Conditioning regimen (myeloablative, reduced-intensity)
The chemotherapy (with or without whole-body radiation) given in the days before a stem cell transplant to destroy the diseased marrow and, for donor transplants, suppress the patient's immune system so the graft is not rejected.
Myeloablative conditioning (busulfan-cyclophosphamide, cyclophosphamide-TBI, high-dose melphalan for myeloma, BEAM for lymphoma) gives maximal anti-leukaemic effect but is tolerable only under about 60; reduced-intensity and non-myeloablative regimens (fludarabine-based, low-dose TBI, treosulfan) rely on the donor immune effect and have extended allogeneic transplant to older patients at the cost of higher relapse. Regimen choice is a trade-off between relapse and toxicity (mucositis, organ damage, infertility, veno-occlusive disease). Lymphodepletion before CAR-T is a milder cousin of the same idea.