The goal of this clinical research study is to find out if giving a boost of natural killer (NK) cells from a donor combined with Rituxan (rituximab), can help to control disease in patients who have already received an allogeneic stem cell transplant. The safety of this treatment will also be studied. Participants have recurrent chronic lymphocytic leukemia (CLL) or lymphoma after non-myeloablative stem cell transplantation.