Some aspects of the pathogenesis of HIV-1-associated Kaposi's sarcoma.

Kaposi's sarcoma (KS) is a very rare tumor except after human immunodeficiency virus type 1 (HIV-1) infection when it becomes common. Most investigators assume that the role of HIV-1 is passive, i.e., via inducing immune deficiency, thereby enhancing cancer development, and specifically, in the case of human herpesvirus 8 (KSHV) by enhancing HHV-8 replication. We suggest that the role of HIV-1 is more active in the disease process by at least two events: 1) promoting an increase in inflammatory cytokines, which through sustained release influences early stage KS by inciting local microinflammatory responses, and 2) by the Tat protein that effects growth of the inflammatory cells. Cultures of all activated endothelial spindle cells, whether hyperplastic or neoplastic, are negative for HHV-8; transmission of HHV-8 does not induce cell growth or transformation; monkeys immune suppressed by simian immunodeficiency virus infection and infected also with HHV-8 do not develop KS; polymerase chain reaction analysis of blood cells shows HHV-8 sequences in monocytes and B cells (about 20% of normal donors in Maryland); M. Starzl showed that early KS has few cells (mostly macrophage) positive for HHV-8, increasing and present in endothelial cells only late in the disease; no increase in HHV-8 has been found in association with progressive immune deficiency; and recent studies in Gambia by others showed that HHV-8 is a very common infection, and though HHV-2 is known to be relatively common, HIV-1 is unusual and so is KS. Collectively, these findings lead me to conclude that there is little evidence that HHV-8 is a transforming virus as has been repeatedly suggested and that its role in KS is more likely to be indirect (like HIV-1), perhaps necessary but hardly likely to be sufficient for KS development.