This phase II trial studies the side effects of cord blood-derived expanded allogeneic
natural killer cells (umbilical cord blood natural killer [NK] cells), rituximab, high-dose
chemotherapy, and stem cell transplant in treating patients with B-cell non-Hodgkin's
lymphoma that has come back (recurrent) or that does not respond to treatment (refractory).
Immune system cells, such as cord blood-derived expanded allogeneic natural killer cells, are
made by the body to attack foreign or cancerous cells. Immunotherapy with rituximab, may
induce changes in body's immune system and may interfere with the ability of tumor cells to
grow and spread. Drugs used in chemotherapy, such as carmustine, cytarabine, etoposide,
lenalidomide, melphalan, and rituximab, work in different ways to stop the growth of cancer
cells, either by killing the cells, by stopping them from dividing, or by stopping them from
spreading. A stem cell transplant using stem cells from the patient or a donor may be able to
replace blood-forming cells that were destroyed by chemotherapy used to kill cancer cells.
The donated stem cells may also replace the patient's immune cells and help destroy any
remaining cancer cells. Giving cord blood-derived expanded allogeneic natural killer cells,
rituximab, high-dose chemotherapy, and stem cell transplant may work better in treating
patients with recurrent or refractory B-cell non-Hodgkin's lymphoma.