Rigid crosslinking of the CD3 complex leads to superior T cell stimulation.

Area of Science:

• Immunology
• Molecular Biology
• Biochemistry

Background:

• Functionally bivalent non-covalent Fab dimers (Bi-Fabs) target the T cell receptor (TCR)/CD3 complex to promote T cell signaling.
• T cell activation and function are complex processes involving interactions within the TCR/CD3 complex.

Purpose of the Study:

• To compare the functional responses, including fratricide, induced by Bi-Fabs, F(ab')2, and monoclonal antibodies (mAbs) targeting the CD3 epitope.
• To investigate the structural basis and molecular mechanisms underlying CD3-mediated T cell fratricide induced by different anti-CD3 formats.

Main Methods:

• Comparative analysis of T cell functional responses to stimulation with Bi-Fab, F(ab')2, and mAb.
• Low-resolution structural studies of anti-CD3 Bi-Fabs and F(ab')2.
• Molecular dynamic simulations to assess crosslinking rigidity.
• Molecular modeling of Bi-Fab and F(ab')2 binding to CD3.

Main Results:

• Anti-CD3 Bi-Fab induced the highest T cell fratricide, followed by anti-CD3 F(ab')2 and anti-CD3 mAb.
• Structural studies showed similar global shapes for Bi-Fabs and F(ab')2, but Bi-Fabs exhibited more rigid CD3 crosslinking in simulations.
• Molecular modeling predicted crosslinking of T cell receptors in opposing plasma membrane domains, consistent with observed fratricide.

Conclusions:

• The rigidity of Fab-CD3 crosslinking influences T cell effector function, with increased rigidity potentially leading to stronger fratricide.
• Findings provide insights into the mechanisms of T cell fratricide and can guide the optimization of bi-specific anti-CD3 drugs for improved clinical performance.