Suppression of immune response via inhibition of cathepsin S

A method for inhibiting invariant chain proteolysis from class II MHC/invariant chain complexes in a mammalian cell, comprising:

• administering to said cell an agent which inhibits cathepsin S.

A method for reducing the competency of class I MHC molecules for binding antigenic peptides in a mammalian cell, comprising:

• administering to said cell an agent which inhibits cathepsin S, said agent inhibiting invariant chain proteolysis from class II MHC/invariant chain complexes to reduce the competency of class II MHC molecules for binding antigenic peptides in said cell.

A method for reducing presentation of antigenic peptide by class II MHC molecules in a mammalian cell, comprising:

• administering to said cell an agent which inhibits cathepsin S, said agent inhibiting invariant chain proteolysis from class II MHC/invariant chain complexes to reduce presentation of antigenic peptide by class II MHC molecules in said mammal.

An inhibitor of cathepsin S comprising

• a peptide-based inhibitor of cathepsin S,
• wherein said peptide-based inhibitor of cathepsin S is based upon a peptide sequence which comprises at least about 2-20 consecutive residues from a preferred invariant chain cleavage site of cathepsin S.