Control of immune responses by immunoregulatory T cells

Immunoregulatory T cells play a key role in modifying the immune responses to self antigens, tumor antigens, and pathogenic organisms. This review summarizes recent data on naturally occurring CD4(+) regulatory T cells that constitutively express CD25 (CD25(+) T-reg). We examine the markers that can be used to differentiate these cells from effector T cells, what is known about their mode of action in controlling the activity of effector T cells, the antigenic specificity of CD25(+) T-reg, and their ability to survive and to be selected in vivo. We also summarize specific information on the role of CD25(+) T-reg in controlling anti-tumor responses, an area were manipulation of this subset holds particular clinical promise.