Prognostic Factors for Postrelapse Survival after ex Vivo CD34+-Selected (T Cell-Depleted) Allogeneic Hematopoietic Cell Transplantation in Multiple Myeloma

Novel Drug Combinations and Donor Lymphocyte Infusions Allow Prolonged Disease Control in Multiple Myeloma Patients Relapsing after Allogeneic Transplantation

Although allogeneic stem cell transplantation (allo-SCT) is curative for only a minority of patients with multiple myeloma (MM), patients who relapse after allo-SCT can experience long-term survival, suggesting a synergy between antimyeloma drugs administered after allo-SCT and donor T cells. We retrospectively evaluated the outcome of MM patients reported to the Gruppo Italiano Trapianto Midollo Osseo e Terapia Cellulare (GITMO) network who underwent allo-SCT between 2009 and 2018, to identify predictors of long-term outcome in the whole population (242 patients) and predictors of prolonged overall survival (OS) after relapse in the subgroup of relapsed patients (118 patients). In the whole population, at a median follow-up of 40.9 months after allo-SCT, the median duration of OS and progression-free survival (PFS) were 39.4 and 19.0 months after allo-SCT, respectively. The cumulative incidence of nonrelapse mortality (NRM) was 10.3% at 1 year and 27.6% at 5 years. The cumulative incidence of grade II-IV acute graft-versus-host disease (GVHD) was 19.8%, and the 5-year cumulative incidence of moderate or severe chronic GVHD was 31.8%. In the multivariate model, older age at transplantation (P = .020), receipt of >2 lines of therapy before allo-SCT (P = .003), and transplantation from an unrelated or haploidentical donor (P = .025) were significant factors associated with reduced OS. Relapse after allo-SCT occurred in 118 patients (59%) at a median of 14.3 months (interquartile range, 7.2 to 26.9 months). Twenty patients (17%) received only steroids, radiotherapy, or supportive care; 41 (35%) received 1 line of salvage treatment; 23 (19%) received 2 lines of salvage treatment; and 34 (29%) received 3 or 4 lines of salvage treatment. Nine patients were treated exclusively with chemotherapy, 9 received at least 1 salvage treatment including immunomodulating agents, 43 patients were treated with at least 1 rescue therapy including proteasome inhibitors, and 37 patients received at least 1 salvage treatment including monoclonal antibodies (33 with daratumumab, 1 with elotuzumab, 1 with isatuximab, and 2 with belantamab). The median OS of relapsed patients was 38.5 months from allo-SCT and 20.2 months from relapse. In multivariate analysis, OS after relapse was significantly prolonged in patients with a longer time to relapse after allo-SCT (time to relapse 6 to 24 months, P = .016; time to relapse ≥24 months, P < .001) and in those who had received at least 3 lines of salvage treatment (P < .036) and donor lymphocyte infusion (DLI) (P = .020). In this study, patients who underwent transplantation in early phases of disease and with an HLA-identical sibling donor had the best chance of long-term survival. Late relapse after allo-SCT, multiple courses of salvage treatment, and an association with DLI could allow for long-term disease control in patients who experienced relapse after allo-SCT.

Cellular Immunotherapies for Multiple Myeloma: Current Status, Challenges, and Future Directions

Multiple myeloma (MM) remains incurable due to relapse, although the use of proteasome inhibitors, immunomodulatory drugs, CD38-targeting antibodies, and autologous stem cell transplantation (auto-SCT) significantly improve the clinical outcomes of patients with newly diagnosed MM. In recent years, the introduction of chimeric antigen receptor T-cell (CAR T-cell) therapy has brought hope to patients with refractory and relapsed MM. The graft-versus-myeloma effect of allogeneic SCT provides the possibility for curing a subset of MM patients. In this review, we summarize the recent advances and challenges of cellular immunotherapies for MM, focusing on auto-SCT, allogeneic SCT, and CAR T-cell approaches. We also discuss future directions, and propose a specific algorithm for cellular therapies for MM and probability of minimal residual disease-directed therapy.