Microchimerism: a lasting legacy of transfusion?

Should microchimerism turn into rejection prophylactics?

Non-self cells can circulate in the body of an individual after any sort of contact with an allogeneic source of cells, thus creating a situation of chimerism that can be transient or prolonged over time. This situation may appear after stem cell transplantation, pregnancy, transfusion or transplantation. Concerning transplantation, many hypotheses have been formulated regarding the existence, persistence and role of these circulating cells in the host. We will review the principal hypotheses that have been formulated for years since the first description of non-self circulating cells in mammals to the utilization of artificially induced chimerism protocols for the achievement of tolerance.

Persistence of male hematopoietic CD34+ cells in the circulation of women does not affect prenatal diagnostic techniques

OBJECTIVE

We aimed to verify whether fetal microchimerism, because of persisting fetal hematopoietic CD34(+) cells from previous pregnancies, could interfere with the development of genetic tests based on using these cells, isolated from maternal blood for the diagnosis of fetal aneuploidies.

STUDY DESIGN

CD34(+) cells, isolated from blood of parous women with at least 1 son and nulliparous women, were analyzed by using qualitative polymerase chain reaction (PCR), quantitative PCR, and fluorescence in situ hybridization (FISH) to establish whether these molecular techniques are concurrently capable of detecting circulating male DNA.

RESULTS

By qualitative PCR, male DNA was found both in parous and nulliparous women, whereas by quantitative PCR and FISH analyses, no male DNA or male nuclei were revealed except in 1 cultured CD34(+) sample from a nulliparous woman.

CONCLUSION

Fetal hematopoietic CD34(+) cells can be used in the noninvasive prenatal testing of fetal aneuploidies because the presence of fetal microchimerism does not affect fetal diagnosis in current pregnancies.

Fetal microchimerism and maternal health during and after pregnancy

Trafficking of fetal cells into the maternal circulation begins very early in pregnancy and the effects of this cell traffic are longlasting. All types of fetal cells, including stem cells, cross the placenta during normal pregnancy to enter maternal blood, from where they may be recovered in pregnancy for the purpose of genetic prenatal diagnosis. Fetal cells can also be located in maternal tissues during and after pregnancy, and persist as microchimeric cells for decades in marrow and other organs. Although persistent fetal cells were first implicated in autoimmune disease, subsequent reports routinely found microchimeric cells in healthy tissues and in non-autoimmune disease. Parallel studies in animal and human pregnancy now suggest instead that microchimeric fetal cells play a role in the response to tissue injury. However, it is still not clear whether microchimeric fetal cells persisting in the mother are an incidental finding, are naturally pathogenic or act as reparative stem cells, and the environmental or biological stimuli that determine microchimeric cell fate are as yet undetermined. Future studies must also focus on investigating whether fetal cells create functional improvement in response to maternal injury and whether this response can be manipulated. The pregnancy-acquired low-grade chimeric state of women could have far-reaching implications, influencing recovery after injury or surgery, ageing, graft survival after transplantation, survival after cancer as well as deciding the protective effect of pregnancy against diseases later in life. Lifelong persistence of fetal cells in maternal tissues may even explain why women live longer than men.

Fetal cells of mesenchymal origin in cultures derived from synovial tissue and skin of patients with rheumatoid arthritis

The transplacental cell transfer naturally takes place during pregnancy and occurs bi-directionally between the mother and fetus. Using real-time polymerase chain reaction (PCR) assay and sex determining region Y (SRY) gene as a marker, we examined the presence of male fetal cells in cell cultures derived from synovial tissues and skin dermis in women with prior pregnancy history suffering from rheumatoid arthritis (RA) who underwent synovectomy. Male DNA was detected in synovial cell samples derived from carpal, hip, metacarpophalangeal and metatarsophalangeal joints in five out of 13 (38.5%) patients with RA in a frequency range of 0.02-62.55 (mean 12.17) male cells per 10,000,000 total cells. SRY gene positivity was found as well in skin fibroblast cultures in four out of 10 (40.0%) RA patients in a frequency range of 3.26-43.47 (mean 15.42) male cells per 10,000,000 total cells, respectively. The difference in a frequency of fetal-derived male cells between both the cohorts did not achieve the statistical difference (p=0.77). We conclude that persisting male fetal cells are able to grow from non-inflamed tissues as well as from those which have many features characteristic of a stressed tissue. We conclude that persisting male fetal cells are also able to proliferate in cell culture since their presence was detected even in consecutive passages.