Generation and expansion of human CD4+CD25+ regulatory T cells with indirect allospecificity:: Potential reagents to promote donor-specific transplantation tolerance

Background. Harnessing naturally arising CD4(+)CD25(+) regulatory T cells (T-regs) for potential adoptive cell therapy ishampered by their innate autoreactivity and their limited number. Methods. CD4(+)CD25(+) T-regs were purified from peripheral blood of human leukocyte antigen (HLA) DRI*0101(+)A2(-) individuals, and stimulated with autologous monocyte-derived dendritic cells (DCs). Results. Here we show that CD4(+)CD25(+) T-regs specific for an HLA A2 (103-120) peptide can be selected from the peripheral blood CD4(+)CD25(+) T cell population of a healthy individual and detected using a tetramer comprised of HLA DRB1*0101 and the A2 peptide. The selected cells can be expanded substantially (i.e., a 1600-fold increase over a two-week period) by T-cell receptor (TCR) stimulation and high-doses of interleukin-2 (IL-2). The CD4(+)CD25(+) T-regs with indirect allospecificity for the A2 peptide showed more potent antigen-specific suppression than polyclonal CD4(+)CD25(+) T-regs. Conclusions. These data may pave the way for clinical studies using CD,4(+)CD25(+) Tregs with indirect allospecificity as therapeutic reagents for the induction of donor-specific transplantation tolerance.