Mesenchymal stem cells made into nucleus pulposus cells

Lumbar disc degeneration is a significant cause of morbidity.  Given that the key cells maintaining the mass of the disc are nucleus pulposus cells, one of the aims in regenerative medicine has been to treat disc degeneration by administration of stem cells. 

However, one major question arises, would it be more beneficial to administer stem cells into the degenerating disc with the hope that they regenerate in vivo, or would it be better to induce new nucleus pulposus cells in vitro by differentiation and then inject them in vivo? 

In a recent paper (Tao et al. Differentiation of mesenchymal stem cells into nucleus pulposus cells in vitro. J Huazhong Univ Sci Technolog Med Sci, 2008 Apr;28(2):156-8)  the generation of nucleus pulposus cells was reported using a very interesting differentiation-inducing protocol. 

The investigators fluorescently-labelled mesenchymal stem cells, which are already in the clinic and co-cultured them with nucleus pulposus cells. 

The mesenchymal stem cells differentiated into cells that morphologically resembled nucleus pulposus cells and expressed the nucleus pulposus markers Sox-9, aggrecan, and collagen II. 

Interestingly, only co-culture in a contact-dependent manner was able to induce differentiation of the mesenchymal stem cells. 

These data suggest that it may be possible to mass-produce artificial nucleus pulposus cells using in vitro systems that can be scalable.