Positive selection of human CD8+ T cells, depletion of human CD8+ T cells and a subset of NK cells CD8 MicroBeads were developed for the positive selection or depletion of human cytotoxic CD8+ T cells from different cell sources. The most commonly used cell sources are peripheral blood and cord blood. In addition, cytotoxic T cells have also been isolated from lymph nodes, thymus, skin biopsies1, and spleen.