Unrelated Donor Hematopoietic Cell Transplantation after Non-Myeloablative Conditioning for Patients with High Risk Multiple Myeloma.

Allografting can induce long-term molecular remissions and possibly cure in myeloma patients. The recent development of non-myeloablative conditionings has reduced the transplant-related mortality (TRM) typically associated with myeloablation and extended the eligible age for transplantation. Moreover, high response rates are reported especially when allografting is preceded by cytoreductive high dose chemotherapy. We investigated the feasibility of unrelated donor non-myeloablative transplantation as either part of the initial treatment plan or as salvage treatment in heavily pre-treated patients. Twenty-two patients underwent non-myeloablative allografting, 10 as part of their initial treatment and 12 at disease relapse. Donors were matched for HLA-A, B, C, DRB1 and DQB1 by high-resolution typing. Only one single class I allele disparity was allowed. Conditioning regimen consisted of fludarabine 90 mg/m2 and 2 Gy total body irradiation. GVHD prophylaxis included oral cyclosporine (CyA) and mycophenolate mofetil (MMF). CyA was administered at 6.25 mg/Kg every 12 hours from day -3; levels were targeted to the upper therapeutic range (450–500 ng/ml, Abbott TDX, Abbott Park, IL) for the first month post-transplant. In the absence of GVHD, CyA was tapered from day +100 and discontinued on day +177. MMF was administered from day 0 after PBSC infusion to day +40 at 15 mg/Kg every 8 hours, and then tapered till day +96. Twenty/22 (91%) patients readily engrafted. Two patients experienced graft failure and eventually recovered autologous hematopoiesis. After a median follow up of 11 months (3–27), TRM was 18% and 16/22 patients (73%) are alive. Deaths occurred in 10% of patients transplanted upfront and in 42% of those transplanted at relapse: 3 patients died from infections, 1 from hemolytic uremic/ thrombotic thrombocytopenic purpura syndrome, and 2 from disease progression (both were transplanted at relapse). Ten/20 engrafted patients (50%) had grade II–IV acute GVHD (10% grade III–IV), and 59% had extensive chronic GVHD. Overall response rate was 60% (including 20% CR): 78% in patients transplanted upfront (no disease progression observed) and 45% in those transplanted at relapse. In the two groups, progression-free and one year event-free survival were 100% and 44% (p<0.025), and 90% and 28% respectively (p<0.005).

Unrelated donor non-myeloablative allografting is feasible with relatively low TRM and high response rate. Graft-versus-myeloma effect appears to be more efficient when patients are treated soon after diagnosis. Longer follow-up is needed to assess response duration.