Allogeneic peripheral blood stem cell transplantation

The use of mobilized peripheral blood stem cells (PBSC) for hematopoietic reconstitution following myeloablative chemoradiotherapy has been well shown to be an effective and probably superior alternative to autologous bone marrow support. Early concerns of increased engraftment failure risk (owing to a decreased number of multipotential stem cells), increased graft vs. host disease risk (due to an excess of circulating T cells) and donor safety concerns, however, delayed efforts to use mobilized PBSC for allogeneic transplantation. Recent reports, however, have demonstrated excellent donor tolerance of G-CSF administration and yields of CD34+ progenitor cell collections. Engraftment with allogeneic peripheral blood stem cells has been rapid and sustained in several early clinical series. Surprisingly, no apparent increase in risk of moderate to severe acute graft versus host disease has occurred with unmanipulated mobilized PBSC. Despite this early promise, long-term safety concerns of administration of recombinant myeloid growth factors to normal donors have been raised. Long-term lymphohematopoietic engraftment also needs to be more conclusively demonstrated. Optimal mobilizing and collecting strategies also need to be defined to ensure donor safety and comfort. The possible roles of PBSC in the matched unrelated donor and mismatched related donor settings need to be defined before widespread adoption of mobilized PBSC as an alternative to bone marrow for allogeneic transplantation. Prospective randomized trials are recommended to definitively evaluate long term donor safety and recipient hematopoietic and immunologic reconstitution.