The role of chemotherapy in hematopoietic stem cell transplantation for autoimmune disorders: From lymphoablative to myeloablative conditioning protocols

Hematopoietic stem cell transplantation (HSCT) is a medical procedure used mainly for the treatment of onco-hematologic disorders. Over the last two decades, autologous HSCT has been explored for the treatment of neurologic autoimmune diseases (ADs), being multiple sclerosis (MS) the most frequent indication in this setting. HSCT is characterized by the sequential administration of a conditioning regimen (CR) and the infusion of hematopoietic stem cells (HSCs), previously collected either by the individual himself in the autologous transplant (AHSCT), or by a healthy donor in allogeneic HSCT. CR consists of the administration of high-dose chemotherapy and/or total body irradiation (TBI), that in ADs is usually associated with an immunodepleting serotherapy, either by an animal-derived polyclonal serum or a monoclonal antibody (MoAb), to induce intense immunosuppression. CRs are classified according to the European Society for Blood and Marrow Transplantation (EBMT) guidelines for HSCT in ADs in three grades of intensity according to the degrees of depletion of the hemato-lymphopoietic system induced. In the present chapter, after a brief overview of mobilization and CR adopted in the neurologic autoimmune setting, the role of chemotherapy in HSCT will be discussed, providing a historical perspective on the use of different regimens and summarizing the available evidence on potential associations between CR and outcomes.