Recovery of megakaryocytopoiesis in vitro in children with acute lymphoblastic leukemia during induction of remission.

In children with acute lymphoblastic leukemia (ALL), megakaryocytopoiesis was investigated in vitro by the semisolid agar culture technique. In untreated ALL the median number of committed megakaryocyte progenitor cells (CFU-Mk) in the bone marrow was 2 (range less than 0.1-8) per 10(5) bone marrow cells instead of 30 (range 14-93) in controls, the impairment being dependent on the degree of leukemic bone marrow infiltration. However, if the number of CFU-Mk was related to residual nonleukemic bone marrow cells only, two-thirds of the children investigated had a frequency of CFU-Mk within the normal range. After 2 weeks of induction therapy the majority of the children had a low number of CFU-Mk in the bone marrow (median 6, range 0.5-40), a fact that could no longer be explained by a dilution of CFU-Mk by leukemic cells. After 4 weeks of chemotherapy (day 29) the frequency of CFU-Mk had risen to 18 (range 3-67) per 10(5) bone marrow cells, a value still significantly (p less than 0.01) below the normal range. In contrast to the changes in the number of CFU-Mk the median cell number per megakaryocyte colony remained constant during induction of remission. After cessation of long-term chemotherapy all children investigated had a normal number of CFU-Mk, suggesting that no permanent chemotherapy-related damage to committed megakaryocyte progenitor cells was induced.

Acute megakaryoblastic leukemia in children identified by immunological marker studies.

Acute megakaryoblastic leukemia (AMkL), defined by the presence of the platelet-associated glycoprotein IIb/IIIa complex on malignant cells, was diagnosed in 4 (4%) of 103 consecutive children with untreated acute leukemia or 4 (21%) of 19 children with acute nonlymphoblastic leukemia (ANLL). Particular features in the four children with AMkL were an age below 12 months at diagnosis (two patients), the absence of a significant hepatosplenomegaly (three patients), a leukocyte count below 20 x 10(9)/L with only a few blast cells in the peripheral blood (four patients), a technically difficult bone marrow aspiration (three patients), the presence of many megakaryocytes in marrow particles (two patients), and an inconclusive cytochemistry (four patients). The four children with AMkL were treated according to protocols for ANLL and a complete remission was obtained in all patients. One patient died from relapse after 3 months, one patient is a long-term survivor (38+ months), and two patients still on chemotherapy are disease-free for 11+ and 13+ months.

Cell cycle analysis in lymphoid neoplasia of childhood: differences among immunologic subtypes and similarities in the proliferation of normal and leukaemic precursor B cells.

Cell proliferation in untreated lymphoid malignancies of children was investigated by an in vitro assessment of the 3H-thymidine labelling index (LI), the growth fraction (GF) with the monoclonal antibody Ki-67, and the duration of the DNA-synthesis phase (ts) with a double labelling technique. Mean cell cycle time (tg) was similar in lymphoid malignancies of precursor B cell and T cell origin (115 h and 102 h, respectively), while B cell neoplasias had a mean tg of only 25 h. A positive correlation between the LI and the GF (r = 0.892) and a negative correlation between the LI and tg (r = -0.908) could be detected in childhood lymphoid malignancies. The proliferation of neoplastic precursor B cells was compared with the proliferation of presumably normal terminal transferase (TdT) positive bone marrow cells that, according to the immunophenotype, correspond mainly to normal precursor B cells. Although mean ts was identical in both cell populations (18-19 h), the neoplastic cell population showed a significantly longer mean tg than the normal counterpart (115 h and 65 h, respectively). However, if malignant and normal precursor B cell populations with a similar LI were compared, the difference in tg disappeared. Therefore, a down-regulation of leukaemic cell proliferation by an increasing cell mass is postulated for most cases of untreated precursor B cell ALL.

Megakaryocyte growth in vitro predicts outcome in idiopathic thrombocytopenic purpura.

PURPOSE: The impact of megakaryocyte growth in vitro on clinical data, especially outcome, was studied in 25 consecutive children with idiopathic thrombocytopenic purpura (ITP). PATIENTS AND METHODS: Twenty children with untreated de novo ITP and five children with pretreated ITP were evaluated. The number of megakaryocyte colonies (cloning efficiency), the mean cell number per colony (mitotic amplification) and the percentages of polyploid megakaryocytes after 7 and 12 days in culture (relative size of the endomitotic compartment) were determined in two separate clonal assays. The culture data were related to clinical findings and outcome of the thrombocytopenia. RESULTS: The mean cell number per megakaryocyte colony was significantly correlated with the observed increase in the platelet count 5 days after starting therapy (n = 23; r = 0.642), and a significant negative correlation was found between the relative size of the endomitotic compartment and the duration of thrombocytopenia after bone marrow culture analysis (n = 25; r = -0.503). If all 25 children with ITP (untreated de novo and pretreated ITP) were considered, a normal frequency of polyploid megakaryocytes was associated with a duration of ITP for < 6 months in 14 of 16 cases, whereas an impaired polyploidization predicted a persistence of ITP for > 6 months in 9 of 9 cases (p < 0.0005); if only children with untreated de novo ITP (n = 20) were considered, 13 of 15 children with a normal polyploidization had an acute course of their ITP and 5 of 5 children with an impaired polyploidization developed chronic ITP (p < 0.003). CONCLUSIONS: The results in this small group of patients suggest that the assessment of the relative size of the endomitotic compartment after 7 and 12 days in plasma clot culture actually appears to be the best method for predicting a chronic course in children with ITP.