Disclosed in this specification is a process for producing ex vivo expanded CD4+CD25+ regulatory T cells. The process includes the steps of extracting a sample that includes peripheral blood mononuclear cells from a human donor. The extracted cells include a certain number of cells which are CD4+CD25+ regulatory T cells. The relative population of the CD4+CD25+ regulatory T cells is enhanced such that the Treg cells constitute the majority of the cells in the sample. Thereafter, the population of the enriched Treg cells, that may include third-party derived Treg cells, is expanded to produce a clinically meaningful population of cells for use in the treatment of GVHD.
