Antigen-targeted liposome-encapsulated methotrexate specifically kills lymphocytes sensitized to the nonapeptide of myelin basic protein

Abstract

Antigen targeting of liposome-encapsulated cytotoxic drugs to specific lymphocytes may be a useful approach for antigen-specific immunosuppressive treatment of autoimmune diseases in which a specific antigen is involved. The feasibility of utilizing this approach was investigated using experimental allergic encephalomyelitis as an animal model for an autoimmune response. The encephalitogenic determinant of myelin basic protein for the guinea pig is contained in residues 114–122, the so-called nonapeptide. We have acylated the nonapeptide at its N-terminal to anchor it in the lipid bilayer of liposomes containing the cytotoxic drug methotrexate. The nonapeptide on the surface of the liposomes then allows targeting of the liposomal methotrexate in vitro to anti-nonapeptide T lymphocytes obtained from guinea pigs with experimental allergic encephalomyelitis. Treatment with the nonapeptide-targeted liposomal methotrexate inhibited proliferation of anti-nonapeptide lymphocytes significantly more than that of control lymphocytes. These included non-sensitized lymphocytes, stimulated with phytohemagglutinin, or lymphocytes sensitized to different, unrelated proteins, the purified protein derivatives of tuberculin and keyhole limpet hemocyanin, and stimulated with their specific antigens. Furthermore, nonapeptide-targeted liposomes had a greater cytotoxic effect on anti-nonapeptide T cells than untargeted liposomes. The results indicated that specific targeting to and killing of anti-nonapeptide cells was achieved, although improvements of the treatment are necessary before its use can be attempted in vivo.