Immune reconstitution in rheumatic disease patients after autologous hematopoietic stem cell transplantation.

High-dose conditioning chemotherapy followed by autologous hematopoietic stem cell transplantation (auto-HSCT) in systemic sclerosis (SSc), lupus erythematosus (SLE), juvenile idiopathic arthritis (JIA), or rheumatoid arthritis (RA) was shown to allow eradication of the abnormal autoimmune compartment and "resetting" of the immune response, all contributing to the observed clinical response. A subset of patients has less favorable clinical outcomes after transplant, as auto-reactive memory cells may escape depletion or the regulatory immune network renewal be incomplete. Conditioning permits non-specific abrogation of the autoreactive T- and B-cell responses and eliminates the autoimmune repertoire. Re-infusion of autologous hematopoietic stem cells shortens the leucopenia duration and contributes to both hematologic and immune reconstitutions. After engraftment and neutrophil recovery, the first phase of immune reconstitution is characterized by clonal expansion of residual memory lymphocytes in response to early antigen stimulation and/or lymphopenia-induced proliferation. Renewal of the immune repertoire follows through exportation of de novo generated thymic-derived naïve T cells and bone marrow-derived naïve B cells, expansion of the regulatory network, and a shift from a pro-inflammatory to a more auto-tolerant profile. We review the well-described mechanisms of immune resetting and their relative contribution to disease control according to the transplantation regimen and the underlying rheumatic diseases.