Expression of regulatory T-lymphocyte phenotype in human fetal hemopoietic and lymphoid cell culture.

Cells with regulatory T-cell phenotype (Treg, CD4+CD25(hi)) were not detected in human fetal thymus, liver, bone marrow, spleen, and among blood mononuclears of 14-28-week gestation. The cells of the majority of these fetal thymuses express Treg specific marker (FOXP3 transcription marker) gene. Culturing of fetal liver and bone marrow cells on a monolayer of thymic epithelial cells induced expression of FOXP3 gene, but induction of CD4+CD25+ membrane phenotype was detected in only 1 of 8 studied cultures (in liver and bone marrow cells). Induction of Treg differentiation is to a greater extent determined by the characteristics of hemopoietic organ cells than of thymic epithelial cells.