Somatic Mutations and Polyclonal Selection Drive Autoimmune Diseases

Research published on April 14, 2026, in the journal Nature indicates that somatic mutations in immune cells may be a primary driver of autoimmune diseases. The study, which focused on thyroid autoimmunity, suggests that DNA changes acquired during a person’s life—rather than those inherited—allow self-reactive lymphocytes to bypass the body’s natural tolerance checkpoints.

The findings provide evidence for a hypothesis first proposed in the 1950s, suggesting that certain forbidden clones of immune cells can escape the constraints designed to prevent the immune system from attacking healthy tissue. While somatic mutations were previously associated primarily with the development of cancer, this research reveals they play a fundamental role in common autoimmune conditions.

The Role of B Cell Mutations

The study specifically examined thyroid conditions, including Graves’ disease and Hashimoto’s disease, which are leading causes of thyroid dysfunction. Researchers identified that B cells in these patients convergently acquire loss-of-function mutations in key immune checkpoint genes, specifically TNFRSF14 (HVEM) and CD274 (PD-L1).

These mutations effectively cut the brakes on the immune system. By disabling these regulatory genes, the B cells are able to escape tolerance constraints and attack the thyroid gland. In biopsies characterized by high levels of inflammation, the team detected tens to hundreds of independent mutant clones.

Analysis revealed that while individual mutant clones typically account for less than 1% of the cells, the cumulative number of these clones represents a substantial fraction of the B cells in the affected tissue. Some clones were found to carry as many as four to six driver mutations, and widespread biallelic loss of TNFRSF14 was observed.

Somatic Evolution and Disease Progression

The research describes a process of polyclonal somatic evolution, where multiple independent clones of lymphocytes evolve to bypass immune checkpoints. This process mimics the early stages of cancer development, where cells accumulate mutations that provide a survival or proliferative advantage.

Evidence suggests that these mutations do not appear suddenly. Reporting indicates that silent B-cell mutations may accumulate over several years before the clinical symptoms of thyroid autoimmunity actually manifest.

Technological Breakthroughs in Detection

Identifying these mutations was historically difficult due to technical limitations. The research team, comprising collaborators from the Wellcome Sanger Institute, the University of Cambridge, and the Cambridge University Hospitals NHS Foundation Trust (CUH), utilized a combination of advanced sequencing and imaging techniques:

• Whole-exome and targeted NanoSeq, an accurate single-molecule DNA sequencing protocol.
• Laser microdissection and methylation sequencing.
• Spatial transcriptomics and immunostaining.
• Single-nucleus DNA sequencing and antibody synthesis.

These tools allowed the researchers to localize the mutations to B cells and confirm that some of these clones were indeed self-reactive.

Implications for Future Treatment

Autoimmune diseases currently affect between 5% and 10% of the global population. Standard treatments typically involve broad immunosuppression, which suppresses the entire immune system to stop the attack on healthy organs.

The discovery of specific somatic driver mutations opens a potential path toward precision medicine. Instead of broad suppression, future therapies could theoretically target only the specific mutated cell clones responsible for the disease, leaving the rest of the immune system intact.

While the current study focused on the thyroid, researchers have noted similar patterns in other autoimmune conditions, suggesting that this mechanism of somatic evolution may be a widespread driver across various autoimmune diseases.

Our results support the hypothesis that somatic mutations in autoimmune lymphocytes may allow them to escape tolerance constraints through a polyclonal cascade of somatic evolution, providing new insights into the molecular basis of autoimmune disease.

Nature