Clonogenic tumor cells contained within hematopoietic stem cell
(HPC) grafts may contribute to relapse following autologous transplantation.
Graft purging involves either in vivo or ex vivo HPC manipulation
in order to reduce the level of tumor cell contamination.
Some phase II trials suggest that patients who receive purged products
may have a superior transplant outcome. Phase I trials demonstrate
the feasibility of purging methods including ex vivo graft incubation
with chemotherapeutic drugs, monoclonal antibodies and complement,
and CD34+ cell selection. A phase II trial in follicular non-Hodgkin’s
lymphoma demonstrates that patients who receive HPC products purged
negative for bcl-2 gene rearrangements have a superior outcome, compared
with patients who receive polymerase chain reaction (PCR)-positive
products. This finding, however, has not been confirmed in a randomized
trial. HPC purging has demonstrated no benefit in a phase III
trial in myeloma. Phase II trials in acute myelogenous leukemia show
comparable outcomes for patients who receive either purged or
unpurged HPC grafts. Limitations of purging include possible progenitor
cell loss, delayed engraftment, and qualitative immune defects following
transplant. Data to justify routine use of HPC graft purging are
insufficient. Phase I and II data support development of phase III trials
of both in vivo and in vitro purging methods.
Department of Hematology and Hematopoietic Cell Transplantation, City of Hope National Medical Center