original articleT h e ne w e ngl a nd jou r na l o f m e dic i ne n engl j med 355;13 www.nejm

In comparison with UW organ preservation, exposure of pancreata to the TLM result in greater islet yields and extended preservation times.

The rate of oxygen consumption is an important measure of mitochondrial function in all aerobic cells. In pancreatic beta cells, it is linked to the transduction mechanism that mediates glucose-stimulated insulin secretion. However, measurement of oxygen consumption over long periods of time is technically difficult owing to the error resulting from baseline drift and the challenge of measuring small changes in oxygen tension. We have adapted an ultrastable oxygen sensor based on the detection of the decay of the phosphorescent emission from an oxygen-sensitive dye to a previously developed islet flow culture system. The drift of the sensor is approximately 0.3%/24 h, allowing for the continuous measurement of oxygen consumption by 300 islets (or about 6 x 10(5) cells) for hours or days. Rat islets placed in the perifusion chamber for 24 h were well maintained as reflected by membrane integrity, insulin secretion, and oxygen consumption. Both acute changes in oxygen consumption as induced by glucose and chronic changes as induced by sequential pulses of azide were resolved. The features of the flow culture system--aseptic conditions, fine temporal control of the composition of the media, and the collection of outflow fractions for measurement of insulin, and other products--facilitate a systematic approach to assessing metabolic and functional viability in responses to a variety of stimuli. Applications to the measurement of effects of hypoxia on insulin secretion, membrane integrity, and the redox state of cytochromes are demonstrated. The system has particular application to the field of human islet transplantation, where assessment and the study of islet viability have been hampered by a lack of experimental methods.

The exciting and extraordinary capabilities of stem cells to proliferate and differentiate into numerous cell types not only offers promises for changing how diseases are treated, but may also impact how transfusion medicine is practiced in the future. The possibility of growing platelets in the laboratory to some day supplement and/or replace standard platelet products has clear advantages for blood bank centers and patients. Due to the high utilization of platelets by patients undergoing chemotherapy or receiving stem cell transplants, platelet transfusion has steadily increased over the past decades. This trend is likely to continue as the number of adult and pediatric patients receiving stem cell transplants is also continuously rising. As a result of increased demand coupled with the short shelf-life of platelet concentrates, providing platelets to patients can stretch the resources of most blood centers, drive donor recruitment efforts, and on occasion platelet shortages can compromise the care of thrombocytopenic patients. The purpose of this article is to review current scientific progress to develop in vitro strategies to manufacture platelets, with an emphasis on efforts to produce functional platelets in quantities that would be required for clinical transfusion. There are a number of publications indicating that human platelets can be obtained in vitro from the controlled differentiation of hematopoietic stem cells. However, the hemostatic quality of such manufactured platelets has not been confirmed and current technologies are inadequate to ensure satisfactory expansion and platelet biogenesis on an industrial scale. Nonetheless, these studies provide proof-of-principle that developing in vitro strategies to manufacture platelets is feasible and also provide a foundation for developing more sophisticated approaches to achieve this goal.