Etanercept (trade name Enbrel) is a drug that treats autoimmune diseases by interfering with tumor necrosis factor (TNF; a soluble inflammatory cytokine) by acting as a TNF inhibitor. Pfizer describes in a SEC filing that the drug is used to treat rheumatoid, juvenile rheumatoid and psoriatic arthritis, plaque psoriasis and ankylosing spondylitis. Sales reached record $3.3 billion in 2010.[1] Etanercept is a fusion protein produced through expression of recombinant DNA. That is, it is a product of a DNA "construct" engineered to link the human gene for soluble TNF receptor 2 to the gene for the Fc component of human immunoglobulin G1 (IgG1). Expression of the construct produces a continuous protein "fusing" TNF receptor 2 to IgG1. Production of Etanercept is accomplished by the large-scale culturing of cells that have been "cloned" to express this recombinant DNA construct.