Cleavage of the Gag and Gag-Pol polyprotein is mediated specifically by the virally-encoded protease [53, 54, 55] . We considered that CIITA might increase viral protease processing of Gag; thus, we examined Gag processing and infectious virus release from CIITA-expressing HIV producer cells in the presence of a protease inhibitor. If CIITA is increasing protease processing, such an enhancement should be overcome by lower doses of the HIV protease inhibitor, Lopinavir. As expected, between concentrations of 0.6 and 1.25 nM of Lopinavir infectious virus release from CIITA-expressing cells was reduced to that of A293T cells treated with vehicle only ( Figure 6A ). To determine if the reduced Gag processing correlated with decreased infectious virus release, we monitored Gag cleavage by western blotting and as expected, between 0.6 and 1.25 nM of Liponavir, Gag processing in virions from CIITA-expressing cells was returned to that of vehicle treated, vector-only control cells ( Figure S3 ). These results directly demonstrate that CIITA-mediated enhancement of Gag processing and infectious virus release is through the HIV protease.