Recent article on stem cells in relation to recurrent pregnancy losses:
Analysis by Braverman Reproductive Immunology
A new study, published last week in the journal
Stem cells, suggest that a lack of endometrial mesenchymal stem cells (eMSC) in the
lining of the womb could be responsible for reccurent pregnancy losses (Lucas, 2016).
Largely commented in recent journal publications as the first work showing
a cause for reccurent pregnancy losses, the British study, although very
promising, showed a correlation between women suffering from RPL and a
lack of eMSC but no demonstration of causality.
In the following blog, we will tell you a little more about endometrial
stem cells as they relate to pregnancy, we will then focus on the main
findings of the current study to finally conclude on the potential of
eMSC use to treat early pregnancy disorders.
- Human endometrial mesenchymal stem cells
- Endometrial mesenchymal stem cell (eMSC) and uterine regeneration
The endometrium sheds and regenerates each month as part of the menstrual
cycle but also after parturition (1).
Endometrial stem cells play key roles in regulating endometrial regeneration.
During the proliferative phase of the menstrual cycle, the estradiol induces
the migration of eMSC to the endometrium. In addition, endometrial cells
secrete an angiogenic factor (PDGF-BB) that will bind on PDGF receptors
localized on eMSC thus leading to their recruitment that allows renewal
of cells in the endometrium (2).
- eMSC and their role during implantation
Endometrial stem cells play key roles in regulating endometrial regeneration
and receptivity, essential step to support a successful implantation and
placental development.
Implantation is a key step in a pregnancy, that requires a fine-tune communication
between the maternal endometrium and the invading embryo.
To allow the establishment of a pregnancy, the endometrium has to be
receptive thus endometrial cells undergo a transformation into decidual cells in
response to elevated circulating progesterone concentration, through a
process called
decidualization (3).
It has been believed for a long time that the endometrium has a passive
role during implantation allowing the “assault” of the invading embryo.
In fact, recent studies showed that the endometrium and its decidual cells
have a much more
proactive role by encapsulating the early embryo to determine its
potential to develop and lead to a healthy pregnancy. In return, the decidual cells can adapt
and support a slightly “weaker” embryo to allow implantation.
This novel notion of endometrium
acting as a biosensor of embryo quality was first developed by a member of our team (4) and requires the transformation
of endometrial stromal cells into decidual cells thus
involving the eMSC (5).
An impairment of decidualization, with the dysregulation of some key factors,
has been described in biopsies samples from patient suffering from reccurent
pregnancy losses (RPL) (6).
- eMSC and their role in immunomodulation
Endometrial MSCs have anti-inflammatory and immunomodulatory properties (7).
In a proinflammatory environment, stem cells exposed to the inflammatory
cytokine tumour necrosis factor-a (TNFα) and/or interferon-gamma
(IFNγ) are activated to secrete anti-inflammatory factors (8).
They are able to synthesize mediators suppressing dendritic, T, B and NK
cell activation including but not limited to IL-10, prostaglandin E2,
IDO, TGFb, HLA-G (9) or IL-4 (10) thus leading to a decrease in IFNγ
and TNFα production.
MSCs can also switch macrophages from an inflammatory M1 to a reparative
M2 phenotype (7).
MSCs also promote the formation of regulatory T cells (Treg), which play
key roles in inducing an anti-inflammatory macrophage phenotype (11).
In addition, MSC can also inhibit natural killer cell proliferation (12).
Altogether, these data suggest that
MSC may contribute to maternal immunotolerance and
endometrial MSC’s disruption could potentially play a role in miscarriage.
- Focus on the study: the facts
Researchers at the
University of Warwick studied 183 endometrial biopsy samples from RPL patients and subfertile
patients with no history of RPL (control group).
They analyzed the methylome (methylation pattern) and transcriptome (gene
expression levels) of endometrial cells, in addition to
in vitro studies and found that:
- endometrial stromal cells from RPL women lack a specific
epigenetic signature associated with pluripotent cells in other words these endometrial cells have lower stem cells as seen by
a lower level of DNMT3A, a key marker of CpH methylation (feature of stem cells).
- endometrial stromal cells from RPL women have reduced levels of HMGB2,
a marker of stem cell aging so basically these cells have more DNA-damage,
which leads to MSC senescence.
- the depletion of endometrial stem cell correlates with the severity of
RPL phenotype.
Altogether, the study shows that
eMSC deficiency with premature senescence correlate with infertility status and could be involved in RPL but
a direct cause for RPL is not demonstrated in the study.
3.Endometrial mesenchymal stem cell: potential target to treat pregnancy failure
a.Use of stem cells as a therapy in RPL patients
Mesenchymal stem cells are plastic, adherent cells, that could proliferate
and differentiate in multilineage (they can give rise to multiple and
different cell types).
We have seen that endometrial MSCs (MSC from endometrial origin) may play
key roles in regulating endometrial receptivity by secreting several factors (13).
In obese women with higher first trimester losses when compared to overweight
or lean control women, studies on endometrial biopsies showed a lower
number of eMSC which can explain the higher risk of miscarriages in obese
women as the endometrium does not have optimal capacity to remodel upon
embryo implantation (14).
The use of stem cells in regenerative medicine to treat infertility disorders
linked to endometrial dysfunction has already been trialed. In a patient
with Asherman syndrome (very thin endometrial lining) who was not responsive
to estrogen therapy, transplant from her own bone marrow-MSC (autologous)
resulted in endometrial regeneration and a clinical pregnancy following
IVF embryo transfer (15).
Small injuries have been shown to improve MSC engraftment (16). Because
endometrial “scratch” increase IVF success rates (17), MSC
transplant in combination to endometrial “scratch” may potentially
improve endometrium regeneration and receptivity in RPL patients.
- eMSC: easy accessible and non-invasive source of stem cells
Bone marrow is a commonly used source of mesenchymal stem cells (MSCs)
for cell-based therapies but it requires at least local anesthesia.
The endometrium has a very important regenerative capacity with over 500
menstrual cycles occurring during a women’s life, where the upper
layer “functionalis” of its bilayer structure is shed during
menses and is replenished from the basalis layer at the following cycle (18).
Endometrial MSC have been shown to be present on the functional layer of
the endometrium, they may be isolated from endometrial biopsies or more
easily from
menstrual blood (19).
After cell culture and purification using specific antibody, eMSC have
been isolated and display the same properties as bone-marrow MSC (20).
Very few clinical trial have been using eMSC. Allogenic intravenous eMSCadministration
(eMSC obtained from another individual) has been used in patients with
multiple sclerosis (21), Duchenne muscular dystrophy (22) or congestive
heart failure (23). Despite showing beneficial effects with no long term
side effects, no conclusions could have been made as the trials were case
studies only, with no control groups. Several clinical trials are underway
and should bring valuable insight in the use of eMSC in liver cirrhosis
or type I diabetes.
In the reproductive field, the effect of eMSC on embryo implantation following
embryo transfer is under evaluation (24). To determine if eMSC could improve
implantation rate, eMSC are deposited into the uterine cavity just prior
to embryo transfer during an IVF cycle compared to a control group (no
cells). Secondary outcomes measured endometrial volume and vascularity
by ultrasound. To date, no results were published.
4.Role of Neupogen (G-CSF) on MSC
G-CSF has long been used as a method to enrich stem cell in the blood stream (25).
In a review focusing on autologous transplant (self-transfer of stem cell),
the only factor that had a significant impact on stem cells engraftment
(when the transplanted cells start to grow and make healthy blood cells)
was the use of
G-CSF prior to collecting stem cells from either blood or marrow (26).
G-CSF seemed to increase the pace of MSC engraftment when MSC were mobilized
after G-CSF treatment.
Several studies have suggested that bone marrow mesenchymal stem cells
can give rise to endometrial cells including stroma, epithelial and endothelial
cell type (27).
In patients receiving HLA-mismatch bone-marrow transplant (donor and recipient
have different HLA haplotype), endometrial cells with the donor HLA “signature”
were found in the recipient endometrium at a high level with 48% of epithelial
cells and 50% of stromal cells of donor origin (28).
In another study, using the Y-chromosome as a marker of bone marrow-derived
cells in the endometrium (as the donor was a male), recipient patient
showed 10% of endometrial cells derived from the donor bone marrow stem
cells (29).
Based on these facts, we propose that one of the multiple beneficial effects
of G-CSF in women attempting to conceive could be mediated through the
regeneration and thickening of the endometrium with G-CSF:
- increasing MSC in the bone marrow
- bone marrow stem cells can then migrate to and regenerate the endometrium,
helping to support a pregnancy.
Many disorders have been treated with MSC transplant including but not
limited to multiple sclerosis, systemic sclerosis, systemic lupus erythematosus
or rheumatoid arthritis (RA) suggesting that MSC alterations could be
involved in the development of autoimmune conditions.
In systemic sclerosis patients, early senescence of bone marrow MSC has
been shown (30). In a similar way, MSCs from SLE patients have been described
as defective with an abnormal morphology and early sign of senescence
(31) and MSCs of RA patients show altered phenotype (32).
Because MSCs have well known immune-modulatory properties as well as immune-suppressive
potentials, we believe that immune related pregnancy loss may be a consequence
of low MSC levels which can be
boost by G-CSF,
therapy already in use in our practice.
Endometrial MSC deficiency as a cause of RPL may be
one of many etiologies.
Although it requires further investigations and clinical trials, transplant
of eMSC prior to conception after G-CSF infusion may be a valid and promising
therapy to treat patients with reccurent implantation failure or recurrent
pregnancy losses.
But you might be well aware that in most cases, RPL patients suffer from
multiple dysregulations requiring a thorough workup to pinpoint the specific causes leading to
these losses.
We, at
Braverman Reproductive Immunology, keep analyzing the latest discoveries in the Reproduction field, to include
new diagnosis and develop even more adapted therapy regimen to provide
you with the best possible care.
References