The prognostic significance of early molecular and cytogenetic response for long-term progression-free and overall survival in imatinib-treated chronic myeloid leukemia (CML)

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Background: In the face of competing first line treatment options for CML early prediction of prognosis on imatinib is desirable to assure favorable survival or otherwise consider the use of an alternative therapy. We sought to evaluate the prognostic impact of early response landmarks. Methods: A total of 1,303 newly diagnosed imatinib-treated patients (pts) from the randomized CML Study IV were investigated to correlate molecular and cytogenetic response at 3 and 6 months with progression-free and overall survival (PFS, OS). Median follow-up was 4.7 years (range 0-9). The BCR-ABL expression was determined by quantitative RT-PCR and standardized according to the international scale (BCR-ABLIS). The proportion of Philadelphia-chromosome positive metaphases (Ph+) was determined by conventional metaphase analysis. To confirm the prognostic significance of early molecular response, an independent validation sample of 174 pts treated with imatinib within the IRIS trial was analyzed. Results: The persistence of >10% BCR-ABLIS at 3 months separated a high-risk group (28% of pts; 5-year OS: 87%) from a group with 1-10% BCR-ABLIS (41% of pts; 5-year OS: 94%; p=0.012), and from a group with <1% BCR-ABLIS (31% of pts; 5-year OS: 97%; p=0.004). By cytogenetics high-risk patients could be identified by the persistence of >35% Ph+ (27% of pts; 5-year OS: 87%) as compared to ≤35% Ph+ (73% of pts; 5-year OS: 95%; p=0.036). At 6 months the >1% BCR-ABLIS group (37% of pts; 5-year OS: 89%) showed inferior survival compared to ≤1% (63% of pts; 5-year OS: 97%; p<0.001); survival of the >0% Ph+ group (34% of pts; 5-year OS: 91%) was inferior to 0% Ph+ (66% of pts; 5-year OS: 97%; p=0.015). Regarding the IRIS pts 3 month BCR-ABLIS >10% (25% of pts; 8-year OS: 81%) was associated with inferior survival compared to ≤10% (75% of pts; 8-year OS: 93%; p=0.011). Conclusions: Failure to achieve the response landmarks of 10% BCR-ABLIS or 35% Ph+ at 3 months of imatinib treatment and 1% BCR-ABLIS or 0% Ph+ at 6 months identifies high-risk patients which might benefit from an early change of therapy.

Collapse of telomere homeostasis in hematopoietic cells caused by heterozygous mutations in telomerase genes

Telomerase activity is readily detectable in extracts from human hematopoietic stem and progenitor cells, but appears unable to maintain telomere length with proliferation in vitro and with age in vivo. We performed a detailed study of the telomere length by flow FISH analysis in leukocytes from 835 healthy individuals and 60 individuals with reduced telomerase activity. Healthy individuals showed a broad range in average telomere length in granulocytes and lymphocytes at any given age. The average telomere length declined with age at a rate that differed between age-specific breakpoints and between cell types. Gender differences between leukocyte telomere lengths were observed for all cell subsets studied; interestingly, this trend could already be detected at birth. Heterozygous carriers for mutations in either the telomerase reverse transcriptase (hTERT) or the telomerase RNA template (hTERC) gene displayed striking and comparable telomere length deficits. Further, non-carrier relatives of such heterozygous individuals had somewhat shorter leukocyte telomere lengths than expected; this difference was most profound for granulocytes. Failure to maintain telomere homeostasis as a result of partial telomerase deficiency is thought to trigger cell senescence or cell death, eventually causing tissue failure syndromes. Our data are consistent with these statements and suggest that the likelihood of similar processes occurring in normal individuals increases with age. Our work highlights the essential role of telomerase in the hematopoietic system and supports the notion that telomerase levels in hematopoietic cells, while limiting and unable to prevent overall telomere shortening, are nevertheless crucial to maintain telomere homeostasis with age.

Human blood cells all originate from a common precursor, the hematopoietic stem cell. Telomerase, the enzyme responsible for adding telomere repeats to chromosome ends, is active in human hematopoietic stem cells but appears unable to maintain a constant telomere length with age. We first document the telomere length of different blood cell subsets from 835 healthy individuals between birth and 100 years, to delineate the normal rate of telomere attrition with age. Telomere lengths of blood cells were found to be slightly longer in women than in men, from birth and throughout life. We then compared this reference data to the telomere length in similar blood cell subsets from individuals with reduced telomerase activity as a result of a mutation in one of the genes encoding telomerase and from their direct relatives. Strikingly short telomeres were found in telomerase-deficient individuals, consistent with their cellular pathology and disease susceptibility, and somewhat shorter telomeres than expected were found in cells of relatives with normal telomerase maintenance. Our data can be used as a reference for blood cell telomere length in studies of normal and accelerated aging.

Early molecular and cytogenetic response is predictive for long-term progression-free and overall survival in chronic myeloid leukemia (CML)

In the face of competing first-line treatment options for CML, early prediction of prognosis on imatinib is desirable to assure favorable survival or otherwise consider the use of a second-generation tyrosine kinase inhibitor (TKI). A total of 1303 newly diagnosed imatinib-treated patients (pts) were investigated to correlate molecular and cytogenetic response at 3 and 6 months with progression-free and overall survival (PFS, OS). The persistence of BCR-ABL transcript levels >10% according to the international scale (BCR-ABL(IS)) at 3 months separated a high-risk group (28% of pts; 5-year OS: 87%) from a group with >1-10% BCR-ABL(IS) (41% of pts; 5-year OS: 94%; P=0.012) and from a group with ≤1% BCR-ABL(IS) (31% of pts; 5-year OS: 97%; P=0.004). Cytogenetics identified high-risk pts by >35% Philadelphia chromosome-positive metaphases (Ph+, 27% of pts; 5-year OS: 87%) compared with ≤35% Ph+ (73% of pts; 5-year OS: 95%; P=0.036). At 6 months, >1% BCR-ABL(IS) (37% of pts; 5-year OS: 89%) was associated with inferior survival compared with ≤1% (63% of pts; 5-year OS: 97%; P<0.001) and correspondingly >0% Ph+ (34% of pts; 5-year OS: 91%) compared with 0% Ph+ (66% of pts; 5-year OS: 97%; P=0.015). Treatment optimization is recommended for pts missing these landmarks.

Telomere length is associated with disease severity and declines with age in dyskeratosis congenita

BACKGROUND

Dyskeratosis congenita is a cancer-prone bone marrow failure syndrome caused by aberrations in telomere biology.

DESIGN AND METHODS

We studied 65 patients with dyskeratosis congenita and 127 unaffected relatives. Telomere length was measured by automated multicolor flow fluorescence in situ hybridization in peripheral blood leukocyte subsets. We age-adjusted telomere length using Z-scores (standard deviations from the mean for age).

RESULTS

We confirmed that telomere lengths below the first percentile for age are very sensitive and specific for the diagnosis of dyskeratosis congenita. We provide evidence that lymphocytes alone and not granulocytes may suffice for clinical screening, while lymphocyte subsets may be required for challenging cases, including identification of silent carriers. We show for the first time using flow fluorescence in situ hybridization that the shortest telomeres are associated with severe variants (Hoyeraal-Hreidarsson and Revesz syndromes), mutations in DKC1, TINF2, or unknown genes, and moderate or severe aplastic anemia. In the first longitudinal follow up of dyskeratosis congenita patients, we demonstrate that telomere lengths decline with age, in contrast to the apparent stable telomere length observed in cross-sectional data.

CONCLUSIONS

Telomere length by flow fluorescence in situ hybridization is an important diagnostic test for dyskeratosis congenita; age-adjusted values provide a quantitative measure of disease severity (clinical subset, mutated gene, and degree of bone marrow failure). Patients with dyskeratosis congenita have accelerated telomere shortening. This study is registered at www.clinicaltrials.gov (identifier: NCT00027274).

Deregulated expression of Kruppel-like factors in acute myeloid leukemia

The known participation of Kruppel-like transcription factors (KLF) in cellular differentiation prompted us to investigate their expression in acute myeloid leukemia (AML) blast cells that are typically blocked in their differentiation. We determined the expression patterns of KLFs with a putative role in myeloid differentiation in a large cohort of primary AML patient samples, CD34+ progenitor cells and granulocytes from healthy donors. We found that KLF2, KLF3, KLF5 and KLF6 are significantly lower expressed in AML blast and CD34+ progenitor cells as compared to normal granulocytes. Moreover, we found markedly increased KLF levels in acute promyelocytic leukemia patients who received oral ATRA. Accordingly, we observed a strong induction of KLF5/6 upon ATRA-treatment in NB4 and HT93 APL but not in ATRA-resistant NB4-R cells. Lastly, knocking down KLF5 or KLF6 in NB4 cells significantly attenuated neutrophil differentiation. In conclusion, we found a significant repression of KLF transcription factors in primary AML samples as compared to mature neutrophils and further show that KLF5 and KLF6 are functionally involved in neutrophil differentiation of APL cells.

Telomeres and prognosis in patients with chronic lymphocytic leukaemia

In the present study, telomere length, telomerase activity, the mutation load of immunoglobulin variable heavy chain (IGHV) genes, and established prognostic factors were investigated in 78 patients with chronic lymphocytic leukaemia (CLL) to determine the impact of telomere biology on the pathogenesis of CLL. Telomere length was measured by an automated multi-colour flow-FISH, and an age-independent delta telomere length (ΔTL) was calculated. CLL with unmutated IGHV genes was associated with shorter telomeres (p = 0.002). Furthermore, we observed a linear correlation between the frequency of IGHV gene mutations and elongation of telomeres (r = 0.509, p < 0.001). With respect to prognosis, a threshold ΔTL of -4.2 kb was the best predictor for progression-free and overall survival. ΔTL was not significantly altered over time or with therapy. The correlation between the mutational load in IGHV genes and the ΔTL in CLL might reflect the initial telomere length of the putative cell of origin (pre- versus post-germinal center B cells). In conclusion, the ΔTL is a reliable prognostic marker for patients with CLL. Short telomeres and high telomerase activity as occurs in some patients with CLL with a worse prognosis might be an ideal target for treatment with telomerase inhibitors.

[Molecular analyses for (early) recognition of hematologic diseases - sense and sensibility for molecular analysis: the art of intelligent decision-making]

During the last 10 years several molecular markers have been established as useful tools among the armamentarium of a hematologist. As a consequence, the number of performed hematologic molecular analyses has immensely increased. Often, such tests replace or complement other laboratory methods. Molecular markers can be useful in many ways: they can serve for diagnostics, describe the prognostic profile, predict which types of drugs are indicated, and can be used for the therapeutic monitoring of the patient to indicate an adequate response or predict resistance or relapse of the disease. Many markers fulfill more than one of these aspects. Most important, however, is the right choice of analyses at the right time-points!

Significantly shorter telomeres in T-cells of patients with ZAP-70+/CD38+ chronic lymphocytic leukaemia

In contrast to other B-cell neoplasias, chronic lymphocytic leukaemia (CLL) is characterized by increased non-leukaemic T-cells. In order to assess their replicative history, telomere length was analyzed in subsets of leucocytes from CLL patients. Naive and memory T-cells from ZAP-70(+)/CD38(+) patients exhibited significantly shorter average telomere lengths than ZAP-70(-)/CD38(-) patients. Compared to the age-related percentiles of telomere length values from healthy individuals practically all values of the naive and memory T-cells from the ZAP-70(+)/CD38(+) CLL patients fell below the 50th percentile. This indicated an extensive expansion and a role for T-cells in ZAP-70(+)/CD38(+) CLL patients.

TINF2, a component of the shelterin telomere protection complex, is mutated in dyskeratosis congenita

Patients with dyskeratosis congenita (DC), a heterogeneous inherited bone marrow failure syndrome, have abnormalities in telomere biology, including very short telomeres and germline mutations in DKC1, TERC, TERT, or NOP10, but approximately 60% of DC patients lack an identifiable mutation. With the very short telomere phenotype and a highly penetrant, rare disease model, a linkage scan was performed on a family with autosomal-dominant DC and no mutations in DKCI, TERC, or TERT. Evidence favoring linkage was found at 2p24 and 14q11.2, and this led to the identification of TINF2 (14q11.2) mutations, K280E, in the proband and her five affected relatives and TINF2 R282H in three additional unrelated DC probands, including one with Revesz syndrome; a fifth DC proband had a R282S mutation. TINF2 mutations were not present in unaffected relatives, DC probands with mutations in DKC1, TERC, or TERT or 298 control subjects. We demonstrate that a fifth gene, TINF2, is mutated in classical DC and, for the first time, in Revesz syndrome. This represents the first shelterin complex mutation linked to human disease and confirms the role of very short telomeres as a diagnostic test for DC.

Flow cytometry and FISH to measure the average length of telomeres (flow FISH)

Telomeres have emerged as crucial cellular elements in aging and various diseases including cancer. To measure the average length of telomere repeats in cells, we describe our protocols that use fluorescent in situ hybridization (FISH) with labeled peptide nucleic acid (PNA) probes specific for telomere repeats in combination with fluorescence measurements by flow cytometry (flow FISH). Flow FISH analysis can be performed using commercially available flow cytometers, and has the unique advantage over other methods for measuring telomere length of providing multi-parameter information on the length of telomere repeats in thousands of individual cells. The accuracy and reproducibility of the measurements is augmented by the automation of most pipetting (aspiration and dispensing) steps, and by including an internal standard (control cells) with a known telomere length in every tube. The basic protocol for the analysis of nucleated blood cells from 22 different individuals takes about 12 h spread over 2-3 days.

Short telomeres and high telomerase activity in T-cell prolymphocytic leukemia

To test the role of telomere biology in T-cell prolymphocytic leukemia (T-PLL), a rare aggressive disease characterized by the expansion of a T-cell clone derived from immuno-competent post-thymic T-lymphocytes, we analyzed telomere length and telomerase activity in subsets of peripheral blood leukocytes from 11 newly diagnosed or relapsed patients with sporadic T-PLL. Telomere length values of the leukemic T cells (mean+/-s.d.: 1.53+/-0.65 kb) were all below the 1st percentile of telomere length values observed in T cells from healthy age-matched controls whereas telomere length of normal T- and B cells fell between the 1st and 99th percentile of the normal distribution. Leukemic T cells exhibited high levels of telomerase and were sensitive to the telomerase inhibitor BIBR1532 at doses that showed no effect on normal, unstimulated T cells. Targeting the short telomeres and telomerase activity in T-PLL seems an attractive strategy for the future treatment of this devastating disease.

Telomere length in paroxysmal nocturnal hemoglobinuria correlates with clone size

OBJECTIVE

To study if telomere length can be used as a surrogate marker for the mitotic history in normal and affected hematopoietic cells from patients with paroxysmal nocturnal hemoglobinuria (PNH).

METHODS

The telomere length was measured by automated multicolor flow fluorescence in situ hybridization in glycosyl-phosphatidyl-inositol anchored protein (GPI)-negative and GPI-positive peripheral blood leukocytes. Eleven patients were studied, two with predominantly hemolytic PNH and nine with PNH associated with marrow failure.

RESULTS

Telomere length in GPI-negative cells was significantly shorter than in GPI-positive cells of the same patient (p < 0.01, n = 11). The difference in telomere length (telomere length in GPI-positive minus telomere length in GPI-negative cells) correlated with the percentage of GPI-negative white blood cells.

CONCLUSION

Our results support the hypothesis that telomere length is correlated to the replicative history of GPI-positive and GPI-negative cells and warrant further studies of telomere length in relation to disease progression in PNH.

Very short telomere length by flow fluorescence in situ hybridization identifies patients with dyskeratosis congenita

Dyskeratosis congenita (DC) is an inherited bone marrow failure syndrome in which the known susceptibility genes (DKC1, TERC, and TERT) belong to the telomere maintenance pathway; patients with DC have very short telomeres. We used multicolor flow fluorescence in situ hybridization analysis of median telomere length in total blood leukocytes, granulocytes, lymphocytes, and several lymphocyte subsets to confirm the diagnosis of DC, distinguish patients with DC from unaffected family members, identify clinically silent DC carriers, and discriminate between patients with DC and those with other bone marrow failure disorders. We defined "very short" telomeres as below the first percentile measured among 400 healthy control subjects over the entire age range. Diagnostic sensitivity and specificity of very short telomeres for DC were more than 90% for total lymphocytes, CD45RA+/CD20- naive T cells, and CD20+ B cells. Granulocyte and total leukocyte assays were not specific; CD45RA- memory T cells and CD57+ NK/NKT were not sensitive. We observed very short telomeres in a clinically normal family member who subsequently developed DC. We propose adding leukocyte subset flow fluorescence in situ hybridization telomere length measurement to the evaluation of patients and families suspected to have DC, because the correct diagnosis will substantially affect patient management.

Longitudinal data on telomere length in leukocytes from newborn baboons support a marked drop in stem cell turnover around 1 year of age

Stem cells of various tissues are typically defined as multipotent cells with 'self-renewal' properties. Despite the increasing interest in stem cells, surprisingly little is known about the number of times stem cells can or do divide over a lifetime. Based on telomere-length measurements of hematopoietic cells, we previously proposed that the self-renewal capacity of hematopoietic stem cells is limited by progressive telomere attrition and that such cells divide very rapidly during the first year of life. Recent studies of patients with aplastic anemia resulting from inherited mutations in telomerase genes support the notion that the replicative potential of hematopoietic stem cells is directly related to telomere length, which is indirectly related to telomerase levels. To revisit conclusions about stem cell turnover based on cross-sectional studies of telomere length, we performed a longitudinal study of telomere length in leukocytes from newborn baboons. All four individual animals studied showed a rapid decline in telomere length (approximately 2-3 kb) in granulocytes and lymphocytes in the first year after birth. After 50-70 weeks the telomere length appeared to stabilize in all cell types. These observations suggest that hematopoietic stem cells, after an initial phase of rapid expansion, switch at around 1 year of age to a different functional mode characterized by a markedly decreased turnover rate.

Impact of culture conditions on the proliferative lifespan of human T cells in vitro

BACKGROUND

In human T cells, telomerase is transiently expressed upon activation and stimulation and, as shown previously, telomerase levels are able to control the lifespan of T cells. To improve T-cell expansion it is of critical importance to understand the effects of culture parameters on telomerase activity and lifespan.

METHODS

We investigated the influence of culture condition (FCS, human AB serum and autologous serum) and stimulation (PHA/feeder cells, anti-CD3/CD28 beads) on the lifespan, clonogenicity (number of positive wells), cell cycle, telomerase activity and telomere length of T cells in vitro.

RESULTS

The proliferative lifespan of T cells expanded with PHA/feeder cells and autologous serum from different donors was doubled compared with stimulation with PHA/feeder cells and AB serum. No or only a small difference was found for T cells expanded with anti-CD3/CD28 beads and autologous or AB serum. The use of autologous serum also increased the clonogenicity to about three-fold compared with the use of AB serum or FCS, without any signs of differences in the fractions of cycling cells. Interestingly, T cells cultured with autologous serum exhibited a significantly higher telomerase activity at day 6 after stimulation and a reduced decline of telomerase activity compared with cultures with AB serum.

DISCUSSION

The use of autologous serum combined with PHA stimulation and feeder cells remarkably extends the proliferative lifespan and clonogenicity and increases the telomerase activity of human T cells in vitro. This might be useful for applications where large numbers of specific T cells are required.

Mutations in TERT, the gene for telomerase reverse transcriptase, in aplastic anemia

BACKGROUND

Mutations in TERC, the gene for the RNA component of telomerase, cause short telomeres in congenital aplastic anemia and in some cases of apparently acquired hematopoietic failure. We investigated whether mutations in genes for other components of telomerase also occur in aplastic anemia.

METHODS

We screened blood or marrow cells from 124 patients with apparently acquired aplastic anemia and 282 control subjects for sequence variations in the TERT, DKC1, NHP2, and NOP10 genes; an additional 81 patients and 246 controls were examined for genetic variations in TERT. Telomere lengths and the telomerase activity of peripheral-blood leukocytes were evaluated in patients carrying genetic variants. Identified mutations were transfected into telomerase-deficient cell lines to examine their effects and their mechanism of action on telomerase function.

RESULTS

Five heterozygous, nonsynonymous mutations (which cause an amino acid change in the corresponding protein) were identified in TERT, the gene for the telomerase reverse transcriptase catalytic enzyme, among seven unrelated patients. Leukocytes from these patients had short telomeres and low telomerase enzymatic activity. In three of these patients, the mutation was also detected in buccal mucosa cells. Family members carrying the mutations also had short telomeres and reduced telomerase activity but no evident hematologic abnormality. The results of coexpression of wild-type TERT and TERT with aplastic anemia-associated mutations in a telomerase-deficient cell line suggested that haploinsufficiency was the mechanism of telomere shortening due to TERT mutations.

CONCLUSIONS

Heterozygous mutations in the TERT gene impair telomerase activity by haploinsufficiency and may be risk factors for marrow failure.

Functional characterization of telomerase RNA variants found in patients with hematologic disorders

Human telomerase uses a specific cellular RNA, called hTERC, as the template to synthesize telomere repeats at chromosome ends. Approximately 10% to 15% of patients with aplastic anemia or other bone marrow failure syndromes are carriers of hTERC sequence variants whose functional significance, in most cases, is unknown. We screened 10 reported and 2 newly discovered hTERC variants from such patients and found that 10 of these negatively affected telomerase enzymatic function when they were used to reconstitute telomerase enzymatic function in human cells. Most functional deficits were due to perturbations of hTERC secondary structure and correlated well with the degrees of telomere shortening and reduced telomerase activity observed in peripheral blood lymphocytes of the representative patients. We also found no evidence of dominant-negative activity in any of the mutants. Therefore, loss of telomerase activity and of telomere maintenance resulting from inherited hTERC mutations may limit marrow stem cell renewal and predispose some patients to bone marrow failure.

Telomere loss, senescence, and genetic instability in CD4+ T lymphocytes overexpressing hTERT

Little is known about the long-term consequences of overexpression of the human telomerase reverse transcriptase (hTERT) gene in T lymphocytes. To address this issue, we transduced polyclonal as well as clonally derived populations of naive and memory CD44 T cells from 2 healthy donors (aged 24 and 34 years) with retroviral vectors encoding green fluorescence protein (GFP) and hTERT (GFP-hTERT) or GFP alone. After transduction, cells were sorted on the basis of GFP expression and cultured in vitro until senescence. T cells transduced with hTERT exhibited high stable telomerase activity throughout the culture period. Relative to GFP controls, minor changes in overall gene expression were observed yet the proliferative lifespan of the hTERT-transduced populations was significantly increased and the rate of telomere loss was lower. Nevertheless, hTERT-transduced cells showed progressive telomere loss and had shorter telomeres at senescence than controls (2.3 +/- 0.3 kilobase [kb] versus 3.4 +/- 0.1 kb). Furthermore, a population of cells with 4N DNA consisting of binucleated cells with connected nuclei emerged in the hTERT-transduced cells prior to senescence. We conclude that overexpression of hTERT in CD4+ T cells provides a proliferative advantage independent of the average telomere length but does not prevent eventual genetic instability and replicative senescence.

CD27 expression promotes long-term survival of functional effector-memory CD8+ cytotoxic T lymphocytes in HIV-infected patients

Human immunodeficiency virus (HIV)-specific CD8(+) T cells persist in high frequencies in HIV-infected patients despite impaired CD4(+) T helper response to the virus, but, unlike other differentiated effector cytotoxic T lymphocytes, most continue to express the tumor necrosis factor receptor family member CD27. Because the ligand for CD27 (CD70) is also overexpressed in HIV-infected hosts, we examined the nature of expression and potential functional consequences of CD27 expression on HIV-specific CD8(+) T cells. Analysis of CD27(+) and CD27(-) T cells derived from the same HIV-specific clone revealed that retention of CD27 did not interfere with acquisition of effector functions, and that after T cell receptor stimulation, CD27(+) cells that concurrently were triggered via CD27 exhibited more resistance to apoptosis, interleukin 2 production, and proliferation than CD27(-) T cells. After transfer back into an HIV-infected patient, autologous HIV-specific CD27(-) T cells rapidly disappeared, but CD27(+) T cells derived from the same clone persisted at high frequency. Our findings suggest that the CD27-CD70 interaction in HIV infection may provide CD27(+) CD8(+) T cells with a survival advantage and compensate for limiting or absent CD4(+) T help to maintain the CD8 response.

Telomere length in subpopulations of human hematopoietic cells

In order to test the hypothesis that the telomere length in human hematopoietic cells correlates with their proliferative potential, we analyzed the telomere length in highly purified subpopulations of bone marrow cells. Cells were sorted on the basis of CD34 and CD38 cell surface markers, and two samples were additionally sorted on the basis of Hoechst 33342 dye efflux allowing isolation of side population (SP) cells. The telomere length in limiting numbers of sorted cells was analyzed using a newly developed fluorescence in situ hybridization (flow-FISH) method in which hybridization of telomere probe in cells of interest is measured relative to control cells in the same tube. In all seven bone marrow samples analyzed, the telomere length in CD34(+)CD38(-) cells was longer than in CD34(+)CD38(+) cells from the same donor (p < 0.02). Results with sorted SP cells were less clear: the telomere fluorescence in these cells was very heterogeneous, and a reproducible difference in telomere length relative to CD34(+)CD38(-) cells could not be observed. We conclude that the telomere length in subpopulations of hematopoietic cells does appear to be correlated with the known proliferative potential of such cells and that further characterization of cells on the basis of telomere length is warranted for enrichment of very rare precursors of hematopoietic and other tissues.

Late presentation of dyskeratosis congenita as apparently acquired aplastic anaemia due to mutations in telomerase RNA

Aplastic anaemia in adults is usually acquired, but rarely constitutional types of bone marrow failure can occur late in life. We assessed two families with onset of pancytopenia in adults and detected two novel point mutations in the telomerase RNA gene (TERC) in each family. This gene is abnormal in some kindreds with dyskeratosis congenita. Individuals in our families with mutated TERC did not have physical signs of dyskeratosis congenita, and their blood counts were nearly normal, but all had severely shortened telomeres, reduced haemopoietic function, and raised serum erythropoietin and thrombopoietin. Bone marrow failure of variable severity due to dyskeratosis congenita, historically characterised by associated physical anomalies and early pancytopenia, may be present in otherwise phenotypically normal adults, and can masquerade as acquired aplastic anaemia.

Telomere length measurements in leukocyte subsets by automated multicolor flow-FISH

BACKGROUND

Telomeres are essential protein-DNA structures at the end of chromosomes which are implicated in genome stability and cell replication. The average length of telomere repeats can be measured by in situ hybridization and flow cytometry [flow-FISH]. Such telomere length values reflect telomere shortening (resulting from cell divisions, oxidative damage and other causes) and telomere elongation (mainly resulting from telomerase activity) of the chromosome-specific telomere length inherited in the gametes. Here we report improvements in flow-FISH methodology that enable measurements of telomere length in subsets of human nucleated blood cells.

METHODS AND RESULTS

In order to measure the telomere length in granulocytes, naive T cells, memory T cells, B cells and natural killer (NK)/NKT cells within a blood sample, we combined flow-FISH with antibody-staining (Multicolor flow-FISH). Most steps in the staining protocol were automated using a 96-well microdispenser device. The minimum detectable difference in telomere length and the reproducibility of the method are in the range of 0.2-0.5 kb and measurements can be made with as few as a thousand cells.

CONCLUSIONS

Automated multicolor flow-FISH will greatly facilitate studies of telomere length regulation in subsets of nucleated blood cells, especially when only few cells are available and when differences in telomere length are small.

Anti-Xa activity in obese patients after double standard dose of nadroparin for prophylaxis

We measured anti-Xa activity before and at 2, 4, 9 and 12 h after subcutaneous injection of 0.3 ml nadroparin (2850 IU anti-Xa) in normal-weight volunteers (median bodyweight 71 kg, n=5) and compared them to the anti-Xa activity after subcutaneous injection of 0.6 ml nadroparin (5700 IU anti-Xa) in obese patients (median bodyweight 134 kg, n=8). The resulting median anti-Xa activity after 4 h was 1.4 times greater in the group of obese patients. This finding suggests that a linear, weight-adjusted increase in the prophylactic dose of nadroparin does not result in a linear increase of anti-Xa activity in obese patients.

Mutations of the human telomerase RNA gene (TERC) in aplastic anemia and myelodysplastic syndrome

Mutations in the human telomerase RNA (TERC) occur in autosomal dominant dyskeratosis congenita (DKC). Because of the possibility that TERC mutations might underlie seemingly acquired forms of bone marrow failure, we examined blood samples from a large number of patients with aplastic anemia (AA), paroxysmal nocturnal hemoglobinuria (PNH), and myelodysplasia (MDS). Only 3 of 210 cases showed heterozygous TERC mutations: both nucleotide 305 (n305) (G>A) and n322 (G>A) were within the conserved region (CR) 4-CR5 domain; n450 (G>A) was localized to the boxH/ACA domain. However, only one patient (with a mutation at n305 [G>A]) had clinical characteristics suggesting DKC; her blood cells contained short telomeres and her sister also suffered from bone marrow failure. Another 21 patients with short telomeres did not show TERC mutations. Our results suggest that cryptic DKC, at least secondary to mutations in the TERC gene, is an improbable diagnosis in patients with otherwise typical AA, PNH, and MDS.

Telomere shortening in hematopoietic stem cell transplantation: a potential mechanism for late graft failure?

Telomeres serve to maintain the structural integrity of chromosomes, yet each somatic cell division is associated with a decrease in telomere length. The cumulative decrease in telomere length can impose an upper limit for the number of cell divisions that can occur before a cell senesces. When studied in vitro with fibroblasts, this limit is referred to as the Hayflick limit and usually occurs after 40 to 80 cell doublings. In theory, a similar replicative potential in a hematopoietic stem cell could support hematopoiesis in a person for more than 100 years. However, stem cells differentiate, and the telomere length differs among chromosomes within a single cell, among cell types, and among age-matched individuals. This variation in telomere length raises the possibility that long-term hematopoiesis by transplanted stem cells could, depending on the telomere length of the engrafted stem cell and the proliferative demand to which it is subjected, reach a Hayflick limit during the life span of the patient. Although significant shortening of telomeres is reported to occur within the first year posttransplantation, as yet no evidence has indicated that this shortening is associated with marrow function. In this review, we summarize reports on telomere shortening in stem cell transplantation recipients and report 2 cases in which graft failure is associated with significant telomere shortening.

Telomeres in hematopoietic stem cells

Hematopoietic stem cells have an impressive regenerative potential, strikingly illustrated in transplantation experiments using limited number of cells. In mice, serial transplantation experiments suggest that individual hematopoietic cells are capable of extensive self-renewal and that any possible limitations in the replicative potential of individual hematopoietic stem cells are not affecting normal blood cell formation. The situation with human hematopoietic stem cells is less clear. Unlike the situation in the mouse, the telomere length in nucleated human blood cells shows a remarkable decline with age. Furthermore, even partial telomerase deficiency in humans typically results in marrow failure, whereas complete lack of telomerase is tolerated up to several generations in the mouse. The decline in telomere length in human leukocytes with age follows a cubic function and is much higher in lymphocytes than in granulocytes. This finding suggests that, under normal circumstances, telomere loss is more likely to compromise the function of lymphocytes than the function of hematopoietic stem cells. To reconcile differences in telomere biology between man and mice, it has been proposed that telomere shortening evolved as a tumor suppressor mechanism in long-lived species that may not exist in shorter-lived mammals. According to this model, telomeres in human cells are intimately involved in signaling cell cycle progression and cell division. Most likely, a minimum number of telomere repeats is required at each telomere to prevent activation of a "telomere checkpoint" and allow cell cycle progression. Telomere length measurements appear useful to distinguish between depletion and exhaustion of hematopoietic stem cells as a cause of marrow failure.

Telomere shortening in leukocyte subpopulations from baboons

To address questions about telomere length regulation in nonhuman primates, we studied the telomere length in subpopulations of leukocytes from the peripheral blood of baboons aged 0.2-26.5 years. Telomere length in granulocytes, B cells, and subpopulations of T cells all decreased with age. Overall, telomere length kinetics were lineage- and cell subset-specific. T cells showed the most pronounced, overall decline in telomere length. Levels of telomerase in stimulated T cells from old animals were lower than in corresponding cells from young animals. Memory T cells with very short telomeres accumulated in old animals. In contrast, the average telomere length values in B cells remained relatively constant from middle age onward. Individual B cells showed highly variable telomere length, and B cells with very long telomeres were observed after the ages of 1-2 years. In general, cell type-specific telomere kinetics in baboons were remarkably similar to those observed in humans.

Longitudinal studies of telomere length in feline blood cells: implications for hematopoietic stem cell turnover in vivo

OBJECTIVE

To address questions about stem cell turnover in relation to telomere length dynamics, we analyzed telomere length in serial blood samples from cats.

MATERIALS AND METHODS

Lymphocytes and granulocytes from two newborn kittens, a 2-year-old cat, a 10-year-old recipient of a double autologous stem cell transplant, and a 10-year-old control animal were analyzed by fluorescence in situ hybridization and flow cytometry at 2-week intervals over a 1-year period.

RESULTS

At study onset, long telomeres were found in granulocytes and lymphocytes from the two kittens (mean +/- SD: 70.2 +/- 3.1 and 72.5 +/- 3.1 telomere fluorescence units [TFU], respectively) compared with the 2-year-old cat (55.6 +/- 2.5 and 64.1 +/- 4.3 TFU, respectively) and the two adult animals (49.6 +/- 1.5 and 45.4 +/- 0.8 TFU, respectively). The rate of telomere shortening in both granulocytes and lymphocytes was most rapid in the kittens (slope: -16.7 +/- 1.4 and -15.6 +/- 0.2 TFU/year, respectively). As in humans, telomere shortening with age was more rapid in lymphocytes than in granulocytes. An average rate of telomere attrition of -0.52 +/- 0.03 TFU per cell division was calculated for cultured lymphocytes from the two kittens, approximately 5-fold higher than the rate observed in human cells.

CONCLUSIONS

The average telomere length in cats is 5- to 10-fold longer than in humans, but the rate of telomere shortening is much higher both in vivo and in vitro. These observations are compatible with similar stem cell kinetics in both species.

Telomere length measurement by fluorescence in situ hybridization and flow cytometry: tips and pitfalls

BACKGROUND

Telomeres containing noncoding DNA repeats at the end of the chromosomes are essential for chromosomal stability and are implicated in regulating the replication and senescence of cells. The gradual loss of telomere repeats in cells has been linked to aging and tumor development and methods to measure telomere length are of increasing interest. At least three methods for measuring the length of telomere repeats have been described: Southern blot analysis and quantitative fluorescence in situ hybridization using either digital fluorescence microscopy (Q-FISH) or flow cytometry (flow-FISH). Both Southern blot analysis and Q-FISH have specific limitations and are time-consuming, whereas the flow-FISH technique requires relatively few cells (10(5)) and can be completed in a single day. A further advantage of the flow-FISH method is that data on the telomere length from individual cells and subsets of cells (lymphocytes and granulocytes) can be acquired from the same sample. In order to obtain accurate and reproducible results using the flow-FISH technique, we systematically explored the influence of various steps in the protocol on telomere length values and established an acceptable range for the most critical parameters.

METHODS

Isolated leukocytes from whole blood are denatured by heat and 70%/75% formamide, then hybridized with or without a telomere-specific fluorescein isothiocyante (FITC)-conjugated peptide nucleic acid probe (PNA). Unbound telomere PNA is washed away, the DNA is counterstained, and telomere fluorescence is measured on a flow cytometer using an argon ion laser (488 nm) to excite FITC. For each sample, duplicates of telomere PNA-stained and unstained tubes are analyzed.

RESULTS

Cell counts and flow-FISH telomere length measurements were performed on leukocytes and thymocytes of humans and other species. Leukocyte suspensions were prepared by two red blood cell lysis steps with ammonium chloride. Optimal denaturation of DNA was achieved by heating at 85-87 degrees C for 15 min in a solution containing 70%/75% formamide. Hybridization was performed at room temperature with a 0.3 microg/ml telomere-PNA probe for at least 60-90 min. Unbound telomere-PNA probe was diluted at least 4,000-40,000 times with wash steps containing 70%/75% formamide at room temperature. LDS 751 and DAPI were suitable as DNA counterstains as they did not show significant interference with telomere length measurement.

CONCLUSIONS

The use of flow-FISH for telomere length measurements in nucleated blood cells requires tight adherence to an optimized protocol. The method described here can be used to determine rapidly the telomere length in subsets of nucleated blood cells.

Gel-filtration of sickle erythrocytes: separation based on cell deformability

Filtration of red blood cells (RBC) through columns of pre-swollen agarose-based beads has been evaluated using cells from subjects with sickle cell disease. Elution profiles from these gels showed elution times close to normal controls for a large fraction of sickle erythrocytes and a prolonged elution time for a sub-population of these cells. Analysis of red blood cell deformability using a computerized micropore filtration system (CTA) indicated that the deformability of sickle red blood cells in the first fraction was similar to controls but that the last fraction contained a sub-population of rigid RBC. We thus conclude that sickle red blood cell separation in columns of agarose-based beads is based upon cell deformability. Gel filtration therefore appears to be an interesting tool for the study of red blood cells in a variety of disorders with sub-populations of rigid, abnormal cells, and seems especially suited for studies in various sickle cell diseases.

KEYWORDS

Deformability, gel filtration, sickle cell disease, erythrocyte

Limited telomere shortening in hematopoietic stem cells after transplantation

The number of cell divisions in hematopoietic stem cells (HSCs) following transplantation of bone marrow or mobilized peripheral blood into myelo-ablated recipients is unknown. This number is expected to depend primarily on the number of transplanted stem cells, assuming that stem cells do not differ in engraftment potential and other functional properties. In a previous study, we found that the telomere length in circulating granulocytes in normal individuals shows a biphasic decline with age, most likely reflecting age-related changes in the turnover of HSCs. In order to study HSCs' proliferation kinetics following stem cells transplantation, we analyzed the telomere length in donor-derived nucleated blood cells in four HLA-matched bone marrow transplant recipients relative to comparable cells from the sibling donors. In each case, the telomeres in granulocytes were shorter in the recipient than in the donor. This difference was established in the first year post transplantation and did not change after that. The telomere length in naïve and memory T cells showed marked differences after transplantation, complicating the interpretation of telomere length data using unseparated nucleated blood cells. Interestingly, the telomere length in naïve T cells that were first observed six months post transplantation was very similar in donor and recipient pairs. Our observations are compatible with a limited number of additional cell divisions in stem cell populations after bone marrow transplantations and support the idea that different populations of stem cells contribute to short-term myeloid and long-term lympho myeloid hematopoiesis.

Extension of cell life-span and telomere length in animals cloned from senescent somatic cells

The potential of cloning depends in part on whether the procedure can reverse cellular aging and restore somatic cells to a phenotypically youthful state. Here, we report the birth of six healthy cloned calves derived from populations of senescent donor somatic cells. Nuclear transfer extended the replicative life-span of senescent cells (zero to four population doublings remaining) to greater than 90 population doublings. Early population doubling level complementary DNA-1 (EPC-1, an age-dependent gene) expression in cells from the cloned animals was 3.5- to 5-fold higher than that in cells from age-matched (5 to 10 months old) controls. Southern blot and flow cytometric analyses indicated that the telomeres were also extended beyond those of newborn (<2 weeks old) and age-matched control animals. The ability to regenerate animals and cells may have important implications for medicine and the study of mammalian aging.

[Patient with recurrent gastrointestinal hemorrhage in acquired von Willebrand disease]

A 61-year-old female without prior history of bleeding experienced several symptomatic episodes of gastrointestinal bleeding in the last few years. A source of gastrointestinal bleeding could not be found although several tests of occult blood in the stool were positive. Diagnostically, a significant deficiency of von Willebrand factor could be found due to a shortened half-life of the von Willebrand factor. This acquired von Willebrand factor deficiency most likely can be explained by an immunological mechanism (e.g. antibodies against von Willebrand factor). Neither an immunosuppressive therapy with steroids nor cyclophosphamide could normalize the von Willebrand factor and the bleeding continued. Only tranexamic acid (inhibiting fibrinolysis) could at last stop the symptomatic episodes of gastrointestinal bleeding despite the fact of decreasing von Willebrand factor.

Ifosfamide-induced stomatocytosis and mesna-induced echinocytosis: influence on biorheological properties of blood

Ifosfamide is an alkylating agent which has poorly understood toxic side effects such as encephalopathy. We hypothesized that ifosfamide and concomitantly applied mesna could have an influence on the flow properties of blood, and thus carried out an in vitro study. Whole blood was incubated in vitro with increasing concentrations of ifosfamide (0-50 mg/ml), mesna (0-20 mg/ml) and combinations thereof. Chloroacetaldehyde, a major metabolite of ifosfamide, was also studied (0-5 mmol/l). Ifosfamide led to a dose-dependent stomatocytic shape transformation and mesna to an echinocytic shape transformation of erythrocytes. These shape changes were reversible upon removal of the causing agent. Both shape changes increased whole blood viscosity. Erythrocyte aggregation was decreased by both drugs at high concentration. Erythrocyte deformability, as measured with the transit time through 5-microm pores, was decreased by mesna and remained unaffected by ifosfamide. These effects were seen at concentrations which may be reached in vivo at the infusion site of the drugs into a vein and in the urinary tract. We conclude that ifosfamide and mesna interact with the lipid bilayer of the cell membrane, which may contribute to the toxicity of the compounds.

Influence of a recombinant hemoglobin solution on blood rheology

BACKGROUND

Red cell transfusion is a matter of great concern because of viral infections. Recently, a genetically engineered hemoglobin, rHb 1.1, consisting of two alpha chains and one beta chain, has been developed; it has good oxygen-carrying and -unloading capacity and is devoid of renal toxicity.

STUDY DESIGN AND METHODS

An in vitro study of the influence of increasing concentrations of rHb 1.1 on plasma and blood viscosity, red cell aggregation and deformability, and neutrophil deformability was performed.

RESULTS

The rHb 1.1 (50 g/L in phosphate-buffered saline) had a viscosity of 0.80 +/- 0.02 mPa-sec at 37 degrees C, which was lower than that of normal Hb solution at the same Hb concentration (0.93 +/- 0.01 mPa-sec, p < 0.001) or of albumin, a protein with similar molecular weight (0.93 +/- 0.01, p < 0.0001). The admixture of rHb 1.1 to plasma or to red cell suspensions, at constant Hb concentration, led to a dose-dependent decrease in their viscosities. The simulation of replacement therapy during blood loss revealed rheologic properties of rHb 1.1 that were superior to those of all other fluids. The rHb 1.1 did not affect red cell aggregation or the deformability of red cells or white cells, as measured by the cells' transit time through small pores.

CONCLUSION

These data indicate that rHb 1.1 has excellent rheologic properties and should hold promise not only as an oxygen-carrying therapeutic agent, but probably also as a hemodilutional agent that simultaneously decreases blood viscosity and provides oxygen-carrying capacity.

The anti-neoplastic drug 5-fluorouracil produces echinocytosis and affects blood rheology

The anti-neoplastic agent 5-fluorouracil (5-FU) in high therapeutic doses can induce angina pectoris and myocardial infarction. The pathophysiological mechanism of this side-effect has not yet been elucidated. We analysed the influence of 5-FU on blood rheology in vitro. Whole blood, blood cell suspensions and plasma were incubated with increasing concentrations of 5-FU (final concentrations 0, 0.08, 0.4, 2, 10 and 25 mg/ml 5-FU) at 37 degrees C. Erythrocyte morphology was analysed after fixation with glutaraldehyde. Viscosity was measured at high and low shear rates (94 and 0.1 s[-1]). Erythrocyte aggregation and the cell transit times of erythrocytes through 5 microm pores and polymorphonuclear leucocytes through 8 microm pores were determined. 5-FU induced a dose-dependent formation of echinocytes within minutes and was reversible upon removal of 5-FU, which reflected a preferential intercalation of the drug in the outer hemileaflet of the cell membrane. High shear blood viscosity was increased at the highest 5-FU concentration (148 +/- 12%), and at low shear rate a dose-dependent decrease was found (0 mg/ml: 100%, 0.08 mg/ml: 87 +/- 10%, 0.4 mg/ml: 80 +/- 19%, 2 mg/ml: 70 +/- 15%, 10 mg/ml: 40 +/- 19%, 25 mg/ml: 33 +/- 5%). Erythrocyte aggregation was decreased by the 5-FU-induced echinocytosis. The transit time of erythrocytes through narrow pores was increased in a dose-dependent manner by 5-FU, whereas the transit time of polymorphonuclear leucocytes was initially decreased at 10 mg/ml and returned to control after 60 min incubation. We conclude that 5-FU interacts with the cell membrane, induces echinocytosis and vesiculation and affects blood rheology in several ways which may contribute to cardiovascular complications.

No influence of echinocytic shape transformation of erythrocytes on phagocytosis by autologous monocytes in vitro

The influence of echinocytosis induced by ATP depletion on erythrophagocytosis was analysed. Monocytes were isolated from peripheral blood of healthy, rhesus-positive volunteers and cultured for a total time of 6 h at 37 degrees C with 5% CO2. Erythrocytes from the same donor, either fresh (discocytes) or incubated at 37 degrees C for 48 h (spheroechinocytes) were added. Phagocytosis was quantified by measuring the chemiluminescence of the ingested heme. The rate of phagocytosis was 0.03 +/- 0.15 discocytes per phagocytic cell and 0.01 +/- 0.08 spheroechinocytes per phagocytic cell. Autologous serum did not affect this rate. The addition of anti-RhD immunoglobulins, however, increased phagocytosis drastically for discocytes and spheroechinocytes (4.22 +/- 2.09 and 5.24 +/- 2.58 erythrocytes per phagocytic cell, respectively). It is concluded that spheroechinocytosis induced by metabolic depletion, certainly one of the most severe forms of erythrocyte shape abnormalities, does not stimulate monocytes to remove these cells.

Erythrocyte deformability has no influence on the rate of erythrophagocytosis in vitro by autologous human monocytes/macrophages

Erythrocytes with decreased deformability are known to be rapidly removed from the circulation by splenic macrophages. The exact mechanism is, however, not well understood. We have analysed the phagocytosis of less-deformable erythrocytes by macrophages in vitro. Human monocytes/macrophages were isolated from peripheral blood and cultured for a total time of 6 h at 37 degrees C with 5% CO2. Autologous erythrocytes of the rhesus positive donor were rigidified by heat treatment (47 degrees C for 1 h). The change in erythrocyte deformability was assessed with a filter aspiration technique; the membrane elastic modulus was found to be increased about 2.5-fold. For controls, untreated erythrocytes and erythrocytes incubated with anti-RhD-antibodies were prepared. The rate of phagocytosis during 2 h at 37 degrees C and 5% CO2 was 0.74 +/- 0.59 (erythrocytes per monocyte/macrophage) for controls, 3.58 +/- 2.72 for anti-RhD-loaded erythrocytes and 0.82 +/- 0.74 for heat-treated erythrocytes, respectively. We conclude that decreased erythrocytes deformability does not cause an increased rate of phagocytosis by monocytes/macrophages compared to normally deformable erythrocytes in our in vitro model. This suggests that the preferential removal of rigid cells in vivo is probably not a specific process, but is due to the increased splenic transit time of rigid erythrocytes and hence longer interaction time between erythrocytes and phagocytes.