CD4 and osteosarcoma: We illustrate the utility of this approach with several different systems: i) surface staining of a U2OS human osteosarcoma cell line that is stably transfected with a vector encoding β1-integrin-HaloTag7 (U2OS-β1Int-HT7); ii) intracellular staining of Jurkat CD4 T cells infected with an HIV-1 reporter virus (HIV-1Lai-Halo) that encodes an unfused HT; and iii) intracellular staining of a HEK-293 cell line that expresses a HT fusion with the nuclear factor (NFκB) p65 subunit.