The MagDot is a dual-purpose reagent, it combines quantum dots and superparamagnetic iron oxide particles within the same nanoparticle. Cells labeled with MagDots targeting specific antigens will be both fluorescent and magnetic. Therefore, after labeling cells of interest, one can look at the feed to determine the percent positive fluorescently via flow cytometry, and then place the labeled cells in a magnetic separator and analyze both the magnetic (for the enrichment) and the nonmagnetic (for the depletion) of targeted cells without the need for further fluorescent labeling. The SK3 monoclonal antibody reacts with human CD4, a 59-kDa cell surface receptor expressed by a majority of thymocytes, a subpopulation of mature T helper cells, and, in low levels, monocytes. CD4 is a receptor for the human immunodeficiency virus (HIV). SK3 blocks HIV binding and mixed lymphocyte reaction. The SK3 and RPA-T4 monoclonal antibodies do not cross-block binding, suggesting recognition of distinct epitopes.