Isolation and cryopreservation of monocytes from plateletapheresis cellular residues

Human monocytes were isolated from the cellular residues remaining after plateletapheresis of donors using an automated blood cell processor. Mononuclear cells were obtained with density gradients and separated from lymphocytes by stepwise elutriation. The isolated cells were frozen using extracellular hydroxyethyl starch and intracellular dimethylsulfoxide. In three procedures, approximately 1 X 10(9) monocytes were obtained. Ninety-nine percent of isolated monocytes were viable in a fluorescein diacetate (FDA)-ethidium bromide (EB) test. Myeloperoxidase-positive cells were 95 percent and 90 percent in the two chambers. Ninety-four percent of monocytes ingested five or more opsonized polycyclic hydrocarbon particles and 95 percent ingested one or more ethidium-treated zymosan particles. After storage in liquid nitrogen for up to 9 weeks, 99 percent of the cells were recovered after thawing. Of these, 95 percent were myeloperoxidase-positive, 94 percent showed intact membranes in the FDA-EB test, 95 percent ingested five or more opsonized polycyclic hydrocarbon particles, and 96 percent ingested one or more ethidium-treated zymosan particles. These results demonstrate the utility of elutriation as a means to isolate large numbers of monocytes. The isolated cells can be cryogenically preserved for at least 2 months with small loss of phagocytic function.