Highly cytopathic CXCR4-tropic virus strains were not considered for these studies because the HIV-1 infection of MDMs with CXCR4-tropic virus induces productive HIV-1 replication in MDMs until day 7 pi, and then it decreases drastically and becomes undetectable at day 10 pi due to viral-induced cell death [6]. The gene discussed is CXCR4; the disease is HIV-1 infection.