Exercise training in women with unexplained recurrent pregnancy loss to optimize receptive endometrial NK cell population and function

Recurrent pregnancy loss (RPL) is defined as two or more miscarriages, which is
the case in 1-2%. Still, in 50-75% of the couples no underlying condition is
found and leaves clinicians without means to treat these women to prevent
recurrent losses. It has been suggested that inadequate adaptation of the
maternal immune system is responsible for a proportion of these unexplained
losses. The composition of the uterine immune cell population is unique as
compared to other mucosal sites as it has to tolerate the presence of a
semi-allogenic fetus, while at the same time providing sufficient plasticity to
counter infectious threats.

In the mid-secretory phase endometrial NK cells (eNK) rapidly increase. In
early pregnancy, approximately 80% of decidual leukocytes are eNK cells,
compared to 5-15% in peripheral blood. These eNK cells express high levels of
CD56 (CD56bright NK cells), in contrast to peripheral NK cells (CD56dim NK
cells). The CD56bright NK cells have a more immunomodulatory function, with the
ability to secrete cytokines. This immunomodulatory capacity of eNK cells
suggests that they play a crucial role in embryo implantation and development
of the trophoblast. Recent meta-analysis showed an increased number of
peripheral NK cells in women with RPL, however no difference was seen in eNK
cells. For research purposes taking biopsies from endometrial tissue is a very
invasive and painful procedure, that limits its feasibility in the routine
investigations for RPL. Instead of using eNK cells, NK cells isolated from
menstrual blood are a good source for eNK cells.The yield of lymphocytes after
collection of menstrual blood is even much higher than with endometrial
biopsies, and menstrual NK cells closely resemble biopsy-derived eNK cells.

In a pilot study we found that 6 out of 19 women with unexplained RPL (32%) had
less than 80% CD56bright NK cells derived from menstrual blood compared with
none of the women with a normal pregnancy, sensitivity and specificity of 72%
and 100%. The lower numbers of CD56bright NK cells suggest that this may be a
possible cause, in a subgroup of women with RPL, for their losses.

Exercise seems an effective intervention to improve the immune system, more and
more evidence in cancer research shows that exercise improves outcome in
patients. Exercise promotes healthy reproduction by reducing the risk on
preeclampsia and gestational diabetes. In women with RPL conflicting results
have been found on the effect of exercise and no studies investigate the impact
of exercise on the chances of a live birth. In addition, the effect of exercise
on eNK cell population has never been studied. NK cells are the most responsive
immune cells to exercise, displaying an activation and acute mobilization to
the circulation during physical exertion. Moderate training showed the highest
increase in peripheral NK cell counts. We observed in earlier studies that
women with RPL have a reduced physical fitness (unpublished data). We did not
study yet whether there was a direct relation with the altered NK cell
phenotypes that we observed.

Is moderate exercise training for 12 weeks in women with RPL improving
CD56bright eNK cell population and function?

Interventional study

Exercise training for 12 weeks.

After inclusion, a questionnaire will be taken once (CRF, SQUASH). Blood
collection, a vaginal internal examination (ultrasound, swap) and a
cardiovascular screening (blood pressure measurement, height, weight,
analysis). autonomic nervous system) will be performed twice (once before and
once after the intervention). Women will also twice undergo an exercise test by
means of a maximal bicycle test. During the intervention, they will follow a
sports program (bike trainings) for 3 months at a gym in their own area (weeks
1-6 2x a week 60 minutes and weeks 7-12 3x a week 60 minutes). They will then
be called weekly to evaluate the sports intervention and also to motivate the
participants. In addition, menstrual blood will be collected four times (once
before, twice during and once after the intervention). 12 months after the end
of the intervention, women will be sent a short questionnaire once more as a
follow-up to analyze the pregnancy outcomes. The risk for the subjects
associated with this study is minimal. We kept the invasiveness of our study
protocol to a minimum see also study protocol section 9.3.