Exploiting graft-versus-tumour responses using donor leukocyte infusions.

Allogeneic stem cell transplantation (SCT) has become the treatment of choice for some patients with haematological malignancies, allowing dose escalation of chemo-radiotherapy beyond the limits imposed by bone marrow toxicity. However, it is now apparent that dose escalation alone does not eradicate the malignancy in many cases and that an associated immune-mediated graft-versus-malignancy effect may be equally important. Its presence is supported by the following observations: anecdotal reports that patients with relapsed leukaemia following SCT may re-enter remission after withdrawal of immunosuppressive drugs; the lower risk of relapse associated with the development of graft-versus-host-disease (GVHD); and an increased risk of relapse in patients receiving syngeneic transplants or T-cell depleted allogeneic marrow grafts. More directly compelling evidence has been provided by the efficacy of donor lymphocyte infusions, particularly for relapsed chronic-phase CML. Issues that remain to be resolved include the precise nature of the effector cells and their target antigens, the best strategies for separating graft-versus-malignancy from GVHD, the role of adjuvant chemotherapy/cytokines, and the role of non-myeloablative transplantation.