Fludarabine-Busulfan Conditioning and In Vivo T-Cell Depletion with Reduced Dose of ATG Followed by Allografting Induces Durable Responses in Patients with Advanced Multiple Myeloma with No Grade III-IV aGvHD.

Background: We have investigated a conditioning regimen with Fludarabine and intravenous Busulfan with reduced ATG dose in patients with advanced and poor prognosis myeloma exploring the possibility that a low dose ATG may be sufficient enough to prevent severe GvHD without completely suppressing the graft vs myeloma effect.

Methods: 15 patients received a conditioning regimen consisting of fludarabine 50mg/m2 on days -6 to -2 and IV BU (Busulfex, ESP Pharma) at a “myeloablative” dose of 3.2 mg/kg daily days -5 to -2 inclusive. All pts received Thymoglobulin (Genzyme) 4.5 mg/kg in divided doses over 3 consecutive days pre-transplant finishing D0, cyclosporine A and methotrexate with folinic acid.

Results: The median age was 49 years (range 40–61). 14 (93.3%) patients had stage III (DS) disease with a median β2-microglobulin 3.12 mg/dl (1.82–5.75) and 7/11 (63.6%) in whom FISH studies were available had deletion 13, 5/15 (33.3%) patients had relapsed or progressed within 2 years of prior autologous stem cell transplant and 4 (26.6%) had progressed while on thalidomide /Dex salvage treatment. The disease status prior to allogeneic transplant was partial response (PR) in 6/15 (40%) and progressive disease (PD) in 9/15 (60%). 2/15 had plasma cell leukemia. The median number of bone marrow plasma cells prior to allo-transplant was 16% (range 3%-85%). Donors were matched siblings (MRD) for 13 (86.7%) and alternate donors in 2 (13.3%, unrelated with 2 C antigen mismatch). Cell source was blood in 14/15 (93.3%). Acute GVHD grade II-IV occurred in only 1 patient (6.6%) with no grade III-IV acute GVHD. Chronic GVHD occurred in 9/15 (60%). The TRM was 6.6%. Among 14/15 patients evaluable for response, the overall response rate (CR+PR) was 53.3% (2 CR, 6 PR, 1 MR and 5 PD); 37.5% (1CR, 2PR, 1MR and 4PD) for pts with PD at the time of the transplant and 71.4% (4PR, 1MR and 1PD) for pts with del13. After a median follow-up of 40.9 months (range 36–65.2), the estimated OS and PFS at 4 years for all patients is 38.9% (CI 95%: 13.1–64.7%) and 20.0% (CI 95%: 0–40.3%) respectively. For patients with del13 the estimated OS and PFS at 4 years is 38.1% (CI 95%: 0–77.9%) and 0% respectively.

Conclusion: In vivo T-cell depletion with ATG results in a low rate of severe aGvHD with low treatment-related mortality and a substantial number of long-term survivors among patients with advanced multiple myeloma. The detection of deletion 13 by FISH however remains a predictor of short progression free survival.

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