Cellular and molecular approaches for the study of maternal-fetal immune tolerance in nonhuman primates

How does a fetus that expresses foreign antigens evade rejection by the maternal immune system? The hypothesis proposed herein is that the maternal immune system recognizes antigens of the fetal-placental unit as foreign, however the subsequent response is suppressed by soluble and membrane bound molecules produced by trophoblasts to enable implantation and development. This thesis presents research directed towards the production of monkeys with altered placental phenotypes for the study of the mechanisms that the placenta employs to evade rejection by the maternal immune system. First, a reliable, noninvasive, nonsurgical method for transferring rhesus monkey (Maccaca mulatta) embryos was established. This provides a technique that can be broadly used to transfer genetically altered or chimeric embryos for the propagation of endangered macaque species. Methods for highly efficient gene transfer to rhesus embryos were then pursued. A novel method using an Epstein Barr virus (EBV)-based episomal vector was developed to produce rhesus monkey embryos expressing a transgene, and the expression of eGFP in preimplantation rhesus embryos was assessed. While this approach was successful at directing in vitro gene expression, long-term stable in vivo expression in offspring may be better served with an integrating vector such as a retrovirus. Lentiviral vectors were selected to direct long-term expression because of their unique biology. Rhesus monkey embryos were injected with lentiviral vectors and transferred into recipient females. Gene transfer into rhesus monkey preimplantation embryos using lentiviral vectors gave rise to transgenic placentas that expressed a reporter transgene. Maternal antibodies directed against eGFP were seen in late pregnancy in maternal serum indicating that there was a maternal anti-placental immune response. Finally, placental chemokine expression and the effects of cytokines on chemokine expression were investigated in early cytotrophoblasts and embryo-derived trophoblasts. It was found that Th1 cytokines can selectively influence the expression of chemokines in trophoblasts. Together, these data provide the groundwork and evidence to support the hypothesis that the fetus produces molecules that interact with the maternal immune system to change maternal physiology during pregnancy.