Spontaneous macrophage colony‐forming units in juvenile myelomonocytic leukaemia

Abstract

An 8-month-old girl was referred to the hospital for cytopenia: the blood count showed haemoglobin 86 g/l, white blood cell count (WBC) 10.9 · 10/l with 9% neutrophils, 60% lymphocytes, 2% activated lymphocytes, 1% eosinophils, 23% monocytes and 5% immature granulocytes without blast cells. The platelet count was 28 · 10/l. The bone marrow aspirate was poor and did not show marked cytological abnormalities; few megakaryocytes were observed. The blood count recovered over several weeks, but the monocyte count remained above 2 · 10/l. When she was 1 year old, splenomegaly was noted, associated with an abnormal blood cell count: Hb 94 g/l, WBC 30AE3 · 10/l with 27% neutrophils, 4% eosinophils, 3% basophils, 36% lymphocytes, 22% monocytes and 8% immature granulocytes. The platelet count was 136 · 10/l. There was a moderate increase in haemoglobin F (9%) and the karyotype, analysed twice, was normal. A bone marrow aspirate showed dysplastic features mainly of megakaryocytes and granulocytes, associated with a high monocyte count (22%). A stem cell culture performed in a serum-free medium based on collagen (Stemcell Technologies, France) showed endogenous macrophage colony-forming units (CFU-M) growth: on day 14, collagen gels were harvested onto glass slides, dried and stained with MayGrunwald-Giemsa then observed microscopically (figures). This spontaneous CFU-M growth in vitro is a specific feature of juvenile myelomonocytic leukaemia and was important in confirming the diagnosis in this patient. Bone marrow transplantation was carried out successfully when the infant was 18 months old.