Juvenile Myelomonocytic Leukemia (JMML) Cells Spontaneously Differentiate into Dendritic-cell Like Populations

Objective: juvenile myelomonocytic leukemia (jmml) is a rare myelodysplastic/ myeloproliferative malignancy of early childhood, characterized by monocytosis, hepatos­plenomegaly and an aggressive clinical course.methods: in semi-solid culture jmml progenitor cells proliferate spontaneously into colony forming units. in order to study the mechanisms of proliferation and differentiation of jmml cells we developed a suspension culture system without additional exogenous growth factor supplement. mononuclear cells (mnc) from peripheral blood, bone marrow or spleen of 14 patients with jmml and 24 controls were studied.findings: jmml cells expressed higher levels of the proliferation marker ki67 (median 24% [7-39%] vs a median of 3.5% in controls). 90% of jmml cells were cd68-positive (vs 35% in controls) and by day 7 all jmml samples contained cd1a- positive cells. electron microscopy demonstrated cytoplasmic vesicular structures resembling multilamellar mhc ii compare­timents, which together with the expression of cd1a - support a dendritic cell (dc)-phenotype.conclusion: differentiation into cd1a-positive dc seems to be a frequent phenomenon in cultured jmml mnc, which in vivo may contribute to clinical characteristics such as skin and organ infiltration.