Preparation of fibroblast-free cytotrophoblast cultures utilizing differential expression of the CD9 antigen

The leukemia-associated antigen CD9 is present on a variety of normal cells, with apparent variable expression on normal human fibroblasts. In this study, we demonstrate by immunoperoxidase staining and direct binding studies that the CD9 antigen is uniformly expressed on normal human fibroblasts grown from first trimester and term placenta, embryonic fetal fibroblasts, and from human adult and fetal skin fibroblasts. Higher CD9 expression was present on fetal cells. CD9 antigen was not present on trophoblast. Over 99% of fibroblasts could be absorbed onto antibody to the CD9 antigen conjugated to magnetic beads. By applying this selective immunoadsorption of fibroblasts to term placental cytotrophoblast preparations, we demonstrated that fibroblast contamination could be nearly completely eliminated. This is a novel technique for purifying primary trophoblast cultures and may have wider applicability in cell culture of other cell types.