Etanercept is a drug that treats autoimmune diseases by interfering with the tumor necrosis factor

Tumor necrosis factor

Tumor necrosis factor is a cytokine involved in systemic inflammation and is a member of a group of cytokines that stimulate the acute phase reaction...

 (TNF, a part of the immune system) by acting as a TNF inhibitor

TNF inhibitor

Tumor necrosis factor promotes the inflammatory response, which in turn causes many of the clinical problems associated with autoimmune disorders such as rheumatoid arthritis, ankylosing spondylitis, Crohn's disease, psoriasis, hidradenitis suppurativa and refractory asthma. These disorders are...

. 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.

Etanercept is a fusion protein

Fusion protein

Fusion proteins or chimeric proteins are proteins created through the joining of two or more genes which originally coded for separate proteins. Translation of this fusion gene results in a single polypeptide with functional properties derived from each of the original proteins...

 produced through expression

Gene expression

Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as ribosomal RNA , transfer RNA or small nuclear RNA genes, the product is a functional RNA...

 of recombinant DNA

Recombinant DNA

Recombinant DNA molecules are DNA sequences that result from the use of laboratory methods to bring together genetic material from multiple sources, creating sequences that would not otherwise be found in biological organisms...

.