The checkpoint for agonist selection precedes conventional selection in human thymus

Area of Science:

• Immunology
• T cell biology
• Thymus development

Background:

• The thymus is crucial for establishing self-tolerance by eliminating self-reactive T cells.
• Strong T cell receptor (TCR) signaling is required for both T cell elimination and the generation of specific T cell lineages.
• The mechanism by which thymocytes differentiate between these outcomes is not fully understood.

Purpose of the Study:

• To identify and characterize human T cell subsets arising from strong TCR signaling.
• To investigate the developmental timing of agonist selection in the human thymus.

Main Methods:

• Analysis of human thymocyte subsets.
• TCR stimulation of immature thymocyte blasts.
• Assessment of T cell receptor alpha variable (TRAV) and T cell receptor alpha joining (TRAJ) rearrangements.

Main Results:

• Identified a novel human agonist-selected PD-1+ CD8αα+ T cell subset with an effector phenotype.
• TCR stimulation of post-β-selection thymocyte blasts generated this specific innate subset.
• This process fixed early TRAV and TRAJ rearrangements in the TCR repertoire.

Conclusions:

• Agonist selection in humans generates a distinct effector T cell subset.
• The checkpoint for agonist selection appears to occur earlier than conventional selection in the human thymus.