PSEUDO-GAUCHER HISTIOCYTES IDENTIFIED UP TO 1 YEAR AFTER TRANSPLANTATION FOR CML ARE BCR ABL-POSITIVE/

The results of polymerase chain reaction (PCR) analysis after transpla ntation for chronic myelogenous leukemia (CML) are difficult to interp ret clinically. Positive findings for BCR/ABL can be seen not only in patients who go on to relapse but also in patients who, after years of follow-up, remain in complete remission. The cause for the lack of co ncordance between PCR findings and relapse is not clear. We identified two patients with CML who had rare pseudo-Gaucher cells in their bone marrow aspirate specimens prior to, and at 1, and 6 or 12 months foll owing syngeneic or allogeneic hematopoietic transplantation. After the transplant, the patients obtained clinical remission and were shown t o be cytogenetically normal and to have germline MBCR in blood or bone marrow by Southern analysis. One patient was PCR-positive for BCR/ABL in the marrow at 12 months. In order to determine whether the pseudo- Gaucher histiocytes were BCR/ABL-positive, eve used fluorescence in si tu hybridization and probes for MBCR and ABL and analyzed Wright-stain ed smears to correlate molecular cytogenetic findings with cell type. On three aspirate smears from each patient (at 6 or 12 months post-tra nsplant), all of the pseudo-Gaucher cells studied (10/10 in one patien t and 12/12 in the other) showed the fusion for BCR/ABL. Other cells a nalyzed randomly (erythroid precursors, granulocytes and rare monocyte s, lymphocytes and plasma cells) did not. Our cases provide the first proof that pseudo-Gaucher cells carry the BCR/ABL fusion, Furthermore, they illustrate that these cells can be found in the marrow for up to 12 months following transplantation. Our results permit speculation t hat pseudo-Gaucher cells or other long-lived histocytes may be one cau se of persistent PCR positivity after transplantation that is not pred ictive of disease relapse.