Viral protease cleavage of the Gag and Gag-Pol polyproteins is required for virion maturation and infectivity [5, 6] . Figure 5A ) [13, 48, 49, 50, 51] . As there is an increase in virion infectivity from CIITA-expressing cells, we hypothesized that the processing of Gag polyproteins may be enhanced in these cells. As suspected, analysis of cell lysates from equal numbers of HIV-1 transfected A293T-CIITA and A293T cells demonstrated a higher ratio of mature CAp24 to Pr55Gag in CIITA-expressing cells ( Figure 5 B&C), demonstrating that Gag processing in the presence of CIITA is enhanced. Additionally, increased levels of processing intermediates are present in A293T cell lysates. Specifically, the p41 (MA-CA-SP1) and p25 (CA+p2) products were increased (Figure 5 B&C) in these cells, indicating that Gag processing in the presence of CIITA is more efficient. Gag processing is also enhanced in cell-free virions from cells either transiently or stably expressing CIITA, as demonstrated by the increased levels of CAp24, and the loss of the p41 and p25 intermediate products relative to Pr55Gag ( Figure 5D&E ). Collectively, these results suggest that CIITA increases Gag polyprotein processing, leading to enhanced production of infectious virions.