Antibody Optimization by Mammalian Display

Summary

An enzyme-inhibitor antibody for subcutaneous delivery needed far higher affinity for its active-enzyme target without binding the near-identical, more abundant pro-enzyme. Using multi-parametric Mammalian Display, FairJourney Bio engineered affinity, pro-enzyme specificity, pH-dependence, species cross-reactivity, and developability in a single selection step, converting a double-digit nanomolar parent into a sub-15 pM lead with greater than 10⁶-fold pro-form specificity, in under 12 months to IND.

Problem

Because the antibody inhibits an active enzyme, binding the near-identical, more abundant pro-enzyme acts as a sink that erodes free-drug exposure and pharmacokinetics. Affinity had to rise without engaging the pro-form, while the molecule stayed developable for subcutaneous dosing.

Approach

FairJourney Bio ran HCDR3/LCDR3 targeted mutagenesis with multi-parametric Mammalian Display. A phage library was enriched against the active enzyme, then over 10⁶ IgGs were FACS-screened in final format, gating for affinity, deselecting the pro-form, and reading developability directly from display level.

Outcome

The lead reached sub-15 pM affinity by SPR, a greater than 1,000-fold gain, with pro-enzyme binding undetectable at 10 µM (specificity above 10⁶-fold). pH-dependence, cynomolgus cross-reactivity, and developability all met the subcutaneous profile. IND followed in under 12 months.

Key Results