Polyclonal selection of immune checkpoint mutations in thyroid autoimmunity.

Area of Science:

• Immunology
• Genetics
• Molecular Biology

Background:

• The immune system has checkpoints to prevent self-reactive lymphocytes.
• Understanding how lymphocytes escape these checkpoints to cause autoimmune disease is crucial.

Purpose of the Study:

• To investigate the role of somatic mutations in immune-regulatory genes in autoimmune thyroid disease.
• To identify specific genetic mutations enabling self-reactive lymphocytes to bypass tolerance.

Main Methods:

• Whole-exome and targeted NanoSeq for mutation detection.
• Laser microdissection, methylation sequencing, spatial transcriptomics, and single-nucleus DNA sequencing.
• Immunostaining and antibody synthesis to characterize mutant clones.

Main Results:

• Identified convergent loss-of-function mutations in TNFRSF14 (HVEM) and CD274 (PD-L1) in B cells.
• Detected numerous independent immune checkpoint mutant clones in inflamed thyroid biopsies.
• Confirmed self-reactivity and multiple mutations within individual B cell clones, including widespread biallelic loss of TNFRSF14.

Conclusions:

• Somatic mutations in immune checkpoint genes contribute to autoimmune disease pathogenesis.
• A polyclonal cascade of somatic evolution allows self-reactive lymphocytes to escape tolerance.
• These findings offer new molecular insights into the basis of autoimmune diseases.