Transmaternal cell flow leads to antigen-experienced cord blood

Savior Siblings Might Rescue Fetal Lethality But Not Adult Lymphoma in Irf2bp2-Null Mice

Interferon regulatory factor 2 binding protein 2 (Irf2bp2), a co-repressor of Irf2, is required for fetal hepatic erythropoiesis through the expansion of erythromyeloid progenitors. Mice with germline ablation of the entire Irf2bp2 transcript produced no viable Irf2bp2-null pups in first litters. In subsequent litters, fewer than 1/3 of the expected Irf2bp2-null pups were born and half survived to adulthood. As in humans with somatic mutations in IRF2BP2, adult Irf2bp2-null mice developed lymphoma. Transcriptome profiling of liver, heart, and skeletal muscle from Irf2bp2-null adult mice revealed a predominant upregulation of interferon-responsive genes. Of interest, hematopoietic stem cell-enriched transcription factors (Etv6, Fli1, Ikzf1, and Runx1) were also elevated in Irf2bp2-null livers. Intriguingly, Irf2bp2-positive mwfi 2yeloid (but not lymphoid) cells were detected in the livers of adult Irf2bp2-null mice. In female Irf2bp2-null mice, these cells carried a Y chromosome while in male Irf2bp2-null livers, no cells with Barr bodies (inactivated X chromosomes) were detected, indicating that Irf2bp2-positive erythromyeloid cells might be acquired only from male siblings of prior litters by transmaternal microchimerism. These cells likely rescue the deficit in fetal erythropoiesis, but not adult-onset lymphomagenesis, caused by Irfb2p2 ablation.

Fetomaternal microchimerism in tissue repair and tumor development

In various placental mammals, the bidirectional exchange of cells during pregnancy can lead to the acquisition of genetically unique cells that can persist in both mother and child for decades. Over the years, it has become increasingly clear that this phenomenon, termed fetomaternal microchimerism may play key roles in a number of biological processes. In this perspective, we explore the concept of fetomaternal microchimerism and outline how fetal microchimeric cells are detected and immunologically tolerated within the maternal setting. Moreover, we discuss undertakings in the field that hint at the significant plasticity of fetal microchimeric cells and their potential roles in promoting maternal wound healing. Finally, we explore the multifaceted roles of fetal microchimeric cells in cancer development and progression. A deeper understanding of fetomaternal chimerism in healthy and diseased states will be key toward developing more efficient anti-cancer treatments and regenerative therapies.

Male microchimerism in females: a quantitative study of twin pedigrees to investigate mechanisms

STUDY QUESTION

Does having a male co-twin, older brothers, or sons lead to an increased probability of persistent male microchimerism in female members of twin pedigrees?

SUMMARY ANSWER

The presence of a male co-twin did not increase risk of male microchimerism and the prevalence of male microchimerism was not explained by having male offspring or by having an older brother.

WHAT IS KNOWN ALREADY

Microchimerism describes the presence of cells within an organism that originate from another zygote and is commonly described as resulting from pregnancy in placental mammals. It is associated with diseases with a female predilection including autoimmune diseases and pregnancy-related complications. However, microchimerism also occurs in nulliparous women; signifying gaps in the understanding of risk factors contributing to persistent microchimerism and the origin of the minor cell population.

STUDY DESIGN, SIZE, DURATION

This cross-sectional study composed of 446 adult female participants of the Netherlands Twin Register (NTR).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Participants included in the study were female monozygotic (MZ) twins, female dizygotic same-sex twins and females of dizygotic opposite-sex twin pairs, along with the mothers and sisters of these twins. Peripheral blood samples collected from adult female participants underwent DNA extraction and were biobanked prior to the study. To detect the presence of male-origin microchimerism, DNA samples were tested for the relative quantity of male specific Y chromosome gene DYS14 compared to a common β-globin gene using a highly sensitive quantitative PCR assay.

MAIN RESULTS AND THE ROLE OF CHANCE

We observed a large number of women (26.9%) having detectable male microchimerism in their peripheral blood samples. The presence of a male co-twin did not increase risk of male microchimerism (odds ratio (OR) = 1.23: SE 0.40, P = 0.61) and the prevalence of male microchimerism was not explained by having male offspring (OR 0.90: SE 0.19, P = 0.63) or by having an older brother (OR = 1.46: SE 0.32, P = 0.09). The resemblance (correlation) for the presence of microchimerism was similar (P = 0.66) in MZ pairs (0.27; SE 0.37) and in first-degree relatives (0.091; SE 0.092). However, age had a positive relationship with the presence of male microchimerism (P = 0.02).

LIMITATIONS, REASONS FOR CAUTION

After stratifying for variables of interest, some participant groups resulted in a low numbers of subjects. We investigated microchimerism in peripheral blood due to the proposed mechanism of cell acquisition via transplacental blood exchange; however, this does not represent global chimerism in the individual and microchimerism may localize to numerous other tissues.

WIDER IMPLICATIONS OF THE FINDINGS

Immune regulation during pregnancy is known to mitigate allosensitization and support tolerance to non-inherited antigens found on donor cells. While unable to identify a specific source that promotes microchimerism prevalence within pedigrees, this study points to the underlying complexities of natural microchimerism in the general population. These findings support previous studies which have identified the presence of male microchimerism among women with no history of pregnancy, suggesting alternative sources of microchimerism. The association of detectable male microchimerism with age is suggestive of additional factors including time, molecular characteristics and environment playing a critical role in the prevalence of persistent microchimerism. The present study necessitates investigation into the molecular underpinnings of natural chimerism to provide insight into women’s health, transplant medicine and immunology.

STUDY FUNDING/COMPETING INTEREST(S)

This work is funded by Royal Netherlands Academy of Science Professor Award (PAH/6635 to D.I.B.); The Netherlands Organisation for Health Research and Development (ZonMw)—Genotype/phenotype database for behavior genetic and genetic epidemiological studies (ZonMw 911-09-032); Biobanking and Biomolecular Research Infrastructure (BBMRI–NL, 184.021.007; 184.033.111); The Netherlands Organisation for Scientific Research (NWO)—Netherlands Twin Registry Repository (NWO-Groot 480-15-001/674); the National Institutes of Health—The Rutgers University Cell and DNA Repository cooperative agreement (NIMH U24 MH068457-06), Grand Opportunity grants Integration of genomics and transcriptomics in normal twins and major depression (NIMH 1RC2 MH089951-01), and Developmental trajectories of psychopathology (NIMH 1RC2 MH089995); and European Research Council—Genetics of Mental Illness (ERC 230374). C.B.L. declares a competing interest as editor-in-chief of Human Reproduction and his department receives unrestricted research grants from Ferring, Merck and Guerbet. All remaining authors have no conflict-of-interest to declare in regards to this work.

TRIAL REGISTRATION NUMBER

N/A.

Male origin microchimerism and ovarian cancer

BACKGROUND

Reduced risk of ovarian cancer is commonly ascribed to reduced exposure to endogenous hormones during pregnancy, using oral contraceptives or not using hormone replacement therapy. However, exposure to hormones alone account for less than half of all cases. Many women carry small amounts of male cells-known as male origin microchimerism-in their circulation and remarkable impacts of these cells on women's health are being published. Here, we pursue the possibility that male origin microchimerism has a role in reducing ovarian cancer risk.

METHODS

We conducted a prospective case-cohort study using blood samples and questionnaire data from 700 women participating in the Danish Diet, Cancer, and Health cohort. Blood samples were analysed for Y chromosome presence as a marker of male microchimerism. We evaluated the association between male microchimerism and ovarian cancer, using weighted Cox regression models reporting hazard ratios (HRs) and corresponding 95% confidence intervals (CIs).

RESULTS

Male microchimerism was detected in 46% of cases and 65.9% of controls. Women testing positive for male microchimerism had a reduced hazard rate of ovarian cancer compared with women testing negative (HR = 0.44, 95% CI: 0.29-0.68). We found no evidence of interaction with measures of hormonal exposures (P = 0.50).

CONCLUSIONS

For the first time we report that women who test positive for male microchimerism in their circulation have reduced rates of ovarian cancer compared with women who test negative. Although the underlying mechanisms are presently unknown, we believe male microchimerism is potent in preventing ovarian cancer.

Low prevalence of male microchimerism in women with Mayer-Rokitansky-Küster-Hauser syndrome

STUDY QUESTION

Is there an increased prevalence of male microchimerism in women with Mayer–Rokitansky–Küster–Hauser (MRKH) syndrome, as evidence of fetal exposure to blood and anti-Müllerian hormone (AMH) from a (vanished) male co-twin resulting in regression of the Müllerian duct derivatives?

SUMMARY ANSWER

Predominant absence of male microchimerism in adult women with MRKH syndrome does not support our hypothesis that intrauterine blood exchange with a (vanished) male co-twin is the pathophysiological mechanism.

WHAT IS KNOWN ALREADY

The etiology of MRKH is unclear. Research on the phenotype analogous condition in cattle (freemartinism) has yielded the hypothesis that Müllerian duct development is inhibited by exposure to AMH in utero. In cattle, the male co-twin has been identified as the source for AMH, which is transferred via placental blood exchange. In human twins, a similar exchange of cellular material has been documented by detection of chimerism, but it is unknown whether this has clinical consequences.

STUDY DESIGN, SIZE, DURATION

An observational case–control study was performed to compare the presence of male microchimerism in women with MRKH syndrome and control women. Through recruitment via the Dutch patients’ association of women with MRKH (comprising 300 members who were informed by email or regular mail), we enrolled 96 patients between January 2017 and July 2017. The control group consisted of 100 women who reported never having been pregnant.

PARTICIPANTS/MATERIALS, SETTING, METHODS

After written informed consent, peripheral blood samples were obtained by venipuncture, and genomic DNA was extracted. Male microchimerism was detected by Y-chromosome–specific real-time quantitative PCR, with use of DYS14 marker. Possible other sources for microchimerism, for example older brothers, were evaluated using questionnaire data.

MAIN RESULTS AND THE ROLE OF CHANCE

The final analysis included 194 women: 95 women with MRKH syndrome with a mean age of 40.9 years and 99 control women with a mean age of 30.2 years. In total, 54 women (56.8%) were identified as having typical MRKH syndrome, and 41 women (43.2%) were identified as having atypical MRKH syndrome (when extra-genital malformations were present). The prevalence of male microchimerism was significantly higher in the control group than in the MRKH group (17.2% versus 5.3%, P = 0.009). After correcting for age, women in the control group were 5.8 times more likely to have male microchimerism (odds ratio 5.84 (CI 1.59–21.47), P = 0.008). The mean concentration of male microchimerism in the positive samples was 56.0 male genome equivalent per 1 000 000 cells. The prevalence of male microchimerism was similar in women with typical MRKH syndrome and atypical MRKH syndrome (5.6% versus 4.9%, P = 0.884). There were no differences between women with or without microchimerism in occurrence of alternative sources of XY cells, such as older brothers, previous blood transfusion, or history of sexual intercourse.

LIMITATIONS, REASON FOR CAUTION

We are not able to draw definitive conclusions regarding the occurrence of AMH exchange during embryologic development in women with MRKH syndrome. Our subject population includes all adult women and therefore is reliant on long-term prevalence of microchimerism. Moreover, we have only tested blood, and, theoretically, the cells may have grafted anywhere in the body during development. It must also be considered that the exchange of AMH may occur without the transfusion of XY cells and therefore cannot be discovered by chimerism detection.

WIDER IMPLICATIONS OF THE FINDINGS

This is the first study to test the theory that freemartinism causes the MRKH syndrome in humans. The study aimed to test the presence of male microchimerism in women with MRKH syndrome as a reflection of early fetal exposure to blood and AMH from a male (vanished) co-twin. We found that male microchimerism was only present in 5.3% of the women with MRKH syndrome, a significantly lower percentage than in the control group (17.2%). Our results do not provide evidence for an increased male microchimerism in adult women with MRKH as a product of intrauterine blood exchange. However, the significant difference in favor of the control group is of interest to the ongoing discussion on microchimeric cell transfer and the possible sources of XY cells.

STUDY FUNDING/COMPETING INTEREST(S)

None.

TRIAL REGISTRATION NUMBER

Dutch trial register, NTR5961.

Chimerism in health and potential implications on behavior: A systematic review

In this review, we focus on the phenomenon of chimerism and especially microchimerism as one of the currently underexplored explanations for differences in health and behavior. Chimerism is an amalgamation of cells from two or more unique zygotes within a single organism, with microchimerism defined by a minor cell population of <1%. This article first presents an overview of the primary techniques employed to detect and quantify the presence of microchimerism and then reviews empirical studies of chimerism in mammals including primates and humans. In women, male microchimerism, a condition suggested to be the result of fetomaternal exchange in utero, is relatively easily detected by polymerase chain reaction molecular techniques targeting Y-chromosomal markers. Consequently, studies of chimerism in human diseases have largely focused on diseases with a predilection for females including autoimmune diseases, and female cancers. We detail studies of chimerism in human diseases and also discuss some potential implications in behavior. Understanding the prevalence of chimerism and the associated health outcomes will provide invaluable knowledge of human biology and guide novel approaches for treating diseases.

Microchimerism of male origin in a cohort of Danish girls

Male microchimerism, the presence of a small number of male cells, in women has been attributed to prior pregnancies. However, male microchimerism has also been reported in women with only daughters, in nulliparous women and prepubertal girls suggesting that other sources of male microchimerism must exist. The aim of the present study was to examine the presence of male microchimerism in a cohort of healthy nulliparous Danish girls aged 10-15 y using DNA extracted from cells from whole blood (buffy coats) and report the association with potential sources of male cells. A total of 154 girls were studied of which 21 (13.6%) tested positive for male microchimerism. There was a tendency that girls were more likely to test positive for male microchimerism if their mothers previously had received transfusion, had given birth to a son or had had a spontaneous abortion. Furthermore, the oldest girls were more likely to test positive for male microchimerism. However, less than half of microchimerism positivity was attributable to these factors. In conclusion, data suggest that male microchimerism in young girls may originate from an older brother either full born or from a discontinued pregnancy or from transfusion during pregnancy. We speculate that sexual intercourse may be important but other sources of male cells likely exist in young girls.

Naturally acquired microchimerism: implications for transplantation outcome and novel methodologies for detection

Microchimerism represents a condition where one individual harbors genetically distinct cell populations, and the chimeric population constitutes <1% of the total number of cells. The most common natural source of microchimerism is pregnancy. The reciprocal cell exchange between a mother and her child often leads to the stable engraftment of hematopoietic and non-hematopoietic stem cells in both parties. Interaction between cells from the mother and those from the child may result in maternal immune cells becoming sensitized to inherited paternal alloantigens of the child, which are not expressed by the mother herself. Vice versa, immune cells of the child may become sensitized toward the non-inherited maternal alloantigens of the mother. The extent of microchimerism, its anatomical location, and the sensitivity of the techniques used for detecting its presence collectively determine whether microchimerism can be detected in an individual. In this review, we focus on the clinical consequences of microchimerism in solid organ and hematopoietic stem cell transplantation, and propose concepts derived from data of epidemiologic studies. Next, we elaborate on the latest molecular methodology, including digital PCR, for determining in a reliable and sensitive way the extent of microchimerism. For the first time, tools have become available to isolate viable chimeric cells from a host background, so that the challenges of establishing the biologic mechanisms and function of these cells may finally be tackled.

Donor parity no longer a barrier for female-to-male hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) is a widely applied treatment for disorders mainly involving the hematopoietic system. The success of this treatment depends on many different patient- and donor-specific factors. Based on higher CD34+ yields and superior clinical outcomes associated with the use of male donors, males are generally seen as the preferred HSCT donor. In addition, female donors are notorious for bearing memory type lymphocytes induced by previous pregnancies; such alloimmune cells may provoke unwanted immune reactions such as graft-vs.-host disease in transplant recipients. Consequently, many transplant centers try to avoid parous donors, particularly when searching the best unrelated donor for a male patient. We recently showed that parous women with female offspring have an anti-male directed tolerogenic immune status comparable to that of nulliparous donors. As discussed in this article addendum, the sex of the donor's offspring combined with the presence of HY-specific T regulator cells are possibly better selection criteria than parity status per se.

Patterns of Immune Regulation in Rhesus Macaque and Human Families

Supplemental digital content is available in the text.

Naturally acquired immune regulation amongst family members can result in mutual regulation between living related renal transplant donor and recipients. Pretransplant bidirectional regulation predisposed to superior renal allograft outcome in a CAMPATH-1H protocol. We tested whether Rhesus macaques, a large animal model of choice for preclinical transplant studies, share these immunoregulatory properties.

Maternal microchimerism in biliary atresia: are maternal cells effector cells, targets, or just bystanders?

The etiology of biliary atresia (BA) is unknown; however, the liver histology is similar to that observed in immune-mediated hepatic disorders. Liver fibrosis in BA progresses even after bile drainage has been achieved by the Kasai operation. Maternal microchimerism has been purported to play a part in the pathogenesis of BA as well as certain autoimmune diseases. However, the role of maternal cells has not yet been determined in BA. Specifically, it is unknown whether these maternal cells function as maternal effector T lymphocytes, or targets or bystanders. We currently hypothesize that the first hit is due to GvHD interaction by engrafted maternal effector T lymphocytes. Furthermore, we suggest that the secondary effects that are manifested by progressive cirrhosis are caused either by maternal chimeric effector T lymphocytes (e.g., GvHD interaction) or targets (e.g., HvGD interaction). Based on our hypothesis, mixed lymphocyte reactions between patients and their mothers might shed light on the etiopathogenesis and prognostic indicators.

HY immune tolerance is common in women without male offspring

Background

Sex difference is an established risk factor for hematopoietic stem cell transplantation (HSCT)-related complications like graft versus host disease (GVHD). CD8^pos cytotoxic T cells specific for Y chromosome-encoded minor Histocompatibility antigens (HY) play an important role therein. Prior to HSC donation, female donors may encounter HY antigens through fetomaternal or transmaternal cell flow, potentially leading to the induction of HY-specific cytotoxic or regulatory immune responses. Whether HY priming occurs independent of parity, and whether HY priming is dependent on the presence of male microchimerism, is as yet unknown.

Methods

We investigated the presence of HY-specific regulatory T cells (Treg) and male microchimerism in 45 healthy women with a fully documented pregnancy and family history. HY peptide-induced linked suppression, a commonly reported functional feature of CD4^pos and CD8^pos Treg, was measured by trans vivo Delayed Type Hypersensitivity testing. As source of HY antigens, male microchimerism was analyzed by real-time PCR and defined by the presence of male DNA in at least one purified leukocyte cell type.

Results

HLA class I or class II restricted HY-specific Treg were detected in 26/42 (62%) women eligible for analysis. The prevalence of HY-specific Treg was significantly higher in women who had never given birth to sons than in women with male offspring (p = 0.004). Male microchimerism could be detected in 24 out of 45 (53%) women but did not correlate with the presence of HY specific Treg.

Conclusions

HY-specific Treg in women with male offspring have been described previously. Here we show for the first time that, in fact, HY specific Treg are more common in nulliparous women and in parous women with female offspring. Their presence is independent of the presence of male microchimerism. Whether HY-specific Treg presence in female stem cell grafts might decrease the GVHD incidence in male HSCT recipients needs to be investigated.

The health effects of fetal microchimerism can be modeled in companion dogs

Fetal microchimerism (FMC) has been described to have a range of effects on health and disease. Y-chromosomal DNA has been detected in Golden Retrievers suggesting persistent FMC. In that report, nine dogs had evidence of microchimerism without prior pregnancy. To further understand this finding, a dam with prior male live births giving birth to her fourth litter of puppies, all females, was evaluated for FMC along with two of her daughters. All three female dogs had evidence of Y-chromosomal DNA in their blood. This suggests that male cells carried by the dam from previous pregnancy trafficked to her daughters to establish microchimerism in younger siblings. Companion dogs share many of the same cancers as humans, have out-bred genetics, and share the human environment, making them optimal models of human disease. Understanding the impact of FMC on health and disease of dogs could elucidate mechanisms useful for clinical interventions in humans.

Birth order and transplantation outcome in HLA-identical sibling stem cell transplantation: an analysis on behalf of the Center for International Blood and Marrow Transplantation

Allogeneic stem cell transplantation (SCT) is the most effective treatment option for many hematologic malignancies, but graft-versus-host disease (GVHD) remains a major cause of treatment failure. Along with well-established risk factors for transplantation outcomes, recent single-center studies have identified a birth order effect in HLA-identical sibling SCT, with lower rates of acute and chronic GVHD and improved overall survival when the donor is younger than the recipient. One hypothesized mechanism for this effect is microchimerism due to fetomaternal and transmaternal sibling cell trafficking during pregnancy as the donor is exposed to recipient antigens in utero. The aim of the present study was to validate previously reported single-center data in a large, multicenter cohort provided by the Center for International Blood and Marrow Transplantation. All adult and pediatric patients (n = 11,365) with a hematologic malignancy who underwent allogeneic SCT with a graft from an HLA-identical sibling donor between 1990 and 2007 were included. When donors were younger than recipients, there was a significantly lower rate of acute GVHD grade II-IV and chronic GVHD in children, as well as a lower rate of chronic GVHD in adolescents. However, the hypothesized overall positive effect of lower relapse and better survival when donors are younger than recipients was not observed. Our data suggest that if otherwise equally matched, a graft from a younger sibling may be superior to a graft from an older sibling for children and adolescents undergoing SCT.

We are all born as microchimera

It is well accepted that pregnancy establishes microchimerism. Lately, transmaternal passage of cells from elder siblings has been suggested as possible source of non-fetal microchimerism in nulliparous women. Recently, we identified both non-maternal microchimerism and minor H antigen specific cellular immune responses against these microchimeric cells in umbilical cord blood. The identification of the latter microchimeric cells from birth onwards explains the high incidence of microchimerism in healthy people and in people with different diseases. The circulating microchimeric cells of different origin can induce a wealth of antigen specific responses. Thus, nobody is born naïve: we are all microchimera's.

Bidirectional alloreactivity: A proposed microchimerism-based solution to the NIMA paradox

The NIMA paradox is the observation that in transplants of allogeneic kidneys or hematopoietic stem cells, siblings benefit from re-exposure to non-inherited maternal antigens (NIMA), whereas re-exposure to a transplant from mother herself, theoretically the ideal "NIMA" donor, does not yield clinical results superior to a father-donated allograft. Recent observations of bidirectional alloreactivity in kidney and cord blood transplantation offer a possible solution to this paradox. If correct, the proposed solution points the way to clinical applications of microchimerism in solid organ and hematopoetic transplants.