Prognostic value of CD34 expression in de novo acute myeloblastic leukaemia

High frequency of CD34+CD38-/low immature leukemia cells is correlated with unfavorable prognosis in acute myeloid leukemia

AIM

To evaluate the importance of the CD34+CD38- cell population when compared to the CD34+CD38+/low and CD34+CD38+/high leukemic cell sub-populations and to determine its correlations with leukemia characteristics and known prognostic factors, as well as with response to therapy and survival.

METHODS

Two hundred bone marrow samples were obtained at diagnosis from 200 consecutive patients with newly diagnosed acute myeloid leukemia (AML) were studied between September 2008 and December 2010 at our Institution (Hematology Department, Lyon, France). The CD34/CD38 cell profile was analyzed by multiparameter flowcytometry approach using 8C panels and FACS CANTO and Diva software (BD Bioscience).

RESULTS

We analyzed CD34 and CD38 expression in bone marrow samples of 200 AML patients at diagnosis, and investigated the prognostic value of the most immature CD34+CD38- population. Using a cut-off value of 1% of CD34+CD38- from total “bulk leukemic cells” we found that a high (> 1%) level of CD34+CD38- blasts at diagnosis was correlated with advanced age, adverse cytogenetics as well as with a lower rate of complete response after induction and shorter disease-free survival. In a multivariate analysis considering age, leukocytosis, the % of CD34+ blasts cells and the standardized cytogenetic and molecular risk subgroups, a percentage of CD34+CD38- leukemic cells > 1% was an independent predictor of DFS [HR = 2.8 (1.02-7.73), P = 0.04] and OS [HR = 2.65 (1.09-6.43), P = 0.03].

CONCLUSION

Taken together, these results show that a CD34/CD38 “backbone” for leukemic cell analysis by multicolour flowcytometry at diagnosis provides useful prognostic information.

High proportion of leukemic stem cells at diagnosis is correlated with unfavorable prognosis in childhood acute myeloid leukemia

In acute myeloid leukemia (AML), the leukemia-initiating cell is found within the CD34(+)/CD38(-) cell compartment. Over the last years evidence grew that AML is initiated and propagated by leukemic stem cells (LSCs). Conceivably, these most immature leukemia cells are more resistant to therapy and subsequently initiate relapse. The authors studied 17 patients with childhood AML treated according to the AML-BFM 98/04 protocol. At diagnosis, the authors determined the characteristic immunophenotype of the leukemic cells by flow cytometry and investigated the expression of CD34, CD38, and CD45 to define a population of immunophenotypically immature cells (CD34(+)/CD38(-)/CD45(-/low)) enriched for LSCs in many cases of AML. The authors compared the fraction of this population of all myeloid cells at diagnosis with event-free survival. Kaplan-Meier analysis revealed significant higher event free survival of patients with low CD34(+)/CD38(-)/CD45(-/low) cell proportion (<0.68%) compared to patients with high burden of this population (>0.83%; log-rank P < .04). This correlation was not found for the total number of CD34(+) cells. This is the first study to show that a higher proportion of immature CD34(+)/CD38(-)/CD45(-/low) blasts at diagnosis correlates with unfavorable prognosis in childhood AML. The results suggest that a large CD34(+)/CD38(-)/CD45(-/low) population reflects a higher fraction of LSCs, leading to increased chemotherapy resistance and elevated relapse rate. Thus the initial frequency of CD34(+)/CD38(-)/CD45(-/low) cells may serve as a prognostic marker in pediatric AML. Future treatment in childhood AML should specifically target this immature population as well as the mature blast population.

High stem cell frequency in acute myeloid leukemia at diagnosis predicts high minimal residual disease and poor survival

PURPOSE

In CD34-positive acute myeloid leukemia (AML), the leukemia-initiating event originates from the CD34(+)CD38(-) stem cell compartment. Survival of these cells after chemotherapy may lead to minimal residual disease (MRD) and subsequently to relapse. Therefore, the prognostic impact of stem cell frequency in CD34-positive AML was investigated.

EXPERIMENTAL DESIGN

First, the leukemogenic potential of unpurified CD34(+)CD38(-) cells, present among other cells, was investigated in vivo using nonobese diabetic/severe combined immunodeficient mice transplantation experiments. Second, we analyzed whether the CD34(+)CD38(-) compartment at diagnosis correlates with MRD frequency after chemotherapy and clinical outcome in 92 AML patients.

RESULTS

In vivo data showed that engraftment of AML blasts in nonobese diabetic/severe combined immunodeficient mice directly correlated with stem cell frequency of the graft. In patients, a high percentage of CD34(+)CD38(-) stem cells at diagnosis significantly correlated with a high MRD frequency, especially after the third course of chemotherapy. Also, it directly correlated with poor survival. In contrast, total CD34(+) percentage showed no such correlations.

CONCLUSIONS

Both in vivo data, as well as the correlation studies, show that AML stem cell frequency at diagnosis offers a new prognostic factor. From our data, it is tempting to hypothesize that a large CD34(+)CD38(-) population at diagnosis reflects a higher percentage of chemotherapy-resistant cells that will lead to the outgrowth of MRD, thereby affecting clinical outcome. Ultimately, future therapies should be directed toward malignant stem cells.

Induction failure in de novo acute myelogenous leukemia is associated with expression of high levels of CD34 antigen by the leukemic blasts

The prognostic significance of CD34 antigen expression in acute myelogenous leukemia (AML) is controversial. Most studies to date have reported on CD34 positivity and not the level of antigen present. In this study of 62 patients with de novo AML, 48 (77%) patients were CD34+ in varying levels (0-85 mean channels of fluorescence (MCF)). Forty seven of 62 were treated with combination chemotherapy and 39 (83%) of them achieved complete remission (CR). Patients with CD34- blasts were more likely to achieve CR; however, this trend was not statistically significant (p = .11). On the other hand, patients with higher levels of CD34 antigen on the blasts were less likely to attain CR (p < 0.001, multivariate analysis). The patients who achieved CR expressed lower levels of CD34 (0-57; median 9 MCF) as compared to those who did not achieve CR (15-85; median 30 MCF). Of the other antigens tested, partial or complete absence of CD33 (CD33 absent in > or =25% blasts) correlated with failure to achieve CR (p = 0.0029). These results are in keeping with the hypothesis that more primitive AML blasts with high levels of CD34 are chemoresistant.

Correlation between CD34 expression and chromosomal abnormalities but not clinical outcome in acute myeloid leukemia

The hemopoietic stem cell marker CD34 has been reported to be a useful predictor of treatment outcome in acute myeloid leukemia (AML). Previous data suggested that CD34 expression may be associated with other poor prognosis factors in AML such as undifferentiated leukemia, secondary AML (SAML), and clonal abnormalities involving chromosome 5 and 7. In order to analyze the correlations between the clinicopathologic features, cytogenetic and CD34 expression in AML, we retrospectively investigated 99 patients with newly diagnosed AML: 85 with de novo disease and 14 with secondary AML (SAML). Eighty-six patients who received the same induction chemotherapy were available for clinical outcome. Defining a case as positive when > or = 20% of bone marrow cells collected at diagnosis expressed the CD34 antigen, forty-five patients were included in the CD34 positive group. Ninety patients had adequate cytogenetic analysis. Thirty-two patients (72%) with CD34 positive AML exhibited an abnormal karyotype whereas 15 patients (28%) with CD34 negative AML had abnormal metaphases (P < 0.01). Monosomy 7/7q- or monosomy 5/5q- occurred in 10 patients and 8 of them expressed the CD34 antigen (P < 0.05). All patients with t(8;21) which is considered as a favorable factor in AML had levels of CD34 >/= 20% (P < 0.05). We did not find any association between CD34 expression and attainment of complete remission, overall survival, or disease-free survival. In conclusion, the variations of CD34 expression in AML are correlated with cytogenetic abnormalities associated both with poor and favorable outcome. The evaluation of the correlations between CD34 antigen and clinical outcome in AML should take into account the results of pretreatment karyotype.

Immunophenotyping of AML and MDS and detection of residual disease

Immunophenotyping improves both accuracy and reproducibility of the FAB classification and is considered particularly useful for identifying poorly differentiated FAB subtypes of AML, such as AML with minimal differentiation (M0), microgranular promyelocytic leukaemia (M3V), and megakaryoblastic leukaemia (M7). Immunological studies of myeloid leukaemic blasts has become critical also in identifying biphenotypic leukaemias and AML expressing lymphoid-associated markers (Ly+ AML). At present, while the prognostic value of individual antigen expressions is still controversial, due to technical questions, the immunological detection of MRD seems to be important in monitoring AML patients in remission and, perhaps, in detecting leukaemic cell contamination into bone marrow or peripheral blood progenitor cells collected for autologous transplantation. In addition, the relationship established between genetic abnormalities and certain phenotypes within different FAB subtypes suggests that, in the future, immunophenotypical studies could be used for the screening of AML cases carrying specific genetic aberrations. Compared to acute leukaemias, little information is available concerning immunological patterns in MDS, and the role of the immunophenotype in diagnosis, subclassification, and prognosis of MDS is currently not well established.

Treatment of the elderly patient with acute myeloid leukaemia

Individuals of 60 years living in western countries generally have a mean life expectancy of 20 years at least. Therefore, when aged individuals present with AML, it is a necessity and a challenge to treat them as efficiently as possible. AML is mainly a disease of the elderly and accounts for more than 50% of its incidence among the general population. The treatment of older individuals with AML has remained difficult and its success is still limited. While in adults with AML of less than 60 years complete responses above 65% and survival rates of 35% are commonly obtained, progress in the treatment of elderly patients has been relatively small. As of today, approximately 50% of older patients may be induced into remission with chemotherapy, and, among these complete responders, only approximately 1 in 10 will survive free of leukaemia beyond 4 years after diagnosis. In fact, on one hand, these results represent the rationale and motivation for offering chemotherapy to the older population. On the other hand, they emphasize that major obstacles to better cure rates still exist. These stumbling blocks apparently relate to the restricted tolerance of older subjects to the exposure of chemotherapy and probably also a greater probability of unresponsiveness of the leukaemia to cytotoxic therapy. The haematopoietic growth factors still hold some promise and may improve outcome, but for the time being there is insufficient direct evidence to indicate a defined and established role. It is evident that new avenues should be pursued and trials specifically designed for elderly people with AML be conducted. These trials would need to address questions related to the choice of chemotherapeutic drugs (e.g. idarubicin versus mitoxantrone), their dose and schedule selection, the use of multidrug resistance modulators (to overcome intrinsic drug non-responsiveness), and the optimal clinical use of haematopoietic growth factors, including thrombopoietin. Since trials addressing specific questions regarding the development of treatment of elderly patients with AML have remained scarce, the initiation of these studies is sorely needed. One may hope that these clinical trials will provide some of the necessary answers and new clues, and will be useful to advance future therapy of elderly AML patients.

Comparative quantitative expression of bcl-2 by normal and leukaemic myeloid cells

Expression of the bcl-2 oncoprotein by AML blasts has previously been demonstrated to be heterogenous with high levels of bcl-2 expression being associated with a low complete remission rate and poor survival. We have quantified bcl-2 expression in AML blasts in relation to expression of the CD34 antigen and in comparison to CD34-positive cells from normal bone marrow. When expressed as molecules of equivalent soluble fluorochrome (MESF) per cell. AML blast cell bcl-2 expression varied from 11.1 to 99.9 x 10(3) (median 39.4 x 10(3), n = 56) with 28.5% of patients expressing high MESF values (> 50 x 10(3)) and 16% of patients expressing low MESF values (< 20 x 10(3), the remainder expressing intermediate values. There was no significant difference between intensity of bcl-2 expression and FAB classification in the de novo AML cases; and there was no significant differences between de novo and secondary AML cases. Blasts from CD34+ AML patients expressed significantly higher levels of bcl-2 (mean MESF 43.6 x 10(3), n = 36) than CD34- AML patients (mean MESF 31.7 x 10(3), n = 19). In five cases of CD34+ AML, bcl-2 expression was determined on purified CD34+ and CD34- blast cell populations. In all cases CD34+ blasts were found to express significantly higher bcl-2 MESF values compared to the CD34- fraction. Purified CD34+ cells from normal bone marrow consistently expressed high levels of bcl-2 (MESF > 75 x 10(3), n = 4), which was comparable to that found on CD34+ AML cells. Our results suggest that the poor prognosis previously associated with AML blasts expressing the CD34 antigen may in part be related to high expression of bcl-2. Also the ability to measure bcl-2 in AML blasts quantitatively by flow cytometry and to categorize patients into discrete groups may be of value as a prognostic indicator in AML.

Acute myeloblastic leukemia with minimal myeloid differentiation (FAB AML-M0): a study of eleven cases

The main clinical, morphological, cytochemical, immunological features and therapy results of eleven patients diagnosed as acute myeloblastic leukemia M0 (AML-M0) are reported here. There were no clinical characteristics, abnormalities on physical examination or initial laboratory parameters that distinguished these eleven patients. Bone marrow aspirates were hypocellular in four patients. The leukemic cells were undifferentiated by light microscopy and myeloperoxidase (MPO) and/or Sudan Black B (SBB) stains were negative in all cases. Myeloid differentiation antigens were present on the leukemic cells of all eleven patients, whereas B and T cell markers were clearly negative except for CD4 and CD7 antigens. Whatever the treatment employed survival was very short. Eight of the eleven patients were treated and two achieved complete remission (CR) but only one of them is alive in continuous CR. Our results like those previously reported, suggest that AML-M0 patients have a very poor prognosis with standard induction therapies and should perhaps be considered for experimental therapeutic approaches.

Intrinsic radiation resistance of primary clonogenic blasts from children with newly diagnosed B-cell precursor acute lymphoblastic leukemia

The radiation sensitivity of primary clonogenic blasts from 44 children with newly diagnosed B-cell precursor acute lymphoblastic leukemia (ALL) was analyzed using leukemic progenitor cell (LPC) colony assays. The derived values for SF2 (surviving fraction at 200 cGy) and alpha (initial slope of radiation survival curves constructed according to the linear quadratic model) indicated a marked interpatient heterogeneity in intrinsic radiation sensitivity of LPC populations. The SF2 values ranged from 0.01 to 1.00 (median = 0.430; mean +/- SE = 0.47 +/- 0.04), and the alpha values ranged from 0.000 to 3.272 Gy-1 (median = 0.280 Gy-1; mean +/- SE = 0.430 +/- 0.093 Gy-1). When CD19+ CD34+ versus CD19+ CD34- immunophenotypes were compared, a trend toward higher SF2 and lower alpha values were observed in LPC from CD34+ patients, consistent with greater radiation resistance. When patients were divided into three approximately equal groups based on increasing levels of CD34 expression, a clear ordering effect was observed indicating that increased CD34 expression levels are associated with significantly higher radiation resistance at the level of B-lineage LPC. The highest CD34 expression group (> or = 75% positivity) had 1.4-fold higher SF2 (P = 0.05) and twofold lower alpha values (P = 0.06) than the lowest group (< 30% positivity). Furthermore, the CD34 positivity of radiation resistant (alpha < or = 0.2 and SF2 > or = 0.5) B-cell precursor ALL cases was greater than the CD34 positivity of radiation sensitive (alpha > 0.2 and/or SF2 < 0.5) cases (56 +/- 9% versus 34 +/- 9%, P = 0.09). Whereas only 6 of 16 (38%) of radiation sensitive cases were CD34+, 11 of 15 (73%) of radiation resistant cases expressed CD34 (P = 0.04). Our results offer new insights into the inherent and/or acquired radiation resistance of primary clonogenic blasts from B-cell precursor ALL patients.