Directed evolution–driven reprogramming of PD-L1 for compact and tunable checkpoint modulation

BACKGROUND: Immune checkpoint inhibitors (ICIs) targeting the PD-1/PD-L1 axis have achieved major clinical success in cancer therapy. However, IgG-based checkpoint inhibitors face limitations such as large molecular size restricting tumor penetration and Fc effector-mediated depletion of PD-1-expressing T cells. While IgG antibodies can be engineered to modulate these effects, such tunability often requires complex modifications. To overcome these drawbacks, alternative protein scaffolds that retain checkpoint specificity while enabling more compact design and greater engineering flexibility are needed. Wild-type PD-L1, a native ligand of PD-1, exhibits micromolar binding affinity and limited therapeutic utility, highlighting the need for ligand-based engineering approaches that provide improved modularity and predictable receptor engagement. RESULTS: We developed a compact and tunable P…