Peptidic complex mixtures as therapeutic agents in CNS autoimmunity

Limited success with antigen-specific immunotherapies has led to the identification of novel approaches which consider the degeneracy of the T cell response, i.e. their ability to respond to multiple antigenic peptides. Random complex mixtures of polypeptides such as glatiramer acetate (GA) were among the first to be applied as immunodulators that take into account T cell degeneracy. While the mechanisms of action are not completely understood, the immunogenicity of GA, its strong major histocompatability complex (MHC) binding, immune deviation and bystander suppression all appear to be important. In the present study we have designed peptidic complex mixtures (CM) of varied lengths and compositions to test their potential as immunomodulating agents. CM were synthesized that had defined lengths and contained aa corresponding to binding motifs of MHC class II molecules relevant in multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE), specifically HLA-DRB1*1501 and HLA-DRB5*0101, which are related to MS, and H2-IA(s) associated with EAE in SJL mice. Additional CM were designed based on specificity profiles derived from positional scanning synthetic combinatorial library (PS-SCL) testing of a GA-specific T cell clone (TCC). Several mixtures were strongly stimulatory for peripheral blood mononuclear cells (PBMC) from MS patients and healthy donors suggesting a high degree of cross-reactivity with other peptide antigens. A subset of these mixtures exhibited cross-reactivity to myelin antigens and prophylactic efficacy in reducing the severity of EAE. Based on these observations we envision mixture-based peptidic compounds can be developed not only for immunotherapeutic purposes in autoimmune diseases and cancer, but also in vaccine development.