We have previously shown that immunomagnetic separation of a highly pure NK cell product from a leukapheresis is possible and that these cells can be expanded up to 100-fold in a GMP-compatible setting. The current study aims to test the tolerability and feasibility of infusions of in vitro expanded haploidentical NK cells for patients after melphalan 200mg/m2 high dose chemotherapy and autologous HSCT in 10 patients. If feasible, the data will provide a basis for further prospective studies.