Latest
Trump signs order to remove endangered species protection for grey wolvesLeftist insurgents are storming the midterms – just don’t call them all democratic socialistsVoters are fed up with data centers. Both parties are trying to cash in for midtermsFlock cameras draw opposition from across the political spectrumMarvel Has Assigned 42 Hours of Homework Before ‘Avengers: Doomsday’How did the Romans build their towering aqueducts?Author Lise Barnéoud on the bizarre and provoking world of microchimerism — when cells from one person live in another, genetically distinct individualTrump signs order to remove endangered species protection for grey wolvesLeftist insurgents are storming the midterms – just don’t call them all democratic socialistsVoters are fed up with data centers. Both parties are trying to cash in for midtermsFlock cameras draw opposition from across the political spectrumMarvel Has Assigned 42 Hours of Homework Before ‘Avengers: Doomsday’How did the Romans build their towering aqueducts?Author Lise Barnéoud on the bizarre and provoking world of microchimerism — when cells from one person live in another, genetically distinct individual
← Signal: Classified

Microchimerism—the presence of genetically foreign cells living in the body—emerges as a field reshaping understanding of immunity and identity

Confirmed1 source · Sep 5, 2026

Author Lise Barnéoud's new book explores how cells from one person can persist in another, a phenomenon first documented over a century ago but only recently understood as widespread and physiologically active.

Microchimerism—the presence of genetically foreign cells living in the body—emerges as a field reshaping understanding of immunity and identity
Image via Live Science

What happened

German pathologist Georg Schmorl first documented microchimerism in 1893 when he discovered fetal cells in the lungs of women who had died during pregnancy. The field lay dormant for decades but has accelerated in recent years due to technological advances. Documented instances of microchimerism include cells transferred during pregnancy (which could mean genetic material from grandmothers), absorbed twins leaving genetic traces in surviving siblings, and a bone marrow transplant recipient acquiring donor DNA in blood and semen. Author and journalist Lise Barnéoud's book "Hidden Guests: Migrating Cells and How the New Science of Microchimerism Is Redefining Human Identity" (Greystone Books, 2025) has been shortlisted for the 2026 Royal Society Trivedi Science Book Prize.

Context

Microchimerism challenges foundational assumptions about the immune system and human identity. The traditional model portrayed immunity as an intolerant military force expelling foreign matter, yet the phenomenon shows the body tolerates and maintains foreign cells long-term. This finding parallels pregnancy (where the body accepts a genetically foreign fetus) and the human microbiota (where microbial cells coexist with human cells). The discovery that these migrant cells are metabolically active—multiplying, producing proteins, and communicating with other cells—means they actively influence physiology rather than existing as inert passengers. The field has faced multiple obstacles: lack of cellular-level technology to study microchimeric cells, ideological resistance from viewing immunity as purely defensive, and initial dismissal of the research by male colleagues as "woman's stuff" focused on maternal-fetal connection rather than universal biology.