A therapeutic composition comprising a poly- nucleotide having at least one nucleotide selected from the group:(i) a nucleotide having the formula P-S-B-Sig wherein P is a phosphate moiety, S is a sugar moiety, B is a pyrimidine, purine or 7-deazapurine moiety, P being attached at the 3' and/or the 5' position of S when the nucleotide is a deoxyribonucleotide and at the 2',3' and/or 5' position wh