Helios is a member of the Ikaros family of zinc finger transcription factors.  It contains a C-terminal region composed of 2 zinc-finger domains that mediate dimerization between the family members.  Helios was originally cloned from a mouse thymoma line. It is mainly expressed in peripheral T cells and thymocytes.  It is found at high levels in regulatory T cells from the Thymus but not peripherally induced Tregs.  Helios plays an important role in T cell development and homeostasis.  Overexpression of Helios profoundly alters αβ T cell differentiation and activation.  It has been determined that silencing of Helios in B cells is critical for maintaining normal B cell function.  Helios is involved in tumor immunity.