Human regulatory T cells undergo self-inflicted damage via granzyme pathways upon activation

Area of Science:

• Immunology
• Cellular Therapy
• Molecular Biology

Background:

• Regulatory T cells (Tregs) are crucial for immune control and hold therapeutic promise.
• Clinical Treg therapies face challenges due to rapid post-transfer Treg decline and high apoptosis rates.
• The mechanisms underlying Treg loss in vivo remain incompletely understood.

Purpose of the Study:

• To elucidate novel mechanisms of Treg apoptosis.
• To investigate the role of granzymes A and B (GrA/GrB) in Treg survival.
• To explore the potential of targeting granzyme activity for enhancing Treg-based therapies.

Main Methods:

• Analysis of granzyme A and B (GrA/GrB) expression and localization in stimulated human Tregs.
• In vitro experiments assessing substrate cleavage upon granzyme inhibition.
• Cytometry by time of flight (CYTOF) to quantify GrB-expressing Tregs in transplant recipients.

Main Results:

• Human Tregs upregulate GrA and GrB upon stimulation, with granzymes leaking from cytotoxic granules.
• Leaked GrA and GrB cleave cytoplasmic and nuclear substrates, inducing apoptosis.
• GrB-expressing Tregs, identified in rejecting allografts, exhibit an activated phenotype but higher apoptosis rates.
• Inhibition of granzyme activity protected substrates from cleavage in vitro.

Conclusions:

• Tregs can undergo self-inflicted damage mediated by intracellular granzymes.
• Increased GrB expression in Tregs correlates with apoptosis, particularly in transplant rejection.
• Modulating granzyme expression or activity presents a potential strategy to improve Treg therapy outcomes.