Discloses a high particle density nanoparticle comprising: a) a nanosphere having a diameter of 4 nm or from 5 to 15 nm and b) an autoimmune disorder- or disease-relevant antigen-MHC complex operatively coupled to the nanosphere. Further discloses the use of said nanoparticle for diagnosing, preventing, or treating an autoimmune disorder or expanding and/or developing populations of antipathogenic, autoreactive T-cells in a subject when administered to the subject.