Promoting immunity during chronic infection—The therapeutic potential of common gamma-chain cytokines

• IL-2 offers no clinical benefit as adjuvant therapy in HIV infection.
• IL-15 shows no efficacy in non-human primate SIV infection.
• IL-7 treatment increases repertoire and function of T cells in HIV clinical trials.
• IL-21 essential for effector CD8+ T cell function during chronic viral infection.
• Clinical and pre-clinical data suggest promise for IL-7 and IL-21 co-therapy.

The continued global burden wrought by chronic infectious disease is unrelenting. Current therapies have curbed the severity of disease for patients, but Human Immunodeficiency Virus (HIV) and Hepatitis B (HBV) infection remain incurable and Mycobacterium tuberculosis (MTB) is rapidly becoming resistant to our existing antibiotics. Much attention has been given to enhancing T cell immunity through the use of certain common gamma-chain cytokines, which have proven to be essential and necessary for T cell survival and function. This article reviews the pre-clinical and clinical literature surrounding IL-2, IL-7, IL-15 and IL-21 and we comment on the potential therapeutic promise of these cytokines as adjuvant treatments for chronic infectious diseases.