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

Area of Science:

• Biochemistry
• Immunology
• Synthetic Biology

Background:

• Immune checkpoint inhibitors (ICIs) targeting the PD-1/PD-L1 axis are successful cancer therapies.
• Limitations of current IgG-based ICIs include poor tumor penetration and T cell depletion.
• Alternative protein scaffolds are needed for improved PD-1/PD-L1 targeting.

Purpose of the Study:

• To develop a compact and tunable PD-L1 variant with high-affinity PD-1 binding.
• To engineer a ligand-based checkpoint inhibitor with improved therapeutic potential.
• To overcome limitations of existing IgG-based checkpoint inhibitors.

Main Methods:

• Yeast surface display-based directed evolution was used to generate PD-L1 variants.
• A mutagenized PD-L1 ectodomain library was screened for high-affinity binders.
• In silico immunogenicity analysis and structural modeling were performed.

Main Results:

• A double mutant (DM) PD-L1 variant with 173-fold enhanced PD-1 binding was developed.
• The DM variant showed low predicted immunogenicity, comparable to wild-type PD-L1.
• Functional assays confirmed restored T cell activity with increased cytokine secretion.

Conclusions:

• Directed evolution successfully generated a high-affinity, low-immunogenicity PD-L1 variant.
• The engineered DM variant offers a versatile platform for next-generation immunotherapeutics.
• This approach expands the design space for ligand-based checkpoint inhibitors.