CD4 and autoimmune disease: Treg cells represent a subset of CD4+ T lymphocytes with significant immunosuppressive capabilities.265 Impairments in the function of Treg cells or a deficiency in their numbers can result in the breakdown of immune tolerance and the development of autoimmune diseases within the body.266 Consequently, induced Treg cells hold promise for the treatment of autoimmune diseases and the restoration of immunological self-tolerance.267,268 Picciotto et al.118 engineered mRNA to encode a fusion protein of human serum albumin IL-2 mutein (HSA-IL2m) with an extended half-life.