INCE ITS INCEPTION as a medical specialty, hematol-S ogy has had the unique perspective of considering therapeutics to include not only small molecular weight pharmaceuticals, but also cells themselves. Recognizing the complexity of the functions performed by the blood cells, hematologists have long understood that our best chance of harnessing the power of these cells for oxygen transport, repair of damaged endothelium, and inflammation was to transfuse large numbers of normal blood cells. By doing so, hematologists could thereby circumvent the need to understand every molecular function of these cells in complete reductionist detail, simply taking advantage of evolution’s wisdom.

Cellular transfusion therapies began with mature blood cells, first with whole blood and then later evolving to the use of fractionated blood components. These therapies proved extremely effective for red blood cells and often useful for platelets, but less so for neutrophils, whose lifetimes were too short to be of practical use. Transfusion of mature longlived T lymphocytes may itself have useful clinical applications as well.