CGP 77116 is an altered peptide ligand (APL) designed around an immunodominant epitope of human myelin basic protein (MBP) corresponding to amino acids 83-99, for the treatment of multiple sclerosis (MS). Substitution of a key T cell receptor contact residue with alanine results in a non-stimulatory peptide analogue. Recent evidence suggests that a T cell-mediated immune response against immunodominant myelin protein peptides such as MBP (83-99) is involved in MS pathogenesis (1). MS results when the immune system is unable to keep autoreactive T cells from entering the central nervous system where they initiate demyelination of myelin sheaths. By targeting MBP autoreactive T cells, CGP 77116 may downregulate the MBP-specific immune response and lead to amelioration of MS.