Nanoparticle compositions for sustained therapy

A complex comprising a nanoparticle core coupled to a plurality of antigen-MHC class II complexes (pMHCIIs), the nanoparticle core comprising iron or an iron oxide and having a diameter which is from about 5 nm to about 25 nm, wherein the antigen is an autoimmune disease relevant antigen and wherein the number of coupled pMHCIIs per nanoparticle surface area is from about 0.4 pMHC/100 nm2 to about 5 pMHC/100 nm2, wherein the pMHCIIs are coupled to a maleimide functionalized end of a polyethylene glycol (PEG) linker that is less than about 5 kilodaltons in molecular weight, wherein a non-maleimide functionalized end of the polyethylene glycol (PEG) linker is coupled to the nanoparticle core, and the non-maleimide functionalized end comprises an alkoxy, an alkyl, alkyl-amide-alkyl, alkyl-ester-alkyl, alkyl-amide, alkyl-acid, or alkyl-ester, wherein the complex differentiates an activated T cell or a memory T cell into an IL-10 producing TR1 cell.