Editorial Egg donation pregnancy as an immunological model for solid organ transplantation Marie-Louise P. van der Hoorn a, ⁎, Sicco A. Scherjon b, c , Frans H.J. Claas b a Department of Obstetrics, Leiden University Medical Centre, PO Box 9600 (location code: K6-26), 2300 RC Leiden, The Netherlands b Department of Immunohematology and Blood Transfusion, Leiden University Medical Centre, Leiden, The Netherlands c Department of Obstetrics and Gynaecology, Sint Lucas Andreas Hospital Amsterdam, The Netherlands abstract article info Article history: Received 9 June 2011 Accepted 10 June 2011 Keywords: Egg donation Immunology Placenta Pregnancy Transplantation In egg donation (ED) pregnancies the fetus is allogeneic to the gestational carrier. During these ED pregnancies the mother has to cope with a higher degree of antigenic dissimilarity compared with spontaneously conceived pregnancies. At the fetal–maternal interface maternal cells and fetal cells come in close contact. Understanding the immune mechanisms at this fetal–maternal interface gives more insight into the question why the (semi-)allogeneic fetus is accepted and not rejected by the mother. The degree of antigenic dissimilarity in ED pregnancies is comparable with that in solid organ transplantations with HLA mismatched unrelated donors. Therefore, the immunologic interactions between mother and child in successful ED pregnancies may be relevant for the induction of immunological tolerance in solid organ transplantation. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The fetus is a semi-allograft expressing both maternal (self) and paternal (non-self) genes. The placenta and fetal membranes are directly exposed to maternal tissue. Therefore during the accom- plishment of uncomplicated pregnancy specific, local immune adaptations are necessary at the fetal–maternal interface. As in egg donation (ED) pregnancies the fetus can be fully allogeneic to the mother, ED pregnancies represent an interesting model to study complex immunologic interactions between the fetus and the pregnant women. During these ED pregnancies the mother has to cope with a higher degree of antigenic dissimilarity compared to spontaneously conceived pregnancies. Understanding immune mech- anisms involved in successful ED pregnancies can possibly lead to new strategies for the induction of immunological tolerance in human leukocyte antigen (HLA) mismatched solid organ transplantations. To elucidate aspects of ED pregnancies as an immunological model for solid organ transplantation, knowledge of maternal mechanisms during spontaneously conceived pregnancies in the acceptance of the developing fetus and placenta is essential. In this review immunoge- netic and immunological similarities between ED pregnancy and transplantation are discussed. In addition an overview of immuno- logical aspects of spontaneous, uncomplicated pregnancy is given, showing why fetal tissues are immunologically tolerated in the maternal host environment. 2. Egg donation pregnancies ED pregnancies are a result of in vitro fertilization (IVF) of an oocyte, donated by a related or, more commonly, by an unrelated donor. Hereby, neither of the fetal haplotypes will match with the gestational carrier. Increased knowledge in the field of assisted reproductive technologies, a more liberal interpretation of medical indications and social acceptance of the procedure has lead to an ever increasing number of ED pregnancies. Clinically relevant complica- tions in ED pregnancies, presumably related to the allogeneic nature of the fetus, occur more frequently. The literature reports on a higher risk of pregnancy induced hypertension, a higher incidence of cesarean sections, an increased risk of postpartum hemorrhage and more first trimester vaginal bleeding complications [1–5]. Although these maternal complications are higher in ED pregnancies compared to spontaneously conceived pregnancies, they are not associated with an increase in fetal and/or neonatal complications [3,4,6,7]. This suggests that downregulation of the maternal immune response preventing a detrimental maternal immunological response is possible, even in a completely allogeneic situation. Histological findings of ED placentas show some resemblance with a host versus graft rejection phenomenon as seen with solid organ transplantations [8]. Severe chronic deciduitis admixed with fibrinoid deposition has been observed in ED placentas compared with non-donor IVF placentas [8]. Histological findings, as chronic deciduitis, found in the basal plate of the placenta where extravillous cytotrophoblast interfaces with the maternal decidua, are thought to resemble immune mediated placenta pathology. Although the possible maternal complications in ED pregnancies are clearly described, relatively little is known on the underlying Transplant Immunology 25 (2011) 89–95 ⁎ Corresponding author at: PO Box 9600 (location code: P3-24), 2300 RC Leiden, The Netherlands. Tel.: +31 71 5263362; fax: +31 71 5266741. E-mail address: m.l.p.van_der_hoorn@lumc.nl (M.-L.P. van der Hoorn). 0966-3274/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.trim.2011.06.004 Contents lists available at ScienceDirect Transplant Immunology journal homepage: www.elsevier.com/locate/trim