Revival of recombinant IL-2 therapy - approaches from the past until today.

Interleukin-2 (IL-2) was one of the first cytokines discovered and its central role in T cell function soon led to the notion that the cytokine could specifically activate immune cells to combat cancer cells. Recombinant human IL-2 (recIL-2) belonged to the first anti-cancer immunotherapeutics that received marketing authorization and while it mediated anti-tumor effects in some cancer entities, treatment was associated with severe and systemic side effects. RecIL-2 holds an exceptional therapeutic potential, which can either lead to stimulation of the immune system - favorable during cancer treatment - or immunosuppression - used for treatment of inflammatory diseases such as autoimmunity. Due to these pleiotropic immune effects, recIL-2 therapy is still a hot topic in research and modified recIL-2 drug candidates show ameliorated efficacy and safety in pre-clinical and clinical studies. The Immune Safety Avatar (imSAVAR) consortium aims to systemically assess mechanisms leading to adverse events provoked by recIL-2 immunotherapy as a use case in order to aid safety evaluation of future recIL-2-based therapies. Here, we summarize the historical use of recIL-2 therapy, associated side effects, and describe the molecular basis of the dual role of IL-2. Finally, an overview of new recIL-2 compounds and delivery systems, which are currently being developed, will be given, highlighting a possible comeback of recIL-2 therapy.