Adverse impact of high donor CD3+ cell dose on outcome following tandem auto-NMA allogeneic transplantation for high-risk myeloma

High-risk (HR) multiple myeloma (MM) has poor outcomes with conventional therapy. Tandem autologous-non-myeloablative (NMA) allogeneic stem cell transplantation (autologous stem cell transplantation (ASCT)-NMA allogeneic SCT) is potentially curative secondary to graft-versus-myeloma effect. We retrospectively analysed ASCT-NMA allogeneic SCT outcomes of 59 HR and relapsed MM patients. At a median follow-up of 35.8 months, the outcomes for HR-MM upfront tandem ASCT-NMA allogeneic SCT and standard-risk (SR) MM upfront ASCT alone were comparable (median PFS 1166 days versus 1465 days, P =0.36; median overall survival (OS) not reached in both cohorts, P =0.31). The 5-year PFS and OS of patients who had ASCT-NMA allogeneic SCT after relapsing from previous ASCT were 30% and 48% respectively. High CD3+ cell dose (>3 × 10 8 /kg) infusion was associated with more acute GvHD (grade 2–4) (47% vs 17.5%; P =0.03), extensive chronic GvHD (80% vs 50%; P =0.04), increased transplant-related mortality (26.3% vs 5%; P =0.009) and inferior OS (median OS 752 days vs not reached; P =0.002). On multivariate analysis, response achieved with tandem transplant (More