Telomeres repress the DNA damage response at the natural chromosome ends to prevent cell-cycle arrest and maintain genome stability. Telomeres are elongated by telomerase in a tightly regulated manner to ensure a sufficient number of cell divisions throughout life, yet prevent unlimited cell division and cancer development. Hoyeraal-Hreidarsson syndrome (HHS) is characterized by accelerated telomere shortening and a broad range of pathologies, including bone marrow failure, immunodeficiency, and developmental defects. HHS-causing mutations have previously been found in telomerase and the shelterin component telomeric repeat binding factor 1 (TRF1)-interacting nuclear factor 2 (TIN2). We identified by whole-genome exome sequencing compound heterozygous mutations in four siblings affected with HHS, in the gene encoding the regulator of telomere elongation helicase 1 (RTEL1). Rtel1 was identified in mouse by its genetic association with telomere length. However, its mechanism of action and whether it regulates telomere length in human remained unknown. Lymphoblastoid cell lines obtained from a patient and from the healthy parents carrying heterozygous RTEL1 mutations displayed telomere shortening, fragility and fusion, and growth defects in culture. Ectopic expression of WT RTEL1 suppressed the telomere shortening and growth defect, confirming the causal role of the RTEL1 mutations in HHS and demonstrating the essential function of human RTEL1 in telomere protection and elongation. Finally, we show that human RTEL1 interacts with the shelterin protein TRF1, providing a potential recruitment mechanism of RTEL1 to telomeres.

Recent evidence suggests that kindlin-3 is a major coactivator, required for most, if not all, integrin activities. Here we studied the function of kindlin-3 in regulating NK cell activation by studying a patient with kindlin-3 deficiency (leukocyte adhesion deficiency-III). We found that kindlin-3 is required for NK cell migration and adhesion under shear force. Surprisingly, we also found that kindlin-3 lowers the threshold for NK cell activation. Loss of kindlin-3 has a pronounced effect on NK cell-mediated cytotoxicity triggered by single activating receptors. In contrast, for activation through multiple receptors, kindlin-3 deficiency is overcome and target cells killed. The realization that NK cell activity is impaired, but not absent in leukocyte adhesion deficiency, may lead to the development of more efficient therapy for this rare disease.

Diamond-Blackfan anemia (DBA) is congenital pure red-cell anemia due to a differentiation block in erythroid precursors. The disease is commonly caused by mutations in genes for ribosomal proteins. Despite the identification of disease causal genes, the disease pathogenesis is not completely elucidated. The ribosomal abnormalities are assumed to inhibit globin translation which may lead to excess free heme, stimulating a generation of free radicals and thereby damaging the precursors. We studied the effect of hemin (heme chloride) on cultured human erythroid precursors and found that contrary to aforementioned hypothesis, although hemin moderately stimulated free radicals, it did not cause apoptosis or necrosis. In erythroid precursors derived from DBA patients, hemin significantly stimulated growth and hemoglobinization. Thus, heme toxicity is unlikely to play a role in the pathophysiology of most DBA cases. Moreover, its beneficial effect in culture suggests a therapeutic potential.

Background Osteopetrosis is a life-threatening, rare disorder typically resulting from osteoclast dysfunction and infrequently from failure to commitment to osteoclast lineage. Patients commonly present in infancy with macrocephaly, feeding difficulties, evolving blindness and deafness, and bone marrow failure. In ∼70% of the patients there is a molecularly defined failure to maintain an acid pH at the osteoclast-bone interface (the ruffled border) which is necessary for the bone resorptive activity. Methods and results In eight patients with infantile osteopetrosis which could be cured by bone marrow transplantation, the study identified by homozygosity mapping in distantly related consanguineous pedigrees a missense mutation in a highly conserved residue in the SNX10 gene. The mutation segregated with the disease in the families and was carried by one of 211 anonymous individuals of the same ethnicity. In the patients' osteoclasts, the mutant SNX10 protein was abnormally abundant and its distribution altered. The patients' osteoclasts were fewer and smaller than control cells, their resorptive capacity was markedly deranged, and the endosomal pathway was perturbed as evidenced by the distribution of internalised dextran. Conclusions SNX10 was recently shown to interact with vacuolar type H+-ATPase (V-ATPase) which pumps protons at the osteoclast-bone interface. Mutations in TCIRG1, the gene encoding a subunit of the V-ATPase complex, account for the majority of cases of osteopetrosis. It is speculated that SNX10 is responsible for the vesicular sorting of V-ATPase from Golgi or for its targeting to the ruffled border. A mutation in SNX10 may therefore result in ‘secondary V-ATPase deficiency’ with a failure to acidify the resorption lacuna. Determination of the sequence of the SNX10 gene is warranted in molecularly undefined patients with recessive ‘pure’ osteopetrosis of infancy.

Cyclosporine (CSA) is the most commonly used medication for GVHD prophylaxis. The initiation time varies from day -4 to day 0. Initially, we gave CSA starting on day -1. However, since 2003 we have changed CSA initiation timing policy in most of our protocols to day -4, to achieve stable and controlled pretransplant CSA levels. Here, we assessed if initiation time impact the outcome of allogeneic stem-cell transplantation (allo-SCT). Data of 261 patients who underwent allo-SCT for hematological malignancies from a fully matched donor, treated with CSA as a single agent for GVHD prophylaxis were prospectively collected. Patients were divided according to CSA initiation time and analyzed for outcome. The acute GVHD severity, cGVHD extent, GVHD-associated mortality were significantly lower in the CSA -4 group. There was no difference in the rate and timing of acute or chronic GVHD. Overall survival did not differ between the groups. We conclude that the initiation of CSA at day -4 reduced the severity of aGVHD, extent of cGVHD, and GVHD-associated mortality without impact on overall survival.

Kindlin-3 is a key lymphocyte function-associated antigen-1 (LFA-1) coactivator deleted in leukocyte adhesion deficiency-III (LAD-III). In the present study, we investigated the involvement of this adaptor in lymphocyte motility and TCR-triggered arrest on ICAM-1 or on dendritic cells (DCs). Kindlin-3-null primary T cells from a LAD-III patient migrated normally on the major lymph node chemokine CCL21 and engaged in normal TCR signaling. However, TCR activation of Kindlin-3-null T lymphocytes failed to trigger the robust LFA-1-mediated T-cell spreading on ICAM-1 and ICAM-1-expressing DCs that is observed in normal lymphocytes. Kindlin-3 was also essential for cytoskeletal anchorage of the LFA-1 heterodimer and for microclustering of LFA-1 within ventral focal dots of TCR-stimulated lymphocytes spread on ICAM-1. Surprisingly, LFA-1 on Kindlin-3-null lymphocytes migrating over CCL21 acquired normal expression of an epitope associated with the conformational activation of the key headpiece domain, β I. This activated LFA-1 was highly responsive to TCR-triggered ICAM-1-driven stop signals in normal T cells locomoting on CCL21, but not in their Kindlin-3-null T-cell counterparts. We suggest that Kindlin-3 selectively contributes to a final TCR-triggered outside-in stabilization of bonds generated between chemokine-primed LFA-1 molecules and cell-surface ICAM-1.

A 58-year-old Ashkenazi Jew presented with fever and dyspnea. Over the 2-month period prior to his admission, he suffered from flu-like symptoms including fever and sore throat. His medical background only included hypertension for which he was treated. On admission his oxygen saturation was 91% on nasal cannula. He had a papular rash on his chest and back as well as enlarged sub-mandibular lymph nodes which were considered to be reactive lymph nodes by sonography. The rest of his physical examination was normal, including his lungs which were clear to auscultation. His laboratory tests indicated an elevated LDH (1773 U/l), cholestatic dysfunction with elevated alkaline phosphatase (191 U/l) and GGTP (316 U/l). He also had leukocytosis (white cell count of 12.2 × 109 cells/l) and an increased C-reactive protein (18.4 mg/dl, normal <1). His chest X-ray and high-resolution CT (HRCT) scan revealed diffuse interstitial disease (Figure 1). He was treated initially for a community acquired pneumonia. Six days after admission, his respiratory condition deteriorated, necessitating …

Background: Gene therapy (GT) with hematopoietic stem cells is a promising treatment for inherited immunodeficiencies.Objectives: Limited information is available on the relative contribution of de novo thymopoiesis and peripheral expansion to T-cell reconstitution after GT as well as on the potential effects of gene transfer on hematopoietic stem cells and lymphocyte replicative lifespan. We studied these issues in patients affected by adenosine deaminase severe combined immune deficiency after low-intensity conditioning and reinfusion of retrovirally transduced autologous CD34(+) cells.Methods: Immunophenotype, proliferative status, telomere length, and T-cell receptor excision circles were investigated at early and late time points (up to 9 years) after GT treatment. Control groups consisted of pediatric healthy donors and patients undergoing allogeneic bone marrow transplantation (BMT).Results: We observed no telomere shortening in the bone marrow compartment and in granulocytes, whereas peripheral blood naive T cells from both GT and BMT patients showed a significant reduction in telomere length compared with healthy controls. This was in agreement with the presence of a high fraction of actively cycling naive and memory T cells and lower T-cell receptor excision circles.Conclusion: These data indicate that T-cell homeostatic expansion contributes substantially to immune reconstitution, like BMT, and is not associated with senescence in the stem cell compartment. (J Allergy Clin Immunol 2011;127:1368-75.)

Abstract Abstract 1143 Poster Board I-165 Introduction Cyclosporine (CSA) is the backbone of graft vs. host disease (GVHD) prophylaxis in the last decades. It is established that CSA levels in the 1st weeks after transplant are critical for the rate and severity of GVHD. Initially, we gave CSA starting on day -1 in all our protocols. However, 8 years ago, we have changed CSA initiation in most of our protocols to day -4 in order to have stable, controlled therapeutic blood levels of CSA prior to transplant. Since nowadays the use of CSA is the most widespread prophylaxis of GVHD, we found it essential to compare the initiation of CSA on day -4 to day -1, consecutively determining the preferred initiating timing of CSA for patients who undergo allogeneic transplantations. Methods Out of 1716 patients that underwent allogeneic transplantation, we identified 2 groups of patients that received T-cell repleted grafts in which only CSA was used for GVHD prevention, starting on days -1 or -4 (n=219 and 261 respectively). The guidelines for CSA cessation and DLI were uniform in both groups. Both groups were compared for age, sex, donor type and matching, disease, disease status upon transplant, graft type, engraftment, GVHD (both acute and chronic), GVHD associated death and overall survival. Results The groups were found to be equal for age (p=0.83), sex (p=0.58), donor type (p=0.54), matching (p=0.98), disease type (malignant or non-malignant; p=0.25), graft type (PBSC or BM; p=0.45) and disease status (remission or active; p=0.42). The median time to ANC>500 was 16 and 15 days in the CSA -1 and -4 groups respectively with a trend toward better engraftment with initiation of CSA on day -4 (figure 1A, P=0.07). However, platelet engraftment was significantly better with CSA -4, with a median of 14 and 12 days in the CSA -1 and -4 groups respectively (figure 1B, p=0.0005). 112 and 138 patients developed acute GVHD (aGVHD) of any grade, respectively. Out of them 54% and 44% had severe (grade 3-4) aGVHD (p=0.45). The median time to aGVHD was similar, with a median of 29 and 28.5 days in the CSA -1 and -4 groups respectively (p=0.54). However, 64 patients developed cGVHD in the CSA -1 group, while 102 did so in the CSA -4 group (figure 2A, p=0.0002. Hazard ratio 0.59, 95% CI 0.37 to 0.73). Of these patients, 46.8% and 40.2% of the patients had extensive cGVHD (p=0.70), respectively. Additionally, despite lower GVHD rate in the CSA -1 group, GVHD associated death occurrence was more frequent then in the CSA -4 group (41/148 and 17/132 patients, p=0.02). Kaplan Meier analysis of all cause mortality showed higher mortality in the CSA -1 group (67.6% and 50.5%, figure 2B, p=0.074. Hazard ratio 1.24, 95% CI 0.98 to 1.58). Conclusions The initiation of CSA on day -4 improves engraftment, conversely increases the risk for cGVHD of any grade (possibly through prevention of tolerance), but reduces the risk of GVHD associated death and improves overall survival. Disclosures No relevant conflicts of interest to declare.

The failure of allogeneic stem cell transplant (allo-SCT) is cumbersome. We analyzed our experience in a second allo-SCT. Between the years 1981 and 2007, 144 patients underwent 2 or more allo-SCT. The first to second transplant interval ranged from 18 days to 13.25 years (median 98 days). The most frequent indications for the second SCT were activity of the basic disease (78), rejection (37), and engraftment failure (25). Twenty-nine of the 144 (20%) patients transplanted survived more then a year with treatment-related mortality of 45.5% as the leading cause of death. Interestingly, despite the low rate of graft-versus-host disease (GVHD) prophylaxis used, only 51 and 16 of the patients developed acute and chronic GVHD (aGVHD, cGVHD), respectively. Factors indicating higher likelihood for survival were nonmalignant disease, a nonrelapse indication for the second SCT, full HLA-matching, and the use of reduced-intensity conditioning (RIC). Age at transplantation, time interval between transplants, the development of GVHD, conditioning regimen, GVHD prophylaxis, or graft source were not shown to influence the prognosis. With a median follow-up of 4.5 years, 25 patients (17.2%) are alive, and 18 are disease-free. We conclude that although toxic, a second allo-SCT can lead to long-term survival.