Advances in allogeneic stem cell transplantation: directing graft-versus-leukemia at solid tumors

Allogeneic stem cell transplantation was originally developed as a method to rescue hematopoietic function following high dose "myeloablative" therapy in the treatment of hematological malignancies. In the first two decades of its use, dose-intensive chemotherapy alone was credited with curing those patients who achieved sustained remission following this procedure. However, more recently investigators have come to recognize that antineoplastic effects mediated by immunocompetent donor T-cells transplanted with the stem cell allograft can be induced against hematological malignancies. Indeed, this graft-vs-leukemia (GVL) or graft-vs-tumor (GVT) effect is now felt to represent the principal modality required to sustain durable remissions of hematological malignancies following this approach. The powerful and potentially curative nature of the GVT effect in hematological cancers has recently lured oncologists into exploring the therapeutic potential of allogeneic stem cell transplantation as an investigational approach for treatment-refractory solid tumors. We review here the development and early clinical results of allogeneic stem cell transplantation as potential immunotherapy for solid tumors.