Fetal cell microchimerism in human cancers

Pregnancy, cardiovascular health, and microchimerism

PURPOSE OF REVIEW

To provide an updated review of scientific literature concerning associations between pregnancy and cardiovascular health among women, and to discuss a possible impact of microchimerism on the association.

RECENT FINDINGS

In most studies, pregnancy and childbirth is associated with increased risk of cardiovascular disease in women. Some ascribe the association mainly to lifestyle, whereas others suggest that pregnancy itself negatively affects women's cardiovascular health. Pregnancy is a natural source of microchimerism, which in turn markedly affects female health. The only study published in the area surprisingly shows that among middle-aged women, male-origin microchimerism (MOM) is associated with half the risk of developing ischemic heart disease (IHD). No similar association is found between MOM and ischemic stroke.

SUMMARY

The sparse evidence published suggests reduced risk of developing IHD among MOM-positive women. Despite the association being biologically plausible, replication of the findings is warranted to support that this is not a chance finding.

A history of cesarean section and future maternal long-term risk for neoplasms: a population-based cohort study

OBJECTIVE

Mode of delivery has long-term implications on the mother, including recent data regarding the level of transmission of fetal microchimeric cells (FMc) and their possible effect on cancer development. We aimed to evaluate the association between cesarean section (CS) and future risk for neoplasms.

STUDY DESIGN

A population-based cohort analysis comparing the long-term risk for neoplasms between patients that delivered only by CS to those that delivered only vaginally (VD). Neoplasms were pre-defined based on ICD-9 codes. Deliveries occurred between the years 1991-2017 in a tertiary medical center. Kaplan-Meier survival curves were used to compare the cumulative incidence of neoplasms and Cox proportional hazards models were constructed to control for confounders.

RESULTS

During the study period 105,992 patients met the inclusion criteria; 14150 (13.4%) of patients had only CS and 91842 (86.6%) had VD (comparison group). The CS group had significantly higher incidence of benign and malignant neoplasms (4.73 per 1000 patient-years versus 3.88 per 1000 patient-years, OR = 1.26, 95% CI 1.16-1.37; p = 0.001; 2.19 per 1000 patient-years of follow up versus 1.93 per 1000 patient-years, OR = 1.16, 95% CI 1.03-1.31; p = 0.013). Specifically, the CS group had higher incidence of uterine cancer (1.2 versus 0.06 per 1000 patient-years, OR = 1.97, 95% CI 1.14-3.39; p = 0.013). The cumulative incidence of benign, malignant and uterine neoplasms was significantly higher in the CS group (Log rank test p = 0.001; 0.036 and 0.014; respectively). Importantly, no significant association was found with breast and ovarian malignancies." When performing a Cox regression model controlling for confounders, the risk for malignancy-related hospitalizations remained significant (adjusted HR = 1.22, 95% CI 1.01-1.48; p = 0.031) but not for uterine cancer (adjusted HR = 1.6, 95% CI 0.9-2.8; p = 0.103).

CONCLUSION

Our findings provide support to linkage between delivery by cesarean section and future maternal malignancy.

Impact of Male-Origin Microchimerism on Cardiovascular Disease in Women: A Prospective Cohort Study

Increasing parity is associated with an increased risk of ischemic heart disease (IHD) and stroke in women. This is probably attributable to biological responses of pregnancy. Male cells of presumed fetal origin are commonly present in women years after pregnancy-a phenomenon termed male-origin microchimerism (MOM). In this study, we investigated whether MOM was associated with risk of IHD and ischemic stroke in women. We evaluated the association between MOM and ischemic events in a cohort of 766 Danish women enrolled in the Diet, Cancer and Health cohort during 1993-1997 when aged 50-64 years. Of these women, 545 (71.2%) tested positive for MOM through targeting of the Y chromosome (DYS14 DNA sequence) in their blood. Multiple Cox regression models were used to calculate hazard ratios with 95% confidence intervals. We found that MOM was associated with a significantly reduced rate of IHD (hazard ratio = 0.44, 95% confidence interval: 0.23, 0.83) but not ischemic stroke (hazard ratio = 0.80, 95% confidence interval: 0.46, 1.41). Our findings show that microchimerism positivity is associated with a lower rate of later IHD development in women. Although the underlying mechanisms are presently unknown, MOM may be relevant in women's cardiovascular health. More studies are needed to confirm these findings.

Fetal microchimeric cells in autoimmune thyroid diseases: harmful, beneficial or innocent for the thyroid gland?

Autoimmune thyroid diseases (AITD) show a female predominance, with an increased incidence in the years following parturition. Fetal microchimerism has been suggested to play a role in the pathogenesis of AITD. However, only the presence of fetal microchimeric cells in blood and in the thyroid gland of these patients has been proven, but not an actual active role in AITD. Is fetal microchimerism harmful for the thyroid gland by initiating a Graft versus Host reaction (GvHR) or being the target of a Host versus Graft reaction (HvGR)? Is fetal microchimerism beneficial for the thyroid gland by being a part of tissue repair or are fetal cells just innocent bystanders in the process of autoimmunity? This review explores every hypothesis concerning the role of fetal microchimerism in AITD.

Microchimerism and survival after breast and colon cancer diagnosis

Recently, we reported microchimerism to be oppositely associated with maternal breast and colon cancer. In women with a blood test positive for male microchimerism the risk of breast cancer development was reduced to one third, whereas the risk of colon cancer was elevated 4-fold. In this article addendum, I report the survival of cases in the original study after being diagnosed with cancer. Despite small numbers, the analysis suggests that microchimerism may be positively associated with survival after breast and maybe colon cancer diagnosis. Despite the findings on colon cancer in our original report, I speculate whether microchimerism could have a general beneficial role in cancer, which in some sites may not be evident because an allogeneic maternal immune reaction hastens cancer development.

The otherness of self: microchimerism in health and disease

Microchimerism (Mc) refers to the harboring of a small number of cells (or DNA) that originated in a different individual. Naturally acquired Mc derives primarily from maternal cells in her progeny, or cells of fetal origin in women. Both maternal and fetal Mc are detected in hematopoietic cells including T and B cells, monocyte/macrophages, natural killer (NK) cells and granulocytes. Mc appears also to generate cells such as myocytes, hepatocytes, islet β cells and neurons. Here, the detrimental and beneficial potential of Mc is examined. The prevalence, diversity and durability of naturally acquired Mc, including in healthy individuals, indicates that a shift is needed from the conventional paradigm of 'self versus other' to a view of the normal 'self' as constitutively chimeric.

Verification of the genomic identity of candidate microchimeric cells

Microchimerism has been studied in the context of a variety of diseases which include autoimmune diseases (such as systemic sclerosis, rheumatoid arthritis, systemic lupus erythematosus and autoimmune thyroid diseases), cancer (e.g., of the cervix, thyroid gland, lung, breast), tissue repair, transplantation and transfusion. It may become relevant in the context of cell-based non-invasive prenatal diagnosis. But how to safely identify individual microchimeric cells? This is a nontrivial question, for which a solution has recently been suggested.

[Fetal microchimerism: self and non-self, finally who are we?]

For a long time, the conventional view was that the fetus and maternal vascular system are kept separate. In fact there is a two-way traffic of immune cells through the placenta and the transplacental passage of cells is in fact the norm. The fetal cells can persist in a wide range of woman's tissue following a pregnancy or an abortion and she becomes a chimera. Fetal cells have been found in the maternal circulation and they were shown to persist for almost three decades in humans, thus demonstrating long-term engraftment and survival capabilities. Microchimerism is a subject of much interest for a number of reasons. Studies of fetal microchimerism during pregnancy may offer explanations for complications of pregnancy, such as preeclampsia, as well as insights into the pathogenesis of autoimmune disease which usually ameliorates during pregnancy. The impact that the persistence of allogenic cells of fetal origin and the maternal immunological response to them has on the mother's health and whether it is detrimental or beneficial to the mother is still not clear. Although microchimerism has been implicated in some autoimmune diseases, fetal microchimerism is common in healthy individuals. On the beneficial side, it has been proposed that genetically disparate fetal microchimerism provides protection against some cancers, that fetal microchimerism can afford the mother new alleles of protection to some diseases she has not, that fetal microchimerism can enlarge the immunological repertoire of the mother improving her defense against aggressor. Fetal cells are often present at sites of maternal injury and may have an active role in the repair of maternal tissues.

Fetal microchimerism and women's health: a new paradigm

Pregnancy is associated with transfer of maternal cells to the fetus and fetal cells to the mother. In both cases, the transferred cells are described as microchimeric. Fetal microchimeric cells include semi-allogeneic stem cells, which are few in number and are capable of long-term survival in the "foreign" host. They are recognized by the maternal immune system but not rejected or attacked. These cells appear to survive and even thrive for years in a mother's body, perhaps for her lifetime. Previously regarded as potentially dangerous interlopers that might propagate autoimmune and even malignant disease, fetal microchimeric cells are now increasingly being recognized and analyzed for their healing, reparative, and perhaps regenerative roles. Fetal microchimerism (MC) may make significant and previously unknown positive contributions to women's health, longevity, and risk of disease. This article reviews the history, major discoveries, and current concepts and gaps in knowledge in the field of fetal MC.