Abstract: The invention provides classes of novel compounds that accelerate peptide loading to DR in the absence of DM and related pharmaceutical compositions. The invention also provides conjugates of these compounds with peptides, antigens or other MHC-based therapeutics, including peptides that self-catalyze their loading onto MHC Class II molecules. Methods are provided for modulating an immune response in a subject. Also disclosed are methods of using the novel compounds, e.g., in combination with MHC-based therapeutics, for the treatment of autoimmune diseases and for the manufacture of medicaments. Methods of improving loading of viral peptides and tumor peptides for enhancing the CD4 T cell response following vaccination against viruses or tumors, and related vaccines, are also provided.