In 1965, Sir Austin Bradford Hill published nine “viewpoints” to help determine if observed epidemiologic associations are causal. Since then, the “Bradford Hill Criteria” have become the most frequently cited framework for causal inference in epidemiologic studies. However, when Hill published his causal guidelines—just 12 years after the double-helix model for DNA was first suggested and 25 years before the Human Genome Project began—disease causation was understood on a more elementary level than it is today. Advancements in genetics, molecular biology, toxicology, exposure science, and statistics have increased our analytical capabilities for exploring potential cause-and-effect relationships, and have resulted in a greater understanding of the complexity behind human disease onset and progression. These additional tools for causal inference necessitate a re-evaluation of how each Bradford Hill criterion should be interpreted when considering a variety of data types beyond classic epidemiology studies. Herein, we explore the implications of data integration on the interpretation and application of the criteria. Using examples of recently discovered exposure–response associations in human disease, we discuss novel ways by which researchers can apply and interpret the Bradford Hill criteria when considering data gathered using modern molecular techniques, such as epigenetics, biomarkers, mechanistic toxicology, and genotoxicology.

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While stem cell cryopreservation methods have been optimized using dimethylsulfoxide (DMSO), the established techniques are not optimal when applied to unfertilized human embryonic cells. In addition, important questions remain regarding the toxicity and characteristics of DMSO for treatment of stem cells for clinical use. The objective of this study was to establish an optimal method for cryopreservation of stem cells using low concentrations (0.2 M) of trehalose, a nontoxic disaccharide of glucose, which possesses excellent protective characteristics, in place of current methods utilizing high concentrations (1-2 M) of DMSO. A human hematopoietic cell line was used in this investigation as a surrogate for human stem cells. Trehalose was loaded into cells using a genetically engineered mutant of the pore-forming protein alpha-hemolysin from Staphylococcus aureus. This method results in a nonselective pore equipped with a metal-actuated switch that is sensitive to extracellular zinc concentrations, thus permitting controlled loading of trehalose. Preliminary experiments characterized the effects of poration on TF-1 cells and established optimal conditions for trehalose loading and cell survival. TF-1 cells were frozen at 1 degrees C/min to -80 degrees C with and without intra- and extracellular trehalose. Following storage at -80 degrees C for 1 week, cells were thawed and evaluated for viability, differentiation capacity, and clonogenic activity in comparison to cells frozen with DMSO. Predictably, cells frozen without any protective agent did not survive freezing. Colony-forming units (CFU) generated from cells frozen with intra- and extracellular trehalose, however, were comparable in size, morphology, and number to those generated by cells frozen in DMSO. There was no observable alteration in phenotypic markers of differentiation in either trehalose- or DMSO-treated cells. These data demonstrate that low concentrations of trehalose can protect hematopoietic progenitors from freezing injury and support the concept that trehalose may be useful for freezing embryonic stem cells and other primitive stem cells for therapeutic and investigational use.

Aggressive natural killer cell leukemia (ANKL) is a rare Epstein-Barr virus (EBV)-associated fulminating disease that is widely disseminated at diagnosis. Because of its typically extranodal presentation, differing degrees of NK cell involvement, and varying bone marrow pathology, ANKL can be confused with a reactive process. These features, coupled with a rapidly fatal course, have hampered systematic study of the pathogenesis of ANKL. Nine cases of ANKL were diagnosed and characterized by a single laboratory over a 2-year period. Constant features at presentation included disseminated disease, high fever, bone marrow involvement, and a high lactate dehydrogenase index. All cases were positive for EBV early region protein and negative for latent membrane protein 1, and all had a germline T-cell receptor gene configuration. Peripheral blood counts were variable, with severe thrombocytopenia being the most frequently encountered abnormality (7 of 9 cases). Hematophagocytosis, dyserythropoiesis, and stromal degeneration were the most frequent findings in the bone marrow. Neoplastic cells in the bone marrow were consistently CD2+, CD56+, CD45+, CD34-, CD117-, CD4-, and surface CD3-. Most cases were HLA-DR+ (8/9) and CD8- (8/9). Complex clonal cytogenetic abnormalities were found in 8 of 9 cases. Because of its aggressive course, rapid and accurate diagnosis of ANKL is essential for a better understanding of the etiology, pathogenesis, and treatment of the disease.

Over the last century, benzene has been a well-studied chemical, with some acute and chronic exposures being directly associated with observed hematologic effects in humans and animals. Chronic heavy exposures to benzene have also been associated with acute myelogenous leukemia (AML) and myelodysplastic syndrome (MDS) in humans. Other disease processes have also been studied, but have generally not been supported by epidemiologic studies of workers using benzene in the workplace. Within occupational cohorts with large populations and very low airborne benzene exposures (less than 0.1–1.0 ppm), it can be difficult to separate background disease incidence from those occurring due to occupational exposures. In the last few decades, some scientists and physicians have suggested that chronic exposures to various airborne concentrations of benzene may increase the risk of developing non-Hodgkin's lymphoma (NHL) (Savitz and Andrews, 1997, Am J Ind Med 31:287–295; Smith et al., 2007, Cancer Epidemiol Biomarkers Prev 16:385–391), multiple myeloma (MM) (Goldstein, 1990, Ann NY Acad Sci 609:225–230; Infante, 2006, Ann NY Acad Sci 1076:90–109), and various other hematopoietic disorders. We present a state-of-the-science review of the medical and regulatory aspects regarding the hazards of occupational exposure to benzene. We also review the available scientific and medical evidence relating to benzene and the risk of developing various disorders following specific levels of exposure. Our evaluation indicates that the only malignant hematopoietic disease that has been clearly linked to benzene exposure is AML. Information from the recent "Benzene 2009," a symposium of international experts focusing on the health effects and mechanisms of toxicity of benzene, hosted by the Technical University of Munich, has been incorporated and referenced.