The Transition between Telomerase and ALT Mechanisms in Hodgkin Lymphoma and Its Predictive Value in Clinical Outcomes

International audienceBackground: We analyzed telomere maintenance mechanisms (TMMs) in lymph node samples from HL patients treated with standard therapy. The TMMs correlated with clinical outcomes of patients. Materials and Methods: Lymph node biopsies obtained from 38 HL patients and 24 patients with lymphadenitis were included in this study. Seven HL cell lines were used as in vitro models. Telomerase activity (TA) was assessed by TRAP assay and verified through hTERT immunofluorescence expression; alternative telomere lengthening (ALT) was also assessed, along with EBV status. Results: Both TA and ALT mechanisms were present in HL lymph nodes. Our findings were reproduced in HL cell lines. The highest levels of TA were expressed in CD30−/CD15− cells. Small cells were identified with ALT and TA. Hodgkin and Reed Sternberg cells contained high levels of PML bodies, but had very low hTERT expression. There was a significant correlation between overall survival (p < 10−3), event-free survival (p < 10−4), and freedom from progression (p < 10−3) and the presence of an ALT profile in lymph nodes of EBV+ patients. Conclusion: The presence of both types of TMMs in HL lymph nodes and in HL cell lines has not previously been reported. TMMs correlate with the treatment outcome of EBV+ HL patients

Hybrid lentivirus-phiC31-int-NLS vector allows site-specific recombination in murine and human cells but induces DNA damage.

Gene transfer allows transient or permanent genetic modifications of cells for experimental or therapeutic purposes. Gene delivery by HIV-derived lentiviral vector (LV) is highly effective but the risk of insertional mutagenesis is important and the random/uncontrollable integration of the DNA vector can deregulate the cell transcriptional activity. Non Integrative Lentiviral Vectors (NILVs) solve this issue in non-dividing cells, but they do not allow long term expression in dividing cells. In this context, obtaining stable expression while avoiding the problems inherent to unpredictable DNA vector integration requires the ability to control the integration site. One possibility is to use the integrase of phage phiC31 (phiC31-int) which catalyzes efficient site-specific recombination between the attP site in the phage genome and the chromosomal attB site of its Streptomyces host. Previous studies showed that phiC31-int is active in many eukaryotic cells, such as murine or human cells, and directs the integration of a DNA substrate into pseudo attP sites (pattP) which are homologous to the native attP site. In this study, we combined the efficiency of NILV for gene delivery and the specificity of phiC31-int for DNA substrate integration to engineer a hybrid tool for gene transfer with the aim of allowing long term expression in dividing and non-dividing cells preventing genotoxicity. We demonstrated the feasibility to target NILV integration in human and murine pattP sites with a dual NILV vectors system: one which delivers phiC31-int, the other which constitute the substrate containing an attB site in its DNA sequence. These promising results are however alleviated by the occurrence of significant DNA damages. Further improvements are thus required to prevent chromosomal rearrangements for a therapeutic use of the system. However, its use as a tool for experimental applications such as transgenesis is already applicable

Retrospective cohort study and biobanking of patients treated for hemangioma in childhood – telomeres as biomarker of aging and radiation exposure

<p><b>Purpose:</b> Cohorts allowing joint epidemiological and biological analyses are essential for radiation risk assessment. The French Hemangioma Cohort (FHC), studied within the European project EpiRadBio, is one of the rare cohorts suitable for studying the effect of low dose radiation exposure (<100 mGy at organs), with a long-term follow-up. This highly homogeneous cohort consists of healthy individuals belonging to a normal population, except for the presence of skin hemangioma (age at exposure: between 6 months and 3 years of age). Published epidemiological studies have demonstrated that the risk of developing cancer is three times higher in the exposed individuals than in the general population. Here, we present the biobanking of samples (nucleated blood cells, cytogenetic slides of T and B lymphocytes) from the FHC and a primary feasibility study of biomarker analysis focusing on mean telomere length (MTL). Telomeres act as an internal clock, regulating the lifetime of the cell by their shortening during cell division. MTL is thus a biomarker of age. Many in vitro studies have linked MTL and radiosensitivity. The FHC will make it possible to discriminate between the effects of aging and radiation on this biomarker.</p> <p><b>Conclusion:</b> The establishment of a biobank of essentially healthy individuals (369 in total), exposed 40–70 years before, during their early childhood, is a logistical challenge. Even among those who previously participated to a self-questionnaire based study, the response rate was only 30%. The first biomarker to be studied was the MTL to discriminate age effects from those of radiation exposure. MTL showed significant variation within age groups (4–11 kb) in both the exposed and non-exposed groups. MTL within the limited age window (i.e. 40–73 year) examined, showed age-dependent changes of 46 bp/year, consistent with the age-dependent decline of 41 bp/year previously reported. We observed no significant changes in MTL according to the average active bone marrow dose. However, we were able to demonstrate that exposure to radiation causes the loss of cells with, on average, shorter telomeres, by applying a model in which both the heterogeneity of the individual dose received at the bone marrow and the heterogeneity of the intercellular distribution of MTL were taken into account.</p

Hypothetical model to explain the inversion of 4.8

<p>Step 1: Integration of a NILV mediated by phiC31-int into a p<i>attP</i> site. Step2: Recombination mediated by phiC31-int between the p<i>attL</i> generated during step 1 and another p<i>att</i> site located at 4 kb.</p

DNA sequence of <i>att</i> and p<i>attP</i> sites.

<p>A) Wild type <i>attP</i> and <i>attB</i> sites. After recombination two hybrids sites are formed: <i>attL</i> and <i>attR</i>. B) Recombination between <i>attB</i> site and the human locus Xq22.1 This recombination generates a p<i>attR</i> which has been isolated by inverse PCR. Xq22.1 had been described previously as a human p<i>attP</i> by MP Calos et al., who isolated the same p<i>attR</i>.</p

Scheme of phiC31-int mediated recombination in bacterial host.

<p>PhiC31 integrase performs precise recombination between an <i>attB</i> site located in the <i>Streptomyces</i> genome and an <i>attP</i> site located on the phiC31 phage genome. The outcome is integration of the phage into the host genome.</p

Repartition in 3 groups of human and murine clones according to the <i>attB</i> and LTR PCR results.

<p>Repartition in 3 groups of human and murine clones according to the <i>attB</i> and LTR PCR results.</p

Mapping and description of pa<i>ttP</i> sites isolated by iPCR on human and murine cell lines.

<p>Mapping and description of pa<i>ttP</i> sites isolated by iPCR on human and murine cell lines.</p

Analysis strategies to detect the specific integrations mediated by phiC31-int.

<p>A) Illustration of the three mechanisms of the phiC31-int mediated integration of a NILV containing an <i>attB</i> sequence. According to the type of integration, the PCR results in three different profiles: - PCRs LTR+/<i>attB</i>− : integration type (1), specific integration. - PCRs LTR−/<i>attB</i>+: integration type (2), residual integration. - PCRs LTR+/<i>attB</i>+: integration type (3), illegitimate integration. P1/P1′ are the primers used for <i>attB</i> PCR and P2/P2′ are the primers used for LTR PCR. B) Schematic representations of the inverse PCR and the adapted inverse PCR strategies used to characterize phiC31-int integration sites.</p

Detection of recombination mediated by phiC31-int between an <i>attB</i> site contained into a NILV and a genomic <i>attP</i> site.

<p>A) Scheme of the DsRed2 PCR before and after the enzymatic restriction treatment. B) PCR DsRed2 results without restriction enzyme treatment. Lanes 1 to 3: cotransduction with CMV-Neo and CMV-PhiC31 increasing vector input of 50–150–300 ng of p24. Lanes 4 to 6: cotransduction with <i>attB</i>-CMV-Neo and CMV-PhiC31 increasing vector input of 50–150–300 ng of p24. Lane 7: <i>attB</i>-CMV-Neo. Lane 8: positive control generated by triple-transfection (CMV-phiC31-int, <i>attB</i>-CMV-Neo and CMV-<i>attP</i>-DsRed2). Lane 9: negative control without vector. Lane 10: negative control of PCR. C) PCR DsRed2 results after restriction enzyme treatment. Lanes are similar to figure B. D) Nested PCR from the product isolated from lane 6 to confirm the specificity of PCR DsRed2 amplification.</p