A patient with progressive prolymphocytic leukemia (PLL) received an allogeneic stem cell transplant using a reduced intensity conditioning regimen to avoid prohibitive toxicities. Early in the post-transplant period, a high donor-derived CD8+ count was observed. One year from transplantation, the patient was in complete remission, fully donor chimeric and with a normal performance status, suggesting that this approach may represent a useful treatment option in patients with refractory PLL.