Immune Suppression by Placenta Derived Adherent Cells (PDAC) Correlate with Monocyte Chemoattractant Protein-1 and IL-2 Secretion.

Abstract

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 defined phenotypes, including for example CD200+ CD105+ CD73+ CD34− CD45− at percentages ≥70% and constitutively secrete IL-6, IL-8, and Monocyte Chemoattractant Protein-1 (MCP-1). PDACs demonstrate in vitro pluripotency in the adipogenic, osteogenic, and chondrogenic lineages. Furthermore, PDACs suppress T cell proliferation in certain Mixed Leukocyte Reaction (MLR) and the autologous EBV regression assays. Because secreted factors can powerfully modify immune responses and influence therapeutic use of cells, we report on the cytokine secretion in certain PDAC MLR and regression assays. Cytokines were measured on a Luminex system in supernatants from 6-day PDAC cultures, PDAC MLRs or PDAC regression assays. MLRs include PDACs, Dendritic Cells (DC)s, and T cells at DC/PDAC/T ratios 1/2/10. EBV regression assays included PDACs, EBV antigen-presenting cells (APC), and T cells at APC/PDAC/T ratios 1/2/10. Levels of IL-6 (11 ng/ml) and IL-8 (16 ng/ml) stayed constant in PDAC solo cultures, PDAC MLRs, and PDAC regression assays. MCP-1 concentration was 2 ng/ml in PDAC solo cultures, and non-suppressive control adherent cell MLRs and regression assays, but increased to 10 ng/ml in suppressed PDAC MLRs and PDAC regression assays. These values are consistent with reported MCP-1 serum levels. Interleukin-2 (IL-2) is both a T cell survival factor and an obligate factor for CD4+CD25+ T regulatory cells. T regulatory cells are not required for PDAC T cell suppression, but IL-2 levels consistently increase when MLR suppression by PDACs occurs. The CD4 MLR supernatants contained 65 pg/ml IL-2, and the CD8 MLR contained 35 pg/ml IL-2. In the 85% and 75% suppressed CD4 and CD8 PDAC MLRs, the IL-2 levels rose 5-fold to 331 pg/ml (CD4) and 2-fold to 67 pg/ml(CD8). These results indicate that IL-2 and MCP-1, traditionally known as stimulators of the immune response, may play a role in PDAC immune suppression. PDACs, which cause the secretion, may thus be useful therapeutic tools in the clinic.