The present invention relates to immunogenic peptides comprising a T cell epitope. Said peptides are modified such that CD4+ T cell responses are obtainable that are much stronger than the CD4+ T cell responses obtained with the same peptides not comprising said modification. In particular the modification is the addition of a cysteine insertion of a cysteine or mutation into a cysteine of a residue at a position adjacent to but outside the MHC binding site of the peptide. Further disclosed are the use of such modified peptides in treating suppressing or preventing diseases such as infectious or allergic diseases and autoimmune diseases in preventing or suppressing graft rejection or in the eradication of tumor cells.
