According to a new study by American scientists, cells that cross from the mother’s body through the placenta into the fetal brain during early development remain there permanently. It was found that these foreign, so-called microchimeric cells perform various functions in the human brain and persist throughout life, even past the age of 80.
Experts were already aware that maternal and other family members’ cells exist in the human body, a phenomenon explained by a small fraction of cells migrating through the placenta during gestation. However, their quantity and role in the brain remained largely unclear. Sami Kanaan, a scientist at the Fred Hutchinson Cancer Center in Seattle, explained that studying this is exceptionally difficult because it requires obtaining matched maternal and child samples, and the cells themselves are so rare that they account for only about 1 in 100,000.
To overcome this challenge, Kanaan and his colleagues analyzed genetic sequences from brain tissue samples of 37 children (ranging from infants to 14 years old), which were collected during neurosurgical procedures for epilepsy. The researchers then compared this data with genetic sequences obtained from oral swabs of the children’s mothers.
The team employed single-nucleus RNA sequencing (snRNA-seq) to identify maternal and child genetic profiles, and then utilized a specialized computational tool, Cellector, to detect patterns in the data.
“It was just magical. The tool parses the data and says, ‘This cell doesn’t fit this profile, so it’s likely foreign,'” Kanaan recalled.
The team identified maternal cells in 26 out of the 37 children—averaging 2.2 maternal cells per 100,000 cells. The authors estimated that more children likely harbored these cells, but the method could not detect instances where mother and child shared identical genetic variants.
Furthermore, the microchimeric cells were found to adopt multiple roles within the brain. They act as neurons (nerve cells transmitting information), microglia (the brain’s immune cells), astrocytes (neuron supporters), oligodendrocytes (cells forming the protective myelin sheath around neurons), and endothelial cells (lining blood vessels).
In the second phase of the experiment, the team analyzed data from three previous studies covering an age span from 22-week fetuses to individuals over 80 years old. It was confirmed that microchimeric cells can be present in the brains of individuals across all age groups, though their numbers decline over time. Scientists hypothesize that this decline is due to apoptosis—programmed cell death, which naturally clears damaged and aged cells from the body.
“It’s incredible that we found them even in gestational samples. It is a widespread human feature that begins early in life and lasts throughout adulthood, which is truly mind-blowing,” said lead author Sami Kanaan.
