BPS3021 Chap.7 Therapeutic Antibody Design

Therapeutic Antibody Design

Choose antibody format, location and assay from the intended therapeutic mechanism.

What this chapter covers

• 01

  Neutralisation and receptor blockade

• 02

  Complement and immune-cell recruitment

• 03

  Antibody-drug conjugates

• 04

  IgG, Fab, scFv and nanobody trade-offs

Worked example · free

Select a blocker and a payload carrier

Key terms

Fc region

The antibody region that can support persistence and recruit immune effector mechanisms.

Single-chain variable fragment

A compact engineered binder linking antibody variable domains without an Fc region.

Antibody-drug conjugate

An antibody linked to a payload designed for selective binding, internalisation and intracellular drug release.

Therapeutic Antibody Design FAQ

Exam move

For every format, state one enabling property, one trade-off and one functional assay; Therapeutic antibodies can neutralise a soluble ligand, block receptor signalling, recruit complement, engage Fc-receptor-bearing immune cells or carry a cytotoxic payload;

The first design question is the intended mechanism; A whole IgG supplies bivalency, Fc-mediated persistence and possible effector activity, but it is large, expensive to manufacture and may penetrate dense tissue poorly;

Fab and F(ab')2 fragments retain binding without Fc; F(ab')2 remains bivalent; scFv molecules link variable domains in a compact engineered format; Nanobodies are still smaller, stable and amenable to bacterial expression, but short persistence and lack of Fc function may require reformatting;

No format is universally superior; A tumour-depleting strategy may need Fc-mediated killing, while a deep-tissue receptor blocker may favour smaller Fc-free access; A strong cell-associated signal shows binding or association;

Receptor phosphorylation, complement deposition, NK-cell killing, payload release or cell viability may be the functional endpoint, depending on the mechanism; Internalisation can be unnecessary for a surface blocker, detrimental if it removes a blocking antibody, or essential for an antibody-drug conjugate;

State the required site before judging the uptake result; The workshop also contrasts hybridoma and phage-display discovery; A therapeutic product benefits from a defined monoclonal sequence; Phage display links displayed binding phenotype to the encoding genotype, enabling iterative panning and sequence recovery;

Controls for nonspecific binding are essential, and affinity improvement must not be confused with guaranteed selectivity, stability or manufacturability; Candidate A binds strongly, internalises little and reduces receptor signalling to 18% of untreated while sparing receptor-negative cells;

Candidate B internalises strongly, localises to lysosomes and reduces target-cell viability to 16%; A better fits reversible surface signalling blockade; B better fits payload delivery and tumour-cell killing; The recommendation follows mechanism, not the largest association value;

A therapy should recruit NK cells to kill target cells; Answer: retain an Fc capable of engaging relevant Fc receptors and measure target-cell killing with appropriate effector and isotype controls; Immune killing is unwanted and tissue penetration is limiting;

Answer: consider an Fc-free fragment or nanobody, then manage shorter persistence and demonstrate that the compact format still blocks signalling; Marks are lost by equating affinity with efficacy, treating internalisation as automatically good, or choosing a format without stating its trade-off;

Close with one discriminating experiment; If two candidates bind similarly, a mechanism-specific functional assay and a receptor-negative safety control provide more decision value than repeating the binding screen; Confirm target association and specificity;

Decide whether internalisation is required, neutral or unwanted; Read the mechanism-specific functional endpoint; Check off-target-cell viability and nominate the next safety test; · ANTIBODY FORMATS Antibody engineering WEEK 10 Format follows mechanism Binding, Fc activity, internalisation and tissue access define the design Therapeutic antibodies can neutralise a soluble ligand, block receptor signalling, recruit complement, engage Fc-receptor-bearing immune cells or carry a cytotoxic payload;

The first design question is the intended mechanism; A whole IgG supplies bivalency, Fc-mediated persistence and possible effector activity, but it is large, expensive to manufacture and may penetrate dense tissue poorly;

whole IgG Fc + bivalent Fab / F(ab')₂ binding fragments scFv engineerable nanobody small + stable Removing or redesigning domains trades persistence and effector function for size and access; Choose the smallest format that still performs the job Fab and F(ab')2 fragments retain binding without Fc;

F(ab')2 remains bivalent; scFv molecules link variable domains in a compact engineered format; Nanobodies are still smaller, stable and amenable to bacterial expression, but short persistence and lack of Fc function may require reformatting;

No format is universally superior; A tumour-depleting strategy may need Fc-mediated killing, while a deep-tissue receptor blocker may favour smaller Fc-free access; Binding does not establish therapy A strong cell-associated signal shows binding or association;

Receptor phosphorylation, complement deposition, NK-cell killing, payload release or cell viability may be the functional endpoint, depending on the mechanism; Internalisation can be unnecessary for a surface blocker, detrimental if it removes a blocking antibody, or essential for an antibody-drug conjugate;

State the required site before judging the uptake result; DESIGN ORDER Mechanism → format → required location → functional assay → safety control; The workshop also contrasts hybridoma and phage-display discovery; A therapeutic product benefits from a defined monoclonal sequence;

Phage display links displayed binding phenotype to the encoding genotype, enabling iterative panning and sequence recovery; Controls for nonspecific binding are essential, and affinity improvement must not be confused with guaranteed selectivity, stability or manufacturability;

Manufacturability remains part of format selection; Aggregation, expression yield, stability and reproducible purification can eliminate a binder that looks attractive in an early screen; Development therefore tests the molecule as a product as well as a targeting reagent;

· · MECHANISM FIRST Candidate comparison Read every assay through the mechanism A blocker and an antibody-drug conjugate should not win on the same endpoint EX 7 Select by intended action Candidate A binds strongly, internalises little and reduces receptor signalling to 18% of untreated while sparing receptor-negative cells;

Candidate B internalises strongly, localises to lysosomes and reduces target-cell viability to 16%; A better fits reversible surface signalling blockade; B better fits payload delivery and tumour-cell killing; The recommendation follows mechanism, not the largest association value;

Confirm target association and specificity; Decide whether internalisation is required, neutral or unwanted; Read the mechanism-specific functional endpoint; Check off-target-cell viability and nominate the next safety test;

P1 Fc decision Practice A therapy should recruit NK cells to kill target cells; Answer: retain an Fc capable of engaging relevant Fc receptors and measure target-cell killing with appropriate effector and isotype controls;

P2 Dense-tissue blocker Practice Immune killing is unwanted and tissue penetration is limiting; Answer: consider an Fc-free fragment or nanobody, then manage shorter persistence and demonstrate that the compact format still blocks signalling;

The winning antibody is the one whose structure makes the intended mechanism measurable and selective; Antibody conclusion Marks are lost by equating affinity with efficacy, treating internalisation as automatically good, or choosing a format without stating its trade-off;

Close with one discriminating experiment; If two candidates bind similarly, a mechanism-specific functional assay and a receptor-negative safety control provide more decision value than repeating the binding screen; Use dose-response data when comparing functional potency;

A single concentration can hide differences in maximal effect, potency or toxicity; The preferred candidate should retain its mechanistic advantage across a justified range and in a model appropriate to the intended target; ·