The interferons (IFNs) and their receptors are a subfamily of cytokines and represent early elements in innate and adaptive immunity. About 10 mammalian interferon species (IFN-α, IFN-β, IFN-ϵ, IFN-κ, IFN-ω, IFN-δ, IFN-τ, IFN-ν, IFN-ζ, and IFN-γ) have been discovered, but only seven are found in humans.

As in most cytokines and growth factors, the actions of interferons are mediated by an interaction with specific cell surface receptors.

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IFN-β1a and IFN-β1b have been approved by the FDA for the treatment of relapsing-remitting multiple sclerosis. Clinical trials for IFN-α, before and after approval, focused on cancers and viral diseases. To date, IFN-αs are approved for the treatment of hairy cell leukemia, malignant melanoma, follicular lymphoma, condylomata acuminata (genital warts), AIDS-related Kaposi sarcoma, and chronic hepatitis B and C; IFN-βs for multiple sclerosis; and IFN-γ for chronic granulomatous disease and malignant osteopetrosis. In addition, off-label use of IFN-α is prevalent in many cancers, especially in bladder and renal cancers, often as an adjuvant in conjunction with other therapeutics.