FIG. 3.

Virion transcomplementation requires a matched HIV-1 envelope-coreceptor pair on donor and target virions. (A) Infection assays were performed by mixing donor particles bearing CXCR4-tropic (CA5) and CCR5-tropic (CA5-BaL) Env proteins with receptor-pseudotyped target virions, and infection was tested using target cells bearing both coreceptors. To demonstrate the requirement for CD4 and CXCR4 on target virions, Env-defective HIV-1 particles lacking receptors (HIV-1ΔE) were used as target virions. Appreciable levels of infection were observed only when the target virions contained CD4 and an appropriate coreceptor. (B) Requirement of the HIV-1 Env proteins on donor virions and CD4 on target virions for infection of CD4-negative target cells by intervirion fusion using dual-enveloped donor particles. Core-defective particles bearing both HIV-1 and VSV Env proteins virions [CA5(VSV) or CA6(VSV)] were mixed with receptor-pseudotyped target virions, and the virus mixtures were used to infect HeLa target cells lacking CD4 (Z24 cells). The mean values of triplicate infections are shown; error bars represent one standard deviation. Results are representative of at least two independent experiments.