Placenta Derived Stem Cells (PDAC) Suppress the Allo-MLR and the EBV Regression Assay.

The placenta is a readily available and ethically non-controversial source of large amounts of therapeutic stem cells. Placenta Derived Adherent Cells (PDACs) are isolated from the placenta by one of several methods including physical disruption of tissue from several different anatomical sites within the placenta that include the amniotic membrane, chorion, placental cotyledons, or any combination thereof. Flow cytometry analysis showed that PDACs isolated from certain sites exhibit phenotypes, including for example CD200+ CD105+ CD73+ CD34− CD45− at percentages ≥70%. Furthermore, PDACs demonstrate in vitro pluripotency. Here, we report on the immune suppressive capabilities of PDACs.

PDACs were introduced in a six-day mixed leukocyte reaction, using purified CD8⁺ T cells as effectors and allogeneic dendritic cells (DC)s. The ratios were T/DC/PDAC=10/1/2. Alternatively, an EBV regression assay, measuring T cell proliferation against EBV expressing antigen presenting cells (APCs) generated from healthy donors was performed. Here, the T/APC/PDAC ratios were 10/1/2. In this system, PDACs inhibited the proliferation, as measured by CFSE dilution, of CD8⁺ T cells >50% (range: 0–95%, SEM 20%). The suppression was the same whether only CD4⁺ or CD8⁺ cells were used, or whether equal amounts of CD4⁺ and CD8⁺ T cells were added. When Natural Killer (NK) cells were used, with 50 U/ml IL-2, as effectors instead of T cells, the suppressive effect was 45% (range: 40–65%, SEM 5%). Different PDAC preparations suppressed the reactions equally well. Separation of certain PDACs and MLR by a transwell membrane reduced the suppression by 21%, suggesting that part of the suppression was contact dependent. Suppression by other types of PDACs, on the other hand, was 75% contact dependent. When CD4⁺CD25⁺ T regulatory cells were removed by magnetic bead separation, the suppression in the regression assay was unchanged.

These results suggest that PDACs may have potential therapeutic use as universal immune suppressive donor cells. The suppression is independent of T regulatory cells.