IL-2-independent generation of FOXP3+CD4+CD8+CD25+ cytotoxic regulatory T cell lines from human umbilical cord blood

Objective Since the existence of mouse naturally occurring CD4+CD25+ T regulatory (Treg) cells was demonstrated, a variety of human Treg subsets have been identified as distinct T cell populations. Here we show the establishment of novel Treg cell lines possessing unique characteristics. Methods Novel Treg cell lines, designated HOZOT, were generated by coculturing human umbilical cord blood cells with mouse stromal cell lines in the absence of exogenous IL-2 or other cytokines. HOZOT were characterized and compared with CD4+CD25+ Treg cells in terms of the CD phenotype, FOXP3 expression, suppressor activity against allogeneic MLR, anergy property, and IL-10 production. Results HOZOT were generated and expanded as normal lymphoblastoid cells with cytotoxic activity against the cocultured stromal cells. HOZOT consisted of three subpopulations as defined by phenotype: CD4+CD8+, CD4+CD8dim, and CD4−CD8+. All three subpopulations showed both suppressor and cytotoxic activities. While HOZOTʹs expression of FOXP3, CD25, GITR, and cytoplasmic CTLA-4 implied a similarity to naturally occurring CD4+CD25+ Treg cells, these two Treg cells differed in IL-2 responsiveness and IL-10 production. Conclusions Our studies introduce a new method of generating Treg cells in an IL-2-independent manner and highlight a unique Treg cell type with cytotoxic activity and a phenotype of FOXP3+CD4+CD8+CD25+.