Regeneration of lesioned corticospinal tract fibers in the adult rat induced by a recombinant, humanized IN-1 antibody fragment

Axons in the CNS of higher vertebrates generally fail to regenerate after i njury. This lack of regeneration is crucially influenced by neurite growth inhibitory protein constituents of CNS myelin. We have shown previously tha t a monoclonal antibody (mAb IN-1) capable of binding and neutralizing Nogo -A, a myelin-associated inhibitor of neurite growth, can induce long-distan ce axonal regeneration and increased structural plasticity with improved fu nctional recovery in rat models of CNS injury. In this paper we demonstrate that a partially humanized, recombinant Fab fragment (rIN-1 Fab) derived f rom the original mAb IN-1, was able to promote long-distance regeneration o f injured axons in the spinal cord of adult rats. When infused into a spina l cord injury site, regrowth of corticospinal fibers in 11 of 18 animals wa s observed after a survival time of 2 weeks. Regenerating fibers grew for > 9 mm beyond the lesion site and arborized profusely in the distal cord. Reg enerated fibers formed terminal arbors with varicosities in the spinal cord gray matter, strongly resembling synaptic points of contact to neurons in the spinal cord distal to the lesion. In animals that had received a bovine serum albumin solution or a recombinant IN-1 fragment that had been mutate d in the antigen binding site (mutIN-1 Fab), no significant growth beyond n ormal lesion-induced sprouting was observed. Neutralization of endogenous n erve growth inhibitors represents a novel use of recombinant antibody techn ology with potential therapeutic applications after traumatic CNS lesions.