Immune mechanisms underlying the beneficial effects of autologous hematopoietic stem cell transplantation in multiple sclerosis.

A recent phase I/II clinical trial drew serious attention to the therapeutic potential of autologous hematopoietic stem cell transplantation (AHSCT) in multiple sclerosis. However, questions were raised as to whether these beneficial effects should be attributed to the newly reconstituted immune system per se, or to the lymphoablative conditioning regimen-induced immunosuppression, given that T-cell depleting combinational drug therapies were used in the study. We discuss here the possibility that both AHSCT and T-cell depleting therapies may re-program alternatively the immune system, and why transplantation of CD34+ hematopoietic stem cells may offer AHSCT a possible advantage regarding long-term remission.