CD8 MicroBeads were developed for the isolation of CD8+ cells. The CD8 antigen forms a complex together with the T cell receptor and acts as an accessory molecule in the recognition of MHC class I/peptide complexes by the TCR heterodimer on CD8+ cytotoxic T cells. The CD8 molecule consists of either an α/β heterodimer or an α/α homodimer. It is expressed strongly on cytotoxic T cells and dimly on a subset of NK cells. CD8 is found on most thymocytes and on about one third of all peripheral blood T cells. CD8+ cytotoxic T cells play an important role in the killing of virus-infected cells and tumor cells.