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Interfacial Adsorption of a Monoclonal Antibody and its Fab and Fc Fragments at the Oil/Water Interface.

The physical stability of a monoclonal antibody (mAb) solution for injection in a pre-filled syringe may in part depend on its behaviour at the silicone oil/water interface. Here, the adsorption of a mAb (termed COE-3) and its fragment antigen-binding (Fab) and crystallisable (Fc) at the oil/water interface were measured using neutron reflection. A 1.4±0.1 µm hexadecane oil film was formed on a sapphire block by a Spin-Freeze-Thaw process in order to retain its integrity upon contact with the protein solutions. Measurements revealed that adsorbed COE-3, its Fab and Fc retained their globular structure, forming layers that did not penetrate substantially into the oil phase. COE-3 and Fc were found to adsorb flat-on to the interface, with a denser 45 and 42 Å inner layer, respectively, in contact with the oil and a more diffuse 17-21 Å outer layer caused by fragments adsorbing in a tilted manner. In contrast, Fab fragments formed a uniform 60 Å monolayer. Monolayers were formed under all conditions studied (10-200 ppm, using three isotopic contrasts), though changes in packing density across the COE-3 and Fc layers were observed. COE-3 had a higher affinity to the interface than either of its constituent fragments, while Fab had a lower interfacial affinity consistent with its higher net surface charge. This study extends the application of high resolution neutron reflection measurements to the study of protein adsorption at the oil/water interface using an experimental set-up mimicking the protein drug product in a siliconized pre-filled syringe.