CXCR4 and infection: In the context of an infection with Nef-impaired or nef-deleted virus, the impact of some host factors may be altered because of the slower replication kinetics of the virus or because they are not inactivated by Nef, such as tetherin and cell-surface receptors, e.g. CCR5 or CXCR4 (Hrecka et al., 2005; Landi et al., 2011; Michel et al., 2006; Zhang et al., 2009).