To assess whether CIITA-mediated alleviation of Gag retention in class II expressing cells correlated with restored virus production, virus particle and infectious virus release were measured by p24 ELISA and GHOST cell infectivity assays, respectively. Virus release, both infectious and particle titers) were reduced when cells were transfected with either HLA-DR or other components of the MHC class II antigen presentation pathway ( Figure  S2 ), confirming a correlation between Gag retention and reduced virus titers in the presence of HLA-DR, as previously demonstrated [8] . These assays also demonstrate a dramatic increase in infectious virus release from CIITA-expressing cells as compared to cells expressing vector only (Figure 2A & S2), despite significantly fewer virus particles being released from a CIITAexpressing cell (as measured by pg/mL of p24 in the culture supernatant, Figure 2B & S2). Therefore, while fewer virus particles are released from a CIITA-expressing cell, those particles are significantly more infectious ( Figure 2C ).