A cell-penetrating peptide characterized in that it comprises an amino acid sequence consisting of a beta-alanine or a serine in N-terminal position, linked to a sequence consisting of 9 consecutive amino acids from the sequence RXWXRLWXRLR (SEQ ID NO:7), wherein X in position 2 is R or S and X in positions 4 and 8 are, independently from each other, W or F.