Marilen Benner

IMMUNE PROFILES IDENTIFY RECURRENT PREGNANCY LOSS 111 5 INTRODUCTION Only 30% of recognized pregnancies progress from conception to live birth (1). Spontaneous pregnancy loss poses a great medical and emotional burden. One to 2% of women suffer from recurrent pregnancy loss (RPL), defined as the consecutive loss of two or more pregnancies before 20 weeks gestation (2, 3). In absence of embryonal chromosome abnormalities, fractions of RPL can be attributed to genetic (2-5%), anatomic (10-15%) endocrine (17-20%) or autoimmune related factors (20%), but over 40% of cases remain unexplained (4, 5). These unexplained cases may be linked to an inadequate maternal immune response during key processes of implantation and placentation at the fetal-maternal interface (6-8). As the mechanisms behind this dysregulation are unknown, it is unclear whether they are contained to the uterus or manifest systemically. Most investigations to identify dysregulation of immunity in RPL have focused on specific immune cell populations isolated from peripheral blood (PB). This sample source is readily available to study large populations and, due to its limited invasiveness, allows inclusion of large control cohorts. Altered levels of circulating T (helper) cell profiles, regulatory T cells (Treg) and ratios of Natural Killer (NK) cell subsets were observed in RPL patients but none of these cell types were observed individually at levels that allowed robust distinction from women without pregnancy complications (9-13). Large variance, due to inter-populational differences, the time point of sampling or the measurement itself, and the complexity of relationships between immunological parameters hamper detection of cohort differences by commonly applied univariate approaches (14). Furthermore, it has to be considered that endometrial and decidual immune cells are highly specialized to enable adequate interaction with trophoblast cells, through mechanisms independent fromPBderived cells (15-19). Consequently, PB cannot serve to detect dysregulation of uterine immunity (20). Menstrual blood (MB) offers non-invasive access to uterine immune cells that display tissues-specific markers and NK cell profiles characteristic to decidua (21-26). This non-invasive sample source is only limitedly investigated until now, yet allows large scale studies to understand reproductive disorders. Here, we assessed immunophenotypic profiles of peripheral and menstrual blood using an ensemble machine-learning strategy. This approach enabled unbiased multivariate detection of immunological differences in women suffering from RPL.