Engineered Trivalent Human IgG1-Fc Proteins for Potent Complement Inhibition

Area of Science:

• Immunology
• Biochemistry
• Pharmacology

Background:

• High-dose intravenous immunoglobulin (IVIG) treats autoimmune and inflammatory diseases.
• The fragment crystallizable (Fc) portion of IVIG can replicate therapeutic effects.
• Recombinant multimeric Fc molecules demonstrate significant anti-inflammatory properties.

Purpose of the Study:

• Investigate recombinant human IgG1 Fc molecules with varying valency and avidity.
• Enhance Fc molecule binding affinity to complement protein C1q.
• Evaluate dual antagonism of Fcγ receptor (FcγR) effector functions and classical complement pathway activation.

Main Methods:

• Developed recombinant human IgG1 Fc molecules with mutations for increased C1q binding.
• Assessed FcγR antagonism via in vitro Ab-dependent cellular phagocytosis assays.
• Measured inhibition of the classical complement pathway.
• Evaluated half-life in human neonatal Fc receptor transgenic (hFcRn Tg) mice.

Main Results:

• C1q-binding mutants showed exponentially increased potency in inhibiting the classical pathway with higher multimerization.
• No complement C4a generation was observed with these Fc constructs, unlike Fc hexamers.
• Reduced FcγRIIB binding affinity extended the half-life of trivalent hIgG1-Fc molecules in hFcRn Tg mice.
• Demonstrated potent in vitro and in vivo anti-inflammatory effects.

Conclusions:

• Recombinant human IgG1 Fc C1q-binding mutants possess potent anti-inflammatory effects.
• Therapeutic mechanisms include FcγR blockade and complement activation inhibition.
• These engineered Fc molecules represent a promising therapeutic avenue for inflammatory diseases.