The p12^I protein increased T-cell proliferation after suboptimal antigen stimulation.

PBMCs from healthy volunteers were purified by the Ficoll method, washed in PBS, and either used as such or after suboptimal stimulation with 0.5 ng/mL CD3/CD28 Ab for 24 hours before infection with HR′CMV p12^I or HR′CMV-Luc pseudotype viruses. Cellular proliferation was measured by using a Colorimetric Cell Proliferation Kit II. SDs were calculated from 2 independent infections of each donor sample, and values are representative of results from 3 separate donors. Similar results were obtained after stimulation with 1 ng/mL PHA (data not shown).