Distribution-free regression analysis of grouped survival data

Methods based on regression models for logarithmic hazard functions, Cox models, are given for analysis of grouped and censored survival data. By making an approximation it is possible to obtain explicitly a maximum likelihood function involving only the regression parameters. This likelihood function is a convenient analog to Cox's partial likelihood for ungrouped data. The method is applied to data from a toxicological experiment.     

Excess smoking in malignant-phase hypertension

The smoking habits of 82 patients with malignant-phase hypertension were compared with those of subjects in three control groups matched for age and sex. Sixty-seven (82%) of the patients with malignant-phase hypertension were smokers compared with 41 (50%) and 71 (43%) of the patients in two control groups with non-malignant hypertension, and 43 people (52%) in a general population survey. The excess of smokers in the malignant-phase group was significant for men and women, together and separately, for cigarette smoking alone, and for all forms of smoking. There were no significant differences between the control groups. The chance of a hypertensive patient who smoked having the malignant phase was five times that of a hypertensive patient who did not. Twelve patients in the malignant-phase group had never smoked. All were alive three and a half years on average after presentation (range 11 months to seven years). Twenty-four (36%) of the smokers with malignant-phase hypertension died during the same period. The mortality rate was significantly higher among patients with renal failure, as was the prevalence of smoking. Eighteen patients with malignant-phase hypertension had a serum creatinine concentration higher than 250 μmol/l (2·8 mg/100 ml); 17 were smokers and one an ex-smoker. Eleven of these 18 patients died.It is concluded that hypertensive patients who smoke are much more likely to develop the malignant phase than those who do not, and that once the condition has developed it follows a particularly lethal course in smokers.     

Biological properties of human melanoma cells in culture

Summary Three human melanoma cell lines derived from one primary and two metastatic tumors from three different patients were characterized for growth properties usually associated with malignant transformation; these include cell morphology, growth rate, saturation density, growth in semisolid media, colony-forming ability on contact-inhibited monolayers of normal fibroblasts and epithelial cells, and tumorigenicity in immunosuppressed mice. Variations in expression of aberrant properties were evident among the lines. One of the metastatic lines satisfied all the parameters of malignancy tested and the other showed a number of these properties, whereas the primary essentially fulfilled only one. These results suggest that cultured melanoma cells reflect the clinical variability often observed among melanoma patients and the metastatic melanoma seems to display a higher degree of malignant transformation than the primary. THis work was supported in part by USPHS Grant No. 5 T01 AI00332-06 from the National Institutes of Health, Contract E73-2001-N01-CP-3-3237 from the Virus Cancer Program of the National Cancer Institute, and USPHS Grant No. 0H00714-02 from the National Institute for Occupational Safety and Health.     

CHANGES IN THE PROLIFERATION RATE OF MOUSE EPIDERMIS AFTER IRRADIATION: CONTINUOUS LABELLING STUDIES

The proliferative response of mouse skin to damage caused by X-irradiation has been tested by giving repeated injections of tritiated thymidine and scoring the percentage of labelled cells in high resolution autoradiographs. Four, nine and fourteen daily fractions of 300 rads of X-rays were used and labelling commenced 4 days after the last fraction. The epidermis of the upper surface and the sole of the foot were scored separately and were compared with the skin of unirradiated feet. In unirradiated skin the proliferation rate of the basal layer cells is more rapid on the sole than on the upper surface. The cell cycle times deduced from continuous labelling curves were 81 hr and 111 hr respectively and the growth fractions were 97% and 85%. After irradiation with small daily doses the homeostatic response to cell killing was slow. More rapid proliferation occurred after nine fractions in the sole, but was not apparent in the skin of the upper surface until fourteen fractions had been given. After fourteen fractions the cell cycle time was about 24 hr on both surfaces and the growth fraction was about 90%. The initial labelling index after a single thymidine injection was a poor measure of proliferation rate. The delay in the time of onset of faster proliferation is similar, both qualitatively and quantitatively, to that measured previously from the additional dose increments needed if large doses were given at different times after the multifraction treatments (Denekamp, 1973).     

The incorporation of nitrogen into products of recent photosynthesis in Anabaena cylindrica Lemm.

In vivo tracer studies with ¹⁴C have been performed to help determine pathways of incorporation of newly assimilated nitrogen into N₂-fixing cells of Anabaena cylindrica. After photosynthesis in Ar:O₂:¹⁴CO₂ for 30 min, the addition of N₂ or NH ₄ ⁺ resulted in increased rates of ¹⁴CO₂-incorporation both in the light and dark, and in increased incorporation of ¹⁴C into amino acids at the expense of sucrose and sugar phosphates. Evidence of enhanced sucrose catabolism and increased pyruvate kinase activity was obtained on adding nitrogen, and, of the ¹⁴C-labelling entering the tricarboxylic acid cycle, more appeared in citrate and 2-oxoglutarate than in malate and oxaloacetate. The kinetics of ¹⁴C-incorporation into various amino acids suggest that in the light and dark the most important route of primary ammonia assimilation involves glutamine synthetase and that glutamate, aspartate, glycine and probably alanine are formed secondarily from glutamine.     

Separation of a proteoglycan fraction from Kurloff cells stimulating protein synthesis in macrophages.

Proteoglycan from Kurloff cells, when present in the medium in low concentrations, increased the incorporation of (3-H)leucine into trichloracetic acid-precipitable material by macrophages from peritoneal exudates, in addition to inhibiting their migration from capillary tubes, as observed previously. After treatment with 0.5 M-NaOH, followed by dialysis or ultrafiltration, material with the distinctive u.v. and i.r. spectra of the whole proteoglycan appeared in the diffusate, and biological activity was lost from the proteoglycan which remained in the dialysis residue. The diffusible material absorbed near 260 nm and had i.r. bands at 805 cm-minus-1 and 1260 cm-minus-1, but did not display the i.r. bands characteristic of chondrotin 4-sulphate. It contained little sulphate, no hexosamine and less than 1% of the uronic acid present in the whole proteoglycan, and there were only trace amounts of amino acids, xylose and galactose. However, significant amounts of ribose and organic phosphate were present, each representing about 1% of the whole proteoglycan. After proteolysis and chondroitanase digestion of the proteoglycan, a fraction with absorbance at 260 mn was eluted from Dowex 1 with water which stimulated the incorporation of (3H)leucine by macrophages and inhibited their migration from capillary tubes.     

The enterotoxin gene (cpe) of Clostridium perfringens can be chromosomal or plasmid-borne

The location of the cpe gene, encoding the enterotoxin responsible for food poisoning in humans, has been studied in a series of enterotoxigenic Ciostridium perfringens strains by means of pulsed field gel electrophoresis of genomic DNA. The cpe gene was found at the same chromosomal locus in strains associated with food poisoning in humans and was shown to be linked to a repetitive sequence, the Hin dlll repeat, and an open reading frame, ORF3, that may be part of an insertion sequence. In contrast, when the strains originated from domesticated livestock cpe was located on a large episome where it was often close to a copy of the transposable element IS 1151. In these cases, the Hin dlll repeat was not linked to the cpe gene although this was generally preceded by ORF3.     

pHG165: A pBR322 copy number derivative of pUC8 for cloning and expression

During the construction of the Messing pUC plasmid series, the rop(rom) gene of pBR322 which mediates the activity of RNAI was deleted. This has resulted in an elevated copy number for the pUC plasmids which makes the expression of beta-galactosidase activity constitutive in a host containing the Iqtss lac repressor. We describe the construction of a new series of vectors which retain the pUC multiple cloning site (MCS) but in which copy number control has been recovered. In addition, the lac alpha/lac promoter expression region has been inserted into a HpaI cassette. This facilitates the movement of recombinant DNA clones within the MCS. It also increases the complementation activity of the lac alpha peptide by an order of magnitude, allowing selection of recombinants by their Lac- phenotype on MacConkey agar.     

Sterile host yeasts (SHY): a eukaryotic system of biological containment for recombinant DNA experiments.

A system of biological containment for recombinant DNA experiments in Saccharomyces cerevisiae (Brewer's/Baker's yeast) is described. The principle of containment is sterility: the haploid host strains all contain a mating-type-non-specific sterile mutation. The hosts also contain four auxotrophic mutations suitable for selection for the various kinds of vectors used. All vectors are derivatives of pBR322 which can be selected and maintained in both yeast and Escherichia coli. The system has recently been certified at the HV2 level by the National Institutes of Health.