Attempts to identify trophoblast in peripheral blood during pregnancy using monoclonal antibody H315

In view of its potential importance in antenatal diagnosis of genetic disease, we have used flow cytometry to attempt to enumerate trophoblast cells in the peripheral blood of pregnant females. As a trophoblast marker we have used the monoclonal antibody (MAB) H315, which reacts with placental-type alkaline phosphatase (PLAP) associated with the cell-membrane of the syncytiotrophoblast. We analyzed blood leucocytes from 62 pregnant females between 6 and 22 weeks' gestation, 26 nonpregnant females, and 21 males. Overall, we detected more H315+ cells in pregnant than in nonpregnant female blood but, because of the wide variation in both groups, we found no statistically significant difference between them. We were unable to detect H315+ cells in 25% of pregnant females within the resolution of the technique. There was, in contrast, a significant difference between the number of H315+ cells in pregnant females and males. Because we were unable to demonstrate other trophoblast markers on H315+ cells isolated from maternal peripheral blood, the origin of these cells is unclear. This implies that these cells may be an unsuitable source of material for antenatal diagnosis.