Circulating megakaryocytic progenitor cells in patients with primary thrombocythaemia and reactive thrombocytosis: results using a serum-deprived culture assay and a positive detection technique.

A serum-free culture method was used to study the growth of megakaryocytic progenitor cells (CFU-Meg) from patients with elevated platelet counts. The culture technique was combined with immunocytochemistry (APAAP, CD61) for the identification of CFU-Meg derived cells in cytopreparations of cells eluted from the culture dishes. Twenty-six patients with primary thrombocythaemia (14 untreated patients, UPT, 12 treated patients, TPT), 14 patients with reactive thrombocytosis (RT) and 9 normal individuals were studied. Unstimulated growth of CD61-positive cells was detected in 8/14 UPT, 8/12 TPT, 12/14 RT and 5/9 normal subjects (with mean CD61-positive cell counts of 75, 579, 236 and 7 per cytopreparation respectively). Cultures supplemented with interleukin 3 contained CD61-positive cells in 11/14 UPT, 7/12 TPT, 14/14 RT and 5/9 normal subjects (with mean CD61-positive cell counts of 157, 589, 250 and 7 per cytopreparation respectively). Thus, this serum-free culture technique combined with sensitive positive identification of CFU-Meg derived cells failed to discriminate between PT and RT. These results cast doubt on the usefulness of serum-free culture assays for the detection of unstimulated CFU-Meg growth in the differential diagnosis of patients with elevated platelet counts.