1. ¹Transplantation Biology Programme, Clinical Research Division, Fred Hutchinson Cancer Research Center, Seattle, WA, USA
2. ²Department of Hematology, University of Liège, Liège, Belgium
3. ³Department of Medicine, University of Washington School of Medicine, Seattle, WA, USA

Correspondence: Dr BM Sandmaier, Fred Hutchinson Cancer Research Center, 1100 Fairview Ave N, D1-100, PO Box 19024, Seattle, WA 98109-1024, USA. E-mail: bsandmai@fhcrc.org

Received 7 April 2006; Revised 1 June 2006; Accepted 13 June 2006; Published online 27 July 2006.

Abstract

Allogeneic hematopoietic cell transplantation (HCT) following nonmyeloablative conditioning has been extensively evaluated in patients with hematologic malignancies who are ineligible for conventional HCT because of age or medical comorbidities. Nonmyeloablative regimens have led to an initial state of mixed hematopoietic chimerism defined as coexistence of donor- and host-derived hematopoiesis. While nonmyeloablative regimens have been associated with reduced regimen-related toxicities in comparison with conventional myeloablative conditioning, graft rejection, graft-versus-host disease (GVHD), and disease progression have remained significant challenges. In this article, after briefly introducing current techniques for chimerism assessment, we describe factors affecting donor chimerism levels after nonmyeloablative conditioning, and then review data suggesting that chimerism assessment early after HCT might help identify patients at risk for graft rejection, GVHD and relapse/progression. Finally, we discuss how these observations have opened the way to further research protocols evaluating manipulation of postgrafting immunosuppression, and/or infusion of donor immune cells.