First-in-human Phase I/II clinical trial with CellProtect, EudraCT No: 2010-0223330-83, was conducted at the Hematology Center, Karolinska University Hospital, Stockholm, Sweden, in a setting of consolidation treatment following high dose autologous stem cell transplantation in patients newly diagnosed with Multiple myeloma. The clinical study was an open, single-arm, triple escalating dose/patient study with the primary objective of studying the safety and tolerability of the product. The product demonstrated a high degree of safety, and no severe adverse events (SAE) were reported. The secondary objectives included deepening in the response, i.e., further decrease in serum Ig level (M-protein) in patients who did not achieve complete remission and deepening of minimal residual disease (MRD) in patients achieving complete remission. Four out of six patients had measurable disease following autologous SCT. Out of these four patients, all showed objective measurable responses to NK cell infusion in terms of reduction in M-component and/or MRD. The explorative analysis allowed extensive characterization of infused NK cells in patients. The treatment strategy opens for the usage of autologous NK cells in clinical settings.