Antibody homotypic interactions are encoded by germline light chain complementarity determining region 2

Area of Science:

• Immunology
• Protein Engineering
• Biotherapeutics

Background:

• Avidity, driven by antibody self-association, is crucial for antibody function and therapeutic mechanisms.
• Homotypic interactions, where antibodies bind to themselves, enhance avidity through transient interfaces coupled with target binding.

Purpose of the Study:

• To map the Fab–Fab interfaces of antibodies targeting DR5 and 4-1BB that use homotypic interactions for receptor activation.
• To identify and characterize the self-association determinants within these antibodies.
• To explore the potential of engineering these determinants into other antibodies.

Main Methods:

• Comprehensive mapping of Fab–Fab interfaces for DR5 and 4-1BB antibodies.
• Identification of self-association determinants within the germline light chain complementarity determining region 2 (CDRL2).
• Grafting of identified determinants onto antibodies with different target specificities.
• Expanded characterization of human germline CDRL2 sequences.

Main Results:

• Both DR5 and 4-1BB antibodies share similar self-association determinants, primarily located in CDRL2.
• Grafting these CDRL2 determinants significantly enhanced the activity of antibodies with distinct target specificities.
• Additional self-association determinants were identified in other human germline CDRL2 sequences.
• The phenomenon appears unique to CDRL2, correlating with lower antigen interaction and somatic hypermutation.

Conclusions:

• A novel avidity mechanism in antibody biology, mediated by CDRL2 homotypic interactions, has been revealed.
• This mechanism can be exploited for the engineering of more effective biotherapeutics.
• CDRL2 plays a unique role in antibody self-association and avidity enhancement.