Monoclonal antibodies (mAbs) are recombinant (laboratory-made) proteins that bind to specific targets in the body. They can be used to treat and diagnose many diseases, including cancer and autoimmune diseases. Another potential use for mAbs is as a biosensor, to detect pathogenic bacteria in the body.
One problem faced in the use of these mAbs is that they can stick to surfaces such as glass, when stored in a vial, the metal of a syringe delivering medication or the tubing taking it into the body. Depending on the dose, this could reduce the amount of active ingredient that makes it all the way to the delivery site, which makes it difficult to know the exact dose that completes the journey. Interfacial adsorption of mAbs can also lead to mAb-surface compatibility issues, limiting manufacturing flexibility and having cost implications.
The interaction between the mAbs and a surface would also be important if they were to be used as biosensors, as the aim would be to immobilise the mAbs onto a surface in a particular orientation.
Although previous research has shown that, when these antibodies stick to an air/water interface, they can be removed using a surfactant, the binding of antibody to a solid surface is robust and rather irreversible.
In this study, published in Applied Materials and Interfaces, the researchers studied an mAbs based on the human antibody IgG1k adsorbed onto a SiO2/water interface, and how its adsorption changed with varying pH.
They used neutron reflectivity on the Inter and PolRef instruments at ISIS. Neutron reflectivity is an extremely useful technique for investigating the interfacial adsorption of protein molecules. This is because it can provide depth-resolved information on the adsorbed layers. It can also characterise the average surface density of the adsorbed layer as a function of the distance away from the surface and is highly sensitive to both the adsorbed amount and the thickness of the adsorbed layer.
However, due to the complexity of these mAbs systems, it can be challenging to understand the data from neutron experiments. For this study, the team combined neutron reflectivity with molecular dynamics simulations to gain a comprehensive understanding of the orientation, structural stability, and conformation of the adsorbed mAbs.
They found that the mAbs underwent a reversible change in orientation when the pH was changed, moving between 'flat-on' and 'tilted' positions, as shown in the figure below.
These findings not only advance the understanding of how mAbs behave at a surface but also highlight the potential to fine-tune antibody conformation and orientation through changing the pH. This opens a route towards developing innovative strategies for optimising mAb adsorption depending on the application.
This pioneering work combining neutron reflectivity and molecular dynamics simulations also sets the stage for novel analytical approaches for investigating the interfacial behaviour of other industrially-relevant proteins.
The full paper can be found at DOI: 10.1021/acsami.4c14407
