P-394 Peripheral and uterine natural killer cell cut-off levels and their correlation in fertile controls and women with unexplained recurrent implantation failure (RIF)
Authors: Dogra Y , Singh N , Kumar P , Mathur S , Sharma A 
Published: June 2022

Abstract

Study question
What is cut-off value for peripheral and uterine natural killer (pNK, uNK) cells and any correlation between them in fertile and RIF women?

Summary answer
Cut-off values were 7% for uNK and 11.6% for pNK in fertile controls. No significant correlation observed among fertile and infertile women with RIF.

What is known already
Association of uNK and pNK cells with infertility is debatable. It is not clear whether measuring NK cell levels in RIF has a role. pNk cell levels however has been used in various studies to guide the need of immunotherapy in RIF women. Definition of normal range of uNK cell numbers has also not been stated clearly because of lack of standardised protocol. Literature reveals the cut off values for pNk cells to be 12% or 18% and for uNK cells between 5-12.9%. Correlation between uNK and pNK cells in fertile or RIF women has not been studied earlier.

Study design, size, duration
A prospective study was conducted at ART Centre, Department of Obstetrics and Gynecology at tertiary care institute during a period from January 2019 to January 2021. Thirty women with RIF and fifty fertile controls with age &lt;35 years having regular menstrual cycles and no hormonal treatment in last 3 months were enrolled in the study for uNK and pNK cell testing. The permission was obtained from the Institute Ethics Committee.

Participants/materials, setting, methods
Subjects included women with RIF with age 20-35 years, tubal and unexplained factors, normal ovarian reserve, normal karyotype and normal uterine cavity. In both subjects and controls, midluteal endometrial biopsy sample was taken for Immunohistochemistry staining of CD 56+ cells to determine uNK cells. Peripheral venous blood was also obtained at the time of biopsy for flow cytometry in peripheral blood mononuclear cells to determine pNK cells. Cut off values were derived from fertile controls.

Main results and the role of chance
The mean age and BMI were comparable between fertile control and study group(29.45±3.3 vs 31.17±3.3 years, 22.97±1.89 vs 23.21±2.2 kg/m2; p-value &gt;0.05). The control group had median value of 7% for uNK cell levels and 11.6% for pNK cell levels. In RIF subjects, the median value for uNK cells was 13.5% and even though higher compared to controls it was not statistically significant(p-value &gt;0.05) . The median pNK values were comparable among controls and RIF group (11.6% vs. 12%). All RIF subjects did not have elevated NK cell levels. 18 (60%) subjects had elevated uNK cell levels (more than 7%) whereas 40% had below the reference value. pNK cells were also elevated in only 53.3% of subject population. There was positive correlation found between uNK and pNK cell levels in RIF subjects, however it was not statistically significant (r 0.312, p-value 0.09). In fertile controls, there was insignificant negative correlation between uNK and pNK cell levels (r -0.231, p-value 0.33).

Limitations, reasons for caution
The small sample size is the foremost limitation of study.

Wider implications of the findings
uNK cell testing may be worthwhile in women with unexplained RIF so as to guide immunotherapy to improve pregnancy outcomes. As no significant correlation has been found between pNK and uNK cells in fertile and RIF women, pNK cell testing in RIF women may be done with caution.

Trial registration number
Not Applicable