Nonmyeloablative Allogeneic Stem Cell Transplantation (NST) for Hematologic Malignancies (HM) Using Pentostatin/Low-Dose Total Body Irradiation (TBI).

Background/Patients and Methods: NST is increasingly being used as a means of establishing a graft-versus-malignancy (GVM) effect with less regimen related toxicity. Between 9/01 and 7/04, 39 patients (pts) with high risk/relapsed/refractory HM who were not candidates for full intensity allogeneic stem cell transplantation underwent NST using Pentostatin/TBI. The median age of pts was 52 years (range 22–70). The median number of prior therapies was 4 (range 0–8) including prior autologous stem cell transplantation in 22 pts. Diseases transplanted included chronic lymphocytic leukemia/indolent non-Hodgkin’s lymphoma (NHL, n=6), aggressive NHL (n=8), mantle cell lymphoma (n=3), Hodgkin’s disease (n=6), myeloproliferative disorders (n=4), myelodysplastic syndromes (n=4), and acute myelogenous leukemia (AML, n=8). Conditioning consisted of Pentostatin 4 mg/m2 daily on day −21, −20, and −19, followed by 200 cGy TBI on day −1. Post-grafting immunosuppression consisted of cyclosporine/mycophenolate mofetil.

Results: Stem cell transplantation was from matched related (n=14) or unrelated (n=25) donors. Death prior to 100 days post transplant occurred in 7 patients. Grade III/IV toxicities included hematologic (n=10 pts), infectious (n=5) and other non-infectious (n=4). The median nadir values (day −21 to day 0) for hemoglobin, neutrophil count and platelet count were 10.7 g/dl (range 7.8–12), 1056/mm³ (range 0–5336), and 174/mm³ (range 24–523) respectively. Three pts failed to engraft; two patients with myelofibrosis (both of whom had autologous reconstitution) and one patient with high risk AML (who died of complications of fungal sepsis without hematologic recovery). The median chimerism values for CD3+ cells and WBC at day 28 are 80% and 95% donor cells respectively. The median chimerism values for CD3+ and WBC at day 70 are 95% and 95% respectively. There have been no late graft failures. The cumulative incidence of all grades of acute graft-versus-host disease at day 100 was 40% and was more common in unrelated donor transplants (60% vs. 15%, P=0.012). Chronic graft-versus-host disease has developed in 69% of patients. The cumulative incidence of relapse for all patients is 30%, and is lower for unrelated donor transplants than matched related donor transplants (46% vs. 20%, P=0.02). The probability of event-free and overall survival at two years is 52% and 56% respectively.

Conclusions: This regimen is associated with acceptable toxicity. Engraftment has not been an issue with the exception of two pts with myelofibrosis. Pts receiving unrelated donor grafts have a higher incidence of graft-versus-host disease and a lower relapse rate. This represents indirect support for the presence of a GVM effect. A prospective study using a modified Pentostatin schedule (starting at day − 10) is ongoing based on the nadir of host T-cells identified in this study.