Dendritic cells in acute promyelocytic leukaemia

Dendritic cell (DC) differentiation was investigated in samples from two ac ute promyelocytic leukaemia (APL) patients with classic translocation t(15; 17)(q22;q21). After 18 d of culture in the presence of granulocyte-macropha ge colony-stimulating factor, interleukin 4 and tumour necrosis factor alph a, 10-15% of pathological promyelocytes had differentiated into DC-like cel ls, as demonstrated by immunological and functional characteristics and by analysis of CD1a(+) cells. In one patient, analysed at relapse and after de veloping a picture of secondary myelodysplastic syndrome (MDS), three diffe rent populations of DCs were demonstrated, two of which derived from pathol ogical myeloid precursors (the APL and the MDS clones). This patient's DCs also presented abnormal dextran uptake. Our results demonstrated that patho logical myeloid precursors in APL can differentiate into DC-like elements a nd that different populations of pathological DCs may Coexist in the same p atient.