Nonmyeloablative Allogeneic Stem Cell Transplant Followed by Bortezomib in High-risk Multiple Myeloma Patients

To date, the only potential curative treatment for multiple myeloma remains allogeneic hematopoietic stem cell transplantation. Achievement of remission in myeloma patients allotransplanted with advanced disease, achievement of complete response in relapsed patients following infusion of donor leucocyte infusions, decreased incidence of relapse associated with chronic GVHD, better survival in myeloma patients who have relapsed after allogeneic transplant with rescue medication and production of an allo-immune response after allogeneic transplant, all support the existence of a graft-versus-myeloma effect. However, chronic GVHD participating to the morbidity and mortality of allogeneic transplantation, in addition to the significant relapse rate despite the transplantation are two important obstacles to this therapeutic modality in myeloma.

Bortezomib (VelcadeTM) is a dipeptidyl boronic acid-based reversible proteasome inhibitor. Several mechanisms of action have been proposed for its effects against multiple myeloma: direct induction of myeloma cells apoptosis, inhibition of NF-κB activation, reduction of myeloma cells adherence to the bone marrow microenvironment (decreasing drug resistance), inhibition of production, secretion and intracellular signalling of myeloma-mediators. It is one of the most effective drugs in the treatment of multiple myeloma. As consolidation treatment after autologous stem cell transplantation, the drug has been associated with an improvement in response rate and more importantly, in quality and depth of response. Maintenance treatment with Bortezomib after autologous transplantation has led to survival improvement, a benefit particularly obvious in myeloma patients with high-risk cytogenetics such as those carrying del(17p13).

In addition to its anti-myeloma properties, Bortezomib has immunomodulatory effects. Indeed, proteasome inhibitors affect several aspects of immune and inflammatory responses by interfering with antigen presenting cell function and effector cell function. Given its immunomodulatory properties, Bortezomib has recently been shown to be safe and effective in HLA-mismatched reduced-intensity conditioning transplantation as a GVHD prophylaxis.

This is a prospective phase II, open label, single institution study evaluating a novel treatment strategy in newly diagnosed multiple myeloma patients with high-risk disease or patients ≤ 50 years old. After an optimal Bortezomib-based induction treatment (VTD, CyBorD, RVD or PAD [in patients with plasma cell leukemia]) for a minimum of 4 cycles, followed by Melphalan ≥ 140 mg/m2 and autologous stem cell transplantation, eligible patients who accept to participate will be included in the study.

Within 6 months of autologous transplantation, patients will receive a non myeloablative allogeneic transplantation. Patients with a 6/6 compatible sibling donor will receive a conditioning regimen with Fludarabine 30 mg/m2 and Cyclophosphamide 300 mg/m2 per day for 5 days from day -8 to day -4 with 3 rest days before donor stem cell infusion on day 0. Patients without a sibling donor who have an 8/8 allele matched unrelated donor will receive a conditioning regimen of Fludarabine 30 mg/m2 per day for 3 days from day -4 to -2 and TBI 2 Gy on day -1 with donor stem cell infusion on day 0.

In sibling transplant recipients, GVHD prophylaxis will consist of Tacrolimus 3 mg p.o. BID starting on day -8, adjusted thrice weekly to obtain blood levels between 8-12 ng/mL. Tacrolimus tapering will start day +50 to be completed by day +100 in the absence of GVHD. In matched unrelated donor recipients, Tacrolimus will be initiated as in siblings, but started on day -4, and taper will be initiated on day +100 to be completed by day +180 in the absence of GVHD. MMF 15 mg/kg p.o. BID will be given from day +1 to +50 in sibling recipients. It will be given at same dose but TID from day +1 to +40, then tapered gradually until day +100 in matched unrelated donor recipients. Patients without progressive disease after allogeneic transplantation will receive Bortezomib 1.3 mg/m2 s.c. every 14 days ± 3 days starting on day +120, for a total of 26 doses (1 year treatment).

Patients will be followed regularly for disease evaluation, using the IMWG criteria. Toxicity will be evaluated using the NCI common terminology criteria for adverse events (CTCAE) version 4.0. Occurrence and severity of acute GVHD will be evaluated using the modified Glucksberg criteria. Chronic GVHD will be evaluated using the NIH criteria. The trial will be terminated when all patients have been followed for 5 years after allogeneic hematopoietic stem cell transplantation.