Env pseudoviruses were generated by cotransfection with the pNL43-ΔEnv-vpr+-luc+ clone that expresses luciferase upon infection and were used to infect a panel of NP-2 cell lines that express CD4 and one of two major coreceptors (CCR5 or CXCR4) or other commonly used coreceptors (FPRL1, APJ, CCR3 or GPR15)19, 20, 21, 22. Here, CXCR4 is linked to infection.