Regulatory T cells that express CD4 and CD25 (interleukin 2 receptor) antigens, with immunomodulating activity.. CD4+CD25+ T regulatory cells (Tregs), a subset of CD4+ T cells expressing high levels of CD25 and the transcription factor Foxp3, are essential in maintaining immunologic homeostasis, preventing autoimmunity by suppressing self-reactive T cells; CD4+CD25+ Tregs may induce tolerance to allogeneic organ transplants such as hematopoetic stem cell transplants (HSCTs).