The reconstitution of a functioning immune system after allogeneic stem cell transplantation takes months to years. Particularly memory B-lymphocytes reconstitute poorly with the current conditioning regimes. During the period of intense immune suppression the patients are extremely susceptible to bacterial, fungal and, most importantly, viral infections.The adoptive transfer of B-lymphocytes from the stem-cell donor might significantly enhance humoral immunity for the patient. Aim of the study is to evaluate a new cellular therapy with B-lymphocytes regarding safety. A booster vaccination after B-lymphocyte transfer will evaluate the functionality of the transferred B-lymphocytes in the patient.