Chronic myelomonocytic leukemia derived from a possible common progenitor of monocytes and natural killer cells

The neural cell adhesion molecule, CD56, is expressed on acute myelogenous leukemia (AML) cells in 17-20% of the patients. However, the clinical and b iological significance of its expression in AML has not been well analyzed from the standpoint of CD56 expression and its association with differentia tion to a natural killer (NK) cell lineage. Here we present a 78-year-old p atient with chronic myelomonocytic leukemia (CMML) whose leukemic cells had features of both monocytes and NK cells. We demonstrated that the leukemic cells were positive for CD4, CD56 and interleukin-2 (IL-2) receptor beta c hain (CD112) in addition to myelomonocytic marker; such as CD33, CD11b and CD11c. These leukemic cells proliferated well in vitro, in response to 10-1 00 U/ml of IL-2, and functionally showed significant cytotoxicity against K 562 target cells in a 4-hour Cr-51 release assay. All the above data indica te that these cells possessed at least some of the biological features of N K cells. Accordingly, we speculate that the leukemic cells in this patient may have been derived from a possible common progenitor of monocytes and NK cells.