Structural basis of checkpoint blockade by monoclonal antibodies in cancer immunotherapy

Area of Science:

• Immunology
• Structural Biology
• Oncology

Background:

• Cancer cells utilize immune checkpoints, such as PD-1, PD-L1, and CTLA-4, to evade T-cell-mediated immune responses.
• Monoclonal antibodies targeting these immune checkpoints have emerged as effective cancer therapies.
• Four such antibodies targeting PD-1, PD-L1, and CTLA-4 are FDA-approved for treating various cancers.

Purpose of the Study:

• To elucidate the precise epitopes and molecular mechanisms of immune checkpoint blockade.
• To provide structural insights for the development of improved cancer immunotherapies.

Main Methods:

• X-ray crystallography was employed to determine the structures of checkpoint molecules.
• Complexes of checkpoint molecules with therapeutic antibody Fab fragments were analyzed, including PD-1/pembrolizumab, PD-1/nivolumab, PD-L1/BMS-936559, and CTLA-4/tremelimumab.

Main Results:

• Crystal structures of PD-1, PD-L1, and CTLA-4 in complex with therapeutic antibody fragments were determined.
• These structures precisely map the antibody epitopes on the checkpoint molecules.
• The findings reveal the molecular basis of checkpoint blockade by these antibodies.

Conclusions:

• The determined structures offer valuable information for enhancing the efficacy of monoclonal antibodies targeting immune checkpoint signaling.
• This research contributes to the advancement of cancer immunotherapy by providing a deeper understanding of antibody-target interactions.