Irreversible myelosuppression after fludarabine-melphalan conditioning: observations in patients with graft rejection

“Nonmyeloablative” conditioning regimens, including the fludarabine-melphalan regimen, are thought to induce engraftment by virtue of host immunosuppression and to spare myeloid precursors.^1-4  At our institution, there were 4 graft rejections among more than 100 patients conditioned with fludarabine and melphalan. Three of these cases occurred in patients with relatively normal hematopoiesis prior to transplantation, providing an opportunity to assess the myelosuppressive properties of fludarabine-melphalan in vivo.

Patient 1 had sickle cell disease. She received 20 mg/m² fludarabine daily for 5 days and 140 mg/m² melphalan for 1 day. Stem cells from her HLA-identical brother were incubated with alemtuzumab. She received no posttransplantation graft-versus-host disease (GVHD) prophylaxis. Neutrophil and platelet recovery of donor origin occurred by day 16. On day 18, a febrile syndrome was followed by rapid decline in blood counts. On day 30, back-up autologous stem cells were reinfused. Autologous recovery occurred by day 40 after the initial donor transplantation.

Patient 2 had refractory anemia with ringed sideroblasts (RARS). White blood cell and platelet counts were normal and marrow was normocellular (Figure 1A-B). Conditioning consisted of 25 mg/m² fludarabine daily for 5 days, 20 mg alemtuzumab daily for 5 days, and 140 mg/m² melphalan for 1 day. Stem cells from her one antigen-mismatched brother were infused on day 0. Tacrolimus was given after transplantation. By day 13 the absolute neutrophil count (ANC) recovered to 0.8 × 10⁹/L, without platelet recovery. On day 16 a febrile syndrome occurred, followed by decline in blood counts. A bone marrow aspirate on biopsy on day 21 was hypocellular without hematopoiesis. On day 28 after conditioning with antithymocyte globulin, she received additional donor cells. She never recovered her counts. A bone marrow aspirate on day 46 was hypocellular without hematopoiesis (Figure 1C-D). She died on day 53 after the transplantation.

Patient 3 had mantle cell lymphoma. Blood counts were normal and bone marrow was normocellular (Figure 1E-F). Small lymphoid aggregates occupied 5% of the marrow space. Conditioning and GVHD prophylaxis for his unrelated donor transplantation were identical to patient 2. The ANC recovered to 6.0 × 10⁹/L by day 13 and the platelet count, to 116 × 10⁹/L by day 20. The counts declined thereafter and he developed profound pancytopenia. A bone marrow biopsy on day 26 was hypocellular without hematopoiesis (Figure 1G-H). On day 29, autologous stem cells were reinfused. Autologous recovery occurred by day 39 after the initial donor transplantation.

The prolonged marrow aplasia after graft rejection in patients with adequate pretransplantation hematopoiesis suggests that the myelosuppression caused by fludarabine-melphalan is not fundamentally different from that caused by “myeloablative” conditioning regimens. This is not surprising as high-dose melphalan is extremely myelosuppressive⁵  and fludarabine also causes cumulative stem cell toxicity. One could argue that, without back-up stem cells, spontaneous autologous recovery might have occurred in 2 of our patients. This is probably correct, but with prolonged follow-up, autologous recovery can also occur after total body irradiation containing regimens.^6,7  Interestingly, irreversible or prolonged aplasia has also been reported after administration of the Seattle fludarabine low-dose TBI regimen,⁸  perhaps because of enhancement of radiation effects by fludarabine.⁹  Further study of the novel conditioning regimens is necessary to elucidate their spectrum of medullary and extramedullary toxicities and the mechanisms by which they induce engraftment.