.
Manufacturing, lymphodepletion and supportive treatment depend on the product and protocol. IL-2 is not a universal TCR-T requirement. Cells may expand and persist, but neither persistence nor durable benefit is assured. Both target loss and normal-tissue recognition matter.
Try it
A tumor loses B2M (beta-2 microglobulin) and no longer presents a class-I peptide target. Which distinction helps assess a proposed rescue?
Explain it back: Surface-target recognition may remain possible, while the affected peptide–HLA recognition cannot. This does not prove that a CAR or engager will work; its target, delivery, immune function, safety and clinical evidence still need assessment.
Explain it back
A mechanism explains a possibility. It does not establish efficacy, eligibility, a preferred format or a safe combination.
Takeaway
A mechanism explains a possibility. It does not establish efficacy, eligibility, a preferred format or a safe combination.
Current application
Treatment status belongs in the care plan, unresolved choices in questions, and provider-specific capabilities in companies. A mechanism lesson does not establish eligibility or a treatment plan.
Sources
Checked October 8, 2026.