Current concepts in allogeneic hematopoietic stem cell transplantation.

Progress in allogeneic SCT will depend on several factors including the advances in the conventional treatment of diseases treated currently with allogeneic SCT, the expansion of the donor pool, the selective control of GVHD, the development of more effective and less toxic preparative regimens to eradicate the neoplastic cell population, the characterization of a new generation of hematopoietic growth factors and cytokines and the development of newer and safer techniques for ex-vivo manipulation of stem cells. The use of hematopoietic growth factor-mobilized donor progenitor cells collected from the peripheral blood has been associated with a rapid hematopoietic engraftment without an increase in the incidence of acute GVHD compared to allogeneic BMT, an increased donor acceptance, elimination of the risk of general anesthesia and a decreased cost. The use of nonmyeloablative conditioning regimens prior to SCT represents a novel treatment approach that may lead to reduced toxicity and an extended use of this treatment in older patients and those with co-morbid conditions and in the treatment of malignant and non-malignant disorders. This approach may play a role in inducing tolerance for solid organ transplantation and in utilizing the GVM effect to treat solid tumors that are not fully responsive to myeloablative cytotoxic regimens. The optimal intensity of cytoreduction and immunosuppression is not well defined. GVHD and disease recurrence remain a challenge. Promising results have been reported in patients with refractory hematologic malignancies as well as in metastatic renal cell cancer, but the ultimate role of this treatment modality remains to be defined pending prospective, well designed, randomized trials.