Reversibility and irreversibility in the temperature denaturation of monoclonal antibodies

There have been numerous studies of the temperature denaturation of monoclonal antibodies (mAbs) using differential scanning calorimetry (DSC). In general, mAbs are characterized by complex temperature denaturation transitions in which the various domains (CH2, CH3, Fab) give rise to different peaks in the heat capacity function. The complexity and overall irreversibility of the temperature denaturation transition is well known and has limited the number of publications with an in-depth analysis of the data. Here we report that the temperature denaturation of the CH2 domain is reversible and only becomes irreversible after denaturation of the Fab domain, which is intrinsically irreversible. For these studies we have used the HIV neutralizing monoclonal antibody 17b. To account for the experimental heat capacity function, a mixed denaturation model that combines multiple reversible and irreversible transitions has been developed. This model accounts well for the DSC data and for the pH dependence of the heat capacity function of 17b and other monoclonal antibodies for which data is available in the literature. It is expected that a more detailed analysis of the stability of monoclonal antibodies will contribute to the development of better approaches to understand and optimize the structural viability of these therapeutic macromolecules.