Regulatory T-cell depletion does not prevent emergence of new CD25+ FOXP3+ lymphocytes after antigen stimulation in culture

Background The removal of human regulatory T (Treg) cells from a cellular product prior to the induction of a T-cell response has the potential to boost the total yield of antigen (Ag)-specific CD4+ and CD8+ T cells. Methods We examined the effect of this manipulation on the generation of human anti-cytomegalovirus (CMV) T-cell responses. Furthermore, we examined the clonotypic composition of Ag-specific CD4+FOXP3+ and CD4+FOXP3− T cells. Results We found that the immunomagnetic depletion of CD25+ cells had an unpredictable effect on outcome, with total yields of CMV-specific T cells either increasing or decreasing after the removal of these cells. The depletion of CD25+ cells both removed a proportion of Ag-specific T cells and failed to eliminate a substantial population of Treg cells. Furthermore, using a novel T-cell receptor clonotyping technique, we found that Ag recognition induces the expression of FOXP3 in a proportion of specific T cells; these FOXP3-expressing Ag-specific CD4+ and CD8+ T cells were no longer capable of producing inflammatory cytokines. Discussion The depletion of CD25+ cells from the starting population has a variable effect on the total yield of Ag-specific T cells, a proportion of which invariably acquire FOXP3 expression and lose effector function