Advances in infectious disease research over the past 10 years have allowed breakthroughs in thediagnosis, prevention, and treatment of infectious disease.

The index case of the Ebola virus disease epidemic in West Africa is believed to have originated in Guinea. By June 2014, Guinea, Liberia, and Sierra Leone were in the midst of a full-blown and complex global health emergency. The devastating effects of this Ebola epidemic in West Africa put the global health response in acute focus for urgent international interventions. Accordingly, in October 2014, a World Health Organization high-level meeting endorsed the concept of a phase 2/3 clinical trial in Liberia to study Ebola vaccines. As a follow-up to the global response, in November 2014, the Government of Liberia and the US Government signed an agreement to form a research partnership to investigate Ebola and to assess intervention strategies for treating, controlling, and preventing the disease in Liberia. This agreement led to the establishment of the Joint Liberia-US Partnership for Research on Ebola Virus in Liberia as the beginning of a long-term collaborative partnership in clinical research between the two countries. In this article, we discuss the methodology and related challenges associated with the implementation of the Ebola vaccines clinical trial, based on a doubleblinded randomized controlled trial, in Liberia.

Differential scanning calorimetry revealed that chromatin melts in four distinct transitions in intact HeLa nuclei at 60°C, 76C, 88°C, and 105°C. Calorimetry of whole cells was characterized by the same four transitions along with another at 65°C, which was probably RNA. Isolated chromatin, however, melted in only two transitions at 72°C and 85°C. Very brief digestion of HeLa nuclei with either micrococcal nuclease or DNase I resulted in the conversion of a structure that melted at 105°C to one that melted at 880C. Further digestion with micrococcal nuclease to the level of the mononucleosome did not result in any further substantial changes in either enthalpy or melting temperatures. In contrast, further DNase I digestion that resulted in cleavage within the nucleosome produced a pronounced shift in melting temperatures to two broad transitions at 62C and 78°C.Eukaryotic DNA exists as long continuous molecules but is condensed on the order of 1000-fold to fit within interphase nuclei (1). The lowest level of folding is that of the nucleosome, a repeating subunit consisting of two each of the core histones H2A, H2B, H3, and H4, along with about 200 base pairs of DNA and one molecule of histone H1. Histone H1 is believed to effect further condensation to a 300-A fiber that has been postulated to be a solenoid (2).Studies of chromatin structure above the level of the solenoid have been hampered due to the tendency of chromatin fibers to form aggregates and turbid suspensions at physiological salt conditions. The use of differential scanning microcalorimetry in studies of chromatin structure has the advantage that samples need not be optically clear as is required for spectral studies (3,4 (7). These workers correlated the intensities of the endotherms observed with the relative amounts of DNA and RNA present in several samples.The results of our study suggest that differential scanning calorimetry can be used to characterize the native chromatin structures in nuclei and that nuclei are to be preferred over isolated chromatin and whole cells. The thermodynamically significant chromatin structures of whole cells were shown to be retained in the nucleus, but a major structure was destroyed by brief micrococcal nuclease treatment. MATERIALS AND METHODSCell Culture. HeLa cells, strain S3, were maintained in suspension culture at cell densities of 2-8 x 105 per ml in Joklik's modified spinner medium supplemented with 5% calf serum. Cells were harvested at cell densities of 5-6 x 105 per ml.Isolation of Nuclei. All steps were carried out at 0-40C. (pH 7.5). NaCl, MgCl2, and CaCl2 were added to final concentrations of 150 mM, 1 mM, -and 1 mM, respectively, and the chromatin was incubated for 1 hr at room temperature. Insoluble chromatin was centrifuged for 10 min at 8000 x g and the pellet was used for calorimetric scanning.Gel Electrophoresis of DNA Digestion Fragments. Following digestion by micrococcal nuclease or DNase I, nuclei were pelleted and dissolved in 5 ml of 1 M NaCl/0.6% NaDodSO4 and then extracted ...

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