Improving therapeutic efficacy of a complement receptor by structure-based affinity maturation.

Area of Science:

• Immunology
• Protein Engineering

Background:

• Complement C3 receptor (CRIg) is expressed on tissue-resident macrophages.
• The extracellular domain of CRIg (CRIg-ECD) inhibits the alternative complement pathway but has weak binding to C3b.
• High concentrations of CRIg-ECD are needed for effective complement inhibition, posing therapeutic challenges.

Purpose of the Study:

• To develop a high-affinity CRIg-ECD variant with improved therapeutic efficacy and reduced immunogenicity.
• To enhance the binding affinity and complement inhibitory activity of CRIg.

Main Methods:

• Phage display technology was employed to evolve high-affinity CRIg-ECD variants.
• Protein engineering strategies guided by crystal structure information were utilized.
• A double mutant (Q64R/M86Y, CRIg-v27) was generated and characterized.

Main Results:

• The CRIg-v27 double mutant exhibited increased binding affinity to C3b compared to wild-type CRIg-ECD.
• CRIg-v27 demonstrated enhanced complement inhibitory activity.
• Treatment with an Fc fusion of CRIg-v27 significantly reduced clinical scores in a mouse model of arthritis compared to CRIg-ECD.

Conclusions:

• Phage display combined with structural insights can generate potent complement inhibitors with improved therapeutic properties.
• CRIg-v27 represents a promising therapeutic candidate for complement-mediated inflammatory diseases.
• Engineered CRIg variants offer enhanced efficacy for complement inhibition with potentially lower immunogenicity.