Abstract
Studies so far indicate that reduced intensity transplantation (RIT) may have an important role in treating patients with primary immunodeficiency disease (PID). Unlike more standard approaches, such regimens can be used without severe toxicity in patients with severe pulmonary or hepatic disease. RIT also offers the advantage that long-term sequelae such as infertility or growth retardation may be avoided or reduced. RIT appears to be most appropriate for those patients with significant co-morbidities (eg T cell deficiencies) and those undergoing unrelated donor haematopoietic cell transplantation. More studies are required using pharmacokinetic monitoring (eg busulphan, treosulfan and alemtuzumab) and varying stem cell sources to optimise graft vs marrow reactions and minimise graft vs host disease. In certain PID patients RIT will be the “first step” towards establishing donor cell engraftment; second infusions of donor stem cells, donor lymphocyte infusions, or a second myeloablative HCT, which appears to be well tolerated, may be required in some patients with low level donor chimerism or graft rejection.