A View from the Plateau: Is There a Role for Allogeneic Stem Cell Transplantation in the Era of Highly Effective Therapies for Multiple Myeloma?

Allogeneic Hematopoietic Transplantation for Multiple Myeloma in the New Drugs Era: A Platform to Cure

Allogeneic hematopoietic cell transplantation (alloHCT) represents a treatment option for multiple myeloma (MM) patients. As shown in several studies, alloHCT is highly effective, but it is hampered by a high toxicity, mainly related to the graft-versus-host disease (GVHD), a complex immunological reaction ascribable to the donor’s immune system. The morbidity and mortality associated with GVHD can weaken the benefits of this procedure. On the other side, the high therapeutic potential of alloHCT is also related to the donor’s immune system, through immunological activity known as the graft-versus-myeloma effect. Clinical research over the past two decades has sought to enhance the favorable part of this balance, along with the reduction in treatment-related toxicity. Frontline alloHCT showed promising results and a potential for a cure in the past. Currently, thanks to the improved results of first-line therapies and the availability of effective second- or third-line salvage therapies, alloHCT is reserved for selected high-risk patients and is considered a clinical option. For donor lymphocyte infusion, bortezomib or lenalidomide have been used as consolidation or maintenance therapies post-transplant—none has become standard of care. For those patients who relapse, the best treatment should be evaluated considering the patient’s clinical status and the previous lines of therapy. The use of newer drugs, such as monoclonal antibodies or other immunotherapies in the post-transplant setting, deserves further investigation. However, acceptable toxicity and a synergic effect with the newer immune system could be hopefully expected.

Presalvage International Staging System Stage and Other Important Outcome Associations in CD34+-Selected Allogeneic Hematopoietic Stem Cell Transplantation for Multiple Myeloma

Despite ongoing therapeutic advances, multiple myeloma (MM) remains largely incurable, and outcomes in patients who develop resistance to immunomodulatory drugs or proteasome inhibitors remain grim. Allogeneic hematopoietic cell transplantation (alloHCT) is an alternative option that may offer potential for cure. Although rates of transplantation-related morbidity and mortality have decreased in recent years, weighing this approach's potential benefits against nontransplantation therapies demands a thoroughly informed pre-alloHCT assessment. Here we assess the impact of pre-alloHCT variables on important clinical outcomes in a large cohort of relapsed refractory MM (RRMM) CD34⁺-selected alloHCT recipients. We included all patients with MM who underwent CD34⁺-selected alloHCT at our center between June 2010 and December 2015. Patients were conditioned with busulfan (0.8 mg/kg × 10), melphalan (70 mg/m² × 2), and fludarabine (25 mg/m² × 5), followed by infusion of a CD34⁺-selected peripheral blood stem cell graft, without post-alloHCT graft-versus-host disease (GVHD) prophylaxis. The 73-patient cohort had a median age of 55 years (range, 37 to 66 years). Overall survival (OS) and progression-free survival (PFS) rates were 70% and 53%, respectively, at 1 year (95% confidence interval [CI], 58% to 79% and 41% to 64%) and 50% and 30%, respectively, at 3 years (95% CI, 38% to 62% and 19% to 41%). The cumulative incidence of relapse was 25% at 1 year (95% CI, 15% to 35%) and 47% at 3 years (95% CI, 35% to 58%). Nonrelapse mortality at 1 year was 22% (95% CI, 13% to 32%). The cumulative incidence of grade II-IV acute GVHD (aGVHD) was 7% at 100 days (95% CI, 3% to 14%), and that of any chronic GVHD (cGVHD) was 8% at 1 year (95% CI, 3% to 16%). International Staging System (ISS) stage II-III assessed before salvage therapy was associated with poorer 3-year OS (30% versus 54%; P = .037) and 3-year PFS (9% versus 33%; P = .013), and increased 3-year relapse incidence (72% versus 39%; P = .004). Older age and GVHD before 6 months (aGVHD grade II-IV or cGVHD of any grade) were also associated with poorer OS, and a greater number of pre-alloHCT lines of therapy was also associated with increased relapse incidence. Our findings reinforce that CD34⁺-selected alloHCT can achieve prolonged disease control and long-term survival in high- risk, heavily treated refractory MM populations. We also identified numerous pre-alloHCT variables associated with OS, PFS, and relapse. Amongst these, presalvage ISS stage II-III was consistently associated with poorer survival and relapse outcomes. Given the lack of established alternate therapies for patients with RRMM, we advocate the identification of adverse pre-alloHCT variables to inform alloHCT decision making rather than to exclude patient cohorts from this potentially curative treatment option.

Tandem autologous/allogeneic hematopoietic cell transplantation with bortezomib maintenance therapy for high-risk myeloma

We evaluated tandem autologous/allogeneic hematopoietic cell transplantation followed by bortezomib maintenance therapy in a prospective phase 2 trial of treatment of high-risk multiple myeloma. The high-dose conditioning regimen for autologous hematopoietic cell transplantation consisted of melphalan 200 mg/m². The nonmyeloablative conditioning regimen for the allogeneic transplant involved low-dose total body irradiation (2 Gy) with or without fludarabine (30 mg/m² × 3 days). Among the 31 patients enrolled, 26 (84%) proceeded to HLA-matched allogeneic hematopoietic cell transplantation at a median of 61 (range, 41-168) days following the autologous transplant. Twenty-one patients (68%) started bortezomib (1.6 mg/m² IV or 2.6 mg/m² subcutaneously every 14 days for 9 months) at a median of 79 (range, 63-103) days after allogeneic transplantation. With a median follow-up of 51 (range, 16-86) months and based on intention to treat, the 2-year and 4-year progression-free survival and overall survival estimates among 24 newly diagnosed high-risk patients were 71% and 75%, and 52% and 61%, respectively. The 7 patients enrolled with relapsed or persistent disease had a 2-year and 4-year progression-free survival and overall survival rates of 14% and 43%, and 14% and 29%, respectively. These findings suggest that for patients with newly diagnosed high-risk multiple myeloma, bortezomib maintenance therapy after tandem autologous/allogeneic hematopoietic cell transplantation is safe and may prevent disease progression until full establishment of a graft-versus-myeloma effect. This benefit, however, does not extend to patients who enroll after unsuccessful prior therapy. This trial was registered at www.clinicaltrials.gov as #NCT00793572.

A review discussing elotuzumab and its use in the second-line plus treatment of multiple myeloma

Monoclonal antibodies (mAb) represent a new frontier to treat newly diagnosed and relapsed-refractory multiple myeloma (MM). Elotuzumab, an mAb targeted SLAM7 in the plasma cells and natural killer cells surface, is the first mAb approved for the treatment of relapsed-refractory MM in combination with lenalidomide and dexamethasone. This approval was the final result of several preclinical and Phase I-II clinical studies leading to ELOQUENT-2 Phase III trial that demonstrated that elotuzumab adds a significant and durable value to standard therapy, paved the way of this new treatment strategy for MM. In this review we will describe elotuzumab mechanisms of action, clinical pharmacology and clinical studies that have led to these developments.