Influence of multiplicity of infection and protein stability on retroviral vector-mediated gene expression in hematopoietic cells

Using retroviral vectors encoding enhanced green fluorescent protein (EGFP), we addressed to what extent expression of retroviral transgenes in hematopoietic cells depends on the multiplicity of infection (MOI) and on the half-life of the encoded protein. We show that an elevation of the MOI not only elevates the frequency of transduced cells, but also increases transgene expression levels and reduces interanimal variability in vivo (hematopoietic cells of C57BL/6J mice analyzed 13 weeks after transplantation). This suggests that the MOI has to be carefully controlled and should be adapted as desired for clinical studies when evaluating vector performance in preclinical models. The impact of protein stability is demonstrated by comparing vectors expressing EGFP or a destabilized variant with a C-terminal PEST-sequence, d2EGFP. The loss of expression with d2EGFP was more pronounced in terminally differentiated cells of the peripheral blood (>30 fold) than in progenitor cells (five- to 10-fold), indicating a stronger transcription of the retroviral promoter in progenitor cells and a predominant role of protein inheritance over de novo synthesis of transgenic protein in mature blood cells. This analysis reveals an important and differentiation-dependent contribution of protein half-life to the expression of retroviral vectors in hematopoietic cells, establishes d2EGFP as a more accurate reporter for determination of vector transcription, and also suggests that preclinical data obtained under conditions of high transduction rates or with vectors expressing stable reporter proteins require careful interpretation.

International epidemiological and microbiological study of outbreak of Salmonella agona infection from a ready to eat savoury snack--I: England and Wales and the United States

OBJECTIVES

To identify the source of an international outbreak of food poisoning due to Salmonella agona phage type 15 and to measure how long the underlying cause persisted.

DESIGN

Case-control study of 16 primary household cases and 32 controls of similar age and dietary habit. Packets of the implicated foodstuff manufactured on a range of days were examined for salmonella. All isolates of the epidemic phage type were further characterised by pulsed field gel electrophoresis.

RESULTS

27 cases were identified, of which 26 were in children. The case-control study showed a strong association between infection with S agona phage type 15 and consumption of a peanut flavoured ready to eat kosher savoury snack imported from Israel. S agona phage type 15 was isolated from samples of this snack. The combined food sampling results from the United Kingdom, Canada, the United States, and Israel showed that contaminated snacks were manufactured on at least seven separate dates during a four month period between October 1994 and February 1995. Voluntary recalls of the product successfully interrupted transmission.

CONCLUSIONS

Rapid international exchanges of information led to the identification of the source of a major outbreak of S agona in Israel and of associated cases in North America. The outbreak showed the value of the Salm-Net surveillance system and its links outside Europe, both for increasing case ascertainment and for improving the information on the duration of the fault at the manufacturing plant.