Telomere biology in hematopoiesis and stem cell transplantation

Telomere biology disorders may manifest as common variable immunodeficiency (CVID)

Telomere biology disorders (TBD) are caused by germline pathogenic variants in genes related to telomere maintenance and are characterized by critically short telomeres. In contrast to classical dyskeratosis congenita (DC), which is typically diagnosed in infancy, adult or late onset TBD frequently lack the typical DC triad and rather show variable organ manifestations and a cryptic disease course, thus complicating its diagnosis. Common variable immunodeficiency (CVID), on the other hand, is a primary antibody deficiency (PAD) syndrome. PADs are a heterogenous group of diseases characterized by hypogammaglobulinemia which occurs due to dysfunctional B lymphocytes and additional autoimmune and autoinflammatory complications. Genetic screening reveals a monogenic cause in a subset of CVID patients (15-35%). In our study, we screened the exomes of 491 CVID patients for the occurrence of TBD-related variants in 13 genes encoding for telomere/telomerase-associated proteins, which had previously been linked to the disease. We found 110/491 patients (22%) carrying 91 rare candidate variants in these 13 genes. Following the American College of Medical Genetics and Genomics (ACMG) guidelines, we classified two variants as benign, two as likely benign, 64 as variants of uncertain significance (VUS), four as likely pathogenic, and one heterozygous variant in an autosomal recessive disease gene as pathogenic. We performed telomere length measurement in 42 of the 110 patients with candidate variants and CVID. Two of these 42 patients showed significantly shorter telomeres compared to controls in both lymphocytes and granulocytes. Following the evaluation of the published literature and the patient's manifestations, we re-classified two VUS as likely pathogenic variants. Thus, 0.5-1% of all CVID patients in our study carry possibly pathogenic variants in telomere/telomerase-associated genes. Our data adds CVID to the broad clinical spectrum of cryptic adult-onset TBD. As the molecular diagnosis greatly impacts patient management and treatment strategies, we advise inclusion of all TBD-associated genes-despite their low prevalence-into the molecular screening of patients with antibody deficiencies.

Donor cord blood aging accelerates in recipients after transplantation

Cord blood stem cell transplantation is an important alternative for patients needing hematopoietic stem cell transplantation. However, it is unclear how cord blood cells, which are 0 years old, age in the recipient's body after allogeneic transplantation. We performed DNA methylation (DNAm) age analysis to measure the age of cells using post-transplant peripheral blood in 50 cases of cord blood transplantation. The median chronological age (the time elapsed from the date of the cord blood transplant to the day the sample was taken for DNAm analysis) of donor cells was 4.0 years (0.2-15.0 years), while the median DNAm age was 10.0 years (1.3-30.3 years), and the ratio of DNAm age to chronological age (AgeAccel) was 2.7 (1.2-8.2). When comparing the mean values of AgeAccel in cord blood transplant cases and controls, the values were significantly higher in cord blood transplant cases. The characteristics of patients and transplant procedures were not associated with AgeAccel in this analysis, nor were they associated with the development of graft-versus-host disease. However, this analysis revealed that transplanting 0-year-old cord blood into a recipient resulted in cells aging more than twice as quickly as the elapsed time. The results shed light on the importance of the mismatch between cord blood stem cells and donor environmental factors in stem cell aging.

The Achilles' heel of cancer survivors: fundamentals of accelerated cellular senescence

Recent improvements in cancer treatment have increased the lifespan of pediatric and adult cancer survivors. However, cancer treatments accelerate aging in survivors, which manifests clinically as the premature onset of chronic diseases, such as endocrinopathies, osteoporosis, cardiac dysfunction, subsequent cancers, and geriatric syndromes of frailty, among others. Therefore, cancer treatment-induced early aging accounts for significant morbidity, mortality, and health expenditures among cancer survivors. One major mechanism driving this accelerated aging is cellular senescence; cancer treatments induce cellular senescence in tumor cells and in normal, nontumor tissue, thereby helping mediate the onset of several chronic diseases. Studies on clinical monitoring and therapeutic targeting of cellular senescence have made considerable progress in recent years. Large-scale clinical trials are currently evaluating senotherapeutic drugs, which inhibit or eliminate senescent cells to ameliorate cancer treatment-related aging. In this article, we survey the recent literature on phenotypes and mechanisms of aging in cancer survivors and provide an up-to-date review of the major preclinical and translational evidence on cellular senescence as a mechanism of accelerated aging in cancer survivors, as well as insight into the potential of senotherapeutic drugs. However, only with time will the clinical effect of senotherapies on cancer survivors be visible.

A study of TERT rare variants in myeloid neoplasia

Telomere dysfunctions are associated with several hematopoietic stem cell (HSC) malignancies. Recent findings have indicated that the occurrence of rare variants of unknown significance (VUS) in the Telomerase Reverse Transcriptase (TERT) gene influences the outcomes of patients with myelodysplastic syndromes undergoing allogeneic HSC transplantation. However, the role of TERT variants has been historically controversial as initially considered pathogenic variants (H412Y, A202T) presenting functional consequences, were found very frequent in general population questioning their pathogenicity and risk allele significance. Herein, we show that overall TERT VUS are non-recurrent in myeloid disorders and cannot be considered risk alleles individually nor can their biological impact. This article is protected by copyright. All rights reserved.

Telomerase-based therapies in haematological malignancies

Telomeres are specialized genetic structures present at the end of all eukaryotic linear chromosomes. They progressively get shortened after each cell division due to end replication problems. Telomere shortening (TS) and chromosomal instability cause apoptosis and massive cell death. Following oncogene activation and inactivation of tumour suppressor genes, cells acquire mechanisms such as telomerase expression and alternative lengthening of telomeres to maintain telomere length (TL) and prevent initiation of cellular senescence or apoptosis. Significant TS, telomerase activation and alteration in expression of telomere-associated proteins are frequent features of different haematological malignancies that reflect on the progression, response to therapy and recurrence of these diseases. Telomerase is a ribonucleoprotein enzyme that has a pivotal role in maintaining the TL. However, telomerase activity in most somatic cells is insufficient to prevent TS. In 85-90% of tumour cells, the critically short telomeric length is maintained by telomerase activation. Thus, overexpression of telomerase in most tumour cells is a potential target for cancer therapy. In this review, alteration of telomeres, telomerase and telomere-associated proteins in different haematological malignancies and related telomerase-based therapies are discussed.

A standalone approach to utilize telomere length measurement as a surveillance tool in oral leukoplakia

Oral squamous cell carcinoma (OSCC) is often preceded by a white patch on a surface of the mouth, called oral leukoplakia (OL). As accelerated telomere length (TL) shortening in dividing epithelial cells may lead to oncogenic transformation, telomere length measurement could serve as a predictive biomarker in OL. However, due to high variability and lack of a universal reference, there has been a limited translational application. Here, we describe an approach of evaluating TL using paired peripheral blood mononuclear cells (PBMC) as an internal reference and demonstrate its translational relevance. Oral brush biopsy and paired venous blood were collected from 50 male OL patients and 44 male healthy controls (HC). Relative TL was measured by quantitative PCR. TL of each OL or healthy sample was normalized to the paired PBMC sample (TL ratio). In OL patients, the mean TL ratio was significantly smaller not only in the patch but also in distal normal oral tissue, relative to healthy controls without a high‐risk oral habit. Dysplasia was frequently associated with a subgroup that showed a normal TL ratio at the patch but significantly smaller TL ratio at a paired normal distal site. Our data suggest that evaluation of TL attrition using a paired PBMC sample eliminates the requirement of external reference DNA, makes data universally comparable and provides a useful marker to define high‐risk OL groups for follow‐up programs. Larger studies will further validate the approach and its broader application in other premalignant conditions.

Special issues related to the diagnosis and management of acquired aplastic anemia in countries with restricted resources, a report on behalf of the Eastern Mediterranean blood and marrow transplantation (EMBMT) group and severe aplastic anemia working party of the European Society for blood and marrow transplantation (SAAWP of EBMT)

Aplastic anemia is a relatively rare but potentially fatal disorder, with a reported higher incidence in developing countries in comparison to the West. There are significant variations in epidemiological as well as etiological factors of bone marrow failure syndromes in the developing countries in comparison to the developed world. Furthermore, the management of bone marrow failure syndromes in resource constraint settings has significant challenges including delayed diagnosis and referral, limited accessibility to healthcare facilities, treatment modalities as well as limitations related to patients who require allogeneic stem cell transplantation. Here we will provide a review of the available evidence related to specific issues of aplastic anemia in the developing countries and we summarize suggested recommendations from the Eastern Mediterranean blood and bone marrow transplantation (EMBMT) group and the severe aplastic anemia working party of the European Society of blood and marrow transplantation (SAAWP of EBMT) related to the diagnosis and therapeutic options in countries with restricted resources.

Epigenetic Aging and Hematopoietic Cell Transplantation in Patients With Severe Aplastic Anemia

Cellular aging in hematopoietic cell transplantation (HCT) is important in the context of immune reconstitution and age-related complications. Recently, several DNA-methylation (DNAm)-based biomarkers of aging known as "epigenetic clocks" have been introduced as novel tools to predict cellular age. Here, we used Cox proportional hazards models to assess the possible associations of donor pre-HCT DNAm age, and its post-HCT changes, using the recently published lifespan-associated epigenetic clock known as "DNAm-GrimAge," with outcomes among patients with severe aplastic anemia (SAA). The study included 732 SAA patients from the Transplant Outcomes in Aplastic Anemia project, who underwent unrelated donor HCT and for whom a donor pre-HCT blood DNA sample was available; 41 also had a post-HCT sample collected at day 100. In multivariable analyses, we found similar associations for donor chronological age and pre-HCT DNAm-GrimAge with post-HCT survival (hazard ratio [HR] per decade = 1.13; 95% confidence interval [CI], 0.99-1.28; P = .07 and HR = 1.14; 95% CI, 0.99-1.28; P = .06, respectively). In donors with 10+ years of GrimAge acceleration (ie, deviation from expected DNAm age for chronological age), elevated risks of chronic graft versus host disease (HR = 2.4; 95% CI, 1.21-4.65; P = .01) and possibly post-HCT mortality (HR = 1.79; 95% CI, 0.96-3.33; P = .07) were observed. In the subset with post-HCT samples, we observed a significant increase in DNAm-GrimAge in the first 100 days after HCT (median change 12.5 years, range 1.4 to 26.4). Higher DNAm-GrimAge after HCT was associated with inferior survival (HR per year = 1.11; 95% CI, 1.02-1.21; P = .01), predominantly within the first year after HCT. This study highlights the possible role cellular aging may play in HCT outcomes.

Telomere Length and Hematological Disorders: A Review

Telomeres compose the end portions of human chromosomes, and their main function is to protect the genome. In hematological disorders, telomeres are shortened, predisposing to genetic instability that may cause DNA damage and chromosomal rearrangements, inducing a poor clinical outcome. Studies from 2010 to 2019 were compiled and experimental studies using samples of patients diagnosed with hematological malignancies that reported the size of the telomeres were described. Abnormal telomere shortening is described in cancer, but in hematological neoplasms, telomeres are still shortened even after telomerase reactivation. In this study, we compared the sizes of telomeres in leukemias, myelodysplastic syndrome and lymphomas, identifying that the smallest telomeres are present in patients at relapse. In conclusion, the experimental and clinical data analyzed in this review demonstrate that excessive telomere shortening is present in major hematological malignancies and its analysis and measurement is a crucial step in determining patient prognosis, predicting disease risk and assisting in the decision for targeted therapeutic strategies.

Immunosenescent characteristics of T cells in young patients following haploidentical haematopoietic stem cell transplantation from parental donors

Objectives

Paediatric and adolescent patients in need of allogeneic haematopoietic stem cell transplantation (HSCT) generally receive stem cells from older, unrelated or parental donors when a sibling donor is not available. Despite encouraging clinical outcomes, it has been suggested that immune reconstitution accompanied by increased replicative stress and a large difference between donor and recipient age may worsen immunosenescence in paediatric recipients.

Methods

In this study, paired samples were collected at the same time from donors and recipients of haploidentical haematopoietic stem cell transplantation (HaploSCT). We then conducted flow cytometry‐based phenotypic and functional analyses and telomere length (TL) measurements of 21 paired T‐cell sets from parental donors and children who received T‐cell‐replete HaploSCT with post‐transplant cyclophosphamide (PTCy).

Results

Senescent T cells, CD28⁻ or CD57⁺ cells, were significantly expanded in patients. Further, not only CD4⁺CD28⁻ T cells, but also CD4⁺CD28⁺ T cells showed reduced cytokine production capacity and impaired polyfunctionality compared with parental donors, whereas their TCR‐mediated proliferation capacity was comparable. Of note, the TL in patient T cells was preserved, or even slightly longer, in senescent T cells compared with donor cells. Regression analysis showed that senescent features of CD4⁺ and CD8⁺ T cells in patients were influenced by donor age and the frequency of CD28⁻ cells, respectively.

Conclusion

Our data suggest that in paediatric HaploSCT, premature immunosenescent changes occur in T cells from parental donors, and therefore, long‐term immune monitoring should be conducted.

The emerging role of cellular senescence in renal diseases

Cellular senescence represents the state of irreversible cell cycle arrest during cell division. Cellular senescence not only plays a role in diverse biological events such as embryogenesis, tissue regeneration and repair, ageing and tumour occurrence prevention, but it is also involved in many cardiovascular, renal and liver diseases through the senescence-associated secretory phenotype (SASP). This review summarizes the molecular mechanisms underlying cellular senescence and its possible effects on a variety of renal diseases. We will also discuss the therapeutic approaches based on the regulation of senescent and SASP blockade, which is considered as a promising strategy for the management of renal diseases.

The Effect of Cancer Treatments on Telomere Length: A Systematic Review of the Literature

Background

It has been hypothesized that cancer treatments cause accelerated aging through a mechanism involving the shortening of telomeres. However, the effect of cancer treatments on telomere length is unclear.

Methods

We systematically reviewed the epidemiological evidence evaluating the associations between cancer treatment and changes in telomere length. Searches were performed in PubMed for the period of January 1966 through November 2016 using the following search strategy: telomere AND (cancer OR tumor OR carcinoma OR neoplasm) AND (survivor OR patient). Data were extracted and the quality of studies was assessed.

Results

A total of 25 studies were included in this review. Ten were solid cancer studies, 11 were hematological malignancy studies, and 4 included a mixed sample of both solid and hematological cancers. Three of the 10 solid tumor studies reported a statistically significant association between cancer treatment and telomere length shortening, and one reported longer telomere length after treatment. Among the hematological cancer studies, three showed statistically significant decreases in telomere length with treatment, and two showed elongation. When these studies were rated using quality criteria, most of the studies were judged to be of moderate quality.

Conclusions

The findings from this review indicate that the effect of cancer treatment on telomere length may differ by cancer type and treatment as well as other factors. Definitive conclusions cannot be made based on the published literature, because sample sizes tended to be small; treatments, cancer types, and biospecimens were heterogenous; and the length of follow-up times differed greatly.

Influence of Donor and Recipient Gender on Telomere Maintenance after Umbilical Cord Blood Cell Transplantation: A Study by the Gruppo Italiano Trapianto Di Midollo Osseo

Physiologic loss of telomerase activity in adult life determines progressive telomere length (TL) shortening. Inflammation and oxidative damage are established causes of TL loss; moreover, males have shorter telomeres compared with females. Despite these notions, mechanisms regulating TL maintenance are poorly defined. Because umbilical cord blood (UCB) cells harbor very long telomeres, not yet exposed to environmental damages, UCB transplantation (UCBT) provides a unique experimental setting to study determinants of TL in humans. TL dynamics were analyzed on peripheral blood mononuclear cells (MNCs) from 36 patients (median age, 42 years) undergoing UCBT. TL was studied at a median of 20 months after UCBT. A significantly longer TL (mean, 8698 bp; range, 6521 to 11,960) was documented in UCBT recipients compared with age-matched healthy control subjects (mean, 7396 bp; range, 4375 to 11,108; P < .01). Among variables potentially influencing TL maintenance, including recipient features, graft type, transplant procedure, and engraftment kinetics, only donor-recipient gender combination was associated with TL, with the longest TL in women receiving male UCB (mean, 10,063 bp; range, 8381 to 11,960). To further investigate this trend, telomerase activation was assessed in vitro. Experiments showed that telomerase subunits were preferentially upregulated in male-derived bone marrow MNCs exposed ex vivo to estradiol as compared with female MNCs. This implies an increased sensitivity of male-derived MNCs to telomerase activation induced by estradiol. The results suggest that extrinsic and modifiable factors such as hormonal status and female milieu could be major determinants of TL in humans, providing the rationale for investigating hormonal-based approaches to counteract telomere erosion and aging-related diseases.

Acute Kidney Injury as a Condition of Renal Senescence

Acute kidney injury (AKI), characterized by a sharp drop in glomerular filtration, continues to be a significant health burden because it is associated with high initial mortality, morbidity, and substantial health-care costs. There is a strong connection between AKI and mechanisms of senescence activation. After ischemic or nephrotoxic insults, a wide range of pathophysiological events occur. Renal tubular cell injury is characterized by cell membrane damage, cytoskeleton disruption, and DNA degradation, leading to tubular cell death by necrosis and apoptosis. The senescence mechanism involves interstitial fibrosis, tubular atrophy, and capillary rarefaction, all of which impede the morphological and functional recovery of the kidneys, suggesting a strong link between AKI and the progression of chronic kidney disease. During abnormal kidney repair, tubular epithelial cells can assume a senescence-like phenotype. Cellular senescence can occur as a result of cell cycle arrest due to increased expression of cyclin kinase inhibitors (mainly p21), downregulation of Klotho expression, and telomere shortening. In AKI, cellular senescence is aggravated by other factors including oxidative stress and autophagy. Given this scenario, the main question is whether AKI can be repaired and how to avoid the senescence process. Stem cells might constitute a new therapeutic approach. Mesenchymal stem cells (MSCs) can ameliorate kidney injury through angiogenesis, immunomodulation, and fibrosis pathway blockade, as well as through antiapoptotic and promitotic processes. Young umbilical cord–derived MSCs are better at increasing Klotho levels, and thus protecting tissues from senescence, than are adipose-derived MSCs. Umbilical cord–derived MSCs improve glomerular filtration and tubular function to a greater degree than do those obtained from adult tissue. Although senescence-related proteins and microRNA are upregulated in AKI, they can be downregulated by treatment with umbilical cord–derived MSCs. In summary, stem cells derived from young tissues, such as umbilical cord–derived MSCs, could slow the post-AKI senescence process.

National Institutes of Health Hematopoietic Cell Transplantation Late Effects Initiative: The Subsequent Neoplasms Working Group Report

Subsequent neoplasms (SN) after hematopoietic cell transplantation (HCT) cause significant patient morbidity and mortality. Risks for specific SN types vary substantially, with particularly elevated risks for post-transplantation lymphoproliferative disorders, myelodysplastic syndrome/acute myeloid leukemia, and squamous cell malignancies. This document provides an overview of the current state of knowledge regarding SN after HCT and recommends priorities and approaches to overcome challenges and gaps in understanding. Numerous factors have been suggested to affect risk, including patient-related (eg, age), primary disease-related (eg, disease type, pre-HCT therapies), and HCT-related characteristics (eg, type and intensity of conditioning regimen, stem cell source, development of graft-versus-host disease). However, gaps in understanding remain for each of these risk factors, particularly for patients receiving HCT in the current era because of substantial advances in clinical transplantation practices. Additionally, the influence of nontransplantation-related risk factors (eg, germline genetic susceptibility, oncogenic viruses, lifestyle factors) is poorly understood. Clarification of the magnitude of SN risks and identification of etiologic factors will require large-scale, long-term, systematic follow-up of HCT survivors with detailed clinical data. Most investigations of the mechanisms of SN pathogenesis after HCT have focused on immune drivers. Expansion of our understanding in this area will require interdisciplinary laboratory collaborations utilizing measures of immune function and availability of archival tissue from SN diagnoses. Consensus-based recommendations for optimal preventive, screening, and therapeutic approaches have been developed for certain SN after HCT, whereas for other SN, general population guidelines are recommended. Further evidence is needed to specifically tailor preventive, screening, and therapeutic guidelines for SN after HCT, particularly for unique patient populations. Accomplishment of this broad research agenda will require increased investment in systematic data collection with engagement from patients, clinicians, and interdisciplinary scientists to reduce the burden of SN in the rapidly growing population of HCT survivors.

A Reduced-Intensity Conditioning Regimen for Patients with Dyskeratosis Congenita Undergoing Hematopoietic Stem Cell Transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) is the only curative option for progressive marrow failure, myelodysplastic syndrome, or leukemia associated with dyskeratosis congenita (DC). HSCT for DC is limited by a high incidence of treatment-related mortality, thought to be related to underlying chromosomal instability and sensitivity to chemotherapy and radiation. We report our experience in 7 patients with DC who underwent allogeneic transplantation using a reduced-intensity conditioning (RIC) preparative regimen that contained chemotherapy only (no radiation). This RIC regimen, designed specifically for patients with DC, contained alemtuzumab, fludarabine, and melphalan (with melphalan at 50% reduced dosing), with the goal of decreasing toxicity and improving outcome. All 7 patients engrafted, with none developing mixed chimerism or rejection. Two patients experienced acute graft-versus-host disease (GVHD) and 1 went on to develop limited chronic GVHD of the skin. Five patients remain alive and well at a median follow-up of 44 months (range, 14 to 57 months). We conclude that a radiation-free RIC regimen results in durable engraftment, acceptable toxicity, and improved overall survival in patients with DC undergoing allogeneic HSCT.

The complex pathophysiology of acquired aplastic anaemia

Immune-mediated destruction of haematopoietic stem/progenitor cells (HSPCs) plays a central role in the pathophysiology of acquired aplastic anaemia (aAA). Dysregulated CD8(+) cytotoxic T cells, CD4(+) T cells including T helper type 1 (Th1), Th2, regulatory T cells and Th17 cells, natural killer (NK) cells and NK T cells, along with the abnormal production of cytokines including interferon (IFN)-γ, tumour necrosis factor (TNF)-α and transforming growth factor (TGF)-β, induce apoptosis of HSPCs, constituting a consistent and defining feature of severe aAA. Alterations in the polymorphisms of TGF-β, IFN-γ and TNF-α genes, as well as certain human leucocyte antigen (HLA) alleles, may account for the propensity to immune-mediated killing of HSPCs and/or ineffective haematopoiesis. Although the inciting autoantigens remain elusive, autoantibodies are often detected in the serum. In addition, recent studies provide genetic and molecular evidence that intrinsic and/or secondary deficits in HSPCs and bone marrow mesenchymal stem cells may underlie the development of bone marrow failure.

Association between donor leukocyte telomere length and survival after unrelated allogeneic hematopoietic cell transplantation for severe aplastic anemia

IMPORTANCE

Telomeres protect chromosome ends and are markers of cellular aging and replicative capacity.

OBJECTIVE

To evaluate the association between recipient and donor pretransplant leukocyte telomere length with outcomes after unrelated donor allogeneic hematopoietic cell transplantation (HCT) for patients with severe aplastic anemia.

DESIGN, PARTICIPANTS, AND SETTING

The study included 330 patients (235 acquired, 85 Fanconi anemia, and 10 Diamond-Blackfan anemia) and their unrelated donors who had pre-HCT blood samples and clinical and outcome data available at the Center for International Blood and Marrow Transplant Research. Patients underwent HCT between 1989 and 2007 in 84 centers and were followed-up to March 2013.

EXPOSURES

Recipient and donor pre-HCT leukocyte telomere length classified into long (third tertile) and short (first and second tertiles combined) based on donor telomere length distribution.

MAIN OUTCOMES AND MEASURES

Overall survival, neutrophil recovery, and acute and chronic graft-vs-host disease, as ascertained by transplant centers through regular patient follow-up.

RESULTS

Longer donor leukocyte telomere length was associated with higher survival probability (5-year overall survival, 56%; number at risk, 57; cumulative deaths, 50) than shorter donor leukocyte telomere length (5-year overall survival, 40%; number at risk, 71; cumulative deaths, 128; P = .009). The association remained statistically significant after adjusting for donor age, disease subtype, Karnofsky performance score, graft type, HLA matching, prior aplastic anemia therapy, race/ethnicity, and calendar year of transplant (hazard ratio [HR], 0.61; 95% CI, 0.44-0.86). Similar results were noted in analyses stratified on severe aplastic anemia subtype, recipient age, HLA matching, calendar year of transplant, and conditioning regimen. There was no association between donor telomere length and neutrophil engraftment at 28 days (cumulative incidence, 86% vs 85%; HR, 0.94; 95% CI, 0.73-1.22), acute graft-vs-host disease grades III-IV at 100 days (cumulative incidence, 22% vs 28%; HR, 0.77; 95% CI, 0.48-1.23), or chronic graft-vs-host disease at 1-year (cumulative incidence, 28% vs 30%; HR, 0.81; 95% CI, 0.53-1.24) for long vs short, respectively. Pretransplant leukocyte telomere length in the recipients was not associated with posttransplant survival (HR, 0.91; 95% CI, 0.64-1.30).

CONCLUSIONS AND RELEVANCE

Longer donor leukocyte telomere length was associated with increased 5-year survival in patients who received HCT for severe aplastic anemia. Patient leukocyte telomere length was not associated with survival. The results of this observational study suggest that donor leukocyte telomere length may have a role in long-term posttransplant survival.

Evaluation of noncytotoxic DNMT1-depleting therapy in patients with myelodysplastic syndromes

BACKGROUND

Mutational inactivation in cancer of key apoptotic pathway components, such as TP53/p53, undermines cytotoxic therapies that aim to increase apoptosis. Accordingly, TP53 mutations are reproducibly associated with poor treatment outcomes. Moreover, cytotoxic treatments destroy normal stem cells with intact p53 systems, a problem especially for myeloid neoplasms, as these cells reverse the low blood counts that cause morbidity and death. Preclinical studies suggest that noncytotoxic concentrations of the DNA methyltransferase 1 (DNMT1) inhibitor decitabine produce p53-independent cell-cycle exits by reversing aberrant epigenetic repression of proliferation-terminating (MYC-antagonizing) differentiation genes in cancer cells.

METHODS

In this clinical trial, patients with myelodysplastic syndrome (n=25) received reduced decitabine dosages (0.1-0.2 mg/kg/day compared with the FDA-approved 20-45 mg/m2/day dosage, a 75%-90% reduction) to avoid cytotoxicity. These well-tolerated doses were frequently administered 1-3 days per week, instead of pulse cycled for 3 to 5 days over a 4- to 6-week period, to increase the probability that cancer S-phase entries would coincide with drug exposure, which is required for S-phase-dependent DNMT1 depletion.

RESULTS

The median subject age was 73 years (range, 46-85 years), 9 subjects had relapsed disease or were refractory to 5-azacytidine and/or lenalidomide, and 3 had received intensive chemoradiation to treat other cancers. Adverse events were related to neutropenia present at baseline: neutropenic fever (13 of 25 subjects) and septic death (1 of 25 subjects). Blood count improvements meeting the International Working Group criteria for response occurred in 11 of 25 (44%) subjects and were highly durable. Treatment-induced freedom from transfusion lasted a median of 1,025 days (range, 186-1,152 days; 3 ongoing), and 20% of subjects were treated for more than 3 years. Mutations and/or deletions of key apoptosis genes were frequent (present in 55% of responders and in 36% of nonresponders). Noncytotoxic DNMT1 depletion was confirmed by serial BM γ-H2AX (DNA repair/damage marker) and DNMT1 analyses. MYC master oncoprotein levels were markedly decreased.

CONCLUSION

Decitabine regimens can be redesigned to minimize cytotoxicity and increase exposure time for DNMT1 depletion, to safely and effectively circumvent mutational apoptotic defects.

TRIAL REGISTRATION

Clinicaltrials.gov NCT01165996.

FUNDING

NIH (R01CA138858, CA043703); Department of Defense (PR081404); Clinical and Translational Science Award (CTSA) (UL1RR024989); and the Leukemia and Lymphoma Society (Translational Research Program).

Direct comparison of flow-FISH and qPCR as diagnostic tests for telomere length measurement in humans

Telomere length measurement is an essential test for the diagnosis of telomeropathies, which are caused by excessive telomere erosion. Commonly used methods are terminal restriction fragment (TRF) analysis by Southern blot, fluorescence in situ hybridization coupled with flow cytometry (flow-FISH), and quantitative PCR (qPCR). Although these methods have been used in the clinic, they have not been comprehensively compared. Here, we directly compared the performance of flow-FISH and qPCR to measure leukocytes' telomere length of healthy individuals and patients evaluated for telomeropathies, using TRF as standard. TRF and flow-FISH showed good agreement and correlation in the analysis of healthy subjects (R² = 0.60; p<0.0001) and patients (R² = 0.51; p<0.0001). In contrast, the comparison between TRF and qPCR yielded modest correlation for the analysis of samples of healthy individuals (R² = 0.35; p<0.0001) and low correlation for patients (R² = 0.20; p = 0.001); Bland-Altman analysis showed poor agreement between the two methods for both patients and controls. Quantitative PCR and flow-FISH modestly correlated in the analysis of healthy individuals (R² = 0.33; p<0.0001) and did not correlate in the comparison of patients' samples (R² = 0.1, p = 0.08). Intra-assay coefficient of variation (CV) was similar for flow-FISH (10.8±7.1%) and qPCR (9.5±7.4%; p = 0.35), but the inter-assay CV was lower for flow-FISH (9.6±7.6% vs. 16±19.5%; p = 0.02). Bland-Altman analysis indicated that flow-FISH was more precise and reproducible than qPCR. Flow-FISH and qPCR were sensitive (both 100%) and specific (93% and 89%, respectively) to distinguish very short telomeres. However, qPCR sensitivity (40%) and specificity (63%) to detect telomeres below the tenth percentile were lower compared to flow-FISH (80% sensitivity and 85% specificity). In the clinical setting, flow-FISH was more accurate, reproducible, sensitive, and specific in the measurement of human leukocyte's telomere length in comparison to qPCR. In conclusion, flow-FISH appears to be a more appropriate method for diagnostic purposes.

Senescence and apoptosis block hematopoietic activation of quiescent hematopoietic stem cells with short telomeres

Telomere shortening limits the proliferative capacity of human cells, and age-dependent shortening of telomeres occurs in somatic tissues including hematopoietic stem cells (HSCs). It is currently unknown whether genomic and molecular damage that occurs in HSCs induced by telomere shortening is transmitted to the progenitor cells. Here we show that telomere shortening results in DNA damage accumulation and gene expression changes in quiescent HSCs of aged mice. Upon activation, a subset of HSCs with elevated levels of DNA damage and p16 expression are blocked from cell cycle entry, and apoptosis is induced in HSCs entering the cell cycle. Activation of both checkpoints associates with normalization of DNA damage and gene expression profiles at early progenitor stages. These findings indicate that quiescent HSCs have an elevated tolerance to accumulate genomic alterations in response to telomere shortening, but the transmission of these aberrations to the progenitor cell level is prevented by senescence and apoptosis.

The diagnosis and treatment of dyskeratosis congenita: a review

Dyskeratosis congenita (DC) is an inherited bone marrow failure (BMF) syndrome characterized by the classic triad of abnormal skin pigmentation, nail dystrophy, and oral leukoplakia. However, patients usually develop BMF and are predisposed to cancer, with increased risk for squamous cell carcinoma and hematolymphoid neoplasms. DC is a disease of defective telomere maintenance and is heterogeneous at the genetic level. It can be inherited in X-linked, autosomal dominant, or autosomal recessive patterns. Mutations in at least ten telomere- and telomerase-associated genes have been described in DC. There are no targeted therapies for DC and patients usually die of BMF due to a deficient renewing capability of hematopoietic stem cells. Allogeneic hematopoietic stem cell transplantation is the only curative treatment for BMF.

Telomere shortening in neurological disorders: an abundance of unanswered questions

Telomeres, ribonucleoprotein complexes that cap eukaryotic chromosomes, typically shorten in leukocytes with aging. Aging is a primary risk factor for neurodegenerative disease (ND), and a common assumption has arisen that leukocyte telomere length (LTL) can serve as a predictor of neurological disease. However, the evidence for shorter LTL in Alzheimer's and Parkinson's patients is inconsistent. The diverse causes of telomere shortening may explain variability in LTL between studies and individuals. Additional research is needed to determine whether neuronal and glial telomeres shorten during aging and in neurodegenerative disorders, if and how LTL is related to brain cell telomere shortening, and whether telomere shortening plays a causal role in or exacerbates neurological disorders.

Changes in the frequencies of human hematopoietic stem and progenitor cells with age and site

This study enumerated CD45(hi)/CD34(+) and CD45(hi)/CD133(+) human hematopoietic stem cells (HSCs) and progenitor granulocyte-macrophage colony forming cells (GM-CFCs) in blood and trochanteric and femoral bone marrow in 233 individuals. Stem cell frequencies were determined with multiparameter flow cytometry and using an internal control to determine the intrinsic variance of the assays. Progenitor cell frequency was determined using a standard colony assay technique. The frequency of outliers from undetermined methodological causes was highest for blood, but less than 5% for all values. The frequency of CD45(hi)/CD133(+) cells correlated highly with the frequency of CD45(hi)/CD34(+) cells in trochanteric and femoral bone marrow. The frequency of these HSC populations in trochanteric and femoral bone marrow rose significantly with age. In contrast, there was no significant trend of either of these cell populations with age in the blood. Trochanteric marrow progenitor GM-CFCs showed no significant trends with age, but femoral marrow GM-CFCs trended downward with age, potentially because of the reported conversion of red marrow at this site to fat with age. Hematopoietic stem and progenitor cells exhibited changes in frequencies with age that differed between blood and bone marrow. We previously reported that side population (SP) multipotential HSC, which includes the precursors of CD45(hi)/CD133(+) and CD45(hi)/CD34(+), decline with age. Potentially the increases in stem cell frequencies in the intermediate compartment between SP and GM progenitor cells observed in this study represent a compensatory increase for the loss of more potent members of the HSC hierarchy.

Telomere dysfunction and hematologic disorders

Aplastic anemia is a disease in which the hematopoietic stem cell fails to adequately produce peripheral blood cells, causing pancytopenia. In some cases of acquired aplastic anemia and in inherited type of aplastic anemia, dyskeratosis congenita, telomere biology gene mutations and telomere shortening are etiologic. Telomere erosion hampers the ability of hematopoietic stem and progenitor cells to adequately replicate, clinically resulting in bone marrow failure. Additionally, telomerase mutations and short telomeres are genetic risk factors for the development of some hematologic cancers, including myelodysplastic syndrome, acute myeloid leukemia, and chronic lymphocytic leukemia.

Telomeres shorten at equivalent rates in somatic tissues of adults

Telomere shortening in somatic tissues largely reflects stem cell replication. Previous human studies of telomere attrition were predominantly conducted on leukocytes. However, findings in leukocytes cannot be generalized to other tissues. Here we measure telomere length in leukocytes, skeletal muscle, skin and subcutaneous fat of 87 adults (aged 19–77 years). Telomeres are longest in muscle and shortest in leukocytes, yet are strongly correlated between tissues. Notably, the rates of telomere shortening are similar in the four tissues. We infer from these findings that differences in telomere length between proliferative (blood and skin) and minimally proliferative tissues (muscle and fat) are established during early life, and that in adulthood, stem cells of the four tissues replicate at a similar rate.

Telomere shortening as a result of cell proliferation has been implicated in human ageing. Here, Daniali and colleagues show that telomere length and the rate of age-dependent shortening vary between adults but are similar within tissues of the same individual.

Key clinical observations after 5-azacytidine and decitabine treatment of myelodysplastic syndromes suggest practical solutions for better outcomes

Clinical experience with 5-azacytidine and decitabine treatment of myelodysplastic syndromes (MDS), complemented by biological and pharmacological studies, has revealed compelling mechanism of action differences compared with traditional myeloid cancer treatment mainstays such as cytarabine. For example, 5-azacytidine and decitabine produce remissions and better overall survival in MDS with high-risk chromosome abnormalities at a surprisingly high rate, consistent with experimental observations that noncytotoxic DNA methyltransferase depletion by 5-azacytidine/decitabine can trigger cell cycle exit independently of p53, thus circumventing a basis for resistance to apoptosis-based DNA-damaging therapy. That responses cut across the chaotic genomic landscape of MDS highlights common threads in disease, such as high expression in myeloblasts of differentiation-driving transcription factors yet paradoxical epigenetic suppression of proliferation-terminating late-differentiation genes. Less toxic regimens (lower dosages but more frequent administration) of 5-azacytidine/decitabine have been more successful, underscoring the importance of preserving functionally normal stem cells, which are rendered more precious by attrition from age, previous cytotoxic treatments, and the disease process and are needed to relieve cytopenias, the cause of morbidity and mortality. Also emphasized is that there can be no therapeutic benefit, regardless of mutation or cytogenetic subtype, if DNA methyltransferase is not depleted by sufficient overlap between intracellular drug half-lives and S-phase entries of malignant cells. Improved understanding of mechanism-of-action differences demands new approaches, from historic (but not scientific) more-is-better and one-size-fits-all empiricism to pharmacodynamic-based designs and combinations directed not solely at suppressing malignant clones, but at improving therapeutic indices.

Age-adjusted recipient pretransplantation telomere length and treatment-related mortality after hematopoietic stem cell transplantation

Telomere attrition induces cell senescence and apoptosis. We hypothesized that age-adjusted pretransplantation telomere length might predict treatment-related mortality (TRM) after hematopoietic stem cell transplantation (HSCT). Between 2000 and 2005, 178 consecutive patients underwent HSCT from HLA-identical sibling donors after myeloablative conditioning regimens, mainly for hematologic malignancies (n = 153). Blood lymphocytes' telomere length was measured by real-time quantitative PCR before HSCT. Age-adjusted pretransplantation telomere lengths were analyzed for correlation with clinical outcomes. After age adjustment, patients' telomere-length distribution was similar among all 4 quartiles except for disease stage. There was no correlation between telomere length and engraftment, GVHD, or relapse. The overall survival was 62% at 5 years (95% confidence interval [CI], 54-70). After a median follow-up of 51 months (range, 1-121 months), 43 patients died because of TRM. The TRM rate inversely correlated with telomere length. TRM in patients in the first (lowest telomere length) quartile was significantly higher than in patients with longer telomeres (P = .017). In multivariate analysis, recipients' age (hazard ratio, 1.1; 95% CI, .0-1.1; P = .0001) and age-adjusted telomere length (hazard ratio, 0.4; 95% CI; 0.2-0.8; P = .01) were independently associated with TRM. In conclusion, age-adjusted recipients' telomere length is an independent biologic marker of TRM after HSCT.

Telomere loss in Philadelphia-negative hematopoiesis after successful treatment of chronic myeloid leukemia: evidence for premature aging of the myeloid compartment

Telomere shortening, a well-known marker of aging and cellular stress, occurs under several conditions in the hematopoietic compartment, including aplastic anemia and following iatrogenic noxae. We decided to verify whether pathological telomere erosion also arises in restored Philadelphia-negative (Ph-negative) hematopoiesis following successful treatment of chronic myeloid leukemia (CML). Eighty-one CML patients in complete cytogenetic remission were compared to 76 age-matched healthy subjects. Myeloid cells of CML patients had shorter telomeres than controls (6521 bp vs 7233 bp, p<0.001). This difference was specific for the myeloid compartment, since it was not observed in lymphoid cells (6774 bp vs 6909 bp, p=0.620). Acquired Ph-negative cytogenetic abnormalities (p=0.010), lack of complete molecular remission (p=0.016) and age (p=0.013) were independent predictors of telomere shortening. Telomere dynamics were assessed over a median follow-up period of 22 months. We documented accelerated non-physiological ongoing telomere shortening in 17/59 CML patients (28%). Patients experiencing grade 2-4 hematological toxicity, during CML remission possessed significantly shorter telomeres compared to those lacking toxicity (p=0.005 for any toxicity, p=0.007 for anemia). CML patients suffer from significant and often ongoing telomere stress resulting in premature and selective aging of the myeloid compartment which might have long-term consequences on function and integrity of Ph-negative hematopoiesis.