FOXP3 and myeloid sarcoma: Regulatory FOXP3+ T cells (Tregs) are indispensable for immune homeostasis, playing a crucial role in suppression of exacerbated inflammatory immune responses and maintaining immune tolerance (1, 2), Accumulating evidence indicates reduced Treg numbers and compromised function in autoimmune diseases such as multiple sclerosis (MS), type 1 diabetes (T1D) or systemic lupus erythematosus (SLE) (3–6).