Telomere shortening is the mechanism underlying replicative aging in fibroblasts. A variety of reports now claim that inactivation of the p16 INK4a/pRB pathway is required in addition to telomere maintenance for the immortalization of cells such as skin keratinocytes and breast epithelial cells. We here show that the premature growth arrest of these cell types can be explained by an inadequate culture environment. Providing mesenchymal/epithelial interactions by cultivating the telomerase-expressing cells on feeder layers avoids the growth arrest associated with increased p16 INK4a. These results do not support a telomere-independent mechanism of replicative aging. The ability to proliferate indefinitely in tissue culture is one of many differences between normal human cells and established tumor cell lines. For nearly forty years (Hayflick and Moorhead 1961), the contrast between the immortality of cancer cells and the senescence of normal cells has been controversial. The major source of skepticism rests on the knowledge that in vitro culture conditions represent a departure from the in vivo environment, and that the aneuploidy and altered growth controls accumulated by tumor cells might simply allow them to divide under conditions inadequate to support the long-term proliferation of normal cells. Although greatly diminished by the recent advances uncovering cellular mechanisms for counting cell divisions (see below), concerns that cellular senescence represents a tissue-culture artifact have continued (Rubin 1997(Rubin , 1998.The best understood mechanism for replicative aging involves telomere shortening. Telomerase, the enzyme responsible for maintaining telomere length (Greider and Blackburn 1985), is down-regulated or turned off in most human tissues early in development (Wright et al. 1996). The inability of the normal replication machinery to copy all the way to the end of a linear chromosome, combined with potential end-processing events (Wellinger et al. 1996;Huffman et al. 2000), results in the progressive shortening of telomeres with each subsequent cell division (Harley et al. 1990). The eventual growth arrest of cultured cells is thought to occur when some of the telomeres become sufficiently short to compromise their interaction with specific telomere-binding proteins such as TRF2 (van Steensel et al. 1998). The resulting failure of these proteins to mask the end of the chromosome from being recognized as a double-strand break induces a DNA-damage response that in turn produces the final growth arrest (Harley 1991). The ability of cDNAs encoding the catalytic subunit of human telomerase (hTERT) to produce telomerase activity, maintain telomere length, and immortalize normal human skin fibroblasts (Bodnar et al. 1998;Vaziri and Benchimol 1998), retinal pigment epithelial cells (Bodnar et al. 1998) and endothelial cells (Yang et al. 1999) has greatly strengthened this model.Replicative aging is thought to provide a barrier against the accumulation of mutations and the formation of cancer. If each m...

IMPORTANCE The association between red blood cell (RBC) transfusion strategies and health care–associated infection is not fully understood. OBJECTIVE To evaluate whether RBC transfusion thresholds are associated with the risk of infection and whether risk is independent of leukocyte reduction. DATA SOURCES MEDLINE, EMBASE, Web of Science Core Collection, Cochrane Central Register of Controlled Trials, Cochrane Database of Sytematic Reviews, ClinicalTrials.gov, International Clinical Trials Registry, and the International Standard Randomized Controlled Trial Number register were searched through January 22, 2014. STUDY SELECTION Randomized clinical trials with restrictive vs liberal RBC transfusion strategies. DATA EXTRACTION AND SYNTHESIS Twenty randomized trials with 8598 patients met eligibility criteria, of which 17 trials (n = 7456 patients) contained sufficient information for meta-analyses. DerSimonian and Laird random-effects models were used to report pooled risk ratios. Absolute risks of infection were calculated using the profile likelihood random-effects method. MAIN OUTCOMES AND MEASURES Incidence of health care–associated infection such as pneumonia, mediastinitis, wound infection, and sepsis. RESULTS The pooled risk of all serious infections was 10.6% (95% CI, 5.6%-15.9%) in the restrictive group and 12.7% (95% CI, 7.0%-18.7%) in the liberal group. The risk ratio (RR) for the association between transfusion strategies and infection (serious infections and selected infections, combined) was 0.92 (95% CI, 0.82-1.04) with little heterogeneity (I2 = 6.3%; τ2 = .0041). The RR for the association between transfusion strategies and serious infection was 0.84 (95% CI, 0.73-0.96; I2 = 0%, τ2 <.0001). The number needed to treat (NNT) with restrictive strategies to prevent serious infection was 48 (95% CI, 36-71). The risk of infection remained reduced with a restrictive strategy, even with leukocyte reduction (RR, 0.83 [95% CI, 0.69-0.99]). For trials with a restrictive hemoglobin threshold of <7.0 g/dL, the RR was 0.86 (95% CI, 0.72-1.02). With stratification by patient type, the RR for serious infection was 0.72 (95% CI, 0.53-0.97) in patients undergoing orthopedic surgery and 0.51 (95% CI, 0.28-0.95) in patients presenting with sepsis. There were no significant differences in the incidence of infection by RBC threshold for patients with cardiac disease, the critically ill, those with acute upper gastrointestinal bleeding, or for infants with low birth weight. CONCLUSIONS AND RELEVANCE Among hospitalized patients, a restrictive RBC transfusion strategy compared with a liberal transfusion strategy was not associated with a reduced risk of health care–associated infection overall, although it was associated with a reduced risk of serious infection. Implementing restrictive strategies may have the potential to lower the incidence of serious health care–associated infection.

Background Severe sepsis is a common and costly problem. Although consistently defined clinically by consensus conference since 1991, there have been several different implementations of the severe sepsis definition using ICD-9-CM codes for research. We conducted a single center, patient-level validation of one common implementation of the severe sepsis definition, the so-called “Angus” implementation. Methods Administrative claims for all hospitalizations for patients initially admitted to general medical services from an academic medical center in 2009–2010 were reviewed. On the basis of ICD-9-CM codes, hospitalizations were sampled for review by three internal medicine-trained hospitalists. Chart reviews were conducted with a structured instrument, and the gold standard was the hospitalists’ summary clinical judgment on whether the patient had severe sepsis. Results 3,146 (13.5%) hospitalizations met ICD-9-CM criteria for severe sepsis by the Angus implementation (“Angus-positive”) and 20,142 (86.5%) were Angus-negative. Chart reviews were performed for 92 randomly-selected Angus-positive and 19 randomly-selected Angus-negative hospitalizations. Reviewers had a kappa of 0.70. The Angus implementation’s positive predictive value (PPV) was 70.7% (95%CI: 51.2%, 90.5%). The negative predictive value was 91.5% (95%CI: 79.0%, 100%). The sensitivity was 50.4% (95%CI: 14.8%, 85.7%). Specificity was 96.3% (95%CI: 92.4%, 100%). Two alternative ICD-9-CM implementations had high PPVs but sensitivities of less than 20%. Conclusions The Angus implementation of the international consensus conference definition of severe sepsis offers a reasonable but imperfect approach to identifying patients with severe sepsis when compared with a gold standard of structured review of the medical chart by trained hospitalists.

Background Severe sepsis is a common, costly, and complex problem, the epidemiology of which has only been well studied in the intensive care unit (ICU). However, nearly half of all patients with severe sepsis are cared for outside the ICU. Objective To determine rates of infection and organ system dysfunction in patients with severe sepsis admitted to non-ICU services Design Retrospective cohort study Setting A large tertiary academic medical center in the United States Patients Adult patients initially admitted to non-ICU medical services from 2009–2010 Measurements All ICD-9-CM diagnosis codes were screened for severe sepsis. Three hospitalists reviewed a sample of medical records evaluating the characteristics of severe sepsis. Results Of 23,288 hospitalizations, 14% screened positive for severe sepsis. A sample of 111 cases was manually reviewed identifying 64 cases of severe sepsis. The mean age of patients with severe sepsis was 63 years, and 39% were immunosuppressed prior to presentation. The most common site of infection was the urinary tract (41%). The most common organ system dysfunctions were cardiovascular (hypotension) and renal dysfunction occurring in 66% and 64% of patients respectively. An increase in the number of organ systems affected was associated with an increase in mortality and eventual ICU utilization. Severe sepsis was documented by the treating clinicians in 47% of cases. Conclusions Severe sepsis was commonly found and poorly documented on the wards at our medical center. The epidemiology and organ dysfunctions among patients with severe sepsis appear to be different from previously described ICU severe sepsis populations.

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