The use of pregnancy serum to obtain trophoblastic cell cultures

Trophoblast invasion

The establishment of a pregnancy depends upon mechanisms of forming close contacts between embryonic/fetal and maternal tissues. The starting point is the attachment of the blastocyst to the uterine wall, and this critical step is followed by a series of different morphogenetic events leading to placentation. These processes depend on the invasive properties of extra-embryonic trophectoderm-derived cells that show their highest expression in species with haemochorial placentation, i.e. Insectivores, rodents, and primates including the human. In this review we will concentrate upon the human with occasional reference to other species.

Culture of syncytiotrophoblast for the study of human placental transfer. Part I: Isolation and purification of cytotrophoblast

Criteria for a successful model for the study of trans-syncytiotrophoblast transfer include isolating substantially pure trophoblast cells from placental villous tissue, and obtaining from them phenotypical villous syncytial syncytiotrophoblast during culture. For studies involving the basal membrane, including overall transfer, basal uptake and output, and controls acting at the basal membrane, a two-sided model is required with a separate compartment of culture medium in contact with the basal cell surface. All current methods of isolating cytotrophoblast, the precursor of syncytiotrophoblast, derive from the original tissue trypsinization method of Thiede (1960), which produces cultures of villous cytotrophoblast cells contaminated with other placental cell types. Lessons learned from successful and unsuccessful development of the model over 35 years are outlined, and recently established methods for purifying the isolated mixed cells discussed. These include sedimentation and centrifugation methods, immunological and receptor binding methods, and more selective release of trophoblast cells from tissue. Immuno flow cytometric cell sorting methods are potentially capable of isolating subpopulations of various phenotypical trophoblast types. We conclude that satisfactory methods are now available for isolating and purifying cytotrophoblast from early or late gestation human placenta.

Villous culture of first trimester human placenta--model to study extravillous trophoblast (EVT) differentiation

During implantation and subsequent placentation the human extravillous trophoblast (EVT) cells invade the endometrium and maternal vasculature within the uterus. The origin of the EVT and signals triggering its differentiation, migration and invasion are poorly understood. First and second trimester human chorionic villi explants were used as a source of EVT and a variety of substrates which resemble extracellular matrix (ECM) in vivo have been tested to induce EVT differentiation and migration. The obtained results demonstrate that villous explants from both 5-7 and 8-10 weeks of gestation give rise to EVT cells in vitro if maintained on the surface of Matrigel or decidual extract supplemented collagen gel. Fetal calf serum (FCS) supplemented media was essential for EVT differentiation and villous trophoblast viability. Immunostaining of both EVT cells and cells from the cytotrophoblastic column with monoclonal antibody Ki67 (cell proliferation marker) indicate that EVT cells differentiate in vitro by proliferation from the tip of anchoring villi. These mononucleated, round-shaped, migrating cells are HLA-A,B,C class I antigen (W6/32) antibody and low molecular weight cytokeratin positive, and do not immunostain with PAI-1 (plasminogen activator inhibitor) and HPL antibodies. Differentiation of EVT was restricted to first trimester villous tissue; explants from second trimester placentae did not give rise to EVT. Tissue viability as monitored by glucose utilization, lactate, progesterone and hCG production rates correlated with EVT differentiation. The production rates for hCG demonstrated significant variation among individual placentae and was maintained constant for 10 days consistently only in explants cultured on decidual extract supplemented collagen matrix. The described villous tissue culture system may be, therefore, a unique in vitro model to study proliferation and differentiation of EVT from cytotrophoblastic columns, the regulation of EVT proliferation and differentiation, the role of ECM in the induction of the migration and the interaction of extravillous and villous trophoblast at the level of the cytotrophoblastic column.

Purification of human cytotrophoblast from term amniochorion by flow cytometry

Term cytotrophoblast do not express polymorphic MHC Class I antigens, unlike other fetal and maternal cells in the amniochorion/decidua. This allows cytotrophoblast to be isolated and purified from this tissue, utilizing 4E, a monoclonal antibody specific for HLA-B, which labels only non-trophoblast. We have developed a method using enzymic dispersion and Percoll gradient centrifugation, followed by flow cytometry, that yields, on average, a total of 5 X 10(6) term extravillous cytotrophoblast, 97 per cent pure. The availability of highly purified extravillous cytotrophoblast, for the first time, permits precise investigation of trophoblast function.

Ratio of fetal to maternal DNA is less than 1 in 5000 at different gestational ages in maternal blood

Using Southern hybridization with the DNA probe pY3.4, we were not able to detect fetal DNA in blood of 36 pregnant women carrying male fetuses. Gestational ages ranged from 8-40 weeks of pregnancy. Using the same DNA probe, we were able to detect the male-specific signal in experimental dilution series down to 1/5000 on autoradiograms. We conclude that the ratio of fetal DNA in maternal circulation, in contrast to previous estimations, must be lower than 1/5000.

Characterization of dispersed baboon placental cells grown in vitro using monoclonal antibodies

A major problem with placental cultures is to distinguish trophoblast cells from mesenchyme as morphological criteria alone are unreliable. Several trophoblast-specific antibodies were obtained from two hybridomas produced after murine immunization with isolated baboon villous trophoblast obtained from animals at day 33 of gestation. Monoclonal antibody BM2, having reactivity against cytotrophoblast on fixed placental sections, was found to give a positive reaction on trophoblast monolayers derived from baboon placental cells cultured in vitro. The majority of cells growing from dispersed baboon placental cells in culture were found to be cytotrophoblast.