Monocytes are being formed out of the myeloid cells of the hematopoietic stem cells. In the presence of GM-CSF and the cytokines IL-1, IL-3, and IL-6, myeloid stem cells mature ‘‘via” precursor cells such as monoblasts and promonocytes to monocytes. Monocytes are counted to the group of the mononuclear white blood cells, and are frequently irregular shaped. In the peripheral blood, the monocyte is the largest cell (10–30 lm) and has a specific weight of 1077 g/mL. In the peripheral blood, monocytes do represent 3–10% of the total of white blood cells. Peripheral monocytes have a phagocytic and cytotoxic function [1]. The peripheral monocyte is not the end stage of the complete cell line. After 1–3 days in the peripheral circulation, the monocyte migrates to the tissues. Here they differentiate into macrophages or dendritic cells. At the same time, the cell will change functionally and morphologically. The most important function of the macrophages is phagocytosis. In dendritic cells, beside phagocytosis, presentation of antigens to other cells of the immune system (with help of HLA class II molecules) is a key function. Dendritic cells are the most potent antigen presenting cells (APCs) of the immune system. These cells can stimulate as well as slow down an immune response. Immature dendritic cells capture antigens by means of phagocytosis and migrate to the draining lymph nodes. During this process, the cells mature to dendritic cells and grow into very strong stimulators of T- and B-cells, but lose their phagocytotic function. They activate naive T- and B-cells to a primary immune response towards the antigen presented by the cell using Fc receptor mediated recognition of opsonizated antigens [2–4]. Collection of sufficient numbers of monocytes from donors and/or patients is performed by using centrifugal apheresis techniques. In these techniques, the differences in specific gravity of the various blood cells are used. Using the so-called close apheresis systems, products with a total number of 1–5 10 9 monocytes per unit with a purity of 20–30% can be harvested. However, a purity of 80–90% is needed for further processing of monocytes. This purity can be obtained using different techniques like plastic adherence techniques, magneto beats, Percoll gradients or Elutriation techniques (Elutra