Abstract: The present invention relates to a polypeptide having a sequence of 7 to 20 amino acid residues, which is capable of modulating the immunosuppressive properties of a viral protein or a fragment thereof, against the host in which it is expressed (immunosuppression-modulatory sequence) when it substitutes the homologous sequence of the viral protein or fragment, the polypeptide including the minimum following consensus amino acid sequence: X1Y9Y10Y11CY12X2 wherein, X1 and X2 are selected to impact on the immunosuppressive properties, and Y9 to Y12 represent variable amino acid residues.