CD8A and thymoma: In a thymoma model expressing ovalbumin (OVA) intraperitoneal (i.p.)administration of recombinant IL-21 significantly inhibited tumor growth and induced durable survival compared to IL-2 and IL-15, the effect being CD8+ T cell-dependent, IL-21 increasing the number and cytotoxicity of (OVA) CD8+ T cells (25).