A composition for modulating the immune response in a mammal comprising a pharmaceutically acceptable carrier solution and a plurality of biodegradable nanoparticles, wherein the nanoparticles comprise a targeting moiety that is able to bind selectively to the surface of a T lymphocyte cell and/or of a vascular endothelial cell and wherein the nanoparticles further comprise leukaemia inhibitory factor (LIF). Nanoparticle-mediated targeted delivery of LIF can be used a means to guide tolerogenesis in a patient and has immediate clinical application for recipients of organ grafts and also for patients suffering from autoimmune disease.