Phase transitions in human IgG solutions

Area of Science:

• Biochemistry
• Physical Chemistry
• Materials Science

Background:

• Protein condensations like crystallization and phase separation occur in concentrated antibody solutions.
• While most Immunoglobulin G (IgG) antibodies are soluble, some can condense under physiological conditions, impacting diseases and biopharmaceuticals.
• The phase behavior of IgG solutions is poorly understood due to high solubility, yet is key for non-spherical protein studies.

Purpose of the Study:

• To investigate the hidden phase transitions in concentrated IgG solutions below their freezing point.
• To explore the liquid-liquid phase separation (LLPS) of various human myeloma and recombinant pharmaceutical IgGs.
• To examine the relationship between crystallization and LLPS in human cryoglobulin IgGs.

Main Methods:

• Developed an experimental approach to study IgG solutions with phase transitions below the freezing point.
• Investigated LLPS in six human myeloma IgGs and two recombinant pharmaceutical human IgGs.
• Studied the crystallization and LLPS relationship in two human cryoglobulin IgGs.

Main Results:

• The coexistence curve shape for IgGs differs from quasi-spherical proteins, but is similar across all tested IgGs.
• All IgGs exhibited critical points around ~100 mg/ml, with significant variations in critical temperatures.
• LLPS in IgG solutions was found to be metastable relative to crystallization.

Conclusions:

• IgG phase behavior is governed by near-identical molecular geometry and diverse inter-protein interaction energies.
• Findings provide a basis for further research into generic IgG phase behavior and outlier condensations.
• Understanding IgG phase diagrams is vital for immunoglobulin deposition diseases and colloidal stability of IgG pharmaceuticals.