Fetal CD34+ Cells in the Maternal Circulation and Long-Term Microchimerism in Rhesus Monkeys (Macaca mulatta)

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Abstract
Studies in humans have shown that during pregnancy fetal cells can enter the maternal circulation and persist for many years. While we have previously reported the presence of cell-free fetal DNA during pregnancy in rhesus monkeys, it is unknown whether cells circulate and persist long term in maternal tissues. In this study, we asked whether fetal CD34+ cells can be found in the maternal circulation and if male fetal cells persist in maternal tissues postdelivery. The presence of the Y chromosome in maternal blood and tissues was assessed using real-time PCR assays for the sex determining region Y (SRY) and testes specific protein Y (TSPY) genes. Analysis was done on CD34+ and CD34− cells isolated from maternal blood collected at select time points during gestation from gravid animals with male or female fetuses, and tissues were analyzed from nongravid animals that had previously delivered male offspring. All animals with male fetuses tested positive for the Y chromosome in CD34+ cells (0–30 cells/50,000 genome equivalents). Y sequences were also found in one or more maternal tissues collected up to 3-years postdelivery (thyroid, heart, spleen, liver, pituitary, adrenals, skin, inguinal lymph nodes). These studies suggest transfer of fetal CD34+ cells during pregnancy and persistent fetal microchimerism in the rhesus model. Thus, rhesus monkeys can be used to further our understanding of fetal:maternal microchimerism and the role of fetal cells in maternal health and disease.