Cellular Subsets of Maternal Microchimerism in Umbilical Cord Blood

Maternal microchimerism may arise in the offspring during pregnancy, and may be favorable or unfavorable. Additionally, maternal cells present in umbilical cord blood used for stem cell transplantation may affect the outcome after transplantation. The aim of this study was to evaluate the cellular subset and frequency of maternal cells in umbilical cord blood following vaginal deliveries and elective Cesarean sections where the umbilical cord clamping time was measured. A total of 44 healthy women with normal pregnancies were included in the study. Of these, 24 delivered vaginally and 20 by elective Cesarean sections. In the fresh umbilical cord blood, cellular subsets of CD3+ (T-cells), CD19+ (B-cells), CD33+ (myeloid cells), CD34+ (hematopoietic progenitor cells) and CD56+ (natural killer cells) cells were isolated and DNA extracted. A single-nucleotide polymorphism unique to the mother was identified and maternal microchimerism in the different cellular fractions was detected using quantitative real-time polymerase chain reaction with a sensitivity of 0.01%. Overall, 5 out of the 44 (11%) umbilical cord blood samples contained maternal microchimerism. The positive fractions were total DNA (whole blood, n = 3), CD34+ (n = 1), CD56+ (n = 1) and CD34+/CD56+ (n = 1). Overall, four of the five (80%) positive samples were from Cesarean sections and one was from a vaginal delivery. The conclusion from this study is that maternal microchimerism in umbilical cord blood is not a common phenomenon but includes both lymphoid and hematopoietic progenitor lineages.