Nanoparticle gels that deliver an immunostimulatory molecule and an inhibitor of an immunosuppressive factor to tumours over a period of a few days are reported online this week in Nature Materials. When injected in melanoma tumours in mice, the nanoparticles facilitate sustained delivery of the molecules, delay tumour growth and significantly increase the survival time of the mice.

One of the mechanisms by which aggressive cancers such as melanomas evade the immune system is by the secretion, from tumours, of immunosuppressive factors such as TGF-beta. This protein inhibits the effects of Interleukin-2 (IL-2) - a signalling molecule used in conventional immunotherapy that mediates immune responses. Tarek Fahmy and colleagues designed a nanoparticle consisting of a protective lipid bilayer surrounding a degradable polymer gel encapsulating a lipid-soluble TGF-beta inhibitor and the water-soluble IL-2 immunostimulatory protein. The researchers show that the nanoparticles enhance the activity of innate and adaptive immune responses against subcutaneous and metastatic melanomas in tumour-bearing mice.