The only potentially curative approach currently available in the treatment of multiple myeloma (MM) is stem cell trans-plantation from an allogeneic donor. Allogeneic HSCT eradicates residual myeloma cells through T-cell mediated graft-versus-tumor effects. Allogeneic HSCT is, however, associated with significant risk of graft-versus-host disease and its use is therefore limited to younger patients with high risk dis-ease. Malignant plasma cells in multiple myeloma are also sensitive to natural killer cell lysis. Natural killer cells do not cause graft-versus-host disease, which has led to interest in their therapeutic use in patients with multiple myeloma.