Telomerase regulation and telomere dynamics in germinal centers

Human anti-smallpox long-lived memory B cells are defined by dynamic interactions in the splenic niche and long-lasting germinal center imprinting

Memory B cells (MBCs) can persist for a lifetime, but the mechanisms that allow their long-term survival remain poorly understood. Here, we isolated and analyzed human splenic smallpox/vaccinia protein B5-specific MBCs in individuals who were vaccinated more than 40 years ago. Only a handful of clones persisted over such an extended period, and they displayed limited intra-clonal diversity with signs of extensive affinity-based selection. These long-lived MBCs appeared enriched in a CD21hiCD20hi IgG+ splenic B cell subset displaying a marginal-zone-like NOTCH/MYC-driven signature, but they did not harbor a unique longevity-associated transcriptional or metabolic profile. Finally, the telomeres of B5-specific, long-lived MBCs were longer than those in patient-paired naive B cells in all the samples analyzed. Overall, these results imply that separate mechanisms such as early telomere elongation, affinity selection during the contraction phase, and access to a specific niche contribute to ensuring the functional longevity of MBCs.

Diverse mutational landscapes in human lymphocytes

The lymphocyte genome is prone to many threats, including programmed mutation during differentiation1, antigen-driven proliferation and residency in diverse microenvironments. Here, after developing protocols for expansion of single-cell lymphocyte cultures, we sequenced whole genomes from 717 normal naive and memory B and T cells and haematopoietic stem cells. All lymphocyte subsets carried more point mutations and structural variants than haematopoietic stem cells, with higher burdens in memory cells than in naive cells, and with T cells accumulating mutations at a higher rate throughout life. Off-target effects of immunological diversification accounted for approximately half of the additional differentiation-associated mutations in lymphocytes. Memory B cells acquired, on average, 18 off-target mutations genome-wide for every on-target IGHV mutation during the germinal centre reaction. Structural variation was 16-fold higher in lymphocytes than in stem cells, with around 15% of deletions being attributable to off-target recombinase-activating gene activity. DNA damage from ultraviolet light exposure and other sporadic mutational processes generated hundreds to thousands of mutations in some memory cells. The mutation burden and signatures of normal B cells were broadly similar to those seen in many B-cell cancers, suggesting that malignant transformation of lymphocytes arises from the same mutational processes that are active across normal ontogeny. The mutational landscape of normal lymphocytes chronicles the off-target effects of programmed genome engineering during immunological diversification and the consequences of differentiation, proliferation and residency in diverse microenvironments.

Epigenetic Mechanisms in Leukemias and Lymphomas

Although we are just beginning to understand the mechanisms that regulate the epigenome, aberrant epigenetic programming has already emerged as a hallmark of hematologic malignancies including acute myeloid leukemia (AML) and B-cell lymphomas. Although these diseases arise from the hematopoietic system, the epigenetic mechanisms that drive these malignancies are quite different. Yet, in all of these tumors, somatic mutations in transcription factors and epigenetic modifiers are the most commonly mutated set of genes and result in multilayered disruption of the epigenome. Myeloid and lymphoid neoplasms generally manifest epigenetic allele diversity, which contributes to tumor cell population fitness regardless of the underlying genetics. Epigenetic therapies are emerging as one of the most promising new approaches for these patients. However, effective targeting of the epigenome must consider the need to restore the various layers of epigenetic marks, appropriate biological end points, and specificity of therapeutic agents to truly realize the potential of this modality.

Telomeres, Telomerase and Ageing

Telomeres are specialised structures at the end of linear chromosomes. They consist of tandem repeats of the hexanucleotide sequence TTAGGG, as well as a protein complex called shelterin. Together, they form a protective loop structure against chromosome fusion and degradation. Shortening or damage to telomeres and opening of the loop induce an uncapped state that triggers a DNA damage response resulting in senescence or apoptosis.Average telomere length, usually measured in human blood lymphocytes, was thought to be a biomarker for ageing, survival and mortality. However, it becomes obvious that regulation of telomere length is very complex and involves multiple processes. For example, the "end replication problem" during DNA replication as well as oxidative stress are responsible for the shortening of telomeres. In contrast, telomerase activity can potentially counteract telomere shortening when it is able to access and interact with telomeres. However, while highly active during development and in cancer cells, the enzyme is down-regulated in most human somatic cells with a few exceptions such as human lymphocytes. In addition, telomeres can be transcribed, and the transcription products called TERRA are involved in telomere length regulation.Thus, telomere length and their integrity are regulated at many different levels, and we only start to understand this process under conditions of increased oxidative stress, inflammation and during diseases as well as the ageing process.This chapter aims to describe our current state of knowledge on telomeres and telomerase and their regulation in order to better understand their role for the ageing process.

Germinal center-derived lymphomas: The darkest side of humoral immunity

One of the unusual features of germinal center (GC) B cells is that they manifest many hallmarks of cancer cells. Accordingly, most B-cell neoplasms originate from the GC reaction, and characteristically display abundant point mutations, structural genomic lesions, and clonal diversity from the genetic and epigenetic standpoints. The dominant biological theme of GC-derived lymphomas is mutation of genes involved in epigenetic regulation and immune receptor signaling, which come into play at critical transitional stages of the GC reaction. Hence, mechanistic studies of these mutations reveal fundamental insight into the biology of the normal and malignant GC B cell. The BCL6 transcription factor plays a central role in establishing the GC phenotype in B cells, and most lymphomas are dependent on BCL6 to maintain survival, proliferation, and perhaps immune evasion. Many lymphoma mutations have the commonality of enhancing the oncogenic functions of BCL6, or overcoming some of its tumor suppressive effects. Herein, we discuss how unique features of the GC reaction create vulnerabilities that select for particular lymphoma mutations. We examine the interplay between epigenetic programming, metabolism, signaling, and immune regulatory mechanisms in lymphoma, and discuss how these are leading to novel precision therapy strategies to treat lymphoma patients.

Older Human B Cells and Antibodies

B cells have a number of different roles in the immune response. Their excellent antigen presentation potential can contribute to the activation of other cells of the immune system, and evidence is emerging that specialized subsets of these cells, that may be increased with age, can influence the cell-mediated immune system in antitumor responses. They can also regulate immune responses, to avoid autoreactivity and excessive inflammation. Deficiencies in regulatory B cells may be beneficial in cancer but will only exacerbate the inflammatory environment that is a hallmark of aging. The B cell role as antibody producers is particularly important, since antibodies perform numerous different functions in different environments. Although studying tissue responses in humans is not as easy as in mice, we do know that certain classes of antibodies are more suited to protecting the mucosal tissues (IgA) or responding to T-independent bacterial polysaccharide antigens (IgG₂) so we can make some inference with respect to tissue-specific immunity from a study of peripheral blood. We can also make inferences about changes in B cell development with age by looking at the repertoire of different B cell populations to see how age affects the selection events that would normally occur to avoid autoreactivity, or increase specificity, to antigen.

Telomerase activity, telomere length and hTERT DNA methylation in peripheral blood mononuclear cells from monozygotic twins with discordant smoking habits

Increased telomerase expression has been implicated in the pathogenesis of lung cancer and, since the primary cause of lung cancer is smoking, an association between telomerase reactivation and tobacco smoke has been proposed. In this work an investigation has been performed to assess the relationship between tobacco smoke exposure and telomerase activity (TA) in peripheral blood mononuclear cells of healthy smokers. The methylation status of the catalytic subunit of telomerase hTERT was concurrently investigated to assess the possible association between epigenetic modifications of hTERT and TA. Besides, the association between smoke and telomere length (TL) has been evaluated. Healthy monozygotic twins with discordant smoking habits were selected as study population to minimize inter-individual differences because of demographic characteristics and genetic heterogeneity. Statistically significant higher values of TA and TL were observed in smokers compared to nonsmoker co-twins. The multivariate analysis of data showed, besides smoking habits (P = 0.02), an influence of gender (P = 0.006) and BMI (P = 0.001) on TA and a borderline effect of gender (P = 0.05) on TL. DNA methylation analysis, focused on 100 CpG sites mapping in hTERT, highlighted nine CpG sites differentially methylated in smokers. When co-twins were contrasted, selecting as variables the intra-twin difference in TA and hTERT DNA methylation, a statistically significant inverse correlation (P = 0.003) was observed between TA and DNA methylation at the cg05521538 site. In conclusion, these results indicate an association of tobacco smoke with TA and TL and suggest a possible association between smoke-induced epigenetic effects and TA in healthy smokers. Environ. Mol. Mutagen. 58:551-559, 2017. © 2017 Wiley Periodicals, Inc.

Age-associated telomere attrition of lymphocytes in vivo is co-ordinated with changes in telomerase activity, composition of lymphocyte subsets and health conditions

Telomeres are essential in maintaining chromosome integrity and in controlling cellular replication. Attrition of telomere length in peripheral blood mononuclear cells (PBMCs) with age is well documented from cross-sectional studies. But the actual in vivo changes in telomere lengths and its relationship with the contributing factors within the individuals with age have not been fully addressed. In the present paper, we report a longitudinal analysis of telomere length in the PBMCs, lymphocytes and monocytes of 216 human subjects aged from 20-90 years assessed at 0-, 5- and 12-year follow-up. For the 5- and 12-year follow-up, telomere length in the PBMCs decreased in 34% and 46%, exhibited no detectable change in 56% and 47% and increased in 10% and 7% of the subjects respectively. The rate of telomere change was distinct for T-cells, B-cells and monocytes for any given subject. Telomerase activity declined with age in the resting T-cells and B-cells and the activated T-cells. Finally, a significant portion of telomere attrition in T-cells with age was explained by a decline in the telomerase activity, decreased naïve cells and the change in physiological conditions such as elevated blood glucose and interleukin (IL)-6 levels. These findings show that changes in the telomere length of the PBMCs with age in vivo occur at different rates in different individuals and cell types and reveal that changes in the telomere length in the T-cells with age is influenced by the telomerase activity, naïve T-cell percentage and changes in health conditions.

How T follicular helper cells and the germinal centre response change with age

Normal ageing is accompanied by a decline in the function of the immune system that causes an increased susceptibility to infections and an impaired response to vaccination in older individuals. This results in an increased disease burden in the aged population, even with good immunisation programmes in place. The decreased response to vaccination is partly due to the diminution of the germinal centre response with age, caused by impaired T-cell help to B cells. Within the germinal centre, T-cell help is provided by a specialised subset of CD4(+) T cells; T follicular helper (Tfh) cells. Tfh cells provide survival and selection signals to germinal centre B cells, allowing them to egress from the germinal centre and become long-live plasma cells or memory B cells, and provide life-long protection against subsequent infection. This review will discuss the cellular and molecular changes in both Tfh cells and germinal centre B cells that occur with advancing age, which result in a smaller germinal centre response and a less effective response to immunisation.

Telomere length and expression of human telomerase reverse transcriptase splice variants in chronic lymphocytic leukemia

Telomerase activity and telomere length (TL) are prognostic markers in chronic lymphocytic leukemia (CLL). The rate-limiting component of telomerase is human telomerase reverse transcriptase (hTERT), for which multiple transcripts exist. Two splicing sites, α and β, have been described that generate deleted transcripts. Only the full-length (FL; α⁺β⁺) transcript translates into a functional protein. The aim of this work was to characterize hTERT splice variants in CLL in relation to disease activity, clinical stage, immunoglobulin heavy chain variable (IGHV) genes mutational status, and TL. Real-time polymerase chain reaction assays were validated for quantification of the hTERT transcripts with either α deletion (del-α; α⁻β⁺)), β deletion (del-β; α⁺β⁻) or both α and β deletions (del-αβ; α⁻β⁻). The splice variant expression pattern was studied in 97 patients with CLL, 6 healthy control subjects, and one CD34 cell sample. TL was assessed with real-time polymerase chain reaction in 71 of 97 samples. Thirty-two percent of the cases did not express any of the splice variants. Average FL expression was 5.5-fold higher in IGHV-unmutated (n = 35) compared with mutated (n = 59) patients (p < 0.0001). FL levels correlated directly with the percentage of IGHV homology (r = 0.34; p = 0.0007) and inversely with TL (r = -0.44; p = 0.0001). Overall, FL expression correlated significantly with that of the other splice variants. All transcripts were more frequently expressed in progressive compared with nonprogressive patients (p < 0.0001 for FL and del-α; p = 0.01 for del-β; and p = 0.006 for del-αβ). This study provides a detailed insight into the hTERT transcript pattern in CLL, highlighting the necessity of subgrouping patients according to IGHV mutation status when analyzing hTERT expression.

Measurement of telomere length using PNA probe by cytometry

Peptide nucleic acid (PNA) probes hybridize to denatured telomeric sequences in cells permeabilized in hot formamide. In reported protocols, the hybridization was conducted in solutions with high formamide concentrations to avoid the DNA renaturation that can hamper binding of the oligo-PNA probe to specific sequences. We postulated that telomeric DNA, confined in the nuclear microvolume, is not able to properly renature after hot formamide denaturation. Therefore, to improve hybridization conditions between the probe and the target sequences, it might be possible to add probe to sample after the complete removal of formamide.

Memory B and memory plasma cells

Vaccination provides a powerful means to control infections. It exploits and exemplifies the ability of the immune system to preserve the information that a specific pathogen has been encountered in the past. The cells and molecular mechanisms of immunological memory are still being discussed controversially. Here, we review the current concepts of memory B cells, the signals involved in their maintenance, and their role in enhanced secondary reactions. Memory plasma cells, secreting protective antibodies over lifetime, have been recognized only recently. Their characterization as cells resting in terms of proliferation and migration, and surviving in dedicated stromal niches, in the absence of antigen, has generated new concepts of how memory cells in general are organized by stroma cells, the 'resting memory'. In autoimmunity and chronic inflammation, memory B cells and memory plasma cells can be essential players, and they require special attention, as they do not respond to most conventional therapies. Their selective targeting will depend on a molecular understanding of their lifestyle.

Variation at theTERTlocus and predisposition for cancer

Telomerase and the control of telomere length are intimately linked to the process of tumourigenesis in humans. Here I review the evidence that variation at the 5p15.33 locus, which contains theTERTgene (encoding the catalytic subunit of telomerase), might play a role in the determination of cancer risk. Mutations in the coding regions ofTERTcan affect telomerase activity and telomere length, and create severe clinical phenotypes, including bone marrow failure syndromes and a substantive increase in cancer frequency. Variants within theTERTgene have been associated with increased risk of haematological malignancies, including myelodysplastic syndrome and acute myeloid leukaemia as well as chronic lymphocytic leukaemia. Furthermore, there is good evidence from a number of independent genome-wide association studies to implicate variants at the 5p15.33 locus in cancer risk at several different sites: lung cancer, basal cell carcinoma and pancreatic cancer show strong associations, while bladder, prostate and cervical cancer and glioma also show risk alleles in this region. Thus, multiple independent lines of evidence have implicated variation in theTERTgene as a risk factor for cancer. The mechanistic basis of these risk variants is yet to be established; however, the basic biology suggests that telomere length control is a tantalising candidate mechanism underlying cancer risk.

Telomerase activity and telomerase reverse transcriptase catalytic subunit expression in canine lymphoma: correlation with Ki67 immunoreactivity

Increased telomerase activity (TA) has been found in human and canine solid tumours, stem cells and somatic tissues with enhanced proliferative potential. The relationship between TA in normal and malignant lymphoid tissues remains unclear. The TA and the expression of canine telomerase reverse transcriptase catalytic subunit (dogTERT) messenger RNA (mRNA) were analyzed in malignant lymph nodes from 30 dogs with lymphoma, from two dogs with non-neoplastic illness and from two clinically normal dogs, demonstrating a statistically significant difference between TA in lymphoma lymph nodes (n = 30) and normal nodes (n = 4) but no significant difference in dogTERT mRNA expression. In addition, the expression of telomerase reverse transcriptase catalytic subunit (TERT) protein and Ki67 was analyzed in malignant lymph nodes from 10 dogs with lymphoma and from two clinically normal dogs by immunohistochemistry. TERT expression was associated with Ki67 in all lymphoma nodes (n = 10), and differences were illustrated between TERT and Ki67 expression between lymphoma (n = 10) and non-lymphoma (n = 2) nodes. This data support further investigation of telomerase in canine haematopoietic neoplasia through large-scale prospective studies.

Telomere length maintenance in stem cell populations

The maintenance of telomere length is essential for upholding the integrity of the genome. There is good evidence to suggest that telomere length maintenance in stem cell populations is important to facilitate the cell division required for tissue homeostasis. This is balanced against the requirement in long lived species for proliferative life span barriers for tumour suppression; the gradual erosion of telomeres provides one such barrier. The dynamics of telomeres in stem cell populations may thus be crucial in the balance between tumour suppression and tissue homeostasis. Here we briefly discuss our current understanding of telomere dynamics in stem cell populations, and provide some data to indicate that telomeres in human embryonic stem cells may be more stable and less prone to large-scale stochastic telomeric deletion.

FISH glossary: an overview of the fluorescence in situ hybridization technique

The introduction of FISH (fluorescence in situ hybridization) marked the beginning of a new era for the study of chromosome structure and function. As a combined molecular and cytological approach, the major advantage of this visually appealing technique resides in its unique ability to provide an intermediate degree of resolution between DNA analysis and chromosomal investigations while retaining information at the single-cell level. Used to support large-scale mapping and sequencing efforts related to the human genome project, FISH accuracy and versatility were subsequently capitalized on in biological and medical research, providing a wealth of diverse applications and FISH-based diagnostic assays. The diversification of the original FISH protocol into the impressive number of procedures available these days has been promoted throughout the years by a number of interconnected factors: the improvement in sensitivity, specificity and resolution, together with the advances in the fields of fluorescence microscopy and digital imaging, and the growing availability of genomic and bioinformatic resources. By assembling in a glossary format many of the "acronymed" FISH applications published so far, this review intends to celebrate the ability of FISH to re-invent itself and thus remain at the forefront of biomedical research.

Immunohistochemical localization of telomerase in myomas and in uterine myometrium

Telomerase activity could be a potential marker for the neoplastic process, because it is absent in normal cells and present in tumor cells. Immunohistochemical studies were conducted using samples obtained from 32 uterine myomas, each sample having a size of 3-4 cm and obtained from women between 35 and 45 years of age. These studies also concentrated on fragments of macroscopically unaltered myometrium, collected 3-4 cm from a uterine tumor. Immunohistochemistry was performed using antibody to the catalytic unit of telomerase (hTERT; clone 44F12, NCL-L-hTERT, Novocastra Laboratories, UK). This study aimed at detecting a possible presence of potentially neoplastic cells in the margins of healthy tissue, which was removed together with the primary tumor. The results were classified according to the number of telomerase-positive cells. Tumors of the first group had up to 50% telomerase-positive cells, while their content in the second group exceeded 50%. Our study demonstrated an almost two-fold increase in the number of telomerase-positive tumor cells compared with myometrial cells 3-4 cm from the tumor. Hopefully, investigating the presence of telomerase in both uterine myometrium and myoma could facilitate the diagnosis of the neoplastic process.

Short telomeres are associated with genetic complexity, high-risk genomic aberrations, and short survival in chronic lymphocytic leukemia

Telomere length is associated with mutation status of the immunoglobulin heavy chain variable (IGHV) gene and clinical course in B-cell chronic lymphocytic leukemia (B-CLL). In a B-CLL cohort of 152 patients, we analyzed telomere length, genomic aberrations, IGHV mutation status, CD38 and ZAP-70 expression to study the prognostic impact and associations among these factors. An inverse correlation existed between telomere length and IGHV homology (P < .001), CD38 (P < .001), and ZAP-70 expression (P = .01). Patients with telomere lengths below median (ie, “short telomeres”) and above median (ie, “long telomeres”) had similar incidences of genomic aberrations (74% vs 68%), 13q− (57% vs 49%), and +12q (5% vs 12%). In contrast, 13q− as a single aberration was more frequent in patients with long telomeres (51% vs 21%; P = .006), whereas 11q− (27% vs 9%; P = .014), 17p− (17% vs 0%; P < .001), and 2 or more genomic aberrations (39% vs 8%; P < .001) were more frequent in patients with short telomeres. Compared with patients with long telomeres, treatment-free survival (TFS) and overall survival (OS) was significantly shorter (P < .001 and P = .015, respectively) in the group with short telomeres, and telomere length was an independent prognostic indicator for TFS. These observations have biological and prognostic implications in B-CLL.

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.

Telomere length and correlation with histopathogenesis in B-cell leukemias/lymphomas

Telomere length was recently reported to correlate with cellular origin of B-cell malignancies in relation to the germinal center (GC). In this report, we measured telomere length by quantitative-PCR in 223 B-cell lymphomas/leukemias and correlated results with immunoglobulin (Ig) mutation status and immunostainings for GC/non-GC subtypes of diffuse large B-cell lymphoma (DLBCL). Shortest telomeres were found in Ig-unmutated chronic lymphocytic leukemia (CLL) [median telomere to single copy gene value (T/S) 0.33], differing significantly to Ig-mutated CLL (0.63). Contrary to this, mantle cell lymphomas (MCLs) exhibited similar telomere lengths regardless of Ig mutation status (0.47). Telomere length differed significantly between GC-like (0.73) and non-GC-like DLBCLs (0.43), and follicular lymphomas (FLs) had shorter telomeres (0.53) than GC-DLBCL. Hairy cell leukemias, which display Ig gene intraclonal heterogeneity, had longer telomeres (0.62) than FLs and non-GC-DLBCL, but shorter than GC-DLBCL. We conclude that although DLBCL and CLL subsets can be clearly distinguished, telomere length reflects many parameters and may not simply correlate with GC-related origin.

Human normal T lymphocytes and lymphoid cell lines do express alternative splicing variants of human telomerase reverse transcriptase (hTERT) mRNA

Alternative splicing of telomerase reverse transcriptase (hTERT) mRNA is known to contribute to regulation of telomerase activity in normal and cancerous cells, however, previous studies indicated that normal human T and B cells exhibited constitutive expression of full-length hTERT mRNA without splicing variants and that activation of telomerase upon stimulation of the cells was due to the shuttling of hTERT protein from cytoplasm to nucleus [Proc. Natl. Acad. Sci. USA 96 (1999) 5147; J. Immunol. 166 (2001) 4826]. We found that typical variants of hTERT mRNA were widespread in human lymphocyte-derived cell lines and normal stimulated T cells. In activated T cells, induction of the full-length hTERT mRNA was coupled with increased hTERT protein expression and telomerase activity. Collectively, human normal and malignant lymphocytes, like other human cells, express splicing variants of hTERT mRNA and require transcriptional activation of the hTERT gene to acquire telomerase activity.

In situ detection of hTERT variants in anaplastic large cell lymphoma

The expression of hTERT and its isoforms is difficult to assess in lymphoma tissues with the commonly used reverse transcription-polymerase chain reaction (RT-PCR) methods, because non-neoplastic lymphocytes expressing hTERT are always present in the lymphomatous infiltrates. The present study aimed to investigate hTERT mRNA variants in anaplastic large cell lymphoma (ALCL) (n = 38) with in situ hybridization (ISH), along with the immunodetection of hTERT protein. Probes for the identification of mRNAs containing (Bplus) and lacking (Bdel) exons 7 and 8 of the hTERT mRNA were used. Normal lymphocyte populations equally expressed both Bplus and Bdel mRNAs. Although all ALCL examined were found positive for hTERT expression with RT-PCR, hTERT mRNAs were identified in 68% of these tumors with ISH, with a higher incidence in the group bearing ALK translocations (10 out of 11; 90.9%) compared to the ALK negative group (17 out of 27; 59.3%) (PPearson's = 0.002). The same results were obtained with immunohistochemistry for hTERT. In approximately 50% of cases, only Bplus positive cells were identified, again with a higher incidence in the ALK positive compared to the ALK negative group (PPearson's = 0.016). In conclusion, ISH for hTERT mRNAs appears to be a valuable tool for the investigation of hTERT expression in lymphomas. Aberrations in hTERT variant profiles and a decline in the expression of the B deleted isoform may be associated with the pathogenesis of ALCL, especially with respect to ALK positive tumors.

Antibody Quality in Old Age

There is very little change in the quantity of antibodies people produce, of any isotype, with age. However, there is a change in the quality of the antibody response. Older people produce fewer antibodies that are specific for the activating pathogen or vaccine. At the same time, the number of nonspecific antibodies increases. Quite often these antibodies have self-reactivity (e.g., anti-dsDNA). The appearance of these antibodies is not associated with pathogenic autoimmune disease, although it is true that the incidence of some autoimmune diseases increases with age. The authors postulate that the process of antibody affinity maturation is compromised in old age. No evidence was found that the process of hypermutation is compromised with age. However, using graph theory to study the dynamics of a germinal center selection process, a decrease in the extent of selection occurring in the germinal centers of mucosal tissue was observed with age. This is a tissue-specific phenomenon because the decrease was not seen in the germinal centers of spleen. Because selection of highly specific cells in the germinal center depends on a number of factors (number and quality of founder cells, help from T cells, and follicular dendritic cells) these need to be investigated further to determine what is needed to improve the affinity mutation process.

hTERT antagonizes p53-induced apoptosis independently of telomerase activity

The p53 tumor suppressor controls cell growth and survival through transcriptional regulation of gene expression. Previously, we found that the human telomerase reverse transcriptase (hTERT) gene is downregulated by p53. To investigate if hTERT downregulation has a role in p53-dependent apoptosis, we tested if constitutive expression of telomerase could inhibit p53-induced apoptosis. Here we show that constitutive hTERT expression results in increased survival following activation of exogenous temperature-sensitive p53 in BL41 Burkitt lymphoma cells. Similarly, constitutive hTERT expression inhibited wild-type p53-dependent apoptosis in response to mitomycin C or 5-fluorouracil in HCT116 colon carcinoma cells carrying endogenous p53. A telomerase-inactive hTERT mutant was equally efficient in antagonizing p53-induced apoptosis. These findings support the notion that hTERT has antiapoptotic activity and demonstrate that p53-mediated downregulation of hTERT is critical for efficient p53-dependent apoptosis.

Telomere length as a prognostic parameter in chronic lymphocytic leukemia with special reference to VH gene mutation status

B-cell chronic lymphocytic leukemia (CLL) consists of 2 prognostic entities where cases with mutated immunoglobulin V(H) genes have better outcome than unmutated cases. V(H)-mutated CLLs display longer telomeres compared with unmutated cases and telomere length has been indicated to predict outcome, although the prognostic value of telomere length has not been fully established in CLL. We analyzed telomere length, V(H) gene mutation status, and clinical parameters in a large series of CLL. Telomere length was assessed by quantitative polymerase chain reaction (PCR), giving a very good correlation to telomere length estimated by Southern blotting (P < .001). The prognostic information given by mutation status (n = 282) and telomere length (n = 246) was significant (P < .001, respectively). Telomere length was a prognostic factor for stage A (P = .021) and stage B/C (P = .018) patients, whereas mutation status predicted outcome only in stage A patients (P < .001). Furthermore, mutated CLLs were subdivided by telomere length into 2 groups with different prognoses (P = .003), a subdivision not seen for unmutated cases (P = .232). Interestingly, the V(H)-mutated group with short telomeres had an overall survival close to that of the unmutated cases. Thus, by combining V(H) mutation status and telomere length, an improved subclassification of CLL was achieved identifying previously unrecognized patient groups with different outcomes.

Telomere length correlates with histopathogenesis according to the germinal center in mature B-cell lymphoproliferative disorders

In this study we investigated telomere restriction fragment (TRF) length in a panel of mature B-cell lymphoproliferative disorders (MBCLDs) and correlated this parameter with histology and histopathogenesis in relation to the germinal center (GC). We assessed 123 MBCLD samples containing 80% or more tumor cells. TRF length was evaluated by Southern blot analysis using a chemiluminescence-based assay. GC status was assessed through screening for stable and ongoing somatic mutations within the immunoglobulin heavy-chain genes. Median TRF length was 6170 bp (range, 1896-11 200 bp) and did not correlate with patient age or sex. TRF length was greater in diffuse large cell lymphoma, Burkitt lymphoma, and follicular lymphoma (medians: 7789 bp, 9471 bp, and 7383 bp, respectively) than in mantle cell lymphoma and chronic lymphocytic leukemia (medians: 3582 bp and 4346 bp, respectively). GC-derived MBCLDs had the longest telomeres, whereas those arising from GC-inexperienced cells had the shortest (P < 10(-9)). We conclude that (1) TRF length in MBCLD is highly heterogeneous; (2) GC-derived tumors have long telomeres, suggesting that minimal telomere erosion occurs during GC-derived lymphomagenesis; and (3) the short TRF lengths of GC-inexperienced MBCLDs indicates that these neoplasms are good candidates for treatment with telomerase inhibitors, a class of molecules currently the subject of extensive preclinical evaluation.

Telomere length and telomerase activity delineate distinctive replicative features of the B-CLL subgroups defined by immunoglobulin V gene mutations

Patients with B-cell chronic lymphocytic leukemia (B-CLL) segregate into subgroups with very different survival times. Because clinical observations suggest that leukemic cells accumulate at different rates, we measured telomere length and telomerase activity in B-CLL cells to distinguish differences in cellular replication. Our data indicate that the telomeres of B-CLL cells are shorter than telomeres of B cells from healthy subjects, indicating that the leukemic cells have a prolonged proliferative history. Leukemic cells of the immunoglobulin V gene mutation subgroups differ in telomere length and telomerase activity. B lymphocytes from the subgroup with poor outcome and with limited IgV gene mutations have uniformly shorter telomeres and more telomerase activity than those from the subgroup with better outcome and with considerable mutations. Differences in telomere length appear to largely reflect the proliferative histories of precursors of the leukemic cells, although differences in cell division, masked by the action of telomerase, cannot be excluded. These results may provide insight into the stages of maturation and the activation pathways of the cells that give rise to B-CLL. In addition, they reinforce the concept that B-CLL is not simply an accumulative disease of slowly dividing B lymphocytes but possibly one of B cells with extensive proliferative histories.

B cell chronic lymphocytic leukemia: lessons learned from studies of the B cell antigen receptor

B cell chronic lymphocytic leukemia (B-CLL) is an accumulative disease of slowly proliferating CD5(+) B lymphocytes that develops in the aging population. Whereas some patients with B-CLL have an indolent course and die after many years from unrelated causes, others progress very rapidly and succumb within a few years from this currently incurable leukemia. Over the past decade studies of the structure and function of the B cell antigen receptor (BCR) used by these leukemic cells have helped redefine the nature of this disease. In this review we summarize and reinterpret several aspects of these BCR-related studies and how they might relate to the disease. In particular, we address the ability of antigens to select out and drive B cell clones from the normal state to overt leukemic cells by binding to BCRs that are relatively unique and characteristic of B-CLL cells. The differential capacity of some B-CLL cases to continue to transduce signals through the BCR during the leukemic phase and the consequences for the in vivo biology of the leukemic clone is also considered. Finally, we discuss current and emerging views of the cellular origin of B-CLL cells and the differentiation pathways down which we believe these cells progress.

Telomerase activity in B-cell non-Hodgkin lymphomas is regulated by hTERT transcription and correlated with telomere-binding protein expression but uncoupled from proliferation

Telomere maintenance is a prerequisite for immortalisation, and in most malignant cells is carried out by telomerase, an enzyme that synthesis new telomeric repeats on the chromosome ends. In normal or reactive tissues with a high regenerative capacity, telomerase is regulated according to the telomere loss that occurs during proliferation. To evaluate the interaction of proliferation and telomerase activity in malignant lymphomas, we quantified telomerase expression in different non-Hodgkin lymphomas in comparison to normal or reactive lymph nodes. Surprisingly, the activity levels were the same in most of the lymphomas analysed as compared to reactive lymph nodes. Significantly higher activity was detected only in Burkitt's lymphoma. Telomerase activity correlated well with hTERT and c-myc expression, but was independent of proliferation. To evaluate interactions of telomere-binding protein expression on telomerase expression in non-Hodgkin lymphoma, the mRNA levels of TRF1, TRF2, tankyrase and hPif1 were assessed by real-time RT-PCR. We demonstrate here that the magnitude of telomerase upregulation does not necessarily reflect the requirement of telomere compensation caused by proliferation. Telomerase regulation in non-Hodgkin lymphomas is therefore uncoupled from proliferative stimuli found in reactive lymphoid tissue. We suggest that the upregulation of specific telomere-binding proteins like TRF2 may contribute to telomere maintenance in malignant lymphoma.

Duration of senescent cell survival in vitro as a characteristic of organism longevity, an additional to the proliferative potential of fibroblasts

More than 40 years have passed since the original publication by Hayflick and Moorhead led to the concept of the 'Hayflick limit' of the maximum number of divisions which somatic cells undergo in vitro. This concept is still regarded as a fundamental characteristic of species longevity. Here we want to emphasize another characteristic of somatic cells, namely, the duration of their survival in vitro in the non-dividing state after cessation of proliferation. This is suggested on the basis of results of recent experiments with so-called Japanese accelerated senescent mice. Results of these experiments reveal a good correlation between the longevity of the mice, the number of duplications of their fibroblasts in vitro, and the survival time of these cells in the non-dividing state. In routine culture conditions, cell survival time may be very long, as much as a few years. However, when the cells are grown under conditions of oxidative stress, cellular longevity is markedly shortened. This new test may serve as an additional marker of organismic longevity. The comparative value of both tests, the classical 'Hayflick limit' and the new test, is discussed.

Association between telomere length and V(H) gene mutation status in chronic lymphocytic leukaemia: clinical and biological implications

The immunoglobulin V(H) gene mutation status can divide B-cell chronic lymphocytic leukaemia (CLL) into two entities with a different clinical course. Cases with unmutated V(H) genes, considered to evolve from pregerminal centre (GC) cells, have a worse outcome compared to cases showing mutated V(H) genes, that is, post-GC derived. Also, telomere length has been reported to be of prognostic significance in CLL. Interestingly, telomerase becomes activated during the GC reaction and an elongation of the telomeres occurs in GC B cells. We performed telomere length and V(H) gene analysis in a series of 61 CLL cases, in order to investigate if the unique telomere lengthening shown in GC B cells could reflect the telomere status in the two subsets of mutated and unmutated CLL. A novel association was found between V(H) gene mutation status and telomere length, since significantly shorter telomeres were demonstrated in the unmutated group compared to the mutated group (mean length 4.3 vs 6.3 kbp). Shorter telomeres also constituted a subgroup with a worse prognosis than cases with longer telomeres (median survival 59 vs 159 months). Furthermore, the Ig gene sequence data revealed that samples with high mutations frequency (>6%) had long telomeres ( approximately 8 kbp). Thus, both the telomere and V(H) gene mutation status in CLL appear linked, which may reflect the proliferative history of the clonal cells with regard to the GC reaction.

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.

Telomere maintenance in human B lymphocytes

Telomere shortening has been causally linked to replicative senescence in human cells. To characterize telomere-length heterogeneity in peripheral blood cells of normal individuals, we analysed the mean length of telomeric repeat sequences in subpopulations of peripheral blood leucocytes, using fluorescence in situ hybridization and flow cytometry (flow-FISH). Although the telomere length of most haematopoietic subsets was within the same range, the mean telomere length was found to be 15% higher in B compared with T lymphocytes in adult peripheral blood. Whereas telomere loss with ageing corresponded to 33 base pairs (bp) per year in T cells, telomere shortening was slower in B cells, corresponding to 15 bp per year. Separation of adult B-lymphocyte subpopulations based on CD27 expression revealed that telomere length was almost 2 kb longer in CD19+CD27+ (memory) compared with CD19+CD27- (naive) cells. Furthermore, peripheral blood B cells were activated in vitro. Whereas B-cell activation with Staphylococcus aureus Cowan strain (SAC) did not increase telomere length, a striking telomere elongation was observed when cells were stimulated with SAC and interleukin 2 to induce plasma cell differentiation. Our observations support the concept that telomere dynamics in B cells are distinct from other haematopoietic cell lineages and that telomere elongation may play an essential role in the generation of long-term B memory cells.