The human gammaherpesvirus KSHV causes a serious endothelial cell malignancy, KS, which predominantly occurs in immunecompromised individuals (e.g. AIDS patients). KS tumors are comprised of distinctive spindle cells of endothelial origin and a variable inflammatory infiltrate [43] [44] [45] [46] . KSHV is detected primarily in the endothelial component of the lesion, and though most of these cells harbor latent KSHV, a subset of them enter the lytic cycle [47, 48] . While there is precedent for a mixed infection type within KS tumors (i.e. both lytic and latent infection), the history of the lytically infected cells remains elusive, though recent reports point to circulating endothelial progenitor cells [41, 42] . In vitro, endothelial cell infection with KSHV is predominantly latent [43, [49] [50] [51] . However, when these cells are transferred into mice, they show evidence of lytic gene expression and virus production [52] .