Isolated extramedullary relapse presenting as autologous lymphocyte response.

Isolated EMR in the CNS is a relatively rare form of recurrent leukemia. We report here a case of a 38-year-old man with inv(16) acute myeloid leukemia (AML, M2) who suffered a central nervous system (CNS) relapse after allogeneic bone marrow transplantation (BMT) from a human leukocyte antigen (HLA)-matched sibling donor. After complete remission was achieved by chemotherapy, he received allogeneic BMT from his HLA-matched sister. His leukemia relapsed in the CNS 2.5 years after the allogeneic BMT. Lumbar puncture revealed 780/muL white blood cells with 67.3% leukemia cells and 32.7% mature lymphocytes. Fluorescent in situ hybridization (FISH) using a probe for the Y chromosome demonstrated that both leukemia cells and lymphocytes in the cerebrospinal fluid (CSF) were derived from the recipient, although the bone marrow cells were from the donor. No leukemia cells with inv(16) were detected by FISH in the bone marrow. This is the first report to clarify the chimerism of lymphocytes in the CSF of patients with isolated EMR in the CNS after allogeneic SCT, in which analysis revealed that autologous immunologic cells rather than donor lymphocytes responded to the recurrent isolated leukemic cells in CNS. This observation suggests that the CNS is a "sanctuary" site not only from chemotherapy but also from the graft-versus-leukemia effect. The present case contributes to our understanding of the possibility of immunological escape phenomenon of recurrent leukemia cells in extramedullary sites.