A reduced-intensity stem cell transplant, also known as a ‘mini’ transplant, is a modified form of a procedure that replaces a patient’s blood-forming stem cells with those of a compatible donor. Mini-transplant patients receive lower doses of chemotherapy than are used in a full-intensity, or myeloablative, transplant, and, in general, receive no radiation therapy. The reduced-intensity procedure was developed for older patients and others who often can’t tolerate the harsh side effects of full-intensity treatments.
Stem cell transplants are used to treat blood-related cancers such as leukemia, myelodysplasia, myeloproliferative diseases, lymphoma, and multiple myeloma, as well as certain non-malignant blood disorders such as severe aplastic anemia. In a conventional transplant, patients receive heavy doses of anti-cancer drugs and/or radiation therapy to wipe out the bone marrow – the source of the cancer cells. Patients then receive an infusion of healthy stem cells from a compatible donor. The transplanted stem cells make their way to the bone marrow space, where they reconstitute the bone marrow and help regenerate the blood and immune system.
Reduced-intensity transplants follow the same course as conventional transplants, but with less taxing levels of drugs. Unlike conventional transplants, which seek to eliminate diseased bone marrow, reduced-intensity transplants simply suppress the recipient’s immune system enough so the donor stem cells can take root – or “engraft” – there. Some amount of killing of tumor cells may occur, but this is not the goal of the chemotherapy given prior to the transplant.
Much like a traditional transplant, the benefits of a reduced-intensity transplant are twofold: the amount of cancerous tissue is reduced, and the transplanted stem cells produce millions of healthy white blood cells, which mount an attack on cancer cells that remain in the body, a phenomenon known as the graft-versus-leukemia effect.
Despite being called ‘mini,’ reduced-intensity transplants are significant medical procedures, involving meticulous preparation and complex levels of care. The side effects of mini transplants tend to be similar to those associated with traditional transplants – including anemia, infections, and rejection, called graft-versus-host disease.