CD4 and HIV-1 infection: Importantly, HIV-1 infection of PBMC-NSG mice mimics early stages of infection in humans, in that the virus replicates exponentially, resulting in large scale CD4+ T-cell depletion within a few weeks (Marsden and Zack, 2015; Kim et al., 2016; Kumar et al., 2008), and this model was previously used to study the effectiveness of anti-HIV-1 therapies in reducing systemic virus spread after intravenous transmission (Kim et al., 2016; Kumar et al., 2008; Balazs et al., 2012, 2014; Hur et al., 2012).