The timing of CypA binding to the core has been indirectly measured using the so-called cyclosporin (CsA) washout assay, an in vitro assay in which the drug CsA is added at the time of HIV-1 infection to the cells constitutively expressing CypA fused to the restriction factor TRIM5α (TRIMCyp). Here, PPIA is linked to HIV-1 infection.