Likewise, the infections of primary T cells by a CXCR4 -tropic virus (HIV-1LAI) were also significantly suppressed only by pan-caspase inhibitors ZVAD-FMK and QVD-OPH but not by Belnacasan (Fig 3C), suggesting caspase activation is required for both R5- and X4-tropic HIV infections. Here, CXCR4 is linked to infection.