A pharmaceutical developability perspective on antibodies with ultra-long CDRs

Antibodies with ultralong complementarity-determining regions (ulCDRs) have unique antigen-binding features with considerable potential for biomedical applications. Despite this potential, their stability and developability remain largely unexplored from a pharmaceutical perspective. Here, we present a systematic analysis of Fab fragments containing ulCDRs using assays for therapeutic antibody candidate selection. Fluorescence- and light-scattering-based analyses across a broad pH range revealed that ulCDR Fabs exhibit good thermal stability and minimal aggregation. Furthermore, we used relative solubility measurements and light scattering to evaluate the colloidal stability of the Fabs and identified the ulCDR as a key determinant of weak self-association. In addition, stress and storage studies demonstrated that ulCDR Fabs maintain high stability under mechanical stress and at elevated temperature. The results show that ulCDR Fabs display overall favorable physical stability. At the same time, colloidal properties governed by weak ulCDR-driven self-interactions represent the main factor likely to differentiate individual antibodies within this class.