Lise Barneoud discusses microchimerism in an interview with Live Science
French journalist and author Lise Barneoud spoke in an interview with Live Science about microchimerism — a phenomenon in which cells from one person enter the body of another genetically distinct individual and may persist there. Her book, Hidden Guests: Migrating Cells and How the New Science of Microchimerism Is Redefining Human Identity, published by Greystone Books in 2025, is devoted to the development of research into this phenomenon and its significance for genetics, immunology and evolution.
Cells that pass through the placenta
The first such cells were described in 1893 by German pathologist Georg Schmorl. He identified cells of fetal origin in the lungs of women who died during pregnancy. According to Barneoud, it took nearly a century before researchers began to recognize the prevalence and significance of this phenomenon.
The author noted that microchimerism calls into question the idea of the immune system as a mechanism that only rejects everything foreign. Pregnancy is an example of the mother's body not rejecting a fetus that is genetically distinct from her. At the same time, according to Barneoud, the placenta is not as impermeable a barrier as it is often imagined to be.
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The active role of microchimeric cells
Barneoud stressed that microchimeric cells do not necessarily remain passive in the body. They can multiply, produce proteins, interact with other cells and affect physiological processes both positively and negatively.
Among the examples cited by the publication is the transfer of cells during pregnancy, through which a person may potentially have cells from their grandmother. A genetic trace may also remain after one twin is absorbed in the womb. A separate case describes a man in whom donor DNA was found in his blood and sperm after a bone marrow transplant.
The role of technology in research
Barneoud named the lack of technologies capable of studying tissues at the cellular level as one of the obstacles to the development of this field. The emergence of such tools has made it possible to advance the study of microchimeric cells. The book Hidden Guests was also shortlisted for the 2026 Royal Society Trivedi Science Book Prize.
