Immunolodulation Therapy for Immunological Endometrial Pathology

2.4.1 Glucocorticoids

Glucocorticoids may influence several aspects of implantation through its effect on endometrial cellular proliferation, apoptosis, remodelling and trophoblast invasion119. The subgroup analysis of a Cochrane review of peri-implantation steroid use in women undergoing standard in-vitro fertilisation (IVF) suggested that

32 pregnancy outcomes were improved120. There have also been published case reports of live births after treatment with steroids in women with RM. In Japan, a patient with 10 previous miscarriages had a live birth after receiving preconceptual steroids121. In our unit, a patient with 19 previous miscarriages, and found to have high uNK cells density, had a successful live birth after steroid therapy122.

Although uNK cells are found in high numbers during a progesterone rich environment for decidualisation in the late secretary phase, progesterone receptors have not been found on uNK cells. Instead, uNK cells express ER-β1, and glucocorticoid receptors which could be directly pharmacologically manipulated with estrogen or steroid treatment, such as prednisolone88. Indirectly, progesterone has been reported to exert effects on uNK cells by modulating their cytokine production via the glucocorticoid receptor123. This is important for further understanding the role of uNK cells and potential treatment mechanisms during the implantation window. Progesterone has also been postulated to exert its effect on uNK cell function through the cytokines such as IL-15, or stromal cells.

A prospective study using 20mg prednisolone from day 1 to day 21 of the menstrual cycle demonstrated a reduction in uNK cells in preimplantation endometrium of patients with RM110. In addition to reducing uNK cell numbers, prednisolone has been shown to reduce the degree of blood vessels maturation, which could be advantageous for the implanting embryo that favours a low oxygen environment124. In the same study, prednisolone also decreased some angiogenic growth factor expression, important for angiogenesis, a vital process in decidualisation and implantation.

The effect of glucocorticoids on uNK cells may not only be regulated by glucocorticoid receptors but also by the expression of steroid metabolising enzymes such as the 11-β hydroxyl steroid dehydrogenase (HSD) family88. Recently, laboratory studies have shown defective decidualisation correlating with high uNK cells and a lack of 11-β hydroxyl steroid dehydrogenase type 1 in stromal cells125. 11-β hydroxyl steroid dehydrogenase type 1 activates cortisol. Hence, administration of prednisolone may overcome this deficit. Prednisolone could exert its therapeutic effect through either one or a combination of the mechanisms

33 discussed and modify the endometrial environment to one more favourable for maintaining a pregnancy.

It is however unclear, if reducing uNK cells density to normality with steroid therapy will improve pregnancy outcomes. This could be examined in a double blinded, placebo controlled, randomised trial. We described a pilot trial of this nature in detail in Chapter 4 of this thesis.

2.4.2 Intravenous Immunoglobulin (IVIG)

IVIG is a costly treatment of fractionated blood product of pooled immunoglobulin (Ig) G extracted from plasma of blood donors, which has in the recent decade been used to treat women with reproductive problems, including RM. Although the exact mechanisms of action are unknown, IVIG is thought to suppress and neutralize autoantibodies, reduce NK cell activity, modify cytokine production and inhibit complement binding and activation126. A few systematic reviews have been performed to assess the beneficial effect of IVIG treatment in improving live birth rates. Although one of the systematic reviews demonstrated a significant benefit in improving subsequent live births in women with secondary RM127, a larger RCT carried out thereafter challenged this conclusion as the trial found no benefit of IVIG treatment in idiopathic secondary RM128. This was further confirmed by the latest systematic review addressing this topic129. Thus, consideration should be given to seek out a marker to identify the subgroup of women with RM and immunological pathology, where the efficacy of IVIG treatment in these women subgroups can be further assessed through RCTs. Although there are potentially significant side effects such as sepsis and venous thromboembolism from this treatment, the reviews have shown a good safety profile of its use.

2.4.3 Other immunomodulation therapies

Therapies such as 3rd party donor cell immunization, paternal cell immunization and trophoblast membrane infusion have previously been proposed and used on women with RM. However, there is conflicting evidence as to their

34 efficacy. A meta-analysis of trials comparing these immunotherapies has found no evidence of a beneficial effect over placebo in preventing further miscarriages52. These treatments are less commonly prescribed now, with the availability of newer treatments such as IVIG, described above, and intralipid.

Intralipid fat emulsion infusion is a standard component of parenteral nutrition. A number of studies have reported that intralipid infusion can modulate the immune system through suppression of NK cells cytotoxicity and pro- inflammatory cytokines formation, and has been shown to reduce abnormal NK cells activity130. This has led to its empiric use to improve pregnancy outcomes for women with abnormal NK cell parameters and reproductive problems. It is considerably cheaper, and thought to be safer than IVIG as it is not a blood product. However, its use is still in the experimental state and there is minimal evidence about its efficacy in recent literature.

2.5 Conclusion

There is considerable evidence for a specialized immune system in the endometrium that potentially plays a major role in the initiation and maintenance of a successful pregnancy. Uterine NK cells are the predominant immune cells during the window of implantation and early pregnancy, implicating an importance in the implantation process. This is further strengthened by evidence of cell-cell interactions between uNK cells and EVT, and possible functions of uNK cells that play direct important roles in the process of implantation. Alternately, uNK cell density may serve as a marker of an underlying endometrial or immunological phenomenon that leads to miscarriage.

Immunotherapy has been empirically prescribed in an attempt to improve pregnancy outcomes in women with RM but systematic reviews of its efficacy have not shown significant benefit. It is possible that the apparent absence of an effect of immunotherapy reflects the lack of a screening test to identify the subgroup of women that may benefit from immunotherapy. Immunomodulation may not be a suitable treatment for all women with idiopathic RM. In-vitro and in-vivo studies

35 have shown these therapies to normalise NK cell density and function. Therefore, NK testing may be a suitable screening tool.

There are studies investigating peripheral blood NK (pNK) cell and endometrium NK cell density and function in relation to reproductive problems as both have been associated with RM. The next chapter will discuss the association of both pNK and uNK cells and subsequent pregnancy outcomes in women with reproductive problems using the method of a systematic review, to assess if a NK cell test can be utilized as a screening tool for poor pregnancy outcomes.

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CHAPTER 3

NATURAL KILLER CELLS AND PREGNANCY OUTCOMES IN