In situ cell cycle kinetics in bone marrow biopsies following sequential infusions of IUdR/BrdU in patients with hematopoietic malignancies

Bone marrow mononuclear cells of MDS patients are characterized by in vitro proliferation and increased apoptosis independently of stromal interactions

Enhanced proliferation of MDS progenitors is abrogated by increased apoptosis of their progeny in vivo. We investigated whether bone marrow mononuclear cells (BMMNC) of MDS patients also showed enhanced proliferation and apoptosis in vitro in comparison with acute myeloid leukemia (AML) and normal BM (NBM). NBM showed a decrease in the number of clusters in time due to apoptosis of clusters and due to development of clusters into colonies with low apoptotic level. In MDS patients, about two-fold more clusters have developed at day 4, and in contrast with NBM, the total number of clusters at day 7 remained high in spite of an increasing percentage of apoptotic clusters (from 52 to 76%) in combination with more colony formation. The number of clusters and colonies showed a sharp decrease at day 10 because of persistently high apoptosis at cluster level and increasing apoptosis in colonies. BMMNC of AML patients showed a decreased proliferation with enhanced apoptosis at cluster level in contrast to a relatively low apoptotic levels in the colony-forming cells. This data show that increased proliferation is abrogated by enhanced apoptosis in MDS, whereas AML showed decreased proliferation with a low level of apoptosis in colony-forming cells. These growth profiles of BMMNC are independent of stromal influences and may represent intrinsic features of the MDS progenitors and accessory cell interactions.

Lingering biologic dilemmas about the status of the progenitor cells in myelodysplasia

Myelodysplastic syndromes (MDS) are considered to be stem cell disorders. High incidence of intramedullary apoptosis has been associated with the peripheral cytopenia and refractory anemia in these disorders. The investigations on the cell of origin in the bone marrow have invariably been hampered by a poor yield of CD34+ cells from these marrows. Interestingly, even though limited in number, these studies raised more questions and dilemmas than providing answers. While the enigma surrounding the clonality of these marrows continues, the controversies regarding incidence of apoptosis, proliferation, and potential of clonogenic expansion may be closer to a settlement. The present review proposes a model depicting interplay between extraneous apoptogenic factors and intracellular apoptosis-susceptibility determinants that contributes significantly toward the progression of MDS and how a shift in dynamics of this interplay may provide grounds to accumulate additional mutations with a probable block in differentiation eventually leading to a leukemic transformation.

Dynamic cell cycle kinetics in vitro and in vivo in myelodysplastic syndromes with special reference to the influence of hematopoietic growth factors

We have investigated the effect of HGF in vivo and in vitro in MDS using a recently developed FCM assay involving the simultaneous measurement of cell surface antigens, DNA content, and BrdUrd or IodUrd incorporation. This allows for the determination of the dynamic cell kinetic parameters: LI, T(s), and T(pot) and we observed that in vitro HGF stimulation resulted in a significant decrease in mean T(pot) values from 6.6 to 3.5 days. Importantly, we demonstrated that in vivo GM-CSF administration to patients with RAEB resulted in a shortening of T(pot) within the 2 first weeks of GM-CSF treatment.

Evaluation of apoptosis as a prognostic factor in myelodysplastic syndromes

The myelodysplastic syndromes (MDS) are a group of disorders characterized by peripheral pancytopenia despite normo- or hypercellular bone marrow. This is thought to be as a result of the apoptosis of haematopoietic bone marrow cells resulting in ineffective haematopoiesis. To clarify the relationship between prognosis and apoptosis and/or cell proliferation in the bone marrow, we studied 51 cases with MDS. Bone marrow biopsies were stained immunohistochemically for MIB-1 (marker for proliferating cells) and CD34 (marker for stem cells). Apoptosis was visualized by detection of DNA fragmentation using TdT incorporation of nucleotides on 3' ends of DNA (TUNEL technique) and expressed as the apoptotic rate. MDS patients included 32 with refractory anaemia (RA), one RA with ringed sideroblasts (RARS) patient, seven RA with excess of blasts (RAEB) patients, eight patients with RAEB in transformation (RAEB-t) and three patients with chronic myelomonocytic leukaemia (CMMoL). In addition, we also studied six cases with acute myeloid leukaemia (AML) arising from MDS (AML-MDS) and ten control subjects. Fatal pancytopenia was the cause of death in 19 out of 51 patients. The apoptotic rate was higher in MDS patients (5.5%) than in control subjects (0.6%) and AML-MDS patients (0.4%). The percentage of MIB-1 positive cells was higher in MDS and AML-MDS than in control. The percentage of CD34-positive cells was higher in AML-MDS, RAEB, RAEB-t and CMMoL patients than control subjects and RA patients. Our findings indicate the activation of both the proliferative and apoptotic rates in MDS. Poor prognosis correlated significantly with higher apoptotic rates, but not with percentages of MIB-1 and CD34-positive cells. Our results suggest that apoptosis might be a useful prognostic factor and inhibition of apoptotic mechanisms may induce leukaemic transformation in MDS.

Cell production rates in human tissues and tumours and their significance. Part II: clinical data

This paper reviews the available data for cell production rates of human tissues and tumours, measured in vivo using halogenated pyrimidine labelling and laser cytometry. The technique has now been widely evaluated, and we draw general inferences from the proliferative data over a broad range of tumour and tissue types. Estimates of the S-phase duration, the time taken for DNA synthesis in cycling cells, are consistent over a narrow range with a median value of around 10 hours, notwithstanding the constraints of the experimental and statistical technique, in normal tissues and tumours. This suggests that Ts values may be a species-specific constant. The more easily measured labelled S-phase fraction, or labelling index, shows much greater intra and intertumour variation within any one tumour class. It may thus be a surrogate for time dependent measurements to a first order approximation. The cell production rate, described by the potential doubling time (Tpot), is remarkably rapid in most tumours, a median value of the order of 5 days, and much faster than clinical volume doubling times for most lesions. The rapid cell production rates in normal tissues and tumours highlight the importance of cell loss in the growth and modelling of biological structures. Cell production rate measurements do not adequately describe the biological aggressiveness of tumours. They may be used to refine adjuvant strategies for radiotherapy and chemotherapy in experimental research. Dynamic halogenated pyrimidine labelling has provided unique and valuable insights into the living biology of human tissues and tumours.

Flow cytometric measurement of DNA S-phase in human bone marrow cells: correcting for peripheral blood contamination

The relationship between bone marrow (BM) cells with S-phase DNA content and the amount of peripheral blood contamination estimated as percentage lymphocytes+monocytes (L+MO) present in BM samples has been investigated in a total of 136 BM aspirates and biopsy expellates from 35 hematologically healthy individuals. A significant negative correlation was demonstrated between total, erythroid and myeloid BM cells in S-phase and the percentage of L+MO in the aspirates (r=0.84, 0.57 and 0.49, respectively; p<0.0001). Based on the equation of the slope of the regression line, a correction formula adjusting the measured value of BM cells in S-phase to varying amounts of L+MO percentage has been worked out for the total and erythroid BM cells. In contrast, highly proliferating myelomonocytic cells and CD34+ cells did not show any significant correlation between cells in S-phase and percentage L+MO, indicating that peripheral blood contamination of BM aspirates estimates the degree of peripheral blood contamination, as well as make possible a correct estimation of the DNA synthesis of several BM populations. The method is especially applicable when frequent BM sampling is required.

Calculating potential doubling time using monoclonal antibodies specific for two halogenated thymidine analogues

PURPOSE

A new flow cytometric technique that allows for two-incorporated thymidine analogues to be measured simultaneously and independently has been used to improve the accuracy of in vivo cell kinetic estimates, i.e., the length of S-phase (TS) and potential doubling time (Tpot).

METHODS AND MATERIALS

The analogues chlorodeoxyuridine and iododeoxyuridine were injected at different times into mice bearing the mouse mammary tumor MCaK. At different times after labeling, the tumors were harvested and prepared for three color flow cytometric analysis of DNA, chlorodeoxyuridine, and iododeoxyuridine. Control experiments showed that similar estimates of Tpot were obtained from each label when administered singly, or as staggered pulses. Comparisons were made between TS and Tpot calculated from a single label (single point), from the averaged result of the two labels from the same tumor (two point-ave), and from the simultaneous nonlinear fitting of the measured parameters from the two labels, from the same tumor (two point-fit). These estimates of TS and Tpot were then compared to reference values obtained by fitting the pooled measured parameters from all the tumors, that were labeled for different periods of time.

RESULTS

While all of the methods resulted in similar mean estimates of TS and Tpot that were close to the reference values, the fewest assumptions, and the least variability in the results, were obtained using the two point-fit data.

CONCLUSION

The estimation of Tpot using two thymidine analogues is more accurate than that obtained from a single label.