Abstract: The invention relates to means for in vivo delivery of a composition into the human or animal central nervous system or spinal cord, wherein the composition comprises a non-toxic, proteolytic fragment of tetanus toxoid in association with at least a molecule having a biological function, and said molecule is capable of in vivo retrograde axonal transport and transynaptic transport into the CNS or spinal cord of the human or animal. In a particular embodiment, the composition comprises a fragment C and a fragment B of tetanus toxoid or a fraction thereof of at least 11 amino acid residues. The composition can further comprise a fraction of fragment A of tetanus toxoid.