Infectivity of HIV particles from cells fused with CEM.NKR cell clones. A) Fusion efficiency between CEM.NKR and 293T cells. 293T cells were transfected with a GFP expression vector in the presence or absence of gp160 expression vector and then co-cultured with CEM-SS, CEM.NKR, clone #2, or clone #5, respectively. After 48 hours, cells were stained with CD4-PE and the amounts of CD4 and GFP double positive cells were measured by flow cytometry. B) Production of infectious particles from heterokaryons between 293T and CEM.NKR or its subclones. The gp160-expressing 293T cells were co-cultured with indicated T cells producing env-defective HIV-1. After 48 hours, production of infectious particles from these co-cultures was determined by infection of TZM-BI cells. C) HIV-1 (NL4-3) replication in CEM-SS, CEM.NKR, clone #2, and clone #5 cells. D) HIV-1 (NL4-3) replication in CEM-SS and CEM.NKR co-cultures. A total of 5 × 105 HIV-infected CEM-SS, CEM.NKR, clone #2, or clone #5 cells were co-cultured at 1:1 ratio with or without a 5 min PEG treatment. Viral production from these cultures was then determined for 10 days.